Hi, everybody.
I modified the spacer on my new 2014 S40, as follows.
The stock spacer is(was) .111"  (2.8mm). Mikuni standard groove width is .035" (.9mm) I decided to be conservative and only shaved the spacer by that amount, .035".
Anyway the bike proved to be practically un-rideable. It would bog down just off idle. After putting in a #4 washer to more or less restore the spacer thickness the bike was almost normal (.108" thickness.) Here in El Paso the elevation is 4000-4500' and the temp at the time was 85-95 degrees.
Also the plug was wet and I could smell gas.
A small change like that doesn't seem to be enough to affect the carb as it did.

Any thoughts? Norman.

It is a new 2014 bike.

I've never had it wide open except when I was having the problem.
The engine simply refused to rev but when I closed the throttle it surged.

The reason I thought it was lean was that at at a quarter throttle and steady speed if I cracked the choke the engine picked up a bit.

I've never seen such a dramatic change from such a small changene notch on the needle so to speak.

Kris01,
The only thing I noticed was that it seemed to have a lean misfire when it was cold.
As I said, at a steady speed and about a quarter throttle if I cracked the choke it was like a bit more throttle.

The first thing I did was to remove the brass plug and adjust the idle for best speed.

Then based on this site and my own gut feeling I judged it to be lean at low power settings.
After shaving the spacer .035" the engine would not produce power.

With my situation at 4000' I knew the bike wouldn't be as lean as most of the other bikes. However one " notch" and the bike would not do much more than idle?

I've adjusted many carburetors but have never seen such a dramatic result from what appeared to be a small change. ????  

Do you think it is possible for the spring to get misassembled and cause this? After I reversed what I did I erased the evidence of course. :'(

I would never have thought of that since it is a new bike.

I did try every position of the petcock and it didn't make a difference.

verslagen1 wrote on 07/30/15 at 21:04:51:


checking each position is not the same.

Lot's of things in play here.

Chances are that at your altitude the needle is just fine where it is. A rich condition will present as "two-stroking" (burbling) while a lean condition will present as a hesitation at throttle input and surging at steady throttle.

"The only thing I noticed was that it seemed to have a lean misfire when it was cold."

Never jet for a cold engine. You only ride in that condition for a few minutes.

Hi,
Thanks for all the suggestions for my problem.(self induced?)

Today I got around to tackling the problem.
I fitted a Yamaha petcock as recommended, it of course worked as advertised. I have never liked vacuum petcocks, why complicate such a simple system.

I put back my shaved plastic washer .076" which is one Mikuni notch, .9mm. The bike ran perfectly with quite an improvement in pick up off idle!

What happened last time- no power- could be due to my putting only a pint of gas in the tank or faulty reassembly of the top of the carb. I did try running on prime but it was the same as reserve. I put a pint of gas in it because I didn't want to have to drain a lot of gas if I didn't like the results.  
Does anybody think it is possible to thingy the slide spring when putting the top of the carb together?

Changing the subject:
New Bonneville .com sells no tool seat screws which fit the Suzuki perfectly and of course make the seat removable with "no tools"

Thanks to everybody who gave me the benefit of their experience.!!

Norman