Author Topic: Loading up at partial throttle (Read 2302 times)

supernutt · « **on:** August 11, 2013, 10:02:04 AM »

I have a Neil ported pro-x 310 cylinder on race gas 38mm pwk trx5 pipe cr250 ignition motor. Went trail riding with it the first time yesterday. Runs real good except that it seems to load up at about 1/8 throttle. Running the sides of the roads to get from trail to trail we are limited to 25mph. I usually just put along in 5th gear low rpm to respect the people that live on the roads. Then when I get back into the trails the quad just sputters and burbles at higher rpms for about 10 or 15 seconds until it gets cleared out. I tried it at 1/2 throttle and at full throttle and that does not make a difference. So I assume there is too much fuel in the crankcase at that time? And should I try a different pilot jet? I think I have a 55 in there now. DGK needle 192 main which is a little rich but not too bad. I have noticed that people in other parts of the country seem to be able to run much leaner jets than I can. Thanks for the help.

C-Leigh Racing · « **Reply #1 on:** August 11, 2013, 10:51:56 AM »

That pilot sounds right for where you live. Its sounding right for what you say is happening at slow speed & low rpm as well.
When you take a modded race engine & try to slow ride it, the jetting will normally be to rich when going slow & will puddle the excess fuel in the crankcase. Once your in the clear & ready to hammer on it, that excess fuel will then be whooped up & sent on into the ports, so the engine will be in kind of a flooded state until the excess is used up.
The only problem with what is happening, if you jet so that it wont happen, once your in the clear & hammering on it, your probably going to seize the piston from being to lean.

Its one of those thing like, say you sold the quad to a guy never had one like yours before, so his riding levels not the same as yours & then during riding he realizes it running rich, so he jets the carb down to his state of riding level. Then one day you come over & ride it hammering on it normal just like when it was yours, next thing you know the back tires are sliding & engine locked up, all because it was jetted for his riding level.

A 250R engine, only if it is a stock build, can be rode slow like that. There may be times on a modded engine, some slow riding can be done, but the throttle needs to be burped quite a bit to keep the in coming fuel cleared out, kinda like you see race cars on a pace lap after a wreck gassing it.

You might could change the slide needle, get one a bit larger to make it leaner at that throttle opening, say maybe a CEL, but you dont want one to make it run leaner on top.
Have you tried a different clip setting on the needle.
Neil

supernutt · « **Reply #2 on:** August 11, 2013, 11:08:03 AM »

I have not tried a different clip setting. I am in the middle right now. I dont think I should lower the needle at all. I think I have a CEL that I can try.....And I THANK YOU for your response. Now that I know this cannot be tuned out I should be able to live with it but I will try a different needle.

udontknowme · « **Reply #3 on:** August 11, 2013, 01:49:19 PM »

dgl/cgl/dgn/cgn depending how the part throttle is sounding. get a few pilots and see the affects when you change em. if it wont run with the choke off thats good indication pilot is alittle small. hard to say on the main just listen how it sounds and check the plug. be sure the pilot and needle is in the ballpark and engine cleaned out before messing with the main. problem is the pilot or needle may be loading it up and your getting a false sense its the wrong main. gonna have to experiment one thing at a time

supernutt · « **Reply #4 on:** August 11, 2013, 08:38:21 PM »

I tried a CEL in the middle and rode it around....It made no difference...It still loaded up.. Then I dropped the needle 1 clip and rode it again and it made no difference when riding slow....But the 1/2 throttle position was definately lean so I put everything back. And I had a 52 pilot in it. I dont know if I should go to a B needle or not? I would assume that a clip change is more than going from D to C? Also it is a #6 slide and I dont know if changing that will help or not...Maybe I should just try to burp it once in a while....Definately dont want to be too lean!!

supernutt · « **Reply #5 on:** August 11, 2013, 09:23:36 PM »

One other thought. I had the cases bored out for a 330 cylinder when I built this for future expansion. Could this be contributing to the fuel puddling problem? They warned me that I would loose 1 or 2 hp....but I was willing to accept that.

rsss396 · « **Reply #6 on:** August 11, 2013, 10:36:16 PM »

the small amount of extra crank crankcase volume is not going to to make a large difference in this problem. Two strokes in general like Neil said need the crankcase cleaned out of fuel and to do that you need the air moving at a higher velocity and it takes rpms for this to happen. Otherwise you have to run real lean and that can run into issues as weather changes or riding conditions change. I would following the tuning tips in the tech section for sizing the pilot jet properly then if you want more lower the needle by moving the clip up 1 slot. You could add a little ign timing and close the plug gap up.

supernutt · « **Reply #7 on:** August 11, 2013, 10:52:58 PM »

I will try the plug gap and add timing and see how that affects it. Thanks