Carburetor compatibility

Joined
Feb 25, 2017
Messages
22
Location
Grayson, GA, USA
Bike
1998 ST1100
STOC #
8940
I just picked up my new, to me, 1998 ST1100 without ABS. The carbs are going to need some cleaning before I can put any miles on her. I know that I can dump a bunch of chems in the tank and see if that will clean things up. I'm coming from some old school late 70's early 80's JDM era bikes and always like to have a spare set of carbs, rebuilt and ready for install, just in case.

My question is: What year carbs are compatible with my 1998? I seem to see a break point somewhere around 1995 but not sure if true or why. The plan is to pick up the spare carbs and rebuild them in advance. Once rebuilt, I can then replace and sync them in short order. That also give me some time and experience with a new style of carb. I'm VERY familiar with rebuilding Mikuni CV and VM carbs but have not done any Keihin carbs. The Keihin carbs are pretty much the same principle as the Mikuni CV's so not expecting any major issues there. I'm pretty much set up to perform the dip and sonic cleaning at the house. Just need to source out the O-rings and gaskets. I have a supplier that I use but any suggestions would be appreciated. Curious if there are any currently doing rebuilds in the US? Don't want to step on anyone's toes but I currently do Suzuki Mikuni carbs and always have a few sets for various bikes laying around. Might consider adding the ST carbs to the bunch.;)

I'm VERY familiar with rebuilding Mikuni CV and VM carbs but have not done any Keihin downdraft carbs. The Keihin carbs are pretty much the same principle as the Mikuni CV's so not expecting any major issues there. I'm pretty much set up to perform the dip, sonic cleaning and bench sync at the house. I just need to source out the O-rings and gaskets. I have a supplier that I use but any suggestions would be appreciated. Curious if there are any currently doing rebuilds in the US? Don't want to step on anyone's toes but I currently do Suzuki Mikuni carbs and always have a few sets for various bikes laying around. Might consider adding the ST carbs to the bunch.;)

Curious if there are any currently doing rebuilds in the US? Don't want to step on anyone's toes but I currently do Suzuki Mikuni carbs and always have a few sets for various bikes laying around for sale. Might consider adding the ST carbs to the bunch.;) I seem to see a lot of used carbs for sale.
 

John OoSTerhuis

Life Is Good!
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Bettendorf, Iowa
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1991 SSMST1100
STOC #
1058
The early model years' California and ABS/TCS ST1100s with charcoal canister have a Purge Control Valve and an Air Vent Control Valve mounted to their carb assembly. Part of the evaporative emission control system. See the Honda Service Manual. I think this carries through to the later ABS/CBS/TCS II models but I don't have a manual for those. Pretty sure these carbs can be mounted to non-ABS models and the valves removed/disabled. Somebody can chime in here to clarify.

All non-ABS carbs should fit any year non-ABS.

John
 
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OP
OP
Joined
Feb 25, 2017
Messages
22
Location
Grayson, GA, USA
Bike
1998 ST1100
STOC #
8940
I'm hearing that the Canadian carb jetting was better than the US Federal carbs. A little richer, providing better performance.
 
OP
OP
Joined
Feb 25, 2017
Messages
22
Location
Grayson, GA, USA
Bike
1998 ST1100
STOC #
8940
I believe that only the pilot jet changes from #38 to #40 and the needles shimmed. I'm assuming that these carbs I'm looking at are pre-emissions carbs from Canada since they don't have the connection to the PAIR system:


Can someone confirm that?
 
Joined
Feb 16, 2008
Messages
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Deer Park, WA
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2006 ST1300
I believe that only the pilot jet changes from #38 to #40 and the needles shimmed. I'm assuming that these carbs I'm looking at are pre-emissions carbs from Canada since they don't have the connection to the PAIR system:


Can someone confirm that?
I can't confirm that they came from Canada but it sure looks that way to me. I would guess that when you drop off the float bowl it will have the #40 pilot jets and the 128 main jets. The California bikes have #125 main jets. I was always curious to know if the needle had a different part number for the Canadian models as well.

Not carburetor related, but the first ST11's had different cams that were slightly different by about 2 degrees and if it was like the auto industry it was to help burn the excess fuel.
 
OP
OP
Joined
Feb 25, 2017
Messages
22
Location
Grayson, GA, USA
Bike
1998 ST1100
STOC #
8940
Just picked them up for $90 delivered from Canada. Pretty sure they were a Canadian pre-emissions model and look relatively complete and clean. I'll know more once they arrive. The plan is to rebuild them in advance and then exchange them with the ones on the bike now. Probably going to remove the PAIR system at the same time. Read up on several ways to do the PAIR removal. Was wondering if anyone makes the block off plates on the exhaust side?
 
OP
OP
Joined
Feb 25, 2017
Messages
22
Location
Grayson, GA, USA
Bike
1998 ST1100
STOC #
8940
I guess, then the ones I just picked up are from a 1990 model ST since it has no provisions for the fresh air intake into the PAIR system. Once more thing I won't have to plug if I decide to remove the rest of the PAIR system. If I do decide to retain the PAIR system then I can use the plenum from the original set.
 
