Where did those two cylinders go?

Ainslie

Ainslie

Joined
Apr 12, 2024
Messages
3
Age
76
Location
Bundaberg, Queensland
I live in Queensland, Australia, and ride a 1995 non-ABS British spec ST 1100 outfit. The bike has developed a puzzling fault, and I will be very grateful for any advice other ST owners may care to offer. The sequence of events is as follows:
1) A few months ago, the bike began losing power after hard acceleration. I would pass a car or zoom up a steep hill, and then the bike would suddenly lose power. This became progressively worse up to the point where the bike would not start or run.
2) I suspected a faulty fuel pump. Pulled this out and found it worked perfectly. Plenty of fuel is reaching the point where the fuel line divides to feed the LH and RH sides of the engine. Removed the air cleaner and started the engine to find that cylinders 1 and 3 weren't firing (this is the LH bank of the V4). There was no air being sucked into the velocity stacks. Effectively, the engine was running on the RH bank only.
3) Removed both coils and tested. Resistance was high on the secondary windings of both coils. This seemed a logical culprit, as one coil serves the LH cylinders and the other serves the RHS
4) Installed new coils, HT leads, and plugs this morning. I now have a big, fat, blue spark on all four cylinders... but still have the same problem. Cylinders 1 and 3 are not functioning.
5) The bike will idle on cylinders 2 and 4 without the air cleaner. However, once the air cleaner is on, the bike refuses to start.

Likely, the LH cylinders are not getting any fuel. This could mean a blockage in the fuel line serving the LH cylinders. However, before gritting my teeth and removing the carbies to reach those well-buried fuel lines thought I would see if there are any other theories out there in STland!

BTW, in my view, the ST1100 is an ideal sidecar tug. My chair is a double, and the Honda propels it along at highway speeds with ease.
 
Check your earth /ground points for the misfiring coils. Worth a try as these often play up. Also read the Fuel Valve Bypass and Red Wire Bypass Articles as these are known to fail on our old 1100s
 
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If the plugs are not firing and they are getting fuel, they should be wet.
If they are dry then the fuel line or the carbs are the problem.
For it to happen all of a sudden does sound like a blockage.
 
Our 1991 is garaged for the same reason. Two wet, non-firing plugs. Could be wiring, could be a coil. Cold be plugs made in Yunowhere and sold as NGK. Got all the just-in-case parts, waiting for temps to rise a bit above freezing.
The bike is 35 years old now my suspicions are a bit open minded.
 
You state there is spark. Easy way to see if there is gas in the carb bowls is to drain them and see how much gas comes out. If they have gas it's not supply issue. You said there is no suction on both stacks. I assume your comparing them to the other side, if so I would check compression next.
 
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One coil fires in both cylinders twice every cycle - once on the compression, once on the exhaust stroke. So if you have two wet plugs it is most likely to be the coil generating the spark that is the issue. And just cos you get a spark with the spark plug out of the cylinder that doesn't nrecessarily mean you will get a spark under high compression in the cylinder.

Take off the left hand side coil from the frame. The earth side of the High Tension 'wiring' is usually a metal strip from the body of the coil to the frame. Make sure that all contacts are clean (they won't be).
If that turns out to be the cause, then do the right hand side as well !

The other suspect is the LT leads - earth and live to the front of the coil. But 'live' is a pulse from the ECU, so difficult to test for.

HT leads to the plugs might be suspect, but it would be odd for both to go at exactly the same time.
 
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My 2007. sT-1300 gave me engine problems in October and November of last year, which turns out to have been corrosion on the ground bolt for the ignition coil (right side only ; I never got around to checking the left side.)
 
Ainslie: Hello. Please ensure you double-check the integrity of the wires and wire connector crimps on the coils. The original factory connector crimps are on extremely thin gauge wire that may be faulty or failing intermittently. I had a similar intermittent issue after riding over cattleguards or at what appeared as random times. I certainly wish Honda provided thicker gauge wiring, more slack and better crimps for the cable harness servicing the coils. Good luck!
 
Hi All,

Thanks so much for all your suggestions... but try as I might, nothing I did made any difference whatsoever.
Had a friend look at my problem today. He earns his living as a motorcycle mechanic and kindly agreed to conduct some diagnostic checks on my bike:
1) Turns out there is almost no compression in the malfunctioning cylinders (LH bank of the V4).
2) Most likely cause is a blown head gasket between these cylinders.
3) Coolant is not leaking because the water jacket does not extend to the thin wall between adjoining cylinder liners.
4) Fuel fails to ignite, and plugs get wet because compression is leaking to the other cylinder in the bank.

I will double-check this diagnosis (with a compression test on a cylinder at TDC. I'm probably on the right track if air escapes to the sister cylinder. So.... I'm now facing the removal of the LH head. The chair (sidecar) on that side (I live in Australia) complicates this work. I think it may be easiest to remove the chair, but I don't want to upset the carefully set-up geometry of the outfit.

Will welcome any suggestions on retaining existing sidecar settings upon removal from bike. Also, has anyone replaced a head gasket on an ST1100? I have the Haynes manual, and I'm reasonably handy with tools... nonetheless, more than happy to hear from someone who has trodden this road before me!
 
head gasket failures are very rare on ST1100s, so make sure you're doing the compression test properly and can be reasonably sure about the gasket failure before going any further. Many things (timing belt, cams, carbs, exhaust) need to be removed before the head can be removed, so its a lot of steps. There's nothing particularly difficult about each step if you're used to wrenching on things, but its not a quick repair job.
 
The information about the cylinders not sucking any air indicates this is a mechanical problem with engine itself. Even without fuel or spark, rotating the engine will still pump air.
I suspect either burned valves or a cam has jumped time on that side. Burnt valves can happen on these bikes for no apparent reason. My ‘93 mode ate one of the cylinder #4 exhaust valves. Others have had similar experience. I’ve never heard of two cylinders doing this at the same time though.

When the burnt valve happened to me it was pretty sudden, just after climbing a steep grade at speed.

As there’s reportedly little compression in those cylinders you can diagnose where the air is going by connecting a low flow air hose to the spark plug hole. With the cylinder under test at TDC (compression stroke), listen for air escaping at the end of the exhausts, at the crank case oil fill opening, and at the intake. If you hear air at the exhaust, you have a burned or stuck open exhaust valve. If you hear it at the intake, then it’s an intake valve issue. Intake valves rarely burn so this might indicate a jumped timing belt. If you hear air at the oil filler opening you have piston problem - a hole or worn/broken ring(s).

Good luck and let us know what you find.
 
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