Carb leak on straight six... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

68_GMC_910 · 09-16-2002, 08:52 AM

when I look under the hood after driving the truck around a little I am greeted by a slow drip of gas off the carb, evaporating on the intake manifold and making a not-so-good smell...

I was wondering what you guys thought would be the most common reasons for this...

I just wanna fix the carb to add resale value to the motor/transmission before I sell them off after I get a 4 speed and small block... plus I don't wanna sell a POS to somebody... thanks in advance.

Kas68c10 · 09-16-2002, 11:01 AM

Check the float level on the carb. If the float is set too high, gas may leak out the top seal. Pop the top off the carb and seel how full the bowl is. Is this a 250 or 292 ? Let me know what it is, where you are located and how much, I may be interested.

68_GMC_910 · 09-16-2002, 06:27 PM

it's a 250 with a three on the tree... runs pretty good from what I see although I just recieved the truck yesterday...

I'm in Canada, in the province Manitoba just outside the city Winnipeg.

The previous owner said the engine is newer than the truck, and it looks like it, too... I just went out and took some pictures of under the hood so I'll see if I can email them or post them soon if you like...

How much for both? I'd ask $250 American for both the motor and transmission... I dunno if I'd sell them seperately... well, maybe but I probably can't get much for the tranny at all so I'd be a little reluctant... but eh, why not?

Thanks for the help and the interest in buying the six...!

68_GMC_910 · 09-16-2002, 06:30 PM

oh, and your truck is awesome! I really like it!

Gordo · 09-16-2002, 06:40 PM

If it runs fine it may not be flooding over, it may be the fuel line fitting at the carb and/or the fitting that holds the fuel filter into the carb that is loose or missing/bad gasket. We need more info as to where it's leaking at the carb.

XXL · 09-16-2002, 08:26 PM

Quote:

Originally posted by Gordo
If it runs fine it may not be flooding over, it may be the fuel line fitting at the carb and/or the fitting that holds the fuel filter into the carb that is loose or missing/bad gasket. We need more info as to where it's leaking at the carb.

Ditto Gordo... Where is it leaking from???

When I bought my truck a few years ago I had to swap out the carb to get it running. I went to my local auto parts store and bought a rebuilt 1bbl done by Holley Rebuild (same Holley as makes carbs, but this was the factory rebuild and quality control is not quite the same). After I installed it (in about 3 minutes including putting tools away

) I noticed it was leaking at the fuel inlet on the large fitting that holds the brass filter. It was O-ringed, but it was still leaking. I swapped O-rings to no avail. So I had to swap out the carb. The next carb had a bad accelerator pump [u[but it didn't leak[/u]! So I swapped that out for yet another rebuilt. This one leaked in the same place. The fourth carb was the charm. It worked AND it didn't leak. It's still on there today, working fine. Apparently after these things have been through the cleaning vats for too many rebuilds, the inlets start to lose a little metal and the fitting no longer seats well.

BTW, to the few minutes it takes to swap out a carb on these inline 6's, add 4-5 days turnaround time for my local auto parts store to get a replacement since they didn't stock the carb.

Kenneth

68_GMC_910 · 09-16-2002, 09:11 PM

well, I got found some time to get out to the truck and take off the airbox and it looks like the gasket is shi*t... it's a rebuilt carb, done by a Canadian company that starts with an A... Can't remember it... I think the inlet maybe leaking too because I don't think a gasket would make the gas leak out when the engine is off... But I'm out of gas so I can't find out!!!!!

argh... this is going to be a hell of a project and I'm definitely going to need every last bit of luck to do it on the small wad of cash I have...

chucks70 · 09-16-2002, 11:02 PM

I was just at a show a couple of weekends ago and took pics of a 292 with dual carbs on a polished offenhauser manifold. No leaks there. Exhaust was split manifold duals goin back. Sounded nice for a straight six. Can't figure out how to post pics

Kas68c10 · 09-17-2002, 09:55 AM

Gordo and XXL make a good point, it can leak there. Wrapping the threads with plumbers tape is a quick and easy fix, although not the best solution. Can purchase a gasket kit for these carbs for less than $20 I thinkk. If you lower the float level, the gas will never get high enough to leak out the top sel. Be careful though,cause lowering it too much will cause truck to die when you step on it or hit a tight curve or big hill.

