chinese atv starts then dies

Bibical.400 · #1 02-23-2011, 09:30 PM

I recently took out my hot cam and just finished putting the stock cam back in. Yes i put the spring and plunger back in. Also put in a HD chain. The timing marks on the cam gear 'almost' lined up with the head. It was very close, would that make a difference?

Ok, got everything back together, go to start it and just cranks. I spray some gas in the carb and it runs for 3 seconds then dies. Did it again then a backfire. Tried a third time and nothing.

I took the carb apart to inspect the jets and clean them. Could there be airlock? The gas flows from the tank, but upon inspection i didn't see any gas being pumped threw when i hit the throttle.

Think thats it? How can i bleed the carb if it is?

I didn't adjust the valves afterwards...Could that also be part of the problem?

Bibical.400 · #2 02-23-2011, 10:10 PM

Also, I loosened the drain screw to see if there was any fuel in the carb, and nothing came out of the hose. Then took the float chamber cap completely off and it was completely dry. When i took the carb off and cleaned it, i might have Fubar'd something up in the process of tossing it back together. I only took off the float bowl (4 screws), took out the float itself, and cleaned the jets. Main was fine, the pilot was a bit clogged. They are stock jets.

90vfradam · #3 02-24-2011, 02:23 AM

Did you measure your valves after changing cams??

90vfradam · #4 02-24-2011, 02:24 AM

sorry I missed that --------- I didn't adjust the valves afterwards...Could that also be part of the problem?

Yes that could be a problem

Bibical.400 · #5 02-24-2011, 02:45 AM

I will check them tomorrow morning. Stock settings are intake .004 and exhaust .005 correct?

Still stumped about the carb...

Should i leave it soak for an hour? Rip it completely apart and clean it inside out?

90vfradam · #6 02-24-2011, 12:38 PM

The carb will fill with gas when there is a vacuum from the engine the intake valve will pull the gas in ,

intake valve .1o mm or .0004 in.
exhaust valve .12 mm or .0005 in.

Here 2 help · #7 02-24-2011, 02:05 PM

Hold on a minute! Where did you guys get your degree in mechanics

You must check the valve adjustment anytime you make a change in the valve train!

Now, there is nothing to pull fuel into the carb other than gravity. The valves have nothing to do with it.

Hard to say what you screwed up when you took the carb apart, but unless you are experienced with carbs they are best left alone. Carbs are one piece of equipment that is very precise.

And you will not see any fuel flow when cranking or running. The only time you will see fuel flow is when the float bowl is empty and filling. Once it is full, flow stops. The flow is completely dependent on two things; 1) the opening and closing of the float needle 2) venting of the fuel bowl.

If you can't figure it out - take it to a qualified wrench.

Sorry if I am a bit short, but accept it - you caused your own problem by getting into something you didn't fully understand before going there. I can't help but wonder what else you might have screwed-up by poking around.

Bibical.400 · #8 02-24-2011, 02:43 PM

Hold on man, this is my first stab with a 4 stroke quad. I have rebuilt numerous engines from v8s to chainsaws, but never one like this. Just need a little help.

From what i can tell the carb isn't gettng any fuel. I'm heading out there now to adjust the valves and see how to get some gas in that carb, using process of elimination.

Then hitting the starter button.

Wish this white boy some luck.

Here 2 help · #9 02-24-2011, 03:15 PM

OK white boy: GOOD LUCK

Once you get the valves checked (and adjusted if necessary), get the carb off. First make sure the float bowl vents are open. I've seen novice mechanics loop the hose from one float bowl vent to the other and from the vent to the bowl drain. Either way effectively closes the vent and then the bowl has to try to vent through the main jet.

If vents are ok, take the bowl off. Hold the carb slightly less than horizontal with the float needle seat at the top. The needle should be unseated and fuel may flow. (check this with a piece of hose attached to the fuel line nipple and blow through it). Tip the carb to above the horizontal. The floats should swing against the needle and shut off the air flow. If the floats do not move freely - find out why. Sometimes the float needle or the needle seat gets corrosion on it and prevents the needle from opening (or in some cases, closing).

Hope this helps

Bibical.400 · #10 02-24-2011, 06:15 PM

Indeed it did. The float was held up, and it is now flowing great. But alas, no fire up. Checked the timing again, and it is dead nuts on. I have come down to 3 things it could be..

1. When i went to adjust the valves, i referenced the adjusting guide and it said there should be some play in the rockers at TDC. Well, the rockers are all tight as hell, throughout the cycle. Maybe they are too tight?

2. The spark plug. It is a oem DPR8Z but it is pretty black, which i don't understand because all the jets are stock and it should be running lean? Also, the metal cap on the spark plug itself was off, with just the threaded post showing, and the plug boot was a very loose fit. My gf and sister are picking up a new one now, told them to make sure it has a metal cap on it. But, would that cap being off affect the spark? It fired before like that, but did not completely run. The plug was wet so it is getting fuel.

3.With the stock cam back in, do i have to mess with the decomp. mechanism at TDC in any way or that self adjusting upon startup? The plunger and spring are in there and functioning.

Thank you