rough run'n

[gaC5]

I have a 78. When I'm driving easy not giving it much gas it runs fine. But if I push the pedal to the metal it spits and sputters ,seems to lose compresion, and is just real rough run'n. It's an L48 but I changed the quadra-jet carb to a Holley 750 double pumper about 10x miles ago. Yesterday I took the front and back fuel filters out of the carb and cleaned them with brake cleaner. They actually didn't look that dirty. A guy at Advance Auto parts was telling me there should be a paper element fuel filter in the gas line but I couldn't see it. The gas line goes down under the engine. I also use 89 octane gas. It's always performed better than premium. I'm just wondering though if maybe I should try a tank of premium again.

 

[waterboy1976]

a 750 is way TOO much carb for a stock/ semi stock L48......My "slightly" modified 350 with almost 10/5:1 compression Dart heads and 420 HP uses a MIghty Demon 650.....Sounds like a carb adjustment issue...Premium gas wont change your sputtering...it would just quiet pinging if the engine actually was pinging however a stock L48 doesnt have enough compression to allow that unless youve modded it heavily.....Good luck...look at those adjustments on the carb....does it have vac secondaries or mech?

 

[JohnZ]

A double-pumper has mechanical secondaries - very poor choice for a street carb in terms of WOT throttle response and part-throttle driveability, and difficult to tune for proper street operation. It's way too big for your stock application to begin with, and it falls flat on its face when you nail it because of the mechanical secondaries. Don't believe everything you read in the Jeg's and Summit catalogs. :eyerole

 

[waterboy1976]

A double-pumper has mechanical secondaries - very poor choice for a street carb in terms of WOT throttle response and part-throttle driveability, and difficult to tune for proper street operation. It's way too big for your stock application to begin with, and it falls flat on its face when you nail it because of the mechanical secondaries. Don't believe everything you read in the Jeg's and Summit catalogs. :eyerole

exactly my thought too....way too much carb......unless he has it HIGHLY modded.......although as with a lot of topics the mech 2nd on mine are awesome but I do agree on most applications vac 2nds are better...as on his application...L48 etc etc.......

 

[gaC5]

I've had it on the car for about 3 years now and it has run good before at WOT. The person that put it on for me said it wasn't too big and he knows quite a lot about tuning.

 

[gmjunkie]

I've had it on the car for about 3 years now and it has run good before at WOT. The person that put it on for me said it wasn't too big and he knows quite a lot about tuning.

Maybe You have washed out the Ring's,With that Over Sized Toilet on Top!! junk!!

 

[waterboy1976]

Maybe You have washed out the Ring's,With that Over Sized Toilet on Top!! junk!!

LOL JUNK.....

He must not know too mych......what cam are you running? Duration? Lift? It still sounds like too much carb...way too much......do the math....Sounds definitely like a carb issue....

Good luck

 

[gmjunkie]

LOL JUNK.....

He must not know too mych......what cam are you running? Duration? Lift? It still sounds like too much carb...way too much......do the math....Sounds definitely like a carb issue....

Good luck

I'd go with 650 cfm, and then it would NOT be a HOLLEY!!!!! Them Flote Stick'n Car Burn'n Peices of Bear Dung!! I would Rather have my Finger's SMASHED!! junk!!

 

[1995 RedVette]

I'd go with 650 cfm, and then it would NOT be a HOLLEY!!!!! Them Flote Stick'n Car Burn'n Peices of Bear Dung!! I would Rather have my Finger's SMASHED!! junk!!

Com'on Junk....tell us how you really feel !!!


Brett

 

[GaryS]

I I'm just wondering though if maybe I should try a tank of premium again.

Too much carb. When was the last time you tuned it up or adjusted it? Secondly, your last line shows how well the gas companies have done their marketing. No offense to you, but if your car runs well on regular at lower rpms, then upgrading to premium won't fix anything except the gas companies bottom line. Remember the old "Put a tiger in your tank" commercials? This is what I am talking about. Fix what is wrong with the carb, check timing, plugs and wires.

Gary

 

[gaC5]

LOL JUNK.....

He must not know too mych......what cam are you running? Duration? Lift? It still sounds like too much carb...way too much......do the math....Sounds definitely like a carb issue....

Good luck

There's always a smart ass in the group

 

[waterboy1976]

ga.............when I say "HE" must not know too much......You said earlier the GUY you talked too knows a lot about carbs etc....thats who I was meaning.....NOT YOU..........a 750 carb is way too big for a stock/semi stock L48....hell even a L82.....stock a 750 would be too big.......Good luck.....not directing anythin bad towards you bro....

 

[gmjunkie]

ga.............when I say "HE" must not know too much......You said earlier the GUY you talked too knows a lot about carbs etc....thats who I was meaning.....NOT YOU..........a 750 carb is way too big for a stock/semi stock L48....hell even a L82.....stock a 750 would be too big.......Good luck.....not directing anythin bad towards you bro....

I have a Stock Q-jet on my L82,and it Run's Just Fine!! 62,000 mi not a miss!! junk!!

 

[gaC5]

No offense taken Waterboy. I thought a 750 might be too big when he first wanted to put it on. But he said he had a street rod with a 350 in it that had a Holly 750. Guess I could put a 650 on it. Know of anybody look'n for a 750?

ga.............when I say "HE" must not know too much......You said earlier the GUY you talked too knows a lot about carbs etc....thats who I was meaning.....NOT YOU..........a 750 carb is way too big for a stock/semi stock L48....hell even a L82.....stock a 750 would be too big.......Good luck.....not directing anythin bad towards you bro....

 

[gaC5]

That's what was on mine. JUNK

I have a Stock Q-jet on my L82,and it Run's Just Fine!! 62,000 mi not a miss!! junk!!

 

[Vettehead Mikey]

ga.............when I say "HE" must not know too much......You said earlier the GUY you talked too knows a lot about carbs etc....thats who I was meaning.....NOT YOU..........a 750 carb is way too big for a stock/semi stock L48....hell even a L82.....stock a 750 would be too big.......Good luck.....not directing anythin bad towards you bro....

The stock Rochester Q jet fitted to all small block Corvettes flows about 750CFM....................

 

[JohnZ]

The stock Rochester Q jet fitted to all small block Corvettes flows about 750CFM....................

But it only does so when the engine's airflow demands it, progressively, based on the deflection of the secondary air valve at the top of the secondary venturis; an elegant design. On the other hand, the double-pumper mechanical-secondary Holley is a "race" carb, and everything goes full-bore wide-open the instant you put your foot down, LONG before there's enough air velocity to handle it. But Jeg's and Summit love 'em

 

[Vettehead Mikey]

But Jeg's and Summit love 'em

You're not saying that people are influenced into making bad decisions by glossy colour catalogs are you???? :L

 

[JohnZ]

You're not saying that people are influenced into making bad decisions by glossy colour catalogs are you???? :L

Only when the word "performance" is emphasized, and that's about 4,000 times per issue.

 

[gmjunkie]

But it only does so when the engine's airflow demands it, progressively, based on the deflection of the secondary air valve at the top of the secondary venturis; an elegant design. On the other hand, the double-pumper mechanical-secondary Holley is a "race" carb, and everything goes full-bore wide-open the instant you put your foot down, LONG before there's enough air velocity to handle it. But Jeg's and Summit love 'em

Yes, just Flush that Toilet!! junk!!