Topic: Could use some advice on tuning..

[Bob Wessner]

I apologize in advance for the long post. I’ll try to summarize the situation.
  1.750 K0 now running
  2.Cleaned carbs last year and installed Keyster kits, but have gone back to stock float valves and needles (another story for another  day).
  3.Jets installed at this time are Keyster 120’s and 40’s (should mention I found 110’s and 40’s, needle clips one notch down on disassembly for cleaning last year)
  4.Exhausts are 2,3, & 4 original, unmarked pipes, baffles in and clips in middle position.
  5.Exhaust #1 had to be replaced and now has a HM341, baffle in.
  6.Plugs are NKG D8EA’s
  7.Timing, good
  8.Valves adjusted
  9.Carbs were sync’d, though they may need tweaking

Since getting it running again, with the Keyster needles installed, my riding has been local, around the Hood so to speak. Rarely getting over 4K, and if so briefly, mostly starting stopping, around blocks, etc. Speed limited to around 35 mph, tops. Not the greatest, but some folks are limited to such local driving so it seemed like I should be able to get it tuned reasonably well, even under these conditions.

On the first day, things seemed fine. Looked at the plugs afterward and they were all pretty sooty, but dry. On the second day I developed a nasty backfire coming from the left side, either #1 or #2. Got back to the garage and the carbon/soot seemed to have accumulated on all electrode surfaces to the point where on at least #1, it was misfiring occasionally resulting in the backfire.

At this point I decided since “rich” seemed to an understatement. I had some reservations about the Keyster needles so I went back to the original needles. At the same time, I dropped the needle one notch (i.e., clip up one notch) on #1, which has the 341 pipe on it.

The next ride seemed better. I should add that once good and warm/hot, the engine idled too high, approx 2K. When I got back to the garage and pulled the plugs, #3 and #4 were very clean. Plugs #1 and #2 were still sooty, but it seemed clear that the faces of both electrodes were keeping pretty clean, but not the rest of the plug like 3 & 4.

Before taking it out today, I returned all the airscrews and idle screws to the spec. positions, one turn out for air, an aligned the “T” on the slide screws. It ran fine, the idle is now too low, so I will adjust that.

If anyone isn’t tired of reading so far, after taking a look at the pics of the plugs removed today, any suggestions or observations would be welcome. I would like to get #1 & #2 looking more like #3/4. However, my main question is, given the riding circumstances described, just how much of it is dependent on the idle circuit vs. the high-speed circuit? I’m thinking I need to tune the idle rather than, at this point do any further adjustment to the needles. Any thoughts? The number one plug in the picture is actually a little sootier than it appears. Thanks in advance.

[mcpuffett]

were's the picture of the plug bob?    mick

[Bob Wessner]

Well, since I originally left out a subject, it spit it back at me. When I inserted the subject, it neglected the pic, so I modified it to include it, one of those days 

[eldar]

Well judging by the plug pics. I would say that 3 and 4 are a bit too lean possibly. With #1 I would say to turn out the air screw to lean the mix a bit more. #2 looks to be about right on MAYBE a tad rich. Since you mostly stay at lower speeds, it is hard to say what might be going on with the mains. I would almost say to move the clip down/ needle up on 3 & 4. Leave needle along on 1 & 2 and turn air screw out about 1/4 turn on 2 and 1/2 on 1.

[TwoTired]

Have you seen the chart below?

I think that red headed step child pipe on # 1 is giving you grief.  #1 cyl clearly needs more air than what it is getting compared to the others.  It might be quite a chalenge to tune #1 carb differently than the others, so as to acheive the same combustion conditions as the others.  That said, do the easy thing first.  Turn out the air screw on number one carb.  At this point, I wouldn't expect it will be the same setting as the other carbs.

Note, you should be cleaning your spark plugs between each test cycle.  So, you will read new deposits rather than old.  Also, during warm up, the rich conditions will leave plug deposits.  The heat of cruise power settings should burn these off after full operating temps are achieved.

Also, I saw you mention elsewhere that changing needle positions was easy on your carbs.  Are you resycning carbs after this is done?  How confident are you that yanking the slides and reinstalling isn't effecting carb balance?

Question:
Are the baffles in your old pipes interchangeable with the newer one?
It might be interesting to swap them and see if the problem follows.  A visual comparison might show different holes sizes, where you could modify the odd one to be like the rest.  I don't know, just a thought...

[Bob Wessner]

I have seen the chart, guess my problem is defining 1/8, 1/4 in my mind.

Note, you should be cleaning your spark plugs between each test cycle.  So, you will read new deposits rather than old.  Also, during warm up, the rich conditions will leave plug deposits.  The heat of cruise power settings should burn these off after full operating temps are achieved.

I didn't clean them after the first run, but do now in between trys.

Also, I saw you mention elsewhere that changing needle positions was easy on your carbs.  Are you resycning carbs after this is done?  How confident are you that yanking the slides and reinstalling isn't effecting carb balance?

I did not resync after the needle change and I am sure they willl require it, doen't sound too bad though and I know what it sounds like when they are noticably out of sync  .

Question:
Are the baffles in your old pipes interchangeable with the newer one?
It might be interesting to swap them and see if the problem follows.  A visual comparison might show different holes sizes, where you could modify the odd one to be like the rest.  I don't know, just a thought...

No, baffles/defusers are not interchangeble between number one and the others.

[SteveD CB500F]

Bob - your problem is simple.

Plug #4 is smaller than the others.

[Jonesy]

In a perfect world, carbs should be resynced after every time the carbs are apart since who knows what can be disturbed upon disassembly. The carbs need to be pretty far out of balance before it gets really noticable in sound and drivability.

[Bob Wessner]

In a perfect world, carbs should be resynced after every time the carbs are apart since who knows what can be disturbed upon disassembly

I guess deep down I knew that  . Guess I know what I'll be doing tomorrow.

[eldar]

Try to get the fuel mix as close as you can before syncing though.

[TwoTired]

I have seen the chart, guess my problem is defining 1/8, 1/4 in my mind.

Don't need to define it in your mind.  Mark the positions with tape temporarily at the grip.

Is your old #1 pipe too bad to patch and try while you get carbs sorted?  I have a CB550F that had a bunch of rust holes in the original muffler 4-1.  I brazed some tin over the holes so all the gasses went out the holes at the end only.  A little VHT paint and well, who's going to lay under the bike and sneer at those patches?  I know it won't last forever.  But, then the new chromed jardine will go on it.  And, I'll deal with the jetting issues then.

[Bob Wessner]

I will give that a try. I guess my momentary confusion about whether to fiddle with the idle circuit or needles stemmed from the initial needle swap. When initially using the Keyster needles (that I sort of measured them and they had a very slender tip area compared to the stock needles) all four plugs were v-e-r-y sootie. As a matter of fact they looked like four little black Gia Pets. Swapping the needles immediately cleaned-up the plugs considerably. It did drop the needle one notch on #1 because I understood the 341 was more restrictive (hmm, did I go the right way?).  But then I realized that the limited riding thus far couldn't be using very much of the needle or high speed circuit.

[eldar]

I think dropping the needle was ok to limit the amount of fuel through the main. Turn out your airscrew to allow more air in to lean it more.

[Bob Wessner]

Bob - your problem is simple.

Plug #4 is smaller than the others.

Steve,

Just like me to overlook the obvious