Engine Bogging - The 1947 - Present Chevrolet & GMC Truck Message Board Network

chevyc1068 · 10-10-2006, 06:28 PM

I got a '68 c-10 with a 307 in it. The only problem is when you step on the accelerater it will bog down and sometimes dies, only if you barely press on it will it rev up but any amount of acceleration will bog it. This is all just sitting out of gear not driving. Although it does the same when driving. Now the funny thing is with the choke on it will run perfectly. Even when it warms up to normal temp it is exactly the same. I put a new accelerater pump in and replaced the carb gaskets along with cleaning the whole carb out. Put in new plugs the other were worn out and black. Put in a new condensor, have new points just have not got there yet. The plug wires don't look like they would be a problem. I have tried tuning it but all it has is two mixture screws but maybe I just have not tuned it quite right yet. I have a new coil for it (again not got there yet).

Please any help on what to replace or what to test or what might be wrong would be very appreciated.

bryanw1968 · 10-10-2006, 06:33 PM

If it runs fine with the choke on you're way too lean. Using the air fuel mixture screws tune for highest vacuum. You should be able to get it pretty close by ear if you don't have a vacuum gauge.

What kind of carburetor is it?

Good luck,
B

70rs/ss · 10-10-2006, 06:37 PM

vacum leak, look around the carb base, use carb cleaner with it running, spray it around the base and if it revs or dies, you found your leak. Not an idle setting issue if it just started, and the running with the choke on is the tell tale sign, cause the leak is allowing too much air, the choke then adds a ton of fuel which is why it runs OK with the choke on. Start by checking the carb bolts for tightness, then follow the carb cleaner steps.

bryanw1968 · 10-10-2006, 06:41 PM

Good point. It does sound like a vacuum leak since it just started. I got thrown by the "I just rebuilt it part".

chevyc1068 · 10-10-2006, 07:43 PM

It is a Rochester 2g with manual choke.

I have noticed that there is a bit of liquid around one of the bolts on the intake manifold, but i haven't got around to checking the torque of that bolt yet. Do you think that could be the problem?

Thanks for the replys keep them coming!!!

Oh I forgot to mention that this pickup has been sitting in the shed for three of four years and I am now trying to restore it so it will drive. so its not like it " just started ".

PanelDeland · 10-10-2006, 08:05 PM

Could be a manifold leak since you have the puddle on the manifold bolt.Maybe coolant to the cyl. or just air into the intake.

**Boog** · 10-10-2006, 09:08 PM

If this truck has power brakes pull the end of the vacumn hose to the booster off and plug it. The brake booster diaphram may have a small hole in it leaking your vacumn or the hose itself may be cracked. See if it makes any difference with it plugged.

chevyc1068 · 10-10-2006, 09:19 PM

It doesn't have power brakes, but good idea.

chevyc1068 · 10-11-2006, 10:27 PM

Can you tell me where some common vacuum leaks are located?

?o you think it is ignition timing or something advanced, or can i take that off the list of probable causes?

Werewolf · 10-12-2006, 07:10 AM

It really does sound like the truck's running way too lean. A hot truck, choked, should start killing itself in short order. If it were an external leak, and if you had a decent exhaust (not loud as hell under the hood) you should be able to just get an ear near the carb and hear the typical sucking noise.

Not to offend, but do you have experience rebuilding carbs? Did you use a good rebuild kit? Did you make sure everything was good and clean before putting it all back together?

I had a problem once where I was changing jets out on a Rochester 2bbl like yours and I didn't want to buy the whole rebuild kit, so I just dabbed a bit of gasket maker around the float bowl. Some got into the bowl, and clogged one of the jets, giving me this same exact problem.

chevyc1068 · 10-12-2006, 06:19 PM

No actually I don't really have any experience in carb rebuilding. This is my first project. But yes I made sure everything was cleaned out real good. The carb rebuild kit I used was from the LMC catalog so I don't know what quality it is. the manifold gasket didn't really look like it had any metal in it, but maybe it was just covered up. I tried tightening the manifold bolt but that didn't help. I keep forgeting though to adjust the micxture screws so I will try that.

Werewolf · 10-12-2006, 07:03 PM

I don't think the mixture screws are responsible. It sounds like you've got a pretty good vacuum leak or lack of gasoline going on. Did you replace the big thick gasket that runs between the carb and manifold? Did you replace the accelerator pump? Did you remember to put the spring under the accelerator pump back in?

