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In all my years I have not seen a coil go bad. And when a Unilite module goes bad you'll know it - it is either 100% good or 100% bad. Always a good idea to keep a spare module in the glove box.
If it happens again - just as an outside thought - pop open the fuel tank and listen for a sucking sound , if so the tank vent is plugged.
Chased that as a kid, after 3 mechanics tried to fix a car and I found it when I went back to basics and wanted to check the tank sock -found it by accident opened the tank and whoosh...
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
When i had a boiling problem its symptom was difficulty srarting like it was flooded. When the ambient air got above 60°… i solved it before the air temp got higher. I used a wooden spacer and an air gap manifold. Yours sounds like a different problem. When was your last tuneup? Has the car been in storage? Is it humid where you live
If it happens again - just as an outside thought - pop open the fuel tank and listen for a sucking sound , if so the tank vent is plugged.
Chased that as a kid, after 3 mechanics tried to fix a car and I found it when I went back to basics and wanted to check the tank sock -found it by accident opened the tank and whoosh...
good comment. I also enlarged the vent slightly on my '64 cap to make sure this is never an issue.
Just circling back, as I've not had any issues since doing the following:
1) Replacing my existing ignition coil with an Echlin coil with primary set at 1.7 Ohms and secondary set to 9400 Ohms;
2) Ensuring adequate fuel flow and pressure at various points -- I feel reasonably certain vapor lock can be ruled out on this case;
3) Ensuring the measurements of the coil stay close to the spec'd numbers after running -- I don't have dramatic changes in resistance on either primary or secondary circuit;
4) I also went to a vented gas cap after removing mine after a test drive and hearing the 'swoosh' of releasing air. While I admit this is symptomatic of other stated problems, I never lost fuel delivery at the carb -- but thought doing this prophylactically would be smart.
I have made several small trips since my original post, including putting about 80 miles on her yesterday in both in-town and interstate driving conditions. No issues. So.......on this one I'm going to say it was a coil/ignition issue.
This forum is an incredible resource -- thank you all for your guidance and willingness to assist!
I wanted to post an update to my initial question - for those who responded, thank you -- all of your responses helped us troubleshoot, and big credit to my buddy ChattanoogaJSB for his assistance in diagnosis.
Initially i thought the coil was the culprit. That lasted for about two weeks, and the high speed lurch occurred again. Massively frustrating, yes. Ended up getting a flatbed back to the house.
About 20 minutes after I had broken down, I shot the temp at the base of the carb -- over 180 degrees. Too hot. Was it possible that I was heat soaking at the base of the carb? Having temporary vapor lock there? Possibly. It gets hot under the hood but considering the consistency of the circumstances surrounding my issue (stop and go driving followed by some cruising in summer temperatures/conditions) it could not be ruled out.
At ChattanoogaJSB's recommendation, we decided to try and remove as much heat from the equation as we could - and I ordered a new intake gasket built for fuel-injected cars with the exhaust port blocked off. I live in the south and we don't need the added help warming up the carb that the exhaust ports gave the carburetor in frozen tundra-style winters.
Here's the process I followed:
First, I drained the coolant, disconnected the fuel line and vacuum, and removed the thermostat.
Next, after labeling the plugs I removed the distributor:
Removed the carburetor to expose the intake:
And the removed the intake. (Having ziploc baggies and a sharpie to label the bolts/screws for each part/area is an obvious must for veterans, but worth mentioning again for good measure.)
I ordered the new gasket from Felpro -- after cleaning, prepping, and painting the intake, we applied some Permatex on the head and put the gasket in place.
Finally, we remounted the carb, filled the block, put the thermostat back on, and reset the timing on the car.
I'm sure there are other things to consider, but I did want to document what we did in the hopes that we have finally cured the problem. Today I took the car back out for the day with our families, and had no issues......
I truly appreciate those of you who lend your expertise.
Nice write up, amigo! Yes, we read about vapor issues in modern gas at 5 psi (small block line pressure) starting at 160 degrees from multiple sources.
For posterity, the subject car would flame out at cruise- on hot days, new DeWitts. It would restart when cooled to at or under 160 degrees at the carb (I witnessed this firsthand meeting Jarrett before a tow and the car restarted after cooling about 25 minutes. We had an IR temp gun. The carb was obviously not squirting gas prior and the fuel line (common vapor lock area at frame) wasn't carrying heat we could see. But the carb base was HOT.
Now carb base temps are 140 degrees or less. No spacer required.
I cannot underscore how gratifying it is to see my friend confidently doing new tasks completely outside his prior comfort zone on these old cars.
the forum is always a great source of knowledge so I thought I would certifying the particulars I saw as well in hopes someone reads this.
Also- the engine is way tidier than ever, buddy!
benton
Last edited by ChattanoogaJSB; 05-27-2017 at 11:57 PM.
Had the initial report been failure to squirt fuel right after the car died, it would have been quite a lot easier to trouble shoot... the insistence that the carb was squirting fuel led everyone down the ignition path.
I think I will look for some BBC intake gaskets with the heat passage blocked off and install a spacer in place of the exhaust riser. In South Florida is never gets cold enough to need carb heat to get the choke to release.
Had the initial report been failure to squirt fuel right after the car died, it would have been quite a lot easier to trouble shoot... the insistence that the carb was squirting fuel led everyone down the ignition path.
I think I will look for some BBC intake gaskets with the heat passage blocked off and install a spacer in place of the exhaust riser. In South Florida is never gets cold enough to need carb heat to get the choke to release.
No doubt it would have. But the first few times it happened I had fuel coming in rather quickly (a minute or two) after the stall - and by then I wasn't catching it. It wasn't until later instances that I could tell that fuel wasn't coming into the bowl.
It's also worth noting that I did not shoot the temp of the base of the carb with an IR gun until this most recent time. I should have done that earlier, and had one in my 'go kit' to do it. Just didn't. But after installing the new gaskets my carb base temps yesterday (after driving on an 80-degree day) remained around 140/150 deg. Much improved.
Had the initial report been failure to squirt fuel right after the car died, it would have been quite a lot easier to trouble shoot... the insistence that the carb was squirting fuel led everyone down the ignition path.
I think I will look for some BBC intake gaskets with the heat passage blocked off and install a spacer in place of the exhaust riser. In South Florida is never gets cold enough to need carb heat to get the choke to release.
if you have a BB I'm sure there are the same gaskets in general as aftermarket heads frequently don't have a crossover at all.
Aftee the fact we discovered as Jarrett said that at 165 degrees or more we'd get vaporization and no fuel through the primaries but when it was "on the cusp" it could be hard to rule out ignition (when you could shut it off and momentarily he could still see fuel)
04-02-2017, 10:37 PM
