Need Help. What would you do? Surging and power loss

congratulations on getting spark to all 4 cyls, that was the first step. it sounds like you still have carburetion issues though, which I have no experience with so I'll just bow out and keep lurking to see how you do with that.

good luck.

FWIW, a carb sync will not likely cure the apparent running rich condition you're experiencing now (idles fine without the choke applied when cold) so you're going to have to dig into it further. I think you got carb help from another forum member earlier, maybe he can sort out what he did before and see what might make sense for your next step in the troubleshooting.
 
The RPM's at idle are 1100. I seems like it idle a little rough. I have let run for about 10 minutes so it is warm. When I slowly increase throttle it tries to go up tp 2,000 to 2,500 rpm than falls back and dies. If I "goose" the throttle quickly I can get it up to 4,000 to 5,000 rpm than when I release the throttle it stutters at about the 2,000 rpm range it wants to die. I can leave it idling at 1,100 rpm and it will run without coughing or dying.
 
1,100 - 1,000 is pretty normal for a 'warmed up' ST1100 to idle. If all is well, they will idle really smooth.
I am a bit confused though - does it idle smooth at 1,100 RPM when it is cold as well as warmed up?
Does it have the fuel cut-off valve still in place?
 
I will leave the bike overnight and see how it reacts after it's cooled down.

I think your talking about the bypass of the fuel vacuum? Right? I will check again but I'm pretty sure the previous owner bypassed it.
 
Okay, outside temperature just now is about 40 degrees so the garage might be a little warmer.

I put the choke on and started the bike, it took about 3 cranks on the starter to get it running. I turned the choke off after about 15 sec and it ran roughly then sputtered out. So I put the choke on for 1 min and then turned the choke off. It ran roughly at about 500 rpm until it started warming up. I let it run for 12 minutes and the rpms came up to 1,000 and it smoothed out. At the 15 minute mark it was idling at just under 1,100 rpm and at the 20 minute mark it was idling almost exactly 1,100 rpm.

Assuming it is a warm engine now, I SLOWLY applied throttle to try to get the bike to go to 2,000 rpm. At the just past the 1,500 mark it drops out and dies. I can then restart without choke and continue to replicate the problem. Slowly apply throttle and then it dies.

The fuel vacuum shutoff has been removed from my bike and so the fuel comes through the fuel filter and goes directly to the carburetor bank.

The fuel pump is working to spec. The one day I had with "jrp" from this forum we tested this by having the fuel pump directly into gas "beaker" and then comparing it to the manual volume measurements for the time period measured.

Any more ideas? So close but so far.
 
ScottyG said:
UPDATE! Real progress made yesterday! I was trying to figure this out again and decided to have another go at it. I read through the entire post to see and if missed anything and then did some more searching to learn more about the ICM. I came across a thread from 2009 - called " ST1100 ignition problem NOT solved Yet!!" In that thread it had the attached picture of the wiring harness to the coils. I inspected mine AGAIN and could see no problems, but use my voltmeter to test continuity of each wire and connection and I found that the ground to (1/3) did not have continuity. I cut of the spade lug connector and crimped on a new connector and then I got continuity I needed! Put it all back together ands visible saw spark to all cylinders!

I said progress....but I haven't ridden it yet! Although the bike is running, it is running very rough my guess is that I need to tune the carburetors. I could get it to idle at about 1000 - 1100 rpm but when I try to apply throttle it would die. It acted a little better if I applied a about 1/2 choke and I could get the rpms up higher and then it might drop out. My guess is that it's running lean? Is this solved by synchronization of the carburetors or are there other things I need to consider?

Thanks to GitSum from the UK for this picture in the 2009 post and ChucksKLRST from Aurora Colorado who posted on the same thread that he had the same problem with a spade lug crimp connector. The weird thing is they posted Dec 21, 2009.....11 years to the day that found their post and solved my ignition problem.

And of course all of you in this thread who have been patient.



ignition.jpg
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I'm just wondering if my replys, comments or whatever you call them are being seen by you people over there. I've said check the earth wire specifically on at least two occasions and very early on in the discussions and it seems you never did it till now, that's why I'm wondering if you read them. Are you seeing them?..... Swede. (in Cornwall, England).
 
Hi Swede, good post.

Rest assured, I read ALL comments and try my best to follow directions. It's HOW to check, WHERE it is (often the close ups in the manual do not help), and in WHAT sequence. Specifically people how talked about "earth" or "grounding" here and finding there are all kinds of earth points on the bike at the kickstand, on the battery, at the coils, and on the fuse box...etc. It was only until I realized HOW to test a wire for continuity with a voltmeter did I realize my problem on "earth" not going through the wiring harness section that goes to the coil. First time I have ever measured "continuity" with a voltmeter....had to look it up!

