First off...............Fuel sytems and electrical are not my thing.
My 76 Chevy K20 has been giving me problems over the past 2 years. The carb that was on it was rebuilt by my brother, and I do trust his work, but 2 yrs ago when it installed it, the truck would start up, run rough, backfire, and pump fuel outside of the carb, and as soon as you let off the gas it stalls out.
Last year, I didnt Fk with it...........just turned over the engine to keep everything lubed.
Today I swapped over the carb off my 67 K20............(which runs fine)...............over to the 76 K20................and the same FKIN problem over again.................runs rough, backfires, pumps out gas..........and as soon as you let off the gas it stalls out.
I dont get it.............all I can think off is that its gotta have something to do with the gas tank/fuel lines or sending unit?????
What do you guys think????
where is gas pumping out ffrom when you say its pumping gas out
to much fuel pressure, you need a regulator
need more info on your fuel system!!! start at the tank and tell us what you have and go to the carb.
how old is the mechanical fuel pump?
Quote from: 4x4xdodgeman on July 04, 2011, 11:04:54 AM
need more info on your fuel system!!! start at the tank and tell us what you have and go to the carb.
X2, if you have a electric fuel pump it is probably giving the carb too much fuel pressure and it need and adjustable fuel pressure regulator.
==hmmm Where does the backfire come from, intake or exhaust..? Sure sounds like too much fuel pressure since it does the same thing with 2 different carbs which Im assumin are quadrajets? ;D
Quote from: old school truck dude on July 04, 2011, 05:28:44 PM
==hmmm Where does the backfire come from, intake or exhaust..? Sure sounds like too much fuel pressure since it does the same thing with 2 different carbs which Im assumin are quadrajets? ;D
truck has a Q-jet on it now.........both carbs I 've used are Q-jets. As to the back fire........its hard for me to tell while sitting in the truck....trying to keep it running........but it sounds like its coming from the exhaust.
The current carb was leaking fuel out the left side (choke side) 1/2 way up, and the leaking fuel out by the excellorator pump..................but again......this carb was off of my 67 K20 and it ran fine on that truck.
Truck has a mechanical fuel pump on it, thats about 4yrs old.
Also, I've never heard of fuel pressure regulator on the carbed truck............since it never had one in the 6yrs I've owned it. I know the carb has set screws on the front of it to adjust fuel flow to the carb.....but I havent messed with those.
In 2007 I put a brand new gas tank in the truck, pretty sure the lines got hooked up properly
Have you tried takin the gas cap off? Maybe not vented properly and buildin up pressure in this heat.. Is there a filter between the pump and the carb? You cant rely on the little one in the inlet fitting of the carb because it has a spring behind it so that if it gets clogged completely it gets pushed off its seat and allows dirty fuel into the carb. You should be using a large inline aftermarket filter and toss the little filter and spring in the weeds. If this truck has been settin up, chances are the fuel is sour and/gelled and may have rust in it. That would cause immediate floodin no matter what carb you put on there. I would clean out the bowl and accelerator pump of the original carb, pump some fresh fuel into a gas can or whatever through the pump. You can hook your suction line up to a boat tank or somethin real clean, hook the carb back up usin the new inline filter, and see how that works. Might have to flush or replace the tank. If its backfiring out the exhaust, that usually means too much fuel, its gettin raw fuel into the exhaust.. Could also mean the valve timing is off, check the cam/crank/distributor position maybe the chain slipped.
Question: Did it ever run right after you put the new fuel tank in it..? Also, why was the carb rebuilt?
Quote from: old school truck dude on July 04, 2011, 10:33:30 PM
Question: Did it ever run right after you put the new fuel tank in it..? Also, why was the carb rebuilt?
Truck didnt run right after the new tank was swapped in. carb was rebuilt thinking that ( IT )was the cause of the problem
I am wondering if its the gas tank, because that tank........while it was brand new and I only paid 25.00 for it.......was for a 87 model year chevy truck which is fuel injected.................now I wonder if that would pose any problem??..............but I fail to see why it would because the tanks look identicle to 73-86 tanks.
it really sounds to me like your getting to much fuel pressure matt, is the fuel pump in the tank getting power? if it is cut it and that'll solve your problems... i had an issure like this with an old car of mine, and cutting the fuel pressure fixed it. for a carb all ya need is 5 to 9 psi
Quote from: Jjay78 on July 05, 2011, 01:01:56 AM
it really sounds to me like your getting to much fuel pressure matt, is the fuel pump in the tank getting power? if it is cut it and that'll solve your problems... i had an issure like this with an old car of mine, and cutting the fuel pressure fixed it. for a carb all ya need is 5 to 9 psi
no fuel pump in tank......truck is a 76......mechanical fuel pump on motor. The GAS TANK I installed in it........brand new.....is for a 87 chevy......and I am wondering if that doesnt have to do with my problems.............but if it does......I am failing to see how.
what year sending unit did you put in the tank?
Quote from: 4x4xdodgeman on July 05, 2011, 01:28:16 AM
what year sending unit did you put in the tank?
