ST1100 won't start when hot

Yup. The glove box is off as well as most of the upper Tupperware. According to the manual I am supposed to test resistance between prongs at the coil end of the white connector. Also resistance between plug cables. How do I check the ECM end of the connector? Resistance? Voltage? What values am I looking for? Thanks!

I'm only suggesting a visual inspection of the ECM connector and wires. I don't believe there are any test you can do with the ECM other than possibly continuity tests of the wiring harness.

Ok guys, carbs are back on the bike. Coils tested OK and I cleaned the connector and plug caps.Runs perfectly but... Failed the test and again wouldn't start when hot. However I noticed something that has me suspecting of the tip over sensor. After heavy cranking and full throttle I got it to start but then if I lean the bike to either side, it will die. Any way of testing the sensor? Bypassing?

Thanks!

Not to threadjack, but why is the rubber mat important to have in place? Thermal insulation to prevent vaporization in the carbs?

Yes, I would expect that's part of the purpose of the mat.

Interesting twist on the sensor. I would certainly think you could bypass it. Hopefully the test helps isolate the problem.

Thanks guys,

Today I took a break from the ST after three weekends and a labor day dedicated to it. Although I can't rule out the bank angle sensor issue, I've been investigating and this sensor works by cutting the ignition when the bike tips. When activated, you should not only not have spark but the engine should not crank at all. Switching the ignition off and on should reset it, which doesn't happen in my case.

Following previous advise I had a spare plug with me yesterday when it failed to start. I checked it as instructed and got a very strong spark from that plug lead. Add to this the fact that it does crank albeit with no signs of ignition or combustion (despite the strong spark on at least one cylinder) and the bank angle sensor would probably not be to blame.

Also, following yesterday's test, right after I turned the engine off, I started it again and it fired inmediately. It only ceased to fire after letting it rest for around 5-10 minutes.

Any new ideas? I know I'm about to run out of ideas myself.

Cheers!

Ok, so it would seem that you have eliminated the ignition circuits from the equation. This really only leaves fuel. One suggestion would be to look at some of the recent fuel pump threads and put one of the low pressure fuel pumps in series with the stock fuel pump. You have mentioned measuring the volume of fuel coming from the pump, but I don't recall if you measured fuel pressure.

This evening I'll look at my service manual and see if I can find anything that might cause a problem with the electrical side of the fuel system.

I talked with my brother (The Dan) about this last week and his suggestion was to look for a faulty ground, especially one going to the engine block. He said he has seen intermittent problems in cars be caused by bad ground wires. Since he has done mechanic work most of his life, I tend to go along with his instincts on things like this.

I don't blame you for being frustrated, but try to look on the bright side, you have eliminated several possibilities already. That leaves fewer left to search through.

Yes Duke, I'm also leaning towards a fuel supply issue. I think I need to check the fuel pump relay and the fuel pump itself. I've not checked fuel pressure as I don't own a suitable gauge for this. Flow has been established at 1500-2000ml per min, hot or cold. However I don't usually carry pliers and a graduated bowl to test the pump as soon as the bike acts up, so I might have to do just that.

It may be important to note that I am checking fuel flow by connecting the pump directly to the battery which excludes the relay from the inspection. Maybe it would be better to test fuel flow while cranking when it fails to start?

Back in 08 I did a big job on my bike which included changing cooling system elbows, o-rings and hoses, and cleaning and synching carbs. I documented the whole thing with pictures and text, and it ended up being one of the longest threads back on the late My-MC. It also covered testing, bypassing and ultimately replacing the fuel pump relay with a second hand relay I bought from a forum member. It's really a shame that all that info went to waste when that forum was shut down. I didn't save any of it and now am having a hard time finding any instructions on how to bypass the fuel pump relay. If I'm not mistaken, it involved shorting two prongs on the connector but I have no idea which.

There is a pretty informative thread here about placing a facet pump in the fuel system which would ultimately be lodged where the cuttoff valve used to be. However, these pumps aren't available in my country and getting it shipped from the states would take some time.