I am a complete NOOB I have no experience with repairing engines much less motorcycle systems. Trouble shooting through this forum is way, way less than ideal but it's my only option right now. I'm surprised I've made it this far. I have learned so much based on the encouragement, especially when folks say don't give up.....your getting close!

I love riding and I love the way this bike rides, but I may have to accept the fact that I'm not a mechanic and I need to sell it as is and by a current model that can be serviced through a reputable repair shop.
 
ScottyG said:
Hi Swede, good post.

Rest assured, I read ALL comments and try my best to follow directions. It's HOW to check, WHERE it is (often the close ups in the manual do not help), and in WHAT sequence. Specifically people how talked about "earth" or "grounding" here and finding there are all kinds of earth points on the bike at the kickstand, on the battery, at the coils, and on the fuse box...etc. It was only until I realized HOW to test a wire for continuity with a voltmeter did I realize my problem on "earth" not going through the wiring harness section that goes to the coil. First time I have ever measured "continuity" with a voltmeter....had to look it up!

I am a complete NOOB I have no experience with repairing engines much less motorcycle systems. Trouble shooting through this forum is way, way less than ideal but it's my only option right now. I'm surprised I've made it this far. I have learned so much based on the encouragement, especially when folks say don't give up.....your getting close!

I love riding and I love the way this bike rides, but I may have to accept the fact that I'm not a mechanic and I need to sell it as is and by a current model that can be serviced through a reputable repair shop.
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OK. Understood. I'll remember in future and try to give more info on how to do what I've suggested. Sorry! On the new problem, I presume that wasn't happening originally? I would strip and clean the carbs, removing jets to make sure they're completely clear and clean (blow with an airline) up the drillings the jets came out from. As its been standing for a while now, you may be having the 'ethanol problem'. Sometimes the ethanol leaves a residue in the jets so you can see through them but they are effectively smaller than they should be. Only way to clear them is to use a suitable size wire or better still, one of a set of jet cleaning wires. (get them on ebay)
Check all the air pipes are on correctly as well just incase one's off. How do you think you'll get on doing that? If you need any further info or help, just say and I'll try to help. Happy Christmas to everyone over there : or anywhere!........ Swede.
Ps. Carb cleaner seems to have little effect on ethanol but is probably still worth using anyway.
 
the fact that it dies without choke when its cold would suggest its not running rich, or at least not way rich, otherwise it would start and idle without the choke (enrichening circuit) applied.

when the bike is idling its running on the pilot jets, and as you give it throttle it transitions from the pilot jets to the main jets. I'm not sure exactly where that transition occurs, and how gradual/abrupt a transition it is, but it seems suspiciously related. As I mentioned before, I'm no carb expert, so I'm not going to speculate any further.

Also, way back when you started having ignition problems, the question was asked about the condition of your carb boots and whether you might have a vacuum leak. I think jrp replied that they "looked OK". Now that you have the bike idling reliably try shooting carb cleaner around the boots and see if the idle speed changes at all. If it changes then you have a vacuum leak.
 
Good ideas! Swede, I was real fortunate to meet "jrp" through this forum. He gave a long full day of his time to work on the bike since he has the same ST. That's the incredible thing about this forum. He checked out the fuel pump, changed the fuel filter, took off the carburetor bank, used a special wire to clean the pilot jets, inspected the diaphragms...and through the whole process cleaned everything, re-installed the bank after inspecting the boots......and had the patience to answer my constant questions. I then synced the carburetors....long day. Since then I've only put in non-ethanol gas.

I like the idea of "check all the airpipes" . I assume that means looking into the vacuum hoses that go to the carburetor bank? A lot a people on this forum have been suggesting a vacuum issue. I did a thumbs down to a $1,500 carburetor re-build offer. Maybe they didn't pay lot of attention to getting it back together right and just wanted to get it our of their shop at that point.

Dwably, your description is "spot on". It feels like it's a transition point from pilot to main jets. Sometimes I can apply fast throttle and make through the transition point and go up to 5,000 rpm but when I easy back on the throttle it drops through that transition zone of about 2,000 rpm then it dies.

Time to put this aside for the holiday.......Merry Christmas Everyone.
 
