Yamaha TDM Riders

Hey Hank,
I used http://www.carbkitscapital.com/carb_kit_list_model.php?make=Yamaha&model=TDM850 for the o rings and needle seat. I did not find a more extensive kit. I also bought some air cut off diaphragms from them as mine were aged and cracked. For jets, it'd be Yamaha or a supplier like Tucker Rocky at a dealer.

I'm running FP tubes and needles and all is good. I believe the tubes are the newer version for better atomization and the needles are full taper. Bike runs great except is a bit weak in the midrange before the top end rush from 5k to redline. I'm gonna get that sorted soon, but I'm back logged with other projects at the moment. MPG is 53 to 60 though.

Curious to know what the symptoms are for ya with the FP set up vs stock.

Rich

For one it has a cold miss. I'm not certain this is carb related though. I'm going to check valve clearances today to make sure I don't have a tight valve, although I'm not sure if I tight valve would cause a miss that goes away after the bike warms up for 30-60 seconds.

Jetting wise, it doesn't run well at partial throttle and acts odd after closed throttle then cracking the throttle again. It definitely ran better with the stock jets.

I'll take look at my cut off diaphragms too.

I've been chasing my tail for a while with this, but one thing is certain - the bike ran better before I put in the jet kit.

I have been told that putting new jets in worn carbs is like putting a new carb on worn engine. It won't solve the problem. I would suggest a complete rebuild with the FP kit and see if that resolves the issue.

Mine has the cold miss too. I think its ignition related though. Its not plugs as I just put in a new set of # 9's. I also replaced the ends of the primary coil leads (one had some green corrosion) and sealed them with dielectric grease. The coils, HT leads, and caps checked out on the ohm test. No visible sign of cracks or during a dry, dark arc test. I also pulled apart the caps and cleaned up some carbon deposits on the resistor. I've seen some good results on Carpe with replacing the HT leads for this problem. So, that is the next step for that.

Its been a month or two since I buttoned things back up, but I think I'm running the larger FP 142.5 main jets and the stock 37(.5?) pilots. I set the float level as per FP to 15mm and the needle clip is in the middle. Top end is Great! Idle is good and can rev from idle with perfect run up, no lag, hiccups etc. Same on the road, smooth roll on with just that bit of weakness in the middle. I should mention that it has a Staintune slip on, stock air filter set up and valves were done about 7k ago.

I also put in new throttle shaft seals as there was a slight leak just off idle on the left one that was throwing the sync out from idle to steady throttle. Besides, they're 20yo. I used Yamaha ones as they are about half as much as the ones in the link above. They originally fit a 650 twin (256) but are the same size and actually fit a lot of bikes: 256-14997-00 sold each.

I also bought a wide band air/fuel gauge, which I still need to have the bung welded on, to help in diagnosing the flat spot. It gets old pulling things off and back on to go for a test run. Besides it should help to dial in real info along with seat of the pants feel for performance improvements. I can switch it to my other carb bikes too.

I hope this helps.

Edit: I just remembered too, that the choke needles were well worn and not evenly. Worn needles will enrichen the mixture even though the choke knob is pushed in. If you've not seen the amount of wear that can happen, there are some pics somewhere in this thread. Yammy has new ones, and they come with new seals too.

Hard to say without all the info, but to be sure the new FP tubes are well seated with the o ring under them. Also, the little o rings that sit to the side on top with the main diaphragm didn't fall out and of course that the main diaphragms are well seated. The one other goofy thing with these carbs is the slightly angled needle and sequence of the plastic piece and the metal washer for correct needle height.

That stumble sounds like a lean condition, but not sure if it being caused by lean jetting or air bypassing from missing or old seals/orings.

Do you have a sync gauge?

Yes I have a sync gauge and I synced them not long ago. The carbs have been off a few times since so I'll do it again.

I checked the valves and had 4 tight intake valves, but 3 of the tight ones were on the left and the miss is on the right... Exhaust valves were in spec.

I'll get all new o-rings and go through the carbs.. again.. sigh..

A few more questions.

I think the FP kit had a washer for the needle too, are you using that under the clip with the clip in the middle? I actually had the stock needle back in but will try the FP needle again.

There is also a plastic washer under the stock needle - is that still used with the FP needle?

I'll order throttle shaft seals, they are only a few bucks. I'll also take a look at the choke needles.

This rebuildl kit: http://www.carbkitscapital.com/carb_kit_list_model.php?make=Yamaha&model=TDM850
is listed as a '91 model. 91? Didn't know there was a 91. Also fits a 92/93?

Does the above kit also include the oring on the main jets? I don't even see it on the 'fiche, but maybe it comes wit the jet. I don't believe the FP kit had new orings.

Thanks for the help!

I'm putting up some house trim with the good weather, but have decided to go ahead and put on the other HT leads tonight. I've lost track of the needle sequence, but will have a quick look tonight and post a pic. Also, I'll take a pic of the different screws I used for the throttle plate - s/s beveled flat allen head from of all places the local Ace that has a very large stock of hardware. If you've not removed them before, its really a one good shot deal to break them loose and can be a bitch to fix if they get messed up. Be good to shoot them with PB blaster to soak a bit and use an exact fit phillips. They're peened on the back side at the factory an drill start to drag when unscrewing that part and there may be some thread lift on the shaft to clean up too. I used blue thread lock to set the new ones.

