i'm stumped.... truck is bogging down like a cheap gas FORD on a tank of DIESEL!!!!!

[jewels.]

ok, i'm stumped!

both Blue_71 and I are stumped....
i dug out my truck for the summer months, and started her up....
did an oil change, and tightened the bolts on the exhaust/donut gasket.....
drove her a few times with no problems....

and then.... problem....
in any gear (its a 3-on-the-tree), the truck will bog down if you give it constant gas....
at idle, it appears to run ok - just fine....
i can take off out of the yard in first or reverse - no problem....
if you get it on the road, and if you go past a particular RPM, it just acts as if it were choked with not enough gas.... bogs down seriously so badly that its undrivable....
you can hear it sucking serious air thru the carb.... it wont kill itself, but it wont go anywhere either.... if i got on a hill, i would probably have to give in...

thought maybe it was out of gas.... just barely made it to the gas station, filled her up, but the problem still exists....

on the way back, discovered that if you pump on the gas pedal quickly, it gets the power it originally was lacking, and the problem disappears for the small second or two when you pump the pedal... but then the problem continues to exist for a constant gas pedal pressure.... so if you pump the pedal, its jerky from the pumping of the gas, but it acts like it runs fine....

so, here is what i've replaced (these are now brand new parts on the truck)....
0. added full tank of gas to truck (93 octane, for good measure)
1. put on new fuel pump
2. put in new fuel filter
3. fully rebuilt 2bbl carb
4. replaced the HEI module with a new one

my truck has a 350 small block, stock cam, stock crank, stock bore, stock pistons, 2bbl carb, HEI ignition, ramshorns manifolds, dual exhaust, no air, no PS, no PB, 3-speed stock tranny, new clutch, stock rearend (3.73), a recently (last fall) replaced drive shaft, tailshaft yoke....

has new oil, new tranny fluid (as of last fall), new antifreeze, and even new washer fluid in a non-functioning washer system.....

any ideas? whats wrong?
here are some we are contemplating, but still not sure whats up....
A. a filter/sock inside the fuel tank - perhaps part of the sending unit?
B. replacing the bottom plate of the carb, which contains the mixture screws?
C. the tail-shaft transmission yoke sticking? (it was not a perfect install... lets leave it at that)....
D. an engine problem?!?!?

the key thing here is the gas..... if you pump the gas, it gets better... but if you increase the gas slowly and constantly, it wont go....

HELP!!!!!!
any reponses are greatly appreciated!
thanks in advance!
ciao!
jewels.

[jhwkns]

Look for vacuum leaks, and make sure your choke isn't sticking,,, g/l

[72 CustomCamper]

My 86 was doing the same thing but I fixed it with a new fuel filter. How do the rubber fuel lines look?


Chuck

[cdowns]

i'd go for the fuel sock in the tank just pull the sending unit out and have a look , you should get a new o-ring when you reinstall it=they're(o-ring0 are available at any good parts store

[724wdcopper]

pulling the sock from the tank might be a good idea. could have gotten some bad juju in there somehow. the other thing is when you rebuilt the carb, i'm sure you replaced the accelerator pump? when my PU was doing this, a fuel filter change fixed it. i WAS using a $50 moroso, hi-zoot gold anodized unit for 3-4 years w/ no problem all of a sudden, it goes hensh!t on me. took it out of the system and replaced the stock Q-jet filter, no more problems. this was after swapping 3 carbs, the dist, and fuel pump(electric). i'm not very quick on easky things i blew thru the filter and it seemed ok

good luck jewels! you too Bloo!

if it were in storage for a while, varnished gas could be the problem. i know you put a fresh tank in, but did you check how well the fuel pump is pumping?

[jhow66]

Sat all winter? Check the exhaust for a blockage-i.e. mouse nest, dead mouse (or a big rat!) Does it try to spit back thru carb when you step on it?

