Curious 1979 Q-jet Problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

cowboy5683 · 03-25-2010, 11:59 PM

I have a 1979 qjet that has been rebuilt ( I did it)..It runs perfect. No leaks stalls or stutters..Here is the weird part..When sitting for awhile (mebbe a week at most) I can look under the hood and cleaner and all the vacuum caps I have used are cracking..I have replaced them twice and yet they still crack within a week..I am thinking mebbe my float level is a tad too high?!?..Mebbe some of you know for sure..I have dealt with and rebuilt qjets for years and never seen this before..what do ya'll think?..I will prolly reset level lower anyways..But just thought i would pick ya'lls brains first.

Restrorob · 03-26-2010, 07:07 AM

Fuel will not enter vacuum ports on a carb so no need in re-adjusting float level, The problem is the cheap rubber the caps are made of. I bought caps from Auto Zone and they cracked with-in a week as well, Since my engine was coming out for the full truck restore I haven't tried to find any different ones yet.

raws67 · 03-26-2010, 10:10 AM

I have had this same problem. It seems that all those vacum caps are made of such crappy rubber they just rot away when exposed to the engine heat. The only thing I have used that holds up is putting a screw in a short piece of vacum hose.

cowboy5683 · 03-26-2010, 03:08 PM

Wow..Seriously?..Thats exactly where I picked up my caps from..lol..Well I guess I am goin old school with sum hose..Unless anyone knows of someone selling some higher quality caps..thanx for the replies!

C10Silverado79 · 03-26-2010, 03:43 PM

what about taking some vacuum hose and filling one end with some epoxy? I have not done this but it seems likely to work.

cowboy5683 · 03-26-2010, 04:58 PM

I did some research and found all kinds of silicone ones online that are supposed to be able to handle the heat etc better..I am gonna go old school for a day or two til I get the silicone ones in...I have used auto zone caps in past and never seen this before..Sure glad I asked..Seems to me it is a common problem..Epoxy in the end seems like it wouldn't have any flexibility to it like the hose would..mebbe filling the hose end with silicone and letting it dry first?

Restrorob · 03-26-2010, 07:04 PM

If you do run across some caps that don't crack right away please let us know where you found them.

cowboy5683 · 03-26-2010, 08:35 PM

Absolutely..The ones I have found are at jegs and summit etc..and also some in the mcmaster-carr catalog and such..I found an interesting link online about the types of caps powder coaters and such use..supposed to be real high heat resistant etc..I am gonna try those first..Then i will let ya'll know.

Damien · 03-27-2010, 02:08 AM

I have the Dorman caps on my s10 and they are all cracked. The best ones I have seen are the Maroso caps. I'm not sure what they are made of, but they do not crack.

03-25-2010, 11:59 PM	#1
cowboy5683 Registered User Join Date: Jun 2009 Location: San Bernardino CA Posts: 94	Curious 1979 Q-jet Problem I have a 1979 qjet that has been rebuilt ( I did it)..It runs perfect. No leaks stalls or stutters..Here is the weird part..When sitting for awhile (mebbe a week at most) I can look under the hood and cleaner and all the vacuum caps I have used are cracking..I have replaced them twice and yet they still crack within a week..I am thinking mebbe my float level is a tad too high?!?..Mebbe some of you know for sure..I have dealt with and rebuilt qjets for years and never seen this before..what do ya'll think?..I will prolly reset level lower anyways..But just thought i would pick ya'lls brains first.

03-26-2010, 07:07 AM	#2
Restrorob The One And Only !!! Join Date: Jan 2007 Location: Hole in the woods Florida Posts: 4,567	Re: Curious 1979 Q-jet Problem Fuel will not enter vacuum ports on a carb so no need in re-adjusting float level, The problem is the cheap rubber the caps are made of. I bought caps from Auto Zone and they cracked with-in a week as well, Since my engine was coming out for the full truck restore I haven't tried to find any different ones yet. __________________ 93 Jeep XJ 88 Buick La Sabra Toys; 88 TA-GTA in the works.... 97 GMC Ext. Cab 502 Crate 5 Spd......Sucks Gas But Haulz Azz ! The primary function of an Engineer is to make it difficult for the Fabricator and impossible for the Mechanic. *"Why go out preserved when you can go out beat up, worn out, sliding in sideways screaming, Holy Sh!t What A Ride" !!!* Last edited by Restrorob; 03-26-2010 at 07:10 AM.

03-26-2010, 10:10 AM	#3
raws67 Registered User Join Date: Jun 2007 Location: lemoore ca Posts: 126	Re: Curious 1979 Q-jet Problem I have had this same problem. It seems that all those vacum caps are made of such crappy rubber they just rot away when exposed to the engine heat. The only thing I have used that holds up is putting a screw in a short piece of vacum hose.

03-26-2010, 03:08 PM	#4
cowboy5683 Registered User Join Date: Jun 2009 Location: San Bernardino CA Posts: 94	Re: Curious 1979 Q-jet Problem Wow..Seriously?..Thats exactly where I picked up my caps from..lol..Well I guess I am goin old school with sum hose..Unless anyone knows of someone selling some higher quality caps..thanx for the replies!

03-26-2010, 03:43 PM	#5
C10Silverado79 Registered User Join Date: Feb 2010 Location: York, PA Posts: 180	Re: Curious 1979 Q-jet Problem what about taking some vacuum hose and filling one end with some epoxy? I have not done this but it seems likely to work. __________________ 1979 C10 Silverado 1998 Camry 5spd 2005 Harley ElectraGlide

03-26-2010, 04:58 PM	#6
cowboy5683 Registered User Join Date: Jun 2009 Location: San Bernardino CA Posts: 94	Re: Curious 1979 Q-jet Problem I did some research and found all kinds of silicone ones online that are supposed to be able to handle the heat etc better..I am gonna go old school for a day or two til I get the silicone ones in...I have used auto zone caps in past and never seen this before..Sure glad I asked..Seems to me it is a common problem..Epoxy in the end seems like it wouldn't have any flexibility to it like the hose would..mebbe filling the hose end with silicone and letting it dry first?

03-26-2010, 07:04 PM	#7
Restrorob The One And Only !!! Join Date: Jan 2007 Location: Hole in the woods Florida Posts: 4,567	Re: Curious 1979 Q-jet Problem If you do run across some caps that don't crack right away please let us know where you found them. __________________ 93 Jeep XJ 88 Buick La Sabra Toys; 88 TA-GTA in the works.... 97 GMC Ext. Cab 502 Crate 5 Spd......Sucks Gas But Haulz Azz ! The primary function of an Engineer is to make it difficult for the Fabricator and impossible for the Mechanic. *"Why go out preserved when you can go out beat up, worn out, sliding in sideways screaming, Holy Sh!t What A Ride" !!!*

03-26-2010, 08:35 PM	#8
cowboy5683 Registered User Join Date: Jun 2009 Location: San Bernardino CA Posts: 94	Re: Curious 1979 Q-jet Problem Absolutely..The ones I have found are at jegs and summit etc..and also some in the mcmaster-carr catalog and such..I found an interesting link online about the types of caps powder coaters and such use..supposed to be real high heat resistant etc..I am gonna try those first..Then i will let ya'll know.

03-27-2010, 02:08 AM	#9
Damien Registered User Join Date: Mar 2007 Location: Farmington, MN Posts: 928	Re: Curious 1979 Q-jet Problem I have the Dorman caps on my s10 and they are all cracked. The best ones I have seen are the Maroso caps. I'm not sure what they are made of, but they do not crack. __________________ I can still count my vehicles on two... wait three hands.



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