ST1100 won't start when hot

Greetings from a new poster, long time lurker. I have a 1993 ST11 with 36k on the clock. Had it for 10 years now. In the last year or so, usually after long rides or traffic jams, I would reach my destination, turn off the bike, only to find that when I tried to return to the road it wouln't start. I have to give it full throttle and crank repeatedly and it eventually sputters and comes to life. For the first few miles it won't take hard throttle. It stalls and dies. Afterwards it will go back to running flawlessly.
I've gone through the board and done most everything. Checked air filter, fuel filter, fuel pump (1200 to 2000 cc per minute, hot or cold). Brand new plugs. Local seafoam equivalent. Pulled the carbs and found a torn vaccum hose (PAIR and fuel shuttoff valve have been removed) so I replaced all four hoses. Put the carbs back on and synched. Runs better than ever but after a couple of sprints and fan cycles, I let it rest while I proudly started to dress her back up. Decided to start her up to turn her around and ...again! won't start! Am I rich? No fuel smell. Lean? Do I need to disassemble carbs? Help appreciated.

Thanks in advance!

Have you tested the vacuum fuel shutoff by routing around it?

I just replaced the coils on my bike and it cured a similar problem to yours,my bike was running very bad when it was hot,though it never died or failed to start.
since I replaced the coils the problem is gone,I fitted aftermarket coils costing only ?18 from davidsilverpares and they have sorted the problem.

Thanks guys.

Mark, I bypassed the vaccum shutoff valve seven years ago. It's been camping in my closet since then. Diaphragm was torn.

Broc, My bike runs great when hot. It has plenty of power and doesn't miss a beat, speacially after yesterdays sync. Say I ride to my local mall, a couple of miles in heavy traffic. Fan kicks in a couple of times. I arrive at the mall running fine. I park the bike, shop for say, half an hour, and then when I get back to the bike and try to start it, no cigar. Needs full throttle and lots of cranking.

I've never even seen the coils. All I know is that the four plug wires all meet under the front frame where a couple of relays rest. Never dug in there before. You think my symptoms still match a faulty coil?

Thanks again!

Glad you've got that one out of the way...

On to Broc's theory!

Is your choke cable working right?

I am sitting here thinking about why it might do this. I had a car do this once and it was a bad coolant temp sensor. It assumed it was cold all the time and the FI would go into cold start mode even though it wasn't needed and flood the engine. Obviously the 1100 is carborated so no need for coolant temp sensor that would impact warm starting. But if the choke wasn't working right or was stuck on it might explain it.

I know when I go back and forth with the 1100 and 1300 that I will choke the 1100 to start it and get my gear on. By the time I am ready to hop on the bike I totally forget about the choke and take off. It rides fine with it on but mileage is a bit worse. Somewhere down the road I usually think of it. So I don't think I have ever tried a hot start with the choke on. I could see where if the choke wasn't hooked up right that you might not notice the issue and assume everything was fine as you went through the motions of applying choke.

You should notice the RPMs change as you tweak with the choke.

A bit of an off the wall possibility but it looked like you already hit the main ones. Fuel pump and cutoff but the fuel cutoff issue usually would result in a loss of power where you said you would run fine until you shut it down and couldn't refire. That symptom doesn't sound right for the cutoff but worth a check none the less.

What about a plugged vent line to the fuel tank. I don't think it sounds exactly like this issue but it is another known one.

maubur said:

I have to give it full throttle and crank repeatedly and it eventually sputters and comes to life. For the first few miles it won't take hard throttle. It stalls and dies. Afterwards it will go back to running flawlessly.
.

Thanks in advance!

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Usually on a carbureted engine, when the only way to get it started is to open the throttle and crankkkkkkk, is the engine is flooded. Opening the throttle fully while cranking leans the fuel/air mixture. The enrichener valves may be sticking open??????????? The next time the bike won't start remove a spark plug (all 4) and see if they are wet. Could be a coil breaking down from heat, but then the bike shouldn't run good after starting.

Thanks guys.

Sennister,

When I apply choke, the lever on the carbs moves all the way forward. When I disengage it it returns to it's aft stop. Choke has never worked as it does on cars. It helps me start the bike on cold mornings when it won't start without it. However, it will only maintain a very slow idle and while the bike warms up, any attempt to reduce choke will kill it as will any throttle input. After a couple of minutes I can gradually remove choke and slowly give it gas until it reaches a point where it will settle fine at idle and allow me to fully disengage the choke.

I definitely can't ride with any amount of choke dialed in. It will run like crap if it runs at all. If I'm not mistaken (it's been a long time since I've owned a carburated car) on cold car engines choke input means higher revs. I've even seen instructions that say you can increase revs on your cold ST by entering partial choke. This has never happened on my bike. BTW, it might be important to stress that I live at 8500 feet ASL. I did lean the pilot screws according to the manual.

Geezer, I'm also thinking I may have a flooded engine. However, aside from the lack of fuel smell, it does seem odd that it runs great until I park it and only floods after sitting still for a couple of minutes. This might divert towards fuel starvation? One or more empty or almost empty bowls? Faulty or out of spec floats leading to the empty (or maybe overfilled) bowls? I took it to a local mechanic when it first started acting up and he supposedly pulled the carbs, cleaned them and synched. However it was way out of synch when I worked on it this weekend. Maybe he screwed up the float needles and position? It was, none the less, acting up way before I gave it to him.

