ST1100 won't start when hot

id bet the coils are on there last legs from what you have posted if you check my old posts theres a post on what needs taken out to get at them

maubur said:

OK guys, I think I just ruled out the cap issue. I pulled the tank cap and tested it. Indeed air flows on both directions. Thanks John. BTW John, I'm the Colombian guy you pulled out of the dumps a while back when you sent me a VR, remember? I'll never forget that.

Back to the current issue. Although air flows both ways, I've always had the rush of air flow into the tank when I remove the cap. An hour ago I warmed up the engine, pulled the cap and went for a short ride, tank open. Hard sprints intercalated with long idling. It has better oomph than ever. Red line comes up pretty quick on first and second and I must confess, in the 10 yrs I've owned this bike, it has never delivered this much power. I must have done something right during last weekend's synch and mind you, I did it without a synch tool. I'm not all than convinced that my idle is as smooth as it should be but with this much full throttle rush, who needs idle?

Anyways, I returned home and let it idle a bit more. Fan kicked in two or three times. Throttle response normal. I turned it off and came inside for about a half an hour. Then I went back to the garage, cranked it and...you guessed it, no cigar. Full throttle, nothing. Half throttle, nothing. Half and full choke, nothing. It wont even attempt to fire. No fuel smell at all. I let it go before I drain the battery. Long story short, fuel cap is out of the question and I am again stranded.

I do believe my next step is to pull the carbs and check the insides, a job that scares the bejesus out of me. It's not only my lack of mechanical background and total dependance on advise from these forums. I am in Colombia, where this bike is almost unknown. No local part sources. That's why Broc's coil solution is not that easy to apply.


Any new ideas?

Click to expand...

John, the shutoff valve has been removed from the bike. PAIR system was also removed (this is an ABS-TCS California spec bike).

I understand inside the tank both things happen: pressure and vaccum. As fuel expells fumes and heat builds up, the tank should pressurize and vent outward. However, as fuel is consumed, it's space is taken up by air and if air supply to the tank is not enough, a vaccum would form. In my case I'm pretty sure when I pull the cap air rushes into the tank, not out of it. The cap vent system is working both ways although it seems blowing air into the tank is a bit more restrictive. Anyhow, yesterday I tested with the cap off, while running and at rest. It still wouldn't start after a 30 min rest so the pressure or vaccum in the tank hypothesis, is ruled out. Today I went back to the bike and it started right away. Go figure...

When this has happened on the road, I've had it start after two or three five second cranks. Other times it can take up to 10 minutes of intermitent cranking and applying full throttle, for it to start. At this rate I'm going to be looking at a new battery shortly

Tomorrow is labor day so I was planning on pulling carbs and checking them out. However I'll probably start by pulling the new plugs to take a look. I was also thinking I might try to adjust the pilot screws before removing the carbs. The only consistent thing I'm seeing is that at idle, revs oscilate quite a bit and I hear some light but frequent popping, as if the mixture was lean. When the engine is cold it won't maintain an idle above 800 rpm but once it warms up, idle speed rises to the specified 1200, + or - 100, all without choke. I'm guessing a lean low speed mixture after lots of idling in hot weather might at least partly explain what I'm seeing.

I'm not so sure I'll be able to perform the pilot screw setup procedure as depicted in the manual. It calls for 50rpm variations and I don't have a tachometer for that. I've heard we should aim towards 2.25 to 2.5 turns out, more towards the lower number if above 5,000 ft ASL. Any suggestions?

Hey Andy, would faulty coils allow the bike to run great and reach it's top power output, only failing to start after short rests? When it fails to start it won't give any signs of wanting to fire. It just cranks and cranks as if there was absolutely no fuel in the mixture or no spark from any of the plugs.

Thanks for your support guys!

Carb intake mounts leaking?

John OoSTerhuis said:

Hi Mauricio,

To start, you need air, fuel, and spark.

