Need help with 85 Sierra running rough

[muddslut]

Having some trouble with a truck I came across last week. I’m gonna try to make it short and sweet with what I know so far. So, the trucks a ‘85 Sierra w/ the 350 paired with the 4 speed manual. It has an edelbrock 600 carb manual choke. And a micro electric fuel pump pushing 4-7 psi. (I have put this carb on another motor to verify there’s no issues there, I’ve also reset the float level and adjusted the fuel mixture screwed to 2 1/2 turns out.) The truck typically starts right up and will idle great. If you try to rev it up real quick it wants to cut out and die and or backfire out of the carb. If you go to drive it down the road it will run good for about a block or two then it starts cutting out and falling on its face typically bogging down to the point it dies. It almost always starts back up instantly but as soon as you give it gas whatsoever it dies. You can let it set 5-10 minutes and it will once again idle good, rev up decent if you ease into it, but if you punch the throttle or go down the road it has the same issue of stalling out/ backfiring out of the carb. Apart from what I’ve previously said I’ve also changed the wires and plugs (gapped all to .035), replaced the edelbrock micro electric fuel pump 2-3.5 psi with a mr. gasket 4-7 psi micro electric fuel pump. I’ve set the timing at an idle and all seems good there. If I rev it up with the timing light on the harmonic balancer the line moves I’d say about a quarter inch from what I believe you would say is “TDC”(also note I could not find a factory mark on harmonic balancer, just a sharpie mark from a PO so hoping that’s where it needs to be). I’ve moved the accelerator pump linkage to all three holes and made little to no difference. I’m assuming this most likely is a timing issue, but I’m not exactly sure. Someone has told me to check if the distributor is 180° off as that’s one thing I haven’t checked, but would it really run good at all at an idle or anything if it was 180° off? I feel like I’ve checked all that I know it could be other than the distributor being off 180°, so I’m now here looking to see if anyone can help point me in the right direction with this. The truck is currently sitting in my buddy’s grandpas yard and am trying to get it running half ass enough to get it back home. I’ve been racking my brain the last 4 days with it. Should be a picture of the truck attached, as you can probably tell it’s a b**** to get up and work on.

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[muddslut]

I should’ve also said I tried to do a fuel pressure test. The fuel pump is mounted on the passenger fender well. I spliced the line between the fuel pump and the carb and put the pressure tester there. I fired the truck up and got no reading at an idle or while revving it up there was no change. I rented the $150 fuel pressure test kit from autozone since I didn’t have one so I dont believe something to have been wrong with it. I also read somewhere that said those little electric fuel pumps are “pushers” not “pullers” and should be mounted within 2 feet of the tank, this couldn’t possibly be an issue could it?

 

[ali_c20]

Welcome From Austria!

The e fuel pumps are pushers, they should be mounted as close to the tank as possible and best below the level of the fuel pickup. This way gravity feedsthe fuel to the pump. Best would be an in tank pump if you want to stay electric or a mechanical fuel pump.
Here's some useful info for inline fuel pump mounting:

https://www.crankshaftcoalition.com/wiki/Mounting_an_electric_fuel_pump

@distributor 180° off: It would not idle smooth if it would run and backfire out of carb and exhaust.

I would check:

How much fuel is coming out of the pump.

Collapsing fuel hoses.

Vacuum leaks at carb, intake, hoses.

I would not trust the PO, make your own timing mark or check if the existing one is right. Than check your timing again, at idle and total.

 

[Shorty81]

Welcome from Ohio

 

[Snoots]

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That's for buying ANYTHING by Mr. Gasket.
You've got to get the timing dialed in first.

 

[muddslut]

@ali_c20 - thanks for the response! I’ll have to try mounting it inside the frame rail closer to the tank and see what that does. As far as the fuel pressure test, shouldn’t I have gotten a reading? Or could that have been a result of the pump location?

Another thing, how would I go about making sure that mark on the harmonic balancer is right? I’ve looked and rubbed by hand all around it and I feel no etched marks and don’t see any other sort of marking beside the sharpie one.

Does anyone have some sort of vacuum diagram or something along those lines? The only one I really see is the vacuum advance that runs to the carb.

 

[muddslut]

@Snoots No go on the mr gasket stuff? The only reason I got it was because I read that edelbrock carbs wanted 4-6 fuel psi ran to them and the edelbrock fuel pump it had on it to start with was only 2-3.5 psi so I went with that mr gasket 4-7 psi.

@Shorty81 Thanks mate

 

[WFO]

Those symptoms sound like it's starving for fuel.

I'm not an Edelbrock carb fan, but when I bought my truck it had a brand new one on it, and it works just fine with the mechanical fuel pump.

Welcome from the Texas Panhandle.

 

[Bextreme04]

@Snoots No go on the mr gasket stuff? The only reason I got it was because I read that edelbrock carbs wanted 4-6 fuel psi ran to them and the edelbrock fuel pump it had on it to start with was only 2-3.5 psi so I went with that mr gasket 4-7 psi.

