Engine won't idle

[Waternut]

Ok so I have a fairly new carb rebuild kit installed (less than a year old) and it hasn't ever been tuned properly. I'm trying to get it ready for spring but every time I start it, it will run for 2-3 seconds and die. If I turn the idle up, the revs will sky rocket and it runs a few more seconds and dies. After it dies, it will not restart unless I choke it. Once the engine warms up it idles a little better but still not consistently.

What I've tried...
I've gotten one of the JRE tuning plates to adjust the pop off from max to min with no real change.
I have an older spare fuel pump...no change.
New needles and adjustment screws.
New fuel lines.
Tried clearing the internal fuel lines and vent lines but never found anything.
I replaced the following gaskets: carb, head, exhaust pipe, exhaust manifold, and intake manifold.
I have the gaskets for the entire top end but I'm not confident enough to replace the rest without detailed instructions.

Anyone have any suggestions?

 

[robertg]

Sounds like an air leak to me.

 

[astral]

Sounds like an air leak or bad reeds.
Check and see if the butterly's in the carbs are in sync.
1 turn out on the high speed screw
1 1/4 on the low speed screw to start with.
Check compression.
Check pulse coming from crank case.

 

[Waternut]

The reeds looked fine when I pulled them out and replaced the intake manifold gasket.
There is only 1 carb.
Compression is at 155 and 156 psi but it has a milled head that supposedly produced 175psi so I guess it's a little down. I wouldn't think that would cause it though but maybe...
I hooked up a clear pulse line to see it in action and fuel flows through it in what looks like giant bubbles. Is that normal?

The leak does sound very possible since the only time the engine stumbles is at low rpms. If I milk the rpms up, it runs normal. What would be the best way to check for leaks and where should I start?

 

[SUPERTUNE]

Pressure check the complete engine to find any air leaks. If an older engine...most likely bad crankshaft seals if a leakage problem exists. Make sure your pilot/low speed circuit is not clogged or restricted.

 

[Waternut]

Well I couldn't find any leaks by spraying soapy water. Then after sinking the engine in partially in water (deep as the kitchen sink went) I managed to find one leak right below the intake manifold in the crankcase seal and I put some epoxy on it as a temporary fix. I also saw what appears to be a crack in the crankcase but it wasn't leaking. I cleaned that up and hit it with some JB Weld so we'll see how that does. I'll check it again tommorrow when everything hardens and see where I stand.

There has to be more though. I pumped it up to 7-8 psi a couple times and it was back down to almost nothing in about a minute.

 

[SUPERTUNE]

Pull the front cover,flywheel and spray the front seal...

 

[Waternut]

I actually took the flywheel cover off before pressue checking it and submersing it in water. It doesn't appear that either of the crankshaft seals are leaking.

 

[keefer]

The reeds looked fine when I pulled them out and replaced the intake manifold gasket.
There is only 1 carb.
Compression is at 155 and 156 psi but it has a milled head that supposedly produced 175psi so I guess it's a little down. I wouldn't think that would cause it though but maybe...
I hooked up a clear pulse line to see it in action and fuel flows through it in what looks like giant bubbles. Is that normal?

The leak does sound very possible since the only time the engine stumbles is at low rpms. If I milk the rpms up, it runs normal. What would be the best way to check for leaks and where should I start?

If you have fuel in the pulse line then you have a leaking diaphragm in the fuel pump section of the carb. This might explain some of your problem. Use a soap / water mixture in an old windex bottle to check for leaks. If it is not holding pressure you will definitely make bubbles if you spray all seals & gaskets.

 

[Waternut]

Ok I've narrowed it down to the head. I have a brand new gasket and it didn't say which way was up so I used the same basic idea as the last gasket that was in there. There were about 5-6 leaks with all the bolts torqued properly. I flipped the gasket over for sh*ts and giggles and it went down to 2 really small leaks.
It's not the head because I have two different heads and they both leak in the same place. I couldn't see any cracks in the cylinder so maybe it's just some buildup that needs to be lightly sanded off with very fine sand paper. What do you guys think?

