Need some carb advice, Q-jet
Thread Starter
Pro
Joined: Feb 2003
Posts: 508
Likes: 1
From: Maplewood NJ
Need some carb advice, Q-jet
Believe it or not, I actually had my car idling nicely yesterday :eek: . Here's what I had to do . . . the regular idle control screw was pushing on the throttle a just a little bit, the idle mixture screws were turned out at least 5 full turns (that's the furthest out I've tried them), and I had to cover 75-80% of the choke blade area. If I stopped covering the choke area, the idle would dip down and just about stall. The timing is set around 10 degrees before TDC.
What could this mean? And is 5 turns out on the idle mixture screws acceptable?
Thanks,
Matt
Carb ---> :boxing <--- Me :lol:
What could this mean? And is 5 turns out on the idle mixture screws acceptable?
Thanks,
Matt
Carb ---> :boxing <--- Me :lol:
Team Owner
Joined: Sep 2003
Posts: 88,393
Likes: 2
From: eville in
Re: Need some carb advice, Q-jet (80Xflags)
sounds lean to me. covering airhorn richens it, i don't know everthing a Q's
still it training. but i'm workin' on them learning from LARS papers from
corvettefax.com and Doug Roe book , i've also picked up info from other
place's :thumbs:
still it training. but i'm workin' on them learning from LARS papers from
corvettefax.com and Doug Roe book , i've also picked up info from other
place's :thumbs:
Melting Slicks
Joined: Aug 2003
Posts: 2,135
Likes: 2
From: Dayton Oh
Re: Need some carb advice, Q-jet (80Xflags)
:iagree: with Comp. Your carb is way too lean. Starting at about 3-4 turns from bottom, keep backing out BOTH idle screws EQUALLY and 1/2 turn at at time until covering the carb does not increase your idle. At this point, don't be concerned about how high your idle is...use your idle adjustment screw to decrease it if you'd like.
If you have to go beyond 7-8 full turns, then I'd suspect that your idle circuit has some crude in it blocking the fuel flow. If so, then you'll need to dismantle it and soak in carb cleaner. Good luck. :cheers:
If you have to go beyond 7-8 full turns, then I'd suspect that your idle circuit has some crude in it blocking the fuel flow. If so, then you'll need to dismantle it and soak in carb cleaner. Good luck. :cheers:
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,392
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Need some carb advice, Q-jet (80Xflags)
80 -
A couple of comments:
First, it doesn't sound like you're running enough timing. Set up your total timing for 36 degrees and make sure your vacuum advance is hooked up corectly and working. With the total set to 36 and the vacuum hooked up, you should be running timing in the mid-20's at idle.
Next, the post-'75 Q-Jets have a nominal idle mixture screw setting of 4 turns out. 5 turns out is perfectly normal, and this can go as high as 7 to 8 turns out on your year carb. However, if it's still running lean (as indicated by a speed pick-up by holding your hand over the choke) at 7 turns out, you need to raise your power piston stop limit screw. Raise it up one full turn and you'll get a noticable change in idle mixture.
A couple of comments:
First, it doesn't sound like you're running enough timing. Set up your total timing for 36 degrees and make sure your vacuum advance is hooked up corectly and working. With the total set to 36 and the vacuum hooked up, you should be running timing in the mid-20's at idle.
Next, the post-'75 Q-Jets have a nominal idle mixture screw setting of 4 turns out. 5 turns out is perfectly normal, and this can go as high as 7 to 8 turns out on your year carb. However, if it's still running lean (as indicated by a speed pick-up by holding your hand over the choke) at 7 turns out, you need to raise your power piston stop limit screw. Raise it up one full turn and you'll get a noticable change in idle mixture.
Thread Starter
Pro
Joined: Feb 2003
Posts: 508
Likes: 1
From: Maplewood NJ
Re: Need some carb advice, Q-jet (lars)
I think I got it :party:
Here's what I did. Last night I took the carb completely apart, triple checked all the gaskets and made sure all the circuits were clear, checked the float height, and set the rod depth as per your paper, Lars.
I put the carb back on the car and got back to my situation where I could cover the choke and idle fine. Then I reconnected my vacuum advance (which was off before . . . I'm still learning here :banghead: ) and VIOLA! holding idle steady all by itself. I backed the idle screws out a bit more to 6 turns out, played with the idle speed settings. Now with all the vacuum lines attached the engine will hold 1500 RPM fast idle, 900 RPM warm in park, and 550 RPM in gear, all with about 18 inches of vacuum and an initial timing somewhere in the 20s.
Three months to figure this out :cry , boy do I feel like a :conehead .
I'm sure it could use a little more tweaking, but I think I'm back in business for now :smash: :D
Thanks guys! :cheers:
Here's what I did. Last night I took the carb completely apart, triple checked all the gaskets and made sure all the circuits were clear, checked the float height, and set the rod depth as per your paper, Lars.
I put the carb back on the car and got back to my situation where I could cover the choke and idle fine. Then I reconnected my vacuum advance (which was off before . . . I'm still learning here :banghead: ) and VIOLA! holding idle steady all by itself. I backed the idle screws out a bit more to 6 turns out, played with the idle speed settings. Now with all the vacuum lines attached the engine will hold 1500 RPM fast idle, 900 RPM warm in park, and 550 RPM in gear, all with about 18 inches of vacuum and an initial timing somewhere in the 20s.
Three months to figure this out :cry , boy do I feel like a :conehead .
I'm sure it could use a little more tweaking, but I think I'm back in business for now :smash: :D
Thanks guys! :cheers:
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,392
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Need some carb advice, Q-jet (80Xflags)
80-
I think I've posted it quite a few times here on the Forum, but my observation has always been:
90% of all carb problems are ignition problems.
I think I've posted it quite a few times here on the Forum, but my observation has always been:
90% of all carb problems are ignition problems.
