145 main jet, running rich? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 10 (permalink) Old 03-08-2020, 09:46 PM Thread Starter
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145 main jet, running rich?

Hey all, I'm in a good mood today. I finished the earshave procedure and gone are my vacuum leaks and flooding issues. The bike runs like a dream! well, almost. I had the bike running open headers since I was doing a degoat at the time (Sounds pretty awesome with straight pipes though). After revving the bike and letting off the throttle, it will pop and shoot flames out of the exhaust. Does this mean it's running rich?

I bought a 145 main jet instead of 142 because it came in a set with the #42 pilots and needle shims for a lot cheaper. Do you think that's too big a jet size? Even if it is a tad bit rich, could it really harm the bike? I don't want to pull the carbs again for the 10,000th time.

Thanks!
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post #2 of 10 (permalink) Old 03-09-2020, 12:54 AM
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Too big!

I'm running 40/140 with full earshave and OEM exhaust.
Runs great.
A little rich on idle.
Probably gonna change the primary jet to 38 when I get the gumption.

"I need yo clothes, yo boots and yo motocycle."- Uncle Bob

Last edited by roadpouring; 03-09-2020 at 01:11 AM.
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post #3 of 10 (permalink) Old 03-09-2020, 08:18 AM
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Could end up with fuel in the oil, and also washing the oil from the cylinder walls/rings/pistons.

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Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #4 of 10 (permalink) Old 03-09-2020, 06:24 PM
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What is your altitude? I'm at an elevation of 850 ft and I run 40/140. I had slight stumbling at the top end with 40/142.

It's possible to rejet without removing the carbs. Pull it off the lower boots and tilt the carbs to one side, and you can change the jets on that side.

The flames out the exhaust are actually from a lean condition when the throttle is snapped off from higher RPM. The engine is spinning fast, but the fuel supplied is only enough to support idle. The mixture is too lean to ignite in the cylinder, so raw gas is dumped into the exhaust, and ignites in the pipe. Making the idle richer will reduce/eliminate this. I went 1/2 to 1 turn richer and it stopped popping, but that's running too richer than optimal when at idle.

I like the pops in any case...


'89 VN750 Bought stock 4/12/18 @ 17805.9 miles $800. Wrecked once. 27454.5+ miles

Completed modifications:
Removed mufflers, straight pipes out of GB. 110/90 Front Tire. Pick-up coil mod. Shindengen MOSFET FH020AA r/r. USB Outlet + Voltmeter. Repainted Metallic Blue w/ new tank bages. Ear Shave (wo/ coasters) 40/140 NO shims 45MPG. MCCT conversion.

Planned modifications:
Custom LED turn signals. Windshield. Highway Pegs. (Possible) ignition adv. Tuxedo Mod. Ignition coil mod.
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post #5 of 10 (permalink) Old 03-09-2020, 06:28 PM Thread Starter
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Quote:
Originally Posted by Jason Pittenger View Post
What is your altitude? I'm at an elevation of 850 ft and I run 40/140. I had slight stumbling at the top end with 40/142.

It's possible to rejet without removing the carbs. Pull it off the lower boots and tilt the carbs to one side, and you can change the jets on that side.

The flames out the exhaust are actually from a lean condition when the throttle is snapped off from higher RPM. The engine is spinning fast, but the fuel supplied is only enough to support idle. The mixture is too lean to ignite in the cylinder, so raw gas is dumped into the exhaust, and ignites in the pipe. Making the idle richer will reduce/eliminate this. I went 1/2 to 1 turn richer and it stopped popping, but that's running too richer than optimal when at idle.

I like the pops in any case...
I'm at around 450'. I think I'll try putting in a 142 main, and then enrichening the screws. The popping and fire is primarily from the back cylinder I've noticed.

Which way do you turn the screws to enrichen it? Out or in?
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post #6 of 10 (permalink) Old 03-09-2020, 06:42 PM
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Save your money and drop down to a 140 main.

Altitude isn't really a factor until around 5000ft and up.

Lean mix can cause popping, but I think the flames are from it being rich.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #7 of 10 (permalink) Old 03-09-2020, 08:58 PM Thread Starter
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Originally Posted by Spockster View Post
Save your money and drop down to a 140 main.

Altitude isn't really a factor until around 5000ft and up.

Lean mix can cause popping, but I think the flames are from it being rich.
Yeah, I just went for my first road-legal ride on this thing and wow, the gas mileage is terrible. I drove 23 miles and went through over a gallon.

Although to be fair, the first 5 miles I drove the petcock valve to the carb was out halfway and ripping gas so that could have been a factor.

So which way should I turn the mixture screws for idle?
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post #8 of 10 (permalink) Old 03-09-2020, 10:09 PM
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Quote:
Originally Posted by rerb View Post
Yeah, I just went for my first road-legal ride on this thing and wow, the gas mileage is terrible. I drove 23 miles and went through over a gallon.

Although to be fair, the first 5 miles I drove the petcock valve to the carb was out halfway and ripping gas so that could have been a factor.

So which way should I turn the mixture screws for idle?

Turn in to lean it out, turn out to richen, the idle.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
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Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #9 of 10 (permalink) Old 03-09-2020, 10:34 PM Thread Starter
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Originally Posted by Spockster View Post
Turn in to lean it out, turn out to richen, the idle.
thanks!
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post #10 of 10 (permalink) Old 03-10-2020, 08:06 PM
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When I tuned my idle mixture, I turned both screws all the way in, then loosened both 2.5 turns. With the bike running and warm with no choke, a turn one screw 1/2 turn looser at a time. If the idle rpm increases, you were too lean. Go another 1/2 turn at a time in the same direction until it no longer increases. If it decreases, you were too rich. Go 1/2 tighter until it no longer increases.

You should find with that screw, a range of about 1 full turn where there's no effect on the idle (1/2 turn either direction does not change the idle). If you go to the tight side of that range, you will be on the optimally lean side. If you go to the loose side of that range, you will be on the optimally rich side. Repeat for other carb.

I chose the lean side for mpg and I liked the popping, but I sacrifice a bit off throttle response off of idle. About 1/2 to 1 turn looser from my settings gets rid of the popping on decal.
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'89 VN750 Bought stock 4/12/18 @ 17805.9 miles $800. Wrecked once. 27454.5+ miles

Completed modifications:
Removed mufflers, straight pipes out of GB. 110/90 Front Tire. Pick-up coil mod. Shindengen MOSFET FH020AA r/r. USB Outlet + Voltmeter. Repainted Metallic Blue w/ new tank bages. Ear Shave (wo/ coasters) 40/140 NO shims 45MPG. MCCT conversion.

Planned modifications:
Custom LED turn signals. Windshield. Highway Pegs. (Possible) ignition adv. Tuxedo Mod. Ignition coil mod.
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