1968 Yamaha YG5T 80cc Trailmaster timing problem

I picked up the coolest old cycle a few weeks ago and have almost completed a near total rebuild. My 21 year old daughter will be riding it around town this summer.





Unfortunately, I've run into a an odd problem while attempting (all afternoon) to set the ignition timing. This bike has to be timed with a dial gauge which I've done before on my snowmobile. The instructions are to locate TDC, back off to 1.8mm BTDC, then gap the points and adjust the points plate so they're just opening at that point. My old dial gauge isn't set up to read millimeters, so I'm using the small metal ruler that Chacal sells to use for setting float heights. I set TDC, then pull the dial and measure down to the top of the piston and move the motor back so the piston is just under 2.0mm lower.

The trouble is that once the gap is set at that point, I do not have enough range/rotation in the breaker plate slots to turn it to a position where the points will close. My suspicion is that either...

A) The spec of 1.8mm BTDC in my original factory service manual is incorrect, (which would not be too surprising because there is a lot of inaccurate info in this book - including that the electrical system is 6V when it's actually 12V!);

OR

B) My method of measuring is flawed somehow. Maybe that 1.8mm does not indicated the vertical length of travel in the cylinder? (I think it does, though.)

OR

C) The points are too worn;

OR

D) The governor is not the original part from this bike and the cam lobe isn't right somehow, or the cam lobe is worn... Not likely.


Anyone who has a thought about this or a theory of their own is welcome to chime in. I tried to attached the two pages from the manual describing how to adjust the timing, but apparently I've reached my "quota." I can send it if anyone is interested.

Thanks!

 

I think the problem is you're trying to set the point gap at the same position (-1.8mm) that you're trying to set the timing.

Try setting your point gap while the points are up on the cam. Then set the timing plate so they close at -1.8mm.

 

That makes sense to me. I've been following the procedure in the manual precisely so I guess I'll add that to the list of errors. Thanks!

 

Actually you want to set the timing plate so they just OPEN at -1.8mm. Opening the points is what makes the coil fire.

But Carl is right. Set your gap when they're "wide open" up on the cam; then adjust the position of the plate so that they open at the correct spot.

Guess how much fun it would be with two (or three) sets of points?

 

Good to hear from you Fitz and thanks for jumping in.

Hey, in addition to this cycle I picked up several other cool bikes this spring:

1985 Virago XV700 (traded for service on a guy's XV1000)
1966 Honda CL77 305 Scrambler
1966 Wards Riverside 125

The Virago is complete but sans title. I'm collecting parts for the Wards but the motor is free. The Honda is seized up and missing a few original parts. Fun projects, though.

 

nice job on the bike, much cooler than a moped

 

My thoughts exactly! Thanks.

 

They really were better looking in the past.
Nice resto.

 

Sooo much cooler than a modern moped or scooter; plus the larger diameter wheels make it one heck of a lot more stable than your average Vespa.

I was noticing some of the cool little "touches" like the way the shift lever snakes around the case. I also think the abbreviated chain guard is nifty and the dual rear sprocket (I'm assuming "street" and "trail") is a unique feature. And that luggage rack is quite a solid bit of engineering if ever there was.

Although it's not clear in the pics, it has one of those funky combined speedo-tachs, doesn't it?

REALLY cool little bike. Good find.

Here's a thought: If Yamaha started selling that EXACT bike again today, with only "invisible" upgrades like electronic ignition, better brakes, etc., how well do you think they'd sell? I'm betting they wouldn't be able to keep them in stock.

 

I'll tell you what's nice about those tires (2.50 x 17 front, 3.00 x 17 rear): new Michelin M62s were $20 apiece plus $5 each for the tubes.

No tach on this bike, though.



Another unique thing, at least in my limited experience is that the handlebar control wiring harnesses run inside the handlebars. Probably weakens the bars a fair amount, but it certainly looks clean.

