67 L71 Carburetor temperature

[Kerry A.]

I'm having a heat soak issue with my 67 L71. I recently installed a 5/16" phenolic spacers and it seems to have helped but I haven't put it through the ringer. Prior to installing the spacers I had a hard start/stalling issue. When it would occur I would check the carburetor float bowl and body temperature as well as the intake. The carb temp ranges from 158 to 170 degrees. After the spacer the temperature ranges from 138 to 145 degrees. My question is what is an average temperature of a carburetor after a long casual drive? I realize there are a lot of factors involved but I'm trying to establish if the carb temperatures I'm experiencing are within a normal range. Thank you in advance for your assistance.

[Mark E.]

Re: 67 L71 Carburetor temparture

Assuming the engine has a 180 degree thermostat, the carb temperatures you measured seem reasonable... A few degrees lower than the engine.

[Kerry A.]

Re: 67 L71 Carburetor temparture

Mark, Thank you for your prompt response. I can always count on the board to come up with an answer.

[Frank D.]

Re: 67 L71 Carburetor temparture

I've dealt with this issue a lot on my C1 and C2 and I can tell you that when your carb bowl temps start heading north of 145* you're in the trouble zone. Typically with a variety of 'fixes' you can drop that 20* - I run a 1/4" phenolic spacer and have the intake manifold heat risers blocked off with fuel injection gaskets and the passenger side heat riser valve wired open - sometimes lowering float levels a bit will help... On my 63 intake manifold I also drilled and plugged the "hot slot" holes..

My temps after a hot run are in the 128*-135* range now with no percolation...

[Kerry A.]

Re: 67 L71 Carburetor temparture

I had a chance to run the car fairly hard last Friday. The engine temp stayed right around 175. The ambient temp was approximately 10 degrees cooler and the carb temps dropped close to 20 degrees below what they were before the phenolic spacers were installed. I pulled off the road in the middle of the drive to let the engine bay heat up and when I checked the carb temps were ideal. I completed my trip and upon arriving at my house, the idle dropped to 500 rpm and lower then bounced up and down and finally quit running. As if it was gasping for gas. The carb temps were still ideal but the car wouldn't start. I let it sit for quite some time before it finally started. But at least I was able to get it into the garage. The round trip time was approximately 45 minutes. The shop I use set the carb lean with a low idle. They recommended I richen the mixture and bump the idle up slightly. I'll give it a try and see what happens. I too have my heat riser valve wired open. By the way the carbs were completely refurbished by Chicago Corvette and they sure as heck work a lot better than before. But I don't think this is a problem with the carb itself.

[Chris H.]

Re: 67 L71 Carburetor temparture

Kerry, what you are experiencing is quite common. There are many factors that contribute to your symptoms. I recommend reviewing the Duke Williams tuning presentation, specifically the "2-Inch Rule" and swapping out your VAC. My L71 was transformed after this mod. Chris

http://stlouisncrs.org/news_files/DukeWilliamsEngineTuningPerformance%26EconomySeminar.pdf

[Bob W.]

Re: 67 L71 Carburetor temparture

Kerry-Frank who did you buy the phenolic spacers from ?

Thanks Bob

[Frank D.]

Re: 67 L71 Carburetor temparture

Kerry-Frank who did you buy the phenolic spacers from ?

Thanks Bob

Ha! Before anybody was making them commercially for the WCFBs I bought phenolic stock from McMasters and made my own...
That material is TOUGH....however now you can buy them off-the-shelf for the WCFBs in 1/4" or 1/2" ... if you go more than 1/4" you'll be guaranteed to have hood clearance issues IMO:

Get them here for the WCFB:

https://www.dashman.net/product.html?id=203

He also sells AFB versions but verify the dimensions work for your application first:

https://www.dashman.net/product.html?id=332

[Kerry A.]

Re: 67 L71 Carburetor temparture

Bob, I purchased mine from hotrodcarbs.com.

Chris, I printed out the article you provided the link to. I will read it through and pass it along to the shop.

[Bob W.]

Re: 67 L71 Carburetor temparture

Kerry-Frank, Thanks for the reply and information . My next question was about hood clearance, Frank like you I have a 63 300 hp &a59 245 hp.

Thanks again Bob

[Timothy B.]

Re: 67 L71 Carburetor temparture

I had a chance to run the car fairly hard last Friday. The engine temp stayed right around 175. The ambient temp was approximately 10 degrees cooler and the carb temps dropped close to 20 degrees below what they were before the phenolic spacers were installed. I pulled off the road in the middle of the drive to let the engine bay heat up and when I checked the carb temps were ideal. I completed my trip and upon arriving at my house, the idle dropped to 500 rpm and lower then bounced up and down and finally quit running. As if it was gasping for gas. The carb temps were still ideal but the car wouldn't start. I let it sit for quite some time before it finally started. But at least I was able to get it into the garage. The round trip time was approximately 45 minutes. The shop I use set the carb lean with a low idle. They recommended I richen the mixture and bump the idle up slightly. I'll give it a try and see what happens. I too have my heat riser valve wired open. By the way the carbs were completely refurbished by Chicago Corvette and they sure as heck work a lot better than before. But I don't think this is a problem with the carb itself.

Usually when everything is hot the engine will like a leaner idle mixture because vaporization and fuel distribution is better. Does this engine have a GM reproduction coil.

[Frank D.]

Re: 67 L71 Carburetor temparture

Kerry-Frank, Thanks for the reply and information . My next question was about hood clearance, Frank like you I have a 63 300 hp &a59 245 hp.

Thanks again Bob

Actually I have a 63 original base motor 250hp mill - which as you know takes the WCFB so the issues could be different, in my case, the phenolic spacer caused a hood "touch", just barely, at the PS snorkel on the air cleaner where the hood horizontal brace comes across parallel with the firewall. By some careful, judicious bending of my repro snorkel I managed to get clearance. You may not want to do that and I don't blame you or your AFB carb may present a different problem.

I use balled up tin foil secured with blue painter's tape at critical points while slowly closing the hood to find trouble spots and the crushed foil tells you exactly how much space you have to work with - and not as messy as Play-Doh...

[Kerry A.]

Re: 67 L71 Carburetor temparture

The coil installed is a USA made reproduction. The amplifier guts have been upgraded to modern circuitry and I have both the original and a Lectric Limited magnetic pickup. Either one works fine. After these changes the TI overheat engine shutdown problem was cured. The car is a three time Top Flight so obviously the car and engine is stock. Not that it makes a difference but engine has been rebuilt from the ground up and blueprinted and runs REALLY good before it heats up. As suggested by the shop I richened the mixture by 1/8 turn and ticked up the idle and it runs worse. Now the engine diesels.

[Bob W.]

Re: 67 L71 Carburetor temparture

Frank, Thanks for that information and the photo . Is that a stock intake painted silver or a aftermarket one?

Bob

[Chris H.]

Re: 67 L71 Carburetor temparture

Kerry, as mentioned Duke's presentation, one of the benefits of the VAC swap is lower exhaust gas temperatures. My L71 operating temp dropped from 205+ to a rock steady 180 even on 90 degree days.

I would measure your manifold vacuum at idle and then test your VAC with a Mighty Vac to see what it's operating range is. This will tell you where the motor stands regarding the 2-Inch Rule.