ST1100 Carb Problem?

[Uncle Phil]

Okay ST Sleuths, here are the sequence of events so far -

1. We removed the carbs to clean the idle jets that were stopped up (bike had been sitting a while before I got it). Upon reinstallation, the bike seemed to have a vacuum leak. We thought that it might be the lower clamps on the carb boots. I decided I would pull them later and check it out.

2. Saturday, I pulled the carbs and found the lower boot clamps to be tight. Since I have 2 extra sets of carbs, I picked one, removed the bowl covers, verified that I could blow through the idle jets, button it up and installed them on the bike. The bike ran fine so I decided to take it to get some fuel and for a test run before I buttoned it up.

3. Put on my gear, got to the end of the driveway to pull out uphill, and the bike acted like it was running out of fuel. If I blipped the throttle it would keep running. I headed down the hill and road a few miles to fuel it up. Then I ran several miles up and down the interstate to check it out. Problem seemed to be getting worse.

4. Bypassed the vacuum fuel valve, thinking it might be the problem. No improvement at all.

5. Pulled new carbs off, installed the idle jets from the new carbs into the original carbs, reinstalled original carbs on bike. The problem got worse. The bike now only will hit if I continously turn the starter over and will not run.

I plan on checking to see if the fuel filter could be clogged and pulling a spark plug to see if it is wet or what color it is.

Sooooooo, any suggestions at this point - besides putting it on a trailer and carrying it to a STealer to get ripped?

 

[Mark]

It sounds like each time you moved or worked on the carbs the problem got worse could you have torn a vacuum line?

Mark

 

[BigTom]

Big Tom tugs wistfully on his ear, twice.

Does sound like a fuel filter, to me. You might check the carb boots themselves while you are there to insure no cracks...BTDT on a v-4 Yammie

You are headed at it the right way, you'll find it sooner or later. I gotta think that a dealer wouldn't do any better than you have.....

 

[Uncle Phil]

MARK - I will check the lines again just in case I missed something. Would a torn vacuum line cause it to run out of fuel with cutoff valve out of the loop?

TOM - I'll double check the boots for cracks. They looked good but I didn't look at them really close.

 

[Mark]

I think a vacuum leak would act like carbs being way out of sync... leaning out your mixture so the bike will barely run...

I can't think of anything else that might make it run (or not run) and since you seem to be covering the gas/fuel I thought I'd add to your debugging mix...

Mark

 

[BigTom]

Jeeze, Phil.

I went away and ate (I always think better when I eat), all I could come up with that you aren't on is the fuel pump/wire. Probably a long shot, but I suppose it could be fuel pump....

Vaccuum leak should not affect the fuel flow with the valve bypassed. Did you plug the vaccuum line to the valve?

 

[Uncle Phil]

The saga continues -

Checked the ignition fuse to be sure that it was good. Then pulled all four spark plugs - all four were wet with fuel and black. Shorted one against the head while cranking and got a really good blue spark. Cleaned them all and reinstalled. Cranked for about 3-4 minutes - no hit at all. Pulled one again to check it and it was wet again. So at this point I am thinking the carbs are flooding instead of starving. I did not pull the fuel line off because the filter appeared to be filling. Any more ideas anyone? BTW, I am trying to start it without the air cleaner or the base installed, but usually they will run without that stuff. Also, this bike has had the PAIR system removed before I got it and it ran 1000+ miles very well except for the idle.

 

[saaz]

New plugs might help, has solved many seemingly intractable problems (or take some out of the other two STs lol!). Make sure the choke is not being pulled on. If it seems to be flooding fuel delivery may not be a problem. I have had a few of the carb boots not done up at all (don't know who did that and the bike ran fine. Are all the vacuum hose connected? If even one is off then the bike will run real rough. Easy to have one come away while doing everything else.

 

[wjbertrand]

It has been found before that the ST1100 runs like crap with the air cleaner removed. What happens if you re-fit it?

 

[Uncle Phil]

SAAZ - It's something else to look at. At this point all suggestions are welcome.

JEFF- Usually they do run a little badly with the cleaner off, but they do run. This one will not even run but at least it's something else to try. Thanks.

 

[freeSTyle]

UP* Give me a call.........

Don

 

[number9]

SAAZ - It's something else to look at. At this point all suggestions are welcome.

