Stumbling after 4-5k rpms

first off you can't change the 3600 timing you can only change base timing. Secondly if you had a regular 351w and added gt40p heads that doesn't instantly make it a ProBoss engine, did you also replace the Cam? did you also flash the computer to the ProBoss specs, hell know you didn't, and it's the F computer that drives weather it's 26 or 30 not your unskiiled mechanics.

so leave the knock sensor attached read timing if it's not at 10 BTDC then you have it WRONG, change it so that it is, then disconnect the knock sensor the timing should advance since all the knock sensor does is retrad timing.

You set base timing and the computer does the rest, get the right tools and listen or just go ....for all I care I'm done d*cking with your stupid ....

What numbers are wrong? I cant think of a single reason why the timing would be any different between the base and HO engines. The only thing that changed between the 2 are the heads.

If you have a factory HO (Proboss) then you have GT40 heads, not GT50p's.

Pick yourself up a decent timing light with an advance feature- theyre really handy.

so called non existant manual that exists here on this site

static timing 10

700 rpm 18

3600 rpm 30


so which one is checked with the knock sensor disconnected? all of them? none of them? two of them? one?

If you don't have the corrrect style timing light how are you even setting timing guessing maybe? must pointer scales are not high enough to use a standard timing light and why a advancing timing light is required so that only the zero mark is used.

tommer12 wrote: I had a hard time listening to you because what you said with the protech was completely wrong. no I wasn't   There is no manual for the protech anywhere. So when you say keep looking at the manual, there is none. yes there is

tommer12 wrote: I did re-time the beast. Started off at 10 degrees, finished at 16-18 degrees. I have not re-timed it since we went out. I dont think I need to since it seemed ok from idle to 3k or so.

so was the knock sensor connected when you set the interupter's timing?

You didn't want to listen then, on either site, I don't think you've learned anything at all, beside you asked, I told.

YEA those PN guys got you all hooked up, too bad they're not to good at reading a manual and how to set the timing correctly.

I know, im waiting for 79nautique to tell me I f'd it up already. (jokes!).    yeah, Im hoping someone will have some insight if not gaping my plugs is what is causing it.   Before my heads a couple years back, I had a stumble and backfire issue around 3k. But I put in new fuel lines and new inline filter and plugs and it solved that problem. Ran fine.

Im wondering if the carb needs adjusting to the new heads.

wonder, wonder wonder right?!

First time out with the new GT-40p heads. Replaced last weekend, ran some test in the driveway for an hour or so at different speeds. All ran good. Solid idle speeds, etc. Between idle to around 4k, she is solid. No issues. after about 4k to 5k rpms, I noticed all of sudden it would jump a little, then continue to 5k, then 5 seconds or so later, start to stumble.

So either Im looking at timing or some kind of carb adjustment.

I did re-time the beast. Started off at 10 degrees, finished at 16-18 degrees. I have not re-timed it since we went out. I dont think I need to since it seemed ok from idle to 3k or so.

She ran good though. No leaks, (water, oil, exhaust) from the head or valve covers. Had some paint burn off. I had painted the exhaust when I had it off and the elbows must have burned away. (and the head).

So to recap-

- Replaced heads with new GT40-ps.
- Holley stayed on the intake, never took off. (nor adjusted)
- re-timed protech ignition to 16-18 degrees with 87/89 octane
- new plugs autolite 764.

Although, I just noticed this:   at skidim site, it says to gap for protech to .045.    Would this be my issue at the high end?

Would i have to gap the plugs, then retime everything??

Or do I have another issue with my holley?

Thanks fellas!