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Stalling in hot weather

  
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Stalling in hot weather

 
projectman projectman
New User | Posts: 1 | Joined: 07/12
Posted: 07/29/12
08:31 PM

I have been struggling with my 1970 Buick stalling when the weather is over 90 deg and I accelerate. The engine is a performance 455, carburated,HEI ignition, headers. I wrapped the headers, added a one inch spacer between the carb and intake, insulated the fuel line, ran a return fuel line back to the tank, ran cold air intake hoses to the air cleaner with K&N filter and the problem persists. Runs just fine after ambient air temp comes down. Does anyone have a suggestion? It does not happen every time I accelerate, it seems to be after running the car for some time around town or even on the hiway, engine does not get hot, runs 190 with air cond on.  

waynep71222 waynep71222
User | Posts: 155 | Joined: 04/12
Posted: 07/29/12
09:48 PM

a few things...

install a fuel injection type of fuel filter directly before the fuel pump... so the pump only gets filtered fuel...

second.. after installing it..

disable the ignition system so NO spark can be created...  so unplug the HEI bat wire..

disconnect the fuel line at the carb... extend the line with a section of rubber fuel hose..  

shove that hose into a clean clear plastic 2 or 3 liter bottle..   have somebody crank the engine for 15 seconds while you observe the pulses of fuel into the bottle...   each pulse should be full and equal to the others...  not diminishing ...  this proves the fuel system can handle the flow..

you will also want to take a old speaker.. knock the magnet off it.. stick it to the bottom of the fuel tank.. the magnet stuck to the outside of the tank.. as long as no body moves it will attract any sediment to it..  keep it out of the fuel pump check valves...

Fuelpumpdiaphragmcheckvalves

look at how the magnets attract the sediment.. it will do it right through the tank wall..
i normally drop neodymium magnets into the tank... these attract the sediment into them..

Supermagnetindirtyfuel1

Supermagnetindirtygas2

sediment can come from gas stations.. can come from the inside of the fuel lines..

what happens is the sediment gets into the check valves.. reduces the ability of the fuel pump to pull fuel up from the tank... and to push it into the line to the carb...   reducing the pressure in the line to the tank reduces the boiling point of the fuel.. the vapors can expand and push backwards into the pump...  the pump cannot handle expanding vapor..

if the inlet check valve gets dirt.. it will not be able to pull a good enough vacuum to lift the fuel from the tank...   when the diaphragm drops.. the fuel will be pushed out the inlet check valve..

this also lowers the pressure inside the pumping chamber of the fuel pump.. causing heat to boil the fuel.. the pump cannot handle the expanding vapor..

if you have a fuel pump pressure tester...   one of those gauges that reads both vacuum and pressure.. you can use that to test the suction ability of the pump.. and the pumps ability to build pressure.. and to hold pressure with the hose to the return line pinched off lightly...

on chrysler models with return type systems.. i know this is not your issue.. but the restriction fails.. the pump output flows right back into the pump.. so the fuel pump can only build a pound or two of pressure. this is not enough to push through the tiny hole at the needle and seat at engine speeds more than an idle or 25MPH.. so the car sort of dies when you go faster...  i have fixed these with a small hose clamp on the return line. to close it down.. but NOT off..  until i could get a replacement sending unit for the tank where the restrictor was.