Newbie ST1100 carb question

[John OoSTerhuis]

Just to note that doing the idle drop procedure in the Service Manual requires an rpm meter/gage/multimeter that can measure 50rpm accurately. Think Fluke or similar in the $200 range. Just say'n...

John

 

[Techman]

Yes, I don’t have that, but I do have a DMM that does frequency. I was going to see if I could get a solid reading with some inductive windings. I’ll find out tomorrow. Going to read the plugs, too, after riding to work for a few weeks.

 

[Techman]

I was able to get a stable-ish reading on the frequency meter.....the color tune would not fire consistantly and was messing up idle. Very difficult to see since these plugs are small and it is about 95 F here. The plugs looked real good, I thought. A touch of tan partway around the ceramic center on all of them. I am thinking I am going to leave it at 1 7/8 turns on the pilot screws. (CA bike with #40 idle jet). It does have a low frequency, low level farting or burbling sound when I close the throttle, but it is not an unpleasant sound (not popping, like I had before I cleaned the carbs). In city stop and go driving I am getting around 35 mpg; I have not gone on a trip yet to get highway mileage, but expect it to be much better. (it is hard to not cruise at 80mph on the freeway on this bike).
In short, I am really starting to like riding this bike around.
I know this is a somewhat crass question, but inquiring minds need to know......Anybody race a Harley? It seems to me that wouldn't be a big deal with this bike, especially on the top end mph. Not much info out there on "racing" though, with this bike.

 

[afrymoyer]

I'm glad that you got her up and running and she's running smoooooth...

To perform the idle drop, you will need a top of the line DVOM with an inductive pick-up, that reads down to 1 rpm. I use either the shops OTC, or my Fluke. It's a very tricky procedure. If your willing to take the time to do it properly, send me a PM and we'll talk over the phone. I also feel that the "color tune" is nothing but a gimmick. It may work ok for another application, such as a lawnmower or a snowmobile, but not an ST. We can tune using vacuum and rpm readings.

I still feel as if the 1 7/8 is a just a squeak rich and would be better set to 1 3/4 as I suggested. If you were to drill a 3/8" hole in each muffler baffle, you could successfully leave it at 1 7/8. The nice thing about putting in those #40's, is that you won't need to use the choke under 50 deg F. Just crank the engine over and roll the throttle a little bit and she'll fire right up. Use your throttle lock to hold 1200-1400 rpm to warm it up.

The ultimate question you have here, is how does the ST1100 stack up against Harley. No matter what, ultimately your ST will win(unless your up against a full racing S&S). Your ST will take them off the line and for top end easily. Off the line, launch hard. Preload and speed shift at 7500 rpm. Redline is 8000 rpm and the rev limiter kicks in at 8500. The ST doesn't make any usable power above 7500. For top end, snick her down into 4th and hold it there. Done... Top speed runs can only be done in 4th. 5th is too high and you'll never build enough high rpm horsepower. However, if your in a mid-range roll-on, they will pull away. The Harley has tremendous torque. Be prepared to tap her down 2 gears to keep up and stay even. Once your holding, shift at 7500 rpm. Leave it in 4th gear to finish him off. After you reach 90 mph you'll sail right by.

You can fool many a sport bike too. Remember that the ST pulls like a tractor. You'll have the advantage for roll-on's. You'll out-pull a sport bike, but after they catch up, it's all over...

 

[Techman]

Great info, Adam. Yes, I believe you are probably correct about 1 3/4 being the magic number. It clearly is close, by looking at the plugs.I got the Honda tool to change it now, but isn’t the easiest getting in there. I may try again next time I have to get in there. Yesterday I changed all the fuel hoses past the fuel filter and took the vacuum shutoff out.
You intrigue me with the hole drilling comment.....would that increase the noise level significantly? I looked around on the site but I’m not finding much info. If the noise level didn’t change much, I would be up for it.

 

[afrymoyer]

It's easy to make the mixture screw changes. Take off seat, side covers, center maint covers, fairing pockets and air filter assy. Pull the fuel hose at the filter. Detach front PAIR hose and the two emission hoses. Leave everything else attached. Loosen the carb boot clamps and pull up the carbs. Tilt the bank one way, then the other, to make the mixture screw changes. Set the bank down in there and re-assemble. 1 hour....

You won't find this sort of information on this particular ST site. This site is too new...