OP
OP
Joined
Feb 25, 2017
Messages
22
Location
Grayson, GA, USA
Bike
1998 ST1100
STOC #
8940
Today I decided to go ahead and dig right in. Stripped her down naked and pulled the carbs.:






Since I'm down this far, would like any suggestions on what maintenance items would be good to do now. Assuming all fluids and filters replaced. Should I remove the PAIR system since the replacement carbs don't have provisions or should I just block the exhaust ports and keep everything else in place? At 72K miles, would it be a good time to do the timing belt?
 

Mark

Gotta make tracks
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Replace the AL elbows and o-rings, there are 2 sets in the valley below the carb-boots.
You'll be glad you did, although you'll never know how smart you were, if you replace them, because you will not know when they would have failed... ;)
 
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Grand Junction, Colo.
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92 ST1100
I suggest you also replace those carb boots with new, preferably Honda OEM;). Before installing carb bank, lighty spray silicone the inside of the carb boots. This allows the carb bank to easily pop on:).
 
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Jun 9, 2012
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400
Location
Paris, TN
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'99 ST1100
STOC #
8606
I just finished this job on both of my ST1100's. I removed the PAIR system as outlined in this linky. I blocked all the vacuum ports on the intakes since I use SK flowmeter to synch the carbs. I also replaced all the rubber hoses, including the breather tube, and thermostat outlined in this linky. I had already did the timing belt last season, but it makes sense to replace the timing belt if the coolant system is already drained. You might want to replace the fuel filter too.
 
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OP
OP
Joined
Feb 25, 2017
Messages
22
Location
Grayson, GA, USA
Bike
1998 ST1100
STOC #
8940
Carb boots, coolant elbows and O-rings now on order. It does look like one of the elbows was leaking a small amount of coolant since there's a distinct green tint around the gasket seam. Also ordered the carb O-ring kits along with new clamp screws, extra valve cover gasket (one was leaking) and fuel filter. Waiting for everything to arrive now. The replacement carb should be here today or Monday. Beginning the PAIR removal and block off process.

Since the PAIR system is being removed, and the automatic petcock has already been removed, I have no need to have any of the vacuum lines connected to anything other than for use to vacuum sync the carbs. I have a 4 port Morgan Carbtune to do the sync with. Was planning to simply expose those lines with caps in place for future use but otherwise not connected to anything else.
 
Joined
Feb 16, 2008
Messages
209
Location
Deer Park, WA
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2006 ST1300
I have done a FEW of the PAIR removals and what I have done is leave the chrome tubes in place and seal the ends by folding the ends near the back of the carbs multiple times and crushing them flat.
I have taken them off and crushed the ends in my vice as well as leaving them on the bike and using a heave duty vice grip. Once I used a headed gasket that is metal reinforced that I cut to fit the heads and then placed the tubes back on and tightened down, along with crimping the ends of the tubes but thought it was over kill. Note: if you want you can also use a Hi-Temp gasket sealant in the tubes before you crush them.

This keeps the bike looking stock and it does not cost anything to speak of.
I also go along with replacing the boots like you are doing. I have sync-ed the carbs on a bike and then determined that it was in need of a cleaning so I replaced the rubber boots when I removed the carbs and as always they should be re sync-ed. I was a little surprised what a difference the boots made when I sync them the second time.
 
OP
OP
Joined
Feb 25, 2017
Messages
22
Location
Grayson, GA, USA
Bike
1998 ST1100
STOC #
8940
I have done a FEW of the PAIR removals and what I have done is leave the chrome tubes in place and seal the ends by folding the ends near the back of the carbs multiple times and crushing them flat.
I have taken them off and crushed the ends in my vice as well as leaving them on the bike and using a heave duty vice grip. Once I used a headed gasket that is metal reinforced that I cut to fit the heads and then placed the tubes back on and tightened down, along with crimping the ends of the tubes but thought it was over kill. Note: if you want you can also use a Hi-Temp gasket sealant in the tubes before you crush them.

This keeps the bike looking stock and it does not cost anything to speak of.
I also go along with replacing the boots like you are doing. I have sync-ed the carbs on a bike and then determined that it was in need of a cleaning so I replaced the rubber boots when I removed the carbs and as always they should be re sync-ed. I was a little surprised what a difference the boots made when I sync them the second time.
The tube crimping was the direction I was originally going with. Can't see why it wouldn't work. Seams like it would work effectively and be the least expensive way to go. If I crimp the pipes under the carbs, then it would look completely stock. Even when the plastics are removed. Would also let me do the crimps without disturbing the head connection gaskets that, so far, aren't leaking. I like the idea of filling the tubes with high temp gasket sealant before crushing. Adds one 1 more seal in the system and safeguards against any leak at the crimp.

One other option would be to leave a small section of existing hose on the pipes and plug/clamp plugs on the open end. That way the pipes are left in place and completely stock in case someone else wants to return it to working order.
 
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