Mikuni idle mixture on Hawk

pcspecialist · 07-08-2016, 04:43 PM

I finally got around to giving a Mikuni a try. I started with 115/30 jets and the needle one notch higher than the middle (clip one notch lower).

The idle speed does not drop until I turn the idle mixture screw all the way in and it is too awkward trying to turn the mixture screw to count how many turns until it drops when richening it up.

First question, should I drop down to a 25 jet? I believe yes I should, but, if anyone knows a good reason not to, I'm listening.

Second, how far out would you turn it after leaning it enough to drop the idle speed? If it were easier to count the turns, I would run it between lean drop in rpm and rich drop in rpm, but, it just isn't going to happen with the micky mouse location of the mixture screw.

Entropy · 07-09-2016, 02:06 AM

I can't really help you on the jetting since I don't know what I'm doing yet but do you think this would help with your mixture screw? I bought one but haven't put it on yet.

http://www.ebay.com/itm/111958216035

pcspecialist · 07-09-2016, 02:13 AM

Quote:

Originally Posted by Entropy

I can't really help you on the jetting since I don't know what I'm doing yet but do you think this would help with your mixture screw? I bought one but haven't put it on yet.

http://www.ebay.com/itm/111958216035

Sure, it would help, but, by the time it arrived I will have already got it dialed in with the existing screw.

pcspecialist · 07-09-2016, 02:15 AM

less expensive in orange:
http://www.ebay.com/itm/111981067209

w0ss · 07-09-2016, 08:34 AM

I have a 27.5 and I believe mine is still a bit rich but it idles/starts ok. It will depend on the mods/altitude you are at.

Adjusting the mixture screw is a pain but I believe it needs to be adjusted no mater what jet your running.

mq1991 · 07-09-2016, 10:44 AM

Hey I had the same problem with the 25, I ended up at the 20 to make it run properly.

mq1991 · 07-09-2016, 10:45 AM

Quote:

Originally Posted by pcspecialist

less expensive in orange:
http://www.ebay.com/itm/111981067209

I purchased that one, it doesnt fit my carb :/

pcspecialist · 07-09-2016, 12:35 PM

Quote:

Originally Posted by w0ss

Adjusting the mixture screw is a pain but I believe it needs to be adjusted no mater what jet your running.

Not suggesting not adjusting it, was hoping someone who has could tell how many turns from the drop in rpm would put it between lean drop and rich drop.

Weldangrind · 07-09-2016, 02:48 PM

I've never thought of it that way. I just adjust the screw until I get a crisp throttle response with no bog. If that takes more than two turns out, I swap to a larger slow jet.

pcspecialist · 07-09-2016, 03:19 PM

Quote:

Originally Posted by Weldangrind

I just adjust the screw until I get a crisp throttle response with no bog.

That's pretty much all I did with the stock carb. I was hoping to more finely tune the Mikuni, but, maybe I'm overthinking it. So far I have turned it lean until rpm drop and then approximately 1/2 turn out (richer) and it seems great there. I guess I could even let it idle for a few minutes and then check the plug.

Ariel Red Hunter · 07-09-2016, 03:19 PM

Quote:

Originally Posted by pcspecialist

I finally got around to giving a Mikuni a try. I started with 115/30 jets and the needle one notch higher than the middle (clip one notch lower).

The idle speed does not drop until I turn the idle mixture screw all the way in and it is too awkward trying to turn the mixture screw to count how many turns until it drops when richening it up.

First question, should I drop down to a 25 jet? I believe yes I should, but, if anyone knows a good reason not to, I'm listening.

Second, how far out would you turn it after leaning it enough to drop the idle speed? If it were easier to count the turns, I would run it between lean drop in rpm and rich drop in rpm, but, it just isn't going to happen with the micky mouse location of the mixture screw.

Let me just say that you have the correct pilot jet when, after very gently turning the screw all the way in, turning it out 1 1/2 turns gives you a nice idle, AND clean acceleration up to 1/4 throttle. Ideally, the needle would be in the middle slot. The needle starts to effect carburetion from 1/8th throttle until transitioning to the main jet at three-quarters throttle. I say ideal because catylitic converters and mufflers effect caruretion.

pcspecialist · 07-09-2016, 04:13 PM

I started with 1 1/2 turns out and it was way too rich. I'll give the 25 jet a try.

Ariel Red Hunter · 07-09-2016, 04:34 PM

Quote:

Originally Posted by pcspecialist

I started with 1 1/2 turns out and it was way too rich. I'll give the 25 jet a try.

