OK, so I just got my car back yesterday from the dyno tunner. The motor is a 388 forged internals, Aluminum Trickflow heads, Air-Gap intake, C&S Blow through aresol carb, Extreame velocity carb hat, CXRacing A-A intercooler, and Procharger F1. I drove the car home yesterday and it was very hot out. Maybe mid 90s. I got home, turned the car off and it stuttered twice, like a small run on. Two distinct mini-revs, then 1 second of silence and then BANG! very loud backfire out the tailpipe. I called the dyno guy I was using and he said the fuel might have been boiling out of the carb, filled the intake, found its way out the exhaust and ignited. He thinks I should install a carb spacer to help keep the carb cooler. I was thinking of going a step further and running a fuel cooler, or a insulation over my lines as well as the spacer.

Good idea, bad idea? Are there better ways to prevent this from happening? Any advice would help a lot.

The car also is running a BeCool circle track radiator with dual puller Derale fans, no thermo state, and a 1/2" restrictor plate. Car would not get over 210°F even sitting in traffic.

Thanks for any help, would love to get this dialed in so I can go to car shows this summer and not have people think a gun shot went off when I pull in!

 

Sounds like the engine is dieseling, carb spacer won't do anything in my opinion. Make sure your idle speed isn't set too high, and that your ignition timing is correct. Did you inspect the carburetor for any possible fuel leaks...?

 

As of right now I havn't done anything. I am headed out to inspect the car this morning. I don't have many tools with me now, so I can't check much but next weekend I will have everything I need so I can do a full gamut of testing.

The motor definetly dieseled. Thanks for reminding me that is the term. My idle was a scratch high I think. It was around 1250 RPM. This was set by the dyno tunner that built the motor. I will try and lowe the idle and we will see where it goes from there.

I think I have a 1/2" phenolic spacer laying around, you don't think this will help at all?

 

I wouldn"t worry too much about it, from just one event. Its a carb motor on an abnormally hot day, one of those 'goes with the territory' things. Wait and see if it makes a habit of it, esp after the weather calms down.

Edit: Yeah 1250 idle is high, probably contributing.

 

How are you retarding the timing for boost?
Seems like you have a combinations of a high idle and your timing is off.

 

I am retarding timing with a MSD BTM box. 2 ° for every psi.

 

whats the timing at idle and at 3000 rpm? Also is ther any way to lower the idle?

 

I know the total timing is 21° under 5 psi, that is a total of 31 with 10 retarted due to 2 degrees for every psi.

I don't know the timing exactly at 3000 RPM. Is that important to know? If so, why?

This weekend I should have some time to test it out and report back.

As for the idle that will the something I will try to adjust today after work. I will let you guys know how low I was able to get it.

 

Unless the motor HAS to idle that high, I would lower it. And I dont see why it would have to idle that high. See if you can get it around 800. If my car idles over 800, it will sometimes do that. My car use to do the loud bang out the exhaust. I advanced the timing a little and it fixed it. Turns out I wasn't running enough timing so I wasnt burning all the fuel in the motor so the burn was continuing out the exhaust and really heating it up. When turning the motor off, it would suck a little bit of fuel in as the motor wound down and then ignited when pushed into the headers.

 

I would go with the dyno tuner's recommendation for cooling the carb down with the spacer. Also, a fuel cooler won't hurt either. Why are you running no T-stat? The 1/2" restrictor and no stat are intended for 1/4 mile only with very short engine runs. The restrictor will restrict coolant flow in very hot conditions and may be causing your head temps to go high. This will contribute to your troubles. Get rid of the restrictor and just go with a 173 stat. Have your fans come on at 190 and be done with it.

Might also think about cooler plugs and a cyl head temp gauge to monitor head temps.

The advice you've received concerning idle speed and timing is also good.

 

Just trying to figure out what springs are in your distributor.
If you are running an msd put the black bushing in, you can also go with the light silver springs if you like.
Then set the total timing back to where it was.
This will give you more timing at idle and should help smooth it out a little so you can lower the idle speed.

Oh and also like ASE said take out the restrictor and put a thermostat in.

 

Your throtte blade is open with the high idle that will cause it.

 

I found a major vacuum leak too. I fixed it today, so I will report back new characteristics next week and we will take it from there. Car might have back fitted due to the leak. I will also check the timing and springs/bushing. I think with the motor running with no leak, I cab lower my idle and have no back fire issue. Thanks to everyone so far for the advice.

 

Are you running an aftermarket water pump? I just installed a Stewart stage 2 pump and 160 thermostat and it's not getting over 190 now, and that's idling in 100 degree heat. With the stock water pump it would heat up so quickly that I couldn't even drive it.

 

can you post a link to it?

 

Stewart Water Pump Stage 2 Aluminum (#23231 IIRC, but check before ordering), and the accompanying 160 Robert Shaw stat. Under $200 for both. I ordered the stat from Ecklers in Florida, and the pump from Capital Motorsports in Mass. There is currently a very high demand/low supply on both of these, so it took some calling around. Google Ecklers for their phone number, and Stewartcomponents.com lists distributors, and click Mass., I think they are the only supplier in that state. Let me know if you need more help.

 

Sooooo.... I found water in my oil. A lot of it. It is strange it is clear, not like the orange coolant I have in the rad. But the radiator is low in coolant so putting 2 and 2 togeather, the head gasket must be toast, or maybe an intake gasket that is letting water into my intake pathways. Something like that. Either way, I had the engine built 30 miles ago, and have had the car for only 2 weeks. 0 miles driven since the drive home. I am contacting the builder and seeing what he has to say.

Looks like this car is not getting off the ground this season. 2012 summer, over. Hoping I will be all set for 2013...