Anyways, I guess I'll bypass the pump relay as soon as someone directs me to a "how to" thread and then do further testing. If that doesn't work I'll have to search around for low pressure electric pumps. If anyone has an idea of an automotive equivalent for a suitable electric pump, I'm all ears.

Please thank your brother for me for his suggestion on an engine ground. I'll keep that in mind once the fuel starving issue is ruled out.

Thanks again!

I am at a loss on how fuel starvation causes wet spark plugs? The only causes of wet plugs that I know of is either a rich fuel mixture caused by stuck choke, floats at wrong height, bad needle valve, too high fuel pressure, saturated charcoal canister and a non firing or weak ignition system.

You have a point there. My plugs weren't necessarily "wet". One of them had a slightly shinny surface which I interpreted as such. If anyone would be so kind as to show me how to post pics, you would now what I'm talking about.

They also had some soot on the edges but the electrodes were mostly tan brown. I am inclined to think that sooted and shinny plugs could result from prolonged riding in stop and go traffic mixed with a slightly rich pilot screw setting for my altitude (8500 ft). IMHO This would not exclude starvation as an intermitent cause for the occasional failure to start after one of those prolonged rides, specially when I have tested spark and coil resistance and they seem OK. I'm also not getting the fuel smell tell tale of flooded engines.

Today I started the bike twice and let it idle until it reached operation temp. Both times after letting it rest it started right away. I couldn't ride it because it was raining but for the moment it seems to require a couple full throttle spins as well as the high temperatures for it to fail.

More to come. Please stay tuned.

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Thanks Mark,

I'll give it a try. Here are pics of #2 and #3 plugs and views of the carbs when removed. I always apply grease to the plug threads as well as the carb throats before installing them.

Let me know what you think.

You're welcome, glad to help!

I'm currently uploading a video to youtube featuring the bike starting and running after last week's carb job. I'll share the link as soon as it is available.

I forgot to mention that I had just finished buttoning up the bike after a general paint job when the starting issue became more prominent. I changed the color from the original metalic wine red to what was supposed to be a faster, ferrari flat red. Maybe that's why it won't start?

Here are a couple more pics showing the new paint job, the hole with and without the rubber mat, the torn vaccum hose on #2 cylinder and a close up of the valves.

Here you go:

http://youtu.be/LbIh6v5XTOk

Bump
Comments on the plugs?
Thx

From what I can tell, plugs look fairly new to me. Also look a bit wet....is the moisture oil or fuel?

Last year I had a vehicle that failed to start intermittently with a warm engine. It turned out that one of the bridge diodes in the regulator for the alternator would only fail when the engine was warm. Before I replaced the regulator-alternator package, all I had to do was to wait for the engine to cool off and it would start every time, no problemo. Have you checked the alternator voltages on a cold and warm engine?

Thanks guys. I really appreciate your feedback.

Indeed plugs are indicative of a rich mixture. That's why I set the pilot screws at 2 1/4 turns all around. It runs great ... when it runs.

I have delt with the regulator issue a couple of times since I own this bike. However symptoms have always been electric and reveal themselves by low charging voltage (I have a voltmeter installed) or failure to crank. Currently my electric system seems in good health to the point that it has enough juice to crank repeatedly when the bike fails to start.

I plan on testing this weekend by bringing it up to temperature and then attempting to restart. If it fails, I'll check fuel flow immediately, collecting fuel after the filter by cranking the engine, not jumping the pump. If either pump or relay are to blame, this test should show it.

I'll let you know how this goes.

Thanks again!

Just an update. Today I took the bike on an early morning run with no traffic. I pushed it hard but it didn't heat up at all. It started every time. However although acceleration seems fine, I ran it full throttle in 6th gear and couldn't get over 95mph. Maybe it did touch 100 but it was out of juice by then. Funny thing is that while at those speeds the engine died on me once. I was at full throttle and it just quit. I pulled over, waited 3 minutes and it started right back up. Got home with no problems. I am thinking this is indeed a pump issue but it hasn't failed to start again, so I can test it. I'll keep going at it and let you know.

Thanks to all who have stayed with me this far.