Stumble @WOT

[rebootej]

Don't know the QF's but regular Holleys were fuel just barely trickling out at bottom of plug threads.

The QF have a little glass window with lines so you dont have to actually open up the plug. My demon had this too. im on the middle line like the directions say, but i could go up hair maybe?

 

[rebootej]

I also have a 79 corvette with a ZZ355 motor with an ACCEL DFI system. I used a wideband for tuning and ended up still reading plugs at the end to get the last bit. An AFR number doesn't mean the engine is happy but usually close to happy.

Yes reading the plugs is definitlely how I'm going now, the ATF is just nice to keep an eye day to day.

I talked to Don at 4 seconds flat. First thing he said was that quick fuel is not what they used to be.. He said i need to fix my timing first. His advice was to back it off 2 degrees to 16 Degrees BTDC, switch my vacuum advance to to full manifold. And to buy his ignition box with mechanical advance limiter plate. His advice is that the orange box is junk and my mechanical advance is probably going too high.

 

[texas69bee]

I do have Dons stuff and like it but I can't say for sure if it will fix your problem. Did he also mention 34btdc?
You can try and work with that before ya buy and see if there is an improvement.

 

[rebootej]

I do have Dons stuff and like it but I can't say for sure if it will fix your problem. Did he also mention 34btdc?
You can try and work with that before ya buy and see if there is an improvement.

Ya he told me to bring my timing back and that i i should limit my overall timing also to have my vacuum advance kicked in at idle. I was trying to get that work but my vacuum advance doesn't seam to be working.. But i cant believe thats all thats causing my problem??

It has to involve the accel pump circuit too right? I brought the floats up a bit.. ill post a pic of what it looks like now tonight.
My car is a complete dog right now.

 

[rebootej]

Update.. I was messing with my timing like don a 4seconds flat recommended first. and discovered that not only was my vacuum advance broken on the dizzy it was sucking air through. Fixed that by putting in my old distributor. Running much better now! but Still the problem is still their just not as bad.
Still stumble/slow when going to WOT and A/F shows engine leaning out until it recovers, then it runs great at about 12.5-12.8

 

[Belle66]

Get your vacuum leaks fixed before carburetor work. Make sure the vacuum reading at idle is reasonable for your cam. If mild or stock cam then stock vacuum should be expected. Vaccum leaks will have a big effect on fuel air ratio.

 

[rebootej]

I think its all good now.. Was pulling 15 inches before so I wasn't thinking vacuum leak

 

[rebootej]

Update... Ive been tweaking looking for issues.. the stumble is still there.. If ease in to WOT then the car is fine but when i punch it. Then the issue occurs and the engine runs like crap for a few seconds till it recovers then it runs great, pull strong! But it is the transition that kills it. Ideas of things I should try? I've got a lot more time on my hands now.

Here is a video clip..

 

[Jcharger]

From the video, it is from initial start, low RPM. My guess is that you are not getting enough gas in there to cover the opening of the butterflies. I don't know, but I believe that this is too low for the secondaries to be opening (You might be able to check with the paperclip trick and a quick stab at the throttle, but let off before it recovers). If it is the butterlies opening, it needs more gas. I would focus on the squirters and the pump cam and the adjustment of the accelerator pump.

I am not an automatic person so I don't know if the issue is just that your converter is tight for the set up you have and it needs to be able to rev past that point so it can really get flowing with that carburetor on your engine with the vacuum it has.

 

[rebootej]

From the video, it is from initial start, low RPM. My guess is that you are not getting enough gas in there to cover the opening of the butterflies. I don't know, but I believe that this is too low for the secondaries to be opening (You might be able to check with the paperclip trick and a quick stab at the throttle, but let off before it recovers). If it is the butterlies opening, it needs more gas. I would focus on the squirters and the pump cam and the adjustment of the accelerator pump.

I am not an automatic person so I don't know if the issue is just that your converter is tight for the set up you have and it needs to be able to rev past that point so it can really get flowing with that carburetor on your engine with the vacuum it has.

I did try the paper clip trick one night. and the secondaries where not opening when i punched it and let off before the engine recovered.

but when i did actually let the engine start to recover from its stumble then the secondaries had opened.

