Honda GX50 Adjustable Carb?

[Sidewinder Jerry]

I'm totally fine with pedal assisting on steep climbs, or even all the time for that matter. I intend to use this as a bicycle with assistance rather than as a small motorcycle/moped.
I also am fine with less than ideal engine performance as I rise in elevation. Altitude is going to be so varied that I'm not going to take time to adjust the carb every few miles. I just want to be able to set it well enough for the range of altitudes I'll be at for any given day.

You don't adjust it every few miles. Take the bike to your highest peak and adjust it there. Then take it back down to start your ascension up the mountain.

The Honda 50 max torque is at 4500 rpm. So if you're on a really steep hill even with pedal assist the engine needs to be turning a minimum 4500 rpm at wide open throttle going up the hill. If it can't you risk engine strain and/or a burnt up clutch. With a multi speed bicycle you may be able to use a bicycle ratio to better pedal assist vs a single speed bicycle drive system. On hills around a 30% grade you also risk tire/roller slippage.

I live in the mountains. My advice is leave your friction drive for the flat lands and get a chain drive system for the mountains. Shifters work really good here.

 

[DieselTech]

What sort of work? I have access to a machine shop, so I would be fine doing any machining work.

Might just have to grind out the factory carb spacer and/or make a new 1 out of a phenolic type material, if you want to go to a 15mm carb. Biggest thing to look for is carburetor mounting bolt spacing.

 

[Karl Snarl]

Here is a carb that should replace yours if need be. Its fully adjustable with a 11mm intake. You could got to a 15mm carb if you feel you need more power & dont mind a little work.View attachment 176305

Those such for making power on a CG. I've tried them. Easy to tune etc, but lack power.

 

[darwin]

OK I need some help here. Tried searching but come up empty. A diaphragm carb in my mind should compensate for altitude. Am I right here in my thinking? At sea level 14.7 psi, as you climb it's lower. Wouldn't that adjust the lean condition with rise in altitude?

 

[DAMIEN1307]

OK I need some help here. Tried searching but come up empty. A diaphragm carb in my mind should compensate for altitude. Am I right here in my thinking? At sea level 14.7 psi, as you climb it's lower. Wouldn't that adjust the lean condition with rise in altitude?

If your carby has an air/fuel adjustment screw, than you do have to readjust for altitude...At least I had to on my cars when I lived up in Big Bear during my time living there in the early 1970s...over 6000 ft altitude and they gasped for air...lol., all those carby's had diaphragms in them and would run like dog if I didn't adjust them for the altitude.

 

[Karl Snarl]

OK I need some help here. Tried searching but come up empty. A diaphragm carb in my mind should compensate for altitude. Am I right here in my thinking? At sea level 14.7 psi, as you climb it's lower. Wouldn't that adjust the lean condition with rise in altitude?

It does nothing to change the hole size the fuel is flowing from. You still need to adjust the needle jets in the carb on a diaphragm carb. The loss of altitude increases the the density, and a gain, reduces the density of the air, but still does not compensate for the flow rate through the jets. Each altitude needs a certain cc of fuel for the amount of air. You'll still run rich climbing, and run leaner when descending. The pump slaps out a certain amount of fuel per pulse, not on density. If you want auto adjusting, you need a lambda sensor to read the exhaust content. An an ecu to adjust the fuel delivery.

 

[Chainlube]

How would I determine which clones would fit? i.e. What are the important measurements? Will the mounting holes all have a standard pattern/spacing?

Measure the intake bore on the engine and the mounting bolt spacing.

 

[darwin]

OK Karl, just 1 more ?. Since the diaphragm is using less psi at altitude to pump the fuel doesn't that reduce the fuel delivery?

 

[Chainlube]

OK Karl, just 1 more ?. Since the diaphragm is using less psi at altitude to pump the fuel doesn't that reduce the fuel delivery?

The diaphragm gets it pulse from the engine, not related to atmosphere.

 

[Karl Snarl]

OK Karl, just 1 more ?. Since the diaphragm is using less psi at altitude to pump the fuel doesn't that reduce the fuel delivery?

Even with less air, the diaphragm still makes one full movement. Delivering the same amount of fuel. The pulse is based off of the engine. Still pulling in how many ever cc's of air, just at a different density. An the diaphragm moves so very very little, the slight difference in psi doesn't effect it at all. It will still pump the same amount of fuel on pikes peak as it will in death valley. Most of them are made so they pump more than can be delivered through the jets, an ones with a return line just send that extra back to the tank. One's without, just take less fuel than a full pulse delivers to re prime the valve for the next charge of fuel.