Click to expand...

and compression.... which leads to my next question (and a long shot too): have the valve clearances ever been checked?
Mr. BR

ive had this issue on a bandit 1200 and the coils were to blame theres less work to take them out for testing than playing with the carbs

No Mr Br., I have not checked valves in 10 years. I'm not sure if the PO had them checked. I have consulted with my not so trustworthy mechanic and he says that if the valve train isn't making any noise he would let it be, specially since the bike has less than 35K miles on it. When the engine heats up, I do hear some slight valve clicks from the right bank but much less than the valve sounds my Mazda makes all the time.

Yesterday I pulled the plugs. For the most part, they have quite a bit of soot and a couple seem wet. I tried to upload a 106kb pic but that didn't work. It opens new explorer windows with some weird xml encoding content.

I then dug in and pulled the carbs. Before taking them apart, I measured the ammount of gas on each bowl which was pretty much even at 40-50cc all around. Had a heck of a time with stripped screw heads on both the bowls and the vaccum chamber covers. All the slides are in great condition, no tears or pinholes. So are the springs and needles. Down under I found three clogged slow speed jets which I cleared with my trusty accupuncture needles. Floats were all set at around 8mm. Float needles look new and the high speed circuits (base and jet) were for the most part, nice and clean. I did give all these parts a treatment with a paint brush and the fuel I got from the bowls, as well as a new 15 second pump test which BTW, generated 1500 cc/min.

Five years ago another forum member loaned me a pilot screw tool and an SK flowmeter. I duplicated the pilot tool before returning the originals to the States. Yesterday I gave my clone a first whirl but it didn't perform to par. The flexible part twisted as I tried to turn the screws and it ended up breaking. Then I noticed the homemade tip did not fit the screws tightly so I had to squeeze it a bit. When I finally got it to hold the screw heads I had already tried it on all the screws so there was no way of knowing how many turns they were set at, seeing it was slipping.

I pulled all the pilot screws and using my dremmel tool, which I had already employed to carve grooves on the bowl and top screws, I carved a groove on each pilot screw head. Then I put them back in and set them exactly at 2 1/4 turns out (compensating for high altitude). Later on I read something about sticking a wire into the pilot screw holes to clean them up, but there are warnings about messing up the bore. My accupuncture needles are way too short to go all the way in. I have no compressed air. Any suggestions?

I found the coil inspection procedure on the Honda manual. It seems pretty straightforward so I'll give it a go and let you know what I find. I understand I'm supposed to check resistance in Ohms and Kilo-ohms between all combinations of the three prongs on the white connector (coil side) and between the two left side plug cables. The diagram doesn't show the right side cables but I suppose resistance must be also measured between these, correct?

Again, thanks a lot for your patience!

The fact that you found a lot of soot on your plugs and the fact they were wet tells me your are dumping raw fuel into your cylinders after shut down. (essentially a flooded engine.) I would drain your oil and check to see if there is fuel in there. If you have fuel you need to get that corrected before you run. Gas in your oil will wear all the internal parts to your engine and ruin it. As far as why there is fuel getting into your intake after shutdown I do not know. I see that you bypassed your vacuum fuel shutoff, I do not have any experience with that but I know many smart people on this forum have done it with no ill effects so I do not think that is the problem. Do you have a way to put a shutoff valve in fuel line that you could manually shutoff the fuel just prior to shutdown? If you do you could try closing that valve just prior to shutdown, this way if there is excess pressure coming from the fuel tank causing the issue it would close that off. if the problem persists then you know it is something in the carburetor system that is pushing the fuel into the cylinders. (maybe a stuck throttle? just guessing) If the problem goes away then you can rule out the carburetors and concentrate in other areas. Could your fuel pump be running after shutdown for some time causing excess fuel pressure? I do not know the wiring for that area so I don't know if there is a relay that could be sticking and allowing the fuel pump to continue running for a few seconds after shutdown. I am sure there is someone here with the knowledge on that area that input on that. Good luck and I hope you find the cause soon. (No matter what the cause if you have wet plugs I would change the oil before you go riding again to ensure you are not frying the inside of your engine.)