[mr402]

While you were in the dizzy did you check the centrifugal advance? The HEI’s advance mechanisms have a tendency to get stuck. Feels like you lost over 100 HP when they do that.

[Green Machine]

Hmm - could leaking exhaust donut be caused by plugged exhaust ?? If you have access to a vacumn gauge, put a long hose on it and put it cab when you go for a test drive. If your vacumn gets real low, then your exhaust is plugged. I have seen double wall pipe colapse on the inside while the outer wall looks ok. My 2 cents---

[fine69]

Its in the fuel system. I say Accelerator pump. Prob needs a fuel filter too. The one in the carb. Not an inline filter prob. But i cant remember if it has one of those or not.

[68LSS1]

Originally Posted by fine69

Its in the fuel system. I say Accelerator pump. Prob needs a fuel filter too. The one in the carb. Not an inline filter prob. But i cant remember if it has one of those or not.

What he said. Accelerator pump. Probably less than $10 at NAPA.

[Mudder]

I'm voting accelerator pump..........

[Huck]

Jewels & Josh---yo guys, Get a vacuum gauge and check to see what it is telling you. At idle you should be getting about 16-18. (Check out GMC Pauls web site for tips on vac gauge use and timing). If you have a vac leak, you may have decent idle but little to no power due to the lack of proper advance and improper air/gas mix. There are lots of possibilities so you have to kind of eliminate each one but use tools like a timing light---is your timing correct, does it advance when you rev? Is the motor missing or just not taking gas. Could have a ruptured vac advance diaphram. Will it rev at idle or does it bog down out of gear too? How are you spark plug wires---if weak, they will allow spark to jump to ground ---try running it at night in the dark--does it give a light show from spark jumping to ground? My first bet is vacuum leak, then vac advance non function, then accelerator pump, in that order.
Perhaps we should have a contest---guess the problem and win a prize!!!hehehhe

[meathead95]

Originally Posted by fine69

Its in the fuel system. I say Accelerator pump. Prob needs a fuel filter too. The one in the carb. Not an inline filter prob. But i cant remember if it has one of those or not.

i agree totally

[biglou55]

Check all rubber hoses in the fuel line. I have had them collapse when you give it gas. they suck closed when the pump starts sucking harder.they deteriorate on the inside and a flap of inner hose will act like a one way valve. after thirty years + anything is possible. I have seen it happen on just three year gas line hose. just my 02 . and fairly cheap.I would change them first then move on to other things if it doesn,t cure it.

[jewels.]

Originally Posted by jhwkns

Look for vacuum leaks, and make sure your choke isn't sticking,,, g/l

there are no vacuum leaks
it has a manual choke, which is not the problem here

Originally Posted by 72 CustomCamper

My 86 was doing the same thing but I fixed it with a new fuel filter. How do the rubber fuel lines look?

i put a new fuel filter on it
the rubber line at the engine was replaced last august...
the fuel line btwn the fuel pump and the tank might be the problem?

Originally Posted by cdowns

i'd go for the fuel sock in the tank

we are seriously considering the fuel sock as a culprit

Originally Posted by 724wdcopper

when you rebuilt the carb, i'm sure you replaced the accelerator pump? when my PU was doing this, a fuel filter change fixed it.did you check how well the fuel pump is pumping?

yes, the accelerator pump is new
the fuel filter is brand new as well
yes, checked how well the fuel pump is pumping --- the truck runs great at idle and low RPMs in every gear... its only when you give it CONSTANT gas that is just sucks air and doesnt go anywhere...

Originally Posted by jhow66

Sat all winter? Check the exhaust for a blockage-i.e. mouse nest, dead mouse (or a big rat!) Does it try to spit back thru carb when you step on it?

an excellent idea! we didnt even consider blocked exhaust...
no it does NOT spit back at all....
it doesnt not miss,
it does not pop, or spit,
it just simply acts over choked...
it never dies, it just idles fine, but it just goes no where when you give it gas...
its like it cannot get above a certain RPM - like it cannot get the gas...

