High RPM miss/2 black plugs/poor MPG


Information and questions on GL1100 Goldwings (1980-1983)
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Johnny Boy
Posts: 24
Joined: Tue Mar 06, 2018 1:32 pm
Location: Crossville, Tennessee
Motorcycle: 1980 Goldwing 1100i, 1998 Triumph Sprint 900, 2002 Kawasaki Ninja 250,
!969 Sportster XLCH

High RPM miss/2 black plugs/poor MPG

Post by Johnny Boy » Sat Jun 23, 2018 4:26 pm



Hello all. I got a problem (the title of this thread) that I think has to do with the carbs. 1980 1100i 28,000 miles. Plugs #1&#4 carbon black fouled. MPG is 33-35 at 50-70 mph, all back roads, no interstate speeds. A miss at high RPM (5500) and when climbing hills.

When the problem started I thought it was electrical, poor spark. I ohm tested the coils and found the 3/4 coil bad. I replaced the coils (Amazon-Caltric brand) and the wires. I also removed the resistor in the plug caps, replaced them with a solid piece of copper. I'm not running a radio or intercom. New NGK plugs. And I ran a hot with a relay to the coils. Pretty sure spark is not the problem.

I pulled the carbs and did the following: Confirmed that the vacuum pistons in the tops slid up and down freely. Inspected the needles for obvious wear. Pulled the main jets and the holders- main jets (Keihin #145) openings and all the tiny holes were clear. I didn't remove the pressed in slow jets, it's starting, idling and low to mid speed are fine. I set the float heights to 15.5mm. I set the mixture screws to 2.5 turns out.

I did not separate the carbs so I couldn't check the air cut-off valve.

I'm stumped, anybody have any suggestions?



User avatar
Johnny Boy
Posts: 24
Joined: Tue Mar 06, 2018 1:32 pm
Location: Crossville, Tennessee
Motorcycle: 1980 Goldwing 1100i, 1998 Triumph Sprint 900, 2002 Kawasaki Ninja 250,
!969 Sportster XLCH

Re: High RPM miss/2 black plugs/poor MPG

Post by Johnny Boy » Sat Dec 15, 2018 8:35 am

Well, no replies on the original post but here's an update in case anybody in the future reads this.

I have been riding the bike regularly for the past 5 months. Ran great but still had the miss. Decided eventually the carbs would need full attention. Either I would do it with a Randakk kit or I might get lazy and drop the carbs at Pistol Petes. He's a short drive from me. In the mean time every tank of gas (non-ethanol, they got it everywhere around here) got either Seafoam, Berrymans B-12 or ATF.

After roughly 4 months of gas additives the high RPM/ high load (climbing hills) miss is gone. Plugs are burning fine and MPG is in the upper 30s. I'm real happy. Looking forward to a run down to Florida in the spring for Bike Week.

DaveO430
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Re: High RPM miss/2 black plugs/poor MPG

Post by DaveO430 » Sat Dec 15, 2018 8:25 pm

Wow, sorry I didn't see this sooner. I could give an educated guess what the problem was. The air jets under the slides that go to the main jets were probably plugged. Glad it got better.

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