I just lost a whole post. Dang! Let me rewrite. I appreciate the feedback and am sorry I couldn't share the pics. My plugs are indicative of a rich situation. Soot is there as well as a slightly shinny surface, not necessarily dripping wet. The cutoff valve has been out for 10yrs now and the float valves seem to be doing their job as I can't blow air into the bowls when the floats are at 8mm.
In the odd year this has been going on I have changed oil and nothing seems wrong with the old oil. Also I get no fuel smell whatsoever from the exhausts when I crank it repeatedly and it won't start. I'm guessing a flooded engine is a possibility but at the moment less plausible than other alternatives. I plan on replacing the carbs and checking the coils and I'll come back with the results.



Thanks!

Thanks John for sticking with me. Somehow it seems like it's only you and me left in this party. Care to dance?

I'm crossing fingers this is an idle mixture issue. Too much gas while standing still in heavy traffic could be fowling the plugs to an extent where they cease to fire when I try to get back on the road. I only wish somebody here would pitch in with comments on where I should set the pilot screws, seeing that setting them with the engine running is out of the question. Also if I should probe the pilot screw hole and how to do it.

Well, I'll stay alert.

Cheers!

California spec bike. A saturated fuel vapor recovery canister can cause a rich condition.

90% of the time, if not always, the no start situation comes up after two or three legs of 15-20 minute rides in stop and go traffic, where the motor spends most of its time idling. However, I usually give it some throttle while waiting in traffic just to keep charge voltage close to 13V. Otherwise the battery will be drained (I have the leaking 28 amp alternator). During each 15 minute ride the fan kicks in many times. Usually it will start OK after the first or second ride, only failing to start after the third ride.

However, when I tested it last weekend with the gas cap off, one 10 minute ride mixing fast sprints with deliberate stand stills in order to allow it to idle a while, was enough for it not to start.

I hope cleaning the jets and setting the pilot screws will be enough to solve this. I'm afraid I may only find time to put the carbs back on and test on saturday. If it does act up again, I would have to steer away from the fuel and air issue and focus on spark which basically means testing the coils and if not up to spec, starting to hunt for new ones. Hope it doesn't get to this.

Thanks again John and please, stay in tune while the carb experts find their way back to the thread.

I've been following the posts here. Lots of good advice but IMO you need to find out if this is actually a fuel problem or an electrical one. I suggest you do a simple test. Varying temperatures can cause intermittent electrical connection and device faults to occur.

Take a spare, working spark plug with you on your next ride. When the "no start" situation occurs, immediately unplug a cylinder plug cap and hook it to that spare plug, resting it against the cylinder head. Crank again briefly with no throttle. If you see a spark then you quite likely have a fuel issue. If not, then it's electrical.

I'm leaning towards fuel, but you should definitely separate electrical from this trouble.

Ross

I'm going to throw another thought in here. What about a bad engine control module that only acts up when it gets hot? The ECM is located in the left front part of the fairing. As long as the bike is running and moving there may be enough airflow to cool it. Turn the bike off and I bet that area gets pretty hot.

This theory may be hard to test, but to me it's more believable than two coils failing simultaneously. The problem also doesn't sound carb related to me. Again, all four carbs, or at least more than one, would need to act up simultaneously.

Ok everyone, return fire.

Duke

BTW...I really like Ross's idea of the extra plug. Brilliant!

Brilliant indeed. I'll carry a spare plug and let you know. I'm also planning on testing the coils as per the manual.

BTW Duke, that's precisely the thing. While the engine is running I am usually stuck in traffic and temps reach their highest. However there is no indication of ECM failure because the bike runs fine. It's after I let it rest a while that it won't start.

Thanks!

