Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
idle issues
Cliff Ruggles:
The distributor advance curve should be steady at idle speed, and start advancing right off idle. 2000 is pretty late and will hurt engine power and throttle response.
Any side play at the primary shaft is NOT a good thing, as it is a vacuum leak, and adds additional air at idle speed, which requires additonal fuel to compensate. The additional air also increases engine rpm's, all else being equal......Cliff
wcumagic:
Cliff, I thought about what you said for a few days and decided to throw a timing light on it. At idle, it was about 20 degrees, which meant you were correct. ::) I looked back over my paperwork for the dist, and it starts advancing at around 1000 or 1250. I set the timing back just a hair (from 12ish to 10 degrees advanced), and set the idle down to around 750. Vacuum, advance (at 10), and idle are now steady. I also double checked my idle screws and gave them a full 2 turns out, I had them at 1.25 or 1.5 previously. I appreciate you suggesting I look at the timing. :) I could put lighter springs in the mechanical advance for the distributor if I backed the timing back down a little bit at idle, are there any advantages to that?
omaha, it is the original fuel pump (originally at 45 psi or so) but I have a good mallory regulator on it with the factory fuel return.
I drove it today and it seems great, but there is a slight bog before it digs and goes. My choke pulloff is around a second or a little plus, I guess I should tighten the tension spring on the secondaries a little to compensate?
also, on a side note, if I drove the 70 miles down the road to get a 5 gallon container of race gas, assuming I'd never driven ANYthing on race gas, with the higher compression, would I be happy I did it? I'd seen something where a hot rod had a 5 gallon fuel cell with race gas in it for when he wanted EXtra on the street. Are we talkin 3 hp difference or more?
Cliff Ruggles:
Good news! I would NOT use lighter springs. The timing curve should be rock solid at idle speed, and start right off idle, or apprx 900-1000rpm's for most set-ups. If all the timing is in by 3000rpm's or so, the curve is fast enough.....Cliff
kelley555:
Cliff,this is Kelley,I'm going to be ordering my Hei vacumn advance 7000 rpm (with a rev limiter module for my column shifter.(No accidents can happen to good engine encase I have a mishap) Probably the distributor going to come from distributor from Performance Distributor soon for my 415ci. With the engine having 9.5 to 1,a Crane cam hyd . roller .585/.595 lift (with the 1.6 ratio rockers) & 234/242 dur. (maybe a tad bigger cause the rockers),Qjet 800cfm,3000 stall,350 turbo,3.73 gear,pump gas around a 89 oct.(maybe even premium some times Eventually I'm gonna buy a taller tire than the street M/T Indy Profile's(25")they suppose to have a softer compound,probably a 28" tall tire that will make the engine turn around 2665 rpm at 60mph will be out cruize range of the engine.Do you think that will be to low rpm to cruize around or stay with the shorter tires around + 320 rpm more. If the car idles at around 900-1000 would you have the distributor advancing soon from idle & all in by__rpm ? How much max timing with pump gas? The timing's a little different on your car due to the cr. & your setup but,What your opinion about timing with these crap gases of today?,I don't want to have a detonation problem so when I order I want to speak with a little knowledge.Later kelley
Cliff Ruggles:
At 9.5 to 1 compression with aluminum heads and that much cam, I'd expect the power curve to start coming in really strong right around 3000rpms. It will probably have low vacuum at idle speed, and may be a little "soft" right off idle.
Crusing rpm's should be OK if over 2500rpm's or so, but it will like to be up around 3000rpm's or a tad higher, IMHO.
The engine will also like a fast timing curve, and all in as soon as possible. The curve still can't start till the engine is just off idle, or about 1000rpm's or so. All in by 2500rpms would be a good thing.
Total timing is always on a case by case basis. I recomend the dyno or dragstrip to find the best total timing setting.
Start out around 28-30 degrees, and make some pulls or runs and watch the power (ET/MPH). When it stops improving, you have found the best total timing setting.
My 455 at 11 to 1 compression easily manages currently available 89 octane fuel, and actually runs fine on 87 octane. I still mix in 92 or 93 octane for track outings, makes me sleep better at night!.......Cliff
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