Yamaha TDM 850 hesitation

[ReptileVPK]

Hello forum members,

A few months ago, I bought a 1992 Yamaha TDM 850 3VD. It needed some work since, after about 20 minutes of riding, it started stuttering at low RPMs and wouldn’t accelerate properly. When giving throttle from idle, it would "hiccup," as if it was skipping a stroke. The spark plugs were pitch black, and the internal carb components (throttle tubes, etc.) looked somewhat worn.

So, I fully rebuilt the carbs (using parts from carburateurwinkel). The carbs weren’t split, but every possible jet and component was replaced. I also installed a used ignition coil, as that was my first suspicion.

 

It seemed like the problem was solved, but unfortunately, the hiccuping returned. Once the engine gets properly warm, it struggles between idle and around 3,500 RPM. Adjusting the needle position and mixture screw didn’t help.

Installing a larger pilot jet (from 37.5 to 40) improved things slightly, making it run 50/50. Now, the issue is random and unpredictable—it just comes and goes. Sometimes it stalls when taking off, other times I can’t keep the front wheel on the ground when accelerating.

I have a USB hub (don’t worry, the issue was already there before installing it) that displays battery voltage, and this voltage remains unchanged whether the issue occurs or not.

Link to the issue in action:
https://youtu.be/Z_LdBUApUQw

In the video, I'm at full throttle the entire time. The bike stutters and bucks up to around 3,500 RPM, and then suddenly kicks in like crazy. After that, you can see the throttle response.

Current setup:

• Stock air filter
• Stock exhaust
• Valves adjusted 500 km ago
• Needle clip: second lowest position
• Pilot jet: 40
• Main jets: 75 and 140
• Air jets: 1.4 and 70
• Mixture screw: 2.5 turns out
• Spark plugs: 500 km old (look a bit too white, in my opinion)

You’d think it needs an even bigger pilot jet, but why? Nothing has changed that should require a larger one.

Could this be an ignition problem? But if that were the case, wouldn’t I hear backfiring from the exhaust? In the video, you can hear popping from the intake instead.

I'm also planning to install a GPR 2-1 Trioval exhaust, but only if I can fix this issue first.

Help!

[Hairsy]

Remote diagnosis is very tricky but my best guess is that you may not have 100% fully cleaned the pilot jets originally. Are you absolutely certain that they were absolutely pristine, with every hole in every pilot jet perfectly clean? If you have any doubt at all then do it again. If it's any consolation, I've been there.

 

My guess is that your replacement pilot jets may have been cleaner but will have messed up the mixture. I'd definitely be wanting everything back to factory sizes / settings.

 

And I agree - don't change the exhaust until this problem is solved.

[ReptileVPK]

6 minutes ago, Hairsy said:

Remote diagnosis is very tricky but my best guess is that you may not have 100% fully cleaned the pilot jets originally. Are you absolutely certain that they were absolutely pristine, with every hole in every pilot jet perfectly clean? If you have any doubt at all then do it again. If it's any consolation, I've been there.

 

My guess is that your replacement pilot jets may have been cleaner but will have messed up the mixture. I'd definitely be wanting everything back to factory sizes / settings.

 

And I agree - don't change the exhaust until this problem is solved.

Thanks for responding Hairsy.

I started with an all original size overhaul kit. So all new parts, in pristine condition. Problem was there, and now slowly ironing out the kinks.

But there are still a lot of kinks to be ironed out. 

[Hairsy]

My apologies - you did say that. I missed it.

 

If you're confident that it was a quality kit with good quality jets then I'm afraid I don't know what to suggest.

[curlylegend]

Try Carpe TDM website, they're very knowledgeable and very helpful too.

[bud]

It might be worth balancing the carbs if you haven't done so already.

[RideWithStyles]

Id agree with hairsy. If it ain’t SUPER CLEAN AND SET CORRECTLY- even if you thing you have it’s easy to over look or fook up. 

I would question three things:

the idle and but the main problem I suspect for you is the pilot circuit, then the jets kit- if they ain’t trust super brilliant quality/certification they are your first line of them problem….seriously it doesn’t take much fook up it up, how do you know they are actually correct? Just trust the bag label? lol 

[ReptileVPK]

Fixed!

 

I changed te plug boots, coil wires and used a different coil. And now it's fixed!

[Simon Davey]

Excellent!! Well done @ReptileVPK, that's good to hear.

[curlylegend]

55 minutes ago, ReptileVPK said:

Fixed!

 

I changed te plug boots, coil wires and used a different coil. And now it's fixed!

As a matter of interest, what did you use ?

[ReptileVPK]

13 hours ago, curlylegend said:

As a matter of interest, what did you use ?

2 NGK XD05F 5ohm spark plug caps, generic spark plug wires and the original coil!

Before i rebuild the carbs, i thought the coils were making the bike run weird (turned out to be the carbs). These were second hand, an apparently were slowly dying.

Put the original coils in which came with the bike, and voila!

[curlylegend]

Good show !  I have heard that this might be a problem with older TDM's and have heard of various solutions. Like sealing and insulating the HT leads etc.  I think most of these problems happen to TDM's that encounter a lot of wet weather ?

I'm fortunate, not having the need to go out in wet weather, but I keep problems and solutions like this in the back of my mind, just in case.