Rebuilt carb problems at higher speeds.

[calixto]

I have a 73 (9/72) FJ40 that I recently had Jim C rebuild the carb for me. Truck has the original F engine with headers and no smog. Carb is mid-74 and is running the original factory configured fuel delivery through the charcoal canister etc. I had an out of tune Rochester carb on it before and am really stoked on the newly re-built carb.

Problem is the truck lurches and acts like it is gasping for air or gas when I hit 40mph +. It starts and runs perfectly up until that speed but once I hit 40 it bucks, sputters, etc. no matter how hard I am goosing the pedal. If I slow down or downshift and go slower it drives fine. I've also wound out the gears under heavy acceleration at speeds under 40 with no problems.

I had a local shop install the carb since the lines were all different from the previous Rochester set up. They were really meticulous with the lines and took the time to run everything back to stock by referencing SOR diagrams. One thing I did tweak was the idle and the idle mixture screw. The idle was set way too low for my truck. I inadvertingly turned the idle mixture screw thinking it was the idle but think I've got it back to where it was set when I got it back from Jim. Pretty sure this isn't the problem?

It really seems like insufficient air/fuel getting to the carb. Need a new fuel pump? Could this be bad even though it worked over 40mph for my Rochester? Maybe a line run the wrong way? I'm not sure they re-set the timing when they installed the carb...could this cause those symtoms? FYI I have new plugs/wires, Pertronix, PCV, fuel filter.

Any ideas?

 

[Pin_Head]

It sounds like a fuel delivery problem. Start by checking the fuel filter and gas tank for dirt.

 

[inkpot]

It sounds like a fuel delivery problem. Start by checking the fuel filter and gas tank for dirt.

Howdy! I don't remember ever seeing fuel delivered to the carb thru a charcoal canister. Post up some pix. You may need to check out the fuel routing. John

 

[71 redwood]

asan carbs rock !!!!!!!!

 

[flash02]

X2 on the fuel delivery check your fuel filter and maybe the fuel pump. The charcoal canister is for the evaporative emissions system, it is for fuel vapor recirculation not for fuel delivery however if your fuel tank can't breathe due to a faulty evap system that may be your problem. I would check all your lines from your gas tank and make sure the fuel delivery lines are going the fuel pump then carb and that your evaporative recirculation lines are hooked up properly. Another thing to check would be timing; perhaps it is not advancing properly.

Good Luck!

Corey

 

[D'Animal]

Make sure you did not connect the fuel lines wrong on the pump or carburetor.

The one with the banjo bolt is the fuel return line.

 

[Pighead]

Indeed, it could be any and all of the conditions listed above. If your engine sounds like it is gasping for air or gas at high speeds, it probably is. It could also be a dirty air filter, mal-adjusted timing or valves...
Mis-routed fuel/return lines would do it too.
One thing to check, try driving it without the gas cap...see if that helps. Might narrow down where to look. And when it does start gasping again, try shutting off the engine and coasting to a stop, immediately check the fuel level in the little porthole window.

 

[calixto]

Thanks guys will try all the recomendations. And yes loving the new carb, can't wait to get this little problem solved. Also excited to see if my mpg is going to change some. Will let you know. Thinking maybe of doing an additional clear view fuel filters in addition to the stock one I have on there so I can see if I am sucking up crude from the tank.

 

[FJ40Jim]

Calixto,
Sounds like insufficient fuel flow into the carb.

If the truck is a '72 and the carb is a '74, is the truck configured w/ both a fuel feed and fuel return line?

Can you post pics of the carb, dissy and vac hose routing?

Wondering how the smog vacuum pics from SOR are of benefit if the carb is desmogged and has ported vac fitting...

 

[calixto]

The truck is a 73. One other thing it is set up with a throttle cable and not the Bell crank. Here are some shots of the set up. Let me know if you need to see any other views. Gonna change the fuel filter today/tomorrow. Also gonna run it without a gas cap like Pighead reccomended. Thanks again guys!

 

[calixto]

Other angles.

 

[calixto]

Last couple.

 

[Pighead]

It looks to me like your charcoal canister is being used as a fuel filter...?
Lose that.

 

[D'Animal]

I don't see how your charcoal canister is connected properly.



Where is the fuel filter?

 

[Pin_Head]

Nice pictures, but they aren't particularly helpful in determining how your fuel tank, fuel pump and charcoal filter are plumbed because you can't see where the hoses go. A hand drawn diagram would be more useful.

 

[calixto]

Looking at these pics again it hard to tell anything from them, sorry guys. You can kind of see the fuel filter in pic #6, just below where the battery sits. It still has a shiny copperish color to it since I only replaced it about a month ago. Looks like the gas line is coming from the tank to the fuel filter(stock mounting location) to the pump to the carb. The other two hard lines are coming from the tank? into the charcoal canister and back....not hooked up to the carb itself at all. It looks like it is entering the c canister from the bottom and return through one of the top lines (or this could be reversed, I can't tell) and the other top line is not attached to anything but simply just hanging tube like maybe an overflow tube? The carb base isolater line is running from the carb to the pcv valve. Vac hose is running from the carb to distributor. I will try to draw a diagram. I will also look through the pics again and blow them up if any of them are better. The shop is letting me bring the truck by tomorrow to double check their work and help me diagnose. Thanks again for all the help.

 

[calixto]

Okay in pic #1 the line on the left going into the carb is coming from the tank to the fuel filter to the pump directly as you see it into the carb. The line on the right is coming from the cab isolator base into the PCV valve and engine.

Picture #5 you can see what looks like additional tank lines (hard lines into tube) going to and from the charcoal canister....not sure if this is entering from the top and existing the bottom or vice versa. The top line on the cansiter closest to the driverside in pic #5 connects to nothing and looks to be a drain tube.

 

[Pin_Head]

That sounds correct.

Pull off the tank line before the filter and check the flow. It should flow about as much as a horse can pee. If the flow is low, just dribbling out, blow compressed air into the line and see if it flows better. If so, there is rust or some kind of dirt in the tank.

Disconnect the fuel line at the carb and pull the distributor center wire. Crank the engine for 15 seconds and measure how much fuel the pump puts out. It should be able to pump about a cup in 15 seconds of cranking.

 

[FJ40Jim]

Can't see real clearly, but it looks like a 63-68 vac advance dissy (Good Thing).
Looks like there is a vac hose coming from carb base over to dissy advancer (Good Thing)

Looks like there is no steel fuel line from pump up to carb. How is fuel getting from pump to carb?

 

[calixto]

Thanks guys and I will check those two items tomorrow Pin Head. The fuel line from the pump to the carb is rubber. In Pic #1 the left line going into the carb is coming from the pump. And you can see the location of the pump in Pic number 6 just right of plug wire 1 and the PCV valve.

I did drive the truck with the gas cap off and resulted in no change. Also re-checked my airfilter and it is clean as a whistle and not blocked. Haven't been able to check the glass bowl on the carb when it starts to cut out like mentioned above yet but will mananna.

Hoping it is just my fuel pump......Don't really have the dough to clean/recondition the tank right now.