Thanks for the compliment on the truck, will be putting air in and a paint job next year I think.

I have a 292 in the garage,waiting to get rebuilt, I woulkd love to put an offy intake and dual carbs on it. Although I really like the Weber progressive I have now....

I am a Canadian too, just displaced here in MI!!! From Ontario !
I think you are too far away for me to buy that engine, shipping would be prohibitive....

Let me know how you make out !

I also have a spare Rochester if you need it, it doesn't leak, float is set right, I just replaced it with the 2 barrel.
Good Luck !

Fred T · 09-17-2002, 02:51 PM

Here's a better solution to the leaky inlet fitting. Get a tube of Permatex Hylomar sealer, it was designed by Rolls Royce for sealing carbs. Gasoline resistant and stays soft. Put it on your threads and gasket. Float level, these guys are right. Probably set a bit to high. And a gasket set doesn't solve all the leak problems with the old Rochester, but it helps. Last one I bought was $22 and had the wrong style accelerator pump for my B model. If you can't get a leak between the horn and bowl stopped, careful application of the Hylomar can help. It doesn't always work, though, due to warpage of the carb.

09-16-2002, 08:52 AM	#1
68_GMC_910 what would Neal do? Join Date: Sep 2002 Location: Winnipeg, Manitoba, Canada Posts: 150	Carb leak on straight six... when I look under the hood after driving the truck around a little I am greeted by a slow drip of gas off the carb, evaporating on the intake manifold and making a not-so-good smell... I was wondering what you guys thought would be the most common reasons for this... I just wanna fix the carb to add resale value to the motor/transmission before I sell them off after I get a 4 speed and small block... plus I don't wanna sell a POS to somebody... thanks in advance. __________________ 1968 GMC 910 Long Step 250/3onTree 1969 Chevy C10 longfleet, 350/350

09-16-2002, 11:01 AM	#2
Kas68c10 Registered User Join Date: Apr 2000 Location: Freeland,Michigan,USA Posts: 312	Check the float level on the carb. If the float is set too high, gas may leak out the top seal. Pop the top off the carb and seel how full the bowl is. Is this a 250 or 292 ? Let me know what it is, where you are located and how much, I may be interested. __________________ 1968 SWB Stepside, 250,pwr disc brake and tilt pwr steering, 5 spd tranny, HEI,Accel coil,K&N filter,Seat from a later truck with built in seatbelts, front and rear sway bars, moved gas tank to under the bed, headman hedders, new chrome bumpers,one wire alternator,Weber k550cub carburator...WORK IN PROGRESS, Freeland MI , Just bought a 72 Jimmy!!!!!!!!!!!

09-16-2002, 06:27 PM	#3
68_GMC_910 what would Neal do? Join Date: Sep 2002 Location: Winnipeg, Manitoba, Canada Posts: 150	it's a 250 with a three on the tree... runs pretty good from what I see although I just recieved the truck yesterday... I'm in Canada, in the province Manitoba just outside the city Winnipeg. The previous owner said the engine is newer than the truck, and it looks like it, too... I just went out and took some pictures of under the hood so I'll see if I can email them or post them soon if you like... How much for both? I'd ask $250 American for both the motor and transmission... I dunno if I'd sell them seperately... well, maybe but I probably can't get much for the tranny at all so I'd be a little reluctant... but eh, why not? Thanks for the help and the interest in buying the six...! __________________ 1968 GMC 910 Long Step 250/3onTree 1969 Chevy C10 longfleet, 350/350

09-16-2002, 06:30 PM	#4
68_GMC_910 what would Neal do? Join Date: Sep 2002 Location: Winnipeg, Manitoba, Canada Posts: 150	oh, and your truck is awesome! I really like it! __________________ 1968 GMC 910 Long Step 250/3onTree 1969 Chevy C10 longfleet, 350/350

09-16-2002, 06:40 PM	#5
Gordo Registered User Join Date: Jan 2001 Location: Killingworth, CT. USA Posts: 3,378	If it runs fine it may not be flooding over, it may be the fuel line fitting at the carb and/or the fitting that holds the fuel filter into the carb that is loose or missing/bad gasket. We need more info as to where it's leaking at the carb. __________________ 1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist.

