TOPIC:

calvin17d wrote: ...135 psi compression all 4 cylinders +/-(5psi)...plugs have been a little sooty....

Compression figures are good.

If not already done, should also assure valve clearances are within specs.
If too tight, valves may seal okay until the engine attains normal operating temperature and then start leaking with resultant loss of compression (and sooty plugs).

Good Fortune!

Paid close attention to valve clearance during the recent restoration (<100 miles).

So as mentioned, my spark was good.

I set up the clear tube and began testing the float level with the carbs on bike. First thing I noticed was that the #2 cylinder was continuously dumping onto the ground. I continued checking #4 then #3, then went around and checked #1 while #2 continued to dump gas. I could not get an accurate reading on #1 although it looked close there was a surging vacuum effect occuring and the level would fluctuate up and down about a 3/4 of an inch.

I then took the carbs off and inspected #2 thinking I would just go back to #1 after fixing #2. I made a measurement and slight adjustment to the tang of #2. I then proceeded to check #2 via the clear tube method. The carburetor would not take on any amount of gas at all.....Had I bent the tang way too far......What the heck.... I pulled the float bowl once more and discovered that the float was binding on excess gasket material. It had previously been stuck below the gasket and was never allowed to close but after bending the tang it had been caught in the opposite fashion above the gasket, never allowing it to open.

So I shaved the gasket and put it back together. Running much better, very smooth, but I would bet I am still on the rich side, as I notice a slight hesitation before really ramping into the acceleration curve. I would pull the plugs but I need to clean them before I can assess those under these new operating conditions.

Can anyone tell me the RPM or throttle position where the main jet takes over the fueling of the pilot jet. I wanted to test each jets effect on the plugs?

Check in the filebase.

Here is what you need calvin,
www.mikuni.com/pdf/vmmanual.pdf
This should help you understand how the carbs work.
Pods, Oh well.

Plug color has improved since the float level adjustment. Throttling is much smoother through the 30-55 mph range. I notice as I roll onto the throttle from about the 60-70 mph range, that it tends to stumble a little bit. Still no significant backfiring, just some rough running and plugs that are still showing signs of running rich. Mwaaaaahhhh thru midrange and Black with a dash of coco on the ground strap.

I have 112.5 jets on hand which were in the bike prior to the resto. Is this too significant a jump for trial and error purposes?

calvin17d wrote: ...as I roll onto the throttle from about the 60-70 mph range, that it tends to stumble a little bit. Still no significant backfiring, just some rough running and plugs that are still showing signs of running rich....

What jet needle clip position?

Imo should be left in the stock #3 middle position.

If set in a richer position (jet needle raised higher in the throttle slide), may cause the reported stumble, rough and rich running.

Good Fortune!

Patton wrote:

calvin17d wrote: ...as I roll onto the throttle from about the 60-70 mph range, that it tends to stumble a little bit. Still no significant backfiring, just some rough running and plugs that are still showing signs of running rich....

What jet needle clip position?

Imo should be left in the stock #3 middle position.

If set in a richer position (jet needle raised higher in the throttle slide), may cause the reported stumble, rough and rich running.

Good Fortune!

This will be my next inspection when I pull the carbs tomorrow. My father rode the bike prior to giving it to me and continues to suggest that I try raising the needle. I would not be surpised to find that he had done this himself several years ago.

Funny

Thoughts on the 112.5 jets???????

calvin17d wrote: ...Thoughts on the 112.5 jets???????

Would use the stock size 115 main jets.
At least for the time being.

Oem Mikuni 26mm carbs on KZ900 are very user friendly, and were designed before the stringent EPA rules became applicable. They perform well in stock configuration with K&N airbox filter and 4/1 exhausts on 1015 bore engine.

Good Fortune!

Patton wrote:

calvin17d wrote: ...Thoughts on the 112.5 jets???????

Would use the stock size 115 main jets.
At least for the time being.

Oem Mikuni 26mm carbs on KZ900 are very user friendly, and were designed before the stringent EPA rules became applicable. They perform well in stock configuration with K&N airbox filter and 4/1 exhausts on 1015 bore engine.

Good Fortune!

Would you say that this suggestion takes into account any amount of elevation? Are the specs based on sea level or are elevations considered mostly negligible?

calvin17d wrote: ...Would you say that this suggestion takes into account any amount of climate elevation?

Main jet size mostly affects mixture at wot. So higher altitude running at wot might benefit from a slightly smaller main jet at wot whereby the mixture might need to be slightly leaner at wot.

At other throttle positions besides wot, the main jet size is far less important, because at less than wot, the jet needle taper inside the needle jet governs mixture during mid-range throttle positions.

At relatively high elevations, mid-range performance might possibly improve with a leaner (higher) jet needle clip position to afford a more "standard" fuel mixture ratio in the thinner air.

Imo, changing main jet size is unlikely to have much if any effect on mid-range performance, regardless of elevation.

Good Fortune!

Excellent! I feel I am learning quite a bit here. I have looked at the Mikuni manual which helps to better understand your verbage. Would you say the speeds I have described fall into the midrange that you speak of? The midrange being the area that is insignificantly impacted by main jet size.

Assuming my clip is in the stock position (#3) would you suggest lowering the needle into the needle jet in lieu of changing the jetting for troubleshooting purposes?

calvin17d wrote: ...Would you say the speeds I have described fall into the midrange that you speak of? The midrange being the area that is insignificantly impacted by main jet size....

Yes.

calvin17d wrote: ...Assuming my clip is in the stock position (#3) would you suggest lowering the needle into the needle jet in lieu of changing the jetting for troubleshooting purposes?

Would begin test runs with carbs in as close to new condition as possible, same as delivered off the showroom floor. Likewise with fuel delivery from inside tank through petcock and inline fuel filter into carbs.

If performance issues persist, would not re-address carbs until first assuring satisfactory compression and valve clearances being within specs, and visually observing fat blue sparks on each plug, and assuring ignition timing is correct, and that advancer unit is properly functioning (use dynamic timing -- engine running -- method with strobe-type timing light).

Even perfect carbs can't compensate for deficiencies in the other components on which the carbs rely.

Good Fortune!