 

[astral]

Scrap the gasket area with a razor blade to remove the old stuff.
Make sure there is no old gasket/glue on the surface..
You can use a deburring wheel also..

 

[Waternut]

Ok it has to be something funky. Depending on which head I use and which way I install the head gasket, the leaks can range anywhere from 1 to 6 and all different locations. One leak is always in the same place but I can't find anything that would cause it. Right now it holds 10 psi for about 5 minutes and then the gauge reads 0. It's not really zero because there's air that can be released but probably close enough.

This game sucks!!! :banghead:

 

[Waternut]

What about spraying this stuff on the metal gasket itself to seal those little imperfections? High temp copper gasket spray.
http://www.permatex.com/products/au...r_Spray-A-Gasket_Hi-Temp_Adhesive_Sealant.htm

 

[route66]

What about spraying this stuff on the metal gasket itself to seal those little imperfections? High temp copper gasket spray.
http://www.permatex.com/products/au...r_Spray-A-Gasket_Hi-Temp_Adhesive_Sealant.htm

i've used that stuff on headgaskets before with good results. Although it's not really a fix for real problems like a warped head sealing suface, it's always seemed to me that it would help seal small scratches and imperfections.

 

[ANT]

Ok this might be a dumb question but, you said you checked the reeds and had cleaned the carb. Did you replace the two gasekts on the bottom of the carb and the two gaskets for the entire manifold, which would be 4 in total? You shouldnt idle weird with your head gasket like it is, you do still have 150lbs of compression.

There is on other thing I was thinking of, if there was an air leak it would most likely start dieseling or running away on you when you reved it up. So when you cleaned the carb did you remove the low-speed adjuster, low speed jet, and the two allen bolts one in the bottom underneath the diaphram and one on the bottom of the carb where the gasket sits against(which are plugs you can remove to access and clean the low speed circuit) and clean it out GOOD? Also check the tip of the low speed adjuster, sometimes if their old the tip will break off inside the passage and the tip of the adjuster will look rounded. With the low speed adjuster out, if you stick the red tip of a can of carb cleaner in the hole and spray, the stream your spaying in should come out in the throat of the carb underneath the butterfly valve (there is a tiny hole), out of both the allen head bolts you took out and out of the low speed jet; and the stream coming out of those passages should be just as strong as the stream your spraying in.

I would clean the carb again. It's easy to come by crappy gas these days with the ethonal sometimes it won't last longer than a couple days or a week and the inside of your carb could get a coat of varnish in it and fould everything up.

So basically thoroughly clean the carb like stated above, replace gaskets, and clean off ALL of the old gasket with a razor blade.

 

[Waternut]

2 gaskets under the carb?
I've got 2 between the reeds and the motor, 2 between the reeds and the intake manifold, and 1 between the carb and intake manifold.

It never diesels when I hit the stop button. It will race when it's started on land if the idle is high enough.

I bought some of the copper gasket spray and that sealed up all the leaks in the head. Then I found one more leak around the crankcase halves and sealed it up. I'll give it another pressure check when I get home later today.

 

[ANT]

2 gaskets under the carb?

for some reason i had single carb yamaha on the mind with that where it uses two gaskets because it has a bracket that mounts under the carb for the throttle cable

whatever you come up with its definetly a lean condition at idle.

 

[Waternut]

for some reason i had single carb yamaha on the mind with that where it uses two gaskets because it has a bracket that mounts under the carb for the throttle cable

whatever you come up with its definetly a lean condition at idle.

That's alright but you definately had me thinking since there were two gaskets in my gasket kit...

 

[Waternut]

OK after sealing 3 leaks in the crankcase seal and using that high temp spray to seal the head, I gave up and completely sunk the entire engine in water. As soon as I did that it was bubble city!! Problem was, almost all the bubbles were coming from the plates sealing off the exhaust and intake manifolds along with the pressure gauge I have laying around. I sprayed all that stuff but never found a leak...

I made a trip to Lowes and after brain storming all the things that could work I bought a ball valve, 2 test fittings, a plumbers pressure gauge, and a T fitting to connect them all.

Put all that crap together and the engine held 10psi for 10 minutes! Finally!!

Thanks for all the help.