Update on the GM Performance Crate Engine "Drama"
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
Yeah, I don't either. I think it's BS but I hope I'm wrong for your sake. A bad valve seal usually won't make a motor smoke when you tromp on the gas, only when coasting down a hill or at initial start up. Like Sperkins said, why is it smoking on both sides then? I sure hope it's simple....both sides indicate something common like transmission fluid, intake etc. Man I would be pi$$ed!
Safety Car
Joined: Aug 2000
Posts: 3,943
Likes: 44
From: Florham Park NJ Port Credit Ontario
I think the most alarming thing is that the dealership actually thought that they could tune it. The dealership people that I have ever deal with couldnt find their A$$ with both hands and a flashlight.
As posted before, if a seal was "rolled" this may explain smoke, but what about the crappy launch? You said it runs like crapola.
As posted before, if a seal was "rolled" this may explain smoke, but what about the crappy launch? You said it runs like crapola.
Advanced
Joined: May 2007
Posts: 79
Likes: 0
From: Somerset New Jersey
i can see it being valve seals. engine not running correct could easily be a tuning issue... I would lean it out to get rid of the bogging and keep a close eye on the Temperture.
Do you have a true dual exhaust? or a 2 into 1 back to 2 exhaust? could be y u see smoke from both sides
good luck
Do you have a true dual exhaust? or a 2 into 1 back to 2 exhaust? could be y u see smoke from both sides
good luck
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
i can see it being valve seals. engine not running correct could easily be a tuning issue... I would lean it out to get rid of the bogging and keep a close eye on the Temperture.
Do you have a true dual exhaust? or a 2 into 1 back to 2 exhaust? could be y u see smoke from both sides
good luck
Do you have a true dual exhaust? or a 2 into 1 back to 2 exhaust? could be y u see smoke from both sides
good luck
Le Mans Master
Joined: Mar 2004
Posts: 7,502
Likes: 1,510
From: Little Rock AR
I have true dual exhaust. I'm thinking maybe the "bogg down" may be the carb's accelerator pump either out of adjustment (gapped to much) or the pump shaft may be bent (this according to Holley). I'm going to have the dealership check these out tomorrow. Right now the idle mixture screws are turned out 1 1/4 turns out...and I've got about 13" of vacuum.
This adjustment spec is tricky because they tell you to check for additional available travel when you set it. At wide open throttle you want to be able to move the accelerator pump lever a few thousandths of an inch farther just to be sure the pump never bottoms out at WOT under normal driving. No slack is allowed though.
-Mark.
Drifting
Joined: Oct 2004
Posts: 1,496
Likes: 1
From: Lafayette Louisiana
Stuart, if it continues to hesitate on part throttle, after they finish with the valve seals, have them set the carb up according to Lar's paper and set the idle mixture with a vacuum guage. Or do it yourself. Also make sure the timing is set up properly. I think you should have more than 13" of vacuum. I have 14 at idle and I have more cam, initial timing than you should.
Limping across the line
Joined: Oct 2002
Posts: 5,299
Likes: 109
From: Peoria Az
Bog when you stomp on it then it picks back up at 2500 is more than likely Ignition related.
Think about it when you stomp the throttle manifold Vacuum goes to 0
you just lost all your advance. as engine comes back regaining vacuum it will pull more advance in. make sure vac adv line is hooked up to a ported manifold source(vac applied only when off idle). Disconnect vac adv and plug. Now set carb with a vac guage. reset timing to at least 8* initial advance. let us know how things progress
Think about it when you stomp the throttle manifold Vacuum goes to 0
you just lost all your advance. as engine comes back regaining vacuum it will pull more advance in. make sure vac adv line is hooked up to a ported manifold source(vac applied only when off idle). Disconnect vac adv and plug. Now set carb with a vac guage. reset timing to at least 8* initial advance. let us know how things progress
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
Stuart, if it continues to hesitate on part throttle, after they finish with the valve seals, have them set the carb up according to Lar's paper and set the idle mixture with a vacuum guage. Or do it yourself. Also make sure the timing is set up properly. I think you should have more than 13" of vacuum. I have 14 at idle and I have more cam, initial timing than you should.
THANKS! Stuart
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Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
Bog when you stomp on it then it picks back up at 2500 is more than likely Ignition related.
Think about it when you stomp the throttle manifold Vacuum goes to 0
you just lost all your advance. as engine comes back regaining vacuum it will pull more advance in. make sure vac adv line is hooked up to a ported manifold source(vac applied only when off idle). Disconnect vac adv and plug. Now set carb with a vac guage. reset timing to at least 8* initial advance. let us know how things progress
Think about it when you stomp the throttle manifold Vacuum goes to 0
you just lost all your advance. as engine comes back regaining vacuum it will pull more advance in. make sure vac adv line is hooked up to a ported manifold source(vac applied only when off idle). Disconnect vac adv and plug. Now set carb with a vac guage. reset timing to at least 8* initial advance. let us know how things progress
Will check that also!
