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Old 10-20-2009, 09:21 PM
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Jet PErformance Q-jet tuning

I have been working on getting my Jet Performance carb to run right. I talked to the tech and was told what jet and rod size I had and it was one off on each. I was told that base on the APT was 5 turns out and I could go 3 more out. I did a check and found that the correct position of the rods in the jets was a little over 1 1/2 turns and 2 more turns put the rods completely out of the jet. They installed a different APT screw from stock. This one uses a philips screw driver to adjust which is a good thing. The stock unit takes a special tool. They did not install a secondary lock out. I had to clear some of the bleeds that were plugged. The carb is a 17058204. I change the rods and jets to stock and the secondary rods to stock and it ran much better. I recently corrected the APT and haven't had to install the carb and check it. I am using a lot of tech tips I found on the internet most from Lars Grimsrud and I have Roe's book on Q-jets. The good thing about all of this is that I can take apart and put the carb back together in a few minutes. I have much more understanding of the Q-jet and realize it really is a simple carb once you understand how it works. It is unfortunate that Jet seems to just through standard parts at whatever carb body they find without regard to its stock configuration. I can understand the mass production aspect of this but as a high end rebuilder they should ensure that what they do will work and that the information they give from the tech guys is correct. I wonder why they don't have an online tech service.
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Old 10-21-2009, 07:45 PM
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Quote:
Originally Posted by Mertz
I did a check and found that the correct position of the rods in the jets was a little over 1 1/2 turns and 2 more turns put the rods completely out of the jet.
Q-Jet primary metering rods come in 2 lengths- it sounds to me like you have an early set of rods in a late application.

Late rods will be just over 2-3/8" (about 2.4"), or just a bit less.
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Old 10-22-2009, 01:48 PM
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I recently put in a set of jets and rods from another carb of the same year and it ran very lean. I now have a good method of setting the APT that gets me very close. I understand the different rod lengths. Unless Jet put in the pre 75 ones they should be correct.

My new set of rods and jets runs lean and cause the truck to overheat when I get on it. Works great about 45.

After a lot of research and other posts on this site, there seems to be a lot of carbs coming from rebuilders that are not clean. Mine was no exception. I can't blame Jet for this one because I bought it used. The guy I got it from might have had the problem and that is why he sold it. The lesson here it that, if you have problems out of the box, take it appart and clean it.

BTW I put eveything back the way Jet installed it except for the APT setting and am going to give it another try. If that doesn't work I am going to take it to a shop and have an infared done on it to dail it in.
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