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  #11  
Old 29th September 2011
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Originally Posted by RRB View Post
... could you have a big intake manifold air leak? Spraying propane around the manifold with the engine just above idle might give you an indication of this, if the rpms increase ...
I have not yet found an intake leak with propane, i think because i have always managed to seal them up well and have not had a leak to be found. However, as a test, i have sprayed it directly into the air cleaner.

The RPM do not increase, rather the engine almost immediately stalls.

Several times i have seen posts where guys say the RPM will increase. Now i am wondering if this is misinformation being unknowingly passed on? or if that is a direct experience?

My expectation is that, if there is a leak, the RPM will decrease.
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  #12  
Old 29th September 2011
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Originally Posted by bhakakha View Post
PG,
Thanks. I will try to start like you have outlined. If it doesn't work I will take apart the carb and clean it. I thought I had read about the priming kicks on this site. Maybe it does not apply to the Mikuni carbs. I can't thank the members of this site enough for all the info I have received. I hope to one day gain enough knowledge to help the newcomers as they come in.
Ben
you did read about priming kicks here. I indicated it in this thread:

http://xlforum.net/vbportal/forums/s...0&postcount=15

My apologies, I wasn't sure at the time what carb you had on the bike. However, you have done the right thing in starting this thread and catching Piniongears interest....you are in good hands now.
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  #13  
Old 29th September 2011
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I did change the intake manifold when I first got the motorcycle. It was old and the it was the only thing holding the carb up (no bracket had been installed). Do you think I should remove it and put it back on. I didn't use a sealant and looking on the web it sounds like I should have. Silicone sealant has been recommended, does that sound okay? Still stuck at work (coming on 20 hours) so haven't had a chance to try starting bike yet.
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  #14  
Old 29th September 2011
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Originally Posted by IronMick View Post
I have not yet found an intake leak with propane....My expectation is that, if there is a leak, the RPM will decrease.
You could be right, Mick. If so, then I am in error. I have never found a leak with propane either, or with WD-40. I've just been following conventional wisdom in that regard.
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Old 29th September 2011
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the vm38 is pretty simple! yes, enrichen is lever down. this system when in enrichen draws air through the float bowl. this being said, it is imperitive that the throttle is not opened or the system is by-passed. if the idle screw is to far in, it can also affect the system as sometimes, the idle is used to cover over other issues which should be addressed first. being that there are air passages, the use and care of a good air filter should be foremost. you might need to clean the carb and look at the plunger to see if the seals are "ok". i have been running this carb since 1975 and it is a great unit especially for a manuel foot. the kids can flood out the engine on a accellerator pump type carb while you are parked and away. my ritual is key off, two primer kicks (hd only turns over once per kick), key on and will either start on next kick or the next.
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  #16  
Old 29th September 2011
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I am not familiar with the 38 round slide mikuni carb so i do not know about the manifold that it uses. Is it the stock IronHead mani? Are you referring to a rubber or whatever connection between that mani and the carb?

With the stock carb/mani there is a rubber seal, either an o-ring or a band depending on the year etc. Some guys wrap the seal with some teflon tape. The t-bolt clamps are highly recommended rather than the stock clamps.

I do not recall anyone recommending the use of a silicone sealant.
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  #17  
Old 29th September 2011
bhakakha bhakakha is offline
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Mick,
I will have to take a picture and post it. It is rubber, I think like the stock (I believe I bought a stock one and it was exactly the same as the one on the bike). I am not familiar with a lot of what is said in this forum and I am learning as I go.
Ben
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  #18  
Old 29th September 2011
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Quote:
Originally Posted by bhakakha View Post
I did change the intake manifold when I first got the motorcycle. It was old and the it was the only thing holding the carb up (no bracket had been installed). Do you think I should remove it and put it back on. I didn't use a sealant and looking on the web it sounds like I should have. Silicone sealant has been recommended, does that sound okay? Still stuck at work (coming on 20 hours) so haven't had a chance to try starting bike yet.
Before you remove the manifold try the starting the engine using the method I described.
This will allow you to have some idea of what made it better.
If you change a number of things at one time and the result is that it does better, you have no idea which did the fix.

If you are in doubt about the O rings sealing the manifold by all means install it again and use new O rings unless you put new ones in before.
DO NOT use any kind of sealer on the O rings.
The O rings seal by expanding when the clamps are snugged down.

When you have the carb and manifold removed, hold the manifold in place and look at the gap between the manifold and each cylinder connection.
The gap should be approximately 1/8 inch and parallel.

If the surfaces are not parallel............ you want to loosen the 4 nuts holding down a cylinder and using a plastic mallet bump the cylinder base to rotate the cylinder enough to line up parallel with the manifold face.
The O rings sit in this gap and expand to fill the gap when the clamps are tightened down.

With the carb off, install the manifold and O rings feeling the inside surface of each ring with your finger as you snug down the clamp(s).
Do not over tighten the clamps.
The O ring should feel the same all around 360° inside the manifold.
If you feel anything other than a smooth surface you will have an air leak.
If that is the case, remove the manifold and start over again.
pg
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  #19  
Old 30th September 2011
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Finally got a chance to try it. PG, I did exactly as you described. Petcock on, ignition on, starter on, no gas given, no primer kicks, kicked it a few times without throttle...nothing. Could hear the air being pulled into the carb, nothing else. So I turned the ignition off, gave a couple priming kicks (as suggested by someone else), turned on ignition, kicked it, still nothing. Figured I would try both suggested ways. Also, I was mistaken. I did not change the manifold, I just put a new connector from the carb to the manifold. The manifold is metal, the connector is rubber. There was a paper gasket between carb and connector. I guess there could still have a leak in that series of connections. Next step will be to take off and clean the carb, along with a new pilot jet. Any other suggestions? Thanks, Ben
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  #20  
Old 30th September 2011
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OK, thanks for the update. Sorry it did not fire up.
So......... remove the carb and take it apart for a good overnight soak in carb cleaner. DO NOT soak any rubber parts in the cleaner.

Then try to blow out the passages with air after a good rinse with HOT water following removal from the cleaner. Put the carb back together.

Before the carb goes back on use your finger to rub around both O rings in the manifold.
You are looking for a part of the O ring that is not smooth.
If they feel even all the way around then they should be sealing.

Make sure you can see through each of the jets to be sure they are not stopped up.
Reinstall and try again.

Also you want to be sure the ignition is firing strong. It takes two things to make the engine run..... fuel and spark.
Then update us with the results.
pg

PS: If you can see light through the pilot jet hole then the jet is good.

Last edited by piniongear; 30th September 2011 at 05:02.. Reason: added PS.
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