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I have a leak at the gaskets between the carb and the manifold. Both surfaces are flat checked with a straight edge. I was sent two gaskets with rebuold kit. One is grey and thin. Other is thicker and black.
Stock 4 bbl Rochester carb on a 350. I marked on the photos where I am detecting the leak. It's where the back ears have the hollowed out area on the bottom. Neither gasket goes past that area on the outside to seal. Which gasket is best and any tricks to seal that area?
I prefer the thicker gasket with the built in plastic pieces at the bolt holes. Looks as if the one in the picture has been uses, so maybe try the other one - or get a new one with the inserts. Your local auto parts store should be able to get one: FEL-PRO 60335.
Are you certain it’s leaking there? The secondary shaft is very close to that spot.
I prefer the thicker gasket with the built in plastic pieces at the bolt holes. Looks as if the one in the picture has been uses, so maybe try the other one - or get a new one with the inserts. Your local auto parts store should be able to get one: FEL-PRO 60335.
Are you certain it’s leaking there? The secondary shaft is very close to that spot.
When I sprayed there it showed a leak. Not 100 positive it isnt the secondary shaft being it is close. If it's the secondary shaft does it require a complete rebuild with new bushings or is there anything that can be used on the shaft to seal it?
Last edited by 72Vert442; August 27th, 2023 at 01:42 PM.
Another question while it's apart. Below is the inside of the intake. Looks to be black from carbon build up. Is this common or a result of a vacuum leak as well?
Are you sure the carburetor base is flat ? In your second picture it looks like the gasket is not being compressed vary much int that area. It is not uncommon for the ears of the Q-jets to warp down some mainly from people over tightening them. You could take a real new flat file across it and see.
Also, the choice of gasket is not a "preference" It depends on which one is correct for the application. Most of them use the thick one but you never know. Is it the original carb for the car ? What is the carb number ?
As far as the leak if you mean a vacuum leak I have never seen a carb where the shafts are perfect. Unless they are totally worn out they shouldnt leak badly enough to cause a problem.
Are you sure the carburetor base is flat ? In your second picture it looks like the gasket is not being compressed vary much int that area. It is not uncommon for the ears of the Q-jets to warp down some mainly from people over tightening them. You could take a real new flat file across it and see.
Also, the choice of gasket is not a "preference" It depends on which one is correct for the application. Most of them use the thick one but you never know. Is it the original carb for the car ? What is the carb number ?
As far as the leak if you mean a vacuum leak I have never seen a carb where the shafts are perfect. Unless they are totally worn out they shouldnt leak badly enough to cause a problem.
I did touch up the rear ears as they were slightly high but when I say slightly I mean barely. Not like there was a noticeable gap. When I put a straight edge on the base I had to shine a light in the backside to see a sliver of light in the area I was finding a leak. Maybe about the thickness of a piece of paper or less so I knocked down the ears to eliminate this. The carb is a 7042250. Local store had to order a new gasket for me so that will be in tomorrow. The one I had was new a month ago when I rebuilt the carb but to be safe Ill just use a new one.
I sometimes put a light coat of bearing grease on my gaskets, just to give a little more seal and relieve any gasket sticking. No more than a very, very light coat.
I sometimes put a light coat of bearing grease on my gaskets, just to give a little more seal and relieve any gasket sticking. No more than a very, very light coat.
I sometimes put a light coat of bearing grease on my gaskets, just to give a little more seal and relieve any gasket sticking. No more than a very, very light coat.
x2
I use those 60335 gaskets cuz they’re thick and have the buttons to limit compression. I paint both sides with copper antisieze, can’t hurt sealing and allows removing the carb without delaminating the paper surface, especially when tuning and the carb comes off a half a dozen times or so.
I antisieze thermostat gaskets, and sometimes intake or header gaskets as well, allows them to come off clean, I hate scraping, especially with aluminum involved.
I never understood the buttons.
Why would you want to limit the compression of the gasket?
(love to hear explanation)
Im not saying I crank down my carb bolts to 100ftlbs…but with the possibility of an uneven surface, I think the limitation might not be advantageous.
This is a blind cavity. There is no connection to vacuum and no way for it to leak. The area directly around the throttle bore is where the seal takes place. I would suggest that either you do have a leak at the shaft (which is not unusual) or the problem is further inboard.
All back together. Leak is in the same spot. Defintely not the shaft seal. Sprayed right on it and nothing. Under the carb right in front of the secondary shaft and it's there. Going to try copper anti seize grease. Back two bolts offer zero co pressing of the gasket. I can feel the front ones give come compression. Back one hit a hard stop with not much noticeable compression. Nothing leaks on drivers side. It's in the passenger side.