Years ago back in the 90's, some guys were experimenting with exhaust changes. Some swore that drilling a 1/4" hole in each baffle would make the ST do a power wheelie. I tried and determined that they were full of shyt. Fred M and I also experimented with exhaust. He went with slip-on cans, which killed the torque and made his bike sound like a big duck fart (don't do this), and I worked with the STOC exhaust. We found it was best to drill 3/8" hole in the baffle for the best compromise of breathability and noise. The sound will be deeper and throatier than the OEM. That's it. Not offensive at all and still very quiet, near stock level. And by the way, you still can't do a power wheelie with the 3/8" holes either.

A special drill bit must be fabricated to reach way down in there. A 3/8 drill bit with a piece of 3/8" metal round stock welded to the end of it. I think it's 12" long. I'll have a look if your interested. I still have mine.

 

[Techman]

So are you saying that you just run the drill bit into the exhaust hole as far as it will go and drill the hole? I might have a bit like that, as I used to be a sound system installer. Oops, looks like it is a dull hammer drill bit. It does slide all the way in there. Interesting! Would it lean out the top end of this California bike, do you think? Do I need to be concerned about that? This bike has #125 mains (although I bought #128's thinking I could put them in).

 

[afrymoyer]

Slide the drill bit in the muffler. You can feel the chamber baffle wall about 2" away from the front of the muffler. Thats were you drill it. The chambered wall is angled, so care and patience is needed to poke a hole in it. Be careful not to go too far! Otherwise you'll put a hole through the front of the muffler! The ST1100 NEEDS back pressure. This is the way it's designed, so this is as far as you can go (3/8").

This hole in both mufflers should make your jetting spot on. No need to change your main jets. Leave them at #125. You could go up to 2 turns out now on the mixture screws. Still just a touch rich, but safe. You'll enjoy the little extra grunt down low.

I am always messing with ST carbs. As mentioned earlier, I'm about to restore a '93 ABS with a swapped non-emission engine. But still has the ABS carbs. I'll buy those #128"s off ya if you have no room for them. I'll be gutting the carbs and the bike, turning it into a 49 state bike.

Remember that I don't spend that much time over here on this site. If stuck with something send me a PM or e-mail for a quicker response...

I'm going to enjoy my Fathers Day now. The boat is calling my name! Good luck!

 

[Techman]

I did decide to give it a go on drilling my mufflers as explained above by afrymoyer. I am writing it here in case someone else finds this info helpful. I first drilled a 1/4"hole deep inside each muffler. It did not increase the exhaust noise significantly (when listened to on the bike). I wish I had taken it for a ride so I could have evaluated the effect on power. Instead I went directly to the 3/8" drill and again I didn't notice much increase in noise. When I drove it (keep in mind I have a CA emissions bike with #40 pilots installed and screws set to 1 7/8 turns and #125 mains) it was pretty much the way Adam advised.....cleaner more stout ride on the low end, smooth all the way thru to high rpm. The response seemed flatter across the rpm range. It was good. I kind of missed the takeoff it had from 4k to 7.5k prior, and I'm not sure if I had less, or the added power on the low end made it seem less pronounced. Can't be sure in my mind without checking on a dyno. I leaned toward preferring the stock curve on the high end, so I found some 3/8 chrome hole plugs and RTV'd them into the holes. That was exciting to do....They are holding for now, don't know about long term. I want to make an effort to tune the pilot screws better with it stock. At a minimum, to set them to 1 3/4 turns as Adam said, because I think he is right. If I can get a DMM with inductive pickup, though, I would really like to try to nail it.
That's where it stands at the moment.

 

[Brant]

I did decide to give it a go on drilling my mufflers as explained above by afrymoyer. I am writing it here in case someone else finds this info helpful. I first drilled a 1/4"hole deep inside each muffler. It did not increase the exhaust noise significantly (when listened to on the bike). I wish I had taken it for a ride so I could have evaluated the effect on power. Instead I went directly to the 3/8" drill and again I didn't notice much increase in noise. When I drove it (keep in mind I have a CA emissions bike with #40 pilots installed and screws set to 1 7/8 turns and #125 mains) it was pretty much the way Adam advised.....cleaner more stout ride on the low end, smooth all the way thru to high rpm. The response seemed flatter across the rpm range. It was good. I kind of missed the takeoff it had from 4k to 7.5k prior, and I'm not sure if I had less, or the added power on the low end made it seem less pronounced. Can't be sure in my mind without checking on a dyno. I leaned toward preferring the stock curve on the high end, so I found some 3/8 chrome hole plugs and RTV'd them into the holes. That was exciting to do....They are holding for now, don't know about long term. I want to make an effort to tune the pilot screws better with it stock. At a minimum, to set them to 1 3/4 turns as Adam said, because I think he is right. If I can get a DMM with inductive pickup, though, I would really like to try to nail it.
That's where it stands at the moment.