What was the truck doing beforehand to make you rebuild the carb? If it's not the carb, it could be the fuel pump, fuel filter, etcetera.

chevyc1068 · 10-12-2006, 10:36 PM

Yes I replaced the gasket between the manifold. Yes I replaced the accelerator pump and put the spring back under it. I don't think that it is the fuel pump or related because remember it runs fine with the choke on. This pickup previously was a repair truck, one we took to the field when something broke down. Then it was put back in the shed and wasn't used for three or four years. I looked for a vacuum leak in some places like around the base of the carb and on some manifold bolts using carb cleaner to spray around with but noticed nothing. I don't know of much else to do except keep looking for vacuum leaks. What do you think?

Solver · 10-12-2006, 10:54 PM

Just a shot but you may have put the accelerator pump lever in the wrong hole as there are usually two holes . Try switching it to the other hole. It changes the amount of gas shot in on accel

chevyc1068 · 10-12-2006, 11:05 PM

Good thought I'll take a look at it tomorrow.

Jerry Jones · 10-12-2006, 11:17 PM

I agree ...By the way welcome to the board... you got pics of your rig???

chevyc1068 · 10-15-2006, 06:30 PM

Turns out there is only one hole for the accelerator. I tried turning the screws to make it richer but that didn't work. After about 5 turns out the idle wasn't as good and I really didn't see any improvment at all in the acceleration. I really don't know what is wrong. It does have five year old gas in it but I didn't see that as being any of a problem since it would accelerate fine on choke.

Does anyone have anymore suggestions as to what would be wrong with it. Or something I could test to see if it is a vacuum leak or something.

**Boog** · 10-15-2006, 07:55 PM

Quote:

Originally Posted by chevyc1068

I really don't know what is wrong with it. It does have five year old gas in it but I didn't see that as being any of a problem since it would accelerate fine on choke.

5 yr old gas? Drain and put in fresh gas and start tuning all over.

texascowboy593 · 10-15-2006, 08:07 PM

Quote:

Originally Posted by Boog

5 yr old gas? Drain and put in fresh gas and start tuning all over.

That gas could be a major culprit. It's a wonder it starts at all...

Werewolf · 10-15-2006, 08:30 PM

And you might want to change the fuel filter again, too, if you haven't already.

chevyc1068 · 10-15-2006, 08:52 PM

Okay I will try that. But how does that explain that it will run good with the choke on?

Werewolf · 10-16-2006, 05:54 AM

If the gas isn't burning as well as it should, it may take more gas (or less air) to really get the engine to fire properly. In addition, old gas will cause a varnish to build up inside the tank and in the lines. If this varnish is thick, it could block the flow of gasoline, clog up a fuel filter, and maybe even goof up a fuel pump. I don't know about all of that, I've never had that type of bad experience with old gas at all. I know a friend who's been dealing with the remnants of 7 year old gas in his tank; for a while he would have to change his fuel filter every 2k miles or so until the new gas finally got the old crap out.

Basically it sounds like what you've got is an engine running way too lean. Only so much can cause that, these aren't very complex vehicles. A lean condition is caused by too much air, or too little gas. You've got one or the other. If the gas is old, only some of it might burn in the mix. I don't know how likely it is, but it makes a certain amount of sense.

chevyc1068 · 10-16-2006, 12:15 PM

True that does make sense. I will have to try that sometime when I have some time.

If it has caused build up in the lines or even a little bit in the carburetor do you think that if I stuck a bottle of the STP carburetor cleaner in the tank that it would flush out the lines or just the carburetor, or do you think that kind of stuff actually works? I've heard some people say that it really does work, but others have said its just a gimmick to make some money.

chevyc1068 · 10-20-2006, 08:02 PM

Ok I put some new gas in it and it seemed to help to some degree. i changed the timing on it to about 8 degrees BTC from 14 but i don't know if that is correct. It still doesn't run very well without choke. It does recover if you put it all the way to the floor, it used to just die. I also put new points in.

