Gt380M wont rev to redline - WOT

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Salmanz8
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Joined: Tue Mar 16, 2021 4:39 am
Location: Edmonton AB Canada

Gt380M wont rev to redline - WOT

Post by Salmanz8 »

Hi guys
Now that i am trying to get everything i have running like they should, heres the next one.
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.

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.
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Salmanz8
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Location: Edmonton AB Canada

Re: Gt380M wont rev to redline - WOT

Post by Salmanz8 »

Sorry for the long post, i wanted to get the max info out there.
Timing is spot on, not sure if i mentioned that already
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Salmanz8
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Re: Gt380M wont rev to redline - WOT

Post by Salmanz8 »

Before doing plug chops or float heights, is there anything else i need to know ?
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Salmanz8
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Re: Gt380M wont rev to redline - WOT

Post by Salmanz8 »

Plugs are br7es, which i am waiting for the non resistive type to switch to b8es instead. Since i do ride highway mostly.
teazer
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Re: Gt380M wont rev to redline - WOT

Post by teazer »

Oil consumption sounds rather high, but let's start with the basics.

Floats: are you sure those new floats are identical to the originals? I had a GT550 problem recently and when I cleaned out the caebs I realized that one float was different. It looked the same width etc but the connecting "bridge" and tang were slightly different and caused that one to flood. Float height is an easy way to determine fuel level but it's not always as accurate as we might hope. I much prefer to set FUEL level at 3mm below the gasket surface of the carb. You will need an adapter to check fuel level.

Ignition: resistor plugs plus resistor plug caps are not recommended. Try no resistor plugs or caps.

Oil: you mentioned oil in the cylinders. Did you mean that the cylinder heads were oily or the crankcase was full of oil? If there's a lot of oil in the bottom end, it's probably the oil feed check valves are stuck open and allowing oil to drain down into the crankcases. The valves open at something like 4-6 psi so do not use compressed air to clean the lines. If you use high pressure the balls end up pressed inside the springs and after that they won't seal.

Assuming that your bike has SRIS valves in the crankcase, you could remove them and allow the surplus oil to drain. There is always a small amount of oil in the crankcase, but more than say a teaspoon of oil indicates a check valve leak.

Crank Seals: you may be lucky but they do tend to stick to the crank if left for years and then tear when the bike is started. I'd recommend a compression test and a leakdown test using a two stroke leakdown tester at no more than 10psi. 4 strokes us high pressure to test leakdown, but that would destroy crank seals, so we use around 10psi to test for leaks.
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Salmanz8
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Location: Edmonton AB Canada

Re: Gt380M wont rev to redline - WOT

Post by Salmanz8 »

teazer wrote: Thu Apr 08, 2021 5:21 pm Oil consumption sounds rather high, but let's start with the basics.

Floats: are you sure those new floats are identical to the originals? I had a GT550 problem recently and when I cleaned out the caebs I realized that one float was different. It looked the same width etc but the connecting "bridge" and tang were slightly different and caused that one to flood. Float height is an easy way to determine fuel level but it's not always as accurate as we might hope. I much prefer to set FUEL level at 3mm below the gasket surface of the carb. You will need an adapter to check fuel level.

Ignition: resistor plugs plus resistor plug caps are not recommended. Try no resistor plugs or caps.

Oil: you mentioned oil in the cylinders. Did you mean that the cylinder heads were oily or the crankcase was full of oil? If there's a lot of oil in the bottom end, it's probably the oil feed check valves are stuck open and allowing oil to drain down into the crankcases. The valves open at something like 4-6 psi so do not use compressed air to clean the lines. If you use high pressure the balls end up pressed inside the springs and after that they won't seal.

Assuming that your bike has SRIS valves in the crankcase, you could remove them and allow the surplus oil to drain. There is always a small amount of oil in the crankcase, but more than say a teaspoon of oil indicates a check valve leak.

Crank Seals: you may be lucky but they do tend to stick to the crank if left for years and then tear when the bike is started. I'd recommend a compression test and a leakdown test using a two stroke leakdown tester at no more than 10psi. 4 strokes us high pressure to test leakdown, but that would destroy crank seals, so we use around 10psi to test for leaks.
Thanks for the reply teazer.
1. Took the air box off, carbs off to get to the oil pump.
Could you believe it almost used half a quart in 50 miles.
So took the pump out to inspect. It certainly seems like the PO had done something to the pump in the past, perhaps 180 degrees out. But the pump feels like its sticking, the arm gets stuck unless the bottom drive shaft is in a sweet spot. Is this how they are supposed to be ?
2. Carb float level i check with an adapter, and is at 2-3mm below the seam.
3. Needle clip is at 2 as per manual, and i wouldnt even want to change it since i just spent 2 days cleaning the melted rubber goo and replacing rubbers and putting the linkage together. Lol
4. Is there any hidden passage for the main circuit ? That i missed ?
5. Plugs are incorrect, and probably a step hotter was put in to compensate for the insane oil.
6. Doesnt have sris, and nothing more than a tea spoon cane out last time i checked. When i originally got the bike the middle pot was full, but that has not happened again.
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Alan H
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Re: Gt380M wont rev to redline - WOT

Post by Alan H »

Also replies on Sundial forum.
Proof that four strokes are over complicated
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Salmanz8
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Location: Edmonton AB Canada

Re: Gt380M wont rev to redline - WOT

Post by Salmanz8 »

Alan H wrote: Sat Apr 10, 2021 6:19 am Also replies on Sundial forum.
Thanks Alan, i replied there and am posting a link for someone else’s benefit in future. I think i have most of the issues sorted out.

http://www.suzuki2strokes.com/forum/vie ... =2&t=14648
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