73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: kopeck on May 28, 2017, 09:13:16 pm
-
The 350 in my '79 C-10 has never idled very well. When I first got the truck 20 years ago the carb was fouled up so I had it rebuilt by the local carb guru and a mechanic friend installed it and adjusted for me. It always idled rough, kind of chuffed through the exhaust. I was told it was a sticky/burned exhaust valve, the paper test confirmed this. It never got worse, it was just there.
Today I figured what the heck, lets play with the carb. So I hooked up my vacuum gauge and went after it. It was set to two turns out from seated on each screw so I set it back to two turns and went from there. What I found was 4 3/4 turns pulled the best vacuum reading (about 18 inches). From what I read on the 'net I was suppose to go 1/8 to 1/4 turns out from there. So I set it to 5 and it runs well, better then I can ever recall. The pop is pretty much gone, the paper test still shows an occasional "suck" so there's probably still a valve issue but it's night and day better, lowed RPM response is improved as well.
My question is, does that seem like a lot of turns? It does to me BUT I've never worked on a Quadra Jet before and the stuff I found googleing is all over the place. I've worked on a lot of carbs but nothing like this thing.
I guess my other question is could they made that left hand screw any more tricky to get too?
K
-
Not necessarily on a 79 year quad if that's what us on it .
In 79 the screws were fine thread which will be 2 turns on the later models and vs 1 turn on the earlier models.
So your ok.
Main thing is how it runs.
-
Depending on application, QJ's run best anywhere between 1 1/2 to about 5 turns out from seated, but 3 - 3 1/2 turns is by far the most common. I wouldn't be alarmed if it runs well and the screws are balanced (the same number of turns).
I used the Snap-On 1/4" drive carburetor adjusting tool (https://store.snapon.com/Product-Details-Adjusting-Tool-Carburetor-Rigid-18-1-4--P631059.aspx) and sockets (https://store.snapon.com/SearchResults.aspx?q=carb%20screwdriver&IsPartsSearch=0&departmentName=Tool%20Catalog) with great success; the TM85 is most applicable to QJ. There are others that are similar.
-
Thanks guys.
I wasn't really alarmed more just confirming that something wasn't out of wack. The fine thread thing makes a lot of sense, most of the stuff I was reading had guys running around 2 1/2 to 3 1/2 turns but I'm pretty sure they were all pre-79 carbs (and mine is original).
That's an interesting tool. I was using the flex shaft Lisle tool. It worked fine, it's just getting the end of it on the screw with out getting your self caught up in fan blades or belts.
I can't believe I waited so long to at least try adjusting the carb. I guess I figured a "pro" did it so it was as good as it was going to get. I should known better. Makes me feel much better about the overall condition of my engine.
K
-
Depending on application, QJ's run best anywhere between 1 1/2 to about 5 turns out from seated, but 3 - 3 1/2 turns is by far the most common. I wouldn't be alarmed if it runs well and the screws are balanced (the same number of turns).
I used the Snap-On 1/4" drive carburetor adjusting tool (https://store.snapon.com/Product-Details-Adjusting-Tool-Carburetor-Rigid-18-1-4--P631059.aspx) and sockets (https://store.snapon.com/SearchResults.aspx?q=carb%20screwdriver&IsPartsSearch=0&departmentName=Tool%20Catalog) with great success; the TM85 is most applicable to QJ. There are others that are similar.
I have the same set. Works awesome, although I barely ever need it
-
That's because your an expert with carburetion (one adjustment is all you need)... and everything new is fuel injected. ;) lol
-
8) there was a reason I bought that tool but we know how to find the sweet spot without it ;)
-
4 turns out from seared is the recommended starting point for most qjet.
Sent from my SM-N900P using Tapatalk
-
Seated
Sent from my SM-N900P using Tapatalk