hi everyone,
i am new to the atv forums and i have a problem with my ac i just cant figure out. it wont start. i have good clean spark it is getting fuel and i set the timing tonight but still same problem, i am wondering if it would be a compression issue i am not sure what the compression should be on this atv, and i havent purchased a gauge yet to check it, any help would be greatly appreciated.
thanks
grill

 

With the throttle wide open (WOT), crank engine 5 to 10 compression strokes. Your numbers should be 157 to 193 PSI.

 

Check your valve adjustments. What do you mean " you set timing"? When you say it is getting fuel do you mean plug is wet or fuel is getting to carb? If plug is wet have you tried new plug?

 

i did a compression test last night and i got about 40 to 50psi wot, i assume thats my problem i pulled the head thinking that that a valve would be my problem, they both looked good, but i cleaned them up anyways and put it all back together, i still ended up with the same compression, am i overlooking something with the valves i dodnt think even with bad rings compression could drop that low, and if it is rings is there a good place to buy ac parts from, which piston and ring combo is recommended. and i assume i should have a valve job done while its apart, should i replace the valves and if so what whold i replace them with.
thanks for all of your help,
grill

 

On that 300 engine, its a known issue of the valves tighten up with use. This leads to a dramatic drop in compression, and shows up as hard starting when cold. You could try bump starting it,...just have another quad pull it with a strap, in gear, until it fires up.
But check the valve clearance...especially the intake valve, and youll probably find no clearance.

 

That no clearance (if that is the case) is holding the valves partially open, dropping the compression. When you did the compression test, did you do it a second time after pouring a coupla teaspoons in the plug hole? If compession increases you have bad rings if no increase, it is a valve issue.

 

you guys are awesome, i backed off the intake valve and the compression went to over 150 and then my battery died. so i need to have the valves replaced or just adjusted, and if adjusted how do i do that and what should they be set at.
thanks for all the help,
grill

 

well i'dd say if you got the compressiopn up to 150 then i'dd leave it.. or you can get some feeler gauges and go to town. but with 150 compression. will it start? might be flooded by now.
just my thoughts....

HR.

 

I agree with HR, why change the valve when all that is needed is to adjust the clearance. If it won't start with 150psi compression then something else is wrong.

 

what clearance shoukd the vakves have, and when i got u this morning and cranked it at wot with a new battery in it i hit amost 200 lbs. its amazing what one little adjustment will do.
thanks,
grill