Suzuki Quadracer HQ
LT250R Quadracer => LT250R - Engine => Topic started by: Motoman-Racerx on September 19, 2013, 03:49:17 pm
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is there a ignition timing that can be backed off alittle, i didn't get much time on the track to test sunday guy was being a dick, was only letting bikes out on track he did let me take 4 laps to feel it out a bit i tried couple differant things. but didn't give me time to rejet or anything sucks living in city i just cant go out a flog on it when i want. but i am goin to make practice day sat and race sunday, hope i can work out some othe bugs, did'nt even get to set power valve maybe rpms to low for 5th???
running a 12 front with 39 rear and 18 tire. that should be about stock gearing if i was to be runnin the 20 tire with a 42 rear.
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Higher gear = more load on the engine , more load creates heat. Especially if your jetted a little too lean. Get you jetting sorted. The thicker head gasket lowered compression a little freeing up the overrev and probably making a little more power.
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well got to take it out for a test ride sunday, i definitly going to have to jet up, i checked the plug and it is a little lean. with the thicker head gasket it seems like it pulls harder after 2 laps my arms were getting tierd from the pull. here is whats funny i tried differant things, if i roll the corner 3rd wfo and bang 4th and keep it wfo to the next corner alittle over rev down the strait and it is fine not to happy how much it is reving but atleast it doesnt fall flat. same corners but if i shift to 5th on the strait is will pull for a few seconds but falls flat and when down shift to 4th it still acts like no power and stubbles alittle into the corner after the strait for about 5 seconds or so. only have one more weekend or racing this year but 2 classes, i think i will just change the front sprocket 1 tooth bigger so i dont have to use fith and start using 2nd in the tighter corners. :-\
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Thanks guys. If your hungry enough, crow ain't all that bad to eat. In my circles, I'm used to teaching about mechanical stuff, on here I'm getting used to listening and learning again. But Im liken it.
BTW I run engine ice in mine, and I haven't taken a temp reading, but it does seem to run cooler on the trails. I'm just runnin a stock bore 1987 250 motor. 93 pump gas. I keep her screaming on these KY hills. I can't understand why it runs cooler with the engine ice, but I really think it does. I also run my main jet right on the border of being too rich for the same reason.
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Agree^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Thanks motorgeek. I think I might start a thread on the books. Hopefully you'll chime in there.
My apologies to motorman since I gave him some bad advice on squish. Luckily you guys got in here before any more damage was done.
Iceracer. My bad dude.
Not trying to thread jack by any means but this dude just gained some major respect points in my book. Swallowed the chill pill, admitted he was wrong and even apologized!! WOW!!! Rock on dude!!! May the 2-stroke deities bless you with many many more years of happy riding, perma-fresh top ends, and zero minutes of down time for the rest of your days
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Thanks motorgeek. I think I might start a thread on the books. Hopefully you'll chime in there.
My apologies to motorman since I gave him some bad advice on squish. Luckily you guys got in here before any more damage was done.
Iceracer. My bad dude.
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thanks for everyone's help, i will keep every one updated on how it does at the dealer ride, whats cool about the dealer ride they let bike on the track with the quads so i will have some vids of me smoking some bike soon.
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Anyone else use the engine ice I tried it once and I got a leak from water pump weep hole.
All i never used is engine ice.
what is the stock setting for the power valve, i notice its not lined up on the 0 like my other one is. this may also be the problem up in 5th on the hard pull that the spring is to tight and power valve is open???
Power valve is supposed to close at high rpm. Dont pay attention to the numbers on it. If you want to reapply tension to the spring to be sure it's correct, be sure there is no tension on the spring then do like Heminutt said. 1 full turn CCW.
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1 turn counter clock wise is the stock setting
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yeah i get a small drip from the water pump seal if its older when i replaced it hasnt leaked since. also got the racer together squish is now .060 not sure how it runs going to the fly sponcer ride saturday and test it then i will keep you posted. also the thicker head gasket didn't do much for the compresion it still at 210 psi. all i can do it ride it and try it
what is the stock setting for the power valve, i notice its not lined up on the 0 like my other one is. this may also be the problem up in 5th on the hard pull that the spring is to tight and power valve is open???
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If you're blowing gaskets you've got a problem. Just need to sort out exactly the cause of the head gasket failures.
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Anyone else use the engine ice I tried it once and I got a leak from water pump weep hole.
