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sjc115
06-13-2005, 05:36 AM
Yesterday I went riding for about 2 hours and, as usual, my quad ran great all day. Made good smooth power, started easy, no hiccups.

I started the quad for what was to be our last run of the day and hit the track. I rolled onto the track and started getting up to speed. I shifted from 2nd to 3rd and pinned the throttle, as I always do, at the base of this one hill (more like a poor attempt at a small step up jump). The quad was way down on power and started to sputter with a real light backfiring sound. After I crested the hill, I backed way off the throttle and rolled around the next turn and up over a table top jump. Then the motor quit. It felt like it was not getting any gas. I checked to make sure the gas was on and there was fuel in the tank, both were ok. I started the quad again (much harder to start now) and let it run for about 30 seconds while revving it a little hoping that there was just some dirt in the carb that needed blown out. I started off again keeping the speed and throttle low for a few corners. As soon I as got on the gas hard, the same thing happened.

We loaded up and went home. Thinking it might be a dirty air filter (it was real dusty at the track). I washed the quad and started it up (again, hard to start like it wasn't getting enough gas). I lifted the rear end of the quad on a jack, put it in 2nd gear and let it run. It would not idle reliably without blipping the throttle periodically. When revved to full throttle, it would pop and backfire. I sprayed carb cleaner down the intake tube (in short bursts while revving the motor a little bit) but that did not seem to make any difference.

I have eliminated the air filter as the cause, what should I check next? Bad plug, bad gas, dirty carb, electrical problem, valve adjustment problem (vavles were adjusted 5 rides ago)???

Like I said above, it acts like it is not getting enough fuel when the throttle is applied. As long as I apply throttle slowly, it will rev up smooth until about 2/3 throttle and then it just starts popping and wants to quit.

The motor is a stock 350x with a 250x carb and has ran very well until this instance.

Help!!

Mobile Dyno
06-13-2005, 06:05 AM
Check the plug and tell us what it looks like? A peice of dirt could be clogging the main jet. You may want to pull the carb and take the bowl off and take the main jet out to see if it is clogged. Try those first!

bwamos
06-13-2005, 09:09 AM
Sounds like the problem.

After that... make sure your battery has a good ground.

Have you had the stator side of the case open lately?

If so you may need to make sure your stator bolts havent loosened up. If not.. then it's non-issue.

Loosing spark feels like loosing gas, sometimes. Some times a poor ground will let it run good at low rpms but at high.. it cant get enough juice and the plug stops firing.

sjc115
06-15-2005, 05:06 AM
I took the carb off, removed the bowl and cleaned the jets last night. I also changed the plug. Based on running it in my driveway, that seems to have fixed the problem. I won't know for sure until the next time I hit the track.

Here is another question for you guys. The plug I just took out was very black, indicating a very rich condition. The last time I changed the plug was after I jetted the carb (right after I installed the motor). From what I remember (it was over a year ago now) the first plug looked pretty good (if it was this black I would have done something about it right then). Could the very dark plug have been caused by the poor running motor this past weekend, or is it more likely that it was happening over time?

The jetting seems good to me. The carb transitions well through the whole throttle range, and there is no backfiring when I let off. Doing a plug chop run is not really practical for me since I have no good place to let it rip (except at the track, but if I need to re-jet I would like to do it at home in the garage). When I adjusted the jetting originally I did it by listening to the motor and using my ears to judge throttle response and rpm. What is the best way to determine a rich/lean condition without doing a plug chop run?

Mobile Dyno
06-15-2005, 05:35 AM
Put it on the Dyno with the A/F monitor. I'll be at the Quadfest event Dynoing July 15-17. It's being held in Heilwood, Pennsylvania. Check out www.thequadfest.com If you could make it I can get your bike dialed in for you. If your plug was really black the you are still real rich but it could be carbon build up to. What Jets are you running in it now?

sjc115
06-15-2005, 07:35 AM
Right now I am running a 135 main and a 38 pilot (I think). The motor is a stock 350x motor with the powroll conversion header pipe and suppertrap silencer (with all the disks installed, 8 disks I think). The carb is stock 250x.

As for thequadfest, I am not sure right now if I will be there. It all depends on whether or not I will be out of town for work. I should know my schedule fairly soon.

ReconRider25
06-16-2005, 05:15 PM
might sound like a dumb question, but have you checked the position of your choke? i rode a whole day and couldnt figure it out. i looked right at it and didnt realize it was on. same syptoms as you had too.:p