Yamaha YTM200 Engine Tick

[Hutch08]

Just finished a complete service on my 1982 Tri-Moto YTM200k.
Completely went through the bike, setting every adjustment to spec as per the manual.
This is a low hour bike that has never been rebuilt but has hardly been used, the valves were still in spec and the motor has over 145psi compression.

One thing that has always been there since I bought the bike is an engine tick, I presumed it was possibly valves or the cam chain and just needed to be adjusted.
Now I know that everything is in spec, it's still doing it. Usually doesn't start "ticking" until it's been running for a few minutes. Doesn't matter if it's in gear or not either.
Also, it doesn't always do it. It seems worse when I let the bike sit and idle for quite some time.

Otherwise the bike starts, idles, runs through the gears, clutch grabs, etc... everything like it should.
I've tried the old "ear on a screwdriver" trick, but I can't tell where its coming from.

Second guessing myself... I pulled the valve covers and re-adjusted the valves. They're now at the tighter end of manufactures specs.
Set to 0.05mm intake / 0.11mm exhaust, with the engine cold. Didn't make a difference to the tick.

Initial fire up it's quiet as a mouse, just after idling long enough to get up to temp the idle kind of drops a bit for a second and then it starts to do it. Almost like the bike slightly hiccups.
A slight increase in idle will make it tick faster, but if you Rev it... it sounds like the tick goes away, but that's also hard to diagnose over the exhaust noise.

Thinking maybe its lower end? Clutch? Rockers? Nothing to worry about? What do you guys think?

Here's a youtube video, note the idle is set a little higher to make the tick more prominent:

[YamaBoss]

From my experience, when the valves are adjusted properly they do have that little tick to them. As frustrated as it may sound even at the tighter clearance they make that sound. I've got three different motors that tick in the exact same way after the valves were adjusted. I've heard someone mention before it was from a worn part in the head, but I can't remember what or if they were even correct, maybe someone knows what would cause that.

[El Camexican]

Grab a wood hockey stick, or a broom handle and place it against an ear and then place the other end on different parts of the engine until you find the source of your tick.

Odds are its in the valve train. I don't want to call it "normal" but mine is silent for the first 5 minutes or so and then ticks a lot like yours. I've checked the valves a number of times and they are within spec. It is much better for your valves to be a little loose VS too tight for a number of reasons. I think a lot of us are getting accustomed to what a water cooled engine sounds like with all the ticks and clicks being muffled by the water jackets, but air cooled engines have only some rubber sound deadeners in the fins and run looser tolerances to deal with the heat.

The only thing that would concern me is if your tick is coming from the con rod or piston slap, but piston slap is usually worse when cold and a roller bearing con rod should make the same noise all the time. The wood handled stethoscope will tell you where its coming from.

PS. Be sure your cam chain is properly adjusted.

[Hutch08]

Thanks for the reassurance that the sound is somewhat "normal" haha. I think there's a good part of that statement that's true, we're accustomed to everything being so whisper quiet nowadays that the slightest tick, bang, or pop sounds like the sky is falling.

My valves are on the tight side of the adjustment, do you think it's worth loosening them a bit?

Yamaboss, I believe the part that wears is the rocker itself... there's no bearing it just rides on the shaft and can elongate over time, especially if it's been revved at higher rpm's for a prolonged time.

As for diagnosing where it's exactly coming from, I'll try again... I think it's valve train for sure though. I'd be pretty dissapointed if it's piston slap or a rod bearing on such a lower hour machine that still has over 145psi compression.

Timing chain was adjusted, although I'm not sure what the manual means when it says to adjust until the rod moves slightly... is that visibly or just by feel.. and how much is "slightly" haha.

[El Camexican]

I shoot for close to max. tolerance when setting the valves on anything (except shim over bucket types). It allows more time for heat to dissipate from the valve to the head and more importantly more time and space for oil to get onto the lobe and whatever it's riding against to activate the valve, so yes, if you don't have at least .001" more than min. on the intake and .002" more than min. on the exhaust side I would reset them. Shimmed valves, specifically shim over bucket types are dangerous if they are set too loose when used with high lift cams.

If anyone trys to tell you that you'll get more horse power by running your valve tolerances tighter ask them how much more

I think (been a while) that the movement of the pin on the Yamaha cam chain is determined by your finger.

Does it have the stock seat? That thing looks to be in great shape! Make sure BOTH your oil filters are clean! A lack of oil could cause that tick too.

Your shifter looks very low, you may want to adjust it or it could get bent on rocks or brush.

Nice Canadian edition reflectors up front, too bad the rears are missing.

Oh, its an 83 trike, not an 82. The sticker on the steering head likely has a manufactured date of 1982 (mine was made in August 1982) Only the 125 and 175 were 82 models.

[Hutch08]

I shoot for close to max. tolerance when setting the valves on anything (except shim over bucket types). It allows more time for heat to dissipate from the valve to the head and more importantly more time and space for oil to get onto the lobe and whatever it's riding against to activate the valve, so yes, if you don't have at least .001" more than min. on the intake and .002" more than min. on the exhaust side I would reset them. Shimmed valves, specifically shim over bucket types are dangerous if they are set too loose when used with high lift cams.

If anyone trys to tell you that you'll get more horse power by running your valve tolerances tighter ask them how much more

I think (been a while) that the movement of the pin on the Yamaha cam chain is determined by your finger.

Does it have the stock seat? That thing looks to be in great shape! Make sure BOTH your oil filters are clean! A lack of oil could cause that tick too.

