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318 question (new owner)

2109 Views 18 Replies 15 Participants Last post by  PA318Guy
Hi guys! I just got my first real lawn tractor last week. It's a 1990 JD 318. 50" deck, 1495 hours, with a rebuild done at 1200. Everything on it works well. A little smoke on startup, but nothing major. I would like it if you guys could confirm my feeling that I need to clean the carb. Or maybe you have some other ideas. The problem is rpm surging unless the choke is open just the right amount. If the choke's in, the rpms go up and down at a regular rate. Doesn't matter where the throttle's set, or if it's under a load, it just keeps going up and down (surging). With the choke out, it evens out and runs pretty good, but smells pretty lean. Is running it like this bad for it? I will take the carb off soon and have it cleaned. I ran some seafoam through the carb and also put some in the gas. But it's still doing it. Thanks.
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^ Had this issue on an Onan powered ( that`s what is in your 318 right?) Ingersoll, carb disassembly and cleaning made it disappear. Would not hurt to "run through" the entire fuel delivery system YMMV
You could do a quick carb cleaning, but there are a few other things to check.
-Check the little vent hole in the gas cap.
-Check your fuel lines for cracks.
-Check the vacuum line to the fuel pump
-Perform a fuel pump volume test
-Check the fuel filter (is it dirty, or the wrong kind)
-Check the air filter and pre-filter
-Check for manifold leaks with an unlit propane torch

And welcome to the forum!
Thanks guys! I will check it out and let you know how it goes.
no reason to pour your seafoam into the carb. mix it strong in the gas. you have varnish in the jets
No need to send it out for cleaning,(you would have to remove the intake and exhaust) just take the top off,it is very simple carb.When you pull out the jet in the front of carb you will find holes in the side BUT there is one hole in the bottom as well,you will find it is plugged anmd thet is what is causing the surging and have to have the choke on,a welders tip cleaner works fine,the hole is so small you may have to do it more than once
Welcome to club. There are a lot of 318 owners past and present here who aren't stingy with helpful advice.

Don't feel bad 'bout having to wrench on your new cylinders, they're kinda old but worth some TLC to keep them working for you. I'm going through the same type of troubleshooting right now. Mine's not surging but rather I'm running too rich so I'm reading all the carb tips I can find here.
As states in a prior post. Lift the top of the carb. Clean the Jet out, It just takes a small screwdriver to get it out. I just wish I would have had all this help Back in the 60s when I started Rebuilding Garden tractors;; You folks are all Outstanding.
Welcome to the forum. I'd like to say you don't have a Lawn Tractor, you have a Lawn & Garden Tractor. Big difference! That 318 is a nice little beast. Congrates on your purchase.
Welcome to the Forum:MTF_wel:
When it happened to mine the dealer's service tech recommended using an air gun to blow down through the carb. He was very specific to set the pressure at no more than 10 PSI so that no damage occurred. Took about 2 or 3 times and then it cleared right up without removing anything but the air filter! When it happened the 2nd time and that didn't work I replaced my 25+ year old fuel lines and I've not had the problem since!
Anytime (that I can think of) that you need to pull the choke to get a motor to run right means that it is lean. This can be due to dirt, varnish or some kind of build up in the jets, air sucking in the fuel lines...ect.

Mine only surged when at idle so I just richened up the air screw and no more surge.
:MTF_wel: clayemt:)

You've come to the right place for help. There are quite a few members here that know what they are talking about.:fing32:

What Kind of fuel filter should be on a 318? I bought 3-4 months ago and it has a surging problem. We put a carb kit and and it cleared up for about 3 days. So this week I have ran through the carb again and split the intake. I need to reseal it. Now not sure what type a silicone to use that is gas resistant.
Right now it has canister type gas filter which doesn't look right but I don't know.
Any help would be great.
Also new to forum.

re: " -Check for manifold leaks with an unlit propane torch "

What's this all about?

Well this week I took everything apart. I took the intake off and Carb. I had gone through the carb about 2 months ago and it ran fine for a few hours. So for the time I blew it off. So I went and cleaned the carb. I also split the intake not bad to do at all. So I searched for a silicon that was gas resistant. I could only find one Motoseal 1 from permatex. Well I couldn't find it anywhere I live. I would have to order it online. So I thought I would call JD to see what they use. They told me they really didn't have much luck with silicon. They told me they use JB weld, they said you will never have problems with it again. They suggested taking your time and making sure everything is clean. So I used JB weld and now I have a on piece intake now. Installed new intake gaskets and with a fresh cleaned carb, knock on wood it would start and run with out issue.
And it did. I mowed a little with and it idled like a dream. I have only had this for about 4 months and it always had a surging or what JD likes to call it (hunting). So I expect to run great later today when I take it out to mow.
That is how I resolved my surging issue.

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re: " -Check for manifold leaks with an unlit propane torch "

What's this all about?

The propane, when sucked into a vacuum leak will change the idle.

Some folks also use carb cleaner.
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