GT750 won't idle on left cylinder.

[m in sc]

...

when wet, take out and see if plug tip can be lit with a lighter. (away from bike of course) if it burns, fuel, if not, coolant.  might be ignition. 

[sav0r]

Teazer is more of an authority on this than me, but the heads on these GT750's are not exactly amazing. A coolant leak is not out of the question.

[Striker1423]

Ha! Good point Mark, I already lit the bell mouth of the left carb on fire once by accident.

I'll try the few things today. Pending spark plug delivery, I need to get a coolant pressure tester that works on these bikes. Also, a pressure tester for the motor itself.

[sav0r]

It could be something as simple as a stuck ring and low compression. We occasionally see this on our race motor if the rings get a bit too carboned up (we run a lot of oil because we don't like rebuilding engines). It is curious you aren't seeing much liquid when turning it over though. If it was a coolant leak you would probably see it in the coolant level and likely get a nice blast out of the cylinder pretty quickly. I suppose when at temp everything changes a bit.

Does the ignition run three separate sensors or does it use one and fire all three with wasted spark? We built our own ignition so I am not familiar with the system you are using.

[Striker1423]

The Accent ignition uses three separate triggers, and is timed off the center cylinder alone. It literally took me like 30 minutes to install.

See here:
https://www.oldjapanesebikes.com/blog/2012/07/30/elz2coil-accent-electronic-ignition-system/

And this video from Peter Ormrod. This chap's an inspiration to me haha.
https://www.youtube.com/watch?v=V9RH2kj8qho

[teazer]

It's unusual for an accent ignition to fail but it has happened on a couple. But before you send it back to Uwe to test it, double check the "points" lead to the coils and the 6 pin coil connector.  It's possible one of the pins is loose or pushed out or corroded.

And check voltage at the coils.  I usually fit a relay to feed the coils and that can make a difference. 

I have not run an Accent ignition on the test rig but have run DYNA and Ignitech on our test rig up to 10,000 rpm.  It's set up for Yamaha twins and I use it to check timing on Motoplat and Hitachi CDI systems but have an adapter that allows it to test GT750 systems as well.

[busa1300]

I have a complete 72 GT750 engine if your looking for good cases.
Even have the radiator...

[Striker1423]

So the spark plugs definitely helped things. It pops and crack's more out of the left cylinder. I'll try pulling just the left carb and cleaning it first. Teazer, the ignition itself works fine. The plugs spark every revolution as it should... However, I will verify the connections as you suggested. I also ordered up a set of coils, wires, and new resistor caps. Those will trickle in over the next week, as well ordered a brand new water pump (new manufactured shaft and all new parts) from a Kettle Club member in anticipation of the eventual rebuild. Might as well start prepping for it now.

EDIT:

Also, don't use an electric ratchet to tighten the loose electrical panel stud nut. Cause it breaks easily. Heh.

[sav0r]

Speaking of electric ratchets, which one do you have? I was thinking about buying one, probably one as a gift for my father as well.

[Striker1423]

I bought the Hazard Fraught (Harbor Freight) Earthquake XT. It's just OK. Their impact is much better. Though mines the first gen Taiwan made silver Earthquake XT not the new black one. Most folks recommend the Milwaukee fuel series. Look up the Torque Test channel on Youtube, or AvE for more teardown videos.

[85RZwade]

I use a 3/8" Milwaukee every day at work, Chris, and it's a fine tool. Home Depot has pretty good sale prices on them fairly often.

[Striker1423]

Took the top end apart. Someone's been into the motor. But, I'm guessing they did a base and head gasket swap. Everything just came apart. No need for puller blocks, etc. Just a bit of wood and light hammer taps. The cooling system has what I think is sand collected in a few spots in the head. Maybe they had it blasted and didn't get it all out of the motor?

There is no markings that say what size the pistons are, but from the looks of the underside, they are indeed Suzuki pistons. Measurements put them just under 70mm, so the stock bore. Bores are fairly clean with only the right hole showing slight scoring (just one line I can barely catch my nail on). A lot of blowby on the top and bottom ring end gaps. Head is in good shape. No nicks or pot marks except on the right hole. With only one small gouge I can see. Pistons had a few love taps with the left hole (trouble side) having a ding on the edge of the piston, but no scratches in the bore...

Crank rods are Suzuki original. Feel OK. Again the right hole has some minor pitting in the little end rod. Big end bearings feel just fine. The crank itself has a lot of surface rust. Wipes right off with a rag, but it's there. Piston pin was worn significantly on the right hole. But the bike sat and ran with no real loud engine noises.

If I wasn't too scared of wasting a top end, I'm tempted to just hone, fit new pistons and rings and run it. Flushing the crank out of course. Top gasket had a lot of shmoo come off and get all over everything. 

[sav0r]

You gotta center those plugs and get a proper combustion chamber. It's all apart...

I know a few guys...

[teazer]

As they said at the end of Shawshank redemption: You have come this far.  Would you go a little further. Or words to that effect.

Top end is off.  The PO used gasket goo on the head gasket?  IS that what I read?  That's not only not necessary, it actually makes it harder to seal. 

Surface rust on the crank is OK but it suggests that perhaps the shafts might be rusty and may have damaged the seals. With the head off, you might as well go the rest of the way and send the crank to Bill Bune, or your favorite rebuilder. You might get away with new rings and if not, pistons are available from Mitaka, or Cruizin or even Wiseco. 

A central plug squish head is a really good upgrade too.  Raise compression and decrease the chance of detonation all in one neat package.  Mr Livengood knows people who can design and machine a head after a short trip to the welder. And at a lower price and better idea than a head from RK-Tek with inserts.

BTW do not use stock or most aftermarket head gaskets.  Get a head gasket from Cometic with say a 71mm finished bore and .043 thickness.  OEM gaskets are about 76mm bore to allow for the fact that casting cores were not always in the same place, so bore to head spacing tends to be shall we say, imprecise.  https://pinkpossum.com/GT750/GT750head.htm  has more details.

[sav0r]

The service at Bill Bune is perfect. Awesome work.