hey Lars i need your expertise, ill try to update you on my issue. i tried replacing the fuel filter on my 79' w/a Q-jet and when i go to tighten everything up and start it, it starts leaking when i turn it on. now this is the procedure on how i replaced it.

1. take old one out
2.install new one into larger filter housing Correctly and thread it in slowly so not to cross thread it.
3. screw on flare nut and hold larger nut while tightening smaller one.
4.pray it doesn't leak.
5. It Leaks.

ive gotten lots of tips,suggestions and advise from others which i appreciate alot. but i was wondering what you might think it could be...maybe a cracked housing?
One problem with that theory is when i put Tape sealent on and a 1/8 inch gasket on the larger nut and tightened it down, it still leaked. now are the threads on the larger nut pipe thread? or are they normal threads, cuz if they are normal then the gasket is just making it leak more.

Thanks Lars!

 

Evil -
The nut is not a pipe thread. The nut is a 1"-20 straight thread. There should be a thin white plastic seal washer on the very end of the nut - right at the very end of the threads. It is retained in a small machined sealing area at the end of the nut.

Make sure that the remnants of the old seal are not stuck inside the carb - deep inside the threaded area of the carb is a flat sealing surface, and I've seen the old sealing washers shreaded into this surface.

Once the thin plastic seal has been snapped into the end of the nut, put a dab of grease on the nut threads. This will allow proper torque. Don't use thread tape - the threads do not seal. Snug the nut into the carb using a 1" box wrench.

The fuel line that screws into the fitting should also be lubed: Place a dab of grease on the back side of the flare where the nut rides up against the tube, and also lube the threads. Hold the 1" wrench on the carb nut as a backup, and snug up the fuel line with a 5/8" flarenut wrench.

I have seen the threads strip out of the carb, but this is more comon on the early 7/8-20 inlet threads (early Q-Jets). I've never seen a casting actually crack to cause a leak. I have seen inlet nuts that were cracked.

Let me know if you need assistance.

 

A 1/8" gasket? There is no 1/8" gasket that can be installed at the end of the inlet nut.... what type of gasket are you using, and where are you putting it? The correct seal is a very thin plastic washer, about .030" thick, that snaps into a groove at the end of the nut.... is this what you have? Is your carb a '79 carb?

 

ohhhhh.... it's all coming back to me now, like a bad dream! that little plastic washer lars is telling you about is the likely culprit. When I changed that in-the-carb filter the first time the plastic washer was in such bad shape it came out in pieces and I didn't even know what it was or recognize its importance ?!?! But without that washer, the fitting leaked pretty badly. I can't remember if I got the replacement out a carb rebuild kit or if they actually carried the right piece at Napa. But I did find the right piece and it turned out to be the "miracle cure" for the leaky fitting at the carb.

 

Yes, you can get the correct plastic seal from NAPA. But be aware that there are 2 types of seals: one is the correct plastic seal that goes right onto the very end of the post-'75 inlet nuts. The other seal is a black rubber-coated steel seal that goes around the base of the hex-portion of the nut on a pre-'75 inlet nut. The latter seal is bigger, and it slips over the threads. The post-'75 seal is smaller, and does not slip over the threads - it installs at the end of the threads.

 

I work at Napa. well Thursday i go back to work and ill try to find the part # or ill just get the kit since its so cheap and grab it outa there. thats wierd cuz last time i did the filter change, the first time on the car it didnt leak, and this time it just wouldnt stop leaking no matter what. Ok so tomorrow if it doesnt rain then I'll take the pipe sealent off and that goofy lookin gasket i put on the end of the filter nut. hey Lars, how hard would it be to rebuild a Q-jet? ive never tried and would probably mess up a few times, is it better left to a pro or someone with Q-jet experience like you? i just dont wanna jack up the original Q-jet and not be able to drive it for a week. i got some other questions that arent related to this thread and ill post em in another thread about some grounding issues...

 

Just replaced that little inlet gasket. NAPA (at least the one here) doesn't sell the individual gasket--you must buy a little kit of about 20 different gaskets. The part number is 730-9573. Only $2.77 though and then you'll have a bunch if they need replacement in the future.

wwaag

 

they must be on crack, cuz the part # is 2-2461 and the line code is CRB. ya im pretty sure they dont know their head from their A5$ if-...wait a minute, that means...wow i must have a butt for a head too! hahaha well i installed the nylon gasket that slips on the end of the larger filter housing nut and went to put it in and it still leaks from the bottom, now is it possible since i was doing this in almost pitch black darkness that i could have had it slip off to the side and not seal properly? i REALLy dont wanna have to take the carb off if i can help it.

 

i just remembered looking at the old nylon gasket and seeing that it was pretty chewed up and stuff. i almost didnt see it and would have gone over it with the new one until i reached in the housing and scrapped it out. well in any case, and the chance of it not seating properly and good chance of it still leaking?

 

Evil -
Have you verified for sure that the leak is between the housing and the inlet nut and not between the inlet nut and the fuel line? The gasket snaps into place on the end ofthe inlet fitig, so there's not much chance of it coming loose and getting cocked in there. Providing the mating sealing surface inside the carb is not damaged, the seal will seal easily. Inspect the sealing surface inside the carb and make sure it is not damaged and that there are no remnants of the old gasket on that surface. If the surface is clean and smooth, and the nylon gasket is on the nut, the surface will seal. If you still have a leak, you either have a cracked inlt nut (I've seen several, believe it or not), or you have a bad sealing surface between the inlet nut and the fuel line - the inverted flare sealing surface. You can get a new inlet nut (brass) from Carbs Unlimited. A leak at the inlet line will often seem like the nut is leaking, since fuel will soak the entire area - make sure you identify the source of the leak. If all else fails, send me the carb and I'll find the leak.

 

You might want to check the threads and make sure they aren't nicked. I went through three float bowls on my Holley 3X2 setup before I figured out the threads had been damaged. Every time I screwed it in, it stripped out the threads on the fuel bowl and the damn thing leaked. Just something to check visually....

 

Had the same problem with my 80, after taking the line off three or four times and still having a fuel drip. I called in my plumber, yep he found a couple nicks in the threads, cleaned them up, used plumbers tape and all is dry.

 

Well! my carb has a ever-so-small crack in the fuel filter housing, so i get a new carb!!....i have lots of questions.

1. Will a Edelbrock hook up Vaccum hose for vaccum hose?
2. will i have to cap anything off?
3. Is there a certain model i should get?
4. My motor is stock, should i just get a rebuilt Q-jet?
5. If i get a Edelbrock, is there any adapter plates i need to go onto the bore for the manifold?

Please give LOTS of advice, tips, suggestions, and experience on several Carbs if possible...

Thanks to all in advance!

 

someone...anyone! LOL

 

Go with the Speed Demon 750 with mechanical secondary.

 

 

Prices people, I need Prices!

 

Well i gave in and just bought a cheap rebuilt from Napa for $160. should there be any adjusting to be done on the rebuilt since this is a fresh unit and the motor has slightly different needs now that the block has aged and im putting a new *rebuilt* carb on it? if so, should i just take it to a compitent corvette shop and have them tune and time my vette as well?

 

are these units *rebuilts* already preset to the proper A/F mixture or should i take it to a shop and have em mess with it.

 

On the commercially rebuilt carbs you can be in for a real bag of worms. You can get something that's pure junk, or a perfectly usable unit. No way to tell. If you have a junk unit and take it in to get it tuned, you'll be spending a ton of money, and they'll never get the car right. If you have a good unit, you can bolt it on and run. I hope you're not in for an adventure - good luck!!