Elevation Carburetion Issues?

[David Allaband]

I had some issues on a recent trip and am wondering if they are elevation/carburetor related?

I rode from LA to SLC, UT. 10 hours with many elevation changes from sea level up to 7,000ft. I rode up in what a local described as the worst rain storm in 20 years. After Vegas I only went 65mph. The way back was different, cool, clear air, I wanted to work it, but couldn't. For the first few hours (the highest overall elevations) I was able to get 70-80mph for a half hour at a time, then the engine would bog down. Sometimes it would resuscitate around 60mph, sometimes just die and bump start. As time went on and elevation got a little lower the bogging came more frequently but always around mountain passes. Finally I got the bogging every three minutes if I rode over 70mph. I kept it under 65 until I got to Vegas. After Vegas it was better but it felt like the engine was something less, less spunky. Now I'm back around sea level and there's still something different, something less then before.

Any ideas? I took the gas cap flap out a few months ago so that's not it. Do I have to adjust carbonation on this bike for elevation? That would be a serious pain in the rear. I always use high grade gas and I cleaned my Unipods about 9 months ago. Bike is my daily commuter but my commute is only 5 miles. Balanced the carbs a week before this trip. Brand new sintered fuel filter, new fuel lines, new petcock and cleaned the tank a couple months ago. I have the ignition relay upgrade for power. Around 160psi in each piston.

One thing I'm suspicious of is the fuel pump. In the past it always clicked when I turned the bike on (before starting). Now it only does that some of the time.

Thanks for any ideas!

[Pat Conlon]

Do you have a '87 like your signature line says?

If so, you do not have a fuel pump. I would look at:
1) water in your gas
2) a pinched fuel line from improper routing.
3) a pinched float bowl vent line

[Zwartie]

What year is your FJ? When I rode my '92 last year to Alaska and back there were many elevation changes ranging from sea level to 6,000-7,000 feet (or more) and there was never a carburetor issue that I could tell. Keep in mind that the '92 has a fuel pump. The only time when I did have any problems with fuel starvation was when I had to bypass the crapped-out fuel pump for two days (and then installed a replacement) and then it was only when the tank was half full or less and I was riding at 80 mph. Perhaps it is an issue with gravity-fed carbs? Just a thought.

Zwartie

[David Allaband]

Sorry, for clarification my bike is three bikes, a 1987, a 1989 and a 1993. 1987 frame, title and engine. 1989 fuel tank and petcock. 1993 fuel pump and carbs. Wiring harness might also be 1989 as it has the socket for the fuel pump.

Thanks for the ideas Pat!
1) I could see water as a problem, it was raining like crazy, but I've run 6 tanks through it since then. Could there still be enough water in there to cause trouble?
2) Fuel lines are not pinched, unless they became pinched during the trip and unpinched themselves before I got back to LA (would not be surprised if one of you told me this happens).
3) The pinched float bowl vent line sounds interesting. Is that one of the two hoses that comes straight down from between the carbs? If so, I don't have hoses on those, they are hose-less and just point straight down. Always been like that on the 93 I had and now this 87.

Zwartie, your post makes me suspect the fuel pump again, but at one point it was happening all the time, tank full or empty.

[David Allaband]

Wait, now that I think about it I once rode this bike to SLC and back WITHOUT a fuel pump and this didn't happen. It was even snowing then, so cold isn't it. Heavy rain is what changed, maybe water in the gas IS the issue. I had a tank bag over the gas cap the whole time and only fueled under roofs. But there was rain EVERYWHERE! Not like desert rain, not huge, heavy raindrops. It was a steaming, misty rain that came from every direction and soaked me even through my Aerostich suite! It only leaked once before in ten years of rain riding back east!

[big r]

Is your tank bag rubber backed? I had the same problem on my 87 after I did the flapectomy. The bag sat to tight to the cap and caused a blockage. Big R

[big r]

Sorry My bike is an 86. Fat fingers

[David Allaband]

Hi Big R. My tank bag is rubber backed but it has bumpy texture and creases to allow air. Even so I took it off during the ride to see if that was the problem and it didn't help. You and me think alike.

[Firehawk068]

I might suspect the "Sintered Metal" fuel filter.......................I am not sure, but I don't believe they flow very well..........Most of the applications that used those, were mounted after the fuel pump....................or maybe a tiny one on a lawnmower.
I would probably get a decent paper or fiber media filter..............

I ride around 9,000-10,000 ft quite regularly, and I have never had any problem with running at highway speed at those altitudes.............I've ridden her to 14,000 ft on a few occasions, and never had an issue there either..........

[aviationfred]

Wichita, Kansas is at 1330 Ft elevation. Last year I rode my 89' to Gunnison, CO. I did some spirited riding through passes as high as 11,000 feet. Absolutely no fuel starvation issues. At about 7000 feet I did start noticing that from a complete stop, I had to give the bike a bit more throttle and slip the clutch a little to get moving.

With the 89' fuel tank and petcock, the fuel pump and carbs from a 93' there should be no fuel starvation issues at any elevation.

With the information that I have seen here, I would say a possibility of water in the fuel, and/or a faulty fuel pump.

One other thought..... with all the rain you mentioned that you rode through. Check the connector for the fuel pump. Clean the pins with contact cleaner and a cotton swap. put some dielectric grease on the pins, reconnect and see if that helps.

Fred