 

[Jcharger]

SO the issue is the air from the primary butterflies is too much when opened from a stop by stabbing the throttle with you set up. I suspect this is asking a lot of the fuel system, but I think it can be addressed with more gas or by getting the rpm up faster so you don't hit that situation.

 

[rebootej]

SO the issue is the air from the primary butterflies is too much when opened from a stop by stabbing the throttle with you set up. I suspect this is asking a lot of the fuel system, but I think it can be addressed with more gas or by getting the rpm up faster so you don't hit that situation.

That what i seams like? but I've already increased my squirter to a 35 and I am running the blue cam. Where do i go from there? Bigger squirter yet and 50cc pumpshot?

 

[oldbee]

I think you need to go back to a pink cam(there's more than 1 setup hole)to play with, for ur engine size it should be enuf. There is an interesting article in HotRod mag this month on carb tuning that kinda sounds like yours. It's about 3-4 pgs long but in a nutshell it makes a case for a big coming from overrich(?),I know I know; it's a never ending battle.

 

[texas69bee]

Here is an article on Quickfuel. Hope this helps a bit.
http://www.hotrod.com/articles/quick-fuel-carburetors/

 

[rebootej]

I think you need to go back to a pink cam(there's more than 1 setup hole)to play with, for ur engine size it should be enuf. There is an interesting article in HotRod mag this month on carb tuning that kinda sounds like yours. It's about 3-4 pgs long but in a nutshell it makes a case for a big coming from overrich(?),I know I know; it's a never ending battle.

I was looking for the article but I didnt see it. It was this months issue? ill see if i can get a paper copy.

 

[oldbee]

Yes the June issue.

 

[Jcharger]

I tend to agree that the pink cam should cover this and would definitely think the blue cam would cover it.

Correct me if I am wrong, but from your video: you hit the throttle from a standstill, the a/f starts to go higher a/f and eventually offscale; when it recovers it comes in from high a/f and then drops into the 11 range, eventually settling into the 12 range. You do not have backfire through carb which would be a symptom of lean. For me, all of this points to too little fuel when you open the primaries. Am I missing something? Did it initially go lower A/F and then move to higher A/F before it went off scale?

If it were me, I would go back to recheck everything, especially how the accelerator pump is feeding gas. It should be an immediate and strong shot of fuel. Not having this has been the most common mistake I have made. The pump lever should not bottom out, but it should be close with the feeler gauge method of checking the travel. I forget what the amount is, but it is a small amount from fully depressed at WOT that is needed. I would think the 35s should work for your set up.

I have also found it informative to take a video looking down int the venturies of the carb to see what the pump is doing with a small deflection and a large deflection of the pedal. I generally start the engine after the tests so I don't leave gas in the manifold and wash the rings of oil.

I have swapped in larger pump diaphragm housings and larger cams on larger engines, but usually find that the sweet spot is more conservative than I originally thought. So I would stick with the cams you have at your disposal. I would probably stick with them using hole #1, but listen to others if they have opinions, and I would probably use the pink or orange cams as initial tests.

 

[texas69bee]

There are a lot of videos on YouTube that may help you. Here is one that may be of interest. You said you have 15 for vacuum so per video you need a 7.5 power valve.

 

[rebootej]

So bad news I broke my collarbone where it attaches to my shoulder and will be unable to do much work on the car for a bit here.

But yes j charger you are correct on what see in the video. There is no backfire through the carb. I think my accel pump is set right but I'll double check.

Thanks Texas bee I've been watching lot of YouTube videos but haven't seen that one. Sounds possibly I could need the 7.5 it would open quicker than a 6.5 yes?

Hopefully this injury won't keep me side longed for long

 

[texas69bee]

So bad news I broke my collarbone where it attaches to my shoulder and will be unable to do much work on the car for a bit here.

But yes j charger you are correct on what see in the video. There is no backfire through the carb. I think my accel pump is set right but I'll double check.

Thanks Texas bee I've been watching lot of YouTube videos but haven't seen that one. Sounds possibly I could need the 7.5 it would open quicker than a 6.5 yes?

Hopefully this injury won't keep me side longed for long

Man than sucks!!!
Thats the way I understand the power valve as well.