[shaker455]

Originally Posted by Scarebird

My 440 runs quite well except for two issues: horrifying mileage and a misfire under light acceleration. They may be intertwined.

The 440 is a KRE 85cc headed 400 with 4" stroke and 0.065 overbore.
Mild roller cam with Edelbrock ProFlow 4 fuel injection. I suspect electrical gremlins, perhaps coil? Engine idles rock steady - though timing varies 2-3 degrees, not sure if this is due to a mediocre timing light or other issue.

Start with a compression test

[Tom Vaught]

Originally Posted by shaker455

Start with a compression test

X2

Tom V.

[Scarebird]

Originally Posted by punkin

I had similar where under light load I was getting misfire chased it for weeks and turned out to be plug wires.

That has been my thinking on this, something electrical.

Originally Posted by steve25

If your hearing the misfire out the exh then it’s most likely a tuning issue or you could even have the firing order wrong.
If the misfire is causing popping back thru the Carb then you may have a intake valve set too tight.

When the misfire occurs you can barely hear it in the exhaust.
I did examine the firing order - it is correct.

Originally Posted by 62posbonny

I am working on fine tuning a pro flo 4 as well. What are your settings for cruise and accel AFR targets? What are your timing settings for idle spark, advance start, total spark and vacuum advance? What is your IAC % at idle when fully warmed up?

So far, I am very impressed at the drivability of the system and have found that fine tuning my spark tables has paid off the most in getting a very smooth and effortless acceleration at mild throttle. My only issue is a surge at 65-70mph that equates to 2700-3000rpm in my car. Pretty confident with some more seat time I will get that ironed out too.

This will take some learning! I plan this morning to change out the cap and reroute the plug wires, especially numbers 5 and 7 and see what shakes out. If that does not work then I will examine the spark curve. It will take a bit to learn this.

Originally Posted by shaker455

Start with a compression test

I did this earlier - thought I had a leak in #7 intake. Pulled the heads and machine shop pronounced them excellent.