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Acceleration Problem

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dancrim

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65 BJ8, starts right up (even when cold) and runs great, but after it heats up and I park for 10-15 minutes it starts right up and when I accelerate it acts like it wants to die and then takes off. Does this for a minute or two, then runs fast and strong.

It's like you're pressing and letting up on the gas pedal.

Any ideas?

Thanks.
 
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dancrim said:
65 BJ8, starts right up (even when cold) and runs great, but after it heats up and I park for 10-15 minutes it starts right up and when I accelerate it acts like it wants to die and then takes off. Does this for a minute or two, then runs fast and strong.

It's like you're pressing and letting up on the gas pedal.

Any ideas?

Thanks.
Click to expand...

Yep. Due to engine compartment heat, the fuel in the line in the engine bay has vaporized, creating a bubble. My BJ8 does exactly the same; I think you'll notice that acceleration and running return to normal commensurate with the temp gauge dropping. This is, most believe, including myself, due to ethanol in the fuel (my car started doing this about the time ethanol became common in gasoline here in California). There are lots of threads on here on overheating engines, but remedies that might help keep the engine cooler when driving probably don't help much, as the latent heat after shutdown is greater than when running (on a hot day the temp gauge will often go to 212deg--boiling--at shutdown). Keeping the running temp as low as possible could possibly help. FWIW, I had my exhaust manifold ceramic coated and wrapped my downpipes, and didn't notice a difference either in running temp or after shutdown.

Edit: SU carbs require fuel pressure between 3-4psi (I think 'spec' is 3.5psi). Theoretically, a higher pressure pump might overcome the bubble faster, but SU carbs wouldn't like it (anyone tried this?).
 
Wrapping the engine compartment fuel lines with heat insulation could help. My wife's '73 Z-car originally had a vapor lock problem with its mechanical fuel pump. A factory recall fitted an additional SW electric pump and wrapped all the engine compartment fuel lines in a silver-coated fiberglass insulation.
 
Thanks guys. Kinda what I wanted to hear instead of some weird carb. or electric problem. And you're right, it does clear up
after a mile or so of driving. I'm in Louisville, and all the gas is ethanol-laced. Will try your ideas and post a result. Thanks again.
 
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dancrim-I had a similar issue with stumbling acceleration especially after stopping at the end of freeway ramps and taking off from that point. I think I have solved the issue by using a cozy like device fitted over the SU Carb bowls sold by Joe Curto called "Koolmat Koozie". This when combined with a thermal wrap on the carb interconnecting fuel line by Thermo-Tec (17075 3/4" X 36"). Seems to work so far. See image attached. Peter. Cozy.jpg
 
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