327 randomly runs bad

['63MurderTruck]

My son's truck is 'randomly' running bad...

It will be running along just fine, then out of no where start running horrible, then... out of nowhere it starts running fine again.

Also, the 'idle' is all over the place. One second it will be at 1500, then drop to 1100, then down to 800 where it is SUPPOSED to be, hit the gas again, and back up to 1500 RPM. Weird.

I thought it was a FUEL issue, so... I've put on a new carb Edelbrock 1406, new fuel filter, and new fuel pump(mechanical), and it still does the EXACT same thing. It has a full tank of 100% gas from the same station that I always get it.

Now I'm thinking maybe the HEI distributor, which is also BRAND NEW. Any ideas what else could be causing this?

This is basically a stock 327 with an aluminum intake, Edelbrock carb, and headers.

[65truckowner]

Sounds like a vacuum leak

['63MurderTruck]

Originally Posted by 65truckowner

Sounds like a vacuum leak

Could that be completely 'random'?

For example: You can be driving for several MINUTES and it runs great, then all of a sudden, it runs like crap... it might even die. Then I get it started and it'll run fine again, 'for a while'

[chevylookin]

Sounds like a potentially failing fuel pump or stuck or partially sticking accelerator pump in the carby. Take em off, inspect, clean or replace. The damn inlet valves on these reproduction fuel pumps can wiggle loose inside the pump housing and the fuel line from the pump to carb can lose pressure.

['63MurderTruck]

Originally Posted by chevylookin

Sounds like a potentially failing fuel pump or stuck or partially sticking accelerator pump in the carby. Take em off, inspect, clean or replace. The damn inlet valves on these reproduction fuel pumps can wiggle loose inside the pump housing and the fuel line from the pump to carb can lose pressure.

I've REPLACED both the Carb and Fuel pump, (both are BRAND NEW). It's doing the EXACT same thing as it did with the old ones.

[chevylookin]

Well, like 65truckowner said, you might have an intermittent vacuum leak or stick accelerator linkage. If the HEI is concerning you, take out the coil and do the ohms test on it. Do you have 12 complete volts to the dizzy? if all else fails, check your engine grounds too. Cant think of much else.

[nail pounder]

Originally Posted by 65truckowner

Sounds like a vacuum leak

X2. Take off the air filter, cup both hands over the carburetor, does it idle up? If so, you have a vacuum leak somewhere. I use a can of starter fluid and while the engine is running methodically start spraying the possible sources. Intake gasket, carb to intake etc. When the motor revs up you've found a leak.

[blown240]

Electric Fuel Pump? IS it mounted solid? I had a 51 where the fuel pump was only mounted with 1 bolt. It would "rock" sometimes and cut the fuel supply....

[64shortbox]

A friend of mine had a work van that at times it would feel like it was running out of gas. He did all the usual, fuel filter, fuel pump etc., etc. He even took it to two Chevy dealers and they couldn't find the problem. Turns out the the fuel pump eccentric was worn so bad it would barely run the fuel pump. The van would run fine until you started climbing a hill or hit the freeway at a decent speed. He replaced the mechanical fuel pump with an electric and all was well.

['63MurderTruck]

I did as you suggested... no vacuum leak.

Originally Posted by nail pounder

X2. Take off the air filter, cup both hands over the carburetor, does it idle up? If so, you have a vacuum leak somewhere. I use a can of starter fluid and while the engine is running methodically start spraying the possible sources. Intake gasket, carb to intake etc. When the motor revs up you've found a leak.

['63MurderTruck]

I just put a BRAND NEW mechanical fuel pump on it today, and yes, it's mounted good.

Originally Posted by blown240

Electric Fuel Pump? IS it mounted solid? I had a 51 where the fuel pump was only mounted with 1 bolt. It would "rock" sometimes and cut the fuel supply....

['63MurderTruck]

I just put a brand new mechanical fuel pump on it today. If all else fails, I'll go to an electric fuel pump.

I'm gonna put a different BRAND NEW HEI distributor that I already have on hand on it Wednesday, then go from there.

Originally Posted by 64shortbox

A friend of mine had a work van that at times it would feel like it was running out of gas. He did all the usual, fuel filter, fuel pump etc., etc. He even took it to two Chevy dealers and they couldn't find the problem. Turns out the the fuel pump eccentric was worn so bad it would barely run the fuel pump. The van would run fine until you started climbing a hill or hit the freeway at a decent speed. He replaced the mechanical fuel pump with an electric and all was well.

[nail pounder]

Cool. Quick question, you said the HEI is new, did you just convert it from the old points type? If so did you remove the resistance wire and run a new 12v to the HEI?

['63MurderTruck]

Yes. And, the current HEI distributor has been on it for about a month and the truck has run great until now. I'm thinking/hoping the coil on the HEI is bad, otherwise, i have absolutely no clue what it could be.

Originally Posted by nail pounder

Cool. Quick question, you said the HEI is new, did you just convert it from the old points type? If so did you remove the resistance wire and run a new 12v to the HEI?

