Heat issues?

[diablo1]

I have a 74' blazer with a 350sb, quadrajet, long tube headers, dual exhaust both to the rear. New radiator, t-state. Possibility running a little lean.

The problem i'm having is what I call vapor lock. It runs fine when outside temps are cool but when they heat up its like its starving for fuel or the fuel won't push through to the carb. I know because I have a clear fuel filter just before the carb so I can see whats going on. (No fuel in the filter when hot but will idle all day long on no fuel).

What I have done is install new mechanical pump. (still the same). Install an electric pump at the tank in conjunction with the mechanical. (same thing). Remove the mechanical pump, reroute the fuel line to the outside of the frame rail. (STILL THE SAME THING).

So whats next?
1)Stock manifolds to single exhaust down drivers side?
2)Shortie headers (center dump or similar) to single exhaust down driver side?
3)Long tube headers to single exhaust down driver side. (seems like this would be a pain in the ass to make work.

Any suggestion, ideas, parts and part numbers you have would be greatly appreciated.

Thanks,
Brian

 

[4X4HIGH]

If it was vapor lock it wouldn't even idle so if what you're saying is that on HOT days it will idle but doesn't want to run properly otherwise it's not vapor lock. What is the coolant temp when the outside temps get hot? In all my experience over the years GM engines start running poorly when they reach around 220*. If your engine is running lean that means the temps will be higher than normal in the cylinders and could also reflect a rise in coolant temps as well.

 

[diesel4me]

If you have no thick gasket inder the carb ,it might get hot enough to boil away the fuel in the carb bowl--..but usually with vapot lock no gas will flow and you cant even start the engine,period..mild caes cause misfiring and bogging..todays gas laced with alcohol tends to boil at lower temps and also can make an engine "leaner" as there is less BTU's in alcohol and more must be burned to get the same amount of power..

If you look up "fuel vapor pressure" on google you will read about how a gas filter that appears "empty" is often of no real concern...my Wix fiter catalog has a whole page in the back section explaining about this strange situation,though its very technical and in engineers terms--I replaced a few pumps and gas lines trying to "cure" my half full fuel filter woes,to na avail myself..I never could figure out why it was always FULL when I bought the truck,but after driving it awhile and doing a routine "tune up" that included a new gas filter,it never seemed to fill up all the way again,and nothing I did "cured" it!..

One truck I had,a 1971 GMC,had a half full fuel filter all the time--one day the steel gas line rusted thru near the rear wheels,so I replaced all of it from the tank to the fuel pump--I found a factory peice of rubber line joining 2 sections of the steel line rught where the frame goes up over the tires--and I replaced it--after I tried blowing thru the rubber hose and found out the inner liner was all gooey and collapsed!.that cured my half full fuel filter problem...my brothers 1966 Suburban with a 283 had troubles climbing a long grade uphill at highway speeds,and would bog down and finally stall if you didn't back off the throttle--replacing the fuel pump and filter seemed to help,but it still did it sometimes...we later found his truck had the same rubber hose in nearly the same spot on the frame joining the 2 steel sections,and sure enough,that one looked perfect externally,but inside it was all soft and falling apart...after it was replaced the truck never stalled on a long hill ever again...

 

[diablo1]

So from the sounds of it, it's not vapor locking. I will replace the last of the fuel line that you recommended. No I do not have a thick spacer under the carb just a 1/4" gasket. The Blazer runs all the time with a half full filter or no fuel in the filter (unless its parked, cold in the garage). It did sputter and die before I put the electric pump on but I had over heating problems too do to a plugged radiator and stuck thermostat. I changed all at once so I really dont know what one thing corrected the motor from sputtering and stalling. I guess ill rich en the carb up a little as well.

What type of spacer would you recommend and how thick? Aluminum or Phenolic?

Thanks for the advice.

 

[diesel4me]

I've just used the thick Q-jey gasket,but here its not as hot as where you are...there is a few different choices of spacers available from Jegs or Summit that are aluminum,phenolic or even wood ones!..I think the phenolic ones may reduce heat transfer best,but I'm guessing..

I had an aluminum spacer under an Edelbrock carb on a 305 that took forever to let the carb heat up enough in cold damp weather to not let carb icing become a real problem before!--I had to rig the exhaust heat riser and air cleaner "door" to stay shut all the time to get the carb to run warm enough not to frost up on me on cool damp days..however,in summer I noticed that aluminum spacer got pretty hot when I put the heat riser and air cleaner back to stock..

Be aware raising up the carb might cause issues with a 700R4 's TV cable,it will need to be readjusted or perhaps a different spot to hook it too,to retain the correct geometry..same for a TH350 's detent cable..your accelerator cable should be OK as is though..if your running a stock Q-jet it might not be an issue,with other carbs it almost always is an issue..

 

[diablo1]

Cool thanks.

 

[ktmoutfront]

There is also a thin plate that used to be under the carbs. It is larger than the carb base by about an inch. Dissipated the heat. Can not count how many guys took them out at rebuild time, and could not figure out why the fuel boiled.