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Acceleration problem.

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dancrim

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When cold, my 65 BJ8 starts and runs great. After the motor is hot and you turn it off for 15-20 minutes
the car will buck when accelerating. The harder the acceleration the worse it is. As if you were pumping
pas pedal. After a mile or two it runs great and strong again....Any ideas? Thanks ahead of time.
 
Yep. It's a form of 'vapor lock,' fuel vaporizing in the system. My BJ8 does exactly the same thing and, of course, we have 10% corn-fraud ethanol in our gas in California. It started in my car at about the same time as all brands started poisoning gasoline with ethanol. On my recent road trip, when I was able to get ethanol-free gas in some locales, the problem went away. I've Jet-Hot coated my exhaust manifold and wrapped the downpipes which helped mitigate the problem, but the car still does it.
 
I think it's hot flooding. When the hot car sits, the fuel boils in the float bowls causing flooding - exacerbated by the ethanol content.

Back in the day, my 4-carb Corvair used to do the same thing. It caused hard-starting with a hot engine.
 
Yep, same problem with my 100. Found a gas station locally that sells non-ethanol and the problem went away
 
This is a very common problem with Healeys. It is caused by fuel boiling in the carburetor bowls when air flow through the engine compartment stops for a while. Once you get going, the air flow cools the fuel in the bowls, and everything is fine. I have been using ethanol-free gas for a while now, and it seems to help the problem a little. Also, I think many suppliers blend gas differently in the winter and summer. The winter blend vaporizes at lower temperatures. If you have gas in your tank that you bought during cold months, it may boil more easily than gas you buy now.
 
This is why I check this forum every day, quick and knowledgeable answers. Here in Louisville it's all ethanol and
I never thought of that. I was thinking some kind of horrible Carb. plunger problem. Thanks again guys.
 
Thanks for the listing Kieth, but nothing near me. Might be a help to some of the other Healey drivers.
I am toying with rigging up a couple of 12V. fans that I could use to cool the Carbs., couldn't hurt.
The way it is now, if you tried to merge onto a high speed highway, it could be a problem.
 
Do you have a fuel filter in the engine bay? We did because it is a nice convenient place for replacement, but I found it absorbed heat easily and added to this heat soak problem. It allows for an additional place for the fuel to percolate, and even has an easier time percolating in the filter because of the air space available in the filter. We too had the bucking and hesitation problem once the car got warm and removing that filter in the engine bay sure helped. We also have switched to trying to only use real gas, but sometimes don't get to the "good" gas stations.
Jim
 
As a general rule a Healey needs 10% richer needles to run correctly on modern fuel, a surprising number will not rev out properly without this change. They're running weak! I've put mine on a rolling road and other makes too. They're all the same and 10% is about average.

You may also experience fuel vaporisation and get quite a lot of ridiculous advice. Symptoms are failing to start when hot and all sorts of misfiring in traffic jams and the solution is to take an outlet of about 3/32" diameter from the banjo furthest from the fuel supply to the carbs and run it back to the tank.

Vapourisation is a real pain because it only happens under certain circumstances and in certain types of hot weather, so you never know if you've fixed it. Most haven't but tell everyone they have.

Fuel is very different now to the sixties and it brings problems they didn't have then. In Europe the expensive high octane fuel doesn't have ethanol.
 
You may also experience fuel vaporisation and get quite a lot of ridiculous advice. Symptoms are failing to start when hot and all sorts of misfiring in traffic jams and the solution is to take an outlet of about 3/32" diameter from the banjo furthest from the fuel supply to the carbs and run it back to the tank.
Click to expand...
Years ago I had a Datsun 240Z and the factory did just this, a small 1/8 or so return line to the tank from the rear carb banjo. I can see how this would guarantee a cool fuel supply to the float bowls but I don't see how it would help with the fuel already in the bowls after sitting a few minutes & re-starting - and that is when it generally has hit me. Unfortunately I never got around to trying it on the Healey. Do you know anyone who has tried it? I have always wondered if it really fixed the problem.
 
red57 said:
Years ago I had a Datsun 240Z and the factory did just this, a small 1/8 or so return line to the tank from the rear carb banjo. I can see how this would guarantee a cool fuel supply to the float bowls but I don't see how it would help with the fuel already in the bowls after sitting a few minutes & re-starting - and that is when it generally has hit me. Unfortunately I never got around to trying it on the Healey. Do you know anyone who has tried it? I have always wondered if it really fixed the problem.
Click to expand...

I agree. I don't see how this solves the problem of the fuel boiling in the carb bowls. I would be very interested to know if it does work, though.
 
It works well on lots of old cars, it's all that does. I had a friend with real problems with his Bentley, so he measured the pressure in the fuel line between the two cars. It was up to 14psi. A return feed to the tank cured. Not surprising when you consider that the manufacturers eventually did the same.
 
Keith_M said:
I agree. I don't see how this solves the problem of the fuel boiling in the carb bowls. I would be very interested to know if it does work, though.
Click to expand...

I wonder if it is acting like a gravity recirculation loop, keeping the fuel recirculating while there is a temperature differential in the system?
 
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