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Carb cutting out at high rpm

Started by Harleynomo, Sat 09, Jun 2018, 20:31:19

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Harleynomo

Sat 09, Jun 2018, 20:31:19
New to the forum and hoping you guys can help. I have a 1999 Interstate and the bike runs great up to about 400-4500 rpm when one of the cylinders starts missing. I suspect a carb issue but how can I isolate the problematic cylinder? Bike only has 31k on it and I love it! Thanks in advance.

Valkorado

#1
Sat 09, Jun 2018, 20:46:45
The experts will chime in with solutions in no time.  I just wanted to say, great handle!   :cooldude:  Welcome to power cruising!
Have you ever noticed when you're feeling really good,
there's always a pigeon that'll come sh!t on your hood?
- John Prine

97 Tourer "Silver Bullet"
01 Interstate "Ruby"

sandy

#2
Sat 09, Jun 2018, 21:03:06
I might suspect a vacuum leak. Check vac lines, base of the intake runners, clamps on the intake and outlet of the carbs. Another issue could be the OEM petcock vacuum system might be failing.

Dusty

#3
Sun 10, Jun 2018, 09:14:35
Pick a stretch of road where you can pull over and work on the bike . Ride the bike so it is stumbling and missing. Pull in clutch and shut off engine with kill switch when it is missing . Coast to side of road and pull all spark plugs. Look for any that look different from the rest. Tell  us what you find.

Dusty

gordonv

#4
Sun 10, Jun 2018, 10:57:20
I'm not up enough on issues like this. But anything with regards to carbs, I always suggest adding in 1/2 can of Berrymans B12 carb cleaner, to a fresh fuel 1/2 tank of gas. You want to run in multiple rpm ranges, and also the one that is giving you problems.

A new to you bike, with sputtering issues, I would do the carb cleaner, inspect the spark plug sockets for moisture (clean out the water drain holes). The suggestions of vacuum leak, inspect the intake tubes at the heads for stains, and I'm sure someone will mention a way of testing with some flammable aerosol.
1999 Black with custom paint IS

Leathel

#5
Sun 10, Jun 2018, 13:50:32
Quote from: Dusty on Sun 10, Jun 2018, 09:14:35
Pick a stretch of road where you can pull over and work on the bike . Ride the bike so it is stumbling and missing. Pull in clutch and shut off engine with kill switch when it is missing . Coast to side of road and pull all spark plugs. Look for any that look different from the rest. Tell  us what you find.

Dusty

exactly what I was going to say, I had an issue with my old bike and thought it was lean until I did this, turned out it was rich and the spark plug fouling and loosing spark, it should also identify the suspect cylinder


Running some cleaning additive might help too :)
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