Elevation changes while riding through the mountains

[ilikeslowbikes]

Hi y'all,

My bike uses a Honda GX 50 and I consistently go on long rides into the mountains from where I live (Phoenix). I have yet to push the bike past 2.5k feet in elevation because I fear the fuel mixture would become too rich and the engine wouldn't run right. There are some places around here like Flagstaff and hopefully the Grand Canyon eventually that I would like to ride to that are 6-8k feet above sea level, will my engine run? I don't have an adjustable carb. Would there be any harm in just trying and seeing how it goes other than fouling the plug?

 

[Chainlube]

You're not going to hurt your engine any running it a little rich.

 

[Sidewinder Jerry]

Adjustable carburetors now cost less than $20. You could get a tachometer and adjust the carburetor in the area you plan to be riding in. These carbs are so cheap you could have multiple carbs setup for different elevations.

 

[SirLurksAlot]

Hello, fellow arizonan!
I don't have a honda - I've got a lifan 79cc. But, it comes jetted for near-sea level just like your honda does. Here in Hellbrook at 5000ft elev, it does run rich. But has never fouled a plug or run poorly, tho the plug is definitely on the dark side of perfect. Installing a non-epa carb and high-elevation main jet fixed the dark plug but made little difference in subjective performance. That said, for daily driver use at my elev the leaner mixture provided by the re-jetted carb will result in cleaner combustion chamber/valves and is a must for daily driver use, imo. For your use, it might be overkill to use different carbs for temporary high elevation use. It certainly would be a pita to swap carbs midway thru the uphill ride and again on the downhill ride home. While you will probably be ok with short-term rich running, running lean (like it would if jetted for 7k ft and then run that way down in phx) is not good and could damage the engine. I'd just give it a try with stock jetting and carry a spare spark plug just in case of fouling. Anecdotally, a buddy has a Staton friction drive bike with a gxh50 running stock jetting, in Show Low ( approximately 7k ft elev) and has zero mixture issues, tho his sp plug is definitely dark...

 

[Sidewinder Jerry]

Hello, fellow arizonan!
I don't have a honda - I've got a lifan 79cc. But, it comes jetted for near-sea level just like your honda does. Here in Hellbrook at 5000ft elev, it does run rich. But has never fouled a plug or run poorly, tho the plug is definitely on the dark side of perfect. Installing a non-epa carb and high-elevation main jet fixed the dark plug but made little difference in subjective performance. That said, for daily driver use at my elev the leaner mixture provided by the re-jetted carb will result in cleaner combustion chamber/valves and is a must for daily driver use, imo. For your use, it might be overkill to use different carbs for temporary high elevation use. It certainly would be a pita to swap carbs midway thru the uphill ride and again on the downhill ride home. While you will probably be ok with short-term rich running, running lean (like it would if jetted for 7k ft and then run that way down in phx) is not good and could damage the engine. I'd just give it a try with stock jetting and carry a spare spark plug just in case of fouling. Anecdotally, a buddy has a Staton friction drive bike with a gxh50 running stock jetting, in Show Low ( approximately 7k ft elev) and has zero mixture issues, tho his sp plug is dark...

A tuned carb will give the engine maximum performance. If you regularly visit/vacation to an area with a significant elevation difference you can have a carb setup for that. Then change it out and store it till the next visit/vacation.

For purely ascending/descending or vice/versa joy rides using carbs with high/low screws; you could have an ascending adjustment and a descending adjustment. This way the closer you get to the area you're going to the better the engine performs. All one would need to know is the number of turns on the adjusting screws for the high and low elevations.

 

[SirLurksAlot]

Rather than swapping carbs back and forth, maybe try a pumper carb (saw style carb). That will allow you to simply make 2 adjustments to compensate for changes in elev, as opposed to swapping carbs and installing new gaskets etc. They're cheap and involve less risk of mistakes while away from the home garage etc. That will also adress any loss of performance due to elevation. IMO swapping carbs repeatedly isn't the best thing generally, IF avoidable.

 

[Sidewinder Jerry]

Rather than swapping carbs back and forth, maybe try a pumper carb (saw style carb). That will allow you to simply make 2 adjustments to compensate for changes in elev, as opposed to swapping carbs and installing new gaskets etc. They're cheap and involve less risk of mistakes while away from the home garage etc. That will also adress any loss of performance due to elevation. IMO swapping carbs repeatedly isn't the best thing generally, IF avoidable.

Maybe you could post a particular pumper carb that'll work on small engines???

 

[SirLurksAlot]

Hmm, not without searching the forum for specific models that are commonly adopted for our kind of use. Iirc, there are dozens of comments that mention specific models of saw/pumper carbs used and some info on mounting requirements - and I definitely should have mentioned that custom manifold work would almost certainly be required.

It's just an alternative to swapping carbs. Once installed, a pumper would eliminate any need for that, no?

Edit - you mention the possibility of using a carb that has both low speed and high speed screw-adjustments - sounds like a pumper/saw carb, to me. If not and you're talking about a carb with float and no diaphragm, I'd like more info myself!

 

[Sidewinder Jerry]

Hmm, not without searching the forum for specific models that are commonly adopted for our kind of use. Iirc, there are dozens of comments that mention specific models of saw/pumper carbs used and some info on mounting requirements - and I definitely should have mentioned that custom manifold work would almost certainly be required.

It's just an alternative to swapping carbs. Once installed, a pumper would eliminate any need for that, no?

I use to commonly switch out carbs every 3 months or so. Then I'd have to clean the removed carb. This was due to no station in my town selling 100% ethanol-free gas. Now that a station does sell it, I haven't cleaned a carb in over a year.

I have a 4 stoke and changing the carb is quick and easy. So I carry a spare with me. It's just when I hear pumper carb I think of something on a motorcycle. I use a diaphragm carb with idle, high, and low adjusting screws.

 

[SirLurksAlot]

Ok... We were talking about the same kind of carbs alllll along, then