Nikki carb OE4215 jet size for Generac 27hp

[tjwid]

I bought a Dixie Chopper with Generac 27hp knowing there was a fuel supply issue. Engine ran fine at idle but ran rich as rpm's increased. Verified choke and air filter were fine. Presumed the Nikki dropped a main jet or two. When I opened it up, in fact the main jets were not in place, nor were they in the fuel bowl. Presumably someone was in there before and managed to lose the jets. Now I'm stuck trying to determine proper jet size and source. This information seems to be kept under lock and key! I found no help with Generac or Dixie Chopper salespeople. I could buy a replacement carb and call it a day, but what a waste that would be!
I would greatly appreciate jet recommendation for std operation, i.e., low altitude. At least jet orifice size would be great. I have a couple of B&S jets that clearly are too small, machine runs hot and pops. Jets I have now are 1.18mm and 1.22mm. I'm willing to drill them out but I would really appreciate a target size to shoot for. Thanks in advance!

 

[Auto Doc's]

Have you tried Parts Tree. I have had luck finding jets on there. The O-rings for press in jets are not available by themselves and only come installed on the jets.

From what I recall the left bank is richer than the right. It has to do with combustion balance and cylinder thermal control.

For what it is worth, I bought an eBay replacement for both my Generac 12.5KW and 15KW generators and both worked great except I had to clip off the tip of the anti-backfire solenoid. I prefer to use the manual fuel shutoff valve anyway.

Does your carburetor float bowl have 2-screws or 4 screws holding it on?

Does it have the plastic center pickup or aluminum inside?

 

[tjwid]

Hi, thanks for your reply. Yes, I've tried parts tree, they have "rebuild kits" etc, but no jets, at least for a Nikki on a Generac. I have found people selling these o-rings on ebay. Yes, there are differences in jet size, my understanding is due to intake runner length.
The float bowl is aluminum, has two screws. The fuel tube is white plastic, also has two screws holding it on. Jest just press into the fuel tube with o-ring friction holding them in.

 

[Auto Doc's]

I think I have what you need.

What are the numbers dot marked in the top of your housing near the fuel inlet tube?

 

[tjwid]

Thanks for your reply. I've attached an image of the id numbers.

 

[Auto Doc's]

Thanks for your reply. I've attached an image of the id numbers.

Well, as it turns out I have only one match. It is a steel bowl aftermarket carburetor (The bowl may not be correct for the application). It has the white center plastic section with 2-screws to retain it, and the jets are held in with tiny O-rings.

My jet drills show the right (on the idle stop adjust screw side) to be a .0460 and the left to be a snug .0465. This carburetor I have was from a 23HP which should not be far off.

Keep in mind that Generac is under the Gen-Tech umbrella which I think owns the Larger commercial and rider grade Briggs and Stratton engines. Smaller push mower engines shifted to overseas production.

The market is so fragmented these days I can hardly keep track of all the changes.

My 30HP Generac parts carburetor has a 4-bolt float bowl and screw in brass jets.

 

[tjwid]

thanks again for your investigation and reporting. The jets I purchased were for a 24hp B&S engine and are very similar to those you report. My 27hp Generac isn't happy with these, just a bit lean. I think I will carefully open them up to obtain the performance this engine is capable of.

 

[hlw49]

What is the serial no. of the mower. Flip the first two digits of the serial and that is the year it was made. Also, what is the model of the mower? The problem is to meet the EPA emission standards around 2011 or 20012 instead of redesigning the engine. Generac just leaned the carb which made the engine run hot causing it to pop the head off the exhaust valve destroying the engine.

 

[Auto Doc's]

Hello T,

Going a little rich will keep the cylinder temperatures down.

A basic rule to remember is fuel cools down and air heats up the combustion process.

The ideal scientific mixture is 14.7 parts air to 1 part gasoline. (Stoichiometric mixture)

Don't "hog out" your jets dramatically. A .002 change above what you currently have may be all that is needed.

When people use the term "rich mixture" it means there is more fuel in the mixture than can be ignited during the combustion cycle. It does not create damage, but it does carbon foul the spark plugs quicker.

The term "lean mixture" is too little fuel, and it burns super-hot. That super heating creates damage over a period of time.


"Reading" the spark plugs is something I learned as a kid (and later riding iron head Harley's) when I was starting out, and it applies to all spark combustion engines. Here are some examples:

Too Rich= The plug electrode end will be very dark tan or black and produce black smoke when it runs.

Too Lean= The plug electrode end will be white or near white, and engine will get very hot quickly and "spark knock" from fuel mixture self-ignition will happen. No smoke just high heat and potential for damages.

Ideal mixture= The plug electrode end will be a faint light tan to sand color. Engine will only lightly puff a little smoke during a hard acceleration. At a steady run, no smoke.

Too much oil= A shiny, wet black plug electrode end and blue smoke when it does run.

I will also try to read the screw in jet numbers in my Generac 30HP generator parts carburetor if you need me to.

 

[StarTech]

thanks again for your investigation and reporting. The jets I purchased were for a 24hp B&S engine and are very similar to those you report. My 27hp Generac isn't happy with these, just a bit lean. I think I will carefully open them up to obtain the performance this engine is capable of.

Since you brought Briggs jets what are there part numbers and I see if I have the jet size and if there are one that are larger that I might have part numbers for.

And of course they are too small as they are for a 24hp not a 27hp.