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Originally posted by Brandon:

I don't feel well versed enough in DIY to rig up an electrical fuel pump .

Some Barths came with electric pumps. Mine did. Just wondering if yours did, too. A weak pump can cause a fuel delivery problem.

As a side issue, electric pusher pumps are a good vapor lock cure.

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Another thing I noticed when I was looking around its that it recommends min 89 grade fuel. I was using 87 the entire trip. Don't know if that would mater at all?

87 Octane is fine. Octane rating is measured by two similar (but slightly different) processes. The Research Method was more tolerant than the Motor Method. Years ago, fuel was rated by the average of the two, then the gummint mandated the rating be strictly by the Motor Method. The octane is the same, just sporting the lower number.

We had similar problems. I let our rear tank get to low & trash ended up in the carb. We removed the rear tank had it recoated @ Ropel in kentucky. I couldn't find a new tank. It was around $250.

Another problem we had was the carb got trash in it & after taking it apart discovered it needed to be rebuilt.

Both problems sound like what you are experiencing, except we couldn't get it to stay under throttle. It just bogged down after giving fuel.

it has been running great since the carb was rebuilt

Of course if I walked through every detail it would take several pages. First starting with the fuel filters & so on.

Did not want to deal w/any more fuel issues.

Eventually replaced all the fuel lines w/marine grade lines, new mechanical fuel pump, had one fuel sending unit refurbed etc.

If you want any of our sources for carb rebuild, sending unit refurb or tank refurb. let us know

Without downloading the above link here are the pictures that Duane took the time to scan.

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I am not sure about the order, but that is the order from the bucket. Windows users should be able to zoom and read them.

I had a 1977 GMC Palm Beach 454 twin tanks with the same problem.

A great deal of heat would collect aft of the engine where the fuel line came "up-hill" from the rear on the port side and entered the carb.

Replacing the fuel filter at the carb seemed to help, but not completely solve the problem.

Idling in traffic and sometimes switching tanks was when the problem usually occurred.

I too assumed it was Vapor Lock.

Some research lead me to check all the rubber fuel lines for rot and cracks

-AND-

I installed a small electric pump just forward of the fuel tanks, mounted to the port side frame rail.

I also replaced the fuel selector valve, which was right in the same area, just before the small electric fuel pump.

The aux (added) fuel pump came on when the ignition was placed in the ON position.

It would make a "clacking" sound at first (reverberating off the frame rail), but you could tell when it began to pull fuel as it would quiet down and run smooth.

I could start that GMC in -20 temps and it would fire-up within 3 seconds of cranking and run all day.

This seemed to completely solve the problem, as I assume it really pushed the fuel towards the engine and overcame the potential Vapor Locking situation.

I really have no idea, since I am no mechanic and have only a very crude understanding of such things.