Stalling in high gear

I have a 6" pulley on front and a 3" on rear. I have a six speed transmission. When I get to 5th or 6th gear the motor will die down and doesnt rev up. Also when I hit the brakes it will stop and stall out. Any suggestions on why it would be doing this?

could be to high of a gearing, your motor not having enough torque to turn it when in that gear, what size tires?

Its 18inch tires on rear with a 12hp.

i might be wrong, but im pretty sure its just to high of a gear ratio on your motor, but let someone else give you advice to, i aint never messed with one with a motor that small

ok thanks. I was making a racer out of it. The track uses a 5 in and 3 in. I went one bigger as I am a bigger driver. Would a 1" pully bigger be that much of a differance?

yea it would be lol

that is at the taller end of what a 12hp can utilize on the track. My advice, if track legal would be to switch out the rear pulley for one 1" bigger. Should just give you what you need to keep going without stalling so much. I ran a 6" front and 4" rear for a long time with bigger tires than that (23") and it worked nicely. Just had to make sure RPM was up before shifting to next gear.

Just before you get to swapping pulleys, read the plug. Make sure that you're mixture is bang on. That said, I agree. Sounds like the gearing is too tall for the available amount of power.

Get a bigger motor or adjust your ratios. Also, be sure to gear up as you would in a car, dont start off in 5th.

Could be a number of things, sounds like at that high rpm its starving for fuel, or the valves are floating depending on the engine rpm.
Or breakdown of oil..or...not enough oil. A good trouble shooting project...

Could be also the rings are bad, caused by too much heat.

Kel wrote:

Could be a number of things, sounds like at that high rpm its starving for fuel, or the valves are floating depending on the engine rpm.
Or breakdown of oil..or...not enough oil. A good trouble shooting project...

Could be also the rings are bad, caused by too much heat.

I doubt it's valve flutter. The OP says it won't rev up in top gear. Valve flutter occurs at high RPM, it does not prevent an engine from revving up in the fist place. What's more, he says if he brakes in high gear it complicates the problem. It's not a lubrication problem either- that would manifest itself in any gear, including neutral.

Worn springs will cause failure at any R.P.M. Contamination along the valve stem,burrs or dirt between the push rod.

As far a lubrication problem,it could in fact be the placement of the engine itself. Tilted or if any of the block bolts missing, who knows.

Remember Doc, this a thrown down of ideas to which he'll have to take a good look at, not a diagnosis, that would be premature. I do hope

he'll find whats wrong and post what he finds, I'm interested.

I too sincerely hopes he gets it sorted. He will indeed have to swashbuckle his way thru all that we have given him, and sort it out. Firm diagnosis? Nah. Playing the odds.

Regarding the valve flutter, I just re-read my post and I should have been more clear. If valve flutter were the limiting factor, it would most likely exhibit in a specific RPM range, regardless of what gear the machine is in.

So to clarify the problem for those of us that can't be there to drive it- does the problem occur in any and all gears, or only in the higher gears?

Thanks everyone for your ideas. It 1st through 4th is fine it runs good, its just when I hit high it bogs down. I have purchased a smaller pully (5") for the front to try out and I will let you know how it goes.