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Missfire at Light throttle , not sure which direction to go.

Canadian1968

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I had this problem last year , and a new set of plugs seemed to clear it up ?

This year its back again. It's a misfire at very light throttle , or as I roll into power. The harder I accell the less it is. I can watch my wideband, it show up on the AF gauge as lean spikes , and you can feel the power hit and miss as I try to accell.

I got home from work today left the car running got out to check things out. I did notice the fuel filter was almost empty , I could barely see fuel coming into it.

This is a brand new filter I just put on the night before. When I started it up last night , filter filled up no prob.

My next thought was vapor lock, I've never really had a problem with it though. Also I tured the car off and was able to fire it right back up, no problem. So not sure about that .

I also pulled the fuel pump pushrod out to check it , all good at 3.22"

I'm not sure what direction to go with next trouble shooting. Could be a bad fuel pump? Some carb tuning ? Something ignition related . I just don't know which way to go.

The only change over last year, was I did pull the heads and did a port job on them, also a new voltage regulator. New set of plugs when the heads were put back on. That's about it .
 
I had this problem last year , and a new set of plugs seemed to clear it up ?

This year its back again. It's a misfire at very light throttle , or as I roll into power. The harder I accell the less it is. I can watch my wideband, it show up on the AF gauge as lean spikes , and you can feel the power hit and miss as I try to accell.

I got home from work today left the car running got out to check things out. I did notice the fuel filter was almost empty , I could barely see fuel coming into it.

This is a brand new filter I just put on the night before. When I started it up last night , filter filled up no prob.

My next thought was vapor lock, I've never really had a problem with it though. Also I tured the car off and was able to fire it right back up, no problem. So not sure about that .

I also pulled the fuel pump pushrod out to check it , all good at 3.22"

I'm not sure what direction to go with next trouble shooting. Could be a bad fuel pump? Some carb tuning ? Something ignition related . I just don't know which way to go.

The only change over last year, was I did pull the heads and did a port job on them, also a new voltage regulator. New set of plugs when the heads were put back on. That's about it .
What is the fuel pressure? Are you running a vacuum advance? If so cap it off and see how it runs.
 
Hook up the vacuum advance. Lean mixture needs more time to burn.
 
Need a whole lot more info...
Carb?
Cam?
Etc.

Comp.cams 274Xe
Holley 3310 with proform 750 main body.
Ported 906 heads
Rpm Intake
Headers

I'm still leaning towards carb tuning, the new mainbody ( Installed start of last year ) is quite a bit different than the stock 3310 unit.

Could be as simple as going up a jet size on my main jets .
 
OK, so some interesting progress.. I pulled the distributor, to check everything out make sure nothing was stuck or binding. Everything seemed in order, reassembled and put back in. I also pulled the carb off and check the front bowl, to make sure everything was clean and working correctly.

Just fired the car up to check timing. I have my base timing set at 17.

Now here is were i think the problem is, when I give it throttle, the timing actually RETARTDS about 8* if I up the rpm more, it will shoot back into proper advancement. WHAT the heck? Just small little revs, I can watch the timing RETARD each time , bigger throttle hits its gets hard to see it , which is exactly the symptoms of the driving conditions.

Vacuum advance is not in play..

What the heck would cause a RETARD in timing ? its seems weight related ? but how?

Scratching my head a bit here
 
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