Hestitation/missing problem

[Will Sampson]

Tried sending this to both the Landcruisers list and the FJ55 list at birfield.com, but they bounced. Hope this goes through here.

My truck just started acting up over the weekend, and I'd like some advice before I start tearing into it.

The truck is a 1972 FJ55 with recently rebuilt F engine, all mostly stock. Carb was rebuilt by Jim Chenoweth at least a year ago. I drove it on Saturday from my house in Connecticut to Maine with an empty military trailer in tow. It drove fine except when accelerating out of a toll booth in Maine it suddenly missed hard twice. I let off on the gas, it returned to smooth running, and we continued on our way. We loaded the trailer up with a bunch of old barn beams we were moving from Raymond, Me., to our property in Dixfield, about 1-1/2 hours farther up. It handled the load fine, and drove fine over hill and dale and dirt roads. My teenage son and I unloaded everything, unhooked the trailer, drove to a hotel, out to dinner, back to the hotel, then back to the property the next a.m. There we hooked the empty trailer back up and headed home. About an hour later, the truck starts the serious hesitating/missing action, gets so bad it stalls as we pull off the road. I look at everything, and the only thing I can find is the points look a bit worn and not gapped right (closed). I tried cleaning and regapping, no luck, so replaced the points with a new spare I was carrying. Truck fires up and idles smooth, engine revs easy with no load. So, we head out again...

No sooner do we start to encounter hills and anything that puts a load on the engine and hesitation/missing returns. We can easily do 60 mph on the flats, but it won't do 50 without lurching on the slightest up incline. Letting off the gas sometimes returns it to smooth running for quite a few miles, then it starts misbehaving again. We nursed it like this all the way back to Connecticut (about 250 miles total) and there were times we couldn't do any faster than 30 going up hills, feathering the gas pedal to try to keep it running smoother.

So, where do I start? Plugs all looked fine (some light brown deposits, no oil deposits, #1 and #6 cleanest, rest only slightly dirtier and identical). Plug wires are 3 months old. Oil looks fine. Coolant looks fine. The distributor is original and when Jim did my carb he said I should replace it with a vacuum advance model, which I have, but never got around to. Some of the corners of the shaft on the original distributor seem more rounded than others. The truck also has an exhaust leak at the flange. My first thoughts were to put in the replacement distributor, fix the exhaust leak and look for vacuum leaks. Even with the exhaust leak, the truck had been running strong lately, and I was getting up to 17 mpg on the highway. This is frustrating. Am I on the right track or should I be looking at something else entirely? Help much appreciated.

Will Sampson
TLCA #16929
1972 FJ55
1968 M101-A1 military trailer

[inkpot]

Howdy! Did you check the fuel level sight glass on the carb? Sounds like limited fuel supply due to bad filter, pump, blocked pickup in the tank, vacuum build up in the tank.... John

[Will Sampson]

John,

Good suggestion but the fuel level is slightly above center on the carb sight glass and the accelerator pump delivers a regular stream of fuel when I push the linkage and look in the bowl. I should have included that information before. Any other thoughts?

Will Sampson
TLCA #16929
1972 FJ55
1968 M101-A1 military trailer

[inkpot]

Originally Posted by Will Sampson

John,

Good suggestion but the fuel level is slightly above center on the carb sight glass and the accelerator pump delivers a regular stream of fuel when I push the linkage and look in the bowl. I should have included that information before. Any other thoughts?

Will Sampson
TLCA #16929
1972 FJ55
1968 M101-A1 military trailer

Howdy! I would guess that you are checking it while parked, not under heavy load. You could have enough fuel supply for lot to moderate throttle, but long, heavy pulls, like uphill at highway speed require high volume flow for a long time. If not fuel, then I would look at vacuum issues, like leaky hose/fittings on the dizzy. I have also seen vacuum advance diaphrams with pinhole leaks that only open up when max vacuum is applied. Good Luck. John

[petescoffee]

This is an abosolute guess but...
How are your point now? Check your Coil. I had a bad coil that acted very similar turned out it was cracked and was grounding out periodically.

[Nomis]

I had a bad plug wire coming off the coil that acted up similar to what you described.

[Pin_Head]

Junk in the gas tank?

[fireflyr]

Mine started doing the same thing when I installed an electric fuel pump. Switched back to the mechanical pump and it ran fine. The pump came from JT Outfitters and was manufactured by MR GASKET. POS.

[65swb45]

Originally Posted by inkpot

... Sounds like limited fuel supply due to bad filter, pump, blocked pickup in the tank, vacuum build up in the tank.... John

That about covers it.

Also, since you have a pre-75 carb, you can take the nut off above the needle and seat assembly to see if you have any obstructions in the inlet of the carb.

This is a CLASSIC fuel starvation scenario.

Best

Mark A.

[Will Sampson]

Thanks, guys! These are all good thoughts. I'll investigate the fuel issues more thoroughly. Maybe replace the fuel filter and blow out the lines before I do anything else.

Will Sampson
TLCA #16929
1972 FJ55
1968 M101-A1 military trailer

[Will Sampson]

Once in a blue moon, the problem is simpler than it seems. I just got back from a fairly rigorous test run, and I'm pretty sure the problem has been corrected. However, most of us here guessed incorrectly. The concensus seemed to mostly be that it was a fuel starvation problem. Then the next in line, which I favored initially, was ignition/electrical. For the few of you who suggested as more or less a last resort to check the vacuum connections, you win the prize. There was a loose vacuum hose that was laying in such a way that it looked connected but was actually completely off. I had taken out the carburetor fuel inlet filter screen to check it (it was clean, as I suspected) and was about to start disconnecting the fuel lines to check them when I looked down and bumped the vacuum lines going to the smog box, and I saw a hose end move. I actually had to look pretty close and grab it to confirm it wasn't connected, which explains why I didn't notice it before. Anyway, I hooked it back up and tightened it up with the addition of a little zip tie as an impromptu hose clamp. Fired her up and the truck runs great!
Thanks to everyone who offered suggestions. I really appreciate the help!

Will Sampson
TLCA #16929
1972 FJ55
1968 M101-A1 military trailer

[jimhendrixx]

WOW, these are all great ideas and awesome help!