running rich
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Novice
Joined: Dec 2009
Posts: 15
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From: washington state
running rich
this is my 1st post on ironhead forum,i have an 1973 xlh with mikuni 38mm roundslide model# 001-200. the bike is running rich and fouling the plug in the front cylinder(sooty black) my question is should i go to a smaller jet? ive read that these carbs are pretty much bullet proof and dont need much adjustment i have the e-clip in the center slot on the needle also i have new points & condenser the points are gapped at 018 on both ends. also new coil, plenty of spark and does anybody know the stock jet # on this carb? any help would be appreciated!
Intake And Exhaust Leaks Tests
You cannot get a good tuneup if there are intake leaks or exhaust leaks.
1. Check for Intake Leaks
With the engine idling spray propane gas or WD-40 around the carb/intake/cylinder head joints. Propane is best because it leaves no mess, and is most easily sucked in thru leaks. WD-40 is said to work well because it has very fine spray droplets. Be careful to not allow any of either to get sucked in thru the A/C as this will invalidate the results.
Any change in engine RPM is a leak which must be fixed.
EDIT: Experience is that this procedure will identify larger intake leaks, but it may miss very small leaks that also must be fixed. And that propane is definetly the better choice.
2. Check for Exhaust Leaks
Pour about 1/2 ounce of oil into each cylinder thru the spark plug holes. Run the engine at idle. You will get lots of smoke for about 5 minutes.
All smoke should come from the ends of the exhaust pipes/mufflers. Any other is a leak which must be fixed.
You cannot get a good tuneup if there are intake leaks or exhaust leaks.
1. Check for Intake Leaks
With the engine idling spray propane gas or WD-40 around the carb/intake/cylinder head joints. Propane is best because it leaves no mess, and is most easily sucked in thru leaks. WD-40 is said to work well because it has very fine spray droplets. Be careful to not allow any of either to get sucked in thru the A/C as this will invalidate the results.
Any change in engine RPM is a leak which must be fixed.
EDIT: Experience is that this procedure will identify larger intake leaks, but it may miss very small leaks that also must be fixed. And that propane is definetly the better choice.
2. Check for Exhaust Leaks
Pour about 1/2 ounce of oil into each cylinder thru the spark plug holes. Run the engine at idle. You will get lots of smoke for about 5 minutes.
All smoke should come from the ends of the exhaust pipes/mufflers. Any other is a leak which must be fixed.
Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
this is my 1st post on ironhead forum,i have an 1973 xlh with mikuni 38mm roundslide model# 001-200. the bike is running rich and fouling the plug in the front cylinder(sooty black) my question is should i go to a smaller jet? ive read that these carbs are pretty much bullet proof and dont need much adjustment i have the e-clip in the center slot on the needle also i have new points & condenser the points are gapped at 018 on both ends. also new coil, plenty of spark and does anybody know the stock jet # on this carb? any help would be appreciated!
Perhaps just swap plugs and see if it still fouls out the front cylinder, or does that make it foul on the rear?.
1) If the problem is still the same, in my opinion the carb is not what is doing this. Look for another cause.
2) If the fouling is now on the rear cylinder after the swap, then you just need to buy a new plug.
For a VM38, the following are the standard jet and needle sizes:
Main jet........ #330
Pilot Jet........ #30
Needle Jet..... #166 Q-2
Jet Needle.... #6DP1
Air Jet.......... #BS30/97 2.0
You have the jet needle in the correct notch (middle of the 5)
I would advise to never re-jet a Mikuni (providing it has the standard jets and needle installed) because there is no reason to do so.
Also, a jet size being incorrect is still going to affect both cylinders equally and is not going to be the reason for your problem.
Regarding the carb and adjusting it........
Always determine at what speed the problem seems to appear.
Does it foul at idle speeds or is this happening out on the highway?
Idling speed is going to be the air/fuel low speed adjustment and out on the highway is going to be the main jet section of the carb.
You may want to adjust the low speed air/fuel mixture screw. If you do not know how to do this let me know and I can provide you with the procedure.
Turning this screw inward enriches the mixture, and turning it out leans it. A Mikuni is a bit different than other carbs, but as I have said many times before, they are one of the best.
pg
Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
It would lean out the mixture, but the result will be rough running, not being able to idle steadily, and backfiring through the exhaust pipes.
The OP seems not to have these things going on.
pg
The OP seems not to have these things going on.
pg
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Road Master
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From: 500 miles south from Artic Circle
To prevent these leaks it's essential to have good bracket holding carb in correct place.
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Thread Starter
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Novice
Joined: Dec 2009
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From: washington state
hi all! BEEN SIDETRACKED THIS WEEK WITH ELECTRICAL PROBLEMS.SEPIXLH & ironmick i checked for manifold leaks and found none.i took apart the carb and it looked clean enough to eat off of! i adjusted the float level to shut off sooner and buttoned it back up. i put a new set of ngk plugs and fired it right up! thats when i noticed my generator was loose,W.T.F.? i shut off the bike to have a closer look.sure as **** the bolts holding it together have backed out. on further inspection i see that indeed the bolt holes are stripped maybe 2or3 threads in each hole at the bottom. also the p.o. had tried to drill & tap new holes that didnt line up so he just put the bolts in the ****ed up holes and called it good! (thanks! just what i need, my generator falling off at 70+)so i was off to the local salvage yard (bent bike) to find parts.i found an old generator for 20.00,tore it down and swapped end caps the brushes & bearings were good enough to keep too.so all is back together and done correctly!piniongear thank you for posting the info on jets and i will heed your advice by not changing out the jets.as soon as it quits raining i will be going out for a test run,maybe some of them gremlins have fallen off! anybody got a bell? ha.ha. *BEARD*
Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
If you are lucky it will just be a bad plug causing you the 'rich' problem. Your Mikuni should be without problems of any kind.
Now that you have disconnected the generator and replaced with another........ I gotta ask, did you flash the field before you started the bike up?
If not, do that now before you run it again. This could save you buying a voltage regulator.
Here is how you do that.....
Keep us posted on your progress.
pg
Now that you have disconnected the generator and replaced with another........ I gotta ask, did you flash the field before you started the bike up?
If not, do that now before you run it again. This could save you buying a voltage regulator.
Here is how you do that.....
Keep us posted on your progress.
pg