quote:

Originally posted by Undertaker II:
Have you tired a new crank trigger pickup?

Have not tried this yet. Would this cause an intermittent miss? I figured the pickup being bad would be throughout the rpm range?

quote:

I figured the pickup being bad would be throughout the rpm range?

The faster it spins the less dwell time it has at the pickup. So it would stand to reason if it was "marginal" it would show at higher RPM..... maybe.

quote:

Originally posted by Holytown:
The miss has always been there slightly right before gear change, but got real bad last night last run of the night.

describe this miss. Is it a stutter like it's on the chip or does it momentarily layover. Is there any unique sound associated with this miss?

Like mentioned above bring down your gap to .020 on plugs and check the cap and rotor for cracks.

Also make sure the carbon tip on the bottom side of the cap is still nice and round.

Just for ****s and giggles check the gap between your crank trigger pick up and wheel.

When I have an issue first thing I do is basic tune up. Plugs, cap, rotor, wires and then go from there to determine if it is ignition or fuel related. All of those things have limited life expectancy in a race car. Also I use good plug wires I use the Smileys racing wires which are Moroso Ultra wires but much cheaper.
If you think it may possibly be fuel related change out carb for a known good one to narrow it down.

We had a miss for several races just as the car would shift and right after it left the line. Sometimes it would miss just once and sometimes several times. We finally traced it to a bad MSD pickup. You could bend the wiring back where it went into the metal part of the pickup and see bare wires. The replacement pickup was better insulated where the wires entered the metal pickup. The new pickup cured the miss.

quote:

Originally posted by excessive braker: Also make sure the carbon tip on the bottom side of the cap is still nice and round.

That’s an important item to check whenever you remove the distributor cap.

I’ve seen several caps that had the carbon ball completely disintegrated because the spring loaded rotor strap was not making contact with the ball and the arcing destroyed it.

Whenever I replace the cap and rotor I make sure that I can feel the cap make contact with the rotor strap at least 1/8 - 3/16” before seating in the distributor.

I also add extra ventilation to my distributor caps.

Have you tried different alcohol had buddy chasing weird problems found he had bad drum

Newest Update:

Just ran 4 days in a row (test and tune, Gamblers race, then 2 5k's) this weekend. Car only misses in 1st gear. No missing after the gear change ever. Got it down to missing 2 times. It builds absolutely 0 heat under any kind of throttle. Builds heat good at idle.

If I go into the burnout box at 160 car will be at 160 when I get back to the trailer. Going up to larger jets got rid of most of the missing. But it still misses about 2 times pretty much every pass after it comes off the brake at about 60' marker.

Car is ultra consistent 330-660. All ET is lost between 60' and 330'

quote:

Originally posted by 1320racer:

quote:

Originally posted by Holytown:
The miss has always been there slightly right before gear change, but got real bad last night last run of the night.

describe this miss. Is it a stutter like it's on the chip or does it momentarily layover. Is there any unique sound associated with this miss?

The Miss sounds like its on the chip just for 2-3 blips.

If the new plugs gapped at .020 don't solve the issue, here are 2 solutions that worked for me in the past, with cars having identical symptoms.
(It sure seemed most likely to be ignition-related, but in both cases after everything ignition-wise was replaced):
1. Fuel supply. What is your pressure going down-track? Is there any possible restriction to fuel flow? (Filter, pump size, undersized or kinked line, etc). Could also be carb issue - Do you have a different carb to try? (Maybe borrow one, if need be).
2. Valve springs. How old? Correct springs for cam? Is lash set properly? Check spring pressures.

Couple things. You thought it was rich and went richer? Not sure why on that.

Does it have and electric shift solenoid that is power on to shift?

Curtis

quote:

Originally posted by FootbrakeJim:
If the new plugs gapped at .020 don't solve the issue, here are 2 solutions that worked for me in the past, with cars having identical symptoms.
(It sure seemed most likely to be ignition-related, but in both cases after everything ignition-wise was replaced):
1. Fuel supply. What is your pressure going down-track? Is there any possible restriction to fuel flow? (Filter, pump size, undersized or kinked line, etc). Could also be carb issue - Do you have a different carb to try? (Maybe borrow one, if need be).
2. Valve springs. How old? Correct springs for cam? Is lash set properly? Check spring pressures.

Lash is good Spring pressure is high for the cam 280# took one off and tested it. Don't know how old they are, came with the motor. Magna Fuel 500 pump and magna fuel regulator. #10 line and #8 to carb.

quote:

Originally posted by CURTIS REED:
Couple things. You thought it was rich and went richer? Not sure why on that.

Does it have and electric shift solenoid that is power on to shift?

Curtis

Needed a quick fix to race this weekend and when it was rich the miss was a lot better, so i went with that.

Yes shifter solenoid is power on to shift

quote:

Originally posted by Holytown:

quote:

Originally posted by CURTIS REED:
Couple things. You thought it was rich and went richer? Not sure why on that.

Does it have and electric shift solenoid that is power on to shift?

Curtis

Needed a quick fix to race this weekend and when it was rich the miss was a lot better, so i went with that.

Yes shifter solenoid is power on to shift

I'm wondering if the shift solenoid might be causing some feedback of some sort.

quote:

Originally posted by CURTIS REED:
I'm wondering if the shift solenoid might be causing some feedback of some sort.

My volt gauge showed 13.4v at an idle. My grid data logs showed when the shifter activated, it dropped to 9.8v and struggled to get back to 12v the rest of the run. I would never have found it without data logging it.

I replaced the solenoid then replaced the alt to fix it.

The car didn't miss but was inconsistent the more runs you made.

I wouldn't rule out the shift solenoid being an issue.

quote:

Originally posted by Tom R:

quote:

Originally posted by CURTIS REED:
I'm wondering if the shift solenoid might be causing some feedback of some sort.

My volt gauge showed 13.4v at an idle. My grid data logs showed when the shifter activated, it dropped to 9.8v and struggled to get back to 12v the rest of the run. I would never have found it without data logging it.

I replaced the solenoid then replaced the alt to fix it.

The car didn't miss but was inconsistent the more runs you made.

I wouldn't rule out the shift solenoid being an issue.

Data loggers have sure helped me many times.

maybe too high of fuel pressure, I just had the same issue, lowering it fixed it.

From what I've experienced with timing sensors either with crank triggers or OEM timing sensors even in diesel engines but if the gap is excessive, it will show up as a high load or high rpm miss. Can't remember the exact number I have my trigger set for. Might be something like 0.080". Too close and you risk making contact with the pickup due to high rpm flexing. Too much of a gap and it won't collapse the field fast enough and you get a miss.

As a suggestion before throwing more parts at it would be to reduce the crank trigger gap slightly and see if the miss goes away. Usually doesn't need a big change. Something like 0.005" at a time.

Have you checked rotor phase.