I would certainly not put antiseize on it. You dont want that getting sucked into the engine. I still say there has to be a low spot or the corner of the carb is warped. What type of straight edge are you checking it with ? Look at my picture below and you can see where the gasket is hardly compressed in that area. If anything I suppose you could try trimming the plastic inserts a little to let the gasket compress a little more ?
I have found a 2" x 6" sharpening stone works real good at finding high and low spots. This is the one I use. You can color the metal with a magic marker to help show low and high spots.
Back two bolts offer zero co pressing of the gasket.
..
Back one hit a hard stop with not much noticeable compression.
Are you using the original bolts or something else? Maybe try putting a washer under the bolt head so there are a bit more threads before bottoming out in the intake holes.
Went backwards somehow. Runs rougher now. Idle surges from time to time. Tried to set AF but didn't help. Hearing faint click in the carb from time to time. Lean pop? Revved it and got a pop in the exhaust on decel. Acts lean but not sure what to do. Opening AF screws didn't make a difference. If I let it idle after a while the idle would drop like it wanted to die. Clearing it up would get it to idle up again at normal idle speed but it is rougher then it was.
Last edited by 72Vert442; August 28th, 2023 at 04:40 PM.
Think Im to end of this saga. Tried 3 different thick gasket types all with the screw hole inserts. None would seal in that spot. Used the grey thin one sent with my rebuild kit and it sealed. That didnt fix my problem so I guess it wasnt the majority of the problem. Described what I was experiencing to quadra jet power and they recommended I plug the hot air compensator. They said what I described was common with the compensator. Plugged it and much better now. I did a final adjustment on AF and now its has a smooth idle in gear. Ill see how it goes from here after drive it more but hopefully this is the end. Want to enjoy the car but hard to get excited when it wouldnt run right.
Leak was still there after it warmed up but I have a better idea where the leak is and maybe why but need some help. I colored both the intake side and the bottom of the carb then used a fine stone to see where high and low spots were. The blue arrow on the manifold was a high spot. I felt like I got the intake flat now. The carb was pretty good but have a question on what the two holes at the rear are for cause the gasket barely covers them and this is where I find the leak. If I spray from the rear it has a pretty good leak. Do I need to plug these holes?
I got a smoke generator today and tried to detect a leak using smoke introduced into the manifold. Could not detect any smoke coming out anywhere other than through the top where it was taped off. Couldnt tape it perfectly.
When motor is running I can spray carb cleaner under the rear base and just above the rear base and the rpms come up immediate and it smooths out. Leak is in the rear of the carb. Could the leak only show with a pull of vacuum from the inside and wouldnt show when smoke pushes out? Dont imagine I an getting any positive pressure during the smoke test.
I mention this as a last resort and may get flamed for suggesting it. Smear some silicone gasket sealer on both sides of the carb gasket. That should take care of any leaks.
Without know how old or "used" the stone is that you used, I would like to see what using a NEW stone would show. The rear bolt pads on the carb should show more contact. Stones do "wear", they don't remain forever. Save the new stone for "checking purposes".
As a last resort, a light smear of silicone gasket sealer as Kenneth suggests would work.
I mention this as a last resort and may get flamed for suggesting it. Smear some silicone gasket sealer on both sides of the carb gasket. That should take care of any leaks.
Yeah that or Aviation sealant. Maybe try using a thin and thick gasket together.
I used some gasket maker around the secondaries and I am not detecting a leak in the back. Now trying to set the AF screws right. Using a vacuum gauge it was reading 17 in hg at 1000 rpm. I turned the screws in until it dropped to 16 then backed it up a half turn. Off idle motor is very smooth but at idle it was surging 100 rpm in park and in gear. I turned the AF screws out a half turn on each side seeing the effect on the surge. 1 and 1/2 turns more out and the surge went away it is much smoother at idle at operating temp.
A few questions - was the surge a sign it was too lean at idle. Not sure how many turns the screws are out now but they seem much farther out then normal. I would guess 5-6 turns out. Could this mean the passage ways are partially block and not flowing properly? Could it mean I still have a vacuum leak somewhere? Another thing that doesnt make sense it the idle screw is backed off and it is around 950-1000 rpm in park. If the idle screw is all the way out wouldnt the idle be very low normally?
Going let it get cold over night and see how it runs tomorrow from cold to operating temp.
Used the car in a local parade. 45 min of idle crawl. Quite the test but it ran good at idle the whole time. Temp normally runs 185 during normal driving. It was 195 with the crawl at idle that long. Only thing was at the end I turned it off for 10 min and when I tried it restart it it was flooded and had to wide open throttle to get it to start. Got home let it sit another 5 min and same thing. What would cause this? Gas bleeding from the carb?
Glad I sent my carb off to an expert. He said Olds set up their Quadrajets lean from factory. Made the several corrections internally and now it purrs like a new car. Not a single hiccup in park or any gear. That was well worth the money. Rebuild kit was never going to fix it.
August 27th, 2023, 12:16 PM