I'm still waiting for new brushes to arrive so, between that and the previously-mentioned timing issue, I haven't attempted to start the bike yet. I thought it was strictly a kick starter, but the manual says, "...(the YG5T) is equipped with a large-sized starter dynamo, which serves as a high-output D-C generator as well as a starter." Interesting.

The other thing that seems very interesting is that I have yet to find a dedicated users group/website/list serve for these bikes. Maybe they didn't sell too many of them. They made the YG1 earlier, then switched to the YG5. Some parts are not easy to find.

The exhaust, for example, is a one piece unit that slants forward. The header section on this bike is predictably rusted out where water could sit at the lowest point. The pipe is 1 1/4" which makes it tough to find anyone who can bend a custom piece, especially in as tight a radius as is required. I got a piece of stainless pipe and found a guy who builds racecars that could bend it, but the radius isn't quite right. I'll be taking it to a shop that can weld with stainless wire, but they're still going to have to salvage the original nut/flange and probably do a couple of mitered cuts to make it fit. The only complete exhaust I've seen come up on eBay in the last few weeks was used and $250.

 

Oh yeah, and one other thing - the bike did not come standard with turn signals, but they were apparently an option. The switch, wiring, and mounting holes are all there. This is a must for a bike I'm putting my daughter on, so I ordered a set. Coming from Taiwan, I think...

 

And it only has 1087 miles on it?

Just wow.

 

damn, that is one sharp lookin scoot scoot

i'll be keepin' my eyes out for your daughter :wink:

 

Thanks for all the props and congrats, guys. Unfortunately, I need to bring this back to my original reason for posting, which I will call PROBLEM #1. I followed MiCarl's advice and gapped the points while on top of the cam. However, when I set the motor to 1.8mm BTDC, the points will still not open through the whole range of the adjusting plate.

I thought, "Maybe it's supposed to be AFTER TDC," so I turned the motor the other way. Under that scenario, the points will almost close way on one end of the adjusting range, but stay open the whole time.

Starting at TDC and testing for continuity, the points actual just begin to open at 22mm BTDC. By the way, the motor turns CCW when it runs, so I'm turning it CW to move BTDC.

It seems to me that the spec of 1.8mm BTDC simply must not be correct. Maybe it was supposed to 18mm in the book???

On to Problem #2: I have no voltage at the ignition terminal on the generator with the points open or closed. Should I have voltage at the heavy positive wire (labeled "Red" in the diagram) coming from the voltage regulator anytime the switch is on? I don't.



The lights and horn work and the motor will turn over with the starter switch. I put in a new neutral switch and tested all wires after making repairs to the harness.

Thanks!

 

The whole mm BTDC thing seems odd. I've never seen anything that wasn't in degrees BTDC. There aren't degree or "F" marks on the flywheel are there?

I don't think I understand your electrical question. I don't understand the phrase "ignition terminal on the generator".

From the wiring diagram it appears all the red wires should be hot whether the ignition switch is on or not, assuming a battery is connected.

When the key is turned to the (I) position there should be power on the brown wires. With the key at the (II) position there should be power on the brown and blue wires.

The coil gets its power from the brown wire. Ground for the coil is provided through the points via the orange wire. With the key in the on position you should read 12V on the orange wire with the points open, 0V with the points closed.

If you're not reading 12V on the orange wire with the points open something is wrong. It'll be one of 3 things:

(1) No power to coil (check brown wire at coil for 12V)
(2) Orange wire shorted to ground. Disconnect orange wire from coil and make sure there is no continuity to ground.
(3) Coil is bad. Remove brown and orange wires from coil and measure resistance of coil winding. Not sure what the value should be, but infinity means it's bad.

 

There isn't really even a flywheel, as I understand it. The commutator is spinning inside the generator and the governor is turning out on the end of the shaft. That's about it. Here's a picture:

In the above photo, the terminals along the right side are (top-btm) M, A, F, I, E. The orange wire (disconnected) is coming from the coil and would be on the "I" terminal. I assume that stands for "ignition." It doesn't show up very well in the picture, but the top wire connected to the "M" terminal is actually light green, not red as indicated in the wiring diagram.