Good to hear your bit of 'expermenting' had some positive results Techman.

 

[John OoSTerhuis]

Without pre- and post-mod dyno documentation it didn’t happen.

John

 

[Techman]

To bring closure and hopefully help others searching this forum in the future, I will report my efforts to tune the carb pilot adjustments. I found a DMM (as John suggested) on closeout on eBay for $50 that could read rpm down to 2 rpm. I took the tupperware off and ran the bike without air filter assembly for this adjustment. I hooked my inductive pickup up the the cylinder I could get the best most stable reading on. For me, this was cylinder 1. Also recall, this is a California bike (different than the 49 states) that I put #40 pilot jets but left the 125 mains. I also had purchased the special honda tool. I was able to tell when the first cylinder dropped 50 rpm (#4, the hard one to get to). It was at 3/4 of a turn. I turned it out 7/8 per manual, to 1 5/8 turns, then rocked it a bit back and forth for best rpm. 1 5/8 turns was pretty much it. Recall that I had set them all to 1 7/8 initially. So the net change was turning it in 1/4 turn from where I have been riding the bike at. All the rest of the cylinders were pretty much the same. Cylinder 3 liked 1 1/2 turns the best. I then recynced the carbs. Put it back together and went for a ride. It seemed to run smoother, and burbled a lot less when letting off the throttle slowing down, then before. I will know more as I ride it this week. I expect to get better gas mileage. The top end seems unchanged.
I think I will leave it this way for now and ride it. If I ever need to get into the carbs again, I think I will follow Adam's advice and go to #128 main jets, drill the mufflers back out with a 3/8" drill, and retune the pilot screws again. From what I have seen, I think that would result in more power overall. The low end was definitely stronger, with no extra noise. Definitely would need the 128's to get the top end right.
While I had the tupperware off, I dug in and checked the valve clearances. This bike is at 34K. I had 3 intakes at .007" and 3 exhaust at .011", basically at the edge of spec. The rest were in the middle of allowable range. I am thinking I must have some crud on the valve seats to open the clearances a bit? Should be OK to run this way.
I also cleaned the shifting linkage and lubed it, and changed my oil to be a mix of shell rotella T4 (15-40 dino) and T6 (5-40 synthetic). It has been so hot here, I wanted to get some dino oil in there to see if it would help the bike to shift smoother. Seemed clunky, especially 1st to 2nd gear.
It did seem to help. Not dramatically, but some.
The last thing I want to do is figure out what to do for handlebar risers. I have a 1" extension on it now and I seem to get sore wrists even just riding around town. I am a bit nervous about going on a long ride. I am not sure if it will be painful. I am not sure I want to go so far as to put helibars on it. I am going on a 1200 mile round trip soon, so I need to figure it out.
Thank you all on this forum for helping me to get this bike in shape to ride!
James

 

[Bush]

he last thing I want to do is figure out what to do for handlebar risers.

Two inch Rox risers will get you pretty much the same reach as a set of Helibars, for a lot less money. No new hoses needed, just re-route.

 

[Techman]

Thanks for the tip...I will check that out.

 

[Techman]

I took Bush's suggestion and bought the 2" Rox risers. What a difference an inch makes! I had a 1" Genmar on there, and thought about adding the Rox to it, but my brake hose wasn't long enough, even re routed. I found the 2" Rox to be as far as I could go on my CA bike. I like the Honda accord look, so I was able to mod the steering cover to fit and not look too bad. The ride is much more manageable for my wrists. Engine running good! Ready to ride somewhere a ways away.

 

[Bush]

I took Bush's suggestion and bought the 2" Rox risers. What a difference an inch makes! I had a 1" Genmar on there, and thought about adding the Rox to it, but my brake hose wasn't long enough, even re routed. I found the 2" Rox to be as far as I could go on my CA bike. I like the Honda accord look, so I was able to mod the steering cover to fit and not look too bad. The ride is much more manageable for my wrists. Engine running good! Ready to ride somewhere a ways away.

Glad that has worked out for you! It does help not only with the wrists, but I found my neck no longer felt kinked too. Have a great ride!