hard start and running rough, help Lars!
Thread Starter
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
From: Glen Allen, VA
hard start and running rough, help Lars!
Ok, here's the scenerio. I started the car for the first time after parking it from the trip home from Carlisle last Sunday. I took FOREVER for it to start. It cranked and cranked and cranked with nothing. Finally a loud BANG out of the exhaust. The next time I turned the key it started. I backed it out of the garage, washed it, and then the same problem when I went to pull it back in. The only difference was, this time it backfired through the carb, as I saw smoke come from under the closed hood. It then started. When it's running, it definitely feels like it's running on 7 cylinders. When you quickly stab the throttle, it hesitates. If you gradually give it gas, the rpms come up smoothly. I checked the header tubes w an IR temp gun, and the outboard ones were around 300 degrees, the center ones were above the gun's range, at 500 degrees. I put my timing light on it, and it showed 15 degrees at idle w the vacumn advance disconnected. At 2500 it first showed 31 degrees, then would jump to 34 degrees, where I had set it, then back to 31. I had the clamp on the #1 plug wire up by the distributor. Does that make any difference? Also, if i restarted it immediately after shutoff it started right up every time. That's all the details I can think of. Can anyone make any suggestions?
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
I'd start pulling plug wires, but to me it sounds like it's either majorly lean or your timing is off.
Things I'd look at:
1. Wires
2. Harmonic balancer slip?
3. EGR (is the valve operating smoothly?)
4. Check accel pump squirt, if it's bad...
5. ...could be Fuel Filter, or gummed up carb
Things I'd look at:
1. Wires
2. Harmonic balancer slip?
3. EGR (is the valve operating smoothly?)
4. Check accel pump squirt, if it's bad...
5. ...could be Fuel Filter, or gummed up carb
Thread Starter
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
From: Glen Allen, VA
Wires looked good, no EGR. How would I know if the balancer slipped? I will replace the fuel filter, to hopefully rule that out. I just noticed my signature doesn't show that I'm running a Qjet carb, if that helps anyone.
Last edited by C3 4ME; Sep 2, 2012 at 04:23 PM.
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
Did you check the squirt of the accel pump? It should be a spray.
When the balancer slips, there will typically be an offset between the center hub and the outer ring.
When the balancer slips, there will typically be an offset between the center hub and the outer ring.
Last edited by Shark Racer; Sep 2, 2012 at 11:32 PM.
Thread Starter
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
From: Glen Allen, VA
Thank you Lars, I will check that. If it is in fact sheared, I'll probably send you the carb, as it's always had other minor issues, so now would be the time to get it working exactly right.
Melting Slicks
Joined: Sep 2010
Posts: 2,413
Likes: 59
From: Emerald Isle NC
Put your timing light pickup on the #1 plug wire down by the plug, not up by the distributor. The timing light will get "crosstalk" due to the close proximity of the other plug wires near the distributor, resulting in a bad timing set.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
From: Glen Allen, VA
ok, finally got another chance to look at it, this time with people much more knowledgeable than me. I forgot to mention that I drove back through a driving rain on the way home. They seem to think that water got in the gas. This time we didn't get the car started at all. They looked down into the tank and said it looks not exactly right. We did pour a capful of gas straight down the carb, and it didn't start. We verified that there is spark getting to the plugs, and also pulled a plug, and it is not gasoline fouled, nor did is smell like gas. Their suggestion was to drain the tank, blow out the fuel line, refill the tank and try again. My only concern, and theirs too, was if there is water in the gas, shouldn't it have started and run for a short period of time on the capful of gas straight down the carb?
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
ok, finally got another chance to look at it, this time with people much more knowledgeable than me. I forgot to mention that I drove back through a driving rain on the way home. They seem to think that water got in the gas. This time we didn't get the car started at all. They looked down into the tank and said it looks not exactly right. We did pour a capful of gas straight down the carb, and it didn't start. We verified that there is spark getting to the plugs, and also pulled a plug, and it is not gasoline fouled, nor did is smell like gas. Their suggestion was to drain the tank, blow out the fuel line, refill the tank and try again. My only concern, and theirs too, was if there is water in the gas, shouldn't it have started and run for a short period of time on the capful of gas straight down the carb?
Stare down the airhorn. Open the throttle via the linkage.
Does it spray a smooth stream of fluid?
If not, you'll need to take the top of the carb off and check the accelerator pump. Actually, if the pump seal is destroyed you may be check by popping the roll pin out of the accelerator pump and manually cycling the pump.
Feel free to get all of this on youtube and I'll gladly take a look at it from remote.
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
I am definitely not up to Lars' knowledge but I would remove the dist. cap and ck. for moisture. Driving rain and high humidity for a few days after will condense moisture inside the cap. I am thinking ignition not fuel. When you get both something is going to happen. Good luck with it. mike...
Last edited by mds3013; Sep 10, 2012 at 08:50 PM.
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
That takes the accel pump out and fuel is unlikely. You can drain the tank if you want but I don't think that's the issue.
What I'd do right now is look long and hard at the ignition. I know you said you have spark but is it reliable and consistent? Have the module checked out.
What I'd do right now is look long and hard at the ignition. I know you said you have spark but is it reliable and consistent? Have the module checked out.
Thread Starter
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
From: Glen Allen, VA
we had the cap off, and confirmed no moisture underneath. BTW, going back to the not starting at all, as I cranked it, it did try to start a couple of times. It wasn't as if I was cranking and absolutely nothing was happening.
Last edited by C3 4ME; Sep 10, 2012 at 09:17 PM.
Thread Starter
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
From: Glen Allen, VA
Time for another update. I stopped and talked to a friend who was a chevy dealer mechanic when these cars were new. His suggestion; a new rotor. He said that was a common problem. Well, he was dead on. With a new rotor, it started like I had just shut it off, and ran smooth. There is a kicker though, I shut it off and let it sit for a while, and then it was harder to start, and again had a hesitation when quickly stabbing the throttle. The old rotor had some rust colored discoloration underneath, and the same rust color is showing on the distributor cap, so of course, that is my next part that I will replace. I'm hoping that the combination of the 2 will put this problem to bed for good.
Thread Starter
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
From: Glen Allen, VA
Ok, wanted to put this one to bed for good. Turned out to be a slam worn out distributor. Just got the new one installed, and it's running great! Thanks to all who helped in the process. That's what makes this forum the best one on the net!