I do have 12v on the orange wire with the key in the (I) position. However, for setting timing the manual says to disconnect the orange lead, connect a test light to that terminal (I), and ground the light to chassis. I assumed that power was coming from the terminal, not from the coil. Is the procedure flawed?

 

The timing set procedure is fine, you're supposed to be using a self powered test light. What may be giving you trouble is the points don't power the coil, they ground it. The coil is powered by the battery. Disconnecting the orange wire keeps battery power from getting in the way on your continuity test of the point timing.

When I'm setting timing I use a multimeter that has an audible continuity indicator rather than a test light.

The (I) terminal should be a ground that is switched by the points.

Why do you have a match stuck in the advance mechanism? If you're forcing it out of its relaxed position your timing will be off.

 

Thanks for all of your help on this. Much appreciated!

The test lights I have are not powered and I don't have that click feature on my multimeter, although I can see where it would be handy.

Regarding the matchstick, I think I need to post the manual's timing procedure pages so you can see what I'm following. I tried to do this initially but apparently there is a limit of 5 files for our accounts?

 

8O

Looks like they're trying to have you set the timing to the ignition advance point - that'd be the reason for using a match to hold the "governor" open.

I can almost assure you that the 1.8mm BTDC won't work - points should be long open by then with the timing advanced.

You're going to need a buzz box or powered test light.

BTW found this: Forum discussion. Nothing about advancing the timing. If I had to guess - the points should open at 1.8mm BTDC WITHOUT turning the "governor" open.

 

OK, so I was able to reach the point at which the points are just opening at 1.8mm BTDC without the governor advanced. I'm way down at the very end of one end of the adjusting plate range. I'll try to start it up shortly and see if/how it runs.

Got to run to the store now, though. Discovered my rear axle nut is stripped. Not good.

 

Well, I got it running so we must be in the ballpark with the 1.8mm BTDC non-advanced timing setting. Thanks!

I've never had a little single cylinder two stroke like this, so I'm learning as I go. I'm a little puzzled by the carb adjustment procedure, (pg.3 of this file).

If I back off the air screw and throttle stop screw until "the engine speed reaches its maximum," the thing will just be racing beyond imagination. There's also a gapping hole in the exhaust pipe so it's REALLY loud and obnoxious.

Also, when I put it in gear and release the clutch, I can't keep it running no matter how much throttle I give it. It just dies.

Right now I just need to get it running well enough to get it over to the shop where they will fix the exhaust for me.

 

Change the word "maximum" in step 3 to "minimum" and it makes sense:

Or my version:

1) Lightly seat air screw
2) Adjust idle stop to the lowest speed where the engine will run.
3) Adjust air screw until maximum idle speed attained.

Repeat steps 2 and 3 several times. This lets you zero in on the mixture that will let the bike idle well with the throttle slide in the most closed position.

It's really the same procedure we do on the XJs, except we're doing 4 carburetors and we know to start the mixture screws (fuel in the XJ case) at about 2 1/2 turns.

 

That makes sense to me, but did you mean to say "minimum" in your step 3? And what would estimate is a good idle speed for this bike?

Also, any idea about about why it's dying when I release the clutch?

 

One other question: Considering the fact that this procedure is done wih the intake side of the carb wide open and the air filter essentially out if play, it appears we are not too concerned about air infiltration like we would be working on the XJ or similar carbs. Why Is that?

 

I meant maximum in my step 3.

Think about it - you want to adjust the mixture to where the engine is happiest. That will be maximum RPM.

Then you slow the engine down with the idle stop screw and adjust again.

Proper idle speed is probably somewhere between 1100 and 1700 RPM. Can't help beyond that.

 

Yeah, I think I was a little toasted when I sent that message last night. I was thinking about what we might call "Step #4" where you back off the idle screw to slow it down.

