73 Series III Bucking issue

[sizod]

I have this frustrating issue with my 73 Series III, Sometimes at speed typical 50mph + my truck starts to buck. It feel like a lose of power, I take my foot of the gas pedal and it seems to recover, but then as a gain more speed it starts again. It's fine going up the gears even at higher revs.

I've replaced the Carb, Coil, new Pertronix Flamethrower Distributor and new proline fuel pump. I'm still getting the same issue. The fuel filter and sediment bowls are clean and clear.

I re-timed it with both a gun and also by ear and feel, Its running right now at about 10˚ advanced, which I read is common with the Pertronix flamethrower setup.

Any thoughts? Cheers

[TriedStone]

Sounds to me like its starving for fuel. My guess and a pretty week one at that would be the pump but since its new that "should" rule that out. What kind of carb are you running? Could be in the ignition but I can't imagine what would cause the spark to become intermittent. Does it ever back fire during the bucking?

[scott]

pick up tube restriction would cause fuel starve symptoms while sed bowl and in line appear clean. if you still have the screens on the pick up tubes i'd remove 'em. i did so crap in the tanks will get sucked up to the sed bowl and filter which are easier to clean or replace than pulling the pick up tube and cleaning those screens

[bmohan55]

Weak fuel pump, even though it's new. I went thru two new pro-line fuel pumps and intermittently had the same issue, and more than occasional vapor locking. Recently bought a posi-flow electric pump at NAPA for $53 and all issues went away. Also starts and idles MUCH better. Wouldn't hurt to check the pick up screen too, as suggested in the above post.

I have a thirsty Rochester carb so you may have different issues.

[graniterover]

I too put a proline fuel pump on and after changing points, fuel lines, fuel filter, spark plugs AND 2 CARBS, it was the pump. Put an electric one on that I found on the floor of my garage and it's been perfect for 4 years.

[LR Max]

You have **** in your fuel lines/a nasty kink. Not stuff, not rust, ****. Straight up ****.

Unlook everything and blow em out. Air compressor works well but if you don't have that, get a straw and you can blow em out call girl style. Use the straw because you don't want gas in your mouth. Oh, and undo the gas tank cap, otherwise you run the risk of actually pressurizing the tank (more of a problem if you are using an air compressor). This is not fun.

Plan on a gas tank cleaning in your future.

[ArlowCT]

3 X the electric fuel pump idea!

I switched a few years back after 2 new mechanical pumps failed. You really can't beat them, it's like a hot rod now:D

[TedW]

[QUOTE=bmohan55;50959]Recently bought a posi-flow electric pump at NAPA for $53 and all issues went away.QUOTE]

Which one did you get?
Where did you mount it?

[bmohan55]

Can't recall the model number but it was a Facet Posi-flow, the only model NAPA carried, it came highly reccommended from the counter people there. Not sure how to discribe where I mounted it. Not on the frame itself as with the attached fuel filter I felt it would be in harms way, I put it on the vertical peice coming off the frame in front of the gas tank.
Hope that helps

[TedW]

My question involved getting the pump with the correct psi - but I suppose I could look that up in the green bible, couldn't I?:o

[bmohan55]

depends on your carb most likely...If I recall this pump is between 4-7psi and has worked will with my Rochester. Just found this...

http://www.facet-purolator.com/index.php?option=com_content&task=category&sectionid=7&id=13&Itemid=35

[TedW]

depends on your carb most likely...If I recall this pump is between 4-7psi and has worked will with my Rochester.

I've got a basic Weber 1bbl. Anyone out there know offhand what the psi should be?

[scott]

I've got a basic Weber 1bbl. Anyone out there know offhand what the psi should be?

don't know about the 1bbl but the 2 likes 2 to 3 psi

[bmohan55]

As I understand it the float on the carb will regulate the fuel delivery and my pump will respond to that. In my search before switching to electric others have experianced flooding of the carb with an electric and routed a return line but I haven't that necessary.

[jgkmmoore]

Ted W-
Facet pump #60104 is what you want. It runs about 4 lbs at idle, and 1.5+ at cruise/hiway speeds. Believe that to be right in the proper range for 1 bbl Weber.
Regards-Jeff

[TedW]

Ted W-
Facet pump #60104 is what you want. It runs about 4 lbs at idle, and 1.5+ at cruise/hiway speeds. Believe that to be right in the proper range for 1 bbl Weber.
Regards-Jeff


Thanks, Jeff! My f-pump is original and untouched - I figure I'm on borrowed time after 40 years. Am also looking at the Carter P4070, which has been suggested on various sites, including the one that specializes in Weber carbs. that said, it sounds like lots of folks here have had good luck with the Facet.

[sizod]

Awesome thanks. Yeah I was apprehensive about getting the Proline Mechanical pump. I do still have the original, maybe I should rebuild it again? The Carb I'm running is a Weber, that was what was on there originally. The pickup tube is relatively new and the fuel was replaced about a year ago with a used one. I did make sense to me that it is a fuel issue I thought it might be clutch shudder, I interested in hearing more about the electric fuel pump, it sounds like folks have had a lot of success with these. This weekend I'll clean and blow out the fuel lines and clean the pickup screen.

[jac04]

I do still have the original, maybe I should rebuild it again?
Just be careful about the rebuild kit you use. I rebuilt my original AC fuel pump with a Genuine Land Rover rebuid kit. Problem is that the diaphram is made improperly. I ended up reusing the original diaphram, which was actually in very good condition. Not sure how it will hold up to the ethanol in our fuel.

[sizod]

Cleaned the lines, sediment bowl and filter again. Didn't touch the timing or adjust the weber carb again, so far so good.. Thanks