Newbie ST1100 carb question

Hi guys....I am new to the ST crowd. I am migrating from an 84 V65 Sabre. I bought a pretty nice 2000 ST1100 and am trying to get adjusted. One thing that puzzles me a bit is that it runs pretty smooth overall, but at under 3K when I let up or maintain throttle it seems to miss or back pop a bit. It idles fine. Seems like something not quite right. The previous owner removed the carbs and ultrasonic cleaned them. He is an aircraft mechanic and says he professionally cleaned and synced them. I wondered if perhaps the mixture screws weren't set optimally. I believe he synced the carbs, it seems to run great over 3K. I have tried running some choke to see if that makes any difference, but it didn't seem to. I did find out the choke linkage was hanging up on a hose down there. The hose was not moveable, I had to slightly bend the choke arm to clear the hose. I thought that might be causing the issue, but it wasn't the problem.
This isn't a biggie, but I am a bit of a perfectionist about how my bikes run.
More information: This bike had some kind of expensive looking cruise control system on it. It didn't seem to work and I didn't like the way the throttle felt, so I removed the part of the system hooked to the throttle cable and hooked it directly back up to the carbs. It took the slop out, but they must have removed the spring return, because there doesn't seem to be any throttle return spring action. I don't mind, because that acts a bit like a cruise control.
Thanks for your expertise on this issue.

I'm not saying that this is the issue for you, but it can be hard to work out whether you have a carb or ignition related issue, or something else. Personally I was chasing coughs and misses on an open throttle over 4k, and that turned out to be a weak spark problem caused by connector corrosion, but I cleaned the carbs 6 times before I looked at the electrics.

Honda don't design parts where choke linkages foul hoses, so something there is not right. The clamps that hold the carbs to the inlets do have to be correctly rotated to ensure such clearance is available.

Suggest you work problem with cables to carbs first.
The throttle needs to close all by itself. It's highly unsafe and not designed to be operated that way.

+1 on TerryS choke cable interference. I suspect the hose is misrouted. I would definitely not start bending parts to make it work. That's flat out a no no in my experience. Bad way to do business.

Can you take a picture showing the interference?

Once you get normal safe actuation of the throttle, then proceed.

Since your engine runs above 3K smoothly, but not below, lean condition is likely to cause popping and back firing. I suspect dirty carbs need overhaul. Until you get in them, your just guessing anyways.

Pull the carbs, and the bowls, visually inspect the condition. Once I got those bowls off, the crud was the fugliest corrosion I have seen in any carb in the past 50 years.

The point is, if you eliminate the carbs as the problem thru rebuilding them, if there is still an issue, address the electrical too.

What's the condition of the spark plugs? Are they gapped correctly? This is all stuff you need to address as a new owner.

I followed TerryS's lead and put dielectric grease on all the connectors. Made even my Exmark 27 hp Zero turn mower run better. Best electrical tip I encountered.

Do you have a shop manual? What's your level of mechanical experience?

We are all here to learn together.

You are in the right place.

I rebuilt my 2001 ST last year. It ran like a slug when I bought it. Maybe put 5 miles on it. Due to older age health problems, and life manageability problems, I parked it 2 years gathering dust in the garage. Couldn't even get it started after the 2 year sit.

Grabbed the bull by the horns, rebuilt all 4 carbs, all new jets, needles. Runs good now.