Your shifter looks very low, you may want to adjust it or it could get bent on rocks or brush.

Nice Canadian edition reflectors up front, too bad the rears are missing.

Oh, its an 83 trike, not an 82. The sticker on the steering head likely has a manufactured date of 1982 (mine was made in August 1982) Only the 125 and 175 were 82 models.

Thanks for the great reply!

Seeing that it's so easy, I'll pull the tapper covers and slightly loosen them... just to be on the safe side. Oil is fresh, new filter and the screen was cleaned.

Good catch on the shifter, it wasn't bent but for some reason it was adjusted that way. I've since moved it up parallel to the peg. The reflectors have all been removed, but I'll keep them in my tool box. They tend to get easily broken anyways and I don't do any night riding. Yes that is the factory seat with no rips and stock tires.

Mfg date was 07/82... I always thought august was the beginning of the consecutive year... that makes sense for it to be an 83 though.

[Hutch08]

Another question seeing this thread has gotten some attention... trying to dial in the carb.

It's been throughly cleaned, clean air filter, etc... and all the brass is factory.

Bumped up the idle then tried setting the pilot screw 2 1/4 turns out.
Turned the screw in and out to where it revved the highest, I think it was right at 2-2 1/4. Backed the idle down and blipped the throttle, seems crisp. Sometimes when I whack it wide open quickly after idle it'll actually kill the motor though. Is that lean or rich?

I was thinking the needle position might help it ? It's currently at middle slot. Also, I've read conflicting info on the mixture screw. I always thought these mikuni's had air screws... but I also read that if the screw is on the engine side of the carb it's a fuel screw?

So is turning it out making it leaner or richer??

[El Camexican]

Ok, you have the 83 and it's a Canadian unit, so I'm assuming you have the short lived rad hose clamp style manifold complete with what looks like a vacuum gauge adaptor on it?

Good luck finding a new manifold if so, I don't think Yamaha put them on any other models. I switched to the bolted flange type as my stock manifold was cracked up.

Anyway, if that's the carb you have and the screw is located closer to the carb inlet than the engine side then it does have an air screw and not a fuel screw like the carbs that followed. Not sure why. (Got a pic?)

Leave the needle clip in the center like you have it now, make sure the float height is set correctly (I think it is 19mm, but check your manual). I can't recall the stock pilot # or the main jet, but the main could be anything from a 95 to a 112. Note what they are and bolt it together and set the air screw 1-1/2 turn out.

I assume it's cold there, so you should need the choke on to start and run it for at least 30 seconds if below 5C, less when warm out, but still needed.

Get it running good and warm, then at idle pull the choke lever. If it revs up high and stays high your pilot jet is too small, if it revs up a little and then dies, or just dies then you pilot is likely fine and you can start playing with the air screw. When you open the throttle fast at idle and it kills the engine its a sign of being lean, Turn the air screw in to lessen this effect, but unless the idle speed is fairly high most 4 strokes will die our momentarily when you whack the throttle open like that. Modern carbs have plunger style injectors to prevent this, so don't expect your 30 year old carb to be flawless in this test.

If when you do the throttle whack test and the engine burbles, but does rev up and you smell fuel it indicates you're air screw can be opened up another 1/2 turn. As long as you can get it to run good with the air screw set between 1/2 and 3 turns out your pilot is fine. Make your air screw adjustments at least 1/2 turn at a time, as less is hard to notice a change.

My recollection is that the only time the stock set up wasn't good was at temps below 20C. Lower than that and they need a larger main if you plan to open them up for more than a few seconds.

You MUST have the air filter on to do this! If it's not sealed and oiled the trike won't run for

[Hutch08]

Yeah you're 100% correct, it's a ytm200K so it had the clamp on style carb. The boot was showing some dry rot although it hadn't completely cracked I replaced it anyways.

I used a short section of 1.25" ID fuel hose that actually fit perfectly, secured with 2 band clamps. You can see it here when I was checking the float:



The float was set bang on to manual specs, 21.5mm and the fuel level is 3mm below the bowl as per specs.
The manual suggest setting the air screw ro 2 1/4 turns out, which seemed excessive to me

[El Camexican]

That's a fuel screw as far as I know. More turns out = richer. Keep in mind that any fuel/air screw is meant to be adjusted as conditions change. The recommended 2.25 turns out is just a base line setting.

[Hutch08]

That's a fuel screw as far as I know. More turns out = richer. Keep in mind that any fuel/air screw is meant to be adjusted as conditions change. The recommended 2.25 turns out is just a base line setting.

Yeah you're right, I think it's the terminology sometimes used that's the most confusing... Regardless if it's metering air or fuel it's often referred to an "air screw".

Excerpt from a Mikuni Tuning manual states "The pilot circuit has two adjustable parts. The pilot air screw and pilot jet. The air screw can be located either near the back side of the carburetor or near the front of the carburetor. If the screw is located near the back, it regulates how much air enters the circuit. If the screw is turned in, it reduces the amount of air and richens the mixture. If it is turned out, it opens the passage more and allows more air into the circuit which results in a lean mixture. If the screw is located near the front, it regulated fuel. The mixture will be leaner if it is screwed in and richer if screwed out. If the air screw has to be turned more than 2 turns out for best idling, the next smaller size pilot jet will be needed. "

Also, after viewing the "correction factor" tables with an elevation of 2000' and average ambient 15-25*C when riding. The factory jetting should be pretty much bang on, only needing minor adjustments. I do have a new replacement UNI air filter on order so I'm not going to bother tuning it anymore until I have that mounted.