09-16-2002, 09:11 PM	#7
68_GMC_910 what would Neal do? Join Date: Sep 2002 Location: Winnipeg, Manitoba, Canada Posts: 150	well, I got found some time to get out to the truck and take off the airbox and it looks like the gasket is shit... it's a rebuilt carb, done by a Canadian company that starts with an A... Can't remember it... I think the inlet maybe leaking too because I don't think a gasket would make the gas leak out when the engine is off... But I'm out of gas so I can't find out!!!!! argh... this is going to be a hell of a project and I'm definitely going to need every last bit of luck to do it on the small wad of cash I have... __________________ 1968 GMC 910 Long Step 250/3onTree* 1969 Chevy C10 longfleet, 350/350

09-16-2002, 11:02 PM	#8
chucks70 Registered User Join Date: Feb 2002 Location: Cadiz, OH Posts: 628	I was just at a show a couple of weekends ago and took pics of a 292 with dual carbs on a polished offenhauser manifold. No leaks there. Exhaust was split manifold duals goin back. Sounded nice for a straight six. Can't figure out how to post pics __________________ 68 1 ton dually 292, 2001 Sebring, 2004 Trailblazer, 11 Camaro Convertible.

09-17-2002, 09:55 AM	#9
Kas68c10 Registered User Join Date: Apr 2000 Location: Freeland,Michigan,USA Posts: 312	Gordo and XXL make a good point, it can leak there. Wrapping the threads with plumbers tape is a quick and easy fix, although not the best solution. Can purchase a gasket kit for these carbs for less than $20 I thinkk. If you lower the float level, the gas will never get high enough to leak out the top sel. Be careful though,cause lowering it too much will cause truck to die when you step on it or hit a tight curve or big hill. Thanks for the compliment on the truck, will be putting air in and a paint job next year I think. I have a 292 in the garage,waiting to get rebuilt, I woulkd love to put an offy intake and dual carbs on it. Although I really like the Weber progressive I have now.... I am a Canadian too, just displaced here in MI!!! From Ontario ! I think you are too far away for me to buy that engine, shipping would be prohibitive.... Let me know how you make out ! I also have a spare Rochester if you need it, it doesn't leak, float is set right, I just replaced it with the 2 barrel. Good Luck ! __________________ 1968 SWB Stepside, 250,pwr disc brake and tilt pwr steering, 5 spd tranny, HEI,Accel coil,K&N filter,Seat from a later truck with built in seatbelts, front and rear sway bars, moved gas tank to under the bed, headman hedders, new chrome bumpers,one wire alternator,Weber k550cub carburator...WORK IN PROGRESS, Freeland MI , Just bought a 72 Jimmy!!!!!!!!!!!

09-17-2002, 02:51 PM	#10
Fred T Cantankerous Geezer Join Date: Aug 2002 Location: Bel Aire, KS Posts: 6,264	Here's a better solution to the leaky inlet fitting. Get a tube of Permatex Hylomar sealer, it was designed by Rolls Royce for sealing carbs. Gasoline resistant and stays soft. Put it on your threads and gasket. Float level, these guys are right. Probably set a bit to high. And a gasket set doesn't solve all the leak problems with the old Rochester, but it helps. Last one I bought was $22 and had the wrong style accelerator pump for my B model. If you can't get a leak between the horn and bowl stopped, careful application of the Hylomar can help. It doesn't always work, though, due to warpage of the carb. __________________ Fred There is no such thing as too much cam...just not enough engine.



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