JEFF- Usually they do run a little badly with the cleaner off, but they do run. This one will not even run but at least it's something else to try. Thanks.

Don't know about riding with the air filter off, but when I did a sync once with the Flowmeter and the Mercury sticks someone asked that I check the sync with the air cover lid ON and OFF to see if there was any difference in the values (thought was that syncing with the flowmeter and the air box lid OFF might not be good). So, I took pics of the mercury sticks with the lid ON and OFF and there was not as can be seen here http://rides.webshots.com/album/550655197ijvFrk .

***now, having posted that link and someone is going to note that the mercury sticks are WAY off of a good sync......yes they are, but I had synced with the flowmeter (and posted pics of the values) and had the mercury sticks hooked up at the same time to get a comparison of the two methods. I don't know why the sticks are way off on the ST, but I do know (and many others can back this up) that the best sync I have ever had on the ST was using the flowmeter. However, I have used the mercury sticks on the inline-4 of my R6 and FZ1 and got good smooth engine results. I have no idea why - maybe to do with the V-4 and inline-4? maybe with the carb arrangement? I have no idea, just stating what I have seen. And didn't mean to drag Phil's thread off-topic because he does need to get his bike sorted and not breakout into a discussion about carb sync methods. Sorry for the tangent UP.

...

 

[Uncle Phil]

The next tale in the saga -

Building a compendium of all the advice thus far received -

1. Installed FroST's fuel filter (the problem bike) on SweetTreat - SweetTreat ran like a champ. Went ahead and installed SweetTreat's filter on FroST.

2. Remove all 4 plugs from FroST and installed them in SweetTreat. SweetTreat ran like a top.

3. Turn FroST over for a couple of minutes before reinstalling the original plugs to clear the cylinders.

4. Ah, FroST finally starts, backfiring through the carbs. Quickly set the aircleaner box and air cleaner on FroST, she smooths out a little bit. I let her run.

5. FroST will not idle but runs a high speed.

6. Turn FroST off and it does not want to start.

My conclusion? The low speed carb passages are cruded up and the floats are a bit hosed on this set of carbs. Which puts me back where I was at the beginning of this adventure. What think ye?

 

[Gymbo]

Have you checked fuel pump output? Just thinking out loud, so to speak.

 

[Uncle Phil]

JIM- Yep, puts out a steady stream.

 

[BigTom]

Well Unc, I think you are probably correct. I've seen Honda (single) carbs crud up like you describe, (on power equipment) and I've seen Yamaha 4x carbs crud up like you suggest (boy have I...), but this might be the first time for a V-4 Honda. It's like you are a trailblazer...

My friend Ray's old bandit had an astonishing habit of fouling a plug on #3 or #4. Could be either one, the 4 carbs were set up identical (a little rich, it was faster than the average Bandit). Never did figure out why. Never. We had the carbs in and out at least 4 times, finally decided that it might be a coil (3 & 4 were shared) when he sold it. It still mystifies me, and yours is starting to. How can four carbs (or 2 coils for that matter) all go ugly the same way at the same time? The chances don't seem good.

 

[Uncle Phil]

I plan on swapping the carbs out and see what happens. My hunch is too much SeaFoam may have coated the plugs when I had the second set of carbs installed. I was low on fuel and was headed to get some. It was interesting that after I ran the plugs in the other ST and 'cleaned' them off, the FroST fired right up and ran good for a while. Then after running it at 4000-6000 RPM for a while it would not idle, then it would not start. I'm getting really good at deinstalling/reinstalling ST1100 carbs - down to about 10 minutes now. ;-)

 

[Uncle Phil]

The Rest Of The Story -

All I did was install fresh NGK plugs and FroST fired up and ran just like she is supposed to, which was my hunch. The final analysis -

1. Original carbs had passages clogged up besides the idle jets. The carbs I got off EBay that I had installed earlier work just fine - just got to get them synced now. She idles well at 1100 rpm.

2. SeaFoam in large volume coats the spark plugs and reduces the fire where it is not strong enough. If you use it, use sparingly and take a long ride to burn it up.

 

[Mark]

UP,

Thanks for the SeaFoam tip... *really* good to know...

Mark

 

[Uncle Phil]

PABLO - Yep, more than the label directs. If a little is good, a lot should be better, right? ;-)