Box Stock

motor starts missing

J

jr23751

New member
At the track the weekend motor would run great for about 3 or 4 laps. Big track flat footing 4850 with a 200rpm drop. Then would start missing for a lap or 2. Would stay around 4000 rpm with the miss. Then clear up and run good 2 or 3 laps. Its a box stock predator strait out the box oil shut off unhooked, 4 holes in gas cap. Surging on the stand at 5350-5400. Tied new plug, pulled jet and tube blow out with air twice. Same thing every time I rolled on track.

it has me scratching my head any suggestions would be greatly appreciated
thanks
 
Is the tank almost full? You at least need to be above the red indicator. Are you sure your choke is staying off and not vibrating open/closed?
 
Its new straight out of the box ?
Might be the rod seizing on the crank .
Fuel system from cap too jet or coil would be good options .
Fuel shut off or sediment bowl .
 
straight out the box

Just seeing if anybody else had a similar problem and get a idea of things to check. Probably open it up this weekend and check rod.

thanks
 
I had a clone do the same thing , sent it back to Jerry Dover . Brand new engine .
He went through the engine so i do not know , what he found .
I also feel i had a venting issue .
 
could still be fuel starvation. are you on an angled motor mount? the pick up point in the tank is 1/4 tall inside the tank and at the high end of the motor. if your on a 15* mount and your tank is sloshing could be an issue... i had a motor run out of fuel and it looked 1/2 full.
i pulled the plastic filter from inside the tank and ground down the height for better flow... down side is ... its you only filter if your using a stock tank in stock location.
 
Nine chances out of 10 you’re starving for fuel. Next time it does it when it starts missing like that reach back right away and shut the fuel shut off down turn it off. When you get to the pits drop the bawl. put a glass jar underneath it to see how much fuel is in the bowl. I think you’ll find out that the bowl is not full therefore the engine is starving for fuel
 
Check that your fuel line is not to long and getting pinched . Sounds like Don said , its getting starved on fuel . Also check that your kill switch wire is not loose or moving where it can be grounding out as you are on the track . I had a clone do that , the wire got a hole rubbed in it and was shorting out the engine while on the track .
 
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