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Racer as far a s the super bowl it could help some but the float level and size of you needle and seat will have the most bearing on fuel supply.
iceracer i guess i may be dumb but i just though of it, if i am blowing headgaskets and have cyl gasses leaking into the cooling system that would raise the coolant temp and overheat. right. i just got my new gaskets in today waiting on my buddy to bring the base gasket home and i will insert the .059 gasket in and do a compression test and also recheck the squish. i did the math it should be around .062 but i will check it with the gasket and everything tight. and keep you guys updated. its just hard to believe that with the 40mm overside rad and the cms silicon hoses and using engine ice for coolant (20 bucks half gal) would still get this hot. maybe i will also look into a eletric fan and use the headlight switch to turn it on and off. might get lucky and high speed and low speed.
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Racer as far a s the super bowl it could help some but the float level and size of you needle and seat will have the most bearing on fuel supply.
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......................... I got that info on squish from gordan jennings book. He's forgot more about two strokes than most of us will ever know. ...............
Gordon Jennings looked at and worked on a lot of two-stroke engines in the 1960s and wrote about many of these engines in the 1970s for Cycle World Magazine. Gordon was good at putting his ideas about how things worked on paper although many of his theories and conclusions to his observations have been proven wrong by engineers and engine developers that have done a lot of dyno and field testing on two-stroke engine. I liked his style of writing and was reading everything that he wrote while I was studying to become an engineer. Gordon Jennings pipe theory and formulas steered a lot of us including myself in the wrong directions for many years. Initially I accepted most of his teaching as divine revelation. As my engineering studies progress I started seeing flaws in some of his teachings.
I started reading SAE papers written by Gordon Blair and his students while I was also studying engineering. The SAE papers were mostly research papers that presented theory and the testing to prove or disprove the theory in question. At that point in my academic career, most of the SAE papers were over my head. As my academic studies progressed Gordon Blair’s research was easier to understand and disproved some of the Gordon Jennings theories and conclusions.
If you really want to learn about two-stroke engine development, read the text books and SAE papers written by Professor Gordon Blair from the from the Queens University in Ireland. Gordon Blair did research projects for all of the major two-stoke engine manufactures around the world from the early 1960s until his retirement in about 1995. Gordon Blair did more during his lifetime to further two-stroke technology than all of the combined research done on two stoke from the early 1900s until his death a few years ago. Gordon Blair’s engineering students are currently working for engine manufactures around the world today and continuing much of the research that Gordon started.
Prerequisites for reading and understanding Gordon Blair's publications are an engineering background, or training at the university level in calculus, differential and partial differential equations, fluid mechanics, gas dynamics, thermodynamics, computer programming, and physics with and emphasis on statics and dynamics.
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Chuckie, no that will make it worse if you don't jet for the fuel ratio remember going from 40- 32 effectively leans a fuel to Air ratio more oil = less gas. just a clip or needle change could help. Possibly a timing change, there's a lot of possibilities
Racer, be careful lapping the dome on a cool head there designed to be thicker than the Shell to put more pressure on the fire ring. There should be @ .010 " protruding from the shell, if you get it even or lower you will have some sealing issues.
Give me a little information on the head and cylinder and I will point you what way to go.
Need to know:
distance piston protrudes from cylinder deck +-
thickness of gasket measured at fire ring.
Bore size
stroke of engine if not stock
It would help to have a cc on the head, actually measured with something accurate. a syringe works
also an installed cc with the head on the bike would be the best. put a dab of grease at the ring end gap bring it to TDC then install the head and gasket. fill the head with Isopropyl alcohol, to the bottom of the spark plug hole. when done rotate untill ex port opens and let it drain out it will run into the pv cavity. just pull the plug and drain
With this info I can calc some head #s and try to see what the issue is from the theoretical side.
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Would going to 32:1, and raising the needle back up one notch help with keeping it cooler?
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James if I got sassy you would of know it. Jenings stuff is great reading, a lot of of it is very outdated and extremely general.
If you run a 250 and set squish at much less that .030 you going to be replacing the head piston rod and probably crank. Now as long as its a trailer queen and only ever idles it might live. But when you spin up to 8k+ your F'ed. It will hit. That's why I was wondering if you ever did one this way. Fyi minimum squish for a 500 is .040-.042 and it should be a tight engine I've seen worn ones ding ring land closed at that also every engine is a little different wear plays into a lot of the SAFE minimums for these machines.