So what do you think I should do now?

chevyc1068 · 10-20-2006, 08:56 PM

I just remembered I want to know if the myth that one good backfire can kill a powervalve. Because I did'nt have one to replace it with when I rebuilt it, and through a buch of this testing I have had quite a few GOOD backfires. So maybe the powervalve is shot and thats my problem???
Also I didn't replace the jets.(LMC's rebuild kit didn't have much in it)

10-10-2006, 06:28 PM	#1
chevyc1068 Registered User Join Date: Oct 2006 Location: Murdock, Kansas Posts: 147	Engine Bogging I got a '68 c-10 with a 307 in it. The only problem is when you step on the accelerater it will bog down and sometimes dies, only if you barely press on it will it rev up but any amount of acceleration will bog it. This is all just sitting out of gear not driving. Although it does the same when driving. Now the funny thing is with the choke on it will run perfectly. Even when it warms up to normal temp it is exactly the same. I put a new accelerater pump in and replaced the carb gaskets along with cleaning the whole carb out. Put in new plugs the other were worn out and black. Put in a new condensor, have new points just have not got there yet. The plug wires don't look like they would be a problem. I have tried tuning it but all it has is two mixture screws but maybe I just have not tuned it quite right yet. I have a new coil for it (again not got there yet). Please any help on what to replace or what to test or what might be wrong would be very appreciated.

10-10-2006, 06:33 PM	#2
bryanw1968 Senior Member Join Date: Jul 2006 Location: Leander, Texas Posts: 850	Re: Engine Bogging If it runs fine with the choke on you're way too lean. Using the air fuel mixture screws tune for highest vacuum. You should be able to get it pretty close by ear if you don't have a vacuum gauge. What kind of carburetor is it? Good luck, B

10-10-2006, 06:37 PM	#3
70rs/ss Registered User Join Date: Dec 2004 Location: Northern AZ Posts: 7,271	Re: Engine Bogging vacum leak, look around the carb base, use carb cleaner with it running, spray it around the base and if it revs or dies, you found your leak. Not an idle setting issue if it just started, and the running with the choke on is the tell tale sign, cause the leak is allowing too much air, the choke then adds a ton of fuel which is why it runs OK with the choke on. Start by checking the carb bolts for tightness, then follow the carb cleaner steps.

10-10-2006, 06:41 PM	#4
bryanw1968 Senior Member Join Date: Jul 2006 Location: Leander, Texas Posts: 850	Re: Engine Bogging Good point. It does sound like a vacuum leak since it just started. I got thrown by the "I just rebuilt it part".

10-10-2006, 07:43 PM	#5
chevyc1068 Registered User Join Date: Oct 2006 Location: Murdock, Kansas Posts: 147	Re: Engine Bogging It is a Rochester 2g with manual choke. I have noticed that there is a bit of liquid around one of the bolts on the intake manifold, but i haven't got around to checking the torque of that bolt yet. Do you think that could be the problem? Thanks for the replys keep them coming!!! Oh I forgot to mention that this pickup has been sitting in the shed for three of four years and I am now trying to restore it so it will drive. so its not like it " just started ". Last edited by chevyc1068; 10-10-2006 at 07:46 PM.

10-10-2006, 08:05 PM	#6
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,993	Re: Engine Bogging Could be a manifold leak since you have the puddle on the manifold bolt.Maybe coolant to the cyl. or just air into the intake. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

10-10-2006, 09:08 PM	#7
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,262	Re: Engine Bogging If this truck has power brakes pull the end of the vacumn hose to the booster off and plug it. The brake booster diaphram may have a small hole in it leaking your vacumn or the hose itself may be cracked. See if it makes any difference with it plugged. __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross Last edited by Boog; 10-10-2006 at 09:09 PM.

10-10-2006, 09:19 PM	#8
chevyc1068 Registered User Join Date: Oct 2006 Location: Murdock, Kansas Posts: 147	Re: Engine Bogging It doesn't have power brakes, but good idea.

10-11-2006, 10:27 PM	#9
chevyc1068 Registered User Join Date: Oct 2006 Location: Murdock, Kansas Posts: 147	Re: Engine Bogging Can you tell me where some common vacuum leaks are located? ?o you think it is ignition timing or something advanced, or can i take that off the list of probable causes?

