Q-Jet Lean?
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,583
Likes: 5
From: Richardson Tx.
Q-Jet Lean?
I read though Lars' Q-Jet tuning article because my car bogs when I floor it - then it will take off. Or if I grab the throttle and quickly open it up with my hand it will bog. If I slow down the throttle opening a little it will raise RPM smoothly - no bog.
So tried Lars' test whereby you disconnect the accelerator pump lever and then rev the throttle by hand. When I do this my stumble becomes much worse - which supposedly means a Lean condition - however, when I cup my hand over the plates to cut off the air supply, the engine does not rev up any further.
It doesn't backfire on decel. as well.
Does this sound like a lean issue?
So tried Lars' test whereby you disconnect the accelerator pump lever and then rev the throttle by hand. When I do this my stumble becomes much worse - which supposedly means a Lean condition - however, when I cup my hand over the plates to cut off the air supply, the engine does not rev up any further.
It doesn't backfire on decel. as well.
Does this sound like a lean issue?
Drifting
Joined: Mar 2011
Posts: 1,886
Likes: 9
Sounds to me like the primary jet/rod combination is lean. And your idle circuit is fine.
Are there any modifications to the engine or exhaust? I just changed over to 2 1/2" pipes with Magnaflow mufflers and had to richen the primary combo quite a bit to make it run right..
Are there any modifications to the engine or exhaust? I just changed over to 2 1/2" pipes with Magnaflow mufflers and had to richen the primary combo quite a bit to make it run right..
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
That's the first thing to check. With engine OFF, remove air cleaner, open choke, look down into the primary venturi and quickly give the throttle linkage a WOT twist. If you don't see a strong stream of fuel from the accelerator pump outlets, or if it is weak or short, that's likely your problem. If it has been more than a couple of years since the carb was rebuilt...and you buy gas with ethanol in it, the accelerator pump piston seal may be wasted.
If you do replace that seal, get an Echlin accel pump rebuild kit from NAPA. I believe that their seals are unaffected by the ethanol.
Racer
Joined: Feb 2007
Posts: 271
Likes: 25
From: Buena Vista Colorado
Echlin/NAPA Q-Jet Accelerator Pumps: Horrible, Dangerous Product Quality
Accelerator pumps sold by Cliff Ruggles have been tested to be compatible with ethanol "enhanced" fuels. You can find them here:
http://www.cliffshighperformance.com/acc-pump.html
Safety Car
Joined: Oct 2005
Posts: 3,570
Likes: 1
From: Algonac Michigan
I disagree. Read this June 2010 post by Lars regarding problems with Echlin accelerator pumps:
Echlin/NAPA Q-Jet Accelerator Pumps: Horrible, Dangerous Product Quality
Accelerator pumps sold by Cliff Ruggles have been tested to be compatible with ethanol "enhanced" fuels. You can find them here:
http://www.cliffshighperformance.com/acc-pump.html
Echlin/NAPA Q-Jet Accelerator Pumps: Horrible, Dangerous Product Quality
Accelerator pumps sold by Cliff Ruggles have been tested to be compatible with ethanol "enhanced" fuels. You can find them here:
http://www.cliffshighperformance.com/acc-pump.html
Thank You 78IndyPace for the link to Lars thread on accel. pumps.
What a great amount of info. is put forth when Lars,Cliff and OlesCarbs. gets together!
