30% of the way there...

Well crap. Now what?

 

By popular demand, I've pulled the carburetors apart, AGAIN... now for a seventh time...

Here are the butterflies, two turns out, all four are the same.



Here are the factory jets, all clear (on all four carbs), and the correct sizes, in the correct locations.



Here is the factory seat, inside and out. Perfectly clean.



Spraying carb cleaner through the orifices, ALL of them are flowing.





Now, can we, for the love of everything unholy, stop with the carbs?!?

 

As I've said before, the condition of the carburetors is absolutely, unequivocally, utterly, not relevant, to an infinite degree if the cylinders aren't reaching the required pressures/vacuum.

If the cylinders are not pulling a strong enough vacuum, they're not going to pull fuel from the idle circuit of the carbs to run at idle, but rather only at higher RPM'S. As is the case.

This is a cylinder/head issue... of which, I have zero clue. I've performed the leak down test, and they're only losing 3%, well within the 10-15% allowable. So that eliminates rings and valves.

There has to be something within the YICS that has gone awry. And unfortunately, I don't know enough about the YICS to test for or determine what that issue is.

 

I didn't see the jet in the float bowl....

 

YICS primer: https://www.xj4ever.com/catalog/yics.html

The punch line is that once the intake valve is closed, YICS is out of the equation. Should not mess with compression numbers.

At this point I am at a loss to even theorize why you are getting such low compression numbers but passing leakdown with flying colors and valvetrain timing is spot on.

 

Nope, not happy yet.
Can you screw the idle speed screw right off, then in to touch. Then in one turn only.
Then a pic of each butterfly at the position of the first progression hole. They should all be at the edge of that first hole - this is them bench synched, adjust each one to achieve this edge of hole. All things being correct the bike should run and idle here albeit fast.
Then I'd like to see the numbers on the idle jets, and the air jets.
Then I'd like to see you remove each idle mixture screw, open the butterfly of each carb in turn, put a finger over the air jet, and squirt carb cleaner in the jet mounting, watching for fuel coming out of the idle screw hole, and each progression hole, on all carbs. Then we will know that the passagways between the idle jet (not the air jet), and the idle and progression circuits is clear. Wear eye protection!
I'm being pedantic, but these simple settings are essential. I could add a test to check that the hole in the bottom of the enrichment chamber is clear also - in fact yes, please check each of these.

 

And another comment, on the pic you show the idle circuit being blasted, there are bubbles forming where I would expect a jet of fuel - this needs investigating.

 

It wasn't the carburetors.

 

Awesome! Don't keep us in suspense though....

 

The issue...

Chinese fuel line.

I figured that I would replace the 42 year old, half dry rotted factory fuel line with new.

There was however, a defect. There was a little flap of rubber on the inside acting like a reed valve. At low fuel demand it couldn't overcome the "reed", but at high demand it'd overcome the resistance and feed it fuel.

I reached in with the highly underrated and humble dental pick, ripped that flap out and she worked.

There's some more fine tuning to do, and a few more parts to replace, but this is huge progress.

When I tested the petcock, I pulled the fuel line off the petcock, cranked the engine a few times and fuel flowed. "Great, the petcock works. It's getting fuel..." or so I thought.

After shining a light into the fuel line, seeing some light at the othe end, and blowing air through it, I assumed, "Yep, it's a fuel line." So who would have ever thought to look deeper into it?

 

Well done.
You're going to have an awkward time with a lefthand throttle, though.

 

Not if I'm left handed.

...and I'm not. lol

I tried to flip the video the right way round, but that's how it recorded when I used that lens.

 

Not the carbs, but it was fuel related....
Well done, I think...

 

Way to go, good basic troubleshooting and why I always start my bikes off an AUX tank and know good fuel lines. Good for you, I hope you can get her fine-tuned now. Wonderful feeling having her running!

 

I swapped out the factory vacuum actuated petcock for a good ol' fashioned old school petcock, and it ran better.

I'm slowly getting the bugs worked out of her and beginning the fine tuning.

https://youtube.com/shorts/_L40sICwSxI?si=-MogbTXBrHipFN7f

 

Glad to see it running. So when you were trying to start it before, the fuel line blocked all flow and the bowls were dry?

When is the road test?

 

Sorry? Good basic troubleshooting?

 

No, it was a partial blockage, which is probably why it was so damned difficult to diagnose. I still have to synchronize the carbs, adjust the clutch, replace the turn signal relay (the aftermarket relay I bought off Amazon was a complete dud), and figure out what is going on with the front brake. I put new (aftermarket stainless braided) brake lines on the front, but I suspect the I.D. is too small and it's not pushing enough fluid through to push the piston out. And find replacement spark plug boots (I accidentally broke the #3 boot).

 

So is the compression problem a red herring?

If it is that far out, even if it ran I would think it would run like garbage.

 

I don't know. I'm still checking that out. It's rather odd.