I live in Costa Rica. Brought 2 Dingo 250's with me last Sept. Got some dirty gas. Engine would not idle. Found the idle jet clogged. Cleaned it and blew out the rest of the carb. Now it idles good, but will not take throttle. Found that crimping the small hose coming from the small vacuum valve will change the idle and allow for throttle, but when I release the hose with the throttle on the engine bogs and and dies/backfires. Can anyone tell me how this carb works? I thought I understood SU type carbs, but this one has me fooled. I understand the elecric choke, but temp is not an issue here (does not get below 75). Engine ran very good before the dirty gas. Only has about 10-20 hours on it. Both atv's got the dirty gas. I think this problem is in the idle mixture and idle speed circuit, but what is the function of the little vacuum valve attached to the upper rear of the carb. Is this valve open or closed during idle? What does this valve regulate? It seems to control an air loop from the side of the carb to the rear or vice versa. Need some help Please.

 

Here is an update on my problem. Engine starts fine. Idles good. Idle mixture adjustment has little effect on the idle, but does affect the throttle to some extent. At steady partial throttle(it will not take full throttle) the engine surges. If I put two fingers over the intake, it throttles up fine all the way to the top. Any ideas anyone?

 

sounds like your main jet is still clogged.
fuel fliter maybe
sticky float or not set properly
dirty air cleaner
sometimes when you get dirty fuel it takes a couple of cleanings to get it all out some times there is crap still there i would pull carb again and inspect
is your choke working properly

 

Hey thanks for the input. Since it starts easily and idles good I do not think the choke is involved. All my efforts are without the air cleaner. So the air cleaner is not involved either. The unit only has about 20 hours on it and it is pretty casual riding. We use our 250's for running around the development we live in down here. Lot of up and down riding with grades up to 30%, but good dirt road. I will tear down and try carb cleaner and blow everything out. The idle jets were plugged good so your assessment about the mains is probably good. Can you steer me to a good aftermarket carb for these engines? Also, a good aftermarket in- line fuel filter? These are our first ATV's so we are not part of the "ATV community" yet. This engine does not have a fuel filter, just a sediment basin in the bottom of the float bowl.

 

You can go to any of auto parts or lawn equipment place to get a simple inline filter. Did you say you were trying to run it without the filter? Alot of these will not run right without the filter because you are giving it a lean mixture. So you say you can put your hand over the intake and it will rev? Sounds lean. Put filter back on. You can get a new carb pretty cheap if needed. Also are you sure the line you talk about is not a vent line? vent lines should be open on the other end. Hooked to just the carb. You may have a line hooked wrong so the carb cant release vacuume.