Nikki carb OE4215 jet size for Generac 27hp

[hlw49]

I just pulled a carb off a Dixie Chopper XFG2700 year 2003 with a 27 HP Generac. Took the bowl off the carb and looked at the jets the no 1 cylinder jet is 130 no 2 cylinder best as I can tell is 138

 

[LMPPLUS]

Wouldn't the jets being loose create the over fueling problem? With many Nikki carbs the main jets are held in place by the mini o-ring when they get hard the flow of fuel moving thru the nozzle will actually lift the jet out of place and more fuel flows around the bad o-ring causing the over fueling.

 

[StarTech]

Wouldn't the jets being loose create the over fueling problem? With many Nikki carbs the main jets are held in place by the mini o-ring when they get hard the flow of fuel moving thru the nozzle will actually lift the jet out of place and more fuel flows around the bad o-ring causing the over fueling.

Yes normally they do but in the OP case the jets were completely missing as apparently someone else had already been in the carburetor. Now he was trying what the correct jets are size wise as Generac does not provide them, just complete carburetors.

 

[RevB]

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.

Too rich means you're washing down the cylinder with excess fuel. Too rich also means excess carbon build up and that is reflected in the deposits and the really black oil that results.

Too lean does not burn hotter as the highest temps are achieved rich of peak temps, not lean of peak. Lean is better for the engine. Less deposits, cleaner oil. You can cool with fuel or with air. Which one is cheaper.

https://www.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2012-12_red-box-red-fin.pdf

Yeah....these aren't aircraft engines. But the principles remain exactly the same for all gasoline internal combustion four stroke engines. If too lean "burns" valves and destroys engines the lean burn Hondas would have littered every road.

 

[RevB]

Yes normally they do but in the OP case the jets were completely missing as apparently someone else had already been in the carburetor. Now he was trying what the correct jets are size wise as Generac does not provide them, just complete carburetors.

Generac probably doesn't know the size of the jets.....

 

[Auto Doc's]

Hello RevB,

You are correct. Generac just builds the generator heads and only some of their own engines. The carburetors are outsourced from other companies such a Nikki.... Nikki builds the OE carburetors to match engine CFM calculations and basic engine displacements.

Most of the time, the same carburetor will be designated to fit many different product lines with similar engine displacements. It is known as "off the shelf sourcing"

Even the aftermarket "copycat" carburetors usually come with a selection of different choke levers or special adapters so they can be used on different equipment configurations.

Small engine carburetor manufacturers do not cater to just one OE engine design (they would go out of business if they did).

 

[Auto Doc's]

Too rich means you're washing down the cylinder with excess fuel. Too rich also means excess carbon build up and that is reflected in the deposits and the really black oil that results.

Too lean does not burn hotter as the highest temps are achieved rich of peak temps, not lean of peak. Lean is better for the engine. Less deposits, cleaner oil. You can cool with fuel or with air. Which one is cheaper.

https://www.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2012-12_red-box-red-fin.pdf

Yeah....these aren't aircraft engines. But the principles remain exactly the same for all gasoline internal combustion four stroke engines. If too lean "burns" valves and destroys engines the lean burn Hondas would have littered every road.

Hello RevB,

Gasoline aircraft engines do have the same operating principles as automotive and small engines.

The big difference is that most automotive engines from the early 70's to present use an EGR system and/or specialized computer timing and fuel injection controls to prevent excess in cylinder temperatures.

The optimal fuel ratio for any gasoline engine is 14.7 parts (grams) of air to 1 part (gram) gas. (Stoichiometric)

Fuel injection and timing modules for larger mower engines are gradually being introduced, but they are going through some "growing pains" due to environmental impacts and component reliability. Along with that is the added expense of digital components to make them function. New equipment cannot take near the neglect and abuse of the older equipment and still be made to run economically.

 

[RevB]

Hello RevB,

Gasoline aircraft engines do have the same operating principles as automotive and small engines.

The big difference is that most automotive engines from the early 70's to present use an EGR system and/or specialized computer timing and fuel injection controls to prevent excess in cylinder temperatures.

The optimal fuel ratio for any gasoline engine is 14.7 parts (grams) of air to 1 part (gram) gas. (Stoichiometric)

Fuel injection and timing modules for larger mower engines are gradually being introduced, but they are going through some "growing pains" due to environmental impacts and component reliability. Along with that is the added expense of digital components to make them function. New equipment cannot take near the neglect and abuse of the older equipment and still be made to run economically.

Except for the part where we can run wide open throttle all the time and use altitude to reduce the power output. I was always a fan of lean-of- peak operation but, again you can do that generally with injected (continuous flow) and mixture control, normally aspirated. Turbos are a whole nother world. IO520 Continental in a Bellanca Super Viking...just for a 5% reduction in power I'd get 50° lower CHT and 200° lower EGTand about a 5 knot reduction in true airspeed to 165 knots at 10 to 14,000 ft.

Just occured to me that if you wanted to really know what your engine was doing slap an EGT one to two inches from the exhaust port(s) and jet for 1150°F to 1200°F or so.

 

[Neo7]

I'm working on a B&S 25HP, Nikki at the moment. So with a lots of magnification I read 111 and 114 ... 111 on the "R" Side (Cylinder 1) of the Carb .... Get these the wrong way round and Cylinder 1 runs a lot hotter than Cylinder 2

 

[StarTech]

For my cross reference chart please post the engine's model and type number so I can add PN to jet size cross reference. I can look up the part numbers myself unless you already them with their jet sizes.

But I suspect you have; although, Briggs may have another PN now.