lacking power at WOT
Thread Starter
Instructor
Joined: Jan 2005
Posts: 146
Likes: 1
From: Roanoke Rapids NC
lacking power at WOT
howdy all,
when i'm driving my 74 vette i notice that half/ three quarter throttle is not bad but it seems like WOT is rather weak in comparison. does this sound like a timing issue or an air/fuel ratio problem? a little about my engine (all done by the previous owner) it has an old accel distributor with vacuum advance and a pertronix points eliminator kit, a holley contender aluminum intake, a freshly rebuilt edelbrock q-jet, K&N air filter, long tube headers, and supposedly a slighty hotter cam, though i don't know what kind. the rest is stock. if not a timing or air/fuel problem, could it be worn or mismatched engine parts like the cam or something? sorry to sound so naive, i can do some engine work but i don't have the experience to fine tune an engine. Thanks a lot guys!
when i'm driving my 74 vette i notice that half/ three quarter throttle is not bad but it seems like WOT is rather weak in comparison. does this sound like a timing issue or an air/fuel ratio problem? a little about my engine (all done by the previous owner) it has an old accel distributor with vacuum advance and a pertronix points eliminator kit, a holley contender aluminum intake, a freshly rebuilt edelbrock q-jet, K&N air filter, long tube headers, and supposedly a slighty hotter cam, though i don't know what kind. the rest is stock. if not a timing or air/fuel problem, could it be worn or mismatched engine parts like the cam or something? sorry to sound so naive, i can do some engine work but i don't have the experience to fine tune an engine. Thanks a lot guys!
Instructor
Joined: Jul 2006
Posts: 208
Likes: 0
From: Hamden CT
St. Jude Donor '12
I had the same problem with mine. Turned out to be the timing. The vacuum advance was frozen in the distrib. Check this and make sure your timing is fully advanced to 36 degrees by 3000 rpm.
Also, have you checked the float levels in the carb?
Also, have you checked the float levels in the carb?
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
If the carburetor has the stock combo in it that is a lot of the problem. The Edelbrock 'Jets were VERY lean in every system from the factory. If I remember correctly they had 69 main jets from the frctory. You may want to bump this up to a 73 or 74 and get some main rods to keep the cruise clean. You'll want to get some richer secondary rods also.
Take a look at the power tips on the primary rods. If they are .036" (truck rods) you could CAREFULLY reduce them to the .026" (regular performance rods).
BigBlockk
Later.....
Take a look at the power tips on the primary rods. If they are .036" (truck rods) you could CAREFULLY reduce them to the .026" (regular performance rods).
BigBlockk
Later.....
Thread Starter
Instructor
Joined: Jan 2005
Posts: 146
Likes: 1
From: Roanoke Rapids NC
i checked the throttle linkage by having someone hold down the pedal, i checked to see if the lever would come back anymore and it wouldn't. i just discovered that 2 vacuum ports on the carb were open so i ran out to get some caps for them, i will let you know it that helps. thanks for the info so far!
Drifting
Joined: Jun 2005
Posts: 1,950
Likes: 498
From: Chino Hills CA
Open vacuum ports would mess up your idle a lot more than wot. You should verify that the secondaries are opening. On q-jets it's hard to tell when the secondaries open, it's fairly seamless, unlike an AFB for example. I would fix the linkage so that the secondaries cannot open and then drive the car. If it behaves the same, then your secondaries are not opening. Then check the vacuum break, and then possibly the secondary air flap spring tension. Check some of Lars's posts, his papers are the best.
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