427/435hp with Ti ignition issues
Thread Starter
Instructor
Joined: Jul 2004
Posts: 232
Likes: 2
From: Langley B.C Canada
427/435hp with Ti ignition issues
Hi i have issues with my 69 vette , which is a stock tri power setup. This has been an ongoing issue for many years. It seems when the car is cold it will start up and run fine for about 1/2 an hour, then once the engine gets hot, or a certain temperature, it seems the car starts to want to stall when breaking for a red light, as well as runs rougher. I have to give the engine a bit of gas or feather the throttle tell I get going again. Once I load it up or accelerate or even tromp on it, it will accelerate great and tons of power. I can feel the front and rear carbs open up, and all is good. Then once i start to brake hard or even lightly she will idle very low and almost stall.
Now here are the things I have already checked. Disconnected main vacuum lines, and even the power booster as I thought the vacuum was the issue, but no change. All carbs rebuilt over and over again. Swapped out distributor to another TI distributor I had laying around. Checked spark Transistor ignition box, and its wiring, still to no avail. Any suggestions??? I haven't changed the coil, still the original coil, but it seems fine. I haven't changed the fuel pump yet, but its obviously working. Any suggestions would be great.
Now here are the things I have already checked. Disconnected main vacuum lines, and even the power booster as I thought the vacuum was the issue, but no change. All carbs rebuilt over and over again. Swapped out distributor to another TI distributor I had laying around. Checked spark Transistor ignition box, and its wiring, still to no avail. Any suggestions??? I haven't changed the coil, still the original coil, but it seems fine. I haven't changed the fuel pump yet, but its obviously working. Any suggestions would be great.
Melting Slicks
Joined: Jan 2000
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From: home
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Sounds more like a fuel management and/or engine tuning issue to me. Certainly, it could be a heat sensitivity of the TI electronics. 40 year old capacitors don't normally react the same a new ones. But, you would have to swap out your TI unit with a known good one to validate that possibility. It might be easier finding a "good" carb to swap over to see how the engine then reacts under the same conditions.
Last edited by 7T1vette; Jun 25, 2019 at 12:29 AM.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
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From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
I agree with 7T1-- fuel management. It sounds like the floats are not adjusted and the slight pitch change under braking is either uncovering the metering block jets or allowing fuel to spill over. Ignition is usually one of those things that will show a failure under load or not work at all.
Race Director
Joined: May 2006
Posts: 18,742
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in addition to checking float levels and making sure the idle mixture screws on center carb are properly adjusted when fully warmed up, trying spraying some carb cleaner around base of carbs and intake to head area to check for a vacuum leak that only occurs when hot.
Thread Starter
Instructor
Joined: Jul 2004
Posts: 232
Likes: 2
From: Langley B.C Canada
Yes thanks for the reply. Im still boggled. I thought the TI box, but the engine will rev and run fine under load, with no miss firing, but once idling it goes into this very low almost stalling idle, but only when the engine gets hot, and a funny tarnish smell comes out of the exhaust at times as though there is a vacuum leak internally or something. then again maybe vapor lock or fuel issue. Its just strange because on Sunday I took it out, and the day was not hot out just regular temperature and after 30 minutes of driving she started to want to stall at intersections. Carbs seem fine no fuel leaks, clean as a whistle, and all vac *** lines seem to be fine. I dunno. Something to do with heat. I hate these kind of problems, because guessing parts to buy like a new TI box, is really expensive. It could be a 2 dollar fix, its just a matter of figuring out what it might be.
Burning Brakes
Joined: Jul 2016
Posts: 767
Likes: 74
From: Blaine MN
I think the others suggesting fuel delivery are correct. You don't specify auto/manual trans, typically you see this problem on auto transmission cars when downshifts don't happen as you come to a stop or as others pointed out fuel level changes due to braking.
Have you tried raising the idle speed to see if it gets better/worse. Will it happen at super slow parking lot speeds?
The end carbs do provide some fuel at idle and if the blades aren't fully closed it can affect all other idle settings adversely. If it never happens with the car sitting still and doing throttle snaps (at the temp you have problems) I'd be focusing on float level/idle mixture settings.
Have you tried raising the idle speed to see if it gets better/worse. Will it happen at super slow parking lot speeds?
The end carbs do provide some fuel at idle and if the blades aren't fully closed it can affect all other idle settings adversely. If it never happens with the car sitting still and doing throttle snaps (at the temp you have problems) I'd be focusing on float level/idle mixture settings.
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Thread Starter
Instructor
Joined: Jul 2004
Posts: 232
Likes: 2
From: Langley B.C Canada
Yes Im leaning towards fuel delivery as well.
Im starting to think vapor lock is the issue. The float bowls boil away the fuel to vapor, or even from the side exhaust causing that fuel line from the tank to get hot, then the pump pumps vapor to the carbs, or some parts vapor and some part actual fuel. The floats then doesn't have a chance to close off the fuel because its not seeing enough liquide fuel to close that valve. Now once I go to brake the small amount of fuel in the bowls moves forward away from the idle circuit, hence starving the engine for that brief moment and puts it into a stalling situation... Just a thought
Im starting to think vapor lock is the issue. The float bowls boil away the fuel to vapor, or even from the side exhaust causing that fuel line from the tank to get hot, then the pump pumps vapor to the carbs, or some parts vapor and some part actual fuel. The floats then doesn't have a chance to close off the fuel because its not seeing enough liquide fuel to close that valve. Now once I go to brake the small amount of fuel in the bowls moves forward away from the idle circuit, hence starving the engine for that brief moment and puts it into a stalling situation... Just a thought
Last edited by darrentpi; Jun 27, 2019 at 11:23 PM.