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what is this????
Posted by
Kreidy818
on 30 Sep, 2013 18:21
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#1 Reply
Posted by
Gillio
on 30 Sep, 2013 18:26
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Fuel pump. He must be sucking the bowl dry with that FMF.
Congrats on your win btw.
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#2 Reply
Posted by
Chuckie25
on 30 Sep, 2013 18:47
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FMF + twist throttle = bone dry bowl + every girl's panties in the guys urinals soaking wet. Mikuni fuel pump, at least it's rebuildable lol. I'd buy the bike just for that lmao.
Is the rear shock linkage pump together wrong in this bike or is the end of the rear shock supposed to be over the swing arm like that,,,? Mine was a no-link so I have no idea what stock looks like..
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#3 Reply
Posted by
Kreidy818
on 01 Oct, 2013 04:02
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Why would you need a fuel pump ? gravity fed should be more than enough. Thanks Gill, it was actually 2nd place but I had to pick off 3 bikes to get there so I was pretty pumped. One guy crashed hard after the finish, had a bad concussion.
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#4 Reply
Posted by
CrustyOreo
on 01 Oct, 2013 06:53
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FMF + twist throttle = bone dry bowl + every girl's panties in the guys urinals soaking wet. Mikuni fuel pump, at least it's rebuildable lol. I'd buy the bike just for that lmao.
Was that sarcasm or does an FMF and twist really dry the bowl?
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#5 Reply
Posted by
Gillio
on 01 Oct, 2013 07:03
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Some of the higher HP modded engines out there with new tech high reving pipes will drain the bowl or lower the fuel height in the bowl causing a lean condition. The keeping a little pressure on the inlet needle will help this. Usually done after the petcock mod, proper sized inlet seat, and or over sized fuel bowl. My .02. Im sure there is more to it.
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#6 Reply
Posted by
Chuckie25
on 01 Oct, 2013 08:22
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FMF + twist throttle = bone dry bowl + every girl's panties in the guys urinals soaking wet. Mikuni fuel pump, at least it's rebuildable lol. I'd buy the bike just for that lmao.
Was that sarcasm or does an FMF and twist really dry the bowl?
Sarcasm lmao. FMF is the junkest pipe around. People think putting a twist throttle on their bike is a HUGE AWESONE AFTERMARKET POWER MOD!!!!! as well lmao. I ride twists so I can make fun of them
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A large float bowl is just a band-aid for not having the correct size inlet seat and fuel pressure to the inlet seat. The fuel level inside the float bowl will be maintained with the correct fuel pressure and inlet seat under wide open throttle whether the track is 300 ft. or 3000 ft.
A carburetor CANNOT be tuned properly when the fuel level inside the float bowl is not staying at a constant level. This is a very very basic concept but it seem the majority of the alcohol drag racing community cannot understand this. Installing a larger float bowl only adds a little more distance before the carb. runs out of fuel. The air fuel ratio is getting leaner as the clock ticks under full throttle as the fuel level diminishes because fuel delivery to the float bowl is less than the fuel being consumed.
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Jerry, so Billet Bowls are more for a Bling Factor than for use? Figured the petcock mod was enough.
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#9 Reply
Posted by
Chuckie25
on 01 Oct, 2013 10:53
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I bet that even if it IS FLOWING enough, you can still suck a stock capacity bowl empty faster than it can fill
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I dont hear any problems with High HP Honda CR500 & KX500 running a float bowl dry? why just our LT500s? and Banshees?
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#11 Reply
Posted by
Chuckie25
on 01 Oct, 2013 11:11
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not just lt's and banshee's,,, the BIG 250R motors are running them too,,,, no clue,, but i'm sure theres a valid reason but im just a know-nothin kid who dont know nothin bout nothin so IDK BRO
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I bet that even if it IS FLOWING enough, you can still suck a stock capacity bowl empty faster than it can fill
If is flowing enough, the fuel level in the float bowl will stay the same at all times. If the flow bowl can EVER be sucked empty IT IS NOT FLOWING ENOUGH.
A float bowl on a running engine could be compared to a water bucket with about 1/8" hole in the bottom. If you want to keep the water level in the bucket at the EXACT same LEVEL at all times you have to be pouring new water into the bucket at the same rate as it is running out the BOTTOM. It does not matter what size bucket you have if you want to maintain the same water level all of the time: SUPPLY has to equal CONSUMPTION!
If the new water supply is less than than the leak in the bottom it just takes the large bucket longer to become empty than than a small bucket
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#13 Reply
Posted by
Chuckie25
on 01 Oct, 2013 13:50
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If you max out the rate of flow IN and still are running the bowl dry, then a bigger bowl would be necessary. More than likely the bigger bowl is a precaution that these guys are taking. I mean if they aren't flowing enough fuel to begin with, and are sucking "normal" size bowls dry, these guys are going 300 ft to an 1/8th mile at a time. It's not like it's a trail motor or dune motor or something to just go cruise around on. They run their run, either shut the bike off or idle back. If they run the bowl out at the end of the run it doesn't really matter.
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Jerry, so Billet Bowls are more for a Bling Factor than for use? Figured the petcock mod was enough.
I view the LARGE billet float bowls as a public admission of the designer/creator and the end user as their gross ignorance about how a basic carburetor functions.