I get what you are saying about temps being highest in traffic, but the engine is already running at that point, and the fans are starting and stopping, which will help keep things under control. Your problem is restarting a hot engine after it has sat for a few minutes. To me this sounds like a possible "heat soak" situation. Whatever is causing the problem works fine cold and when the engine is running, but malfunctions after your shut the bike off hot. I'm speculating that the heat from the engine is "soaking into" something and causing it to malfunction. This could be electronic (ECM), electrical (broken wire, or corroded connection), or fuel system related. Back in the day it was not uncommon for fuel to boil in the float bowl, fuel pump, or a misrouted fuel line in a car engine after shutting the engine off, which would sometimes cause a vapor lock condition and the car wouldn't start. I'm not saying this is your problem, I'm just giving an example of heat soak. I think you probably have a weak or corroded electrical connection somewhere that is only causing a problem after it gets heated up. I have a hard time believing that all four carbs or both coils are acting up at the same time. It seems like it is one item involved with all fuel delivery or ignition that is causing problems.

Have you checked the electrical connections for the ECM and coils? There is a connector located in the left front part of the engine under the air cleaner area. It connects the ECM to the coils. If that connector isn't making solid contact, the engine won't start (DAMHIK). That's where I would start my electrical search. From there you'll need a wiring diagram to chase the ignition circuits to see where else to check.

Keep us posted. You'll find the problem. It will just take a little more time.

I get what you are saying about temps being highest in traffic, but the engine is already running at that point, and the fans are starting and stopping, which will help keep things under control. Your problem is restarting a hot engine after it has sat for a few minutes. To me this sounds like a possible "heat soak" situation. Whatever is causing the problem works fine cold and when the engine is running, but malfunctions after your shut the bike off hot. I'm speculating that the heat from the engine is "soaking into" something and causing it to malfunction. This could be electronic (ECM), electrical (broken wire, or corroded connection), or fuel system related. Back in the day it was not uncommon for fuel to boil in the float bowl, fuel pump, or a misrouted fuel line in a car engine after shutting the engine off, which would sometimes cause a vapor lock condition and the car wouldn't start. I'm not saying this is your problem, I'm just giving an example of heat soak. I think you probably have a weak or corroded electrical connection somewhere that is only causing a problem after it gets heated up. I have a hard time believing that all four carbs or both coils are acting up at the same time. It seems like it is one item involved with all fuel delivery or ignition that is causing problems.

Have you checked the electrical connections for the ECM and coils? There is a connector located in the left front part of the engine under the air cleaner area. It connects the ECM to the coils. If that connector isn't making solid contact, the engine won't start (DAMHIK). That's where I would start my electrical search. From there you'll need a wiring diagram to chase the ignition circuits to see where else to check.

Keep us posted. You'll find the problem. It will just take a little more time.

Grasping at straws here, but is the rubber mat between the carbs and the top of the engine installed...?

John

Yes John. The rubber mat is in place. It's seen better days but it covers the hole all the way. The hole is pretty much empty since I removed the PAIR system. Aside from the cooling hoses and hardware I connect to the carbs one hose coming from the cannister and the drain hose to the spider below the carbs.

Duke, I really appreciate your thorough explanation and I think you are spot on. I am planning on checking the coils at the connector and while I'm at it, I will check the connector for corrosion or looseness. I'll let you know what I find.

Thanks a million for your support!

I really hope you find something definitive. I hate problems that don't have an obvious cause or fix. On the other hand, I love it when I find a clear fix for a problem. That is the definition of satisfaction.

While you are checking the coil connection, check the connection to the ECM. You will have to remove the left glove box to get to it, but I'm pretty sure you'll already have that off anyway.

John, that was a great question. That's what is awesome about posting here. One question leads to another, and another, and eventually a fix.

I need to look at my shop manual, but I wonder if there is anything in the starting circuit that could cause this problem. I wonder if it could be a relay gone bad or possibly related to the starter solenoid. Time for some research.