Stumbling after 4-5k rpms

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!

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?!

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.

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.

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?

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

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.

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.

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 ....

I don't expect lip, I give it back very harshly at times,

so either your not too good at reading a timing light or your's isn't very good and you need the correct style light. The timing will not vary, so the 16-18 something is wrong, your technique, timing light, or the protec module. It should be steady at 18 BTDC knock sensor disconnected and this is only for verification not adjusting. So if it's not steady at 700 rpm, did you even look at that after the knock sensor was unpluged? and at a steady 18 BTDC there isn't a range for this then it's screwed up and not set correctly or the module is going out.

Its a love/hate relationship. I see it already.

From being on the trailer, I do not have it gear at 700rpms. It was 700 in neutral. So this could be why also.      The knock sensor is a wire with a nut on it. You have take the nut off, remove the wire. So its off.

Should I be in the water, in gear at 700 RPM and time then? I clearly have a white line I put at 18 BTDC. So my light is hitting the point at that line. Unless my light is screwed.

if idle isn't steady or the timing you have other issues that are not fuel related.

So for the umptenth time, set base timing at 10 BTDC knock sensor wire connected, setting the interruptor's base timing, disconnect knock sensor verify timing is steady, verify timing at 3600 rpm

but get a real timing light so that the timing can be set properly.

It's a good thing I haven't ever mentioned the timing light I have to Chris. No advance feature!!! The one before this one was a simple zenon light!!

8122pbrainard wrote: It's a good thing I haven't ever mentioned the timing light I have to Chris. No advance feature!!! The one before this one was a simple zenon light!!

Pete There's one at the shop that I bet is older than you, looks like a small light bulb with leads and aligator clips. BTW why the hell would you have a good timing light your still d*cking around with points, but hey at least you don't loose any judges points

I dropped a call to my local CC dealer. The guy there said it is possible the computer getting mixed readings at higher RPM and putting the engine into power reduction mode. The mixed readings are from radio frequency waves from the plugs arhing (I think that is what he said). He said its pretty hard to diagnose the issues, but after 3200 rpms and power drops or surges like that, the computer could be causing it to this. He said to try some diaelectric grease on each plug wire boot to make sure its connecting solid and try again.. otherwise... its time to replace the protech.


Wait for it.... wait for it..... "I told you to get rid of the POS protech system!"