GT380M wont rev WOT - excessive smoke & oil consumption

[Salman_z8]

Hi guys

Been reading for a while, never posted or commented, you guys are doing a great job. The info available on this forum is invaluable.

I am in alberta canada, have a few vintage bikes, h1, gt750a, gt380m, rd400 and rest 4 strokes. They are either restored or original, i like them the way factory made them. This year my plan is to get minor issues sorted out with the 2 strokes, that i just never had the time to do before, and ride them instead of my indian.

Here goes;
75 Gt380 - original 9000 miles and it shows.
Original pipes, i removed the insulation from baffles.
Dont know much about the history, other than it sat for a long time, and cylinder chambers were full of 2 stroke oil, good i guess.
Carbs were varnished, nothing i hadnt seen before.
Lower rubber boots were melted. But after a carb clean, ultrasonically and manually, and they are clean now, it fired up second kick.
Idled great.
Airfilters had perished as well.

Fast forward, i got the new rubber bellows, replaced em.
New air filters. Replaced all three floats with spare original mikuni ones off a gt750, originals were a little crushed.
Needle clip is at 2.
Floats are at 25.7mm with carbs tilted and just touching.

I put it all back together, fired second kick. Idle was wonky, but the sync was a touch off, adjusted and it was fine.
Now for the issues;
1. Wont go wide open. Has strong midrange, well rev to 6 and then break up.
2. Lots of smoke, and it is 2t smoke, i am running klotz.
Oil consumption is just insane. Arm seems the right way, i can feel the notch if turning manually.
3. Air screw is at 1 out, otherwise it wont idle for long.
Right off idle with minimal throttle, is a little difficult, once warm it likes some revs for take off. Around 2K. But its a little inconsistent issue, comes and goes.
4. Oil drips from pipes at idle on center stand, it has reduced but still drips.
5. Its not from the pipes because my oil tank is going down fast, half a quart in under 80 miles, thats crazy.

Any thoughts ?
Timing is perfect, doesnt seem like a seals issue.
Carb boots have been softened. No leaks.
Plugs are br7es, i have ordered b8es.

I havnt clear tubed the carbs, honestly, because in my arrogance after working on the carbs i almost never, because i never had to.
But i doubt that float height would make a repeat issue even after floats were replaced and reset.

Before i take the carbs off again and start plug chops, is there anything stupid that i am missing ?

Thank you

[Salman_z8]

Anyone ?

[jabcb]

Ignition? Could be rev limited because the coils aren’t getting enough dwell time because of the state of the ignition system.

Start with a fully charged ignition system.
Then check for voltage drop from battery to coil +. Drop across the coil primary. And from the coil - to the points.
Check coil primary & secondary resistance.
Check condition of the points.

Voltage drop from battery to coil + might be excessive -- a fairly common problem on vintage bikes.
Coils and/or plug caps might need replacing. Or points and/or condensers.

[Alan H]

Fast forward, i got the new rubber bellows, replaced em. Good move.
New air filters. Replaced all three floats with spare original mikuni ones off a gt750, originals were a little crushed. 380 floats are different to 750 ones, use correct parts.
Needle clip is at 2. Normally 3
Floats are at 25.7mm with carbs tilted and just touching. See picture from service book, below. I had to doctor this as it's on 2 pages and early bike, but better than nothing.

I put it all back together, fired second kick. Idle was wonky, but the sync was a touch off, adjusted and it was fine.
Now for the issues;
1. Wont go wide open. Has strong midrange, well rev to 6 and then break up. See above comments
2. Lots of smoke, and it is 2t smoke, i am running klotz. WTF is klotz? Use semi synthetic 2 stroke oil.
Oil consumption is just insane. Arm seems the right way, i can feel the notch if turning manually. How much does it actually use? Insane is not a recognised measurement.
3. Air screw is at 1 out, otherwise it wont idle for long. Should be 1 1/4 turns out.
Right off idle with minimal throttle, is a little difficult, once warm it likes some revs for take off. Around 2K. But its a little inconsistent issue, comes and goes.
4. Oil drips from pipes at idle on center stand, it has reduced but still drips. It needs a 20 mile run to clear the engine out,
5. Its not from the pipes because my oil tank is going down fast, half a quart in under 80 miles, thats crazy. Oil pump is feeding far too much and needs setting correctly.

Any thoughts ?
Timing is perfect, doesnt seem like a seals issue.
Carb boots have been softened. No leaks.
Plugs are br7es, i have ordered b8es. BR7ES will give weak spark as they are resistor plugs.

I havnt clear tubed the carbs, honestly, because in my arrogance after working on the carbs i almost never, because i never had to. Never heard of that term, and I've been working on bikes since 1967.
But i doubt that float height would make a repeat issue even after floats were replaced and reset. But they are the wrong floats and the height isn't correct.

Before i take the carbs off again and start plug chops, is there anything stupid that i am missing ?

Thank you

carbs.jpg

[Salman_z8]

It seems like i have this figured out.
I would like to blame all of it on PO but i guess some is on my part.
Here’s what i did;

Because of excessive smoking i removed the oil pump and took it apart. I had taken arm of earlier to check the 180 out of phase, but wanted to be sure and not chance it, while inspecting other parts as well.
It was in fact 180 degrees out, and at full stroke at idle.
Pistons and rotating shaft but were in pretty good shape otherwise. The cam shaft had wear marks, where its not to supposed to have it. After a good run once the pipes have cleared, i am sure it will improve. Lines bled and all put back together.

While removing the oil pump, there was a mysterious aluminum crush washer sitting in there, which i only found upon removing the pump. Can some one guess where that came from ?

It was infact the sealing washer for the bolt to cover the inspection hole on number 3 carb.
I did take the bolt of while checking the oil pump, but working in a bit low light, assumed that the washer was stuck to the carb body and carefully put the bolt back.
Not realizing that was none, and what shined like the edge of the washer, was just a wear mark.
Had i not missed that, i would have never had the trouble i was having.

Float height for the new style carbs on M models is listed as 25.75mm, i believe the 24.25 is for the earlier models.
Anyone ?

For the pilots needing 1 turn once warm, i think is a gas tank issue, which is not venting the way it should.
I will check tomorrow, but i think once that is corrected, 1.25 out will be just fine.
Floats were indeed damaged, and replaced with oem floats out of gt750 cv carbs.

The clear tube method i had mentioned, is what use on cb750 setups. To make sure the fuel level is 2-3mm below the bowl mating surface, using an adaptor and a clear hose.

I will clean the cap on monday and report back.

[Salman_z8]

Just waiting on b8es plugs, i only had two left in stock with me, should be here next week

[Salman_z8]

New plugs are in.
Bike runs much better, smoke has reduced a lot.
If anything, i had to turn the air screws in a bit, to get the idle steady.
While i had the carbs off i found two very little foam particles from the previously disintegrated foam filters in the pilot passages.
Floats at 25.75, but its running and idling good.
Now gota finish the seat pan welding, and back in business.

[Alan H]

Good news all round.