Carburetor Swap

Has anyone put a carb on an engine that was originally off of another completely different engine? What im hoping to do is put a honda gx style carb on my tractor.

It depends. What GX model is it coming off from and what engine is it going on? Why is it going onto a different engine? I know people have used snowmobile carbs on small engines before.

Doug Fackler wrote:

It depends. What GX model is it coming off from and what engine is it going on? Why is it going onto a different engine? I know people have used snowmobile carbs on small engines before.

Its off a 6.5 hp honda clone motor. Itll be going on an 11hp briggs I/C. After typing that out im realizing that it probably wont work because of the HP difference. I need a temporary carb for this engine while i wait for the carb kit to come in.

wouldnt work. It would however work on a tecumseh of that range (oddly) but you'd have to run it nearly full-choke to make it work.

Either way, the briggs has a different mount pattern.

You can run bigger hp engine carbs on smaller hp engines. It just runs funny sometimes depending on the difference. I ran a 17.5 hp on a 12.5 hp without a problem and gained some power

could u put an atv carb on a 12hp briggs and stratton? or if i was going to put a bigger carb on, how much bigger hp would i have to take it off of or buy it for to gain extra power?

I couldn't tell you. You could if you could make a adapter. But im sire there's a point whenever its not worth it. Maybe a few hp bigger because all it does is allow more airflow into the engine for a better burn

There is a fair amount of things to consider when attempting such a carb swap. Some points to consider-

1)Too big is just as bad as too small. A carb that is too large will not have a sufficient venturi effect, and won't create enough vacuum to draw the fuel in properly. Too lean no matter what you do.

2)Mounting- Unless the carb came off a very similar engine, the mounting studs will be spaced differently, and often, not even level. You'd have to fab an adaptor, and if what you make is not perfectly airtight, it will never run right.

3)Governor- If your engine is still governed, and you swap to a completely different carb, your governor will NOT work. This will result in you having to completely rework the throttle mechanism, and (best bet) open the engine to remove the governor's internals.

4)Jetting- Unless the replacement carb is coming off a pretty much identical engine, it's a safe bet that the jetting will be way off. Depending on carb design, it can be QUITE a challenging process to get the carb tuned to the engine. More often than not, this process can also necessitate the purchase of additional jet needles, needle jets, main jets, idle jets, and sometimes slides.

So- Is this a good idea? No- Not as a temporary solution. Swapping carbs is a commitment, that will require more time/effort/money than you'd want to put into a "temporary" solution while you await parts. And, done wrong, your engine will run like crap, if at all. Been there, done that...

And FWIW- a bigger/better carb will NOT make more power. At best, it will improve throttle response, allow smoother running, better transitions. There IS such thing as too big. A proper mixture is a proper mixture. Thanks to the venturi effect, too big will NOT inprove airflow for a better burn or whatever, and can actually kill fuel delivery.

Oh. Lol. I had a bit more power out of it. Well it seemed like it. Maybe it was just throttle response seeming like it.

crazykid1994 wrote:

Oh. Lol. I had a bit more power out of it. Well it seemed like it. Maybe it was just throttle response seeming like it.

That's possible. Also, if the old carb was not functioning 100% or a bit clogged up or whatever, you could have gotten some power back, seeming like a gain.

Common setup Ive used (outside of my current tractor mod hobby) on briggs/tecumseh/honda and yes, one kohler, was make a flange-barbed pipe fitting adapter. IE one side bolts to engine intake port other gets pipe from carb squished on.

Broadly similar to motorcycle intake setups using hoseclamps instead of flanges and gaskets.

The most common and I found easiest to tune was a mikuni PK series that had needle adjustment for the high speed. I can't remember the complete model # but basically its a small (20-25mm?) slide carb with a manual butterfly choke and a float bowl. The one I used on my honda 240 had a busted choke, so I removed it and polished the insides. The engine would snap to redline like a weedeater. Very responsive, and probably throwing 14h from 9 stock.