Random stutter

panjab

Joined
Aug 24, 2019
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10
Age
65
Location
portugal
When I start out everything seems OK, but after it warms up a little, my bike will randomly stutter on throttle. Usually after a few minutes riding through town and then accelerating. When I rebuilt the bike I stripped, cleaned and balanced the carbs. It seemed to run well when static and only started the stutter once I had started riding.

I know it is a bit of a 'wooly' explanation but it is hard to describe.

Any ideas?
 
dwalby

dwalby

Joined
Mar 13, 2012
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soCal
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'97 ST1100
STOC #
687
If its a sharp stutter, then its probably ignition related, if its a more burbling stutter then it could be fuel delivery related.

ignition issues tend to be load and/or RPM dependent, which could indicate an issue with the coils or sparkplug wires. From the description you have given, I'd suspect ignition. Keep trying to replicate it and see if there is any pattern to RPM or load. Also run it through the RPM range in idle and see if there are any stutters without a load. One clue about ignition issues is it will run great above and below the RPM at which you get the stutter, if you have fuel delivery issues then I'd expect it to get progressively worse at higher fuel delivery rates.
 
OP
OP

panjab

Joined
Aug 24, 2019
Messages
10
Age
65
Location
portugal
Further to the stuttering issue, I went out again today and it seems to be between 2500rpm to 3000rpm under load. I have removed the fuel cut-off valve. She seems smooth enough at 120+ kph.

I am going to order somenew plugs and see if that helps.
 
ST1100Y

ST1100Y

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Vienna, AuSTria
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Also the feed of the coils might be worth a closer look...
Not corrosion per se, but IIRC was there an issue with loose crimp connectors; just re-press with the correct die seem the fix...
Ignition lock switch-plate as well as the mains connectors come to mind as well...
 
klaproth

klaproth

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Apr 9, 2011
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Canton, GA
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2006 ST1300
Sometimes. observing the coil wires and coils under low light conditions can be beneficial- if there is a spark "leak" it is easily seen then.

Also, inspecting the coil towers for carbon tracks, and the boots for integrity is a good idea.
 
Al st1100

Al st1100

Joined
Aug 11, 2013
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3,559
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kankakee
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R1200rt
klaproth said:
Sometimes. observing the coil wires and coils under low light conditions can be beneficial- if there is a spark "leak" it is easily seen then.

Also, inspecting the coil towers for carbon tracks, and the boots for integrity is a good idea.
Click to expand...
also inspect porcelain of the spark plugs for cracks or carbon tracking. If there is carbon tracking on the plugs the boot are also no good. Spraying a solution of soapy water will help in detecting spark leak.
 
OP
OP

panjab

Joined
Aug 24, 2019
Messages
10
Age
65
Location
portugal
What are the coils like to get at? They seem like they are buried in the depths of the bike :(
 
newtonhubcap

newtonhubcap

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Apr 15, 2022
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53
Age
66
Location
Wisconsin
Bike
1994 Honda ST1100
From what I gather bike idles fine until you start to put a load on the bike (ie pulling away from stop sign up to 2,5 to 3000 rpm). Agree with checking electricals but does seem to be more of a pilot/slow jet issue (lean) until the slides pull up to take over onto the needle slide. If you get a chance just as it starts to studder start applying choke - if it smooths out then would look at cleaning the pilots/slow jets and may want to check setting of the air/fuel ratio screws.
 
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