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Before dropping $80 on a carb bowl I think you should set the float height, and get the head done so your staying within temps, then adjust jetting if need be. THEN if she still sputters get the bowl see if it actually just needed to suck up more fuel or something else going on. 2c
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iceracer, i did pull the jug and checked it the same way i did the head, because like i said there was a small wobble in the head so i did want to check the jug. i know this thing is getting hot. thats why i was debating on goin to a 20 cc dome. its tough trying to keep the old lt competive on the mx track with the 450's cause they can ride the whole track in 3rd and never have to shift. where i try to keep up mometom up in the corners and run most the time wfo. i was doing some math and if i use the new gasket thats thicker my squish goes from .046 to .062 i also did notice the dome seemed to be recesed in the head slightly, so when i pulled the dome out i lapped the head down now its flush or just slightly out, just catch the side of it with you finger nail not enough to get feeler gauges under though. what you think about a bowl up grade like this
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=390657638503&fromMakeTrack=true&ssPageName=VIP:watchlink:top:en#ht_1474wt_872
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Not sure iceracer, how bout you? The one I'm running right now is at .043. By the way bud, I did state my reference for all to see, and also my disclaimer that I'm not a champion engine builder. I was just saying what I would do. Right or wrong I stand behind all my statements on here. I want this guys motor running right as much as anybody on here. I guarantee ya that. And I don't want any of his money, or any brownie points with my favorite builder by sending his cash there. I got that info on squish from gordan jennings book. He's forgot more about two strokes than most of us will ever know. I stated my freakin references and told the guy that that is what I would do. Now you can tell him whatever you want but you don't gotta go get sassy with me in the process.
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That 38mm cast APT smart carb does LOOk bad ass. Slot more affordable than the billet units too
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James how many engines have you ran at .018 squish? Or under .030 for that fact. Just curious.
That plug looks terrible. Its showing signs of massive overheating. Unless the black on the base ring wipes of with no solvents. What I am seeing is the plug is running so hot the fresh mix is flashing and baking onto the base ring, don't confuse that with anytbing to do plug wise yet. Its all from too much heat in the head. The plug can't transfer heat as fast as the alum head. So its the first thing to show overheating. From what your describing your getting preignition also, this is likely the cause of the wide open issue. For the record , a 18 cc dome can't really be cut to work with a big bore engine properly.
Just for kicks cut It the threads off that plug so you can see up in side. Where the porcelean meets the steel.
As far as the head good move lapping it. But you also need to check the top of the cylinder. The ruler trick is only good for a quick obvious issue. I'm thinking the top of the cyl is not flat or that the sleeve has sunk. Slightly causing some of the head gasket issues along with too much compression and preignition.
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here is tthe other one also there is a vid about it.
http://www.powerapt.com/smartcarb.php
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When I put my keihin on my 87 I loved it. I'll trade two flat slide 34mm keihins. One needs rebuilt, the other I have never ran. For 1 PWK 36mm-40mm.
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pretty sweet carbs
http://www.psicarbs.com/snow/home.php
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Junk pwk is propably your whole problems
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well just check the float height, it is 16mm from the edge to the carb to the bottom of the float with needle seated and spring plunger not pushed in also checked to the line on the float a 7.7 mm.
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You check that float height yet? That's the only tricky thing about them PWKs man. Betcha it's about 3- 5mm too high. It sounds exactly like mine did when I was tuning my 39mm. When u get it right, it pulls and pulls thru all the gears man. I went from a junk 34mm mikuni to my 39 PWK and once tuned right, it made a HUGE difference mid-top without losing any at all on the low end
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i belive its the way i bought the carb NEW. i did lower the needle 1 notch so raised the clip one groove, basicly bought the carb and bolted it on and ran it. the slow jet that came in it was a 50 it seem to run good down low and doesnt load up so i left it alone i did have to jet up on the main the plug was a bit white think the main was a 158 might have been a 160 i do remember i was running almost a 175 on the main for a while but when i went to a track that was mainly sand and she was wfo on long pulls in the straits it was spittering out on the big end so i ended up leaning it out to a 165 or 162. that got rid of the sputtering. also found the bolts holding the coil on started to come loose that could of defintly been a grounding problem.
What needle are you running? What clip setting?
Nice race qwads you have there (Y)
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What needle are you running? What clip setting?
Nice race qwads you have there (Y)
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Hmm I wonder if a raptor 660 petcock would flow more fuel then the zilla.. I have one bolted up to my 250 tank right now just haven't had a bike to put it on.
