Mikuni Tuning Issue

Redtail250 · 07-01-2022, 01:30 PM

Hey all! I’m back in need of Hawk wisdom. Calling jerryhawk and megadan lol. So I’m having trouble tuning my carburetor on my 2020 Hawk 250. My problem is I have an off idle bog, yes, lean bog. Once warm, at any speed in any gear in any atmospheric condition, with any load combination (just me or 2 up, luggage or not), at various altitudes in Pennsylvania, it will bog right as you take the throttle up from its rest point. After that, it will pick up and go and I mean haul ass with no bog. Doesn’t do it when the engines cold. Have chopped plug and it’s a perfect lightish hazy brown indicative of clean thorough burn. I’ve experimented with many jetting combinations to no avail and yes I’ve looked and searched through the forum for information and have my Hawk set up as per recommended jet sizes/screw settings, and still have this problem. I am using genuine mikuni jets from jetsrus. Specifications are as follows:

Main: 110
Pilot: 25
Mixture screw: 1.5 turns out from snug, to the left, counter clockwise.
Needle clip at 1st notch down from middle (1 notch richer, needle is 1 notch higher).
Valve lash: .003 on intake and .005 on exhaust
Lawn mower fuel filter installed and clean.
Single stage pod filter
eBay SS exhaust
Idle speed approximately ~1200
Mileage: 2,500 miles
Tuning altitude: ~800+ (Chambersburg PA)
Fanatically serviced/maintained/washed and detailed
No leaks, no backfires, starts immediately with full/half choke depending on ambient temperature.

BrokeAss · 07-01-2022, 03:14 PM

Too rich also causes a bog. I followed the recommendations on this site for a VM26 and had myriad issues.

Redtail250 · 07-01-2022, 03:37 PM

Have you had this particular problem with this platform? And if so, how did you remedy it?

BrokeAss · 07-01-2022, 08:55 PM

Big bore, cam, flat top piston, ported head and Nibbi carb.

Try lowering the needle.

Megadan · 07-02-2022, 12:16 PM

First, idle speed is too low. 1500rpm +/- 100rpm.

Second, the 25 pilot tends to be too small when combined with an exhaust and intake modification. A 27.5 will likely sort out the issue since the just off idle to 1/8th throttle is quite literally where the pilot jet has the strongest influence.

CheapThrills · 07-03-2022, 10:18 AM

I live in Pa too, but eastern part. Looked at my previous settings on my Mikuni carb and found I was running 1.5 screw open, 20 on pilot, mid on needle jet and 110 on main. Have photos: https://mymotorcycleblog.com/taotao-tbr7-mikuni-carburetor-jet-sizes/

New at motorcycles and when I had those settings I was even newer than now. Hope this helps.

07-01-2022, 01:30 PM	#1
Redtail250 Join Date: Aug 2021 Posts: 7	Mikuni Tuning Issue Hey all! I’m back in need of Hawk wisdom. Calling jerryhawk and megadan lol. So I’m having trouble tuning my carburetor on my 2020 Hawk 250. My problem is I have an off idle bog, yes, lean bog. Once warm, at any speed in any gear in any atmospheric condition, with any load combination (just me or 2 up, luggage or not), at various altitudes in Pennsylvania, it will bog right as you take the throttle up from its rest point. After that, it will pick up and go and I mean haul ass with no bog. Doesn’t do it when the engines cold. Have chopped plug and it’s a perfect lightish hazy brown indicative of clean thorough burn. I’ve experimented with many jetting combinations to no avail and yes I’ve looked and searched through the forum for information and have my Hawk set up as per recommended jet sizes/screw settings, and still have this problem. I am using genuine mikuni jets from jetsrus. Specifications are as follows: Main: 110 Pilot: 25 Mixture screw: 1.5 turns out from snug, to the left, counter clockwise. Needle clip at 1st notch down from middle (1 notch richer, needle is 1 notch higher). Valve lash: .003 on intake and .005 on exhaust Lawn mower fuel filter installed and clean. Single stage pod filter eBay SS exhaust Idle speed approximately ~1200 Mileage: 2,500 miles Tuning altitude: ~800+ (Chambersburg PA) Fanatically serviced/maintained/washed and detailed No leaks, no backfires, starts immediately with full/half choke depending on ambient temperature.
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07-02-2022, 12:16 PM	#5
Megadan Join Date: Apr 2017 Location: Omaha, NE Posts: 7,986	First, idle speed is too low. 1500rpm +/- 100rpm. Second, the 25 pilot tends to be too small when combined with an exhaust and intake modification. A 27.5 will likely sort out the issue since the just off idle to 1/8th throttle is quite literally where the pilot jet has the strongest influence. __________________ Hawk Information and Resource guide: http://www.chinariders.net/showthread.php?t=20331 2018 Hawk 250 - Full Mod list here. http://www.chinariders.net/showpost....62&postcount=1 2024 Royal Enfield Shotgun 650 https://chinariders.net/showthread.php?t=34124
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07-03-2022, 10:18 AM	#6
CheapThrills Join Date: Jan 2021 Location: Lehigh Valley Area Posts: 148	I live in Pa too, but eastern part. Looked at my previous settings on my Mikuni carb and found I was running 1.5 screw open, 20 on pilot, mid on needle jet and 110 on main. Have photos: https://mymotorcycleblog.com/taotao-tbr7-mikuni-carburetor-jet-sizes/ New at motorcycles and when I had those settings I was even newer than now. Hope this helps. __________________ - My 2 Bikes: TaoTao TBR7 Boom Vader Gen 2 (BD125-10) Testing a YouTube Channel
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07-01-2022, 03:14 PM	#2
BrokeAss Join Date: Mar 2021 Location: Ohio Posts: 43	Too rich also causes a bog. I followed the recommendations on this site for a VM26 and had myriad issues.
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07-01-2022, 03:37 PM	#3
Redtail250 Join Date: Aug 2021 Posts: 7	Have you had this particular problem with this platform? And if so, how did you remedy it?
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07-01-2022, 08:55 PM	#4
BrokeAss Join Date: Mar 2021 Location: Ohio Posts: 43	Big bore, cam, flat top piston, ported head and Nibbi carb. Try lowering the needle.
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