Please tell us how the 25 pilot jet works out for you. I think the #20 jet is usually the best choice at below 1000 feet above sea level, but will be interested in your experience with the 25.

pcspecialist · 07-09-2016, 10:39 PM

The 25 pilot seems to work great with the idle mixture screw somewhere around 1 turn. Next time I have the carb off, I'll verify exactly where the screw is set at. I'm shocked just how low I can adjust the idle speed and not only keep the engine running, but, also do a quick twist of the throttle and not kill it nor have it die on deceleration. Even with my 17/45 sprockets, I was able to drive pretty darn slow.

pcspecialist · 07-09-2016, 10:45 PM

The Mikuni is a small improvement over the rejected stock carb. I'll have to do some more riding before I can say if it is worth the price.

Next upgrade will be to slap a Pro Circuit Quiet Insert (1.50in) on the end of the muffler. I already decatitated the head pipe and drilled some holes in the plate in the middle/interior of the muffler (with a very long drill bit I have for running cables), but, there's too much restriction at the outlet which the Pro Circuit insert is a perfect replacement if the dimensions are accurate.

https://www.amazon.com/dp/B001654JK0

Code:

https://www.amazon.com/dp/B001654JK0

07-08-2016, 04:43 PM	#1
pcspecialist Join Date: May 2016 Posts: 583	Mikuni idle mixture on Hawk I finally got around to giving a Mikuni a try. I started with 115/30 jets and the needle one notch higher than the middle (clip one notch lower). The idle speed does not drop until I turn the idle mixture screw all the way in and it is too awkward trying to turn the mixture screw to count how many turns until it drops when richening it up. First question, should I drop down to a 25 jet? I believe yes I should, but, if anyone knows a good reason not to, I'm listening. Second, how far out would you turn it after leaning it enough to drop the idle speed? If it were easier to count the turns, I would run it between lean drop in rpm and rich drop in rpm, but, it just isn't going to happen with the micky mouse location of the mixture screw.
	0

07-09-2016, 08:34 AM	#5
w0ss Join Date: May 2016 Posts: 231	I have a 27.5 and I believe mine is still a bit rich but it idles/starts ok. It will depend on the mods/altitude you are at. Adjusting the mixture screw is a pain but I believe it needs to be adjusted no mater what jet your running. __________________ Hawk 250 with following performance mods: 17t, Mikuni with 110/25, Uni filter, Exhaust.
	0

07-09-2016, 02:48 PM	#9
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	I've never thought of it that way. I just adjust the screw until I get a crisp throttle response with no bog. If that takes more than two turns out, I swap to a larger slow jet. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	1

07-09-2016, 10:45 PM	#15
pcspecialist Join Date: May 2016 Posts: 583	The Mikuni is a small improvement over the rejected stock carb. I'll have to do some more riding before I can say if it is worth the price. Next upgrade will be to slap a Pro Circuit Quiet Insert (1.50in) on the end of the muffler. I already decatitated the head pipe and drilled some holes in the plate in the middle/interior of the muffler (with a very long drill bit I have for running cables), but, there's too much restriction at the outlet which the Pro Circuit insert is a perfect replacement if the dimensions are accurate. https://www.amazon.com/dp/B001654JK0 Code: https://www.amazon.com/dp/B001654JK0
	0

07-09-2016, 02:06 AM	#2
Entropy Join Date: Feb 2016 Posts: 98	I can't really help you on the jetting since I don't know what I'm doing yet but do you think this would help with your mixture screw? I bought one but haven't put it on yet. http://www.ebay.com/itm/111958216035
	0

07-09-2016, 02:15 AM	#4
pcspecialist Join Date: May 2016 Posts: 583	less expensive in orange: http://www.ebay.com/itm/111981067209
	0

07-09-2016, 10:44 AM	#6
mq1991 Join Date: Mar 2016 Location: Gurnee, Illinois Posts: 277	Hey I had the same problem with the 25, I ended up at the 20 to make it run properly.
	0

07-09-2016, 04:13 PM	#12
pcspecialist Join Date: May 2016 Posts: 583	I started with 1 1/2 turns out and it was way too rich. I'll give the 25 jet a try.
	0

07-09-2016, 10:39 PM	#14
pcspecialist Join Date: May 2016 Posts: 583	The 25 pilot seems to work great with the idle mixture screw somewhere around 1 turn. Next time I have the carb off, I'll verify exactly where the screw is set at. I'm shocked just how low I can adjust the idle speed and not only keep the engine running, but, also do a quick twist of the throttle and not kill it nor have it die on deceleration. Even with my 17/45 sprockets, I was able to drive pretty darn slow.
	0