Classic Winnebagos & Vintage RVs

I took our 1986 27' P30 Komfort motorhome to the coast this last weekend, and I am still having issues with vapor lock when temps are above 90*

I'm still also using the brand new mechanical fuel pump on the engine too, I wanted to utilize the fuel return system that is built into the pump...I cant see blowing a diaphram in a pump when it has a fuel return system? Am I wrong? I would like to hear opinions on that!!! anyway...

I've had only one common clue when it happens....cruising down the highway at 58 mph's and you approach a 3,000 ft mountain pass.....If you keep your foot in it...say 3/4 throttle, and dont lift, it will pull the hill all the way to the top just fine (say 2 minutes of hard pulling), but if you approach a slow moving semi during that pull...and back out of the throttle to slow down and maintain a slow speed behind that semi...It will just about immediatly start popping and surging...and then you half to pull off to the side of highway. I can sit on the shoulder and the engine will idle right away, I just cant give it any throttle for awhile. I can leave it sit and idle for a few minutes, then I can creep up the hill and get back on my way?

I put a Carter 5/16 input/output electric pump in the rear by the fuel tank (I know...small) I couldnt find any 3/8 or 1/2 pumps in stock anywhere...thats my excuse!! I didn't really want to spend alot of money for a 1/2" Holley input/output pump, and regulator, but is this what I need to do? Or?

Am I having a volume issue with the smaller i.d. pump?

Well Yes 5/16 is too small Also make sure all fuel lines are out of engine exaust heat stream  3/8 is a minimum and it should be 1/2 all the way from tank to carb  A return is not necc unless you are experiencing flooding at idle . Frank

Yeah....Im going to order the correct 1/2" pump and reg....we'll be burnin fuel all day long......................on pay day!