Please stay with me guys. I'll have to find some time this week to pull the carbs again (yey!) and courage to take them appart.

Cheers and agin, many thanks!

just a thought but have tried removing the gas cap and see if air rushes in? My St1100 had spyder webs blocking the vent tube.

On my bike, air has always rushed in when I remove the gas cap. I was told this is normal. The cap venting system seems to work one way only, allowing air out of the tank but not in. At least that's what I got when I tested it. I did remove the cap once when I was stranded and it didn't help much with starting the bike. However, it would be reasonable to think that vacuum buildup inside the tank could eventually lead to fuel starvation. Once bowls are empty, it would take some cranking to fill them up...

Should I try to run it with the cap off to see if this helps?

bigjimbo1957 said:

just a thought but have tried removing the gas cap and see if air rushes in? My St1100 had spyder webs blocking the vent tube.

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I also had an issue with the 'gas' cap vent,I just blew it out with an air line and removed the little rubber diaphragm inside the cap, My bike ran fine alot of the time but the coils were breaking down when they got hot,causing the bike to run on 2 or 3 cylinders sometimes,anyway the coils are easy to get to and in my opinion worth doing to at least eliminate them from the list of possibilities,it was very frustrating for a while but the bike is going brilliantly since.
I hope this helps.

Minor point, but the ST1100 fuel tank cap vents both ways, pressure and vacuum. I've got a schematic somewhere in my desktop's archives, if really interested. IIRC I've posted it sometime ago.

John

I had a car once that exhibited the same issues that you are having trouble with. The final cause was determined to be an improperly installed spring that would not let the fuel pressure in the fuel line be shut off when the car was shut down. It would dump all the fuel into the combustion chamber to sit there. Since you do not have the vacuum shutoff installed and it was obvious the previous mechanic did not sync your carbs correctly I would be looking at how the insides of the carbs were put together. I would do it sooner rather than later. All that raw gas gets in your oil and thins it out pretty quick. My whole engine was ruined because of the excess gas in the oil. Check your oil for any gas smell or see if there is any gas in it when you drain it. Hopefully if this is your problem it has not done too much damage. If he did not install the needle properly you could get excess fuel in there when you shut off the bike. Good Luck

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?

How is your MPG numbers? Did you track it before to know where you were compared to now? Since you are at high altitude and changed your jetting it may be hard to compare to others here.

George was talking the other day about an issue with a Fuel Pressure Regulator. That might be a possibility. His complaint was MPG numbers that were poor compared to normal. Not sure if he was getting a hard start when hot issue. I asked him in the thread but he is out on a trip now so not sure when he will see it or when he will get a chance to reply.

Here is his post in case you didn't see it.

https://www.st-owners.com/forums/showthread.php?127539-Ongoing-saga-of-the-1100-fuel-pump&highlight=

Hi Mauricio,

To start, you need air, fuel, and spark. I'd walk through the troubleshooting schematic in the Honda Service manual. But I'd do a fuel flow check immediately after the no-start event.

Had a car that did the same thing a few years back, alright it was 30 years ago. Figured out the timing was off. A turn of the distributor cap fixed everything from there on. Not sure how the ST runs if the timingbelt is off one tooth. Your bike is 20 years old. Maybe the timing belt or tensioner is giving up and you jumped a tooth? Just a guess. Good luck getting it sorted.

Sennister,

As you say, it's not easy to compare MPG. Last time I checked, milage was around 25-30 but I ride this thing 90% of the time in stop and go traffic and don't pass an opportunity to smoke everyone else leaving traffic lights. Local gas is low octane (84) and 10% ethanol. I did mention I am at 8500 ft ASL which means higher octane is throwing money down the drain. Also I weigh in a bit short of 260 pounds. Anyways, thanks for bringing my issue up on the other thread.

I agree with you and John about the fuel pump possibility. John, after I pulled my carbs last weekend to replace the torn vaccum hose on the #2 manifold, when it failed to start after testing, I immediately did the flow test as described on one of your threads. I took a lead from the + spade on top of the tank to the + battery terminal and measured flow. First time, when hot, it gave me around 2000 cc/min. Nice and constant flow. Pump sounds great. Two more tests performed later on that day gave me around 1500 cc/min. Never went below 1200. Manual says minimum is 650 so I think I'm OK here, unless of course, the fuel pump relay is acting up. I changed the relay about 5 years ago but as far as I can recall, when the relay failed the bike would always stall when pushed, but it would start and idle fine. Exactly the opposite of what's going on now.

As I said on my first post, I went through most of the troubleshooting. Checked filters and confirmed clean and unrestricted. Put in brand new plugs. Went through half a can of carb cleaner. This along with the pump flow test, ripped hose replacement and carb synch, basically covers it all with the exception of carb disassembly to set float needles, clean jets and check and reset pilot screws. My bike's current performance when demanded, would not be consistent with torn diaphragms.

I'm really sorry for putting you all through all this trouble and please bear with me.

Cheeers,
Mauricio

maubur said:

I'm really sorry for putting you all through all this trouble and please bear with me

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Don't apologize...its a good read and will prob help someone else down the line.

agreed... i read mos these posts, not because i have the problem described, but so when I DO have the problem I hope something will have soaked in and I might recognize it on my own... i doubt I will, but I will try...lol