Truck won't start when engine is warm

[sarocu]

Howdy!

I have just changed out carbs on my 86 V6 - I installed a rebuilt carb on it and after I was finished, she started up perfectly fine and idled better than she has during the time I have owned the truck. Turned it off, then a few minutes later tried to start again and it wouldn't turn over. The next day same thing - on a cold start it fired up right away and idled great (possibly a little low on the RPMs). After taking it around the block a few times I turned it off and then could not get it to start. 

 

I suspect the problem is that there is too much fuel, however I have not found a good resource for adjusting this. Another clue - when driving, the truck seemed to lose power in the higher RPMs. 

 

Any ideas or resources on the Rochester carb would be great, thanks!

[jdog]

1 hour ago, sarocu said:

Turned it off, then a few minutes later tried to start again and it wouldn't turn over.

The motor wouldn't crank? Or it wouldn't start? Turning over means cranking

What carb was installed? Did you adjust the air fuel mixture? Set the idle? Are you my spark when it doesn't want to start?

[sarocu]

The ignition is operating as expected however there is no combustion and she refuses to fire up. 

 

I installed a rebuilt Rochester Varajet - which, while it came with instructions they didn't actually mark any of the adjustment screws nor provide pictures so it was unclear which screw is the curb idle, though I'm pretty sure it's the one on the left (passenger side) and bottom of the unit - if anyone knows that for a fact it would be nice to confirm before fiddling with it :) 

[MiNi Beast]

Sounds like you said perhaps to much fuel  perhaps you installed the float upside down in the rebuild..  

[sarocu]

The rebuilt Varajet came as a unit all pieced together and supposedly was flow tested at the shop. 

 

I'm pretty confident that it's fuel delivery but I am also unsure what to adjust on the carb to dial that in 

[jdog]

Are you sure it's the carb? What made you replace the carb? Pictures help a lot

[Eagle]

5 hours ago, sarocu said:

The ignition is operating as expected however there is no combustion and she refuses to fire up. 

 

I installed a rebuilt Rochester Varajet - which, while it came with instructions they didn't actually mark any of the adjustment screws nor provide pictures so it was unclear which screw is the curb idle, though I'm pretty sure it's the one on the left (passenger side) and bottom of the unit - if anyone knows that for a fact it would be nice to confirm before fiddling with it :) 

 

"No combustion" would indicate a lack of spark. Have you checked for spark?

 

Is the choke adjusted correctly?

[sarocu]

18 minutes ago, Eagle said:

 

"No combustion" would indicate a lack of spark. Have you checked for spark?

 

Is the choke adjusted correctly?

 

 

The vehicle starts perfectly fine from a cold start - I was assuming that the fuel had evaporated and the carb could balance the air/fuel mixture at that point, so that would indicate that spark is happening. 

 

I am not sure about the choke - I did not adjust this at all when installing the carburetor. I will dig up some resources on the choke and give it a try. 

[MiNi Beast]

Can you check for fuel pressure? 

[Eagle]

3 hours ago, sarocu said:

 

 

The vehicle starts perfectly fine from a cold start - I was assuming that the fuel had evaporated and the carb could balance the air/fuel mixture at that point, so that would indicate that spark is happening. 

 

 

Respectfully, assumptions don't indicate anything. What would indicate spark is pulling a spark plug wire and seeing a spark when cranking. You could have a coil that doesn't generate enough spark for starting when hot.

 

I am not sure about the choke - I did not adjust this at all when installing the carburetor. I will dig up some resources on the choke and give it a try.

 

The vehicle starts when cold, so the choke must work when cold. But does the choke stay open for hot starts, or is it closed and causing an over-rich mixture that can't fire?

[sarocu]

Hey @Eagle I think you are right on the money. Attached is a picture of the choke side of the carb without the air cleaner. The choke is closed for hot starts. A YouTube video for this model of carb mentioned that adjusting the choke is a matter of bending the connecting rods; unsure if that is wise or not however. 

[sarocu]

FWIW while driving, I start to lose power at higher RPMs in 2nd and up as well

[rokinn]

I'm not familiar with that system but it sounds like one good possibility is that the choke i not opening up after the engine warms up.  Bending connecting rods for adjustment seems a little too low tech to be true but adjustment and opening after the engine warms up would be different issues.