Atc90 stroker help

[vroomy]

need some help from experienced peeps with performance atc90 motors. A while ago a had an atc90 engine built at great expence and could never get it running good. Its got a stroker crank, 54mm piston and performance cam. I tried to run a mikuni 22mm carb with no luck whatsoever. Now tried an xr75 kiehin carb which started right up and seemed perfect till you hit the sand or any load and the motor has no torque at all, totally gutless. What am i missing here?? I jump on my mates atc70 with a 125cc chinese motor and it smokes the atc90 motor. Any advice will be greatly appreciated

[shortline10]

Do a compression test and if your able I would check the cam timing .
Did they install a high compression piston ?
Also what cam ?
Hopefully it’s not the one from dtatv lol .

[DAM shop]

I agree with shortline, the vm 22 should be the correct carb for that set up jetted At a 100 main. You could even stick a jetted 110 carb on it and it should perform well. We have several bored and stroked trikes and one of our 90’s has that 110 carb set up and it’s a beast.

Also is that mikuni genuine?

[vroomy]

Mikuni is genuine. Cam timing all lines up. When i run the mikuni carb iy spits fuel out the air cleaner side when pull starting. Its a brand new carb. Pretty sure it was a high comp piston. Any idea what comp i should be running?

[DAM shop]

Just did a search on some old post, you’ve been messing with that for some time now. So you happen to have a 110 carb laying around that you could try? Did you ever try a long manifold or are you still running the short one. What are you using for an exhaust? Is your head modified? Ported and matched to the intake? If not maybe your fuel is stumbling at that juncture

[350for350]

The part about spitting fuel out toward the air filter sounds like timing to me. Since you said that the cam timing is good, I'd look at the valve clearances next. Maybe your intake valve isn't closing all the way?

[vroomy]

Manifold is matched to the head, running a fairly short sudco intake (bought a long one but wrong bend) with the xr75 kiehin carb the motor runs well on the street/flat terrain but soon as it get hits any load like sand or incline it just dies like it has no torque. Running a DG pipe. And yes being messing with this for a long time and spent alot of money....extremely frustrating

[vroomy]

Valve clearances are all good. All the timing marks line up, im guessing that means cam timing is correct?

[shortline10]

What brand cam ?

[vroomy]

Yeah thats problem i honestly cant remember its been so long

[vroomy]

How far advanced should i set the timing?

[DAM shop]

I believe the XR carb is a 20mm. Loosing power going up hill or heavy load sounds like the carb isn’t keeping up with the fuel needs. Have you tried a bigger main in that carb? I take it your mikuni is running a 100 main and a 30 pilot?

[vroomy]

I did try going from a 95 main in the xr carb to a 110 and ijust coughed a sputtered. Yes correct on the mikuni jetting