Originally Posted by mr402

While you were in the dizzy did you check the centrifugal advance? The HEI’s advance mechanisms have a tendency to get stuck. Feels like you lost over 100 HP when they do that.

could you tell me more about what you mean? i checked the inner workings of the HEI when we replaced the module, and it all looked functioning (of course, thats my best guess).. the roter looked a little carboned up, so i did some lite cleaning... and those metal swinging tabs in the center underneath the rotor looked good.... are those what you are referring to? how would i check centrifugal advance? are you refering to the timing? i believe the truck is setup very well timing-wise... most of the board members at one of the truck meets helped me set the timing on the HEI module when we installed it... it ran great then... but i will re-check timing....

Originally Posted by Green Machine

Hmm - could leaking exhaust donut be caused by plugged exhaust ?? If you have access to a vacumn gauge, put a long hose on it and put it cab when you go for a test drive. If your vacumn gets real low, then your exhaust is plugged. I have seen double wall pipe colapse on the inside while the outer wall looks ok.

this is the best suggestion yet! i need to get a vacuum gauge... i wonder if Blue_71 (Josh) has one? i might test this theory out tonight if i can... again, block exhaust may be a culprit as well...

Originally Posted by fine69

Its in the fuel system. I say Accelerator pump. Prob needs a fuel filter too. The one in the carb. Not an inline filter prob. But i cant remember if it has one of those or not.

mike, you need to learn to read... :P (j/k) i just rebuilt the carb monday (again), which includes replacing the accelerator pump, and i also stated that i replaced the fuel filter too (on monday)... any other ideas?

Originally Posted by Touch_of_Madness

Its really hard to do any diagnostics on line like this but it does sound like exhaust blockage of some type.

i agree - its difficult, but we are looking for ideas... we have stumped all three mechanics here, and we are looking for which direction to head next... even Josh's grampa (Odell) who has been a mechanic for more than 40 years is totally stumped....

Originally Posted by Touch_of_Madness

Is there a ballance pipe?

no

Originally Posted by Touch_of_Madness

Does it sound like one side of the engine lags while the other tries to pull through when it bogs down?

no, all running of the engine is equal side to side... no pulling, no missing, no obvious problem other than it just feels massively choked and bogged down

Originally Posted by Touch_of_Madness

Idaho68 and I also agreed it could be the heatriser valve if still equipped.

there isnt one

Originally Posted by Touch_of_Madness

Other options could be anything from the parking brake,

the parking brake is functioning properly, and is totally disengaged... this is not a problem with the braking system... it is something that occurs with the fuel and the air and the engine

Originally Posted by Touch_of_Madness

vacuum and or mechanical advance,

the timing is correct, but would that little vacuum-advance piece on the HEI cause this? if i unplugged the vacuum advance, would that tell me if the vacuum advance is the problem?

Originally Posted by Touch_of_Madness

open vaccum line,

there are no open vacuum lines

Originally Posted by Touch_of_Madness

junk carb gasket,

there is a brand new carb gasket on it

Originally Posted by Touch_of_Madness

to low gear lube in the trans and or rear end

fluid levels are all good

Originally Posted by Touch_of_Madness

On the same idea line its always a good idea to take an old pair of socks and put them over the tail pipes when ya store the truck at the end of the year

i absolutely LOVE this idea, and i am going to do it next time... because i am worried about the exhaust here
BTW, Touch_of_Madness, those were all some great suggestions... you have us both talking about all kinds of things we might not have considered before! are you a mechanic? he he (j/k)

Originally Posted by 68LSS1

What he said. Accelerator pump. Probably less than $10 at NAPA.

no

Originally Posted by Mudder67

I'm voting accelerator pump..........

NO

Originally Posted by Meathead95

i agree totally

NO!!!! Its not the accelerator pump - its new!!!

