Long road trip - now sick idle

[ybt502r]

I've got a two parter here - the good part first. My son and I just drove an early 80's SIII 88" (it's got a 77 registration but made up of most parts from an early 80's) from Colorado up to Calgary. 1400 miles of high plains and noise. The old girl ran without a hitch, though I think we passed maybe five vehicles, and four of them passed us back. Even the "wide load" trucks passed us. I've got the thick rubber mats in it, but the inside noise was still loud, so much so that when we turned on the CD player (my one modern addition) at a stop light (when the truck was still and not running 60 mph), the noise level of the CD player (set for road speeds) just about deafened us. We only did that once.

It never failed to start, and it never hesitated throughout. We averaged around 18 mpg and could only take it for about 450 miles a day, but everything worked and the overdrive was wonderful to have. That's the good news.

The second part is that now my idle is nasty, unsteady with black smoke. Also, the truck will start to surge and buck when running steady/slow in low gears, so much so that I have to put in the clutch to stop it - or floor it. The carb is a Zenith, installed new out of a box a couple years ago. I had a Weber when I got the truck, but that never worked right, and the Zenith has been much better. I tuned everything before making the trip, but the surging was sort of there before I left. It's worse now, and the black smoke is new.

I believe it's the idle settings/mixture (I tried upping the idle speed to smooth out the idle surging when on the road, but that didn't have any effect). I intend to look at it this weekend. Can anyone recommend something specific to start with? If this is the "Zenith warp", I'm in trouble as I'm living in a rental flat with little access to tools etc. right now. I'm hoping it's something else (easier) to address.

[scott]

not to be insulting but what is the altitude difference between your start and calcary? maybe you're just running rich. that will cause black smoke.

[gudjeon]

I've had a very similar problem with an out of the box Zenith. The rich running idle crept up gradually. Check the float level and reset it. That cured mine.

[xsbowes]

I had the same problem when I bought a 70 IIA in Hamburg Germany and drove it down to Catania Sicily. I ended up rebuilding the zenith carb and cleaning out the fuel filter. The quality of gas from Germany to Southern Italy changed drastically. There was a larger amount of grit in the filter due to Mt Etna(active volcano) in Sicily and for some reason it got into the tanks at a few of the gas stations there.

The carb ended up being warped also so I ground the surfaces with emory paper and oil on a sheet of glass, rebuilt it and it ran great after that. I used a sharpie and colored the surfaces so i could tell when it was flat enough to seal properly.

[Firemanshort]

non-rover experience - but back in college, I drove my car form Virginia to Key West for Spring Break - ran like a top the whole time. When I got home - the idle was a bit off. I ran acompression test and I burnt a valve in the trip.

Its a long shot - but a compression test just takes a few minutes.

[ybt502r]

Re the altitude, I was at 8800 feet above sea level in Colorado (and it was rich then, though I have a high altitude jet that I never got around to installing), and Calgary is about 3500 feet in altitude, so in theory I've made it better my moving down towards sea level. I'm actually at the altitude of the jet I've got, so I might still get it installed. I added a brand new fuel filter for the trip, so I'll recheck that too. I'm hoping it's the mixture and perhaps some plugging that I can easily remedy. I'm hoping.

[ybt502r]

OK, I've joined the Zenith warp crowd. I rechecked all the settings, then started with the mixture screw. Nothing I did with it really made any kind of difference. The truck just "chug-chugged" along in its now raspy idle, puffing black smoke, and didn't respond to any changes in the mixture screw. Before I left Colorado, I could get the idle to rev up/down by adjusting it. I guess the long days of high speed (and engine heat) cooked the carb, and when it cooled, it warped. Darn it. I'm not in a position to make the fix, assuming I'm that good, right now.

If anyone has got a better insight, I'm listening.

[pvkd]

Fixing the warp is not expensive (RN charges about $20 for the gasket set) and it takes about 1-2 hours to remove, lap the joints, check the float hight and replace the carb. You will also need new gaskets to remount the carb to the inlet manifold.