Bought my first 2 stroke - started for a bit & now doesnt :(

[bpapachr]

I would start by cleaning the carbs out and setting float levels.

Then clean out the petcock and fuel lines

Then fit new plugs and set points gap and ignition timing

Then test the kill switch to see if it stops sparks ie make sure it works. The PO may have messed with the wiring and jumped that switch.

Which crankshaft bolt did you use to turn it over - left side or right side? One is through the alternator and the other is on the ignition gear which is made of plastic and breaks if you turn the motor with it.

I can find all this step by step stuff on the forum? (Petcock, fuel lines, Points gap and ignition timing)

[bpapachr]

Craig,

That's good to know. I thought it was both small triples. Learn something every day.

And with clicking on the left side, it's the left side cover I'd remove first and then the head and then the left barrel - going only as far as I need to. If it's blown left side crank seals and a shot rod, all bets are off.

Just beautifully put! ha. If I was to take off the side cover, then the head is will come off for all three cylinders. Does the motor have to be removed from the bike first? And how would I take apart the left barrel if I have to go that far?

[tz375]

The answers are simple. Head comes off with the motor still in the frame.

To remove the cylinder (if it's necessary) remove the exhaust system and then the carbs and undo the 4 nuts holding the barrel to teh crankcases.

Info on cleaning out stuff and setting things is basically a combination of common sense and a Factory Service Manual (or Clymer/Chilton/Haynes) manual.

There's a copy of a shop manual on Ian (oldjapanesebikes) site.

Another great resource are the many on line parts lists with exploded diagrams. They can be misleading at times but generally are a great way to see the many parts and how they fit together.

[bpapachr]

The parts diagram helps a lot. Thanks! Sorry for my ignorance, just want to try and get it right and not over spend on parts I don't need...I have a good feeling this bike's gonna become my summer money pit...

Whats a good site to buy parts other than ebay?

[Craig380]

Craig,

That's good to know. I thought it was both small triples. Learn something every day.

I can see why Suzi did it on the 380 - to stop any issues with the crank being slightly out of true causing the points cam to wobble and affecting the timing - but if they thought it was such a big deal, why not do it on the bigger triples too?

I mean, the 550 and 750 cranks are really hefty pieces of metal, but the 380 crank is hardly a delicate sapling either ...

[yeadon_m]

On the 380, I wonder if it had more to do with design and minimising already ride motor width? I haven't looked, but maybe the plastic gear reduces width a few cms?
Other than that, no idea either!
Yes, the 380 plastic points cam gear can break, even if you never crank on the points cam nut. Mine went after 43,000, as I was riding it
I think thats one of very few failures that in no way could be fixed by the roadside and which can stop a GT triple dead. I thought hard about it and cannot think of such a one thing breaks you're stopped fault option on the 550 or 750. There's a reassuring thought if you go touring on a 380.
Cheers,
Mike

[tz375]

Craig,

On the 750 the points cam rides on its own short shaft in a couple of bearings and is driven by a peg on the starter gear bolted to the crank. That allows for any slight misalignment but adds 6 inches to an already wide engine.

[jabcb]

Perhaps the GT380 used the plastic gear because otherwise the points plate would have been too close to the clutch.

The GT750 has a lot of stuff on the left end of the crank.
Could have been narrower if they used the same starter setup as the GT550 but then they probably would have had the same starter clutch problem.

Given the small engineering teams & budgets they probably had back then, I think they did a quite good job at designing these motors.

[bpapachr]

First of, thanks again to everyone replying and helping me out with this. An update from taking off the head and barrel from that far left piston didn't really show me much. I heard the tinking noise coming from the crank, underneath the piston. As the the rings, most of it looked in pretty good shape. I will post some pictures tomorrow (I finally have a day off from work!) when I take more of it apart and hope you all can give me a better idea of what kind of shape the bike is in. I think it may be time to replace the piston rings on this bad boy as the gap seemed pretty large. I have to go buy feeler gauges now since the bike needs one for just about everything. ha. I wonder if that noise is coming from the starter motor (since there is a switch but no wires running anywhere)

Anyone have suggestions on the best way to clean the pistons? Havnt really ventured this far into the realm of mechanics so I apologize for the dumb questions.

If I do take apart the crank case halves is there anything I need to know before I crack them apart? And/Or when I'm putting it back together?

As for the vacuum leak, I started the bike and sprayed carb cleaner on the intake tubes, parts of the carb, etc. and I didn't really get much of a spike in RPM's. The intake boots are pretty beat up though. The interesting part is the boot on the far right cylinder (running rich) has a huge tear along the part where they meet and the clamp goes over. I'm gonna trying finding a ghetto fab boot for the carbs because for timing purposes I think it will be better to seal this off and run the bike. I also pulled apart the carbs and re-sat the floats and made sure everything was properly set up. The one awesome part to my night was this...

Snapped right off but the good thing is none of them worked properly anyway so I opted to order replacements and do this part of it the right way. Luckily there was a small chunk that I was able to use a flat head screw driver on and push around and remove it pretty easily.

[tz375]

With the head off, turn the motor over and stop after the left pistons just starts to fall. Then press down on that piston with a finger. If it clucks, it's play on the small or big ends. Repeat on each and see if that's where the clunk is coming from.

If not, then that's not the issue.

Any pictures of the piston crowns and the combustion chambers?

[bpapachr]

I didn't think to push on the pistons. Great call. I will do that tomorrow before ripping into everything. My phone died and I was to tired to get some tonight but I'll have pictures of everything for tomorrow.

[bpapachr]

Also, my bike has a speedo on it but it's working more like a tach (the bike idles at 20MPH)...the cable that goes into the condeser/points box is the line for the tach or the speedo? If its the tach, how does the speedo get hook up properly?

[yeadon_m]

Both instruments are cable driven. Someone has connected the tach drive cable from the left case to the speedo! have never heard of a bike idling at 20mph, love it
Speedo cable goes to left side of front wheel where there is a small gearbox on the axle.
Wires into the points cover area are....for the points, three wires in a small loom.
Mike

[bpapachr]

Anyone have insight on these plugs? The shorter ones were on the bike currently and I think this may have been the problem. The ones from the Clymer seem long for the barrel


Did this guy out the wrong plugs on the bike?

If so what's the correct ngk part number for the plugs?

[tz375]

AFAIK they used B7Es - 3/4" reach, 14mm plugs on all years, but we need a 550 expert to confirm that. Does the field Guide give any insight into that?