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Good luck man! I'm betting this does the trick, and with the high compression your running, getting too lean like that could sure be the cause of all your frustrations.
I'd still get the head checked out. I think when I get my factory head milled, I'm gonna get the squish band as wide as I can. I really want it like 10-12mm wide and then the combustion chamber deeper, to get the cc I want, but I havent worked the math out yet and I don't really know if that's possible with the factory head, but I hope so. I'll be keeping an eye on your build and how this pans out.
With that head, you have options. You just gotta have your numbers spot on. If it's gotta be milled, you gotta know how much. You can order a custom dome to your specs.
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yeah i havent checked float i will do that tomarrow sound like that may be the issue, running a 50 slow and a 165 main. i was even thinking goin to a boysen bowl or even the edelbrock oversized bowls next. but i will check the float first.
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Float height 16mm, needle valve seated spring loaded button not depressed. I know it's 16mm for the 39mm, pretty sure same for the 38. I had to hold mine kinda on it's side, and support the float with my left middle finger while measuring with the calipers with my right.
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I had a similar problem with mine when I was tuning my carb. I run a 39mm PWK. I got it used and it's a sudco racing like yours, bug not air striker. It measures 39.75ish mm
I run a 160 main jet with my needle at the second notch down. 2-1/2 turns on the air screw with a 58 slow jet (I think) can't remember slow jet for sure.
Anyway, mine was leaning out like that and I found that I had set the float height incorrectly. It has to be set with the needle down, but the little spring loaded button NOT depressed! I had done everything you've done, bigger hose, I drilled out a fuel petcock (ruined it), heck I even tried a freaking flutter pump! Then it turned out my float height was wrong. When I made sure the needle valve was just seated, and button NOT depressed, that baby would rev 6th gear to the moon 70mph all the way! (at least that's how fast it felt)
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here is what i have done, i use sunoco gt110 fuel maxima castor 927 oil at a 50 to1 mix, new piston with 3 moto's on it since last head gasket, new wrist pin, i always check ring end gap gap was .012 on both rings, new wrist pin bearing and thrust washers every top end. i did check my head on my counter top witch is granite. it did wobble slightly thou ?? not sure, used a 320 grit with breakaway oil for lube and lightly rubbed it down without the dome, dome was flat did slight rub and no witness marks or being warped, head differant story. but still have a over heating problem or even just thought of it fuel bowl is running out, i am using zilla fuel petcock with the 5/16 fuel hose and 38 airstriker. on long hard pulls 3 and 4 ok but when i get into 5th it starts fallin on its face like i grabbed the rear brake, thought i was having brake problems at first, so got new caliper, caliper mount, rotor and ss brake line and rebuilt master with no help to the problem. to where either getting to hot or running out of fuel. i guess once i get it back together i should look into a coolant temp gauge to see actually how hot it is getting, the pipe is purple and blue all the way to the stinger. i do know i bought a 18 cc dome for the head but someone told me they had to cut the dome to get the right squish, so the cc now ?? i will find that out soon. thanks for everyones help.
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well, spark plug looks good to me. The head looks funny how u can see that little swirl mark. Were u using pump gas? Or 110?
Here's what I would do:
1)Get a brand new precise metal ruler and a set of feeler gauges. Sit at a well lit table or bench and lay that ruler on the head at every angle possible and try sliding in the small feeler gauges to check for warpage.
2) check the piston rings. Particularly the gap between the ring and ring groove.
3) check and make sure wristpin and rod bearings still feel right. I'd just pull up and down to feel for play
4) read the link I sent. You can use that math to figure out your compression ratio. If you are not sure how many cc's the head is, then you can fill it with water then measure the water in a graduated cyl to find out the cc's
5) If the ruler shows the head is warped, don't worry, just have it cleaned up by a machine shop, but tell them to take exactly what you need off (whatever the largest feeler that fit under the ruler was) as long as it's not more than .030. That would leave your squish at .018.
6) decide what compression ratio would best suit you and order the corresponding dome per the formulas in the link I sent. Buy a cometic gasket kit, put a little dab of never seize on your head studs, properly torque the nuts, then retorque after the next few rides.
This is just what I'd do man. I'm not a champion engine builder by any stretch, but I'm no dummy either.
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here you can see where the gasket is blowing in 3 spots
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pic of the head
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here is a pic of how the plug looks
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The .048 squish is close where it needs to be. Squish is another detonation preventative. It hides the a percentage of the fuel/air from the radiant heat from the spark plug. Squish should generally be between .015 and .060 to be effective. Sounds like you need a larger dome. Read the section on combustion in this book. It'll give you a good understanding of what needs to be done.
