Author Topic: Coolant Leak Under the Carbs ( ST1100 ) *  (Read 8523 times)

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Coolant Leak Under the Carbs ( ST1100 ) *
« on: March 27, 2009, 09:26:51 PM »
Coolant Leak Under the Carbs

Original article on Mike Martin's web gage here:

Do you occasionally get a whiff of coolant smell, or do you find a tiny spot of coolant on the ground under your ST? It may be caused by the small hoses that attach to the elbows on each cylinder head. It could be the hose is too short, and the clamps aren't tight enough. Or maybe the O-rings under the elbows attached to the heads have started to leak. Here's a picture of the top of the engine with the carbs removed, showing these connections. All the pictures on this page were furnished by Michael Moore, of Toronto, Ontario. Thanks, Michael.

    First read this tip from Whit Brown: "It's much easier to remove the carb assembly (or even tighten up the coolant hose clamps secreted under the carb assembly) if you remove the fuel tank first. It's an easy two-minute job ...only four bolts, four electrical connectors - three on top AND one hidden down on the left side - plus the fuel supply line."

Method 1 - The Easy-Easy Way

This first write-up is from Bill Zucker.

"I've been monitoring this list and saving anything to do with maintenance for about 6 months now. I had saved about a dozen message about the common coolant leak, which my '97 had a slight case of, although I never saw fluid on the ground. Just stains on the black frame and a mild antifreeze smell after stopping the bike.

Anywho, I was dreading the removal of the carbs (the most cited method) or the removal of the tank (also mentioned a couple times), or having to finesse a custom tool. Then I removed the right side vent panel, and saw that the leak was the from right side (as most had reported), and that if you look under the headlight assembly backward on the right side, you'll see a 5/8" (or thereabouts) hole through a black plastic shield that lets you easily get at the hose clamp in question. I've got to believe the hole was put there by Honda expressly for that purpose, so you can credit Honda

I did have to use an extension and a swivel with the 6mm socket on a 1/4" drive, but I was able to very painlessly tighten the clamp as much as I wanted.

Just to let you know your leak may not be as hard to fix as you might have been led to believe."

    And George Catt adds: "Someone mentioned that you can reach the two front coolant clamps (see this picture) through a small hole just above the radiator on the right side. Even with the carbs off, I couldn't get a tool through that hole onto the clamp screws. BUT WAIT! The hole is in a small plastic panel that can be removed with one screw (see picture). NOW, it's a simple job to tighten those clamps."

Method 2 - The Easy Way

This write-up is from Robert Kienlen.

"I guess what goes around comes around. Been reading the posts on the leaking radiator hose thread for the past couple of weeks, thinking "man, I'm glad I don't have that problem - sounds like a real pain".

So I'm sitting on the garage floor last weekend working on some forward-mounted front pegs, and a drop of green "blood" hits the floor under the bike. Then another, and another. Bike had been sitting in the cold for about three weeks, so it all sounded like what I'd been reading. Peered through the plastic with a flashlight, couldn't see where it was coming from.

Remembering the posts though, I figured the most likely places were where the main hoses attach to the engine, under the carbs. Started to tear it all down - tupperware, air cleaner, the whole bit. While looking at the whole carburetor bank still sitting there and grinding my teeth, I remembered one post where the guy said to remove the gas tank - "made the job easier", he said.

Tank came out in a couple of minutes (with only two torn gas gauge wires), and after sticking my head down in the cavity where the tank was, and looking under the rubber blanket under the carbs, I saw the hose clamps - halleluhah. Sure 'nough, there was green stuff coming out of the joint under the right hose.

Was able to get a 6mm box end wrench in there and slowly tighten both the right and left clamps, 1/8th of a turn at a time. Piece of cake, carbs never had to move.I had to tighten the clamps in small increments, since there's not a lot of room to swing a wrench under there, but I'd bet the total tightening was between 1/2 to 1 turn per clamp. I was careful not to overdo it and damage the hose.

For the right side hose clamp, it also helped to strap the small 6mm box end wrench to a small screwdriver (or any straight metal tool) to extend its length 3-4 inches (just overlapped the end of the wrench and the blade of the screwdriver and used stainless tie wire wrapped around them to hold them together - duct tape wouldn't have been strong enough). Otherwise, the typical wrench of that size is not long enough to reach all the way in there.

The left side clamp is easier to reach.

Sometimes this ole liST sure helps out - thanks all."

    George Catt sez,"Another trick for this is to pull the carbs loose from their boots, and juST lift them up (I used a ratchet tie-down hung from the garage door track.) Ya don't have to take anything else loose. This provides enough clearance to pull the rubber sheet out from under and get at all the fittings without pulling the tank.

Method 3 - In Case Your Hands Are Too Big For The Easy Way

This write-up is courtesy of John Prince.

"Having just done the carb removal, here was my experience. BTW, I am not a mechanic and this is my first motorcycle since a dirt bike in my teens so if I can do it, anybody can. I would give this job a difficulty of 5 from 1 to 10 and that's only because it is tough to get the carbs seated back in place. You can't get to the main coolant hoses coming off the heads without removing the carbs. Check everyplace else first. Removed all the tupperware to check all other locations of hoses first. No luck. Used the Honda Service Manual for the following:

1. Removed air filter and housing. Masking tape on the carb air intake tubes.

2. Several items on the carb assembly to remove as per the manual. Air hose on the very front, air hose on the right side, choke cable on the left side, fuel hose on the back side (next to the gas tank), and the throttle cables on the back side. I should have waited to remove the throttle cables until I had the carb assembly out 'cause it was very hard to get the cables out with the carbs in place. Just remove the screws on the bracket and take the lead shots out of the "gas wheel".