[nail pounder]

Originally Posted by '63MurderTruck

Yes. And, the current HEI distributor has been on it for about a month and the truck has run great until now. I'm thinking/hoping the coil on the HEI is bad, otherwise, i have absolutely no clue what it could be.

Ok cool. I'm just trying to rule out all the things that don't cost $ to check (I always do cheap first). You might be right about the bad coil or just a bad connection, I had an HEI that when I plugged in the pig tail it pushed the (hot/tack) prongs up. The other thing that I was thinking was maybe the sock on the pick up tube in your fuel tank has some crud in it, or possibly your tank. Do you still have the tank behind the seat and easy to access?

['63MurderTruck]

It has a BRAND NEW fuel tank under the bed.

The connection thing is a possibility. I'll double check that.

Originally Posted by nail pounder

Ok cool. I'm just trying to rule out all the things that don't cost $ to check (I always do cheap first). You might be right about the bad coil or just a bad connection, I had an HEI that when I plugged in the pig tail it pushed the (hot/tack) prongs up. The other thing that I was thinking was maybe the sock on the pick up tube in your fuel tank has some crud in it, or possibly your tank. Do you still have the tank behind the seat and easy to access?

[nail pounder]

Yep, I'm out of ideas. Sounds like you narrowed it down to spark though.

[chevylookin]

The problem is that your idle rpm's are going crazy. The idle rpms go up, not down and dont stay stable which is evidence of a vacuum leak but you have ruled that out. Did you gap the spark plugs to about .50? The edelbrock 1406 is an incredibly easy carb to adjust out of the box but make sure that youre using the correct vacuum port on it. There is the timed vacuum port and the manifold one. I cant remember which one you use on your application as I get them confused but I think its the manifold vacuum. This WILL screw up your rpms and idle if you dont use the right one. Also, do you still have the exhuast heat riser on your 327? Make sure that thing isnt gummed up and or rusted shut. It will screw things up big time too if it isnt working properly

[TJ's Chevy]

valves

['63MurderTruck]

It has HEADERS. No heat riser.

Yes, spark plugs are gapped.

Yes, correct vacuum port.

As I mentioned earlier... the truck has ran perfectly for about a month. The 'random' running bad just started 2 days ago, out of no where.

Originally Posted by chevylookin

The problem is that your idle rpm's are going crazy. The idle rpms go up, not down and dont stay stable which is evidence of a vacuum leak but you have ruled that out. Did you gap the spark plugs to about .50? The edelbrock 1406 is an incredibly easy carb to adjust out of the box but make sure that youre using the correct vacuum port on it. There is the timed vacuum port and the manifold one. I cant remember which one you use on your application as I get them confused but I think its the manifold vacuum. This WILL screw up your rpms and idle if you dont use the right one. Also, do you still have the exhuast heat riser on your 327? Make sure that thing isnt gummed up and or rusted shut. It will screw things up big time too if it isnt working properly

['63MurderTruck]

Valves as in they aren't adjusted properly, or as in there is something WRONG with them? And, would this cause it to run bad 'randomly'? It seems to me like if were valves that it would ALWAYS run poorly, not perfectly 'at times'.

Originally Posted by TJ's Chevy

valves

[TJ's Chevy]

Not true, the solid lifter valves in my 305 v6 were adjusted to tight on 2 cylinders. The engine ran fine for awhile, but one day it lost power and wouldn't idle right. Found two cylinders with valves to tight. After adjusting the engine ran just fine. Hydraulics can be the same way. A valve adjustment probably wouldn't hurt if you haven't checked them yet.

[chevylookin]

Well, I guess do a compression test. Check for a bent pushrod and install that electric fuel pump and see what happens. The cam gear for the fuel pump could have worn down enough but to not contact the fuel pump but long shot. Sure your something didnt happen to it like the someone shoving a tennis ball up the tail pipe or pour sugar in the gas tank or something. I think we covered everything here. Sorry your having so many problems amigo. Hopefully it is something simple, but hard to see. If its got boobs or wheels its gonna give ya problems..

['63MurderTruck]

Thanks, I will adjust the valves, can't hurt.

Originally Posted by TJ's Chevy

Not true, the solid lifter valves in my 305 v6 were adjusted to tight on 2 cylinders. The engine ran fine for awhile, but one day it lost power and wouldn't idle right. Found two cylinders with valves to tight. After adjusting the engine ran just fine. Hydraulics can be the same way. A valve adjustment probably wouldn't hurt if you haven't checked them yet.

[geezer#99]

Valves won't do that intermitent thing.
Leave them alone for now.
No electric fuel pumps either unless you install a fuel reg set at 5 psi. In fact you might need a reg anyway.

Try this instead.
Initial timing at 14 degrees, hook vac advance to manifold vac port and turn down your idle to 700 rpm or less.

Sounds like you're just on the edge of kicking in the mechanical advance since the rpm goes up and down.