There are a few excellent photo-documentaries on refurbishing an old 1100. Use the search function and look for 'ST1100 Carbs', 'ST1100 refurbishment', 'ST1100 hoses'...and similar.
Misfire - noob questions
- Thread starter Cyclehead
- Start date
There are 58,000 Miles on the bike. Cosmetics are all decent. I didn’t get any maintenance records, save a few entries marked in the owners manual. I’m pretty sure nobody has removed the carburetors before me. Oil in the sight window looks pretty black to me, and clutch fluid is pretty Carmel colored in the master cylinder sight window.
ReSTored
Site Supporter
I'd suggest joining ST-Riders. Many of our ST-Owners members are members there as well. The ST-Riders site focuses more directly on very detailed maintenance issues vs. ST-Owners.
The Carb Removal and Rebuild ( ST1100 ) post has hundreds of photos of removal, complete disassembly and with detailed instructions and then a parts list. Probably the most comprehensive write-up I've ever seen, a fantastic resource in particular and overall for the site as a whole.
This is the link, it may only work for you if you're a member and logged in. http://www.st-riders.net/index.php?topic=10249.0
I ordered JIS screwdrivers, and a factory manual on eBay. I drained all the fuel in case it was stale. Poured in a gallon of new fuel with Techron to make a concentrated mixture of the stuff. Installed four new iridium NGKs. So far the misfire remains. Is there a good way to determine if a coil is failing? Is there a way to eliminate spark problems, that would point me to carburetor problems? (Waiting on my STOC approval)
Slydynbye
Will ride for Pie
Have you run a full tank of gas through it yet? Once that Techron gets into the carbs it needs some time to work and dissolve things. Then a good full tank run on the highway to blow the carbon out. If you tell me the previous owner never took it over 55, I hope he never got over 3rd gear because if he was in 5th he bogged the snot out of it.
What did the old plugs look like?
What did the old plugs look like?
a spark problem is very abrupt, carb problems are a slower rumbling symptom.
Never tried it, so I don't know how well the bike runs on 3 cylinders, but one thing you could try is to remove one spark plug wire at a time, and run it into the problem RPM range and see if the issue goes away on one particular cylinder. If you can isolate it to one cylinder that's half the battle. Then you can swap coils and see if the miss follows the coil or the cylinder. Never had to do this, so I don't know if you can swap coils and keep the wires attached (preferred), or if you'll have to remove the wires, swap the coils, and reattach the wires. Then do the 3-cylinder test again. Based on the different coil/wire/cap combinations you should see a pattern in the failure and narrow down the cause. If you had marginal wire/coil/cap connections to begin with, and have to swap the wires around, there's even a possibility that you'll cure the problem while troubleshooting.
Also keep in mind that one coil fires two cylinders, so if you have a bad coil it may show the symptoms on both cylinders. And, if its missing on both cylinders it might seem more severe when you remove one of the plug wires from the other coil, since you'll have 2 bad and 1 good vs. 2 and 2. Conversely, if you remove one of the bad cylinders you'll have 2 good and 1 bad, so it might seem a little better in that case. Just speculating, I think its possible that the coil could be bad on only one cylinder instead of both, I don't know all their failure modes.
The professional way to troubleshoot a misfire is to put all 4 cylinders on a scope and the glitch will show up on the scope trace. If you have access to someone with a scope, that's the best approach.
I’m impatient. It will be a while before I get a tank through the bike. Old plugs looked decent to me, not glopped with carbon or oil that I could see. I am hoping bowls full of techron will do their magic if it’s a carb problem.
Today I shuffled the ignition wires and coils around trying all combinations. Cylinder #3 is the one that is dead at idle. Nothing I did with wires and coils would bring it to life. Test ride after shuffling the coils and wires around showed exactly the same behavior. It will come to life as soon as I give it some throttle. I plan to tear into the carbs tomorrow, hoping that there’s some crud in #3 carb that I can blow out and get this engine running smoothly.
Slydynbye
Will ride for Pie
Did you open the idle screws and clean those out? you will need the special idle adjustment tool and will want to replace the o-rings while in there.
Item #5 on this diagram
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Slydynbye
Will ride for Pie
Found the o-rings
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Fixed! It was a piece of crap in the “pilot/slow speed jet”. I could see daylight through three of the jets, but not the fourth. Tiny tiny hole needed a strand of wire to clean it out. Whew. Of course it all makes sense now - dead cylinder at idle and low speed, only comes alive with throttle would make sense it was something wrong with the idle/low speed circuit. Thanks for all the guidance and tips, guys! This post on ST-Riders was invaluable to get me through the disassembly, so a big thanks to Adam Frymoyer. http://www.st-riders.net/index.php?topic=10249.msg94765#msg94765
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Slydynbye
Will ride for Pie
That's Excellent news! I thought you had already cleaned out the idle jets once...?
Adam is amazing for his knowledge and perseverence with Carbs, he covers so much ground with that article which helped me enormously when I was stripping my carb block down, also gave me the confidence to be able to re-jet if necessary after an overbore and change in compression ratio.
PS. I was tempted to avoid pulling the big intake plenum that’s required to remove the two hidden “air cut diaphragms”. But I had already bathed everything in carb cleaner. I’m glad I removed them for cleaning. The chambers were full of liquid, and Adam says that will destroy the diaphragms. I had to get creative with the cutoff tip of a screwdriver. Getting them out was real heart surgery but it worked! 
Since I hate posts that never report the final outcome ... carb cleaning and balancing cured all the misfire problems. I believe there was trash in the carbs, but balancing them with the borrowed synchronizer set was the last trick that got it running smoothly. A little unrelated problem surfaced later: I got a misfire that would develop during low rpm driving through town. It would clear after high rpm riding for 5 minutes. I tried different fuel with no success. And finally found that my battery was dying. I believe it was dropping voltage to the coils at low rpm (when the alternator couldn’t keep up), but firing correctly at high alternator speeds. A new battery fixed it completely. It will now happily idle through town without a single hiccup.
On the 40A alternator bikes ('96 and later) the alternator puts out almost full voltage at idle, so you may want to check your alternator output at various RPM. I haven't checked mine in years, but I seem to recall it was in the high-13s even at idle, and it gradually works its way into the 14s as the revs increase. Hopefully replacing the battery is the end of your latest issue, but just to be sure that you don't have an alternator problem that caused the battery to die in the first place it would be a good idea to check it out.