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  #1  
Old 14th August 2008
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Default Bike Running Like Crap

Hey guys, I have a weird problem that I can't figure out. I just got my (79) IH running but shes not running very well. When I first got her started she seemed to be doin alright. After letting her idle for a bit I pulled the plugs (new NGK's gapped to .040) and checked em out, they were a light grey. Decided that she was a tad rich but that was fine and took her out for a ride. The first night was a short ride and seemed to have went well. I took her back out the next night for a short ride and she started running really hot, pulled the plugs and the tips were white.

So I pulled the carb (Mikuni VM38) apart thinking maybe something got stuck in a jet, cleaned it and put it back on. So I decided to install a new set of NGK's just to see what color they would be after idling for a bit. When I pulled them out they look clean like they have never been used. The bike is also getting kinda hot. Also I noticed the the front cylinder exhaust pipe is smoking (white) a little.

As of now I pulled the carb apart and did a thorough cleaning (looks like new), adjusted the push rods and checked the timing. The push rods were a little tight but adjusted them according to the sticky. The timing mark at 2k is a little to the left of the timing hole and bounces around a bit. I also played with the enrichment screw on the carb quite a bit and it doesn't seem to get me anywhere.

As of now the plugs look new after idling for awhile and the bike smells rich at idle. This is what confuses me so much. The plugs looking clean and the bike running hot are both symptoms of a lean condition. But the bike smells of fuel at idle. Any ideas fellas?

-Chris
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Old 14th August 2008
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First thing that comes to mind for me is exhaust leaks. These cause the plugs to be whiteish and for the engine to run hot. The test is in a Sticky.
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  #3  
Old 14th August 2008
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When you say the timing mark is "to the left of the timing hole" if you mean over at the left edge, or past it, you need to adjust the timing. It should be within 1/32" or so of dead centre in the timing hole.

I would be suspicious of the jetting on that carb too. Do you know what are the recommended jets for that carb on an Ironhead? Is that what you are running?

I am not familiar with that particular carb, but if you say adjusting the idle mix is making little difference, it sounds like the carb is not jetted right at the low speed, either the fixed low speed jet or the slide needle might be too lean.

I would pay more attnetion to the colour of your plugs and the hot running and say the bike is lean. "Smell" is not really a reliable tuning tool, specially with modern gas.
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Old 14th August 2008
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Quote:
Originally Posted by White Nightmare View Post
... The timing mark at 2k is a little to the left of the timing hole and bounces around a bit ...
This is precisely why i use 3000 RPMs or slightly more when doing timing. The books etc all say 2500 [i think?] and it behaves as you say on each of the 3 ironheads i have timed. Has to be 3k or more.
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Old 14th August 2008
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Quote:
Originally Posted by IronMick View Post
This is precisely why i use 3000 RPMs or slightly more when doing timing. The books etc all say 2500 [i think?] and it behaves as you say on each of the 3 ironheads i have timed. Has to be 3k or more.
+1 on that. Full advance is full advance, so give it a full handfull of throttle when checking.
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Old 14th August 2008
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... and also, if you have a VOES disconnect it while doing the timing.
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Old 14th August 2008
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Please check for intake leaks also - my '79 has been prone to them.
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Old 14th August 2008
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Let me see if I can help out as much as I can.

Quote:
Originally Posted by White Nightmare View Post
I took her back out the next night for a short ride and she started running really hot, pulled the plugs and the tips were white.
If your plugs are gray/white then that usually indicates a lean condition, it would need to be richened. But look below first.

Quote:
Originally Posted by White Nightmare
So I pulled the carb (Mikuni VM38)
Probably one of the best carbs for these bikes.

Quote:
Originally Posted by White Nightmare
Also I noticed the the front cylinder exhaust pipe is smoking (white) a little.
This tells me you have an exhaust leak, just take the pipe off clean the exhaust port, put the pipe back on and make sure everything is tightened as much as you can.

Quote:
Originally Posted by White Nightmare
The timing mark at 2k is a little to the left of the timing hole and bounces around a bit.
You'll notice this quite a bit with points ignition. But if you want to get the timing mark as close to center as possible try lowering or increasing the points gap by one thousandth's of an inch. Much easier than trying to adjust the plate.

I also played with the enrichment screw on the carb quite a bit and it doesn't seem to get me anywhere.

