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Vapor lock?

nad

nad

1/2 ton status
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Festus, MO
So as some of you know, I just had a carbureted 350 put in my 87 Jimmy, and I'm having some problems with the carb because it needs a rebuild, but the truck is still drivable. But after I drive it for awhile, like 30 minutes to an hour, you can smell something like it's burning and the truck starts running like crap. If I leave it sit in park, it will stay running, but idle rough. If I put it in gear, it will run really rough, and eventually die.

In order to start the truck, I have to pretty much floor the gas, and once it's started I have to keep pumping the gas to keep it from dying. The guy that helped me put the motor in seems to think it's possibly vapor lock or a bad fuel pump. Any other suggestions, or does one of these sound about right?
 
If it's vapor *lock*, you'd get no fuel. Doesn't sound like the case to me. Typically mechanical fuel pumps fail totally, not partially, but you can check your oil for gas smell.

Choke is working correctly?
 
The burning smell almost makes me think maybe something's going on on the spark side of things.

I would bet that you could tell if its vapor lock or not by doing this:

When the truck is cold (engine not running), take off the air cleaner and look down the throat of the carb. Move the throttle with your hand and you should see two nice streams of fuel squirt out thanks to the accelerator pump. This is so you know what it should look like.

Then, when the truck is acting up shut it off and take off the air cleaner, move the throttle linkage again and see what the fuel stream looks like. If its weak or non-existant you have vapor lock issue.
 
As experienced by another member here, the carb may be getting too hot, but that wouldn't be something that affects the fuel pump. Pretty hard to diagnose I'd think, except by measuring fuel pressure between the pump and carb. Different solution(s) based on the actual problem.

Does the setup have a fuel return from the pump?
 
Well I believe the choke is working correctly, the choke plate moves when I rev the motor.

What could possibly be happening with spark that would only happen after driving for a long period of time? I do not know if my fuel pump has a return line on it, but I can't figure out where my fuel would be boilng for vapor lock because it's never close to anything really that hot.

I'm not sure where to even begin. I know the carb needs to be rebuilt, so I'm thinking about doing that first.

Also, could this have something to do with my kickdown cable on my late model 700R4? It seems that on this motor there is really no way of connecting it, and I keep finding different ways, but it comes disconnected after a period of driving time.
 
The burning you are smelling then is probably the transmission. It's probably cooked. The 700 doesn't take any time at all to fry with the TV cable disconnected or misadjusted.
 
Well it must only act up when it gets really hot then. It does kind of shift funny. The guy that put it in for me called the cable a "kickdown cable" then i later researched to find out that it pretty much controls every shift of the tranny. I guess it's time to figure out how to put a 400 turbo in it. Even if that's not the problem, I'm sure the tranny's going bad, since I drove about 100 miles without that cable connected.
 
Gas tank could be pluged up. But that doesn't really explain your problems but mine just died one day becuase the sending unit was plugged.

Edit: it definately seems like your tranny
 
THe 400 swap is EASY! just bolt it in with anew adapter!

Then mount a switch that when at WOT it sends spark to you solenoid and bam your done! (with more work)
 
Lol, is that a sarcastic response? I'm sure it's more complicated than that. I have a 350 turbo sitting in my driveway right now that came with the motor. The guy that helped put the motor in says it would be a lot of work to swap them. The tranny is leaking from the dipstick tube though. What do you think? Another 700R4, 350 turbo, or 400 turbo? Will my current T-case work with all of them?
 
If its Th350 4X4, no problem. If its TH350 2X, a little bit of work and some $$. Visit AdavanceAdapters.com.
If the TH350 has a drive shaft output, its 2X.
Looking at your original post though, it sounds like its engine, not trans.
 
nad said:
Lol, is that a sarcastic response? I'm sure it's more complicated than that. I have a 350 turbo sitting in my driveway right now that came with the motor. The guy that helped put the motor in says it would be a lot of work to swap them. The tranny is leaking from the dipstick tube though. What do you think? Another 700R4, 350 turbo, or 400 turbo? Will my current T-case work with all of them?
Click to expand...

No, i was being serious. Sorry if i came off that way, besides geting a 4x4 tranny for ease, and locating the correct adapter, its basically the same as any other tranny swap.

Drop old, remove x-case, install adapeter onto new tranny, install x-case, bolt back into truck. Hook up necessary wires/calbes etc.
 
Well the electronics/cables is what I'm most worried about, since everything from different years is different.
 
your 700/208 setup is a 27 spline output from the trans to the T-case. If your TH350 originally had a 208 behind it then it is an easy swap to put it in place.

Edit: there are a number of different GM vehicles that came carbed with 700R4. It shouldn't be too difficult for you to find a a throttle linkage that will allow you to hook up your TV cable properly
 
Just wondering????????? Are you using the orginal TBI intank fuel pump to supply fuel to your carbed engine?
If so it has way too much pressure for a carb. And must have a regulator with return line plumbed in or the pump will burn out.
 
I just went thru a situation I thought was vapor lock, and it turned out to be fuel percolation. Heat from the intake was soaking into the carb, and after driving a while, it acted like it was running out of gas.
I put a carb spacer under it, and that cured it.
Next time it does it, shut off the engine, jump out and pull off the air cleaner assembly. You'll be able to hear if the gas is boiling.
Just FYI, while mine was having this problem, the gauge never topped 200 degrees, so the enging doesnt have to be running hot to cause the problem.
Its worth checking before you spend $$ on a tranny.
 
That's exactly what it sounds like Kp. I'll have to check that out. Yeah, I'm not jumping right into a new tranny quite yet. I'm gonna try resolving my other problems first, rebuilding the carb and such.

Thunder, no I dropped the tank and ran a removed the TBI pump and ran a line to the pump under the hood.
 
Well one other thing to check is your Distributor module. If it is bad it is common for them to start causing problems when they get hot. Most auto parts stores will test them for free if you pull it out.
 
The whole distributor? Or just the module? What exactly is the module?
 
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