Hard Starting ST1100

I have a 1991 ST1100 that is well maintained, it has 54k miles. I have had the bike 3 seasons and no issues, even during cold temps in the winter.

The starting problem started when I was at TexStoc in September. The bike used to just start right up with full choke. At TexStoc I had to crank it a bit to start it. I have put 4500 miles on since TexStoc and starting is progressively getting worse. When the engine is warm or hot it starts fine. The bike has sat for 10 or 11 days with out being touched prior to this it would take 30 to 40 seconds to start and now today it pops but won't run.

Yes there is gas in it and yes the battery has a full charge. Plugs got about 20k on them, air filter and fuel filter are clean.

A full battery charge may not be indicative of a fully functioning battery.

How old is the battery?
Do you have a battery place that will test it while it is 'under load'?

The battery is a year old. Brad is a SHORAI lithium Ion.

Use any fuel conditioner like Seafoam ?

Sorry the battery is a SHORAI not Brad. LOL fat fingers

1 year old battery ought not to be the problem; but, I'd say a load test might still be in order.

I use Lucas injector cleaner normally a couple of times per year. It does make the bike run smoother and the idle does rise a bit after riding a while. I have not noticed anything related to starting good or bad. I have used Seafoam in the past on other bikes and felt that it didn't do anything noticeable.

If this has gradually gotten worse, makes me suspect that plugs may have cracked porclien from wet fouled eanh time it HAS finially fired up. I'd put new plugs in, in spite of the low mileage on them.

I was kind of suspecting the same but thought I would get a few opinions before I drop the $$ for the plugs.

I guess the plugs could be bad, but if they were not good enough to start the bike, you would know it especially accelerating under load. The key is, the bike starts good when hot but not cold. I would bet you have an enrichner problem or they aren't feeding fuel into the carbs. they could be dirty and running fuel cleaner won't clean them as one doesn't ride with the choke (enrichner) open. Also the wire that opens them could not be connected. Check that 1st.

Starting is getting progressively worse since Sept. Prolly getting colder since Sept and I'll bet really cold now.

I must say that the choke has crossed my mind. I had a CB900F and the choke cable was in a little clamp that pinched the casing of the cable. Some how the casing started to move in the clamp and the bike became very hard to start. not so dissimilar to what is happening on the ST. I cannot remember does the ST have a clamp on the choke cable or does it have a little fitting like a throttle cable?

Grabcon said:

I cannot remember does the ST have a clamp on the choke cable or does it have a little fitting like a throttle cable?

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It has the same end fitting as a throttle cable, the circular lug on the end of the cable. But the end of the cable casing fits into a clamp a few inches upstream from the end of the cable, and is what provides the leverage for the cable to actuate the choke lever. If the cable casing came loose from the clamp, then you will lose the leverage needed and it may only be moving the choke lever by a small amount.

The problem characteristics described in the thread-opening post perfectly mimic the mystery I dealt with for a couple months, and for which the problem turned out to be a gradually dying fuel pump relay.

The problem suggests a thousand possibilities, and since the relay is dying gradually, the problem is hard to solve. Didn't solve mine until many things were tried, until I had been "towed" home twice, last time hard down, i.e., never started again. Went so far as to replace fuel pump, no help. Getting pretty pissed, I hot-wired a relay bypass sourcing pump power from, and grounding to, battery: Success! (Still haven't put the new relay in, but...)

HelmetHead said:

The problem characteristics described in the thread-opening post perfectly mimic the mystery I dealt with for a couple months, and for which the problem turned out to be a gradually dying fuel pump relay.

The problem suggests a thousand possibilities, and since the relay is dying gradually, the problem is hard to solve. Didn't solve mine until many things were tried, until I had been "towed" home twice, last time hard down, i.e., never started again. Went so far as to replace fuel pump, no help. Getting pretty pissed, I hot-wired a relay bypass sourcing pump power from, and grounding to, battery: Success! (Still haven't put the new relay in, but...)

Click to expand...

p.s.: when the relay is the problem, you can't leave the pump's negative wire in place, as it goes back to the relay, hence my grounding back to the battery. I went this screwy route because I was pissed, and the manual's description for testing the relay involves (I thought, and kinda still think) getting to the relay itself, behind the instrument cluster (which is why I'm only this week getting around to properly replacing the relay itself). If you look at the wiring diagrams, which are provided somewhere on this site, you can deduce that the relay also handles the fuel light circuit. As that has never failed on me, I presume only the pump side of the relay failed, probably because it handles considerably more power than the fuel light circuit. Alternatively, I'm too amateur for my own good, and decidedly lucky.