Quote:
Originally Posted by White Nightmare
As of now the plugs look new after idling for awhile and the bike smells rich at idle. This is what confuses me so much. The plugs looking clean and the bike running hot are both symptoms of a lean condition. But the bike smells of fuel at idle. Any ideas fellas?
The mikuni carb is a very unique carb in that it doesn't use the same jetting as any other types of carb. There should be only two screws on the carb, both on the right side. The small screw closest to the air cleaner is the air adjustment screw. The larger one is the idle speed screw. The original "jetting" on these carbs:

Main Jet = 330
Pilot Jet = 30
Needle Jet = 166 Q2
Needle = 6DP1
Air Jet = 0.5

The needle in the middle of the slide (if you take it out) has 4 notches if I recall correctly. By default the e-clip comes in the middle notch of that needle. If by chance you need to richen the mixture or lean it out slightly raise and lower that e-clip. Raising it up (towards the top of the needle) will lean it out. Lowering it (towards the point of the needle) should richen it.

If your at normal idle speed (between 900-1100) RPM and you move the air mixture screw and it does nothing at all, then either it's seat has been damaged or the bike is really rich.

Take the carb apart and see if everything matches what I put above. That should be what you run in that carb and then richen it or lean it out by the e-clip on the needle.
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  #9  
Old 15th August 2008
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Default

Thanks for the help fellas. I checked the front exhaust pipe and it was slightly loose and was not on all the way. I'm hoping this is the reason for the slight white smoke.

I did the WD40 trick on the intake and came up empty, the idle did not change. I decided to pull the intake manifold off and everything looked good. Both o-rings are in good shape so I don't think its an intake leak.

I was playing with the enrichment screw earlier today and was able to get the front plug light grey. The rear plug stays clean and some steam rises from the spark plug hole when I remove that plug after running.

As of now it seems that the rear cylinder is running lean for whatever reason. I'll keep playing with things tomorrow and keep you all updated. Thanks again guys.

-Chris
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Old 15th August 2008
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Quote:
Originally Posted by supr2nr View Post
Let me see if I can help out as much as I can.
Thanks Randy for the excellent post.



Quote:
Originally Posted by supr2nr View Post
Probably one of the best carbs for these bikes.
I was thinking about changing out the carb at one point because I'm not super familiar with Mikuni's but I have been told numerous times that its an awesome carb and I would be dumb for getting rid of it. So its gonna stay on the bike for awhile.



Quote:
Originally Posted by supr2nr View Post
This tells me you have an exhaust leak, just take the pipe off clean the exhaust port, put the pipe back on and make sure everything is tightened as much as you can.
I checked the front exhaust pipe and it was slightly loose and not seated on all the way. The allen head screw that was in the clamp is rounded off (PO) and was difficult to get out. I'm going to pick up a new one tomorrow so I can tighten that thing down.



Quote:
Originally Posted by supr2nr View Post
You'll notice this quite a bit with points ignition. But if you want to get the timing mark as close to center as possible try lowering or increasing the points gap by one thousandth's of an inch. Much easier than trying to adjust the plate.
My bike has the dreaded first (and last) year electronic ignition. Its similar to the 80+ but everything is enclosed in the ignition housing its self. From my understanding it can get very hot in there and is prone to failure.



Quote:
Originally Posted by supr2nr View Post
The mikuni carb is a very unique carb in that it doesn't use the same jetting as any other types of carb. There should be only two screws on the carb, both on the right side. The small screw closest to the air cleaner is the air adjustment screw. The larger one is the idle speed screw. The original "jetting" on these carbs:

Main Jet = 330
Pilot Jet = 30
Needle Jet = 166 Q2
Needle = 6DP1
Air Jet = 0.5

The needle in the middle of the slide (if you take it out) has 4 notches if I recall correctly. By default the e-clip comes in the middle notch of that needle. If by chance you need to richen the mixture or lean it out slightly raise and lower that e-clip. Raising it up (towards the top of the needle) will lean it out. Lowering it (towards the point of the needle) should richen it.

If your at normal idle speed (between 900-1100) RPM and you move the air mixture screw and it does nothing at all, then either it's seat has been damaged or the bike is really rich.

Take the carb apart and see if everything matches what I put above. That should be what you run in that carb and then richen it or lean it out by the e-clip on the needle.
I pulled the carb apart and everything is exactly the same as you listed above. My jet needle is the same one you have listed but mine has 5 slots in it, I currently have my e-clip in the middle.

I listed some more info in the post above this one. Thanks again Randy.

-Chris
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