1975 chevy c-10 running like poo

[ronald_durst]

so my 1975 c-10 is in the second shop of the day. I got a feeling its gonna be passed around like a cheap ho. The vacuum hoses were put back to where they go at least according to the first shop mechanic who also said that he wont work on old cars. The next guy i brought it to said he'd look at it tomorrow. It idles fine but give it gas and the engine goes down. I put my hand over the carb intake and it runs great at least in park anyway. I changed my plugs and wires and also the air filter. I checked the fuel filter connected to the carb and that looked fine. It takes about a minute to get to 40mph and the more i gas it the slower it goes.

Its got a straight six.

There have been mods done to the engine or maybe even a new engine. One difference i believe is the dist coil is outside the distrubuter instead of inside it. The trans was converted from a three on the column to an automatic.

Any help would be greatly appreciated. Thanks

[60Falcon351C]

Sounds like it might be a distributor problem?? Had a problem like that on my budyd;s mustang. The tab for the vacuum on the advance broke off and it was bogging down when it was revved. Check all of the vaccum line going to the distributor. Or the carb float may be gunked up with some dirt or something

[Blue Bowtie]

I'm not very technically versed, so you'll have to talk down to my level. What is this "poo" of which you speak? I've heard of misfire, stumbling, choking, stalling, and leaning, but "poo" is beyond my level of training and experience.

Sounds like you're running lean, or at least lean at throttle tip-in. If you have to feather the throttle to increase RPM, it probably is NOT the accelerator pump, since that's only good for about a 1-1/2 second shot of fuel at best. After that, it's all on the transfer ports and main fuel circuit in the carb.

I'm guessing it's the 250-inch six, unless it's a 3/4 ton, in which case it might be the 292 six. Either way, there's a good chance it has the 1GC carburetor. Verify a clean fuel filter and good fuel supply from the pump. Check the float level, and make sure the main jet is clean and clear.

[ronald_durst]

yeah sorry about the poo. DIdnt wanna curse on here. Anyway, im actually pretty much ignorant to most of the technical terms
just mentioned above and thats why im looking for advice. The motor bogs down as it accelerates. It is the half ton. I checked the fuel filter but it looked clean. I'll wait to hear from the shop tomorrow and go from there.


im lookin at an invoice from july 10 2003 for $3000 that included a carb assembly and a remanufactured engine. It says the odometer in at 111496. Although you cant see the first one the odometer now says (1)33xxx. Another invoice from 12-01-06 for valve spring or seal remove and replace.odometer reading 133399. So it looks like this engine doesnt have to many miles on it. Could it be that it sat up for too long and now its gunked up? What kind of things happen when an engine sits for a while?

[Blue Bowtie]

I'd suspect the carburetor may have accumulated some sediment. With any old, stale gasoline which may have been left in the tank, the risk of pumping garbage into the carb is higher. The original fuel filter should have been a sintered bronze element mounted at the inlet seat of the carb. It will filter until it is clogged, then go to bypass and allow anything into the fuel bowl.

The fuel pickup sock filter in the tank is also suspect on a vehicle this old, but if the shop performs a fuel pump flow test, they should be able to determine if that is a problem.

If the truck is currently in the shop, expect them to open and clean the carb, and possibly perform a half-rebuild in the process.

[ronald_durst]

Thanks. Actually i changed the fuel filter out and i talked to three different shops and none of them would even mess with it. I also talked to the shop who put the motor in and he said they have been dealing with this problem on this particular truck for a long time and he thinks its electrical. I dont know about that though. Anyway...i checked the flow of gas and it seemed alright but i need to do a volume check also for the gas pump. Would that effect the way it runs if the correct amount of volume isnt coming from the pump?

[Blue Bowtie]

If the fuel pump cannot deliver about one pint in fifteen seconds, it is suspect. The pump should also be able to maintain 2-5 PSI.

The issue seems to be off-idle, however, and presuming the fuel bowl has adequate level to idle the engine, it should have adequate level to accelerate the engine, at least briefly, without stumbling. That's why I suspect a problem in the carb and not the pump.

An electrical problem is possible, but since you can eventually get the vehicle to 40 MPH, and the ignition system presumably provides enough spark energy to make that happen, it should not be falling off immediately, at throttle tip-in. The one possibility there would be weak secondary voltage, allowing the spark to be blown out by compression.

[bobss396]

If you put your hand over the carb and it smooths out, you have a vacuum leak, the problem is to find it.

Spray around the carb base to see if it smooths out, also those 6-cylinder carb sections loosen up with age, so you might be into a carb rebuild, which is easy to do. Check all vacuum hoses, make sure you have no open ports on the manifold or carb. You can clamp off (gently) vacuum hoses to rule out a vacuum advance. A '75 vintage truck should have a minimum of pollution devices on it. Also see if you can find an old Chiltons or Motors manual that shows the vacuum hose routing.

My money is on the carb sections being loose or the gasket under the carb.

Bob

[ronald_durst]

Yeah i talked to another mechanic today who said the motor needed to be rebuilt.

I did spray around the base of the carb and you can tell its breathing it the carb cleaner in. I think im gonnna change out that gasket and maybe all vaccuum hoses jus to be safe. I actually lost my job because this truck couldnt get me there in time. Sucks alot.