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Quad Runner runs rough when hot ... help please

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Quad Runner runs rough when hot ... help please

Postby TerryUrb » Wed Jul 18, 2007 12:07 pm

I have a LT-4WD 1991 Quad Runner. A couple of years ago I started having problems with the carb flooding and hard to start when hot. I subsequently rebuilt the carb, but the same issue. I took it to the local Suzuki shop and $400 later, they told me that I needed a new carb as there was a problem with the carb. He apparently did set the valves, etc.

I bought another carb. The flooding issue is gone, but the hard starting when hot and running rough when hot is still there. When the engine is cold, it starts and runs great with lots of power. I set the carb pilot valve at 2 7/8 turns. I was told the problem was the pilot valve adjustment. Unfortunately, getting at the pilot value is not an easy task. I subsequently remove the carb and adjust it. It is sitting at approximately 1 3/4 turns ... no difference. When it is hot, it simply will not start properly.

I changed the spark plug and I have noted that it looks sooty. Yesterday when it was hot I forgot to check to see if it was getting a good spark.

Also, this new carb has an air intake on the top of the carb which is different from the original. If I plug it, the idle slows down. If I leave it open, it idles faster. Where does this connect? Obviously it is for a newer unit. The carb off the bike is a Mikuni BST31SS. The new carb is exacltly the same except that it has this extra hose. I check to see if this intake made any difference when it was hot. NO difference. However, I would like to know where this should go if anyone knows.

Any thoughts? :?:
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Postby TerryUrb » Sun Jul 22, 2007 11:45 am

So, I guess I have a very complicated issue with this unit. I stopped into the Suski shop and the mechanic suggested in making sure that the needle valve is being seated all the way in. There is a C-clip which varies the depth of the needle valve and apparently the deeper it seats the leaner it will run.

Have any of you guys run into this situation?

:cry:
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Postby TerryUrb » Tue Jul 31, 2007 8:11 pm

I tried changing the setting of the Jet Needle. I found the unit was hard to start , which leaned it out, but when it was hot, it did same thing ... hard or impossible to start.

I reset the needle valve back to its setting. When I start it, it starts first crank and runs good until it gets hot.

I was told that maybe I have a compression problem ... maybe a leaky valve. So I will try to get the compression checked, hot and then cold.

Does anyone know a good suzuki carb guy? :cry:
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Postby TerryUrb » Sun Aug 12, 2007 7:10 pm

The compression is 150 psi (after a few cranks) and is 115psi when it is hot. Is that enough decline to indicate a problem? I see in the manual, the bottom end is 110psi although the operational psi is between 144 and 188.

Any thoughts?
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Postby jnewell123 » Sun Aug 12, 2007 10:31 pm

TerryUrb wrote:The compression is 150 psi (after a few cranks) and is 115psi when it is hot. Is that enough decline to indicate a problem? I see in the manual, the bottom end is 110psi although the operational psi is between 144 and 188.

Any thoughts?
You are loosing compression somewhere, maybe in your Air-box since it is the wrong one ! Try going back to the original Air-box system. My Quad-Runner is very temperamental an does not like any changes hardly. Especially when it comes to fuel an air!Change or clean your plug if you do this!
Also check for hairline cracks that may open when hot or something is not tight when engine is hot.
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Postby TerryUrb » Sun Aug 12, 2007 11:09 pm

Thanks for your response. Excuse my ignorance, but what is the "air box system"? Are you refering to carb? The old carb was leaking before the needle valve and need to be replaced.
The only change I did on the carb was the pilot valve adjustment. The manual said it should be 2 turns out, and I tried it, but with the advent of this problem, it is now at 1 3/4 turns. The Quandrunner runs great when cold/warm but really goes down hill when it is hot.

Do you think it could be intake valve clearance? They say in the book 1 - 3 thousands, which is pretty small clearance.

Terry
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Re: Quad Runner runs rough when hot ... help please

Postby jnewell123 » Mon Aug 13, 2007 7:44 pm

TerryUrb wrote:I have a LT-4WD 1991 Quad Runner. A couple of years ago I started having problems with the carb flooding and hard to start when hot.

Also, this new carb has an air intake on the top of the carb which is different from the original. If I plug it, the idle slows down. If I leave it open, it idles faster. Where does this connect? Obviously it is for a newer unit. The carb off the bike is a Mikuni BST31SS. The new carb is exacltly the same except that it has this extra hose. I check to see if this intake made any difference when it was hot. NO difference. However, I would like to know where this should go if anyone knows.

Any thoughts? :?:
I am talking about what you are talking about in the second paragraph above! I think if you read what you wrote here is where your problem is. Get the right carb pluged on that hose if nothing else. Go back to the correct "Air Intake"on top of the Carb.
The valves were adjusted by the dealer according to one of your threads. If over 100 hours since the last adjust then yea do it again or spot check the clearance if you feel comfortable in not messing anything up, if not let the Dealer!
:wink:
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Postby TerryUrb » Mon Aug 13, 2007 8:29 pm

So what you are saying is that this carb is not the correct carb and go back to the original type of carb?