Also check the vacuum hoses coming from the carbs are properly closed. Is the cruise control vacuum operated? One of the connectors to the vacuum line may have come loose and there is a leak.

sounds like the carbs need balancing. on mine I experienced a bit of miss fire when throttling down... not bad but troubled me...balancing ironed that out

Thanks for your input. I need to take the air cleaner assembly off and get a better look at what is going on. I just spent a lot of time over the last couple years working on my V65 to get it right and spent a lot of time on the carbs there. I was hoping when I bought this bike I could get down to some serious long trip riding and not spend a ton of time working on it. It is a 2000 model with 32K on it and it is very clean. I will take the air cleaner assembly off (although I was nervous about it as I read here somewhere it is a bit of a pain to get it back on again) and have a closer look at the throttle and choke linkages. I will look at the vacuum hoses for something obvious. I have a Haynes manual I bought to figure out how to get the tupperware off without busting it.
To me it seems like the mixture screws may not be exactly right....Is there a commonly used setting to get them close, like 2 1/2 turns or something? I emailed the previous owner to see if he remembered where he set them.
Should I be concerned about the water hoses under the carbs at this years/mileage juncture?
I like the bike.....it is zippier than I thought it might be. Not a high rpm motor like the V65, but after shifting through the gears I look down and it's at 95mph.....almost electric like an older goldwing.
I tried a ST1300, but the seating position lean over was too much for me.
thanks.

Techman don't know what the jet settings are, never had to mess, but the air cleaner removal is a doddle, nothing to fear. The tank cover comes off easy too, I just think you have to remove the painted side plastics first to get at the bottom fixings. I'd change the fuel filter whilst you're in there.
Good luck.
Upt'North.

Upt' North said:

Techman don't know what the jet settings are, never had to mess, but the air cleaner removal is a doddle, nothing to fear. The tank cover comes off easy too, I just think you have to remove the painted side plastics first to get at the bottom fixings. I'd change the fuel filter whilst you're in there.
Good luck.
Upt'North.

Click to expand...

And........don't forget about the little foam filter. It's in the little rectangular box on the front of the main air cleaner housing. These are often neglected. If old enough, they will harden and crumble. The residue may end up in your carbs and can cause some mixture issues if it does.

Techman said:

I will take the air cleaner assembly off (although I was nervous about it as I read here somewhere it is a bit of a pain to get it back on

Click to expand...

As Upt' North says, the air filter housing is no problem, but I think you might be referring to the "snorkel" assembly on top of the carbs. DO NOT remove that from the carb cluster. It is not necessary to remove it to pull the carbs and it IS a PITA to put back on if you do.

Thank you all for your input. I will pull the air cleaner assembly in the next couple of days and inspect the carb return spring, choke linkage, vacuum hoses, foam filter, and spark plug gap. Should help to get me moving in the right direction.
With the stock carb jet sizes, is it best to stick to a honda air filter or is there a preferred filter? K&N, or sport filter cause a too lean condition?
Thanks

Techman said:

Thank you all for your input. I will pull the air cleaner assembly in the next couple of days and inspect the carb return spring, choke linkage, vacuum hoses, foam filter, and spark plug gap. Should help to get me moving in the right direction.
With the stock carb jet sizes, is it best to stick to a honda air filter or is there a preferred filter? K&N, or sport filter cause a too lean condition?
Thanks

Click to expand...

OEM is my choice, but you will get lots of opinions on that, just like brand of oil and oil filters. I view K&N as crap, but that is JMHO.

I like the drop in K&N. If you put that in and it furthers the popping, you have a great indicator of the leaning out condition. This is another step towards diagnostic evaluation. Still would pull carbs and fix the throttle and carb bind first, before any syncing, or anything else. Good hunting.

Now that the weather is good I have been riding/working on the ST. I found and fixed the loose screw on the temp gauge so that indicates correctly now. I still had the slight miss/popping going on from above idle to around 3.5K. I replaced a bad looking original stock air filter with a new HIFLO filter. Added some seafoam and have been riding to work and around quite a bit. Ran a bit better at first with the air cleaner new. By the end of the week it was running ragged at the lower rpms. Seems smooth above 4K to me.
Tonight I decide to check the plugs and I am not seeing anything ugly. I decide to fire it up and start pulling spark plug wires off to find the trouble cylinder......TURNS OUT THAT BOTH CYLINDERS ON THE RIGHT HAND SIDE (as seated) WERE DOING NOTHING AT IDLE AND UP TO 3K. (I don't know about above that....didnt' want to rev it that high). Absolutely nothing!! I checked for spark on plug and they are sparking. The only thing I can think of that could cause that would be grossly off carb sync??? I am not seeing any evidence of vacuum leaks. Anyone have any idea what could be going on here??? Is there an adjustment that affects both right hand cylinders at the same time?
I am going to try to search the forum for pictures on carb syncing. I am familiar with the procedure on other hondas, but not sure where to hook up to these carbs. Haynes manual is useless for this.
The fuel vacuum valve was slightly dripping, so I tightened it up......not seeing any way those right carbs could be starved. The PO just had them out and ultra sound tanked.
This thing out to really Zoom with all 4 cylinders running!!!
HELP!

