Suzuki GT380 Top End Rebuild Project

Easter Bunny said:
re the oil tank, shouldnt there be a painted cover over it like the other side?
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Yes sir! It exists but the 1972 version mounts differently than any other year of GT380 so mine is pretty difficult to find in good shape. No matter the avenue I go, I have initial purchase price + painting costs so I was thinking a nice looking oil tank made the most sense. Something aluminum and tig welded up nice.

Who knows, I need to get it on the road before anything so we'll see how I feel later down the road.
 
To say today's first ride was a success would be such an understatement. This thing is so freaking cool and fun to ride! I didn't get on it too hard (new pistons and all) but I probably put somewhere around 10 miles on it before it started raining in my town. It's a very casual riding experience since it has a pretty upright seating position, it feels excellent in corners with the wide handlebars, and the clutch is so light and easy. I also got a lot of head nods while cruising around the neighborhoods near my house. Still have a little leak coming from one of the carbs but that gasket is on its way. That won't stop me from enjoying this thing though for a bit while I wait for it to come in. I'd also like to see if I can soften the shocks/springs in the rear because it's a little stiff for my skinny frame. All in all, it was a great day and I definitely love this thing.

Here are some photos out in the wild:
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Here's an unnecessarily long video of me riding around down:
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As it's been sitting in the shed for the last few days, I noticed that the other 2 carburetors were leaking fuel. Replaced those gaskets last night and it seems it's all sealed up tight now! I also had a cool idea for a little toolkit to carry on board. If you buy a motorcycle specific toolkit, it's usually like $50-$60 for a fancy little screwdriver and that just seems like too much. I am thinking I can make it look classsy and still be cheap by getting something like this:

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And fastening it to my frame near the oil reservoir around here:

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It would fit right into that gap between the frame and tank and should easily be able to hold the 2-3 wrenches and screwdrivers needed to fix/adjust just about anything on the bike.

I also have the passenger pegs on their way from eBay so those large brackets on the side don't look silly anymore and I will be fabricating up a small steel/aluminum bracket to tie the exhaust hangar tab to the passenger peg mount as well. Once that's complete I'll be good for a while so far as additions to the bike go.
 
Since I used a "good enough" method in the past for the spark timing, tonight I thought I might as well get timing into perfect specification. Printed a timing degree wheel out and taped it to a piece of mechanic grade cardboard.

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From there, I found tdc on each cylinder and dialed it back 24* as per the manual's spec. Once at the correct position, I set the point so it juuust opened at that spot. I didn't get to start it yet since it was about 9:30pm but I feel like the timing was a little uneven and overly retarded before. Might pick up some power from this little job! I'll report back my findings.

Other than that, I did go on a 35mi round trip the other day with a buddy and the bike worked flawlessly.
 
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I didn't ride a ton last weekend even though it was nice outside, but she's definitely got a little more get up and go! It seems to idle smoothly off of choke a little more quickly as well which makes me feel the advanced timing helped the engine run a little stronger.

Here's a nice warm-up idle clip post timing adjustment
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And just like that, I got more things to replace on the bike! Had it idling last night and it was running pretty lazily and realized it was only running on the R&C cylinders reliably. Checked the points and sure enough, we had one that seems to be a little unhappy. I knew I'd need to replace them soon anyway, I just wanted to have the bike running before replacing things that didn't NEED to be done before kicking it over.

Take a look and I bet you'll be able to identify the bad point -
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That top point also doesn't make contact with the center shaft for the full rotation of the motor (when the circuit is closed, the coil is charging) so I'm willing to bet the L cylinder was never really getting a strong spark anyway.

Ordered a NOS set off eBay for around $27 shipped and they'll be here Saturday. Luckily since the timing is already set perfectly, I just need to set the points gap to the spec .014" and the timing will still be right in place. Also, when I have all the old points off, I can polish that points shaft up a bit since it's worn from age. Should be back up and running better than ever in no time!
 
Easter Bunny said:
Can you get an electronic ignition for this bike?
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They exist but most are shipped out of somewhere in Europe and cost a decent amount of money. I don't see much an advantage to that though as after this the points system should be solid for a good amount of time to come so long as every year or so I ensure the gaps are still set properly. It's not difficult to adjust the points gap, ignition timing, etc. so it wouldn't give me many benefits in my opinion.

I might get a bit more power out of it and possibly some reliability but at the end of the day, this bike will be seeing 25-50mph for most of its life with me so I'm not sure a few horsepower would be worth the >$150 investment.
 
We made the change on a buddies boat and honestly it was a world of difference but that was a 305 Chevy so the parts were like $20

If you are sticking with points I highly recommend finding a dwell meter to set them as you will get much better time between service anyone that complains about points only experienced setting them by gap
 
Easter Bunny said:
We made the change on a buddies boat and honestly it was a world of difference but that was a 305 Chevy so the parts were like $20

If you are sticking with points I highly recommend finding a dwell meter to set them as you will get much better time between service anyone that complains about points only experienced setting them by gap
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My birthday is coming up in mid-March and I realize I asked for a multimeter that measures duty cycle. Seems like you can utilize that to measure dwell either directly or through an equation done separately. I'll probably get them into their 0.012" - 0.017" spec upon delivery and then if I get the multimeter I can give that a go.
 
thats what i would do, no need to not ride just because the points could be adjusted better but once you have the tools i would take another stab at it.
 
Easter Bunny said:
Can you get an electronic ignition for this bike?
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Well I may have just invested in an electronic ignition setup... Upon further digging, I have a Kokusan ignition setup, rather than the check Denso. I guess the bikes came with both? And I am just one of the unlucky ones to have the ignition that costs like 8x more than the other. Pricing out points came to around $100 shipped, and then if the condensers ever went back they would've been even more.

Bit the bullet and picked up an electronic ignition setup made by a company overseas called NewTronic. It has great reviews and everyone who's gone electronic has said the bike is more reliable and powerful than ever. I kinda wanted to stay with points for the oldschool cool factor but I think a reliable bike I can ride is definitely more valuable than a bike in the shed I can't ride.

ETA of ignition: March 10th - 20th so I will have updates within the month of how she's running. In the meanwhile I might have to ride my CBR as my right cylinder doesn't seem to be sparking at the moment :(

Ignition setup:
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Ignition was delivered yesterday and as of today we're riding again! Interestingly enough, this ignition works via light sensors and a beam tripper. When the beam is blocked, the coils are charging, when the beam opens, the spark fires. Installation was straight forward - remove points plate & points cam, install digital ignition plate and the beam tripper. Wire the new points plate to the ignition box as per the directions, plug the plate into the coils and the ground on the battery and then re-time the engine.

All in (with some annoyances with the little wires in the plug) it took ~3-4hrs. Once the engine was timed right, the bike literally started in 1 kick.

I'm big-time excited to have the bike running again and happy that the new ignition will apparently require zero maintenance.

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After first kick on a still cold motor:
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This all makes me want to work on my bike so bad. But 40° highs and a miata to fix make me not.
 
Not much to update this thread with as the bike's pretty reliable and still running great. There's a small mess of wires inside of the headlight bucket I might clean up someday but it seems to be mostly a factory created mess, so fixing it up will just be a perfectionist kinda thing. Here's where she's chilling for this quarantine -

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I was thinking of creating a little level gauge for my oil tank while I have nothing else to do. I'm imagining having a bulkhead at the top and bottom of the tank with a clear plastic tube between the two to show the level from the outside of the tank. Finding small fittings like the below is a little tricky though.
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