St90 carb and clutch help

S

skillet1234

New Member
I have a 1973 Honda ST90 and have two issues.
Problem #1: I have completely rebuilt/restored this bike. I did a complete teardown of the Carb, cleaned it, put it back together and set it to the factory adjustment settings. The bike will not idle. It either races too high and I have to hit the kill switch or it wont idle without using the throttle to hold an idle. I have adjusted and re adjusted the idle and pilot settings but still cannot get it to idle.
I have ordered a cheap 30 carb off eBay to see what changes if any occur.

Problem #2: The centrifugal auto clutch pack did not have the 6 small springs in it when I got the bike. I bought those and 3 new fiber clutch discs. When I put the bike into first, it is supposed to idle and when I give it throttle the centrifugal part kicks in and off I go. My bike doesnt idle, it immediatley stalls. If I roll the bike then kick it into first, it will stay running and I can ride it. Is there a break-in period to the new clutch discs? Any help is appreciated. Scott
 
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Problem 1 - it could be that the throttle slide is not all the way down the slide hole. Rotate it 180 degrees and make sure the slide slot lines up with a small brass post in the slide hole. This would explain the high rpm situation.

Low idle? Did all of the jets get cleaned? That would be the idle jet, the main jet and the emulsion tube above the main jet. All have multiple holes that need to be cleaned. I also rod out every passage with copper lamp cord and spray Brake Kleen through the red straw into every passage.

Replacement carb? I hope you got the one with the fuel valve and choke on the riders left. These new carbs are also shorter than stock such that they do not reach the air cleaner bellows. I predict you will be buying a regulation NHL hockey puck in the near future to remedy this - more later if this is the case.

These new carbs also have a plastic choke arm that hits the air cleaner base. You will be clipping a bit of the plastic off to solve this.

And keep your current carb's throttle topset. The topset on the new carb will hit the ST90 frame but the old one still works.

Problem 2 - new clutch fiber disks must be soaked in motor oil for 24 hours prior to use. The disks can be damaged if used dry.

There is also a simple clutch test I use before installing one. Put the assembled clutch basket in one hand and the big gear on the clutch shaft in the other hand. Try to twist the gear. It should freely spin in one direction and immediately lock up very solidly if spun in the other direction.

Rick

Two Honda ST90 and Two CT90 Bikes
2006 Honda Foreman 500 (Resto In Progress)
 
Skillet,
did you make sure that the o-ring and the gasket on each side of the spacer (plastic thing) are properly seated and that the two screws are properly torqued and not stripped?
Mark
74 Yellow ST90
75 Topaz Orange ST90
06 Kingpin
 
Carb - The slide and needle look ok. It only fits in one way so that the "ramp" is aligned with the idle adjust screw.
I have cleaned and rebuilt the carb twice. This included soaking it in one of those "paint can" solutions for carbs. This actually worked very well and gave back some of the rainbow effects you see on these old carbs. Adjusted the float level and needle position to the stock settings. I cleaned the jets, emulsion tube, etc both with air and mechanically with wire.
As for the new carb, I will just have to wait and see what I get. I honestly just want it to be a test to see if there is something I am missing with the stock carb.
I made a new gasket where the carb meets the manifold. (Manifold, new gasket, spacer, oring, carb) I am going to replace the oring but I dont think it is bad.
This is the carb I bought. http://www.ebay.com/itm/180908290096?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Clutch - When I got the bike the 6 springs that go on the posts of disc A were missing. I bought these on Ebay (Only place to get them), and also bought 3 new fiber discs on DrAtv.com. The discs are a little thicker than stock but the DrAtv site says they work. I am NOT able to rotate the assembly by hand in one direction but I think thats because of the new springs and the thicker discs. Im hoping this is just something that will correct itself during break in??? I didnt soak the discs but I did use a good amount of oil during assembly.

Any help is appreciated. Let me know if I need to order different parts such as clutch discs etc. Also let me know if pictures would help with any of the above. Remember, its a 40 yr old bike and im kind of new to this. I could be missing something I dont even know is supposed to be there like the 6 clutch springs.