Yes, the TDM started in '91 and I believe Canada got them like other cool Dakar looking bikes, but we had to wait until '92 and '93 to show Yamaha that the US masses like either sport or cruisers.... Arrrghhh.

I am going to say yes on the jet o rings in the rebuild kit, including the ones for the emulsion tubes... I think my memory is serving well there. And no, they don't come with the stock jets from Yammer. Don't remember if FP included them or not, but same, don't think they did supply them.

Oh wow.. here are my choke needles. This can't be helping:

The mangled one is from the right.. the cyl with the cold miss.

And.. of course carb kits capitol is sold out of the kits. There are some on ebay though for about double the money..

Yeap, that'll do it. I'm not sure if the ethanol in the fuel is eating them or the aged rubber choke shaft seal leaks letting air flow through so they trickle fuel past in the tight passage, but they should be off when closed.

Bummer on being out of stock. They're Mikuni BDST38 and also came on Ducati's and I think the R1 of the day if that helps with cross referencing a cheaper version.

Again, many thanks for the pointers. I have (hopefully) all the parts I need ordered. I did not order the shaft seals or coil leads at this time as I'm thinking the main culprit was the choke needles. If you get a chance I'd love to see how your needles/washers/clips are arranged.

If you hadn't brought up the choke needles, I'd likely have never gone there. I've gone through the carbs multiple times, had a local mechanic with many years of experience also take a look (twice I think) and neither of us saw this.

Carb parts and valve shims hopefully within the week, then we'll give it a go and report back!

Hank have you replaced your fuel pump? I just did mine and it is way better at starting, idling cold and throttle response. I read quite a bit about this and was frankly skeptical. My experience with fuel pumps has been entirely on 4 wheeled vehicles and mechanical or electrical fuel pumps either work or do not work. I replaced mine mostly because it looked pretty old and as I want to moto in out of the way places I am trying to replace things likely to strand me out there. Also the fact that I could get one for wayyy less than stock didnt hurt.

Yesterday I replaced the pump as an afterthought. My main goal for the day was to take pictures of the swmotech rack so that the somewhere there would be some directions in English,. but I have the pump and while I am farting around in the garage I might as well and so I did... and what an amazing difference! No hard start, no missing at idle when cold, no "on off switch" feeling on the throttle. I am not saying that rebuilding the carbs isnt a good idea for you, but while you are at it you might want to consider the fuel pump. I took mine apart and the membrane was indeed badly stretched, and the lines were full of white powdery crud. From the thread over at carpeTDM my guess was that it was the original pump.

I was thinking about the why of this as I was drinking a beer and letting the bike idle for half an hour. (I wanted to test the fan on the radiator as this was the first day we have had near 70) and as best I can figure when the diaphram warps the pump has to suck harder to get the same amount of fuel, which robs the carbs of the vacuum they need do their thing. so in situations where a strong "pull" from the carbs is needed (like when cold, going up a long grade or 1/4 throttle the fuel pump steals enough suction that the carbs cannot force gas through the needle- so you got WOT, create enough suction to feed both the carbs and the pump and suddenly you feel like your doing a carrier take off, Now it accelerates smoooooth from 1500 to the redline in any gear :eek1 with new fuel pump.

Yep, I put an electric pump from an R6 in it a year or two back.

just checking. I never would have believed it w/o the experience I had this morning of a new bike. I went with the stock replacement to save my volts for a heated suit.

Yup and I appreciate the pointer.

Very shortly after I got the bike I was riding it and hit reserve. I didn't get it switched quick enough and it ran out and died. I crank and cranked and cranked with that worthless stock vacuum pump until my battery was dead. I was pissed. I let the battery recover and it just started as the battery faded away again, so I got home. I put an electric one on as fast as I could after that. Click click click and the bowls are full.

Hey Hank,

Yeah, happy to help. Thanks.

Here is a pic of the needle spacer/washer sequence. It was a bit of detective work as the bike had dynojet needles in it when I first opened it up. I believe this is the correct sequence though. The large metal washer underneath the plastic spacer is a friction fit and holds the plastic piece snug to the clip. There's also (not in the pic) a small metal washer that I put on top of the clip to act as a smooth bearing surface for the plastic insert that fits in the spring.

Also, two of the four old shaft seals which stiff and slightly formed compared to the new ones which are pliable. Also, an original throttle plate screw and a new allen one for comparison.

Hope this helps and yeah, a post on how it comes along would be good.

Cheers,
Rich

Glad to hear the new pump is working great for ya. I'm the same with getting stuff sorted so I can ride more and not get stranded out in the boonies on some of the more remote rides.

Cheers,
Rich

Starkmojo, I forgot to mention about your reference to SW Motech rack. I don't have the rack, but I do have the pannier mounts if that's any help with installation info.

Picked me up a purty, new (old ass) tdm a couple weeks ago and finally got some proper pictures this weekend. Loving this bike so far. I've had this thread bookmarked for like 3 years, now I finally get to use it. Threw some brand new shinko 705's on it after a long tire search and they seem awesome.