@Shorty81 Thanks mate

Realistically the edelbrock wants anything less than about 5psi. Any more than that can push the fuel past the needle. You want volume more than pressure and as long as the edelbrock can maintain enough volume at that 3.5psi, it will be great. If you had the edelbrock mechanical, I'd put that back on and hook it up and see if your problem goes away. 0 PSi reading with that POS Mr. Gasket micro electric pump tells me that it has either quit on you, or you have a restriction clogging the fuel strainer in the tank. Those Mr. Gasket pumps are known to be complete garbage, especially if exposed to heat or placed anywhere that isn't gravity fed by the fuel tank. Unfortunately, there isnt really any place on a square that meets those requirement... even mounted on the frame rail right next to the tank it still needs to PULL the fuel up through the sending unit for the first prime and every time if you dont have a perfectly sealed fuel system because it will lose it's prime. There a few members here that have had recurring failures of the Mr. Gasket pump, usually in a week or less after installation.

 

[muddslut]

@WFO Ive been looking to a Holley but I put this edelbrock on on my buddies camaro with a 355 and it ran perfect, no revving issues, backfires, nothing, granted the car has no trans so we couldn’t really put a load on it, but it revved out a 100x better than on my truck. The truck has what looks like a newer mechanical fuel pump on it still, but the copper/brass lines (whichever they are) that are suppose to run to the carb are cut, so I haven’t fooled with it yet. Maybe that’s where I need to start now.

@Bextreme04 Another reason I should’ve previously stated for taking the edelbrock mini electric pump out was because there was a couple times I pulled the line that feeds from the pump to the carb off and flipped the pump on and fuel was just barely dripping out, I pulled it off once and blew through it, put it back on and it was squirting like it should and it did it once again a couple days later so I said screw it. But then also I got to reading and thought maybe it wasn’t pushing enough psi so I put the mr gasket one on. But like you said either way it still has to pull the fuel up out of the tank and all the way to the front of the truck so maybe I’m getting just enough to get the truck to idle, and then when I put it under a load it starves itself of fuel cause it’s not getting enough pressure?

 

[muddslut]

@Bextreme04 The truck also has a new fuel tank, but if they left the old strainer and stuff in there, maybe it could possibly be clogged up enough it can’t pull enough fuel out when put under a load? Or is that hoping for the best? Lol

 

[Bextreme04]

@Bextreme04 The truck also has a new fuel tank, but if they left the old strainer and stuff in there, maybe it could possibly be clogged up enough it can’t pull enough fuel out when put under a load? Or is that hoping for the best? Lol

I'd say if you blew through it and it started pumping better, you have a clog in the system somewhere. I thought you meant an edelbrock mechanical pump. I would recommend hooking the electric pump to a separate fuel tank with no strainer(like a 1 gallon red can) and see if it pumps good. If it still starves for fuel, the pump is probably the issue and you should try hooking the mechanical pump back up. Chances are the mechanical is going to have too much pressure for the edelbrock and you will get a rich condition. You can get a lower pressure pump on rockauto or you can put shims between the pump and block to lower the pressure a bit. Sometimes the edelbrock doesn't have that issue though, so I would suggest trying it first before you try to fix an issue you might not have.

 

[Snoots]

@Bextreme04 The truck also has a new fuel tank, but if they left the old strainer and stuff in there, maybe it could possibly be clogged up enough it can’t pull enough fuel out when put under a load? Or is that hoping for the best? Lol

My last fuel problem. Clogged strainer.

BTW: I presume you have an HEI distributor? You plugs should be gapped at .045, no less or more.
Less and they will foul, more and you will burn up the ignition module.

You need a piston stop to find TDC. Remove the #1 plug, put your finger over the hole and have a friend bump the starter until your finger gets blown out. Then you are very close.

There is a more professional way to do this (find exact TDC) but I'm keeping it basic.

 

[muddslut]

@Bextreme04 Ill try that first as soon as I get up to Indianapolis to the truck. If I did hook the mechanical pump back up, would I be okay to run some 3/8ths hose from where it’s cut off on the metal line near the alternator up to the carb? I’m not exactly sure what it’s suppose to look like since a PO’s done been in here hacking it up.

@Snoots Dropping the tank and checking that strainer is for sure on the list now. I believe it to be an Hei distributor just by the looks. While changing the wires and messing with the timing I didn’t notice any marking saying hei or nothing buts it’s all red and appears that’s what it is. Should I pull the plugs and regap them then? Almost all the ones I pulled out of it were gapped .035-.038. If that were the case then maybe my ignition module could be bad also if that’s the way they’ve been for however long?

 

[Bextreme04]

@Bextreme04 Ill try that first as soon as I get up to Indianapolis to the truck. If I did hook the mechanical pump back up, would I be okay to run some 3/8ths hose from where it’s cut off on the metal line near the alternator up to the carb? I’m not exactly sure what it’s suppose to look like since a PO’s done been in here hacking it up.

@Snoots Dropping the tank and checking that strainer is for sure on the list now. I believe it to be an Hei distributor just by the looks. While changing the wires and messing with the timing I didn’t notice any marking saying hei or nothing buts it’s all red and appears that’s what it is. Should I pull the plugs and regap them then? Almost all the ones I pulled out of it were gapped .035-.038. If that were the case then maybe my ignition module could be bad also if that’s the way they’ve been for however long?

You can't run the hard line all the way to the carb because you dint have a factory quadrajet. Thats probably why its cut. Yes, you can just run a 3/8 hose from the hard line to the carb with good clamps.

.035 is the factory spec for the plugs. .045 runs better with the HEI. Anything after ~1975 is pretty much guaranteed to be HEI. Try pulling from the separate tank tied up in the engine bay first, if it runs great, then you need to check the strainer and fuel pump location. If it doesn't fix the issue, reconnect the mechanical pump and see if that fixes it.