I resused the sending unit from the old tank that I took out.
does your fuel pump have the excess fuel return line on it?
Quote from: Jjay78 on July 05, 2011, 10:49:35 AM
does your fuel pump have the excess fuel return line on it?
Now theres a real good question! If it dont, it sure needs one! and it needs to be hooked up correctly, some folks plug them off. This is startin to sound like its got to do with the lines.. Might want to drop the tank back down, pull the sending unit, and see exactly which line is which - one of them is excess fuel return, one is the pickup, one should vent to somethin - I wonder if that year had a charcoal canister..? ;D
i've seen some pumps that only have the feed and the output to carb lines on them, and nothing but trouble with them, i think it's an 84 trans am that is the easiest look up to get the pump with the return line, if your new pump doesn't,
Quote from: old school truck dude on July 06, 2011, 01:06:05 AM
Quote from: Jjay78 on July 05, 2011, 10:49:35 AM
does your fuel pump have the excess fuel return line on it?
Now theres a real good question! If it dont, it sure needs one! and it needs to be hooked up correctly, some folks plug them off. This is startin to sound like its got to do with the lines.. Might want to drop the tank back down, pull the sending unit, and see exactly which line is which - one of them is excess fuel return, one is the pickup, one should vent to somethin - I wonder if that year had a charcoal canister..? ;D
Good question, if I remember right, the old fuel pump had a 3 line fitting because the truck had dual tanks..........when I swapped in the new tank and did away with the right side tank (because it had a leak in it) My brother told me to get a new fuel pump with a 2 line fitting on it because the truck only has 1 tank now.......................so what jay and old school are asking might be adding up to somthing. Also I am quite certain that truck has a charcoal canister......most older chevys had those.
that's probly your problem bud, the pump can't send the excess fuel back to the tank, it can only go to the carb, get one with the return line and ya should be all good
http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_Mechanical-Fuel-Pump-Airtex_5404134-P_52_R (http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_Mechanical-Fuel-Pump-Airtex_5404134-P_52_R)|GRPFUE2AMS_774958191____
Quote from: Jjay78 on July 06, 2011, 04:55:26 AM
that's probly your problem bud, the pump can't send the excess fuel back to the tank, it can only go to the carb, get one with the return line and ya should be all good
x2 and make sure you get the lines figured out, should be fine
Quote from: old school truck dude on July 07, 2011, 02:05:29 AM
Quote from: Jjay78 on July 06, 2011, 04:55:26 AM
that's probly your problem bud, the pump can't send the excess fuel back to the tank, it can only go to the carb, get one with the return line and ya should be all good
x2 and make sure you get the lines figured out, should be fine
Checked the fuel pump when I was at my woods today...........it does have 3 fuel outlets on it......so thats not the cause.
But I didnt check to see if the lines are hooked up how they should be, obviously the tank to pump line is hooked up since the carb is getting gas, but as to the other 2 lines, not sure on those yet.
The other 2 lines are probably close to the same size, easy enough to get crossed up and cause major problems.. If the charcoal canister is real heavy, its full, saturated, and will need to be drained somehow or replaced.. Hopin we are on the right track with this for ya ;D
Quote from: old school truck dude on July 10, 2011, 03:17:56 PM
The other 2 lines are probably close to the same size, easy enough to get crossed up and cause major problems.. If the charcoal canister is real heavy, its full, saturated, and will need to be drained somehow or replaced.. Hopin we are on the right track with this for ya ;D
Shitt, I never even checked the charcoal canister, forgot all about that, is there a line running up to it?
Your vent line off the fuel tank should go straight to it. If the canister is full/saturated it makes it be as though the line is plugged off, and youll build pressure in the tank. The line off the canister should go to the carb/intake somewhere if I recall correctly. I got nothin to look at around here to jog my memory ;D
Quote from: old school truck dude on July 14, 2011, 01:18:30 PM
Your vent line off the fuel tank should go straight to it. If the canister is full/saturated it makes it be as though the line is plugged off, and youll build pressure in the tank. The line off the canister should go to the carb/intake somewhere if I recall correctly. I got nothin to look at around here to jog my memory ;D
fuel cap vent should eliminate tank pressure.
after running the motor for a while.. open the cap.. do you hear air? if so your vent is plugged.
fuel pump "could" be the issue however most single line pumps have a relief valve in them to prevent
forced fuel to the carb..
Tank is only a canister to hold fuel.. should'nt be the issue unless your vent is plugged.
quick redneck test, disconnect the fuel line @ the carb and put it in a beer bottle..disconnect the + wire @ distributor (no start)
spin the motor over 3-5 turns.. how much fuel do you have in the bottle.. should be 1/2 - 3/4 full.
fuel coming out of the carb is a bad needle/seat, incorrect float adj, bad gaskets (vacume leak) excess pressure.
all of these will cause the symtoms you describe. backfire (lean condition from vacume leak) stalling (flooding or vacume)
I wouldn't worry about the charcole cannister.. alot like the air pumps installed years ago.. quick fix for emissions.