[Blownchevelle68]

I've been chasing a few gremlins with a new build and think Im finally getting it figured out-Still having a couple problems though.

I built a 388ci with stock heads, lunati voodoo 60103, 9.7 comp, Performer RPM and a Holley 670 Avenger. I have a pretty bad stumble going from cruising idle transitioning into full throttle. This stumble is there when I ease into throttle or when I mash it. I installed the black colored secondary spring and it seemed to help a little (used to have the purple spring).

Put new plugs in yesterday and drove it for about 1 hour then took it home. Plugs came out very clean but with a ash grey color to the wire and the ceramic itself. I could not hear any detonation, however it was pretty cool (45 degs) yesterday.

Ignition is set at 12 deb initial timing with 36 total, using a summit mechanical advance dist and CD box.

Carb settings are factory, jets 65/68, 31 squirter and 6.5 PV. Vacuum readings at idle are pulling 14-15hg.

Im thinking of starting with jetting up a size or two and possibly changing to a 9.5 PV. I have also read that mechanical advance distributors are'nt the best, so Im going to change out to a MSD billet ready to run vacuum advance.

Would it be best to start jetting up or does it sound like a power valve? Once you hit full throttle it does well, but has a big stumble getting there. It also seems to surge a little when under light cruising throttle (45mph) surge....Any help appreciated !

 

[fleming23]

I did a ton of looking around on this site and a few others regarding the Holley Avenger Stumble and found quite a few different ways of going about correcting it. There is a good bit of talk on this forum about checking your transfer slot, power valves, etc. I am not going to say what I did was the right way because I know I might have tried to make a tourniquet out of a bandaid, BUT it worked for me so I am happy. I have the 770 Street Avenger and went from a stock 25 or 27 squirter (can't remember what it comes with stock but small) to a 35. This completely corrected my off idle stumble and my WOT stumble. This might not help with you but I thought I'd at least share my experience.

Here is a link to one of the TC pages talking about tuning this carb....
http://www.chevelles.com/forums/showthread.php?t=274005
Read RB69SS396Conv 's comments about half way down. Even though I basically ignored his suggestions it was still very helpful to read everything.

 

[Dave427]

Jet the front and rear up 2 sizes.
So go to 67 Primary and 70 Secondary.
By installing a stiffer spring you are slowing the rate of your secondary's and masking the lean condition.
Personally I would of put a 770 on it.

Dave

 

[Blownchevelle68]

Thanks for the info, that was good information that I had not read yet. I have searched around alot and found many different responses, but Im going to up the squirter size as well. I believe 31 is factory. Going to try that first along with upping jet sizes like Dave reccomended.

I should have researched this carb a little more before buying it. It was used with 100 miles or so from the previous owner who went with a 750DP on his 406.

I'll see if that helps-Thanks again guys.

I did a ton of looking around on this site and a few others regarding the Holley Avenger Stumble and found quite a few different ways of going about correcting it. There is a good bit of talk on this forum about checking your transfer slot, power valves, etc. I am not going to say what I did was the right way because I know I might have tried to make a tourniquet out of a bandaid, BUT it worked for me so I am happy. I have the 770 Street Avenger and went from a stock 25 or 27 squirter (can't remember what it comes with stock but small) to a 35. This completely corrected my off idle stumble and my WOT stumble. This might not help with you but I thought I'd at least share my experience.

Here is a link to one of the TC pages talking about tuning this carb....
http://www.chevelles.com/forums/showthread.php?t=274005
Read RB69SS396Conv 's comments about half way down. Even though I basically ignored his suggestions it was still very helpful to read everything.

 

[Tom Mobley]

squirter first, up it 2 or 3 sizes, see if helps, hurts or no change. Post the results here we'll where to go next.

 

[Xtreme70SS396]

squirter first, up it 2 or 3 sizes, see if helps, hurts or no change. Post the results here we'll where to go next.

I agree also - but given the surge at cruise, your jets and/or idle mixture has the carb running too lean anyway IMO. I'd certainly do the shooters - but you should richen up your idle screws a little, and "probably" go up a couple jet sizes in the primaries too.

12° initial (with vacuum adv disconnected) seems a bit on the weak side also - Id run that up to 18° and limit your mechanical advance to keep you at 36° total.

Regardless of your choices - do ONE thing at a time and see what the results are, ALWAYS starting with timing.

 

[Blownchevelle68]

I agree also - but given the surge at cruise, your jets and/or idle mixture has the carb running too lean anyway IMO. I'd certainly do the shooters - but you should richen up your idle screws a little, and "probably" go up a couple jet sizes in the primaries too.

12° initial (with vacuum adv disconnected) seems a bit on the weak side also - Id run that up to 18° and limit your mechanical advance to keep you at 36° total.

Regardless of your choices - do ONE thing at a time and see what the results are, ALWAYS starting with timing.

Ok Thanks!! I've looked on several different forums and the Avenger series seems to be causing many people the same problem. Some are saying the idle circuit needs to be drilled out larger, etc etc. I figure if I can't cure it by regular tuning and changing jets or squirters, etc that I'll just sell it and get a different carb.....

But Im going to try doing what you all have mentioned first-I will post what happens then...Thanks !!

 

[mr 4 speed]

12° initial (with vacuum adv disconnected) seems a bit on the weak side also - Id run that up to 18° and limit your mechanical advance to keep you at 36°

:yes: that is more than likely the stumble problem. I would run a minimum of 18* base and also put the purple spring back in there.The secondaries will never fully open with the black spring.

 

[Tom Mobley]

what he said. more timing, but watch the total.

another quick and dirty diagnostic is to raise the float levels 1/2 turn of the nut. don't take the sight plugs out, gas will run out, fire hazard. If it runs better like that you have a pointer to a permanent solution. Don't forget to put them back.

 

[lg1969]

Jason,I suggest you read this post. Hope this help you.
http://www.hotrodders.com/forum/holley-hesitation-193226.html