Norwood

[Sieg]

Originally Posted by Vegas69

Did the engine temperature change? That amount of timing shouldn't make much difference to a bog. You aren't going to tune out a stumble with idle mixutre and transfer slot. It's time to start playing with accel pump cams.

Todd,

Started with engine temp at 175* it got up to 195*

The bog was instant with throttle opening and no load, and it appeared to be initiated with the timing change, the temp could be a factor but I didn't think it would cause a substantial bog.

I'll throw a different pump cam in and see how it responds.

I checked with MSD tech and they didn't think the +/- 1* timing fluctuation was abnormal.

Here's the cam specs FWIW:

[intocarss]

When you give it gas right off idle, (bog) does it cut out or does it blubber then catch?

[Sieg]

Originally Posted by intocarss

When you give it gas right off idle, (bog) does it cut out or does it blubber then catch?

Big flat spot (as I'd call it) no blubbering, then it's fine. If I rev it and don't let it come all the way down to the 1K idle, say 1500 rpm, and crack the throttle it's fine. This has all been while actuating the throttle by hand.

[Vegas69]

One degree of fluctuation isn't worth thinking about. Battery voltage or a slightly different signal to your light could easily cause the difference. You can verify the timing is reacting properly with your timing light. If it is, I'd rule it out. Especially if the drivability problem is present. A fully warmed up engine vs. colder engine absolutely will change a stumble. Everything I advise you is from experience.....

[intocarss]

Originally Posted by Sieg

Big flat spot (as I'd call it) no blubbering, then it's fine. If I rev it and don't let it come all the way down to the 1K idle, say 1500 rpm, and crack the throttle it's fine. This has all been while actuating the throttle by hand.

Then I agree with Todd's posts.

Blubbering = to much fuel

Dead spot = not enough fuel. ie squirters or accelerator pump or cam, maybe even PV . Is the accelerator pump arm gap adj properly?

You could try and push the primeary accelerator pump arm almost all the way down by hand just as you crack the throttle from idle or a split second before, which will send a bunch of fuel in. If it doesn't have a dead spot then this will tell you it's lack of fuel right at the hit. Just and old school trick. YES eng temp can effect and or make the stumble too

Have you thought about blocking off the PV's (if you have 2) jetting it up a few sizes and trying it again? I took the PV's out of mine and it runs better down low

[Sieg]

Originally Posted by Vegas69

One degree of fluctuation isn't worth thinking about. Battery voltage or a slightly different signal to your light could easily cause the difference. You can verify the timing is reacting properly with your timing light. If it is, I'd rule it out. Especially if the drivability problem is present. A fully warmed up engine vs. colder engine absolutely will change a stumble. Everything I advise you is from experience.....

Originally Posted by intocarss

Then I agree with Todd's posts.

Blubbering = to much fuel

Dead spot = not enough fuel. ie squirters or accelerator pump or cam. Is the accelerator arm adj properly?

You could try and push the primary accelerator pump arm almost all the way down by hand just as you crack the throttle from idle or a split second before, which will send a bunch of fuel in. If it doesn't have a dead spot then this will tell you it's lack of fuel right at the hit. Just and old school trick. YES eng temp can effect and or make the stumble too

Thanks guys.

I've made sure the thermostat has opened and it up to temp before any tuning adjustments.

I'll say it acts like a lean bog, similar to the warm up throttle response with no choke system.

I'll toss a green pump cam on and see what happens.

[Sieg]

Pink pump cam is stock..........and lean down low.

http://www.holley.com/data/Products/...mpCamGraph.pdf

[Vegas69]

Mine came with Pink as well. It's for drag racing and absoutely horrible for throttle response. I'd jump up to orange as it delivers better volume on tip in..... I'm pretty positive that's the cam I used.

[Sieg]

Originally Posted by Vegas69

Mine came with Pink as well. It's for drag racing and absoutely horrible for throttle response. I'd jump up to orange as it delivers better volume on tip in..... I'm pretty positive that's the cam I used.

Sounds like a plan. I ran the green on the previous carb and it was a big improvement over the pink.

Did you end up with matching cams on both pumps?

[Ron in SoCal]

Green is better than Pink. Got it.