Thanks!
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
Bog when you stomp on it then it picks back up at 2500 is more than likely Ignition related.
Think about it when you stomp the throttle manifold Vacuum goes to 0
you just lost all your advance. as engine comes back regaining vacuum it will pull more advance in. make sure vac adv line is hooked up to a ported manifold source(vac applied only when off idle). Disconnect vac adv and plug. Now set carb with a vac guage. reset timing to at least 8* initial advance. let us know how things progress
Think about it when you stomp the throttle manifold Vacuum goes to 0
you just lost all your advance. as engine comes back regaining vacuum it will pull more advance in. make sure vac adv line is hooked up to a ported manifold source(vac applied only when off idle). Disconnect vac adv and plug. Now set carb with a vac guage. reset timing to at least 8* initial advance. let us know how things progress
. I think anytime the throttle is fully open, the vacuum is near zero regardless of engine rpm's. The vacuum advance is not in the picture until the throttle is less than fully open. I also believe the better source is manifold vacuum, not ported.
Limping across the line
Joined: Oct 2002
Posts: 5,299
Likes: 109
From: Peoria Az
Big G and S489 you are correct. There are soem heated arguments over at Chevelles.com about ported and manifold vacuum.
Big G where did I lose you? Maybe I can 'splain it better.
These are all hypothetical numbers
Say at part throttle cruise(30mph /2000rpm)vacuum would be 15"hg.Total advance(30*) all in at 2000
Dizzy has initial adv of 10*, mech adv of 10*, vac adv of 10*,
Now say you matt the throttle from that 30mph cruise,throttle blades go wide open thus dropping manifold vacuum to 0. What happens to the vac adv?? you lose it. you just lost 10* of your total advace. until engine recovers vacuum you only get 20* of total advance. As vacuum is regained timing advance would be added.
Hopefully that clears it up a little
Big G where did I lose you? Maybe I can 'splain it better.
These are all hypothetical numbers
Say at part throttle cruise(30mph /2000rpm)vacuum would be 15"hg.Total advance(30*) all in at 2000
Dizzy has initial adv of 10*, mech adv of 10*, vac adv of 10*,
Now say you matt the throttle from that 30mph cruise,throttle blades go wide open thus dropping manifold vacuum to 0. What happens to the vac adv?? you lose it. you just lost 10* of your total advace. until engine recovers vacuum you only get 20* of total advance. As vacuum is regained timing advance would be added.
Hopefully that clears it up a little
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
****UPDATE*****UPDATE******
The fuel pump was WAY to powerful!! Changed to a smaller fuel pump and WHAM!!! she's running like a "raped-ape"!!! No more bogging down...not hestiation...just smooth, raw power!
Thanks for all the input and thoughts!!!
Later Guys!
The fuel pump was WAY to powerful!! Changed to a smaller fuel pump and WHAM!!! she's running like a "raped-ape"!!!
No more bogging down...not hestiation...just smooth, raw power!Thanks for all the input and thoughts!!!
Later Guys!
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
............but what happened to the smoke coming from both sides of a true dual exhaust setup that started this problem? They replaced one bad valve seal and it's gone??
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
I see. Huh, brand new GM engine with 7 bad valve seals.......wonderful. Chinese imports assembled in Mexico I guess.
Glad you were able to get things fixed pretty easily. Could have been much worse.
Bill
Glad you were able to get things fixed pretty easily. Could have been much worse.
Bill
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
Bog when you stomp on it then it picks back up at 2500 is more than likely Ignition related.
Think about it when you stomp the throttle manifold Vacuum goes to 0
you just lost all your advance. as engine comes back regaining vacuum it will pull more advance in. make sure vac adv line is hooked up to a ported manifold source(vac applied only when off idle). Disconnect vac adv and plug. Now set carb with a vac guage. reset timing to at least 8* initial advance. let us know how things progress
Think about it when you stomp the throttle manifold Vacuum goes to 0
you just lost all your advance. as engine comes back regaining vacuum it will pull more advance in. make sure vac adv line is hooked up to a ported manifold source(vac applied only when off idle). Disconnect vac adv and plug. Now set carb with a vac guage. reset timing to at least 8* initial advance. let us know how things progress
The only differance between manifold vacuum and ported vacuum is timing. You seam to be implying that ported vacuum is better than manifold vacuum from a performance standpoint. This is not correct. Ported vacuum was origionaly developed as a way to lower emissions. Most engines will run better with the vacuum advance connected to manifold vacuum.
BigBlockk
Later.....
Melting Slicks
Joined: Jan 2006
Posts: 3,028
Likes: 2
From: North NJ
Enjoy
Burning Brakes
Joined: Jul 2006
Posts: 1,047
Likes: 12
From: SoCal
Although it looks like you've solved the bogging problem, you should read this for more info from Lars on the Holley SA carbs: Street Avenger Stumble Issue Solutions