10-12-2006, 07:10 AM	#10
Werewolf Woof? Join Date: Jun 2005 Location: Raleigh, NC Posts: 276	Re: Engine Bogging It really does sound like the truck's running way too lean. A hot truck, choked, should start killing itself in short order. If it were an external leak, and if you had a decent exhaust (not loud as hell under the hood) you should be able to just get an ear near the carb and hear the typical sucking noise. Not to offend, but do you have experience rebuilding carbs? Did you use a good rebuild kit? Did you make sure everything was good and clean before putting it all back together? I had a problem once where I was changing jets out on a Rochester 2bbl like yours and I didn't want to buy the whole rebuild kit, so I just dabbed a bit of gasket maker around the float bowl. Some got into the bowl, and clogged one of the jets, giving me this same exact problem. __________________ 1968 LWB CST BB 2004 Avalanche Z71 LT3. 2003 S-10 ZR2 (hers). 1997 Astro 1992 Caprice wagon, 500k stock miles. Nursing wounds after a bad wreck. 1997 Saturn - need gas mileage from something!

10-12-2006, 06:19 PM	#11
chevyc1068 Registered User Join Date: Oct 2006 Location: Murdock, Kansas Posts: 147	Re: Engine Bogging No actually I don't really have any experience in carb rebuilding. This is my first project. But yes I made sure everything was cleaned out real good. The carb rebuild kit I used was from the LMC catalog so I don't know what quality it is. the manifold gasket didn't really look like it had any metal in it, but maybe it was just covered up. I tried tightening the manifold bolt but that didn't help. I keep forgeting though to adjust the micxture screws so I will try that.

10-12-2006, 07:03 PM	#12
Werewolf Woof? Join Date: Jun 2005 Location: Raleigh, NC Posts: 276	Re: Engine Bogging I don't think the mixture screws are responsible. It sounds like you've got a pretty good vacuum leak or lack of gasoline going on. Did you replace the big thick gasket that runs between the carb and manifold? Did you replace the accelerator pump? Did you remember to put the spring under the accelerator pump back in? What was the truck doing beforehand to make you rebuild the carb? If it's not the carb, it could be the fuel pump, fuel filter, etcetera. __________________ 1968 LWB CST BB 2004 Avalanche Z71 LT3. 2003 S-10 ZR2 (hers). 1997 Astro 1992 Caprice wagon, 500k stock miles. Nursing wounds after a bad wreck. 1997 Saturn - need gas mileage from something! Last edited by Werewolf; 10-12-2006 at 07:04 PM.

10-12-2006, 10:36 PM	#13
chevyc1068 Registered User Join Date: Oct 2006 Location: Murdock, Kansas Posts: 147	Re: Engine Bogging Yes I replaced the gasket between the manifold. Yes I replaced the accelerator pump and put the spring back under it. I don't think that it is the fuel pump or related because remember it runs fine with the choke on. This pickup previously was a repair truck, one we took to the field when something broke down. Then it was put back in the shed and wasn't used for three or four years. I looked for a vacuum leak in some places like around the base of the carb and on some manifold bolts using carb cleaner to spray around with but noticed nothing. I don't know of much else to do except keep looking for vacuum leaks. What do you think? Last edited by chevyc1068; 10-12-2006 at 10:37 PM.

10-12-2006, 10:54 PM	#14
Solver Registered User Join Date: May 2000 Location: Storm Lake, Ia Posts: 1,449	Re: Engine Bogging Just a shot but you may have put the accelerator pump lever in the wrong hole as there are usually two holes . Try switching it to the other hole. It changes the amount of gas shot in on accel Attached Images __________________ 1972 Cheyenne Super 20 LWB-Blue 1972 Cheyenne Super 10 LWB-Black 1972 Cheyenne Super 10 LWB-Red 1972 Cheyenne Super 10 LWB-green 1972 GMC 4x4 LWB-White 1971 Cheyenne 10 LWB-Ochre 1971 Cheyenne 20 Longhorn-Copper 1971 Cheyenne 20 Longhorn-Black 1969 Custom 10 LWB-lt blue 1968 GMC 3/4 ton-green 1968 1/2 ton swb stepside-silver 1967 Chevrolet CST 10 LWB-green 1967 Chevrolet custom 20 LWB-Maroon

10-12-2006, 11:05 PM	#15
chevyc1068 Registered User Join Date: Oct 2006 Location: Murdock, Kansas Posts: 147	Re: Engine Bogging Good thought I'll take a look at it tomorrow.