We see a lot of guys replace the float valve with the wrong size. A gravity feed fuel system needs a 3.5 mm float valve to supply the high hp engines. 3.5 mm is the stock size on the TM 38 OEM carburetor.
The petcock mod will allow more than enough fuel to get to the carburetor if the vent in the cap is working properly and the fuel filter has sufficient flow rate. Some of the small clear bullet shaped fuel filters will not flow adequately if they have much time on them.
We have replaced enough burned pistons to fill a 55 gallon drum from gas caps using the billet piston shaped fuel cap vent check valves. The check valves fail closed and prevent the tank from venting and it leans the carbs and burns pistons. Some of these little bling valves require to much vacuum to open the check valve with the same piston burning results.
If the billet float bowls are the same volume as the stock bowls I view those billet float bowls as bling
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Thank you Jerry for the info, Matt Shears mentioned that also to me awhile back, that those Aluminum aftermarket Vents clog to easily, and how those aftermarket aluminum gas caps vent holes are too small, had to drill mine out to 7 mm, still left enough metal.
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My carb flows enough fuel i just use the oversized bowl as a little insurance. But if i just had a duner i wouldnt even bother with it.
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Damn! few months back i did pick up a nice billet cap for cheap and it had one of then vent thingys on it. I didnt think much of it till i read this thread i just took it off and could barely even suck any air thru it. Man am i glad i read this! The cap itself seems to breath nice as it just has a straight thru hole with no guts.
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#18 Reply
Posted by
Chuckie25
on 01 Oct, 2013 15:18
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Thank you Jerry for the info, Matt Shears mentioned that also to me awhile back, that those Aluminum aftermarket Vents clog to easily, and how those aftermarket aluminum gas caps vent holes are too small, had to drill mine out to 7 mm, still left enough metal.
We drilled the one out on my uncles 500 4-stroke Suzuki as well. His is a mud bike though so we've got a little more than a crispy piston to worry about if it vacuum locks lol
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#19 Reply
Posted by
Mtsnieg
on 01 Oct, 2013 18:20
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I've heard about the 'petcock mod' but searching turned up nothing. A freer flowing petcock would be keen. Shed some light on it. Worrien about the wrong bowls being not big 'nuf.
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#20 Reply
Posted by
Kreidy818
on 01 Oct, 2013 18:21
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Wow I was just about to order one of those check valves. Thanks
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The petcock mod flows from both the reserve tube and the on tube.
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#22 Reply
Posted by
Gillio
on 01 Oct, 2013 18:33
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I've heard about the 'petcock mod' but searching turnud up nutin. A free'ier flowin petcock would be keeen. Shed some lite on it. Worrien about the wrong bowls being not big 'nuf.
The petcock mod is where you grind an extended channel into the fuel valve letting it turn 180 degrees from the "off" position allowing both "on" and "reserve" to flow at the same time. Flow is noticeably increased. I removed both pick up tubes off of mine too, but I remove and drain my tank on the regular and keep it clean.
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#23 Reply
Posted by
Mtsnieg
on 02 Oct, 2013 10:12
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I was thinking it would be nice to have the reserve. Gonna try a couple 1 hour ice races this winter with the Zilla. Kinda like a signal to pit for gas. But a better flow is better fot the beast. Gonna pull the petcock and take a looksee.
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I was thinking it would be nice to have the reserve. Gonna try a couple 1 hour ice races this winter with the Zilla. Kinda like a signal to pit for gas. But a better flow is better fot the beast. Gonna pull the petcock and take a looksee.
NEVER RUN A HIGH PERFORMANCE TWO STROKE ON ANYTHING BUT THE RESERVE POSITION ON THE PETCOCK unless you have done the petcock mod where it is always drawing fuel from the on and reserve ports in the petcock.
When the fuel level gets low enough to "give you a signal that the fuel is low" it may be one that you were not expecting. A seized piston or blowing a hole in the piston crown or caving in the top of the piston is the signal that is often sent to the rider
A two stroke that is slightly rich runs well. A two stroke that has the air/fuel ratio perfect runs well. A two stroke that has the A/F ratio a little lean runs well. A two stroke that that has the A/F ratio real lean also runs well. Most racers cannot tell the difference in the way the engine is running if it is real lean or running the perfect A/F ratio.
The fuel level in the tank while riding is constantly moving up and down around the petcock's on position stand pipe. When the fuel level is still a inch or so above the stand pipe that feeds the on position of the petcock, you may be constantly flirting with small periods of leanness due to fuel slosh. As the fuel level gets lower and lower the periods of leanness can get longer and longer.
An engine that is tuned well and running hard like on oval track racing, cannot be teased with brief periods of leanness because the fuel slosh is not feeding the petcock that is positioned to the on position. The reserve fuel port of the petcock feeds off of the very bottom of the tank while the stand pipe that feeds the on position of the petcock is up off of the bottom of the tank 2 to 3 inches.
You can constantly monitor your fuel level by placing a "T" in the fuel line feeding the carb and hooking the other barb of the "T" to a piece of clear fuel line. This clear line will become a sight gauge. Take a felt marker and place a line on the clear tube where you think you should refuel. Run the clear line in a place that is easy to glance at at while racing. The fuel level in the clear line will be the same as the fuel level in the tank in the area of the petcock. One end of the clear line has to be open to the atmosphere. The open end must go high enough to prevent fuel from sloshing out of it. The opening in the open end of the clear line (sight gauge) only needs to be as large as a pin hole.
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