Alright, now it doesn't run at all
09-20-2008, 10:58 PM
#1
Burning Brakes
Thread Starter
Alright, now it doesn't run at all
Here's the last thread, for those who missed it:
http://forums.corvetteforum.com/show...805&highlight=
Now it's not a "chuffing" sound. It makes no sound, cause it doesn't run. I'll start from the beginning on something. My BG carb has been driving me nuts because the tune seems to "wander". I'll dial the idle in, get her running good, park her for a week or three, and when I go to work on her again she won't idle or run right at all.
I've been blaming the carb, but I haven't been able to figure out what exactly has been going on. Today it got worse. I tuned the carb in a couple days ago, as per my post. Left the car overnight, and the next night it ran worse. Still ran, idled, etc, but definitely rougher. Today, won't stay running AT ALL. Fires immediately, revs once, and then dies out.
Fuel pressure is a rock-solid 6psi the whole time. I figured out after a few experiments that the car is running almost entirely on the accel-pump. So I got my Dad to help out, and we hooked a vacuum gauge to it. Here's where it gets annoying. With the choke on full (100% closed) the engine will start and run fine. The vac gauge is only reading 14 in Hg however. A bit low. Open the choke plate, however, and the vac drops to 0 and the engine dies immediately. Took the carb off, replaced carb gasket, put it back together. Plugged all the vac lines to eliminate a problem with the brake booster or something, still the same readings.
So, I assume this is a massive vacuum leak and it's most likely an intake gasket. Anyone else care to comment? The only way the engine should produce no vacuum at idle would be a massive vac leak, and it's not the carb gasket or any of the vac accessories. I've never lost an intake gasket seal, so I'm not sure if this is teh typical symptom. It could explain the wandering tune if I've had an intermittent vac leak in an intake gasket.
http://forums.corvetteforum.com/show...805&highlight=
Now it's not a "chuffing" sound. It makes no sound, cause it doesn't run. I'll start from the beginning on something. My BG carb has been driving me nuts because the tune seems to "wander". I'll dial the idle in, get her running good, park her for a week or three, and when I go to work on her again she won't idle or run right at all.
I've been blaming the carb, but I haven't been able to figure out what exactly has been going on. Today it got worse. I tuned the carb in a couple days ago, as per my post. Left the car overnight, and the next night it ran worse. Still ran, idled, etc, but definitely rougher. Today, won't stay running AT ALL. Fires immediately, revs once, and then dies out.
Fuel pressure is a rock-solid 6psi the whole time. I figured out after a few experiments that the car is running almost entirely on the accel-pump. So I got my Dad to help out, and we hooked a vacuum gauge to it. Here's where it gets annoying. With the choke on full (100% closed) the engine will start and run fine. The vac gauge is only reading 14 in Hg however. A bit low. Open the choke plate, however, and the vac drops to 0 and the engine dies immediately. Took the carb off, replaced carb gasket, put it back together. Plugged all the vac lines to eliminate a problem with the brake booster or something, still the same readings.
So, I assume this is a massive vacuum leak and it's most likely an intake gasket. Anyone else care to comment? The only way the engine should produce no vacuum at idle would be a massive vac leak, and it's not the carb gasket or any of the vac accessories. I've never lost an intake gasket seal, so I'm not sure if this is teh typical symptom. It could explain the wandering tune if I've had an intermittent vac leak in an intake gasket.
Last edited by JLeatherman; 09-21-2008 at 07:39 AM.
09-21-2008, 07:42 AM
#3
Burning Brakes
Thread Starter
Gee, thanks, I'm sure FI would run great at 0 vacuum. That'd solve all my problems, huh?
Anyone actually care to comment on whether an intake gasket leak can cause me to actually drop all my vacuum? Is it possible to test without yanking the intake again?
Anyone actually care to comment on whether an intake gasket leak can cause me to actually drop all my vacuum? Is it possible to test without yanking the intake again?
09-21-2008, 08:15 AM
#4
Instructor
Member Since: Oct 2006
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09-21-2008, 09:45 AM
#5
Le Mans Master
Do you smoke? If not, maybe a friend? Sounds goofy huh? Get a smoker to light up a cigar and blow the smoke into a manifold vacuum line, the smoke will eventually find it's way out of the leak. Don't forget to remove a valve cover breather so if it's internal the smoke will still be seen. Cover the carb so it doesn't come right back out through there. This just a poor man's smoke machine some mechanics use and it does work.
09-21-2008, 10:26 AM
#6
Melting Slicks
Do you smoke? If not, maybe a friend? Sounds goofy huh? Get a smoker to light up a cigar and blow the smoke into a manifold vacuum line, the smoke will eventually find it's way out of the leak. Don't forget to remove a valve cover breather so if it's internal the smoke will still be seen. Cover the carb so it doesn't come right back out through there. This just a poor man's smoke machine some mechanics use and it does work.
09-22-2008, 06:04 AM
#7
My apology for the earlier post, I'll try to be more constructive this time. You may have a vacuum leak, but as you stated such a massive one does seem unusual. Based on your comments concerning the choke and accelerator pump, I'm more inclined to believe the idle circuit may be restricted or plugged in your carb.
You can try removing both idle mixture screws, making sure to retain any gasket or o-ring that may present then give each hole a blast of compressed air with a blow gun. Reinstall the mixture screws and adjust about one and one half turns out on each side as a starting point and then see if it will start and idle.