3. No need to drain the carbs first, I didn't get any gas out of the fuel hose connected to the carbs. Maybe it needs a vacuum to open the fuel valve. Not sure.

4. Push up, down, back, whatever, the black rubber mat around the 4 rubber boots to find the boot clamp screws. I had to rig up a phillips on the end of a 1/4 socket extension to get the correct length to reach the clamps. Loosen all 4. I counted on the one I could see the nut and it is safe to say that about 20 turns of my full wrist motion sufficiently loosened each boot clamp without dropping the nut off the end of the phillips bolt. The black mat would have caught it anyway to retrieve later.

5. The carb assembly will feel very stable where it sits like you forgot to remove something. Some use a broom stick or other prying device. I just stood on the pegs and pulled with increasing pressure until it just popped out.

6. There are 4 goofy little carb drain hoses on the bottom all "T"eed into a larger drain hose going down. If you fall off the pegs properly when the carbs pop out the drain hose will come loose with no worries. If you don't want to fall over backasswards, then hold the carb assembly up slightly with one hand while reaching under with the other and pull the big hose off the T or the 4 little ones off the carbs. You aren't going to hurt anything here as they are only for draining the carbs and don't hold pressure or anything. You can properly hook them back up later before putting the carbs back in place.

7. Handle the entire assembly very carefully and gently set it down on a table somewhere threatening anybody to touch it. Don't mess around with the carb synch screws or bend anything. Take this chance to see what the carb synch screws actually adjust and find the carb drain screws for future reference if ever needed. Put masking tape on the open bottoms.

8. Do a good job putting masking tape over the 4 big holes going down into the engine before you drop anything in there. Stretch the black mat out around the 4 boots and remove it. Take this time to get your service manual and identify the parts and hoses under the black mat such as the pulse secondary air injection, etc.

9. You will see two large hoses coming off the inside top of each head, one on the left and one on the right. Most likely one of these will be leaking. Mine was on the right side. I loosened it up a bit so that I could twist the hose slightly and then reset the clamp. Maybe you could just tighten it. Since mine leaked after setting in the cold garage for a month I let it set this way a few days to see if any more came out. I probably should have taken a liSTer's suggestion to rig up a bicycle pump to the radiator overflow tube connection and pressure tested it (see Cooling System Pressure Test) but I didn't for whatever reason. I may regret not doing this.

10. Put some sort of lubricant on the inside of the carb boots and the carb inserts. Since the rubber carb boots are usually exposed to gasoline, some WD-40 or silicone lube shouldn't hurt them.

11. Put the rubber mat back in place.

12. Install the throttle cables before putting the carb assembly in the hole. Check out how to adjust them if needed later in life. It's just a couple of lock nuts on the cables and there should be a little slack so that it snaps back against the stop screw which is actually the screw you are turning when you set the idle.

13. Have a buddy hold the carb assembly in the hole so you can get one hand in from each side and re-connect the carb drain hose to the T.

14. Set the carbs down on the boots and check the alignment all around. My '00 model has clips that hold the 4 boot clamps in place so they will not turn on me when trying to tighten later. Things will not align at all until they pop in place. Try all different angles and motions possible while pushing down but don't screw up the boots. Others have used a rubber mallet to put things in place but I just used my weight and gravity. Two will probably pop into place but it will be very hard to get the others to go in. I had to get all 4 to pop in at once. There is no doubt when it goes in that they are all seated. Tighten the 4 boot clamps."

    The installation may be a bit more difficult if your bike is older and the carb boots have hardened. Here's a tip from Whit Brown:
"If you haven't put the carb assembly back on the engine before, you might try this to gain enough pressure to ease the insertion job (learned after about an hour of unaided struggling).

    Apply a little silicone grease inside the rubber boots. Loop a nylon strap around something firm on the lower left side of the engine, I used the head. Bring the top of the loop up almost level with the base of the carb assembly.

    Slip a 1/4" x 1-1/4" x 4' (or so) steel bar, edge-wise, between the center-most carbs and under the looped strap on the left side. Then after aligning the boots over the carbs, press downward on the right-side end of the bar. The nylon strap becomes the fulcrum point and provides tremendous leverage to seating the carb assy. While applying downward pressure on the end of the steel bar, the boots will seat with a definite 'drop'.

    (And remember, there is a rubber hose at the forward end of the assembly, the open end of which REALLY doesn't go anywhere. [It comes off the forward tee of the front-right carb.] It just tucks under a retainer and vents to the outside atmosphere.)"

"15. Hook up the rest of the items as they were removed. Start it up and run it.

16. Change the oil, plugs, and air filter if it's time since you have it stripped.

PS - identify the carb vacuum hoses so you won't be afraid to synch the carbs in the future. Since I didn't turn the screws I didn't worry about synching mine right now. It seems fine.

I'm sure there are a few minor things that I may have forgotten here and a few things that could have been done easier. I have no doubts that you will probably hear from other liSTers on their own procedure and maybe a few comments to make better what I wrote up."

Photos! John Oosterhuis has posted some nice pictures which will help you with this work at

Last updated on October 22, 2007      2001-2004 M. E. Martin, All rights reserved

Thank You again for your contribution Mike Martin
« Last Edit: March 08, 2017, 08:24:14 PM by John OoSTerhuis »