Just an idea, but I wonder if your idle jets are restricted; at fixed low throttle plate position, the enrichment can maybe compensate for an otherwise too lean condition, it sounds like you can achieve a stable idle by finessing the enrichment position, but once you crack the the butterfly valves from that minimum position you're too lean, and incorrect rate of fuel spilling through the idle transfer slots through the transition phase to main jets. I almost get the sense that once you're under way and the throttle position is beyond the transition, it runs pretty good.
So goes my vacuum theory, I guess it's red jello tonight.
Another thing that comes to mind is I'm wondering how wise it is to use these common aluminum stake on connectors; for resistive loads who cares, but on ignition circuits where ____ happens fast or very low signals aluminum oxide might be a problem; there's some delicate circuits where I would use brass instead, or even try to scrape the aluminum terminal with an appropriate gauge of solid copper before crimping.
One of the best instances I had of the brass solving everything was on a millivolt system that drove me nuts.
Glad you nailed the _____ ground!
All good jolly fun, Rome wasn't built in a day... it took several thousand years!
 
ScottyG said:
Good ideas! Swede, I was real fortunate to meet "jrp" through this forum. He gave a long full day of his time to work on the bike since he has the same ST. That's the incredible thing about this forum. He checked out the fuel pump, changed the fuel filter, took off the carburetor bank, used a special wire to clean the pilot jets, inspected the diaphragms...and through the whole process cleaned everything, re-installed the bank after inspecting the boots......and had the patience to answer my constant questions. I then synced the carburetors....long day. Since then I've only put in non-ethanol gas.

I like the idea of "check all the airpipes" . I assume that means looking into the vacuum hoses that go to the carburetor bank? A lot a people on this forum have been suggesting a vacuum issue. I did a thumbs down to a $1,500 carburetor re-build offer. Maybe they didn't pay lot of attention to getting it back together right and just wanted to get it our of their shop at that point.

Dwably, your description is "spot on". It feels like it's a transition point from pilot to main jets. Sometimes I can apply fast throttle and make through the transition point and go up to 5,000 rpm but when I easy back on the throttle it drops through that transition zone of about 2,000 rpm then it dies.

Time to put this aside for the holiday.......Merry Christmas Everyone.
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ScottyG said:
Good ideas! Swede, I was real fortunate to meet "jrp" through this forum. He gave a long full day of his time to work on the bike since he has the same ST. That's the incredible thing about this forum. He checked out the fuel pump, changed the fuel filter, took off the carburetor bank, used a special wire to clean the pilot jets, inspected the diaphragms...and through the whole process cleaned everything, re-installed the bank after inspecting the boots......and had the patience to answer my constant questions. I then synced the carburetors....long day. Since then I've only put in non-ethanol gas.

I like the idea of "check all the airpipes" . I assume that means looking into the vacuum hoses that go to the carburetor bank? A lot a people on this forum have been suggesting a vacuum issue. I did a thumbs down to a $1,500 carburetor re-build offer. Maybe they didn't pay lot of attention to getting it back together right and just wanted to get it our of their shop at that point.

Dwably, your description is "spot on". It feels like it's a transition point from pilot to main jets. Sometimes I can apply fast throttle and make through the transition point and go up to 5,000 rpm but when I easy back on the throttle it drops through that transition zone of about 2,000 rpm then it dies.

Time to put this aside for the holiday.......Merry Christmas Everyone.
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Although they are generally called 'idle' jets they do still play a part above that and I'd say the vacuum piston /diaphragm is probably only taking over about 2000-2500 rpm. Then, it's the needles rising in their tubes metering the fuel (the fuel is coming through the main jet but too slow for the jet to play a part). Then, when the needle is getting right up the flow has got high enough for the main jet to take over but, that will be at very high throttle opening and revs. That's basically how it goes. As you can see at about 2-3 thou up until the main jet it's the needle in the tube, that won't block but as its fed by the main, if that's blocked enough; or water in the bottom it could restrict the flow. Vacuum pistons could affect it at those revs too! Carbs can really be a pain, I think a strip down, close inspection to make sure everything is fitted back correctly and clear /clean is the way to go! If you're up to it, you've done well so far so you should be okay.... Swede.
 
Final Update - I have decided that this project is just beyond my experience and although I have been close I just don't have patience to sort out the final details. Thanks everyone who offered advice and support along the way. This is a special forum. Once I put the plastic back on I will list it for sale on this site.

Happy New Year,
Scott
 
Happy New Year Scott, dont know why this is italics, plenty of fish in the sea, spring hopes eternal, come april youll set your sights on another and...
move on, let us know what you get, besides better luck, this ones been a bit exascberating, and life is short
 
End of story.....listed the bike in the For Sale section:confused:. Thanks again for everyone's help, I think I got close but time to move on.

Scott
 
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