Lars, step on in
Thread Starter
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
Lars, step on in
Lars...I am the recipient of a "Dog" from another shop. '79 with Q-Jet, (17058204) bad bog only at >75% throttle. Previous shop changed carb. 2X. Feels like the secondary air valve is opening too soon, but I have adjusted the spring tension to max. I noticed the secondary lock-out dash-pot has no vacuum at idle. Souldn't this be the same vacuum source as the dist. vacuum? I pull the top plate off and the channel coming up from the dist. vacuum port has a plug in it! It renders the dash-pot useless. Any ideas? TIA
BTW, the plug looks exactly like the gasket alignment stud at the rear of the top plate, between the secondary air valves.
BTW, the plug looks exactly like the gasket alignment stud at the rear of the top plate, between the secondary air valves.
Last edited by big_G; Jun 18, 2007 at 04:49 PM.
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
The choke pulloff needs to have a manifold vacuum source pulling it tight, or you will get the bog you describe. I have seen many commercially rebuilt carbs with plugs in various orifaces - you should be able to trace the vacuum route for the choke pulloff and identify the blockage. Most plugs installed by builders are lead plugs that can be knocked out. But you do need to make that pulloff operable. Many people do not understand its function, and see that it is "preventing" the secondaries from opening. So the "performance" mod is to inactivate the pulloff, with the consequence that the choke does not work right, and the secondary airvalve flops open to produce a secondary stumble. 
Thread Starter
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
Well, it did have a lead plug in the vacuum port, I removed it. It still has another problem, same symptoms. I have no faith in this carb, I have another one coming in the A.M. I just wish I had the original one.
Thread Starter
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
Update, FYI. We installed the 3rd. rebuilt carb. this morning. Great power and gets good rubber in 2nd (auto). High 14 second ride. One problem...the rebuilder monkeys put the choke coil in backwards..(the choke closed when warmed up)... 3 friggen rebuilt carbs. and every last one of them had problems. Best advice is rebuild the one you have, if at all possible.
3 friggen rebuilt carbs. and every last one of them had problems. Best advice is rebuild the one you have, if at all possible.
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
That's absolutely correct. I have a "warning" in my services info sheet that I send out to people about "commercially rebuilt" carbs. Without a doubt, the "rebuilt" carbs (and especially Q-Jets) that you buy "rebuilt" from various sources (including name-brand sources such as Holley) are the most horrible, screwed-up carbs you can ever find. In the 700+ Q-Jets that I have rebuilt over the last 10 years, not a single commercial rebuilt carb has been right - every one has had significant problems, and some have not been repairable.
Advice to everyone: Avoid any commercially rebuilt carb. They are messed up. Seriously. If you need a used Q-Jet, find one in a junkyard or in somebody's parts stash that has not been screwed up by a commercial rebuilder. Find a carb that is covered in grease and dirt - the worst looking piece of crap you can find (except, do not go for the rusty carbs...). This is the carb that is correct and original - it is a great builder. Build it yourself, or I can help you. There are also a couple of other guys here on the Forum who know how to do these right. But the builders who send these carbs across our border to have cheap labor rebuild them are not good sources for hi perfromance parts...
Advice to everyone: Avoid any commercially rebuilt carb. They are messed up. Seriously. If you need a used Q-Jet, find one in a junkyard or in somebody's parts stash that has not been screwed up by a commercial rebuilder. Find a carb that is covered in grease and dirt - the worst looking piece of crap you can find (except, do not go for the rusty carbs...). This is the carb that is correct and original - it is a great builder. Build it yourself, or I can help you. There are also a couple of other guys here on the Forum who know how to do these right. But the builders who send these carbs across our border to have cheap labor rebuild them are not good sources for hi perfromance parts...
Race Director
Joined: Jul 2002
Posts: 13,858
Likes: 0
From: A 12/8 man in a 4/4 world
I have the original QJet.
With Lar's help and advice Ive managed to get it running good.
It took several tries but the puzzle has been fun.
Still a few tuning things I need to do but overall good performance.
With Lar's help and advice Ive managed to get it running good.
It took several tries but the puzzle has been fun.
Still a few tuning things I need to do but overall good performance.
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