Just went at it again and the bike is now running and idling like a champ. Thanks for all for your help. The clutch problem persists, though, so I think I'll start a separate thread for that.

 

Good to hear; except I'm worried that your timing is running way advanced, and here's why:

In the pic you showed us of you doing the "matchstick trick" it's supposed to be blocking the "governor" (auto advance unit) at full advance. It's not; the springs aren't stretched. When the unit "advances" it should stretch the little springs.

I re-read the procedure you posted the link to, they definitely want you to set the timing with the advance unit blocked in full advance.

If you set it with the auto advance unit "relaxed" then when it does advance, it's advancing way too far.

A two-stroke will usually idle fine with the timing way advanced, but it won't have any power. This may be at the heart of your "clutch" problem.

 

I agree with you they are saying the "governor" should be fully advanced. Here is my issue:

If it's firing at 1.8mm BTDC with the timing advanced it's going to be firing after TDC at idle. Doesn't seem right to me (I'm assuming it has more than a 4mm stroke).

Late timing will definitely lack power.

 

Got the NOS points late this afternoon. I just finished installing them and going through the timing procedure again. Having set the gap at .33mm while on the top of the cam, positioning the motor at 1.8mm BTDC and fully opening the advance mechanism, the points will still not close within the entire adjusting range of the plate.

Throw me a bone or any hair-brained theory you've got, O wise ones.

 

Lets do this:

Measure the stroke (full travel of piston) on it. I'll look up a similar engine and convert the degrees BTDC to mm BTDC for your engine. Then we can at least get an idea of that 1.8mm number is even in the right ball park.

I'm leaving tomorrow after work for the weekend so you probably won't get an answer until next week.

 

Bore is 47mm and the stroke is 42mm. Thanks.

 

I looked in the service info for the GT80A. It is also 47X42.

The book is quite specific that the timing is set with the advance weights fully spread. The distance is 1.8mm.

Doing the math that 1.8mm comes out to 16.83 degrees. Off hand, that sounds like advanced timing, not idle. So I think I gave you bum advice before.

I think Fitz is probably correct - the timing is set so far advanced it's not generating any power.

The GT80 book says to rotate the crankshaft until the points are open their widest and check the gap there. I'd double check that. Then you need to look at the timing plate and see if something is mounted wrong preventing you from rotating it to where you need to be.

 

Thanks for doing that research, MiCarl.

I did gap the points when they were wide open/top of the cam.

There really isn't anything that can hang up the breaker plate. I can rotate it fully from one end to the other. The plate to which it mounts is not adjustable in any way. I even loosened the two screws that secure the generator to the engine to see if there was a little wiggle room there. There wasn't.

So, to try and be deliberate about analyzing this, here are a few thoughts/questions:

1) Please confirm again my procedure. The motor turns counterclockwise, so to find a point BTDC, I'm turning the motor clockwise.

2) Right now, using the manual's procedure of gapping at 0.30-0.35mm (0.012-0.015"), at 1.8mm BTDC I can only get the points to close to 0.20mm. I'm wondering if there's any chance that inch gap numbers should have been metric, (e.g., 0.12-0.15mm). That would about get them closed. What's the gap on GT80?

3) I'm coming back again to thinking there might be something hinky with the advance mechanism. I don't think there's really any way the cam could wear down with only that plastic (or whatever material) points tab rubbing against it. Maybe it's not the right governor? Stranger things have happened, I guess.

 

I think I figured it out.

I went back and reviewed Yamaha's instructions that you posted the link to.

THEY do not have you setting the points gap when the breaker arm is on the cam at "full open" position. (This would be where Carl and I may have given you bad advice.)

They specifically have you (and in order

Position the motor using the dial indicator;

Then SET THE GAP with the motor in THAT position;

Then turn the "Governor" to open the springs (full advance) and block it;

Then adjust the timing plate so that the points are just opening at the 1.8mm BTDC point.