The old carb and the replace carb do the same thing. The only thing different was when it was in the shop, they adjusted the intake and exhaust vales. Before this heat problem, the old carb was leaking excess fuel and as long as I was travelling the leak was no problem however, when I took it in to them, afterwards this heat problem became an issue. I replaced the carb thinking that was the problem thinking that both problems were associated. You are saying they are associated.
All the hookup on this carb are exactly the same as my old one except that the newer carb has this intake. I asked the Suzuki mechanic and he said that because it came from the USA that it probably was hooked up to some type of air polution. ??
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Postby jnewell123 » Mon Aug 13, 2007 8:57 pm

I said your air intake was different. The new Carb is prob good but Plug the hose for the polution or what ever it is. It may cut off, ifit does that is for breathing possibly when it is hot or not. That hose bothers me a little but the biggest thing is the change of that "AIR Intake" position. It may not be breathing well if an when it gets hot from where it is pulling the air from outside the Quad! Yes I am guessing but it makes sense possibly when you said the Air intake was moved after changing the Carb. OBTW The Air box is the area where your filter sucks air when your Quad is all sealed up.
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Postby TerryUrb » Mon Aug 13, 2007 11:28 pm

The replacement carb fits into the air box with the filter attached, so there is no other input into the carb body except from the airbox. The other side of the carb fits into the engine air intake. I have blocked off the extra input which is a 1/4" opening. I put a hose on it and put a plug in the end of the hose with a clamp.
I am planning to first check the input valve clearance, hot and cold. That might tell me if it is still open when it is hot. The Suzuki shop is open tomorrow so I am planning to go in and have another talk with them.
Thanks for your help.
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Postby jnewell123 » Tue Aug 14, 2007 6:40 pm

TerryUrb wrote:The replacement carb fits into the air box with the filter attached, so there is no other input into the carb body except from the airbox. The other side of the carb fits into the engine air intake. I have blocked off the extra input which is a 1/4" opening. I put a hose on it and put a plug in the end of the hose with a clamp.
I am planning to first check the input valve clearance, hot and cold. That might tell me if it is still open when it is hot. The Suzuki shop is open tomorrow so I am planning to go in and have another talk with them.
Thanks for your help.
If they can not fix it go somewhere else . The mechanic may just be stumped! A different dealer may know or just call around in your area or state! :wink:
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Postby TerryUrb » Tue Aug 14, 2007 7:56 pm

You could be right. I chatted with another mechanic and he said it was a complicated problem which might take some time and $ to solve. I chatted with another Suzuki mechanic and he suggested looking at both the intake and exhaust valve clearances and said that the 250cc ATV is notorious for this issue. So I have my stealthy feeler guage in my hand and I am about to check it out and will let you know what I find. He said it will cause the bike to backfire, which it does when it is hot. So, the test will tell. 3th for intake and 5th for exhaust with the engine cold.
Thanks,
Terry
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Postby TerryUrb » Tue Sep 11, 2007 12:34 am

Just of complete this thread and hopefully for some benefit to another, I did get my ATV running just fine ... like it was when it was new.

1st the valves were misadjusted or were not adjusted at the susuki shop and we set the valves as outlined in the service manual.

2nd after fixing the valves the engine ran better but boggingout, which turned out to be a problem of too much gas by needle valve ... my problem in taking the carb in and out adjusting the needle valve.

3rd ... the screen between the air intake box and the carb was shellacked. As I cleaned the screen, I noted this brown stuff dripping off the screen. It looked clean, but it was plugged, not enough to stop the engine but enough to affect it's performance.
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Postby ext-man » Tue Sep 11, 2007 5:01 pm

Sounds like you had 3 issues thats always a hard one! Looks like some of the answers helped any of this on your own or did the repair shop do it all an how much did it cost you parts an the shops labor??
Got to Ride!
I use to ride fast!
Now I just Ride!

2007 Polaris 335 Magnum
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Postby TerryUrb » Wed Sep 12, 2007 1:09 am

Hi EXT-MAN,
Yes, it was quite a difficult problem to solve. I am sure it would have cost lots of $$$ if I had to have it fixed by a shop. I am quite good mechanically and have always fixed by own equipment. When the susuki shop charged me $400 and did not solve any problems, I was a bit gunshy to take it into a shop again. I did look for advice and I methodically went at every angle to figure out what was going wrong. It was a difficult problem.
Thanks for your comments. I hope this helps someone in the future. I did buy a used carb off Ebay for $69 and rebuilt it. All the time was my own.

TTFN
Terry
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