[img]i/expressions/face-icon-small-confused.gif[/img] Fellow riders and tinkerers, My 99 LT-500 started running like CACA this weekend. It won't idle unless I choke it down and when I let off the throttle it back-fires real bad. I believe my fuel is ok but can bad fuel cause that much trouble? How often should the fuel filters be changed in my machine. Should I add an aftermarket fuel filter to help protect the carb from trash? If I turn up the idle screw on the carb it seems to idle better but you can still hear it struggling along and missing. Any ideas??

 

I havent had experience with your quad before but i know enough to probably help you. it sounds like a jetting problem. By what you say about choking it you are probably running too lean. First, slowly turn the airscrew in for a little (leaner), the idle should go up, and then start to very slowly turn it out (richer), waiting a few seconds in between turns (try to turn it about 1/8 turn each time) until the idle starts to slow again, then turn it back in 1/8 of a turn. Once you have that tuned in work on the pilot jet. Does it bog or sputter and sound like its missing? If it is bogging, then go richer on the pilot jet, if its sputtering then you probably need to go leaner. Is it ok on the top end and just does it at first when you try to rev it? Make sure you check the plug first and check it throughout the process(make sure you use a new plug) It might also be a broken reed. Check that and also take your carb apart before you go through the jetting, and make sure you dont have anything floating around in there that could may be be clogging up the jets. Clean it out real well with carb cleaner. Also clean your air filter and make sure that isnt restricting the airflow. A fuel filter is always a good idea. I may be able to help more if you can be a little more descriptive like what is happening with your motor. good luck, let me know if you have any more questions.

If anybody can add to my post or correct what i said please do.

 

OOPS!!! SORRY I WAS THINKING YOU HAD THE LT500 AS OF THE QUADZILLA TWO STROKE!!! SORRY. Well anyway you might have your idle too low and that might be it, still might be a jetting thing. Do you already have a fuel filter that you havent changed? You might not be getting gas through there if you are too clogged up, check for pinched fuel lines that might just restrict the flow of gas. Disregard the reed thing and some of the other stuff that applies to two strokes only. Check your fuel filter first. AND SOMEBODY WHO KNOWS A LOT MORE ABOUT 4 STROKES THAN ME PLEASE REPLY SO I DONT MESS THIS GUY UP. good luck again

 

It could be the fuel, but it probably is something else. When you say you need to "choke it down" to get it to run, do you mean it runs better with the choke on?

Also, when it's back firing, is it coughing thru the carb, or popping out the exhaust?

Did the problem just start all of a sudden, did it show up after doing any maintenance, or is it something that got progressively worse as the day went on?

With these questions answered, we can probably help you target the first few things to check to fix the problem.

Thanks!
Pam

 

Yes, it backfires through the exhaust---a lot. I talked to the head mechanic at Suzuki yesterday and he told me almost the same thing. That it was likely too lean and had something in the kets. Is thewre a way to blow that junk out of there without removing the carb?[img]i/expressions/face-icon-small-happy.gif[/img]

 

Nope, you gotta take off the carb and clean it out real good with carb cleaner in the float bowl and take out the jets and shoot it through there so it flows smoothly. Also make sure you shoot it through all the holes and passages of the carb to make sure nothing is floating around in there to clog the jets up again. Once youre done, spray some wd40 on the slide to lubricate it. Make sure to clean it very well. And while your at it you might want to pick up some bigger jets, just go size by size, dont skip a few sizes. Good luck, let us know what happens.

 

Well, if it's backfiring thru the pipe, it's not lean. A lean bike will "cough" through the carburetor (too little fuel gets the cylinder too hot and the fuel ignites before the intake valves shut, and it "back - fires" into the carb).

Backfiring thru the pipe is extra fuel (from a rich condition) that didn't get burned in the cylinder. The fuel ends up in the hot pipe, and bang-o! It goes off!

Incorrect timing can also cause this problem (ignition not occurring at the right places, or the cam not opening or closing at the right places), or poor spark from ignition problems or a crappy plug.

Putting on the choke reduces the amount of air going into the carb & cylinder. If an engine runs better with the choke on, it normally means something is lean.

However, if it's backfiring out the pipe, it's rich. This leads me to believe it's not a jetting problem (since your two clues lead in opposite directions!).

You can try cleaning the carburetor. It means completely disassembling the carb and carefully cleaning each orifice with carb cleaner (don't stick a wire in the jets).

I'd try something easier though. I'd try a new spark plug first, and clean your air filter. Make sure the pipe doesn't have any obstructions.

If these things don't do the trick, you might want to take it into a mechanic and have him take a listen to it.

I really don't think it's a carb problem.

 

we have had several quads with the same exact symptoms. In both cases it was dirt in the pilot jet. You have to be able to remove the bowl to get to this jet. Not sure how much room there is on a Suzuki. We have had very dry conditions here in NY which I think has contributed to the problem.

 

you are running lean if you backfire through the eghaust you might also want to check for air leaks(carb boot cracked)

 

<< you are running lean if you backfire through the eghaust >>



Nope. Lean conditions cause a bike to cough thru the carb. Rich conditions cause it to backfire thru the pipe.

In some cases, a lean condition on the pilot circuit can cause tiny backfires in the pipe on decelleration (poppp...poppp...poppp). This is the condition that Joelpolaris was able to fix by cleaning the pilot jet.

But the basic rule of thumb is - unspent fuel in the pipe = rich. unspent fuel thru the carb = lean.

There is also the timing issue with a four stroke (cam and ignition). I've gone over this ad-nauseum in other answers. If you're really interested, I can repeat the whole thing, but my fingers get tired!

C'mon guys. Please have your facts correct before answering a tech question. We don't want to do more harm than good! As thumper said in Bambi &quot;if you don't have anything right to say...don't say anything at all!&quot; Okay, so I paraphrased [img]i/expressions/face-icon-small-wink.gif[/img]