150cc gy6 not starting
 

I have a 150cc Baja reaction that will not start. I had just replaced the top end with a 155cc bore kit and at first it was just cranking and blowing air out of the Carb and sucking air in the exhaust, i took the carb off and tried starting it and it acted like it wanted to. Well I figured I put the piston in backwards, so I turned the piston around so the arrow is facing the exhaust. It still just cranks over, it is getting fuel and air and has compression. But after I turned the piston around I took the Carb off and tried it and it backfired and caught the gas on fire that was on the engine. My timing is tdc I double checked it to make sure. All my electrical is connected correctly. I am puzzled on this one.

Im no expert at this, but did you put your head on proper? maybe its upside down and you got the intake and exhaust valves backwards!:dunno:

I put the head on correct, I do know that. The exhaust bolts are a little bigger than the intake bolts.

Ok. Sounds like a few possibilities. Timing sounds like it is off, or the valves are not adjusted correctly, holding them open too long. That being said, these are 'interference' engines, meaning if the timing is off too far, the valves will hit the top of the piston.

I believe the head can only be installed one way, with the cam chain coming through the head.

I would check to see if the valves are too tight, then report back your findings.

Dooh!
 

You're so right "Yota man" I should have thought about that! Its gonna take me some time to knock the rust off! thanks fir chimming in! :biggthumpup:

Good to have you back, rusty or clean.

Good 2 be back, hope I never have to be away that long again! I really dig this site!!!

Make sure the cam is in correctly. Many install the cam with letters and or numbers up. The large hole in cam sprocket should be pointer straight up( pointed at back of seat) with the 2 small holes, dimples or scribes parallel with the top of the head. When this is all checked to be good then set the valves Intake @ .003 and exhaust @ .005 . Always make sure when setting the timing that the tensioner is relieved ( no tension ) once done release the tensioner putting tension on the chain than check to make sure the flywheel is still lined up with the pointer on the case.

(Bear) Its all good and hey it was worth a shot, i am new to all of this. The only engine i some what know is a 302 sbf.. But everyone i took the top off and got the timing dead on, i loosened the valve bolts and put them on finger tight (just testing it) and after i put it all back together it fired right up and it wanted to idle. Thanks everyone, i rode it today in the snow and it does really good. But now there is another problem it only goes around 10 mph maybe slower and it is terribly. I figured it has to do something with the clutch, belt or transmission really. Any ideas??? Thanks

Yup, I was thinking the valves were open too long, just didn't know if it was the cam or the valve adjustment. Adjust your valves as per Tom above, if the valves are now too loose, the engine won't run at full strength. In this case, make sure the engine is 100%, then look to the CVT and clutch. Otherwise, you may be chasing your tail trying to find the issue.

Did this buggy run prior to the top end rebuild?

If it has been beaten on or has sat up for extended time, then the CVT may need to be serviced, or the rollers may be toast.

Ditto

I adjusted them but the tool i have only goes to 0.008 so i adjusted them to that and it runs better a lot better now. It ran alright before the top end rebuild but the ppl before me rode it hard and then it sat for 6 months.

Get a set of the correct gauges Auto Zone should have them. Running at .008 is too loose and will cause premature ware to the valve train. You should also have a compression gauge. I know of many who have spent money on parts only to find in the end that they have low compression. Just because it has new parts doesn't mean you have top compression. In order to TS any engine you need to know the vitals which are air fuel spark and Compression. Oh and also make sure you have fresh gas, if the gas in your can is more then 2 weeks old it has already started to break down and is spoiling. Can't tell you how many people have I have come across who just could not figure it out and run out of parts to throw at it and all it was is it turned out to be bad gas. Smell it and if it doesn't smell like it did out of the gas station pump it is bad and if it has a yellow tint to it it is bad.