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Author Topic: What size pilot jets fit the 1987 LT500r with Mikuni carb  (Read 1756 times)

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What size pilot jets fit the 1987 LT500r with Mikuni carb
« on: June 30, 2013, 12:51:14 pm »
Hi
I am wondering what size pilot jets to buy. I am kinda striking out. I am looking at Rocky Mountain ATV site and see tehy offer a Pro X vm22/210 series Mikuni pilot jet.  I am currently running a 25 but am sure that I need to bump it up as the bike is a real bear to start. It takes 5 to 6 prime kicks after killing to to get it started again. Pulled the plug and it is dry so fouling has been ruled out. Just wanting to pick up some larger pilots but want to make sure I am getting the ones I need. Anyone know which ones will work? I had Halls precision bore it out to 41mm and it is currently running a 560 main and 25 pilot. The bike idles awesome and seems to run good at the upper end (going to take it to the dunes this next weekend)!!!!!

Thanks
Anthony
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Re: What size pilot jets fit the 1987 LT500r with Mikuni carb
« Reply #1 on: June 30, 2013, 01:02:44 pm »
Contact Jerry Hall themotorgeek@gmail.com he stocks mikuni jets and carb parts for the lt500 stock mikuni tm38.
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Re: What size pilot jets fit the 1987 LT500r with Mikuni carb
« Reply #2 on: June 30, 2013, 02:25:05 pm »
If it idles good the pilot jet and air screw combination are in the ball park unless the slide has to be open 1/8 inches to get the idle speed you want. 

If the slide has to be open about 1/8 inches to make it idle, the pilot jet and or the needle jet is too rich.  The slide being open 1/8 inches will make the choke not work and the pilot jet cannot work properly at cranking speeds.  Set the idle stop screw to provide the absolute lowest idle RPM.  A fast idle setting will make a bike hard to start.

How much compression does the engine have?

Make sure your reed petals are not not missing a piece or ****.  Check your pickup air gap on the ignition stator.  I set the air gap to .025" to .030".

Starting a 500 single cylinder is about 60 % technique, 20 % carburetor setup and 20% determining whether the engine needs choking or it may need the throttle open about 1/4 throttle because it is hot and partially loaded up.   ALWAYS position the piston at top dead center and the kick starter at the position that will rotate the engine the maximum number of revolution on one kick.  Kick starting with the piston up against the compression stroke on any 500 will make starting very difficult.

If you have the choke on, the throttle must be completely CLOSED or the choke will not work. 
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Re: What size pilot jets fit the 1987 LT500r with Mikuni carb
« Reply #3 on: June 30, 2013, 04:03:19 pm »
Thanks for the replies. I just pulled the carb again. The slide is all of the way down when I screw out the throttle screw. When I turn it in slightly it just raises it. I have tried to choke the bike to get it to start easier when cold. It does not seem to have any effect.  Five or six prime kicks and then it usually fires up. Once it has been started and is warm, I am still having to prime it again to be able to start it.

I put new reeds in when I put the top end together. There is less than an hour of running time on it currently since it was all replaced.

I will have do a compression check. It seems to have great compression. I will do one anyway just to know.

I am not sure how to adjust the air gap on the pick up coil. I replaced the stator assembly after I first put this back together as I was not getting any spark.  This also has less than an hour on it. I just took the side cover off and can't see how to adjust. Do I need to pull the flywheel? Am I measuring the gap between the contact on the pick-up coil and the raised strip on the flywheel? If so,  I measured and it was approx .020. I then loosened it I put the a .030 feeler gauge in between and tightened it back up. Other than that, the pick-up coil has two screws to hold it in place, but there is no room for adjusting.  I looked in my manual, but am still not seeing. What am I missing or is it now where it is supposed to be?
Thanks
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Re: What size pilot jets fit the 1987 LT500r with Mikuni carb
« Reply #4 on: June 30, 2013, 09:26:25 pm »
Quote from: Rem28ga on June 30, 2013, 04:03:19 pm
Thanks for the replies. I just pulled the carb again. The slide is all of the way down when I screw out the throttle screw. When I turn it in slightly it just raises it. I have tried to choke the bike to get it to start easier when cold. It does not seem to have any effect.  Five or six prime kicks and then it usually fires up. Once it has been started and is warm, I am still having to prime it again to be able to start it.

I put new reeds in when I put the top end together. There is less than an hour of running time on it currently since it was all replaced.

I will have do a compression check. It seems to have great compression. I will do one anyway just to know.

I am not sure how to adjust the air gap on the pick up coil. I replaced the stator assembly after I first put this back together as I was not getting any spark.  This also has less than an hour on it. I just took the side cover off and can't see how to adjust. Do I need to pull the flywheel? Am I measuring the gap between the contact on the pick-up coil and the raised strip on the flywheel? If so,  I measured and it was approx .020. I then loosened it I put the a .030 feeler gauge in between and tightened it back up. Other than that, the pick-up coil has two screws to hold it in place, but there is no room for adjusting.  I looked in my manual, but am still not seeing. What am I missing or is it now where it is supposed to be?
Thanks


There is a little slack in the two ignition pickup coil mounting screw holes to allow for adjustment.  The air gap is measured between the trigger bump on the outside of the flywheel and the pickup coil. 


Was the replacement stator OEM or aftermarket?  Does the engine run well without miss-firing under full throttle and at  higher RPMs?
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Re: What size pilot jets fit the 1987 LT500r with Mikuni carb
« Reply #5 on: July 01, 2013, 08:15:36 am »
The stator is aftermarket. I picked it up when my other one tested out bad. The bike seems to do just fine as you up the throttle.  There is some fine tuning to be done but seems to run okay. I don't hear or feel any misfiring.
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Re: What size pilot jets fit the 1987 LT500r with Mikuni carb
« Reply #6 on: July 01, 2013, 01:10:07 pm »
I don't remember for sure, but I think the stock pilot jet size for the '87 is like a 30.  '88 through '90 use a 22.5 pilot when stock.
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Re: What size pilot jets fit the 1987 LT500r with Mikuni carb
« Reply #7 on: July 04, 2013, 03:12:39 pm »
Just upped the bike to a 30 and remixed my fuel. So much easier to start now!
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