I'm betting that what we all missed was having you set the points gap when they're fully open; the book CLEARLY has you position the motor and then check the gap with the crank in that position.

How about following the book to the letter and see what happens?

**what brought this to mind is that my Norton has a "datum point" on the breaker cam where you position the breaker arm to set the gap; and it's NOT on the "fully open" profile of the cam.**

 

Thanks, Fitz. Although, I was pretty sure that I had already tried this with the governor fully open, and I was also pretty sure it would just make it worse, I just went back out to the garage and tried it, step by step, exactly as written. Doing so just made the point gap wider (and obviously still not closing within the range of of the adjusting plate.

I mean, think about it: Gapping the points in any position other than on top of the cam will necessarily have them opening wider, right?

I was sure wishing you had nailed it, though. Thanks for giving it another shot.

There is an NOS advance governor that I can buy for $60 delivered. I'm feeling like I might need to give that a try, at this point.

 

REMEMBER: It's not the CLOSING of the points that fires the ignition, the coil fires when the points open.

That's why they're called "breaker points." When closed, they ground out the system; when they open, the coil fires.

I'm still stumped. If I had it in my hands, I'd have had it figured out.

 

Right, the points opening is when they fire. I just keep referring to them closing because they're open through the whole adjusting range and there is not place to set them where they're just opening.

And if you don't have any other plans, you might as well ride over here for the weekend and help me get this thing finished up. Just get on the Seca and head west, take a right onto I-29, and call me after about 15 hours. You should be close by then.

 

Sorry I didn't get your PM till this morning. I left you my number to call tonight.....

jeff

 

OK, the new advance governor arrived and, although the numbers stamped on top of the two of them match, there are a couple of things about it that are slightly different from the one on the bike. I hate to jinx it, but I'm hopeful this might make enough of a difference to get it timed properly.

Wish me luck! I'll report back in a couple of hours.

 

OK, first the good news:

With the new governor, I was able to get it timed precisely according to the manual's instructions. I lied about the stamped numbers on top of the two units. They both say G-175, but the one on the bike also had an LY code while the one I bought had HZ.

Here's the one that was on the bike...



...and here's the NOS unit I received today...



As you can see, the pin that limits the movement of the mechanism is much larger on the new unit. Also, it appears to me to be in a slightly different position on the shaft - maybe just a degree or so. Lastly, the moving arms of the governor open wider on the old one.

Anyway, started up easily and I retuned it. Idled and revved well.

Now the bad news:

It made almost no difference in how the bike ran. I was able to just barely get it to run by having the clutch half open and very slowly coaxing it faster and faster. And, Jeff, your suggestion about testing it with the choke half on didn't seem to have any effect.

The strange thing is that I seemed to have better luck starting out in 2nd gear. Got it going pretty good so I decided to up-shift, at which point the rear wheel locked up, the motor quit, and I skidded to a halt.

Then, while futzing around with the upper gears, suddenly THE NEUTRAL LIGHT COMES ON FOR THE FIRST TIME! I had replaced that switch and checked wiring and the bulb, but I couldn't get that dang light to come on in neutral. This leads me to a sobering question: Is it possible that a PO had attempted to repair the transmission and reassembled it incorrectly? I haven't worked on a cycle tranny yet, but can you even put the gears in the wrong position? If 5th gear was where 1st gear is supposed to be, it would kind of act the same way, wouldn't it - no power?

Eventually, while trying to ride it over to the welding shop to get the exhaust fixed, it quit and wouldn't start again. I'm guessing the plug is really fouled. I pushed it the rest of the way. A proud moment...

I think I mentioned early in the thread that there is a gaping hole in the header pipe. Maybe this is having some effect on how it runs?

 

It very well could. Especially with a motor that small.

 

Then I guess the next step will be to see how it runs when I pick it up tomorrow with the exhaust intact.

 

Picked up the bike this afternoon and started it up. The hole in the exhaust was not producing the lack of power, unfortunately.