Note: I did try to measure compression in one of the cylinders not firing and had around 95lbs, (the gauge adapter I had was not long enough to thread in but a few threads and I am sure it was leaking), at least there seemed to be some compression happening.
Also: I have a borrowed carbtune set up for sync. Do not have a Honda 'D' type pilot screw tool.

Cmon, its not a Harley, rev it a bit higher and see what happens, 3k is barely above idle.

at very low revs the low-speed carb circuit might be suspect, but at a wider rev range I'd start to look at the ignition coil, since its common to both of those cylinders. It may be able to spark with the plug out of the cylinder, but with normal cylinder pressure its not up to the task. Carb sync isn't going to explain what you're describing, no matter how far its off, but fuel starvation might. Are the plugs wet? If they're not firing, and are still dry, then that's something to check.

Also, ignition problems tend to be RPM specific, so if you're getting good power in most of the RPM range, but not in a specific range, that's another symptom of ignition coil issues.

I was messing around with my carbs over the weekend (replacing the air-cut valves) which involved removal of the plenum and loosening the screws that connect the two banks. When I reinstalled the carbs, I had a rattly rough idle, and when I used my vacuum gauges the right side was way low on vacuum. The quickest fix was to pull the carbs off, re-check the tightness of the bank-bank connections, and then I synched the throttles by eye so that all the plates were in the same position relative to the pilot jet orifice on #4. After that, the bike fired up with a much closer vacuum balance, and I was able to use my gauges to fine tune from there.

Having said all that, the bike would run on all 4, just with a rough idle. I'd be more suspicious about something amiss with the right side coil maybe giving a weak spark?

I can't recall if you have had the carbs off and checked the jets yet? Blocked idle jets would certainly account for poor running below 3k.

I would start with the basics first. Pull the carbs and remove the idle jets and clean or replace them. The very fact the previous owner said he "ultrasonically cleaned them" indicates there was an issue. Sometimes when individuals attempt to qualify themselves by telling you their a so and so or a such and such... usually indicates they're not competent. After cleaning or replacing the idle jets, sync them again. Another quick check while the carbs are off the bike, carefully pull the vacuum pistons and check the diaphragms for rips.

Techman said:

The fuel vacuum valve was slightly dripping, so I tightened it up......
HELP!

Click to expand...

If this vacuum valve was dripping fuel, it also has a vacuum leak. How did you tighten it? Usually the diaphram inside is ripped.

The fuel vacuum valve was slightly dripping, so I tightened it up......

Click to expand...

Common problem as the 1100 ages. The rubber diaphragm splits and leaks. A simple bypass can be done to see if it is the problem. 5 minute job when the plastic is off. Top and right side cover.

http://www.st-riders.net/index.php?topic=3919.msg30239#msg30239

Oh yeah, I meant to mention the fuel shutoff valve and forgot. I think he said he already checked the plugs, but if not, the #3 cylinder (right rear sitting on bike) supplies the vacuum for the valve. If you get enough leakage past the diaphragm that plug tends to foul, so he should check that if he hasn't already. Other than that, I doubt it has anything to do with his performance issue, but wouldn't say its impossible either. While he's at it, he should do the bypass and be done with it.