Re: suburban tow truck fuel issue
 

I have repaired that type of problem many times. The frame is getting hot enough to boil the fuel. If you do not have a return line you need one. If you have a return line then insulate the fuel lines or move the to the outside of the frame to get away from the exaust. Here in south Texas i have done this type of mod with good results.

Re: suburban tow truck fuel issue
 

The inner fender is the wrong place to route fuel lines. Chevrolet put them on top of the frame rail on cabureted trucks because air flows there.

The big block carbureted trucks had a 1/2 fuel line from the tank all the way to the fuel pump, it was necked down for a 3/8" hose. They also had a different pick up in the tank. I always used a genuine Delco fuel pump for a 70 Chevelle on my big block trucks, that seemed to be the most reliable and effective mechanical pump, the big Holley race style pumps would at times have pressure spikes that caused a Q-Jet to flood.

See if you can find the correct fuel tank and the correct sending unit and pick up for an earlier truck with a big block and a carburetor. You can probably even find the fuel lines.

Re: suburban tow truck fuel issue
 

Oops. Sorry, I missed part of the original message.

Re: suburban tow truck fuel issue
 

?? Alan, I put 386K miles on an 86 454 GMC Suburban (last carburated model), but it had a 3/8 line. The line did run outside the frame rail mounted toward the top of the frame channel, if that is what you mean by the top of the frame. I replaced the fuel pump once and used a NAPA pump. No problems ever. I replaced the tank once (the original developed a split along the bottom) with a tank from an 89 model. I used my pickup and sending unit, still no problems. 40 gal tank.

Jack, that's weird!!

Re: suburban tow truck fuel issue
 

Dwight, most of the 454 trucks (3/4 ton and up) we had in the shop, Suburbans included, had 1/2" lines. Not all did though, you're right. Yes, the fuel lines do run outside the frame, high on the side and on the top in places. They were out there to keep them cool, and keep them away from shrapnel from failed drive shafts and such.

Now that you mention in though, around here, most every C/K 20 series truck was a "C6P" truck, which had a heaver GVWR. The dealers just ordered them that way. But you could get the C/K 20 series without that option, and those did not have all the heavy duty equipment. A "C6P" truck was just about a 1 ton truck. I'm pretty sure that the few trucks we had through the shop that did not have those lines were not "C6P" trucks, that would explain it.

Re: suburban tow truck fuel issue
 

If you have (after market), rear A/C, make sure they didn't tie the A/C lines to the fuel line as they will cause vapor lock. On my '85 we finally went to a 454 R/V (HD- motorhome) mech pump, with no more headaches. Good Luck.

Re: suburban tow truck fuel issue
 

If the fuel line was tied to the low side AC line it would get cold.

Re: suburban tow truck fuel issue
 

Captain ,, When you get it all figured out call Fred and Jo Anne they got the same problems and would buy cold beer ,,lots of it,,,, for the cure.:cool:

Re: suburban tow truck fuel issue
 

nice to see not only one with issue... thought it was something i did converting from efi to carb for a while but now im just baffled... am considering tapping pickup fitting into bottom of tank and using areomotive setup for pump... sounds like overkill but im tired !!!

captain
thanks guys

Re: suburban tow truck fuel issue
 

Jack, the factory in-tank pump would have made a nice pump with a return-style regulator, using the factory return line. Could have also been used as a booster pump, with a regulator, for the mechanical pump. Guys around here have done it both ways.