66 Sat
Well-Known Member
My engine has developed a problem yesterday after some hard running at the track. I put a Wind Tunnel intake manifold on the Poly about 2 months ago and it has been running great. Been on a few long drives (200+ miles last weekend) no issues other than a lean stumble on very light throttle. I fixed that with some smaller idle air bleeds, but it felt a little sluggish so I changed the main jets from 70 to 72 and put the air bleeds back to what they were (.068). That seemed to work, had the car out Saturday checking it, had 19 inHg on the vacuum gauge, running great. Idle set to 800 rpm, rock solid.
Yesterday I drove the 80 miles to the track, no issues, then did 8 passes, the last 4 in quick succession as the lanes were thinning out. Broke 100mph for the first time (!), each run was 100 - 101 mph, fastest time was 14.023 (still trying to get into the 13's...), need some better tires.
On the last 2 runs the carb felt a bit lumpy low down driving slowly back up the return road to get my timeslips. Temperature was ok though. I then parked up and my son took it on a few very slow cruise laps in a big parade, probably running at about 10mph for about 10 minutes. When he brought the car back it wouldn't idle evenly, like it had a vacuum leak. The revs were bouncing from 800 to almost stalling - I had to give it some throttle to keep it alive.
The temperature gauge was up a bit, but nothing catastrophic, and the radiator hadn't puked or anything.
I couldn't find any leaks so we headed for home. Drove the 80 miles, had a bit of stumble occasionally (which I though would be the vacuum leak) but got home with no issues. Going along at about 70 mph I shifted into neutral and the rpm was steady at 800 - I thought it might have just been heat soak and the issue was resolved, but when we slowed down for the last few miles it was back to not wanting to idle and the revs bouncing from 800 to stall territory.
Today I fired it up, started ok, nursed it for few minutes while it came up to temperature and was idling steady at maybe 700 rpm. Put the vacuum gauge on it and noticed no change in idle when I pulled the vacuum line off the distributor to attach to the gauge. Needle was steady but only 14 inHg, not 19 inHg like usual. When I revved it the gauge went to zero briefly (I think) before flying up - when I later looked at the chart that said "oil or rings". I wasn't really paying attention though, maybe it was only going to 5 before going up, which the chart says is normal. I will need to re-check this.
Put the timing light on it - 14° base timing as normal, but when I reconnected the line it stayed at 14° instead of increasing to 25+ (I'm running MVA).
Sprayed carb cleaner around the manifold and carb - no change to idle.
Took the brake booster line off and plugged it - no change to idle.
Turned it off, scratched my head, thought I'd take it for a drive. Started it and it was all to crap again, revs bouncing around wanting to stall.
Put the car away waited for it to cool.
Pulled the plugs - a few rich but nothing standing out as dramatically wrong.
So in summary:
1. Vacuum gauge is steady but down from 19 to 14 inHg.
2. Idle timing isn't affected by connecting to MVA.
3. Hasn't used any coolant. No coolant in oil, no oil in coolant.
4. Idled steady from cold until warm on driveway today, but then started playing up.
Thanks for reading all this - I wanted to give as much info as possible. Any ideas what could be the issue or where to look next?
Yesterday I drove the 80 miles to the track, no issues, then did 8 passes, the last 4 in quick succession as the lanes were thinning out. Broke 100mph for the first time (!), each run was 100 - 101 mph, fastest time was 14.023 (still trying to get into the 13's...), need some better tires.
On the last 2 runs the carb felt a bit lumpy low down driving slowly back up the return road to get my timeslips. Temperature was ok though. I then parked up and my son took it on a few very slow cruise laps in a big parade, probably running at about 10mph for about 10 minutes. When he brought the car back it wouldn't idle evenly, like it had a vacuum leak. The revs were bouncing from 800 to almost stalling - I had to give it some throttle to keep it alive.
The temperature gauge was up a bit, but nothing catastrophic, and the radiator hadn't puked or anything.
I couldn't find any leaks so we headed for home. Drove the 80 miles, had a bit of stumble occasionally (which I though would be the vacuum leak) but got home with no issues. Going along at about 70 mph I shifted into neutral and the rpm was steady at 800 - I thought it might have just been heat soak and the issue was resolved, but when we slowed down for the last few miles it was back to not wanting to idle and the revs bouncing from 800 to stall territory.
Today I fired it up, started ok, nursed it for few minutes while it came up to temperature and was idling steady at maybe 700 rpm. Put the vacuum gauge on it and noticed no change in idle when I pulled the vacuum line off the distributor to attach to the gauge. Needle was steady but only 14 inHg, not 19 inHg like usual. When I revved it the gauge went to zero briefly (I think) before flying up - when I later looked at the chart that said "oil or rings". I wasn't really paying attention though, maybe it was only going to 5 before going up, which the chart says is normal. I will need to re-check this.
Put the timing light on it - 14° base timing as normal, but when I reconnected the line it stayed at 14° instead of increasing to 25+ (I'm running MVA).
Sprayed carb cleaner around the manifold and carb - no change to idle.
Took the brake booster line off and plugged it - no change to idle.
Turned it off, scratched my head, thought I'd take it for a drive. Started it and it was all to crap again, revs bouncing around wanting to stall.
Put the car away waited for it to cool.
Pulled the plugs - a few rich but nothing standing out as dramatically wrong.
So in summary:
1. Vacuum gauge is steady but down from 19 to 14 inHg.
2. Idle timing isn't affected by connecting to MVA.
3. Hasn't used any coolant. No coolant in oil, no oil in coolant.
4. Idled steady from cold until warm on driveway today, but then started playing up.
Thanks for reading all this - I wanted to give as much info as possible. Any ideas what could be the issue or where to look next?
