TDM900 : Cold start trouble
Part II by E.T.

For a little while the fast idle hadn't been working properly, so at long last I decided to do something about it. I hope the following will help others. Incidentally the fast idle unit can't be bought as a separate unit, you can only buy it as part of the complete throttle body assembly, list price about £1300...yes thirteen hundred!!!


Originally the symptom was one of no high idle on start up on a cold engine, making it difficult to start and keep running. After a service, and I can't remember the exact circumstances was months ago...the symptoms changed to having a fast idle at start up, but then remaining fast.

What is the problem

The fast idle plunger is a little unit screwed onto the front of the throttle body. It has two pipes off the radiator which heat a wax stat. As the wax stat heats it expands, pushing a plunger side ways. This pushes against a slider arrangement (which is sprung loaded) and adjusts the throttle setting (independently to the twist throttle).

All of this is exposed to the elements and the water and spray tends to work into the plunger and seize it up. Hence it can get stuck in one position.

What to do about it

The repair is simple in theory. The fast idle assembly is held onto the throttle body by two screws. Remove these and remove the two radiator hoses and take it off the bike. The whole thing comes apart with two screws. Free it up, lubricate and replace on the bike.
Easy eh!?

Except...getting to the bugger!

(image)Prop up the fuel tank. I've made myself a holder-upper. Consists of a bit of aluminium shower curtain rail, flattened either end. An 8mm hole drilled in either end at 400mm centers. Use the tank bolt and a nut bolt of suitable type and prop the tank up so... it's nice and secure and great for lots of those under tank jobs.

(image)Once the tank is up you need to remove the air filter box. I didn't remove this altogether, I just disconnected the hoses, undid the jubilee clips on the air intakes, and the securing bolt at the very front, then lifted it to one side.

(you'll notice from the picture 1, that I placed a clean sandwich bag over the air inlets to the engine to keep any potential dirt/dropped screws etc out)

(image)Now you can easily see the Fast Idle plunger. This is on the right hand side of the bike at the top of the throttle body (its the cleanest looking bit in the photo, at about "7pm").

(image)Disconnect the two pipes, having something suitable to plug the ends (to save draining the coolant down)...BUT see below before you look for plugs. I ended up using a couple of 6.5mm twist drills (blunt end in, of course)

Now you will notice that you have just two screw to take out. will also notice that there is a radiator pipe in front of the screws. I got a ratchet with a 6.5mm socket and a screwdriver bit (Philips), but it was far too tight to undo - I was beginning to damage the head. The only real way to get that out was confront it head on!

Drain down the coolant (don't bother with the plug screw on the water pump) just drain using the screw on the front of the cylinder block, this will get the coolant level low enough. Don't forget to catch the coolant in a clean container, ready to stick back in later.

(image)Remove the offending pipe. Now wouldn't you think that would be easy. Two Jubilee clips and a bit of tug...but oh no! If you look here, you will see Mr Yamaha has carefully placed the jubilee clip facing downward, meaning no way to get a screw driver on it to undo. This was a careful shuffle with a small spanner...6mm (I think...I can't remember. sorry), moving it 2 degrees at a time.

Remove all the bolts that hold the radiator (no need to disconnect the rad altogether - removing these bolts the rad can just be dropped enough)

(image)Now you can get to the screws from the front - here's how I did it...


(image)And finally off comes the fast idle assembly...

(image)Undoing the two screws reveals the inside of the assembly.
...and the offending part is this stainless steel pin.

(image)It was pretty solid, but lightly tapping it back and forth freed it up until I could push it out of the body (you need to take it out from the inside). This was then cleaned, and I used copper-slip grease on the pin (I wondered whether it was genuinely road grome, or some electrolytic corrosion between the aluminium and the stainless that caused the partial seizure..??)

Sticking it all back together is pretty much the reverse of the above. I like to stick copper-slip on everything as I replace to make next time easier. When you replace the radiator hoses, and bolt it all together, do remember to do up the jubilee clip otherwise coolant pisses out every where......then you have to take the tank off again, and the air filter box.

One other point was I found it difficult to get the air box located onto the throttle body air intakes. In the end I split the box took out the air-filter so I could guide the rubbers over the intakes - lot easier.

Text & pics in this page are from E.T. / Carpe-TDM Forum.
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