340 Starting Problems - no fuel

[73LemonTwist]

I have a friend with a 340 Challenger (yes I know this is B bodies only - but he needs help guys ) that he just can't get fired up unless he dumps gas down the throat of the carb multiple times. Cranking the engine just doesn't seem to get fuel to the carb. Once its running, it runs fine. it will hot restart fine. Its that cold start after sitting for a day that is a problem.

He has replaced the mechanical pump multiple times, and has swapped TQ carbs. I put his carb on my 340, and it starts and runs sweet, so its not a carb issue.

He had the gas tank cleaned and re-installed and new fuel line run up to the fuel pump by a mechanic.

He has his fuel filter on the inlet side of the mechanical pump. I know mine is on the outlet. Don't know if the makes a difference, or might be a cause of vapour locking.

Thoughts guys? Thanks for the help...

 

[73LemonTwist]

I should note, that he has considered the electric pump idea, would prefer not to if he can solve this problem.

 

[Don Frelier]

I would check the pickup screen on the sending unit.
And put the filter where it belongs.
Maybe a slight air leak on the suction side allowing it to syphon back into the tank

 

[Red63440]

If he has a slight air leak on the suction side the fuel may be draining back to the tank which would explain why it takes so long to get it started.

 

[73LemonTwist]

I would check the pickup screen on the sending unit.
And put the filter where it belongs.
Maybe a slight air leak on the suction side allowing it to syphon back into the tank

Don, are you suggesting the correct location of the filter should be on the discharge of the pump? My shop manual does not specify. Checking for air leaks is a good idea - thanks much

 

[Don Frelier]

Yes the filter should be on the pressure side of the pump.

 

[Photon440]

You might find some ideas in this thread: https://www.forbbodiesonly.com/moparforum/threads/crank-crank-crank-crank-crank-crank-crank.152082/

 

[joeb73]

Just went threw the same thing on my GTX the car has 3/8 fuel line but the pumps that are offered at the local parts stores and was on the car was all 5\16 inlet. The rubber suction line felt tight and would not twist but leaked enough to cause a suction leak and it would loose it's prime within 20 min of turning it off.

 

[RJRENTON]

I would check the pickup screen on the sending unit.
And put the filter where it belongs.
Maybe a slight air leak on the suction side allowing it to syphon back into the tank

YES.....the filter should be on the pump outlet or pressure side of the pump. IF the filter is placed on the suction side, or inlet side of the pump, the suction pressure is INCREASED making it harder for the pump to pull the fuel from the tank innitially, which results in fuel starvation, or difficulty to start pumping. Once the pump "gets its prime" it will usually function normally. Just my opinion of course.
BOB RENTON

 

[73LemonTwist]

Thanks for the help guys... will get the filter moved over to the discharge side of the pump as a starter.

Then to isolate the air leak possibility, I am thinking about running a hose from the suction side of the pump to a jerry can of gas and give her a crank. If the carb will prime from the jerry can, then we know for sure its an issue with the new feed line or in the gas tank, not an issue with the pump to the carb.

Will check the feed line size vs the pump inlet. If its mismatched, then that would be a prime source of air leak. Good idea.

 

[73LemonTwist]

Some success... took the fuel line from the tank off of the pump. Discovered free flow of gas from the tank. Put a vacuum pump on the pump suction and noted that the valves in the pump leak somewhat, they are not fuel tight. Cranked the car and measured 11" vacuum on the pump suction so the pump has lots of grunt to get the fuel from the tank to the carb.

Pulled the carb off of the Challenger and put it on my car as I had my TQ off for an epoxy job. Carb performed horribly. Put his spare rebuilt TQ on my car and it started and ran like a champ. Put this carb on his car, and filled the fuel bowls manually with a hose and funnel connected to the pump suction. Fired up the car, and she ran not too badly.

Reconnected the tank supply and the car ran pretty good. However, while adjusting the fast idle speed we noticed that the choke thermostat linkage was wrong, and binding on the carb linkage preventing proper choke operation and the choke was never getting off of fast idle. The owner rebent the linkage on the choke thermostat to match my stat for shape and length. Yesterday's start on second crank.

So, looks like a combination of the pooched carb and inoperable choke system combined to create the issues. Should get some cold starts in over the next few weeks and see if in fact the problem is solved. if not, its electric pump time.