Build own high altitude carburetor

[HawkeyeScott]

A couple of years ago, I ended up with a nice $600 Ryobi generator for $300. It had been returned to Home Depot and now I'm fairly sure I know why. It runs perfectly at home, which is about 2800 ft. elevation. But the intended use - supplying power while camping in the higher country - hasn't worked out yet.

When above 5000 ft. (or so), it will start and idle fine. But any sort of load - even a tiny one - will trip it. It just won't run with any load and, as such, is almost worthless to me in its current state.

I've talked with Ryobi's tech people in South Carolina. They've been great, but have shared that that model of carb is new and was supposed to work at high and low altitudes. (Older models had high alt. versions but this one does not, at least not yet.) Their take is that the fuel/air mix is off because of thin air. Too much fuel, not enough air.

So, I'm kicking around the idea of getting a second carb and trying to fashion my own high altitude version. Anyone ever tried this? My initial focus would be on the main jet. I'd try to somehow close it (JB Weld?) and then re-drill with a micro bit that is obviously smaller than the original. It'd be an inexact science, for sure.

Could it work? Other ideas?

 

[MrMoody]

The older carb can't be adapted?

Here's a brainstorm: run a mix of E85 in it to lean it out.

 

[eljefino]

I don't see how you can guarantee that little nub of JB won't get loose.

I wonder how you could get feedback on how it's running. Maybe take exhaust temps with an IR gun, under a certain load (hair dryer).

What about something like a propane conversion?

Small engine OPE has a mandated EPA warranty on stuff like carburetors. Check into this. Briggs version but the law's the law.

Maybe you could make a carb spacer with an air bleed? Seems like it would be hard to get to work over a full range of loads though.

 

[beanoil]

Altitude tuning
If the jet is brass, solder it, and redrill. You'll need a wire drill set to determine the initial hole size, then reduce it. It may be a fixed setup of some kind cast into the carb body to meet no adjustment standards. In that case you'll have no choice but to tune the fuel. There are several highly oxygenated race fuels you could blend in with pump gas to help out.
Wire drill bit set

 

[JimPghPA]

Jb weld may not hold up to being soaked in fuel.

Solder will probably last a couple of years.

 

[MichiganMadMan]

Originally Posted by MrMoody
The older carb can't be adapted?

Here's a brainstorm: run a mix of E85 in it to lean it out.



I agree on the E-85 idea, at least to prove the thing works properly before you turn it into a project. If I recall, optimum air fuel ratio for ethanol is around 10:1 (versus 14.7:1 for gasoline), so this gives you the ability to "swing" AFR by using fuel mix. I'd make sure that there isn't some other issue at work before I started making custom carbs.

I'd have a look at the new carb and see what type of jets it uses. Manufacturers generally pick from a giant catalog of jets that have the same OD and threads, with different center hole sizes to suit different applications. I'd also look at the "old" carb and see if I could figure out what jet it used, especially for the high altitude version. You might be able to order the old jet size for the new carb and have a good place to start. Usually they are a few dollars from an online carb specialty shop. If it didn't work correctly, you could drill it out a bit. I'm not a fan of JB Weld or soldering it, as they'll eventually work loose, especially in something like a generator that shakes like it's meant to mix paint.