Originally Posted by Huck

Jewels & Josh---yo guys, Get a vacuum gauge and check to see what it is telling you. At idle you should be getting about 16-18. (Check out GMC Pauls web site for tips on vac gauge use and timing).

i think this will be our next step - test vacuum and timing....

Originally Posted by Huck

If you have a vac leak, you may have decent idle but little to no power due to the lack of proper advance and improper air/gas mix.

yeah - we've been talking about improper gas/air mix... thats why we were speculating the baseplate of the carb working incorrectly... but i'm leaning more towards vacuum problems at the moment... perhaps that little module on the outside of the HEI - the cone-shaped lookin thing...

Originally Posted by Huck

There are lots of possibilities so you have to kind of eliminate each one but use tools like a timing light---is your timing correct, does it advance when you rev?

we are trying to eliminate things, we just needed more ideas to eliminate (this this post)....
i will re-check the timing tonight.... including advance....

Originally Posted by Huck

Is the motor missing or just not taking gas.

it does not miss... not at all... never....

Originally Posted by Huck

Could have a ruptured vac advance diaphram. Will it rev at idle or does it bog down out of gear too?

i have not been able to get it to bog down out of gear... which seems strange to me... when i rev it up out of gear, it acts normal.... but i will retest tonight to double-check.....

Originally Posted by Huck

How are you spark plug wires---if weak, they will allow spark to jump to ground ---try running it at night in the dark--does it give a light show from spark jumping to ground?

spark plug wires were replaced brand new in august of 2003 (less than two years old)... i doubt those are the problem... we did drive it late last night in the dark, and i noticed no unusual sparking going on....
[QUOTE=Huck]My first bet is vacuum leak, then vac advance non function, then accelerator pump, in that order. [/HUCK]
vacuum leak has been ruled out
accelerator pump has been TOTALLY ruled out :ROTF: :LMAO: :LOL:
but i am agreeing with vac advance..

Originally Posted by Huck

Perhaps we should have a contest---guess the problem and win a prize!!!hehehhe

NOW WE'RE TALKING!
i wonder if josh and i can come up with a good prize for the winner - let me discuss it with him!

Originally Posted by biglou55

Check all rubber hoses in the fuel line. I have had them collapse when you give it gas. they suck closed when the pump starts sucking harder.they deteriorate on the inside and a flap of inner hose will act like a one way valve. after thirty years + anything is possible. I have seen it happen on just three year gas line hose. just my 02 . and fairly cheap.I would change them first then move on to other things if it doesn,t cure it.

this is an excellent idea - i remember reading an old post about crazy rubber hoses a few years ago - the one way flap could be the culprit, and its an easy, cheap replacement..... we will check all rubber hoses too


ok - so here is my "to-do" list for this evening:

1. check vacuum advance (either remove the cone-shaped piece from the system by plugging off the vacuum ports, or use a vacuum gauge to test it while driving)
2. check for bogging when the truck is out of gear at high RPMs
3. check timing & advance settings with the timing light
4. replace all rubber fuel lines (just in case) (esp since its cheap)

if all that doesnt work, then we'll start down these roads:
5. pull the bench seat and check the fuel sock
6. check for blocked exhaust - stick wires into all pipes to make sure there are no mice or paper blockages... then perhaps look for a donor set of exhaust to bolt-on temporarily to make sure the mufflers arent clogged...

altho - i am really doubting the blocked exhaust thing for one reason --- i have dual exhaust from each manifold all the way to the back bumper --- surely both sides of the exhaust cannot become clogged at the same time, right? the engine doesnt do this on ONE side or the other - it does it equally - would this make any difference?

ok - thats enough for now - looks like i have my work cut out for me tonight.... i'll keep yall updated
ciao!
jewels.