This will often clear the idle circuit short term but is usually an indication the carb requires dis-assembly and cleaning. Internal debris might also explain your difficulty maintaining adjustment, hope that helps, good luck.
You can try removing both idle mixture screws, making sure to retain any gasket or o-ring that may present then give each hole a blast of compressed air with a blow gun. Reinstall the mixture screws and adjust about one and one half turns out on each side as a starting point and then see if it will start and idle.
This will often clear the idle circuit short term but is usually an indication the carb requires dis-assembly and cleaning. Internal debris might also explain your difficulty maintaining adjustment, hope that helps, good luck.
09-22-2008, 07:13 AM
#8
Burning Brakes
Thread Starter
Thanks toptech. I am always a little suspect of BG carbs because they have serious quality-control issues regarding machining debris. Since so much of them is CNC'd there are frequently reporst of metal shavings found in the passages of new BG carbs. This particular one has been remanufactured once already, but that doesn't mean they've got it right yet. I'm gonna try and switch carbs later as a last check.
I retorqued the intake manifold bolts, several were about 5 pounds loose, and replaced the carb gasket, but I haven't had time to leak-test it or re-start it again. We loaded it dead yesterday and trailered it to the exhaust shop since I had an appointment and didn't want to get put back in line on the waiting list. Once I get it back with the new exhaust I'll start from the top-down on this problem.
I retorqued the intake manifold bolts, several were about 5 pounds loose, and replaced the carb gasket, but I haven't had time to leak-test it or re-start it again. We loaded it dead yesterday and trailered it to the exhaust shop since I had an appointment and didn't want to get put back in line on the waiting list. Once I get it back with the new exhaust I'll start from the top-down on this problem.
09-22-2008, 10:05 AM
#9
Le Mans Master
Don't even get me started on BG's quality. Call BG and ask for Travis, ask him about some big bastard that was going to seriously alter his looks in St. Louis at a show, all because of BG's customer care.
09-22-2008, 10:35 AM
#10
Le Mans Master
Maybe this site will help
http://www.secondchancegarage.com/public/186.cfm
http://www.secondchancegarage.com/public/186.cfm
Last edited by rick lambert; 09-22-2008 at 10:38 AM.
09-24-2008, 07:23 AM
#11
Burning Brakes
Thread Starter
Ok, I've made some progress. I picked up my car from the exhaust shop yesterday. They put on an LT1 system and amted it to my longtube headers. It's actually a little too quiet for my taste now, but that's a subject for another post. Got home and got her started. The retorqued intake manifold and carb gasket helped as I could now get her to idle, but it was pretty rough and the power seemed way down. On a whim I reached over and twisted on the distributor and not only did it move, but the idle picked up to about 2200 and smoothed out. Bizarre wandering tune solved!
Seems my distributor slightly loosened up, and as I was tuning the car it was creeping more and more retarded. So, I'd get the car warmed up and tuned, and the dizzy would retard the timing slightly. Next time I'd go try to start it cold, the tune would be off. Get it tuned in, but the timing would be changing again. I guess the last time the timing changed enough to where it wouldn't run at all. Haven't gotten around to really tuning it back in fully, but it does now idle at a nice smooth 900 again. we'll see what happens next time I start it up.
Seems my distributor slightly loosened up, and as I was tuning the car it was creeping more and more retarded. So, I'd get the car warmed up and tuned, and the dizzy would retard the timing slightly. Next time I'd go try to start it cold, the tune would be off. Get it tuned in, but the timing would be changing again. I guess the last time the timing changed enough to where it wouldn't run at all. Haven't gotten around to really tuning it back in fully, but it does now idle at a nice smooth 900 again. we'll see what happens next time I start it up.
09-25-2008, 04:55 AM
#12
Ok, I've made some progress. I picked up my car from the exhaust shop yesterday. They put on an LT1 system and amted it to my longtube headers. It's actually a little too quiet for my taste now, but that's a subject for another post. Got home and got her started. The retorqued intake manifold and carb gasket helped as I could now get her to idle, but it was pretty rough and the power seemed way down. On a whim I reached over and twisted on the distributor and not only did it move, but the idle picked up to about 2200 and smoothed out. Bizarre wandering tune solved!
Seems my distributor slightly loosened up, and as I was tuning the car it was creeping more and more retarded. So, I'd get the car warmed up and tuned, and the dizzy would retard the timing slightly. Next time I'd go try to start it cold, the tune would be off. Get it tuned in, but the timing would be changing again. I guess the last time the timing changed enough to where it wouldn't run at all. Haven't gotten around to really tuning it back in fully, but it does now idle at a nice smooth 900 again. we'll see what happens next time I start it up.
Seems my distributor slightly loosened up, and as I was tuning the car it was creeping more and more retarded. So, I'd get the car warmed up and tuned, and the dizzy would retard the timing slightly. Next time I'd go try to start it cold, the tune would be off. Get it tuned in, but the timing would be changing again. I guess the last time the timing changed enough to where it wouldn't run at all. Haven't gotten around to really tuning it back in fully, but it does now idle at a nice smooth 900 again. we'll see what happens next time I start it up.
Thanks too for posting the solution, seems many forget that courtesy once the car is repaired!