HELP! my engine is surging at idel. why?
Thread Starter
Intermediate
Joined: Apr 2008
Posts: 31
Likes: 0
From: everett wa
HELP! my engine is surging at idel. why?
its a 77 with quadrajet. it idels at 6 hundred and then soots to 2 grand. i cant even driv the car its so bad. and its my only tranportation for a month or so. car ran fine last fall minus the chock woundnt stay on long to warm the moter up. please help me!!
Thread Starter
Intermediate
Joined: Apr 2008
Posts: 31
Likes: 0
From: everett wa
great! not really. thanks fr at least responding though. i have a funny suspision it might be this vacume diafram that is conected to my disributer. it hangs of the right side of the distributer and has a vacume hose running to the front of the carb. what is it and what does it do?
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
great! not really. thanks fr at least responding though. i have a funny suspision it might be this vacume diafram that is conected to my disributer. it hangs of the right side of the distributer and has a vacume hose running to the front of the carb. what is it and what does it do?
While adding or removing vac advance will affect idle speed, the behavior your describing is really strange.
You can remove the hose temporarily though to see if the surging stops.
Instructor
Joined: Jan 2008
Posts: 143
Likes: 1
From: Beaumont TX
That would be your vacuum advance unit on the distributor which increases your spark advance as manifold vacuum increases. Your idle speed will increase when it is engaged. This still doesn't easily explain things.
Is there any chance it was not working at all last Fall and your idle was adjusted then? Now, for some strange reason it has resumed working intermittently and is raising your idle when it does?
Admittedly, this is a far-fetched scenario but I can't think of anything else other than possibly some carburetor problem that could possibly cause an rpm increase like that. I don't have any carb expertise that could explain this but maybe someone else does.
The good news is that a vacuum advance unit is only $15-$20 and very easy to change out. You might want to check out this "Sticky" on timing at the top of the C3 Tech page http://forums.corvetteforum.com/c3-t...long-post.html. It will help you get your engine running its best. I just used their tips and my car has never run better in the nine years I have owned it.
Is there any chance it was not working at all last Fall and your idle was adjusted then? Now, for some strange reason it has resumed working intermittently and is raising your idle when it does?
Admittedly, this is a far-fetched scenario but I can't think of anything else other than possibly some carburetor problem that could possibly cause an rpm increase like that. I don't have any carb expertise that could explain this but maybe someone else does.
The good news is that a vacuum advance unit is only $15-$20 and very easy to change out. You might want to check out this "Sticky" on timing at the top of the C3 Tech page http://forums.corvetteforum.com/c3-t...long-post.html. It will help you get your engine running its best. I just used their tips and my car has never run better in the nine years I have owned it.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Intermediate
Joined: Apr 2008
Posts: 31
Likes: 0
From: everett wa
tried it. it semmed to help kind of. it made it a litlle better but still doin it. if i drive it i have to put it in nutral at a stop light. and then it just lump lump lump whaaaa lump lump lump whaaaa!
Thread Starter
Intermediate
Joined: Apr 2008
Posts: 31
Likes: 0
From: everett wa
thanks for the help. il try the advance and go to the sticky. ill let you guys know what it turns out to be. give me a couple days. i dont think napas open till tus wit the holiday and all. and of course if anyone has a for shur fix it pointer please give it to me at any time. ill be watching. thanks gents
Melting Slicks
Joined: Dec 2006
Posts: 2,669
Likes: 3
From: Kingston Ontario
Electric or mechanical choke?
Warm enough outside right now to wire your choke mechanism in the off position, and operate the engine. If your RPM remains stable you know you have a choke control issue. If choke is electrical, check for a lack of voltage to choke. If choke is mechanical, the problem could be linkage seizing or binding, or an adjustment is required.
If the RPM is still fluctuating it is a fuel delivery issue.
Warm enough outside right now to wire your choke mechanism in the off position, and operate the engine. If your RPM remains stable you know you have a choke control issue. If choke is electrical, check for a lack of voltage to choke. If choke is mechanical, the problem could be linkage seizing or binding, or an adjustment is required.
If the RPM is still fluctuating it is a fuel delivery issue.
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
thanks for the help. il try the advance and go to the sticky. ill let you guys know what it turns out to be. give me a couple days. i dont think napas open till tus wit the holiday and all. and of course if anyone has a for shur fix it pointer please give it to me at any time. ill be watching. thanks gents
Not hearing it or seeing it:
FLoat valve leaking
Vacuum leak, Smog device
Carb vacuum break
Timing chain loose
Power valve spring riding on vacuum surging causing flutter
Hei Ignition module
Idle set wrong and air screw adjust wrong magnifying power valve flutter
Timing wrong
Ported vacuum from carb signaling the advance- carb misajusted
Melting Slicks
Joined: Dec 2006
Posts: 2,669
Likes: 3
From: Kingston Ontario
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
not right.
Vacuum advance "should" not add much if any advance at idle.
Vacuum line removed should not kill motor.
When you set timing did you remove and plug vac advance line?
Sounds like a combo of wrong basic timing and bad carb idle adjust
Or advance weights and springs sticking or loose.