fuel help needed

T-bone71

T-bone71

Well-Known Member
Joined
Jan 4, 2007
Location
Conover
I went to start my new rig w/ my new 358 chevy motor, i put an Edelbrock AVS offroad carb on it until i can save for fuel injection. so here's the delima. It idles great, BUT off idle it dies, sometimes it will spit fuel back out of the carb when it dies. I have already gone back and adjusted the hyd. valves and double checked for vacumme leaks, i've also set the timing about 15 degrees at idle. I'm running out of ideas, it has a new fuel pump on it. Tommorrow i plan to check fuel pressure, the fuel filter is full, and hasn't run out yet. I'm running out of ideas. Anyone out there have any ideas, It is a new carb so i guess i could check float level, to make sure it wasn't messed up in shipping or assembly. What do ya'll think?
 
Are the squirters workin when ya open the throttle?

Can ya VERY GENTLY advance the throttle or "peddle the throttle" and keep it runnin?
 
Squirters i'm not sure, i'll check that tomorrow. No, i can't play with the throttle to keep it running off idle.
 
are you sure you arent a tooth off?
Spitting back through the carb screams timing issue to me....
 
If timing was an issue, why does it run so smooth at idle? It'll idle all day long just as smooth as can be. It only spits back after it dies.
 
just another thing to think about.

Sounds like a fuel starve problem. They will often spit back when they die because there wasnt enuff charge to spin the motor one more revolution to over come the last full charged cylinder, so it reverses and fires back thru the carb. Or doesnt fire at all and the reversion causes the cylinder to empty itself up thru the intake valve.

With this in mind, it could be anything that is causing a real weak "pop" in the combustion cycle and lets the engine "back up". This could be;
Insufficient squirter to add the needed fuel from the initial vacuum drop of throttle opening.
Too much fuel from the squirts causing a too rich charge...wont "pop".
Lack of coil saturation...takes more spark to fire a more lean or rich charge associated with initial throttle opening
Timing just enuff of that it idles well but as soon as the fuel charge becomes larger...more volatile... it reverses

Fuel, ignition and timing. Thats all there is!
 
Ok tonite, i pulled the carb to check the floats, i disassembled the carb to find that the floats were off but not that far. So i reset them, and reassembled the carb and put it back on. I also put a fuel pressure gauge on it to find it pumping ( out of a stock pump) 8-9psi between the inline fuel filter and the carb. I know fuel pressure is a potential issue. So then i decide to double check my timing , i pulled the cap and checked the rotor position at TDC, double checked my firirng order and wire routing. It is still doing the same thing won't run off idle and spits back after it shuts off. So my conclusion is timing is correct, firing order is correct, plenty of fuel, squirter are working, floats heights and drop are correct. I also made another ground strap from the frame to motor to ensure a good ign. ground. Anything else anyone can think of?
 
Wow! Hmmmm...:confused:

Make sure coil is good. At this point, dont assume. No vacuum leaks?

Got another carb to slap on it for a test? Me still thinks it could be fuel delivery. Blocked passage...something weird like that.

Can ya idle it stupid way up with the idle adjust screw? This will pretty well start opening the butterflies so the main circuit starts to feed? See what it does?

Scott
 
I changed the carb tonite, no change same thing, double checked the voltage at the dist( just to make sure there wasn't something funky going on), pulled the suction side of the fuel pump off and put it in a can of gas to eliminate the original fuel lines, no change. The spark plugs are wet fouled, which tells me fuel starvation is not the problem. Anymore ideas? I'm going to try to get with a racing engine builder tommorrow to see if he has any ideas? Thanks again guys.
 
Hmmm...two carbs...wet plugs...she sound like she be doin the opposite, eh?! Dumpin fuel? Or not firing once ya crack the throttle. Whats the Vacuum or mechanical advance doin in the distributor?


By all means let us know what it ends up being! Now ya really got me scratchin my head!
 
Wait....


"NEW" Chevy 358?

Give us some details.
Namely, is it a stroker or just an overbore.
who did the machine work?
what was done to the heads?

Next Im gonna ask you to do a comp. test....

then I may get where I am going....
 
Chevy 358-- 350 bored .040, JE ultralite flat top pistons, Lunati 6" rods, GM steel crank, Comp Hydraulic flat tappet cam (436\454 lift i think), new World Product's 67cc 2.02/1.60 valve heads - box stock, GMPP dual plane intake, Performance Dist hei, Summit Racing shorty headers, Off the shelf box stock Napa mech fuel pump. The bottom end of the motor is one of my left over limited late model motors Built by Exact Engines in West Palm Beach FL. where i used to live. It was only used maybe 100 laps. When i sold the car i kept the motor it has been on the engine stand about 2 years. I freshend it up with bearings, oil pump, new cam and heads(lower compression, much less radical cam). Compression check and vacumme test will be done tonite. It's way more motor than i'll ever need ( and probably break more stuff), but i'm a horse power freak.
 
Compression test (all plugs removed,and throttle plates w.o.t.)
#1 155-160 #2 150
#3 155-160 #4 155
#5 155 #6 150
#7 155 #8 155
vacuum 13 in hg (at idle, what little it will idle the plugs are wet fouled)
my cam specs are 449./456. lift
256/268 duration
Hydraulic flat tappet cam
 
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