Carburetor Jet Sizes

[Merkava_4]

Somewhere on the internet someone said a #100 jet is equivalent to 1.0 millimeter and a #35 jet is equivalent to 0.35 millimeter; is that correct?

[KE4AVB]

Somewhere on the internet someone said a #100 jet is equivalent to 1.0 millimeter and a #35 jet is equivalent to 0.35 millimeter; is that correct?

Yes. The jets are numbered in hundredths of a millimeter. And matter of fact I have a partial listing of Briggs Nikki PN to jet sizes listed in downloads, under the Briggs service info APSI directory. File name start with Briggs Nikki PN. Even includes a few Kawasaki jets which are interchangeable with the Briggs jets. IE Nikki jets are the same ones.

The list would be more complete if members had help a little but alas that didn't happen so it just the ones I have used or found on my own.

[Merkava_4]

It's a KEIHIN carburetor on a Honda mower. The mower has always ran lean at idle ever since day one out of the box. The engine does fine with the choke on at fast idle, but as soon has the choke pulls off, the engine goes into its surging routine. When engaging the blades via the blade clutch, the engine runs fine because I assume the engine is running off the main jet at that point. No amount of cleaning or poking with wires has cured the problem. The carburetor was never dirty in the first place, but I went through the cleaning procedure anyway just in case there might have been some debris in it from the factory. Just to prove to myself that it's a design issue and not a freak incident, I bought a second carburetor off eBay. A Genuine Honda carburetor with the same part number has the factory mounted carburetor. The replacement carburetor makes the engine surge just like the original.

[bgsengine]

. The replacement carburetor makes the engine surge just like the original.

In that case, I would be looking elsewhere beyond fuel system - close inspection of gaskets (and correct assembly order) careful checking of the gaskets to be sure they show a seal impression all the way around (Honda has so many intake gaskets that some can be "close" but not correct and have areas where they don't seal to flanges) careful inspection of insulator (and spacers) make sure when things are snugged down that it still sits square (if part of insulator or something hangs up somewhere it can cock over to one side slightly leading to air leaks) - lots of other things (including valves, spark plug type & brand, ignition aberration, anything related to air and air/fuel mixture and compression, as well as governor sensitivity, governor spring, harmonic vibrations of spring (sometimes just hooking up spring in different direction can do the trick!) and more..) So many things can cause a surge, and I have seen a lot of them myself (but not all) in my 40-odd years in small engines...

[KE4AVB]

It still be a carb problem BGS. I have had some Nikki carbs where they intentionally put in an idle mixture jet that was too small. In this case it might be the idle mixture is just set too lean but in order to correct it you must remove the idle mixture screw because glue on the limiter cap. This means you have break it off and install a new screw and cap.

[Merkava_4]

I'm really thinking the idle jet is too small since the mower started surging from day one out of the box. And then with it doing the same exact thing with a different carb, that tells me it could very well be an idle jet designed too small. I'm not a hundred percent sure, from I'm definitely leaning in that direction. I think what I should do is just swallow my pride and take the mower to a pro shop. I'll give them the extra carburetor and all the new gaskets too. I started this thread because I thought maybe one of you guys might have ran into this problem before. I was hoping somebody would say they've been there and done that and would tell me exactly which size jet reamer to use.

[KE4AVB]

I wish I could but walk behind mowers seldom come into my shop any more. Most customers have switch here to string trimmers and riders.

[38racing]

Try static governor adjustment.

[Merkava_4]

Gentlemen - you're not gonna believe this. I took the mower to three different professional mower shops today. They all said the mower runs perfectly normal for a Honda designed to meet California Emissions. They said as long as the engine doesn't surge while under load with the blade engaged, forget about it. They said I will never have to worry about fowling spark plugs.

[bgsengine]

Ah CARB.. sounds like Commiefornia, yep. As I understand it they're also working to outlaw most gas powered stuff anyways (how the hell do they expect to run emergency generators, chainsaws for firefighting/forestry bureau and the like?) But yeah, even EPA has caused us techs endless headaches. (and is a major reason why Tecumseh bit the dust)

Same thing I mentioned on a wheelhorse collector's forum - As engines became more "fuel efficient" they actually caused MORE fuel use (I.E. I can mow my acre and a half with my 10 HP Kohler cast iron K series with 36" mower deck on LESS FUEL than with my 22 HP Columbia/MTD with 46" Deck...and you couldn't run that 46" deck on anything much less, although you could run it on a 10 HP Briggs L-head from back in the day- and again less fuel burned to mow the lawn, even though the engine would have been less "fuel efficient" ... go figure...)