Hawk carb jetting/tuning, fine tuning a surge....

Deckard_Cain · 07-09-2020, 11:46 AM

I've got the stock pilot jet in my bike, 2 turns out on the mixture screw, swapped the stock 98 main for a 105.

I'm at 600ft elevation.

I've got a slight surging while cruising at any speed (but haven't gone much above 35-40mph, cruising along at roughly 4000rpm). Applying half choke doesn't seem to help.

It seems to be a 1/8-1/4 ish throttle surge, pulls good without issue at half throttle or higher.

I'm thinking maybe the needle needs a shim or two, and maybe I should go to a 110 main, but half and full throttle seems fine, so the main jet shouldn't apply here. Right?

Any thoughts?

Adjusting the valves later today too. I've currently got about 30 miles on the machine. Thanks!

CaptainKP · 07-09-2020, 11:55 AM

I'm around 1000ft elevation and using a 110 Main 27.5 pilot jet and set the needle at the 4th notch from the top/1 down from center & 1 1/2 turns out on mixture

Only issues I've run into with that setup was fixed when I adjusted the valves. I've adjusted them a few times now as the engine breaks in.

Magician16 · 07-09-2020, 03:30 PM

I agree with CaptainKP, adjust the valves first. My Magician(same engine) runs great on the lower half with a 42 Pilot and A/F screw at 1 3/4 out. When stock the 105 Main with the clip in the 4 down position, the top half ran strong as well. I'm having a hell of a time getting the top half adjusted after gutting the cat and putting on a pod.

Deckard_Cain · 07-09-2020, 03:39 PM

Quote:

Originally Posted by Magician16

I agree with CaptainKP, adjust the valves first. My Magician(same engine) runs great on the lower half with a 42 Pilot and A/F screw at 1 3/4 out. When stock the 105 Main with the clip in the 4 down position, the top half ran strong as well. I'm having a hell of a time getting the top half adjusted after gutting the cat and putting on a pod.

Hmmm. I want to gut my cat too... Hope you get yours tuned in. I hate how hot the cat gets next to your leg; way hotter than the engine or other exhaust pipes.

Deckard_Cain · 07-09-2020, 04:54 PM

So I put in a 110, shimmed the needle with a plastic needle shim I stole from a vm22 for my Hellcat (my shim kit is at my other work area), and checked my pilot (stock k40a) and made sure it was at 2 turns out on the mixture screw.

It runs a lot better. Maybe only a slight hint of the surging now at 1/8-1/4 throttle. Of course it is 90F outside this week.

I feel it could stand to have a 42 pilot jet and back off the screw a half turn...

I'll run it and see how she does from here.

07-09-2020, 11:46 AM	#1
Deckard_Cain Join Date: Aug 2019 Location: Bay City, MI Posts: 397	Hawk carb jetting/tuning, fine tuning a surge.... I've got the stock pilot jet in my bike, 2 turns out on the mixture screw, swapped the stock 98 main for a 105. I'm at 600ft elevation. I've got a slight surging while cruising at any speed (but haven't gone much above 35-40mph, cruising along at roughly 4000rpm). Applying half choke doesn't seem to help. It seems to be a 1/8-1/4 ish throttle surge, pulls good without issue at half throttle or higher. I'm thinking maybe the needle needs a shim or two, and maybe I should go to a 110 main, but half and full throttle seems fine, so the main jet shouldn't apply here. Right? Any thoughts? Adjusting the valves later today too. I've currently got about 30 miles on the machine. Thanks!
	0

07-09-2020, 04:54 PM	#5
Deckard_Cain Join Date: Aug 2019 Location: Bay City, MI Posts: 397	So I put in a 110, shimmed the needle with a plastic needle shim I stole from a vm22 for my Hellcat (my shim kit is at my other work area), and checked my pilot (stock k40a) and made sure it was at 2 turns out on the mixture screw. It runs a lot better. Maybe only a slight hint of the surging now at 1/8-1/4 throttle. Of course it is 90F outside this week. I feel it could stand to have a 42 pilot jet and back off the screw a half turn... I'll run it and see how she does from here. Last edited by Deckard_Cain; 07-09-2020 at 06:11 PM.
	0

07-09-2020, 11:55 AM	#2
CaptainKP Join Date: Apr 2020 Location: Atlanta, GA Posts: 58	I'm around 1000ft elevation and using a 110 Main 27.5 pilot jet and set the needle at the 4th notch from the top/1 down from center & 1 1/2 turns out on mixture Only issues I've run into with that setup was fixed when I adjusted the valves. I've adjusted them a few times now as the engine breaks in.
	1

07-09-2020, 03:30 PM	#3
Magician16 Join Date: Aug 2019 Posts: 469	I agree with CaptainKP, adjust the valves first. My Magician(same engine) runs great on the lower half with a 42 Pilot and A/F screw at 1 3/4 out. When stock the 105 Main with the clip in the 4 down position, the top half ran strong as well. I'm having a hell of a time getting the top half adjusted after gutting the cat and putting on a pod.
	1