misfire when cold.

[buffblazer]

well i have another thread started about the motor being weak so i figured this should be under a new thread.

the 350 has been tuned on the dyno like previously stated but before they did, i had a horrible misfire if i went WOT, and the rpms got to 2200-2700

the shop determined it was because the 650 holley out of the box was to much for my mild built 350. so they changed the jets to get rid of the misifre.


so now the motor runs great just hardly any power, now after the truck has reached operating temp and then shut down if it sits for more than an hour, on re start if i take off it kinda hesitates and misfires like its cold, and then runs just fine after it gets warm.


now my question is, why would it cool down that fast in 85 degree temps outside to cause it to misfire and hesitate within the first 5 mins of startup?

 

[apache]

Makin power creates heat,makin nothing creates nothin. How could a 650 be to big for a 350 when a Rochester is 780 or 800 CFM?

 

[NEK5]

Makin power creates heat,makin nothing creates nothin. How could a 650 be to big for a 350 when a Rochester is 780 or 800 CFM?

Even though the Rochesters are advertised as 750 or 800 CFM, they only use what they engine needs, unlike the holley.

 

[buffblazer]

Makin power creates heat,makin nothing creates nothin. How could a 650 be to big for a 350 when a Rochester is 780 or 800 CFM?

well that was problem with my low numbers on the dyno, it was over fueling the motor causing it to misfire so they put smaller jets in it.

thats the question i have been trying to figure out with this motor

 

[apache]

Still sounds screwy, my 76 350`ed sub had a Holly 600 on it and it ran fine except for when the damn float hung up. Put a Carter 625 on it and problem solved. I suppose it may have been jetted so fat your rig wouldent run but dang. If it was rich it should have run good when cold acting like a choke and crappy when hot as it needed less fuel,your sayin its the other way around. Timing issue,lack of advance,vac and mechanical hung up?,cam timing right? I screw with bikes more than cars and for me to make something so fat it misses it high rpm it would be pukin black smoke as well as washing down the cylinders which isnt good obviously. I had a brand new Holly outta the box be screwed up but it was 20 years ago and cant recall what the issue was, not much to them maybe its time to have a look.