Mikuni RS36-D3K tuning help needed

[Jaymo]

Edit: Yep. Valves are tight. Will measure clearances again this weekend, just to confirm the numbers I got today.
Also, to measure the thickness of my shims so I can do some math and order the thicknesses I need.

Cam cover gasket, cam plugs, and exhaust gaskets arrived.
I got a leakdown tester, because I can always use one.
Warmed up the engine today and did a leakdown test.
Leakdown tester shows leakdown is less than 10%, and that's through the crank case.
However, I decided to cut out the middleman and connect my air compressor hose straight to the spark plug hole adapter.
When I did that, I got leakage past the exhaust valves.
So, I either have insufficient valve clearances, burned exhaust valves, warped/bent exhaust valves, or my valves and seats need to be lapped and/or recut.
FML.
Temps here are hovering right at 100 degrees F.
I'll wait until tomorrow morning to pull the cam cover and check clearances.

IF I need to replace valves and/or shims, do any of you know of any sources?
I'm in the USA, so USA sources would be great.
However, my front brake pistons came from the UK.
I'm not opposed to ordering parts from my brothers and sisters in AU, NZ, and the UK.
For that matter, I'll take my parts from anywhere in the world.

[SCARFEY]

Just finished a set of carbs for Jonesy, Jaymo,
You,d swear the bottom end was about to fall apart all it was was air fuel screws balancing at the end of it they growled

I bought my first XS very cheap because the guy said the engine was stuffed but all it needed was a carby tune and balance. The HiVo primary chain was banging on the crankcase because it was running so rough.

[Jaymo]

I picked up a leakdown tester and a new spark plug cleaner.
Now, I can check leakdown. And clean my spark plugs.
Waiting for cam cover gasket.

[steptoe]

Just finished a set of carbs for Jonesy, Jaymo,
You,d swear the bottom end was about to fall apart all it was was air fuel screws balancing at the end of it they growled

[Jaymo]

Been very busy at work. Had some people quit and are very shorthanded.
Haven't gotten around to ordering cam cover gasket yet.
Yesterday, I removed the intake manifold gaskets and just used sealer between the intakes and the head.
Still having backfire at idle, but not at higher RPMs.
My old exhaust gas analyzer says 1&2 and 3&4 have and A/F ratio of 12.8:1 at idle and gets richer (up to 11.5:1 at higher RPMs) as engine speed increases.

What is the correct A/F ratio or A/F ratio range for these engines.
My next step is a valve clearance check.
If I have warped valves, I have a good friend who is an automotive machinist and charges me fairly.
I hope it doesn't come to that. If it does, I may get the big bore kit and get him to bore my cylinders.

[AussiXS11G]

I bought Yamaha cam cover gasket a couple of weeks ago - $36.58

[Jaymo]

cam cover gaskets are still available from your scamaha dealer

The downside is the dealer will rape me on the price.
The upside is the gasket will be OEM.

[Jonesy :-)]

cam cover gaskets are still available from your scamaha dealer

[steptoe]

Gaskets on intakes are bad news,, always end up failing,, remove them

[makzy]

Well it dose sound like it’s sucking air somewhere, compression is ok, mine only has around 145
across the board with a slight sound of piston slap. But, who cares! E-Bay used to have heaps of top end gasket sets at reasonable prices but have never seen just rocker cover gaskets, if all surfaces are nice & clean 3 Bond is all you need.

[Jaymo]

UPDATE: Ran the engine today. #3 and 4 are lean. Both (mostly #3) backfire at idle. Spraying carb cleaner into them (mostly #3) clears that up. Spraying it around the juncture of the intake boots and the cylinder head at 3 & 4 seemed to clear it up.
I'll check the intake bolts for looseness, when the engine is cool.
If that yields nothing, I'll pull all the intake boots and get rid of the gaskets. Probably will anyway.

Warm compression test resulted in 152 psi, dry, for 1, 2, and 3. 158 psi for 4.
4 also looks to be the most coked up. I don't see a need for a wet compression test at this time.

I believe I need to pull the cam cover and check valve clearances.
What's a good source for cam cover gaskets?

[Jaymo]

Funny thing about the filters drying out, is that even if I don't run the engine at all after oiling them, the top halves of the filters will dry out in two or three days

Hmmm, I'd be having a word with gravity and ask it to back off

I told gravity to do something I shan't repeat here.

I did a compression test today. Sort of.
I did a cold compression test. I know I should've done it hot, but I had a senior moment.
Cold compression is 135 dry for all. Nice and uniform.
When I'd done a hot compression test before, they were 150 dry, didn't feel a need to do a wet test.

Back to today. Cylinders 2, 3, and 4 went up to 180 wet.
Cylinder 1 only went up to 150 wet.
So, intake valve sticking due to the crappy US ethanol gas, combined with the months the engine sat.
Or, I need to get a new valve cover gasket and check/shim the valves.
Possibly an exhaust valve leaking, but I should've had muffler explosions all the time, from cylinder number 1, if that were the case.

There is a definite possibility of some intake valve sticking and even ring sticking, since it sat for a good long time.
Considering all the carbon I've found in the cylinders, I wouldn't be surprised.
I've run into Mazda engines on Yale forklifts whose rings would stick if the engines sat for any length of time.
We'd squirt some automatic transmission fluid into the spark plug holes and that would free them up enough to run.

I shot about 10 CCs of Marvel Mystery Oil into each spark plug hole, after the "compression" test.
Then, I shot about 10 CCs of Marvel Mystery Oil into each intake runner.
I've got the battery on charge, because the battery is weak. Possible charging issues? Battery is only about a month old.

I'll let it sit overnight and fire it up.
Then, I may feed it some Seafoam or some Dexron ATF while running.
If any rings or valves are sticking or not seating due to deposits, that should free them up.
THEN, I'll check compression while the engine is warm.

[Jonesy :-)]

Funny thing about the filters drying out, is that even if I don't run the engine at all after oiling them, the top halves of the filters will dry out in two or three days

Hmmm, I'd be having a word with gravity and ask it to back off

[Jaymo]

You’ll have to relocate to Australia😃
We have pleanty of spares
Amthough that would be a bit xsive

If I could, I would.

[Jaymo]

I have determined that gasket got the exhaust crossover pipe (right before the mufflers) is leaking.
I don't remember how much it will affect running.
I'm going to pull the carbs and rubbers, remove the intake gaskets, check compression again, and reinstall the rubbers without the gaskets.
First, I will do another test for vacuum leak.
I tested for vacuum leaks with a propane torch (not lit, just propane flowing from the nozzle).

I discovered the exhaust crossover leak because I made and installed temporary oiled foam filter wraps.
Running it like that caused it to backfire out the exhaust (sometimes) upon acceleration, not deceleration.

Funny thing about the filters drying out, is that even if I don't run the engine at all after oiling them, the top halves of the filters will dry out in two or three days.

Going to remove the seat and tank, and set the tank in place of the seat (facing backwards), to allow better access to #2 & 3 intake boots for vacuum leak test.

Any recommendations for an aerosol spray product for checking for vacuum leaks?
Starting fluid? Carburetor cleaner? WD40?