High Altitude plug fouling (1 Viewer)

[Cruiserdrew]

I've had this issue twice, and so thought I would post if anyone else has the same. This is in my FJ40 with 76 2F.

1st time-About 6 years ago, I was doing Dusy Ershim for the first time. For those of you not familiar, this is a 3 day long trail in the central Sierras with most of the terrain above 9,000 feet and a significant portion above 10,000 feet. On the second day, the truck developed a significant misfire-idle and power both dropped a bit, found several plugs badly fouled. Cleaning the plugs resulted in complete cure.

2nd time. Same truck, same trail, same day of the trip. Only now it's desmogged, with fresh JimC carb, and recurved FJ60 distributor/ignition. Same deal, fouled plugs. After cleaning with a wire brush and some emory paper-back to normal running.

I've never had this problem on Rubicon, Fordyce, or any other Sierra trail, but both of those top out about 7000 feet.

Any thoughts? I was on the trail with 2 fuel injected trucks with no problems, and 2 FJ60s that both had 2Fs, and another 2F with a Weber carb. No one else developed any misfire/fouling problems.

Would it help to run different heat range plugs?

I'm thinking I should just carry a spare set of plugs and change after day 1. Any thoughts appreciated.

 

[sfrolich]

less (thiner) air = more (richer) fuel mixture = fouled plugs. I don't think hotter plugs will help. My motorcycle with a carb I need to have adjusted for high altitude driving.

I would check to make sure that you are not already running rich at the altitude you drive at often. Or perhaps you can pop the carb open when you get to high altitude and adjust the float level (just a thought). I've never worked on a 2F so I'm not sure about the mixure adjustment on the carb.

 

[inkpot]

Howdy! Sounds like you may need to tweek the timing a bit, and/or lean out the idle mix. I used to have to crank up my idle speed at altitude, otherwise it would just load up and crap out. I was usually too lazy to lean out the idle mix. For a while I ran a non-USA dizzy, and that made it easy to manually adjust timing without a light. John

 

[pb4ugo]

I advance the timing in higher elevations.

 

[65swb45]

Andy, are you willing to 'dig' into the carb and change parts if necessary to run the trail?

The effects of elevation are cumulative, and you cant forget that to get to that 2nd day point on the trail, you also had to pull grade to the trailhead [i'm assuming you don't trailer your rig; maybe not a safe assumption]


In any event, you're running at lower vacuum because of the altitude AND the ascent, which means that your power valve is getting a lot more use than normal. While it's nice having the fatter jetting in the PV for climbing the grade to Shaver, it really is a bit much for the trail.

Smaller PV jets are readily available, and I'd be happy to send you one no charge. LMK

Best

Mark A.

 

[Cruiserdrew]

Hmm..Interesting.

If I would not give up anything on the long run down the valley and then up the grade to Shaver, I'd be willing to mess with the carb. If it would kill my already inadequate power, then not as interested.

I figured it was a matter of leaner jetting, but if it's just the PV, that would be a lot easier to consider.

Thanks for the reply.

I did advance the timing to 11 degrees for the trip-it does run a bit better at altitude.

 

[FJ40Jim]

Drew, with the FJ60 dissy and an open chamber head, it oughta be OK running 10 degrees at sea level. At 8000', the engine might want 17* base timing.

Hotter plugs can help delay fouling. Stock 2F plugs are W14EXR-U. Hottest plugs available in that size range are W14EXR-U. So you might be kinda stuck there.

The idle mixture screw can be adjusted for altitude. Best to set it a little lean at idle, so when ticking over on the trail or coasting, it is frying the plugs clean. Not perfect, but simpler than a jet change.

Ultimately, the solution to the problem is changing jets to suit the altitude.

 

[Cruiserdrew]

Ultimately, the solution to the problem is changing jets to suit the altitude.

I only do this trip once per year, so likely not worth it. I may up my timing even further at the trailhead, since that's a trivial job. It is odd, that the circumstances and even the spot it happened were exactly the same.

Thanks. I'll see what plugs it has, and see if they are already the hot ones.