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10-12-2006, 11:17 PM	#16
Jerry Jones Happy Camper Join Date: Feb 2006 Location: Northern California Posts: 8,408	Re: Engine Bogging I agree ...By the way welcome to the board... you got pics of your rig??? __________________ RIP El Jay! Love you brother! Last edited by Jerry Jones; 10-12-2006 at 11:18 PM.

10-15-2006, 06:30 PM	#17
chevyc1068 Registered User Join Date: Oct 2006 Location: Murdock, Kansas Posts: 147	Re: Engine Bogging Turns out there is only one hole for the accelerator. I tried turning the screws to make it richer but that didn't work. After about 5 turns out the idle wasn't as good and I really didn't see any improvment at all in the acceleration. I really don't know what is wrong. It does have five year old gas in it but I didn't see that as being any of a problem since it would accelerate fine on choke. Does anyone have anymore suggestions as to what would be wrong with it. Or something I could test to see if it is a vacuum leak or something.

10-15-2006, 08:30 PM	#20
Werewolf Woof? Join Date: Jun 2005 Location: Raleigh, NC Posts: 276	Re: Engine Bogging And you might want to change the fuel filter again, too, if you haven't already. __________________ 1968 LWB CST BB 2004 Avalanche Z71 LT3. 2003 S-10 ZR2 (hers). 1997 Astro 1992 Caprice wagon, 500k stock miles. Nursing wounds after a bad wreck. 1997 Saturn - need gas mileage from something!

10-15-2006, 08:52 PM	#21
chevyc1068 Registered User Join Date: Oct 2006 Location: Murdock, Kansas Posts: 147	Re: Engine Bogging Okay I will try that. But how does that explain that it will run good with the choke on?

10-16-2006, 05:54 AM	#22
Werewolf Woof? Join Date: Jun 2005 Location: Raleigh, NC Posts: 276	Re: Engine Bogging If the gas isn't burning as well as it should, it may take more gas (or less air) to really get the engine to fire properly. In addition, old gas will cause a varnish to build up inside the tank and in the lines. If this varnish is thick, it could block the flow of gasoline, clog up a fuel filter, and maybe even goof up a fuel pump. I don't know about all of that, I've never had that type of bad experience with old gas at all. I know a friend who's been dealing with the remnants of 7 year old gas in his tank; for a while he would have to change his fuel filter every 2k miles or so until the new gas finally got the old crap out. Basically it sounds like what you've got is an engine running way too lean. Only so much can cause that, these aren't very complex vehicles. A lean condition is caused by too much air, or too little gas. You've got one or the other. If the gas is old, only some of it might burn in the mix. I don't know how likely it is, but it makes a certain amount of sense. __________________ 1968 LWB CST BB 2004 Avalanche Z71 LT3. 2003 S-10 ZR2 (hers). 1997 Astro 1992 Caprice wagon, 500k stock miles. Nursing wounds after a bad wreck. 1997 Saturn - need gas mileage from something!

10-16-2006, 12:15 PM	#23
chevyc1068 Registered User Join Date: Oct 2006 Location: Murdock, Kansas Posts: 147	Re: Engine Bogging True that does make sense. I will have to try that sometime when I have some time. If it has caused build up in the lines or even a little bit in the carburetor do you think that if I stuck a bottle of the STP carburetor cleaner in the tank that it would flush out the lines or just the carburetor, or do you think that kind of stuff actually works? I've heard some people say that it really does work, but others have said its just a gimmick to make some money.

10-20-2006, 08:02 PM	#24
chevyc1068 Registered User Join Date: Oct 2006 Location: Murdock, Kansas Posts: 147	Re: Engine Bogging Ok I put some new gas in it and it seemed to help to some degree. i changed the timing on it to about 8 degrees BTC from 14 but i don't know if that is correct. It still doesn't run very well without choke. It does recover if you put it all the way to the floor, it used to just die. I also put new points in. So what do you think I should do now?

10-20-2006, 08:56 PM	#25
chevyc1068 Registered User Join Date: Oct 2006 Location: Murdock, Kansas Posts: 147	Re: Engine Bogging I just remembered I want to know if the myth that one good backfire can kill a powervalve. Because I did'nt have one to replace it with when I rebuilt it, and through a buch of this testing I have had quite a few GOOD backfires. So maybe the powervalve is shot and thats my problem??? Also I didn't replace the jets.(LMC's rebuild kit didn't have much in it)

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