[jfrank133]

[ (Check out GMC Pauls web site for tips on vac gauge use and timing). If you have a vac leak, you may have decent idle but little to no power due to the lack of proper advance and improper air/gas mix.

would you have a link to his site. Thanks

[fine69]

I didnt understand that you rebuilt the carb AGAIN. I knew you rebuilt it last year. Why would you do it again? If the Accelerator pump bore wasnt totally smooth you could still have the same problem.

[70GMC_BOB]

it seems the problem is still happening so I vote put in a vote for the winshield washer bottle!! good luck!

[smokekiki]

To check the vac advance,if You don't have a vac pump,take the cap and rotor off,and while one of You looks at the inside of the dist the other one suck on the hose that is connected to the vac can.If it moves,and is not leaking it should be alright.If it doesn't move,either the can is ruptured(You would hear it or would not have any resistance when sucking on the hose)or the advance plate is rusted or stuck.It doesn't take a lot of sucking to get it to move.The truck I bought,that sat for 6months,had the advance unit stuck.

[HuggerCST]

I have to say you've done an excellent job describing the symtoms. As a mechanic, I've heard a bunch of 'em, most of which don't help me at all. I'm going to say either clogged exhaust,(even just one side), or fuel starvation, such as the fuel sock, or fuel line. The vacuum gauge should help, or you can just loosen your exhaust at the donut and test drive it. Good luck & let us know what you find.

[67ChevyRedneck]

When you do the vacuum test, hook up the gage and as said, you should somewhere between around 18-21 depending on altitude. The needle should not move. Give it a strong shot of gas, pull the throttle wide open, and your needle should smoothly move to somewhere around 26-30 and then drop back to idle vacuum. My thought (other than the fuel sock, which could be your culprit) is a bad coil. Mine went bad. Killed my HEI. Truck had the same symtoms as yours. Hope I'm not reposting info, there was tons to read.

[farmaller]

A few years ago I had the same sort of problem with my truck, after changing this and replacing that we found out it was the fuel pump.
I put on a clear fuel filter and was watching the gas flow through it and noticed the filter would fill up and then get almost empty and the engine would start stalling.
Another thing to think about is the gas tank vent along with all the above suggestions including the washer bottle

[Huck]

Jewel's & Josh, I would attack as follows:
1- With a timing light and the engine ideling, rev engine and see if the timing changes big time---you should have centrifical and then vacuum advance moving your timing.
2- If not much advance, pull dist cap and rotor and look at the two half moon weights with springs--make sure they are free and the plate they are attached to, moves to turn the rotor. Then as suggested before, use some vacuum---either a pump or suck on the end of the vacuum advance hose from the carb--to see if the dist plate moves as the diaphram within the canister for the vac advance moves the dist plate to change timing.
3 - Next I would pull the fuel sending unit from the gas tank to check the sock. While there, I would also pull the line off the fuel pump and using some air pressure, blow out the fuel line and watch to see what comes out--not to close!!
4 - then loosen the manifold to exhaust pipe connection to see if you have too much back pressure from nests within the muffelers.
Question---when you changed the dist to HEI, did you use heavier wire from your fuse box bringing 12V to the dist??? You need to step up aoubt 2 gauges of wire to get adequate juice to the HEI dist verse the point dist.
Let us know what you find tonight~~~~~~

[jewels.]

Originally Posted by Huck

Question---when you changed the dist to HEI, did you use heavier wire from your fuse box bringing 12V to the dist??? You need to step up aoubt 2 gauges of wire to get adequate juice to the HEI dist verse the point dist.

yes, its a monstrous size wire that the guys picked out for me at the board meet, you can be sure of that.... and andy left a whole load of it extra, underneath my dash

i'll let you know what we find out
jewels.

[68gmcdually]

I had the same problem with a newer truck, changed nearly everything and finally out of desperation cut the catalytic convertor out and presto ran like a new truck, replaced the cat with a new one and haven't had a moment's trouble since. So needless to say my vote is with the exhaust system.