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1986 JD 318
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Discussion Starter #1
Hello again everyone,
Here's another question for the 318 brain trust and I mean that in a good way. As you may recall I have a problem with my 318 starting in the cold weather. The opinion is that it may be a leak in the intake manifold.. So before I jump into that project I was wondering if there could be anything else that would cause the problem but also I have a surging problem unless I have the choke partially out. Even after the engine is warmed up.

I have a great spark, electric fuel pump with glass fuel filter so I know it's getting fuel. Last year I disassemble the top portion of the carburetor and cleaned it out with standard carb cleaner. Reassembled it and adjusted the idle and mixture after warm up. I will say that as I recall the ball park setting for the mixture is normally 1 & 1.2 turns out from bottom. It didn't seem to matter how much I backed out the screw that there was almost no noticeable difference in how it ran. Could there be something going on with the carb ?

Any ideas would be greatly appreciated.
 

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If you have not checked for a leaky manifold, no amount of carb cleaning and adjusting will fix a leak. Get busy checking for the leak (it does follow after the carb), so adding more gas via the choke seems to help from what I've read of your post. The only other thing is head decarbon and valve adjustment may be needed.
 

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1986 JD 318
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Discussion Starter #3
If you have not checked for a leaky manifold, no amount of carb cleaning and adjusting will fix a leak. Get busy checking for the leak (it does follow after the carb), so adding more gas via the choke seems to help from what I've read of your post. The only other thing is head decarbon and valve adjustment may be needed.
OK. Thanks for the tip.
 

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A quick way to check if manifold is leaking is with a propane torch. Start engine, move propane torch along seam in manifold and at intake gaskets. Do NOT light torch, just open valve. If something is leaking, the propane will get sucked into the leak and your rpm will change... no change in rpm means no leak. Bob
 

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1989 318
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Thanks for the reminder Bob, I should do that on mine today just for 'fun'. I am bust replacing tires on my new-to-me-110RF, it is a beautiful day here in the Midwest, a tad cool but not bad. I hope the crappy weather moves out of the great northeast, it has been messing with them folks too long.
 

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If the carburetor is spotlessly clean, you have an air leak somewhere...that is what may be causing it to surge. Check the intake manifold and search this forum for "318 surge." One of our late contributors posted it and it is very thorough...and very good at leading you through the surging problem.
 

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1989 318
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I did the propane trick on mine this afternoon and did not hear any surging as I swept the intake manifold. I had it at idle at the time, and even if I held the torch directly above the carb I did not detect much increase in rpm. No, my torch was not empty. I was thinking after the experiment that maybe I should have had the throttle more open sucking more air??
 

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1986 JD 318
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Discussion Starter #8
A quick way to check if manifold is leaking is with a propane torch. Start engine, move propane torch along seam in manifold and at intake gaskets. Do NOT light torch, just open valve. If something is leaking, the propane will get sucked into the leak and your rpm will change... no change in rpm means no leak. Bob
Bob, I finally got around to trying your suggestion. A full disclosure I did not completely remove all sheet metal surrounding the intake manifold. I was however, with a flexible tubing attached to the the torch so I was able to reach most of the manifold. No change in RPM. It was about 45 degrees this morning and the 318 started right up after 2 or 3 rpms. I figures this would be a good opportunity to clean off the engine etc. I used my garden sprayer with Dawn Liquid cleaner and water. Amazing job it did. Rinsed off with clear water. I did protect the mouth of the carb and the breather hoses. What I did notice after the cleaning was two things. Most of the bolts that you would have to loosen to remove the sheet metal exposing the intake manifold had previously been worked on. Looking at the intake manifold it looked original meaning it was riveted together. But clearly there was a gasket between the two halves. It was of thin rubber type membrane (heat resistance). I have owned the 318 for almost ten years so I can only assume that the original owner may have had some work done. I purchased it from a guy who bought it at an estate sale.

Any thoughts ?
 

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I've never tried the propane torch thing, just something I read and wanted to pass along, as it make sense to me! My next step would be dismantle & clean carb using a soak tank type cleaner. This tends to clean a little deeper inside the carb than the spray can cleaners. Auto parts stores usually carry it. Get a gasket kit and do a proper rebuild. Bob
 

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1986 JD 318
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Discussion Starter #10
I've never tried the propane torch thing, just something I read and wanted to pass along, as it make sense to me! My next step would be dismantle & clean carb using a soak tank type cleaner. This tends to clean a little deeper inside the carb than the spray can cleaners. Auto parts stores usually carry it. Get a gasket kit and do a proper rebuild. Bob
Thanks for the suggestion. It's on my next to do list.
 

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All good advice but my first step before digging into the manifold is focusing on the jet shown in the photo. This can be accessed from the top and make sure the bottom of the jet is not occluded.

If you go down the path of resealing the manifold, Boomer gave me good advice to test it for leaks with water. Just cap off the place where the carb sits, turn it over and fill it with water and test for leaks after 30 min.
 

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Discussion Starter #12
All good advice but my first step before digging into the manifold is focusing on the jet shown in the photo. This can be accessed from the top and make sure the bottom of the jet is not occluded.

If you go down the path of resealing the manifold, Boomer gave me good advice to test it for leaks with water. Just cap off the place where the carb sits, turn it over and fill it with water and test for leaks after 30 min.
In the photo your referring to the vertical rod with the holes in it ?
 

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1989 318
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As far as testing a sealed manifold for leaks using water.........water is something like 50 times as dense as air so even though it may not leak water it certainly may leak air. Oops, just checked, water is actually 750 times more dense than air, I love Google!
 

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Tom, Don't let your wife see this post. She will wonder who you are calling Google.
 

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LOL. Boomer’s rational for the manifold water test is do it right. Should the Onan still surge there is high confidence it’s not due to the manifold and the culprit is the carb. If you’ve ever spoken with him you will quickly learn he’s one of the leading authorities for Onan engines.
 
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