Thanks to those that responded. I have not had a chance to look into this, kind of a busy week. This weekend though and I will report back if anything is found.

So I am reaching my limits here on solving this no start issue.

What's been done to this point.
Fixed several vacuum leaks - Sync hoses were capped off, New caps
New park plugs
Finally got my charger for the Shorai Battery and that now has a full charge
Checked the choke cable to make sure it was tight and positioned properly and tight.
Fuel pump pumps for a few seconds and then stops. Cycling the key or kill switch will make the pump cycle and pump gas. I have not tested fuel pressure but a finger over the fuel filter will stop the flow.
Vacuum fuel shut off has been removed.

So a question for Helmethead before I go and replace the fuel pump. What exactly did you do to by pass the Fuel Cut Relay? Was that just removing the Negative from the pump and connecting to Ground?

So what good has become of this since everything is apart.
New head lamps - Learned how difficult it is to replace head lamps. How does one do this on the road?
Replaced the black cowl around the speedo and tach. Mine was broken.
Put a newer lens on the speedo and tach. Mine was cloudy.
Have not thrown any tools yet. Either have learned my lesson from previous events or I am just getting to the point where I really don't get that angry.


I spoke with a Honda mechanic on Saturday and he says the valves need adjusting. I think he is blowing smoke but once running the valve check is next since everything is apart.

So anymore thoughts out there?

I spoke with a Honda mechanic on Saturday and he says the valves need adjusting. I think he is blowing smoke but once running the valve check is next since everything is apart.

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I can smell the smoke from here. Ask him if there will be "no charge" if that doesn't fix it.

Valve adjustment has nothing to do with it. He may be right that they are due or overdue for adjusting, but not as part of the hard starting issue.

So one thing I'd like to ask, if the bike starts and runs fine when its warm, wouldn't that indicate that the fuel delivery system is functioning OK? Seems like if you have a problem with that, even an intermittent one, wouldn't you be seeing other symptoms like coughing or cutting out at speed? I'm not saying I know anything about this, I'm just thinking out loud and asking questions. But since jumpering the fuel relay should be simple enough, and free, you have nothing to lose by trying that first.

The only time that I have experienced any issues with sputtering is at high RPMs in the 7500k range and higher. The bike has never stalled while riding. But I have noticed at higher altitudes 10000 feet plus that it does buck unless I drop a gear and get the RPMs up. This also started about the same time as the Texas trip. Although what I have notice is very erratic and broad range of MPG. Until the trip to Texas I was consistently in the 43 to 48 MPG range. While on the way to Texas and back I had a very broad range, as much as 51 down to 30 MPG. Since trip it has been up and down but nothings with any consistency. Yes there were some high winds along the way but I have run into them before without the extremely change in MPG. Maybe as low as 39 with two up.

dwalby said:

Valve adjustment has nothing to do with it. He may be right that they are due or overdue for adjusting, but not as part of the hard starting issue.

So one thing I'd like to ask, if the bike starts and runs fine when its warm, wouldn't that indicate that the fuel delivery system is functioning OK? Seems like if you have a problem with that, even an intermittent one, wouldn't you be seeing other symptoms like coughing or cutting out at speed? I'm not saying I know anything about this, I'm just thinking out loud and asking questions. But since jumpering the fuel relay should be simple enough, and free, you have nothing to lose by trying that first.

Click to expand...

The deal is, the carb bowls on these bikes seem quite large. To bypass my relay, I had put a household light switch in the middle of the positive (power supply) line to the pump; otherwise, the pump would run continuously.

Plenty of times I forgot to switch pump power on, and successfully drove 8 - 10 miles. The reason the failing-relaay bike starts when hot is, I believe, because the relay was in its intermittent 'working' status, and pumped gas to get you where you were going. Come back out from whatever, and engine starts because the carb bowls are full of gas. A few times, I have run so far without pump power as to have the bike start to die while rolling down the road; I reached down and switched the power on, and continued without a hitch.

When trying to start after the bike has been sitting overnight or more, the carb bowls are (mostly or completely) drained, I presume, hence the cold start failures (if relay is taking the day off).

Since the relay is in an intermittent failure pattern, sometimes one probably gets rolling, and even though the relay is maybe going on and off, it's on enough to keep the bowls supplied during off periods.

So, that's probably most of the theoretical power of my explanations...