odd performance

[OZ FMX]

ok she a 91 1.3L carb festiva, if i go out and let it warm up for a few minutes it runs fine BUT if i go out get it running and start to drive when the motor isnt fully warmed up its gets realy bad flat spots

i know being carbed it has to warm up but if i just drive it i can go on an hour long trip it runs exactly the same after an hour of running as it does at the start , motor is red hot and still flat spots.

it only goes good when the motor is totaly cold then allowed to warm up on its own
i run 98 octane fuel which is the highest octane fuel sold at the pumps here in aus so its not cheap fuel and i doubt its a bad batch cause its been doin it for a while and i've been getting fuel from diffrent stations

[htchbck]

it could be the fuel you are running. I don't know a whole lot about carbs, but on my '93 1.3L EFI I had to run 93 octane once because that was all the gas station had and I was almost out of gas. I normally run 87 which is the lowest we have in the US. By the time I was 20 miles down the road the motor was running really rough and backfiring and it wound up burning one of the valves really bad. I think maybe the gas was just too good for the motor, and it was causing detonation and other problems.

[warlocke]

in my 95 aspire i run 87 and runs great, i think ur running to high octane for our small engines, go to mid grade or low and see if it helps

[5.0zone]

My guess would be the accelerator pump on the carb. When you step on the gas it squirts a small amount of gas into the carb.