Dynojet kit for V Star seems much too rich with recommended settings - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 31 (permalink) Old 10-08-2014, 06:51 PM Thread Starter
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Dynojet kit for V Star seems much too rich with recommended settings

I have a 2013 V Star 650. About 4 months old. I put Roadburner Exhaust, K&N Filter and used a dynojet kit main jet and jet needle. I turned the screw out 3 turns. I carb synced and adjusted the idle. AIS is removed.

The engine sounds good, but I must be running rich. I get loud decel pop when I downshift or roll off the throttle. When I cold start with the choke pulled all the way out it doesn't start easily.

I live in Charleston, SC so the air is not thin.

The whole reason I broke down and bought a Dynojet kit is because the nearest dealers didn't stock Mikuni jets and Roadburner recommended it. Though I think Roadburner just recommends Dynojet so if you have problems you call Dynojet customer service to complain instead of Roadburner customer service.

Should I be able to lean it out with just the air mixture screw, or should I ditch the dynojet parts and start trying different sized Mikuni Jets?

I guess I could also try the smaller sized main jet that came with the kit.

I definitely need to do something, because I want to get the smartpartz quiet baffles and if anything that will make it richer.
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post #2 of 31 (permalink) Old 10-08-2014, 07:27 PM
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Just a small word of caution.....if you're popping on decel...you are lean on the idle circuit, not rich.

Sick Mick* 2006 V Star 1100 Custom

--- Striping, lettering and paint by Sick Mick – 6* Tree - 2" extended forks – 21" front wheel - HK Sideburners - Progressive rear shock – Pods – Sick Mick solenoid delete - Spring seat - and other stuff
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post #3 of 31 (permalink) Old 10-08-2014, 11:45 PM Thread Starter
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Just a small word of caution.....if you're popping on decel...you are lean on the idle circuit, not rich.
The Dynojet troubleshooting guide says for decel pop says to turn air screws out more. Which I believe would make it leaner.
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post #4 of 31 (permalink) Old 10-09-2014, 08:30 AM
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OK... I'm not sure what an "air screw" on a Mikuni carb is........ but if you mean pilot mixture screws...turning out=more fuel=richer mixture.

Directly from the Mikuni tuning guide...

"Why This (normally) Happens:

1) When the throttle valve is in the idle position, fuel does not flow out of the main system (needle, needle jet, main jet). Fuel is only delivered to the engine by the pilot (idle) system.

2) The combined effect of the closed throttle and elevated engine rpm is to create a fairly strong vacuum in the intake manifold. This vacuum, in turn, causes a high air flow rate through the small gap formed by the throttle valve and carburetor throat.

3) Under these conditions the pilot (idle) system cannot deliver enough fuel to create a normal, combustible air/fuel ratio. The mixture becomes too lean to burn reliably in the combustion chamber. It gets sent into the exhaust system unburned and collects there.

4) When the odd firing of the lean mixture does occur, it is sent, still burning, into the exhaust system where it sometimes ignites the raw mixture that has collected ---- the exhaust then pops or backfires."

Sick Mick* 2006 V Star 1100 Custom

--- Striping, lettering and paint by Sick Mick – 6* Tree - 2" extended forks – 21" front wheel - HK Sideburners - Progressive rear shock – Pods – Sick Mick solenoid delete - Spring seat - and other stuff

Last edited by Sick Mick; 10-09-2014 at 09:21 AM.
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post #5 of 31 (permalink) Old 10-09-2014, 10:40 AM Thread Starter
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I'm talking about the screws you unplug on the bottom right side of the carbs. The side with the brass caps that you remove to adjust the needle.



I looked at the crude Dynojet installation guide and it actually calls them "fuel mixture screws." 650ccnd.com calls them "pre-mixture screws." Cruiser Customizing calls it the "air/fuel mixture screw" in the V Star 650 re-jet how to video. Other people are calling it "air mixture screw" online.

My confusion is that all the diagrams for Mikuni carbs I find are oriented a lot differently.
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post #6 of 31 (permalink) Old 10-09-2014, 04:18 PM Thread Starter
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When I cold started it today, it idled great with the choke pushed in, but the idle would get worse and worse as I pulled the choke out. All the way out, the engine would just stall.

Last edited by Kyle76; 10-09-2014 at 04:26 PM.
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post #7 of 31 (permalink) Old 10-09-2014, 04:23 PM
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think the way it goes if the screws are in the front of the carb they are fuel mix. screws so turning them out would allow more fuel to go in thus enrichening. air screws are opposite turning them in decreases the amount of air thus enrichening the mix. although you may find in reading that the fuel screws are in the back and the air screws are in the front confusing no.
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post #8 of 31 (permalink) Old 10-09-2014, 06:02 PM
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Mikuni calls them "Pilot Mixture Screws".....and that is exactly what they are. The pilot jets control the fuel flow up to about 1/3 throttle and the PMS allows a small amount of fuel to bypass the slide so that you get fuel into the engine with the throttle closed. So basically they control the throttle closed fuel mixture through the pilot jets.



Opening them gives you a richer mixture at idle, closing them makes it leaner. If you are getting backfire through the exhaust on decel...you are too lean. I have mine dialed in to just barely backfire on occasion.....it just takes some riding and tuning to get it right. One of the best investments I've made is s pair of PMS thumbscrews from Metric Magic.....quick and easy PMS adjustment when you need it.


Sick Mick* 2006 V Star 1100 Custom

--- Striping, lettering and paint by Sick Mick – 6* Tree - 2" extended forks – 21" front wheel - HK Sideburners - Progressive rear shock – Pods – Sick Mick solenoid delete - Spring seat - and other stuff
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post #9 of 31 (permalink) Old 10-10-2014, 08:40 AM Thread Starter
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Do you have a V Star 1100 or 650? Because all the aftermarket PMS screws I can find for Star Motorcycles are V Star 1100 and Road Star 1600 and 1700. Not for V Star 650.

I played around last night trying to get to the screws without removing the gas tank. No such luck. The rubber piece of the airbox joint that goes on the side of the airbox silencer is in the way. I took the tank off last night. I'll try adjusting it and putting the tank back on this evening. If I could find a comically short screwdriver maybe I could do it.

Quote:
Originally Posted by Sick Mick View Post
Mikuni calls them "Pilot Mixture Screws".....and that is exactly what they are. The pilot jets control the fuel flow up to about 1/3 throttle and the PMS allows a small amount of fuel to bypass the slide so that you get fuel into the engine with the throttle closed. So basically they control the throttle closed fuel mixture through the pilot jets.



Opening them gives you a richer mixture at idle, closing them makes it leaner. If you are getting backfire through the exhaust on decel...you are too lean. I have mine dialed in to just barely backfire on occasion.....it just takes some riding and tuning to get it right. One of the best investments I've made is s pair of PMS thumbscrews from Metric Magic.....quick and easy PMS adjustment when you need it.

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post #10 of 31 (permalink) Old 10-10-2014, 12:39 PM Thread Starter
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I just picked up some allen wrench style screwdrivers, so I won't have to take the whole gas tank off next time.
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