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Nikki carb OE4215 jet size for Generac 27hp
#1
T
tjwid
T
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!
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!
#2
A
Auto Doc's
A
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?
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?
#3
T
tjwid
T
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.
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.
#4
A
Auto Doc's
A
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?
What are the numbers dot marked in the top of your housing near the fuel inlet tube?
#6
A
Auto Doc's
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.
A
Auto Doc's
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.Thanks for your reply. I've attached an image of the id numbers.
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.
#7
T
tjwid
T
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.
#8
H
hlw49
H
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.
#9
A
Auto Doc's
A
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.
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.
#10
StarTech
And of course they are too small as they are for a 24hp not a 27hp.
StarTech
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.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.
And of course they are too small as they are for a 24hp not a 27hp.
#11
H
hlw49
H
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
#12
L
LMPPLUS
L
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.
#13
StarTech
StarTech
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.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.
#14
R
RevB
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.
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.
R
RevB
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.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 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.
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.
#15
R
RevB
R
RevB
Generac probably doesn't know the size of the jets.....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.
#16
A
Auto Doc's
A
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).
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).
#17
A
Auto Doc's
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.
A
Auto Doc's
Hello RevB,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.
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.
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.
#18
R
RevB
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.
R
RevB
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.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.
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.
#19
N
Neo7
N
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
#20
StarTech
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.
But I suspect you have; although, Briggs may have another PN now.
#21
N
Neo7
Anyway, I know they're correct on my engine because I've checked the temperatures on the cylinders, and they are close to the same.
N
Neo7
Sorry, I'm not sure if I recalled this correctly, as this guy says the larger jet is on the "R" side.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
Anyway, I know they're correct on my engine because I've checked the temperatures on the cylinders, and they are close to the same.