My mostly stock 87 motor reads about 160psi compression. I'm gonna hone and do piston and rings in it this winter. 210psi is a little high. but like what motorgeek said, if everything else is cool, such as bearings, crankshaft, piston, ect, you should be okay with race fuel.
Read this link. Great info.http://www.datafan.com/Horsepower_Blog/gordon-jennings-two-stroke-tuners-handbook/
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No your right, as far as general assumptions go. But beyond that squish clearance and width have a an effect on head and piston temps along with head shape.
What size head studs?
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ok i guesse i have been informed wrong, i always thought higher compression higher temps, more low end power, lower the compression and you would lower cyl temps and also get more rpm. i will pull the head off tonight or tomarrow and get a pic of it. i did order a stock thickness gasket with 70 mm bore maybe the 72 mm bore the head is not hitting the fire ring enough and thats why i am blowing them out i will also get some pics of the gasket so you can see where it is burning threw at. the fire ring is usually still intack just seeping by and burning the graphite out and starts pushing into the water jacket.
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I agree with everything jerry has said. TO properly set up you cyl and head you need to know the installed CC at TDC. This allows you to calculate Static and more importantly Trapped comp ratio. From there a couple assumptions need to be made on the Dynamic Ratio of the Engine. It would also help to know if your issue is actualy detonation or a overheating issue. I would guess without being able to look at it, its a combination of both.
Have you looked at your head off the cylinder? if so is there step machined into the Squish band? If there is, your looking at a new dome or Blank to get you where you need to be for Squish. If not The head gasket will need to be eliminated or the top of the cylinder machined to get proper squish.
Have you tried a better fuel, like C12 or C14 to see if its a detonation issue? also a couple sizes up on the main will cool the mixture and could point you to a detonation preignition issue.
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if to thick of gasket makes the squish to big so i look into a bigger dome maybe a 20cc
Unfortunately there is a lot more to cylinder head design than selecting a head volume and setting the squish clearance to this weeks most popular number found on the internet. Squish clearance and head volume are very popular topics on almost every forum. I have not read any threads in any of the public forums where the authors seem to have a very deep understanding of what they are writing about when it comes to the above mentioned topics.
When we use a cool head I just order a blank dome and then machine our own combustion chamber shape on it. It is very difficult for me to try to answer questions on the subject without having listeners that are also engineers.
Lowering the compression ratio raises the exhaust temperature and will usually make the engine rev a little higher. Lowering the compression ratio has a similar effect to the power curve as does shortening the exhaust pipe. Raising the compression ratio lowers the exhaust temperature and has a similar effect on the power band as making the exhaust pipe longer. (More low end at the expense of moving the power peak to a lower RPM.)
A chrome pipe should turn blue for the first foot or so. Lowering the compression ratio will add a little more blue to your pipe. How far the pipe turns the chrome blue depends upon the exhaust temperature, the RPM and how long the throttle is wide open at any given period.
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if to thick of gasket makes the squish to big so i look into a bigger dome maybe a 20cc
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If your squish is .048" it is already a little on the high side for a 250. Adding a thicker gasket will make your squish clearance too wide making the engine more apt to having detonation problems even when you are running 110 octane fuel.
210 PSI on a 250 is a little high but not that high if everything else is spot on with the 110 fuel.
Low compression does not eliminate detonation when the squish clearance are excessive
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well i am runnin a coolhead with a 18cc dome, i talked with cometic and they are makin a new gasket with a 70 mm bore and .059 thick to try to help me drop some of the compression. i am hopin to get down to around 190, motor always ran good but on a hard long pull 3 4 wfo and then you would click into 5 it felt like someone smashed the rear brake. also the pipe turned blueish and purple. runnin sunoco gt110 and maxima caster927 at a 50 to 1 mix. hopin the new gasket helps and doesn't drop compression down to low
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Setting the squish clearance to a reasonable number does not guarantee the compression ratio will be correct.
Squish clearance is one design parameter and compression ratio is another parameter.
Squish clearance and compression have to be set simultaneously with the correct machine work.
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sorry the squish measured at .048 not the gasket.
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i am starting to get confused here, what should cyl head squish be i just check mine and it is running with factory oem 85 86 headgasket measured at .048. but i am still hitting around 210 psi in about 7-8 kicks. it is a 80over 250 motor