1974 GMC 4x4 carb issues

[SlackScotty]

I will check that out tonight. Good to remove it completely or should be replaced? Your thoughts

[motornut]

Originally Posted by SlackScotty

I will check that out tonight. Good to remove it completely or should be replaced? Your thoughts

i'd remove it,or just remove the butterfly
to remove it you need to change the studs,and lengten the pipe,or weld it open
I've seen holes drilled from pipe below/welded closed after ,coat hanger used poking up to make sure it's open,then tacked/welded,and plug the vac hose

[SlackScotty]

Thanks motornut

[SlackScotty]

Hi gang. Well, that unit is disconnected Motornut. took a look at it and its already done. Dont know if its open or closed though. Weather has been cold and white lately but today is sunny stuff so hopefully this evening. I'm working on the street so its sucky at best.

Picking up a fuel pump today and looking to put it in tonight. I understand there is a bit of a trick to this with inserting a bolt so a rod doesnt come down? Anybody got experience and suggestions for me before I make the attempt?

Thanks.

Will let you know if this does the trick or not.

[motornut]

good hope its open
i finger it,left hand, slide in the arm,up to fit, bolts
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[SlackScotty]

Well, fuel pump is in... no problemo. Easy peasy. Took it for a spin and it drove a hair better than before but I attribute that to it being much warmer out.

So... what is happening? When it automatically goes into 2nd gear it struggles and gag's along. Any kind of a hill which requires more fuel to climb it stalls the truck. Attempting to aggressively apply gas stalls it. I have to gently bring the rpm's up in order to avoid this. I also get stalling when coming to a stop on occasion also. At idle the engine is fantastic. Manually revving up the engine is pretty good as well... very little stutter whereas there was much more a few days back but it was much colder that day.

I notice the choke isn't working as the flap remains wide open at startup. I'm confident its all carb at this point in the diagnosis. Not sure however if its too much fuel or not enough when driving. At startup I tend to put too much in the carb and have occasionally seen flames come out the carb. I get no carb backfire when driving so thinking its not enough fuel.

SHould I pull the carb and rebuild (attempt it) or hit the wrecker and see if I can find one off another wreck and put it on and see what comes of it. They run about $30 at the pick and pull I hear.

[motornut]

Originally Posted by SlackScotty

Well, fuel pump is in... no problemo. Easy peasy. Took it for a spin and it drove a hair better than before but I attribute that to it being much warmer out.

So... what is happening? When it automatically goes into 2nd gear it struggles and gag's along. Any kind of a hill which requires more fuel to climb it stalls the truck. Attempting to aggressively apply gas stalls it. I have to gently bring the rpm's up in order to avoid this. I also get stalling when coming to a stop on occasion also. At idle the engine is fantastic. Manually revving up the engine is pretty good as well... very little stutter whereas there was much more a few days back but it was much colder that day.

I notice the choke isn't working as the flap remains wide open at startup. I'm confident its all carb at this point in the diagnosis. Not sure however if its too much fuel or not enough when driving. At startup I tend to put too much in the carb and have occasionally seen flames come out the carb. I get no carb backfire when driving so thinking its not enough fuel.

SHould I pull the carb and rebuild (attempt it) or hit the wrecker and see if I can find one off another wreck and put it on and see what comes of it. They run about $30 at the pick and pull I hear.

for 30 i would,even just to try it,used start at 50 here

[SlackScotty]

Well I found no carbs what so ever in the wrecking yards. Turns out... they are in high demand and last about 5 seconds when they enter the yard. People are refurbishing them and selling for mucho deneros. I decided for the hell of it I would put the other carb on it that came with the truck to begin with.

This carb is a quadrajet as well but with a few different hose connectors on it. I think I might need to locate a guide that tells me what connects to what as far as that carb is concerned.

When I got the truck, I drove it around the neighbourhood for about a half hour and it ran great. I went to the gas station, filled up the passenger side tank (the driver side is disconnected because the tank switching unit underneath is broken) and drove out of the station when it started to choke and gag and suddenly couldn't climb even the slightest incline. I got through the intersection, pulled over and it stalled. From that day on... nothing but headaches. The hose that comes out of the engine and through the firewall that has the hot water in it rests right on the metal fuel line and I wonder about vapor lock. Today I raised the hose off of it and still no luck. Rule that out. It's ironic that this carb and the one I pulled off both are reacting exactly the same way when I throttle the gas. At idle... I can throttle it and rev it and its smooth as silk. When in gear... a totally different story. Two carbs, slightly different models, behaving the same way?