However, the transmission definitely is operating differently from every other bike I've ever owned or ridden. Maybe this was the way it was designed, but it sure seems strange. Here's how it's configured:

At the very top, meaning shifter clicked upwards as far as it will go, is neutral with the indicator illuminated.

Then I can move it down half a click (although it doesn't actually click) and the light goes out, but it's still in neutral.

Next click down is low gear, then down to 2nd, then down to 3rd (I think).

Then it drops into neutral again but the light doesn't come on.

Then at the very bottom is another gear, although I haven't shifted it down that far while riding it...


...because after a minute or so of riding, the thing loses power and quits! It's like it isn't getting any fuel, which is possible, I suppose but I can start it up again fairly soon and it will run and idle nicely.

I will say that the throttle seems just a little sluggish. Never ridden an 80cc before, though, but it does make me wonder if the timing is still a little off.

Like I said yesterday, I'm not even sure if a tranny can be put together incorrectly and still operate. This is new for me. FOr what it's worth, it will kickstart. Here are the two pages from the service manual on the transmission.

 

I've spent awhile searching on the web and it appears that this bike came with a 4-down shift pattern, which is pretty much what I think I have. Not sure what to think about the little gaps where the bike is out of gear, though.

 

Patience.

I think you may have a "Roundy-Round" gearbox there. (What we called them when I was 16 and that bike was new.) That "extra" gear beyond the neutral beyond fourth may be first again. Be careful. Back in the early days of motorcycles, "down for up" was almost as common as "up for up." My Norton shifts down-for-up, and on the right-hand side no less! And some companies had unusual ideas about gearboxes.

Those little "in-betweens" will probably go away once some oil gets worked into it; or go back and inspect the bits in that shift linkage, but it's probably just more primitive than you'd expect. Yamaha hadn't been doing motorcycles for very long at all in '68.

Dude, I wish one or the other of us were rich enough to afford a plane ticket for me, or the bike. I still think the timing is off.

What we need to do is figure out the DEGREE spec for timing it, and then you could use a degree wheel to fab a pointer and use a timing light. Sooo much easier.

And it'll run like a top.

 

So, if my timing is off by enough, would that make it quit even though it idles well? I just went out to try and ride it again, and as I was trying to accelerate in 3rd gear it lost power and died. Fuel isn't getting burned and it's fouling the plug, is that the deal?

MiCarl estimated earlier in the thread that 1.8mm with my 47mm bore x 42mm stroke is 16.83°. What is involved in fabricating a pointer using a degree wheel? I'm game for anything at this point and I have a timing light, of course.

 

if this has been mentioned before then sorry just forget it, im setting my timing on the rd lc with a dial gauge, i dont have points i know but you may be able to prove were your piston is actually sitting, just a thought.

 

Yes, I've been timing it with a dial gauge which is the factory procedure as described in the service manual. Fitz is suggesting an alternate procedure.

Thanks.

 

I've read up on degree wheels, downloaded a few images, and am in the process of making one. Here's the process I'm planning to follow:

1) Find TDC using my dial gauge;

2) Make a mark on the generator housing;

3) Remove advance governor bolt and insert it through the hole in center of degree wheel;

4) Reinstall bolt, align 0° point on wheel with mark on housing, and tighten;

5) Hook up timing light, start motor, and check timing at idle and while revving.

If you see anything goofy with that process, let me know. Since there's no tach on this bike, I'm not sure how exact I can be. I'll report back later this morning with my results (and probably a couple of questions, as usual).

 

Using degree wheel and light to check timing, it appears that I am running ~33* before (to the right of, as indicated on the wheel) TDC. Pretty close both at low idle and revved up a ways. This is without the advance mechanism blocked open. I'm not positive whether or not the governor is actually able to move freely with the degree wheel installed.

After lunch I'm going to adjust the timing back to about 17° (MiCarl's estimated conversion of 1.8mm) and see how it runs.

Any input welcome...