Thanks again for the support b52bombardier1 and Mark A.
 
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You will be frustrated using that carb. The fuel inlet barb and the choke are on the wrong side. Reaching past a hot exhaust pipe to work the choke and to actuate the fuel valve will not be any fun.

If your clutch will not freely spin in one direction and then immediately and solidly lock up in the other direction, then something is wrong. It will not perform well for you if mounted on your bike. Maybe there is a LiLHonda member close to where you live that can assist?

Your local Honda dealer might also assist you on something like this. They will not usually touch our bikes because of the points ignition but for a clutch, they might.

Rick
 
Carb - Well I just got done trying to fit the carb and the mounting holes are about 42mm apart and I need something around 48mm apart. Not sure what to do now. Do you have a recommended replacement carb?

Clutch - The problem is I dont know what could be wrong. I followed step by step directions on reassembly and still think it is too tight. Is it possible that the centrifugal weights are in backwards? I didnt tear the clutch pack down that far.

Also, is there anyone to send my carb and/or the clutch pack to for review?

Scott
 
I like this Dr ATV carb for an ST90 if you can adapt to the caveats I noted above.

19MM CT90_CARB FITS K2_THRU_1979 ATC90 (ST90'S_READ) (19MMCT90)

This one should also work better for you:

Left Side Choke PZ19 ATV Dirt Bike Carburetor 70 90 110 125cc CT 70 90 110 Carb | eBay

Neither of these have the altitude knob if that matters.

Try taking your clutch to a Honda dealer. A half an hour of labor plus parts is all it should cost. The worst they can say is no. I am about to get both clutches on my Foreman done (never done clutches like these before) at my local dealer for a half an hour of labor so I know it is possible.

Rick
 
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skillet where are you located?

Regardless of what dr.atv (parts salesman) say, those disks might be too thick. the clutch pack is, for sure, designed to NOT have tension on it at rest. those little weights that go under the clutch pack (cam looking things on the ring) are what actually engage it, as they put pressure on the pack as the assembly rotates faster and faster. Also, yes it's supposed to lock up in one direction (known as an over-running clutch in auto trans world, the only other place i've seen them) Also, make sure 4 of those little springs, located on the studs, pass through the other 2 steels, and push the 4th and final steel plate away from the other plates. there's 2 smaller springs (to my understanding) that only push the 3rd steel away from the 4th one. let me know if your clutch is oriented like that, and if it is, it should free-run in one direction, and lock up in the other.


good luck and happy motoring
 
Enginedoctor said:
skillet where are you located?

Regardless of what dr.atv (parts salesman) say, those disks might be too thick. the clutch pack is, for sure, designed to NOT have tension on it at rest. those little weights that go under the clutch pack (cam looking things on the ring) are what actually engage it, as they put pressure on the pack as the assembly rotates faster and faster. Also, yes it's supposed to lock up in one direction (known as an over-running clutch in auto trans world, the only other place i've seen them) Also, make sure 4 of those little springs, located on the studs, pass through the other 2 steels, and push the 4th and final steel plate away from the other plates. there's 2 smaller springs (to my understanding) that only push the 3rd steel away from the 4th one. let me know if your clutch is oriented like that, and if it is, it should free-run in one direction, and lock up in the other.


good luck and happy motoring
Click to expand...

Sorry it took so long to reply. I am in Michigan. I have purchased a new clutch pack off of Ebay for 10 bucks including shipping. I couldn't pass up that price. It operates by turning in one direction and locking up in the other direction so I am going to install it and see if it works. I think the 6 small springs I bought off Ebay for my original clutch pack are not the right ones. The new 10 dollar clutch has the same springs but with considerably less tension on them.
 
alright good to hear you're getting it sorted out. i was gonna say if you're from new england, i could figure out a way to go through it or help you to go through it. if you can turn it one way okay and it locks the other way it's getting to where it needs to be. post your progress here and let us know.
 
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