Honda GX 140 Mikuni Carb Questions

[Pellethuntr]

Hey guys long time no see, glad there are still some fermiliar faces around here.. Well I got a hold of an older GX 140 and cleaned it up, everything is in great working order now except the carb.. I spent countless hours trying to clean all the rust out and get it functional but I have had limited luck and I found that it had some missing part.. So I decided that if I am going to by a new carb I might as well upgrade in the process.. My questions are: What size Mikuni carb do I need? And what adapters/boots do I need to get to put the carb on and one of those "cone shaped" (forgot the actual name) airfilters? And what kind of performance upgrade can I expect? I am not expecting much but just curious.. Thanks

 

[r_chez_08]

Get a free flowing header. A gx200 wiener pipe would probably be plenty for a mild gx140 build.
I would say either a 20mm or a 22mm. You will need an adapter, available in many places online. Arc, NR and agk stock it as far as I know.
There is a new adapter from arc. It is an aluminium one that is really short compared to the old one.

You may even be able to fabricate one yourself with a few drill bits, 2x m6 Allen head bolts, 15mm or so thick aluminium sheet, rat tail file and a 6mm tap.

As far as performance, I would guess a new filter and header would add almost a HP alone. I would guess 6-7hp after mods and governor removal, considering a gx200 with a high flow header and filter and gov removal puts out approx 9hp.
Good luck!

 

[Pellethuntr]

Get a free flowing header. A gx200 wiener pipe would probably be plenty for a mild gx140 build.
I would say either a 20mm or a 22mm. You will need an adapter, available in many places online. Arc, NR and agk stock it as far as I know.
There is a new adapter from arc. It is an aluminium one that is really short compared to the old one.

You may even be able to fabricate one yourself with a few drill bits, 2x m6 Allen head bolts, 15mm or so thick aluminium sheet, rat tail file and a 6mm tap.

As far as performance, I would guess a new filter and header would add almost a HP alone. I would guess 6-7hp after mods and governor removal, considering a gx200 with a high flow header and filter and gov removal puts out approx 9hp.
Good luck!

Thanks! Do you have any links for the adapters or any pics on how to build one? Also what would you recommend for a filter and header? And is there any other cheaper brands than Mikuni? I have heard other people say that there are cheaper brands that do the same thing.. links are good

 

[r_chez_08]

You could probably get a 19-22mm chinese bike carb, like this. If you don't plan to get billet (which I really wouldnt bother) then this carb should be ok. The stock carb is only approx 16mm IIRC.

Here is the adapter I was talking about. I think the GX390 and a 22mm mikuni have the same mounting holes. However, for $17, personally I would make one myself.

There are other adapters here, but they are more money.

For an air filter a cheap k+n style should do. Just go on ebay or a kart website and buy one which has the same i/d as the filter mount o/d.

For a header, a wiener pipe would probably do, as the gx140 has small ports, so it would probably be quite a boost. IIRC my wiener pipe has an i/d of approx 16mm. Check your gx140 ports. The pipe should have a similar I/D to the port. Here is a wiener pipe, and here is another.

You could also get any other GX160/200/clone exhaust IIRC. If you want, measure between the exhaust studs, and tell me the measurement. I will double check against my clone.
Here are some cool part sites:
nr-racing.com
affordablegokarts.com
arcracing.com
bmikarts.com
ebay.com
and maybe some info here?
karting.4cycle.com.

Cheers

 

[Pellethuntr]

Thanks r-chez those links were helpful, I should be able to fab up a decent adapter out of some alluminum stock.. Those carbs are much cheaper than the Mikuni's, now im not so worried about if it will work or not

 

[r_chez_08]

Yeah they are not a bad price. Quality will be lower, but how much are you really going to spend on a 5hp industrial motor?
You should get a decent power increase.
Don't forget to remove the governor! Also for extra power you can deck the head by .050 or so, and/or get a thinner head gasket.

 

[Pellethuntr]

Yeah they are not a bad price. Quality will be lower, but how much are you really going to spend on a 5hp industrial motor?
You should get a decent power increase.
Don't forget to remove the governor! Also for extra power you can deck the head by .050 or so, and/or get a thinner head gasket.

Probably not gonna remove the governor on this one.. This engine cost me too much money to have it rip a hole in my cylinder.. What exactly do you mean when you say "deck the head" never heard that one before