Weber 48IDA Heat Soak/Hot Start Problems

RCR40 is finally on the road after just over 3 years build. Massive thanks to Chris Kouba, Ron McCall, Mahlon Miller, Dennis Quello, and so many others on this forum without which there is no way in hell this would be anything more than a pile of bolts at this point.

First few drives have involved major carburetion issues as fuel sat in the floats for over a year between when the engine was complete/dynoed and when we finally got it in the car and running. So after a thorough disassembly and cleaning of the jets and passages, it is running well throughout the power range. Setup is 4x 48IDA Webers, put together by Jim Inglese, and a 363 small block ford (Dart block) put together by Craft Performance Engines in Arkansas. Jim Inglese spec'ed the cam and intake manifold and set up the float heights as well as custom jetting for this specific engine. Fuel pressure is set to 2.5 psi per Jim's instructions.

Cold starts are fine -- two shots of throttle and it starts up fairly easily. But once the engine has been warmed up, it won't restart when shut off and it takes 45 minutes to an hour of cooling down before it will start again. I can hear fuel bubbling in the carbs and a stream of fuel drips out of the accelerator pump jets onto the throttle plates ever few seconds for up to 25 minutes after shut down. This happens even when I have shut the fuel pump off well before shutting off the car and the fuel pressure is reading zero. In fact, pulling the tops off the carbs doesn't stop the fuel from dripping out of the pump jets into the venturis with no new fuel coming in.

Clearly, my inability to restart the car when hot is due to this flooded state, but what is the solution? I have tried wrapping the fuel lines in heat sleeves with no effect. Using an infrared thermometer, the carb bodies are reading about 140-150 degrees F with the top of the intake manifold beneath about 200 degrees. Is this hot enough to boil the fuel?

I want to avoid the "turkey pan" if possible and considering phenolic spacers under the carbs as a next step. Any ideas are appreciated. Today's drive ended up in a tail pipe fire that had me scrambling for the fire extinguisher but thankfully burned itself out after a few seconds. Not wanting to drive more until this is under control!
 

Randy V

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Try turning off the electric fuel pump when you’re still a block from home. You’ll be running out of gas in the carbs as you pull into the garage. No fuel in the carbs = no fuel to boil over into the chokes…
 
Thanks, Randy. I've been doing that but maybe need to start further out. What is the root cause of this issue? Why is fuel boiling like that when the carbs themselves are almost not too hot to touch? My worry is stalling out in traffic somewhere and not being able to get going again for an hour!
 
At least she was looking pretty while sitting there cooling down...
IMG_4504.jpg
 

Mike Pass

Supporter
Fit phenolic spacers. Aluminium is a very good conductor of heat. You need a heat insulator between the hot manifold and carbs.
e.g.
A 9 hole top vent will help to allow heat to escape when stationary.
Ceramic coating of the exhaust pipes will help with under clip temperatures.
A turkey pan will help to deflect convected exhaust heat away from the carbs.
Cheers
Mike
 
This car uses a full fuel dump system the moment the engine is stopped. The car had identical problems to yours, and the solution has worked perfectly since fitting.
 

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This car uses a full fuel dump system the moment the engine is stopped. The car had identical problems to yours, and the solution has worked perfectly since fitting.
The car Frank refers to is mine. I experienced the same problems. Stopping to refuel after just a few miles I had to wait around 30 minutes before the car would restart. After a 30 mile run, I parked but was asked to move but the car would not restart, again for around 30 minutes.
Frank recommended his fuel dump system. Quite simply it works. Two years after Frank worked his magic I have never had a problem starting when the engine is hot, in fact never a problem starting - period. Listen to the man who knows - Frank.
 
Thank you, Frank & Richard! Can you describe the parts needed for the "fuel dump" system? It looks like a T-fitting and return back to one of the tanks? I'm using the tanks independently (effectively two separate fuel systems, each with its own pump and no crossover) so would there be an issue with the fuel returning only to one tank and possibly overfilling it?
 
Another issue could be the fuel. I have a similar problem with vapor lock with my Holley. Someone told me that high octane fuel has more volatiles than standard fuel, so it's more likely to suffer from vapor lock if the carbs get too hot.
 
There are a couple of possible issues (the others people have suggested are also good). Timing would be the first I would confirm. Webers need more advance than other carbs. Make sure you are getting 38deg of full advance. Too little (or too much) and it will run hot. Another thing to check (I have battled this a lot!) is that you are getting enough flow. I have some Earl's check valves that I have found are stopping the amount of flow (they shouldn't affect it as much as they do). This is causing me to run lean and therefore too hot. It drove me crazy!! I am now switching over to EFI (from Jim Inglese) to help with my range. I also had my carbs set up from Jim quite a few years ago.
 
Thanks, Karl! Did you experience a crazy amount of backfiring on deceleration with your Webers? I think I have finally set the idle mixtures perfectly and they run great throughout the whole power range, but if I stomp on it up to 5,000 or so RPM and let off, I have this (glorious) cacophony of snapping and crackling through the pipes, complete with flames. No amount of fiddling with the idle mixture changes it. Jim has confirmed all the jetting and emulsion tubes are correct. Maybe that's just how it is with such a short exhaust system? I'm using Remflex header gaskets and they seem to not be leaking.
 
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