This leads me then to think its a problem with the tank or the fuel regulator thing inside the tank. The guy I got the truck from told me that both tanks were missing gas caps and had rags in them when he first picked up the truck. He bought it to flip it so didn't know much about it. I wonder if the tanks are polluted somehow. Would this allow the truck to rev up at idle without issue but choke and gag under load when in gear? I cant imagine it but I know nothing. I have installed a new fuel pump so not that. Timing possibly? The timing effects the fuel pump right? The timing seems bang on though as it runs so nice at idle. Right now my thoughts say there is a plug of some kind in the tank restricting fuel delivery. At idle or when revved up its okay as the engine isnt demanding enough fuel to notice but when in gear and under load, the demand for the fuel is higher (please correct me on this if I'm off). Not enough fuel is getting to the carb and it chokes out I'm thinking. The truck also stalls when I slow down a great deal. This stalling when slowing... is that due to too much fuel in the carb or not enough?

Your thoughts gang? I appreciate it

[motornut]

Originally Posted by SlackScotty

Well I found no carbs what so ever in the wrecking yards. Turns out... they are in high demand and last about 5 seconds when they enter the yard. People are refurbishing them and selling for mucho deneros. I decided for the hell of it I would put the other carb on it that came with the truck to begin with.

This carb is a quadrajet as well but with a few different hose connectors on it. I think I might need to locate a guide that tells me what connects to what as far as that carb is concerned.

When I got the truck, I drove it around the neighbourhood for about a half hour and it ran great. I went to the gas station, filled up the passenger side tank (the driver side is disconnected because the tank switching unit underneath is broken) and drove out of the station when it started to choke and gag and suddenly couldn't climb even the slightest incline. I got through the intersection, pulled over and it stalled. From that day on... nothing but headaches. The hose that comes out of the engine and through the firewall that has the hot water in it rests right on the metal fuel line and I wonder about vapor lock. Today I raised the hose off of it and still no luck. Rule that out. It's ironic that this carb and the one I pulled off both are reacting exactly the same way when I throttle the gas. At idle... I can throttle it and rev it and its smooth as silk. When in gear... a totally different story. Two carbs, slightly different models, behaving the same way?

This leads me then to think its a problem with the tank or the fuel regulator thing inside the tank. The guy I got the truck from told me that both tanks were missing gas caps and had rags in them when he first picked up the truck. He bought it to flip it so didn't know much about it. I wonder if the tanks are polluted somehow. Would this allow the truck to rev up at idle without issue but choke and gag under load when in gear? I cant imagine it but I know nothing. I have installed a new fuel pump so not that. Timing possibly? The timing effects the fuel pump right? The timing seems bang on though as it runs so nice at idle. Right now my thoughts say there is a plug of some kind in the tank restricting fuel delivery. At idle or when revved up its okay as the engine isnt demanding enough fuel to notice but when in gear and under load, the demand for the fuel is higher (please correct me on this if I'm off). Not enough fuel is getting to the carb and it chokes out I'm thinking. The truck also stalls when I slow down a great deal. This stalling when slowing... is that due to too much fuel in the carb or not enough?

Your thoughts gang? I appreciate it

how bad do the tanks look to come off,to clean and check
being able to evap with no "cap" dosn't help, the gas degrades fast enough these days
and you never know, maybe somebody dumped a "can of old gas....in" ,
to clean the can out,or get it running

[SlackScotty]

Success. Sort of. I disconnected the fuel line at the tank and at the pump and used a can of air to blow the line through. Never seen anything come out but must have worked because after I connected it all up.... running. Not fantastic but running. Still a bit tough to start now and then but the electronic choke is currently disconnected and wired open. Need to work on that now. It still stalls when slowing down at times so thinking the idle is down a bit too much. More tweaking to do. Thanks for your help gang and I will be in touch with more problems to solve I'm sure. This truck is a big fixer upper.

Cheers

[geezer#99]

You've been flogging a dead horse Scotty! Changing carbs, new fuel pump, plugs etc and all you need is a timing light and set your timing first.
It's always been that way!
Timing first, carb second.
Get a light and learn how to use it!!

[Corts60]

I agree with geezer. Also, you said you had no problems until you filled up? Ever think to drain your tank and put fresh gas in it? Sounds like you got a bad batch.

Basic troubleshooting will tell you to always look at what was last done to the engine before the symptoms started.
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