Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Idleproblems on my Cadillac 500 stroker
77cruiser:
How far can you open your throttle before you get into nozzle drip. Maybe you can open them more than 1 turn. I know they show a lot of transition slot but they're not Holleys. Can't believe I said that word. :o
Cliff Ruggles:
The tendency to get "nozzle drip" can vary dramatically from carb to carb. This simply happens because there were quite a few different boosters used in different carb numbers, and vastly different calibrations.
Carburetors with much smaller MAB's, such as Marine units for example, can see nozzle drip at very low throttle angles. This simply happens due to the sensitivity of the boosters and overall calibration of the carb combined with the specific parts used in it.
Fuel level is another player as a higher fuel level allows the fuel to flow easier from the bowl, all else being equal.
Fuel pressure and fuel seat diameter are also players here. The higher the fuel pressure and/or larger the inlet seat diameter, the higher the fuel level will be at any given float setting.
The size of the float also becomes a contributor here as well. These are a few items folks never even take into consideration when custom tuning.
It is also why I push using are parts, because we have already tested them and will supply the correct ones for what you are doing, and follow that up with specific tuning advice.
This fact is also why I often shy away spending countless hours on the phone helping folks with "free tech" when they have purchased EVERYTHING someplace else, it doesn't work well, the folks where you bought the parts are useless for advice.........then I'm being asked to crawl thru the phone and fix all the issues.
This scenario plays itself out here WAY too often for my liking so I have my calls screened so I can stay on the job and get the carbs the very patient folks have sent here for us to work on finished up.
Besides, if I took every phone call that came in here for "free technical assistance" we'd be out of business in a month, maybe less!
That's the facts of life here folks, pardon my attitude and comments, but we do this FULL TIME and for a living and really do want everyone to have a good end result with these things, just throw a bone our way once in a while so we can continue to provide this service.....many thanks.....Cliff
MonteCarlo:
--- Quote from: 77cruiser on September 20, 2017, 01:24:43 PM ---How far can you open your throttle before you get into nozzle drip. Maybe you can open them more than 1 turn. I know they show a lot of transition slot but they're not Holleys. Can't believe I said that word. :o
--- End quote ---
I only know it was way to open when I started. Probably I can open a little bit more without nozzledrop. I am going to work with this during the weekend.
Erik
MonteCarlo:
--- Quote from: MonteCarlo on September 21, 2017, 12:07:08 PM ---I only know it was way to open when I started. Probably I can open a little bit more without nozzledrop. I am going to work with this during the weekend.
Erik
--- End quote ---
Hi again. Getting a pretty god idle now. The trick was to change a little bit here and there.
Opened up the the bypass a little more. Raised the timing a few degrees. I get a better idle when using manifold vacuum, good or bad I dont know. Opened up the idle fuel a little bit but then I think it is going a little bit rich of idle. I think I will reverse that.
Called up MaximumTorqueSpecialities in California and talked about the camshaft and low vacuum. The guy at MTS sad that 10 hg was around the expected value with this cam.
Thanks for help and all the tips.
Erik Olsson
Cliff Ruggles:
540cid with 237 degrees @ .050" and 112LSA isn't really a big cam. I'd expect considerably more vacuum at idle speed that what you are seeing, unless the static compression ratio is pretty "low".
I seldom use manifold vacuum to the advance but have seen a few combinations that require a lot of timing at idle for one reason or another, which is usually a bit too much cam and/or not quite enough compression.......Cliff
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