Suzuki GP 100 won't run without carb cover

[wileecoyotee]

Hello, helpful GP100 owners. I am new to this forum, so please bear with me if I get the protocols wrong.

I have acquired a 1986 GP 100 which will not run properly despite my best efforts. At first it would only start occasionally and would splutter and fart (a bit like its owner).
I replaced the timing side main bearing so the points did not bounce around and now it starts and runs.

I was pleased with this diagnosis and thought I had fixed it, but it is still not the best starter and will not rev hard in higher gears. The symptoms feel like fuel starvation - ie if you back off the throttle it seems to go better. Also, it seems to run much better with the carb cover off - this bit is weird.

so - I have....
Cleaned the fuel filter
Flushed the petrol tank
Cleaned the carb
Checked the float height
Replaced the float valve
Replaced the fuel line
Checked the carb overflows are not blocked
Drilled a new vent hole in the filler cap.
Replaced the main jet (with a bigger one, then a new standard one).

None of this made a shite of difference, so I thought maybe it is the electrics...
New condenser
New points
New ignition coil
New generator coil

By this time, I am running out of ideas, so I ditched the petrol tank and bungied an outboard motor tank to it in case there was something floating about in the tank blocking up the inlet.

I then stripped the engine and put in new crankcase seals.

It still won't run properly and I am proper fed up with it.

It has had about 4 new spark plugs, the petrol is new and I have tried it with and without the air filter. The points gap and timing is correct and there is plenty of compression - it even has a new piston & rings (discovered the old one was cracked when I stripped the engine).

Has anybody got any ideas? I feel that I have missed something really obvious - but what?

Thanks

[wodge]

Blocked Exhaust????

Maybe it just needs a decoke!

Is the disc valve timed correctly.. Not sure if it is adjustable but just a thought.
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Yamaha RXS100 RS100

[wileecoyotee]

Thanks for your input

I forgot to mention that I gave it a decoke.

I had assumed that the valve timing is correct or it would not run at all, however at this stage I should not be making assumptions. I will check the valve timing

[stinkwheel]

It has a GOOD spark? So fat, blue and jumping across the middle of the electrode?

When you had it apart, how did the woodroffe key/taper for the flywheel look. Could it have moved/spun?

How are you setting the timing? By points gap? Flywheel markings? Piston position? Crank position? Check it's correct using one of the latter two methods (so measured at mm BTDC or with a degree wheel. I've known timing marks to be out due to historic fiddling.

I'd be tempted to jury rigg the ignition direct to the the coil too.

Why all the above? Because electrics are the most cfommon problem.

Now to fuelling. Running better with the cover off suggests it's running rich.

Running better winding off from WOT suggests it's running lean.

It could be both. Maybe it's running rich at lower revs but lean at higher revs because you took the carb cover off to make it run right at lower revs.

If you can be arsed a) Taking the carb off again and b) Spending more money. A carb service kit isn't the worst thing to try. I put one on the wifes YB100 and it's now ringing like a church bell. Remember, these bikes are getting old now and have had years of teenagers messing with them.

https://www.wemoto.com/parts/picture/px-ips-0235/

One other thing to think about. Did the seals get replaced before or after the shot bearing? If it was before, it could have gone again.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[bypass2]

What groove is the throttle slide clip on. check which groove it should be on.