So once again I find myself fighting this new combo............at idle to car runs fine a little rich......cruise runs fine about middle(not rich not lean).........WOT car works great rich slightly............the transfer from idle to just off idle is bad.......when rolling down the road if you lightly apply the gas it goes ba!!s lean and stumbles.....phoned HOLLY they said try different power valve (6.5 to 9.5) helped but not much.....The carb. is a HOLLEY street avenger.....670 CFM. any HELP???? Thanks

 

check for vaccum leaks......also check the accelerator pump and squirter size may need larger depending on your combo it's hard to guess with out knowing all specs of motor. when I built my combo after install I had the smae issue maybe not as bad but a hessitation and with the cam I used they reccommended a base timing of 15 degrees using the 650 carb I had. check timing too.

 

No leaks......16hg at idle......squirter size is a 31 but I don't think I'm in the pump stroke when this happens........car has 5.0L(90 block)....roller cam .530 lift (INT/EXH).....RPM air gap manifold......full msd......heart shaped cast heads....timing is at 34d total.....

 

what did you set the base timing to at idle. and when I check for vaccum leaks if you have access to one a smoke machine works great. not saying you have one just trying to cover all bases. you have a lean spot in the cruise mode. I recently built 3 motors for various people all with msd and to cure to cruise mode stumble we set base timing at min of 15 degrees. not saying that's your problem because without riding in your car it's hard to say aaaaahhhhhh that's what you feel.

 

Have you adjusted the acc pump arms? Usually need to tighten the nut down some to get the full travel. What about the secondary spring?

 

There is no vaccum leak!!!(LOL)..........I just put this carb on the old carb was runing out of fuel........the pump rod is set to spec... and I even went tighter and looser just to see.....no change....the car goes lean I have an A/F meter......so I'm sure the timing is ok......like I said the only change from good runing (old carb) to stumble has been the carb....(old carb 600 CFM new one 670 CFM).......car still runs 1/4 at same times(little better).....just a stumble.....seems to be 2000 rpm or less.......again thanks for all the info.....keep it coming.

 

i have a 650 if you wanna buy something a little smaller

 

Hey I know your car isn't a barry grant but principle is the same anyway they base the sale of their carbs on specs of your motor so the reason I was stuck on the timing issue is it'll affect hesitation issues if initial timing is late or early it doesnt matter what total advance is that only comes into play on full throttle acceleration. anyway go to www.barrygrant.com and click on products and look to the right of the page and click on demon selection guide then scroll down page untuil you find a carb that matches your cam profile and they tell you what timing spec should be and they also have a troubleshooting page for hesitations off idle besides if you haven't set initial timing to 15 degrees what could it hurt try it if it doesn't work set it right back it'll take two seconds to do anyway I would use a 650 even that's a big carb for my heavily modded 302.....anyway good luck I'm just trying to give you ideas that have yielded me good results in the past.

 

NOOOOO!!!!! I think the size is good.... I run a 100 shot when it runs right....have not run it with new motor but soon as I get it dailed in.........looooook out!!!!!

 

again thanks for all the help!!!!! I will goto B/G and check that out thanks.........