GS650E Jetting, stock airbix with V&H 4into1

[Vintageman]

OK I just did two reply in a row.

I still would like to know how you guys adjust the Pilot mixture screw while running. That is how you get access to Pilot screws due to Gas Tank in the way. Please let me know.


Some Low speed carb theory (as I see it first review) ->

From the welcome packet, I did see the Low speed carb theory in the 650E service manual. There is a relationship between Pilot Jet size, Pilot air jet size (at carb throat), and Pilot Mixture screw.

From figure in manual, there appears to be 3 low speed passages, 2 are exposed when butterfly closed (idle). One of these is fixed (controlled by Pilot air jet and Pilot jet size and the other is controlled not only by the Pilot Air jet and Pilot Jet size, but the Pilot mixture screw following. The third passage kicks in when you start to open the Butterfly (off Idle) and its contribution is fixed determined by Pilot Air jet and Pilot jet size (which I increased).

I also found two interesting posts explaining this tuning with respect to pilot jet size versus Pilot Screw setting, etc. The first implies if you up the Pilot size one step you have to back off Pilot Mixture Screw by about 1.5 turns. The latter post tells you how to know if Pilot Jet too small or too Large. If too large turning Pilot Screw All the way in won’t cause Idle to stumble since the one remaining passage is supply enough fuel. This is easy to know if a single cylinder engine though

http://www.gixxer.com/forums/showthread.php?t=13944
http://www.exriders.com/archive/topic/229923-1.html

It may be wise I change the pilot jet size back to 42.5 stock versus the 45 it has. They also say in manual the factory jets are extremely accurate. No offense to EBC, but there Pilot jets I have in there (here I go again being cheep. Actually in this case I wanted true Mikuni, but supplier gave me EBC and I should have waited and got Mikunis).


Now I am thinking my issue is when the third low speed passage kicks in. Maybe it is too rich as first thought… why it is not consisted If I rev out and return since not loaded up anymore, but comes back after a while with sustained cruising. Also explains why two turns out versus 1.5 was better for this issue. If when stock it should have been 2.5 turns out, per the first web link it should no be at one turn out If you believe the 1.5x rule.


So I’ll see if I can tune it via pilot screw. Or I may just get four 42.5 Mikuni Pilots, take off carbs again.

I am getting good at taking of carbs. The hard part is the airbox boots to carbs alignment and staying on carb throat.

Well I f I do it again I can check to see if the boots are turned properly. My thought in hindsight they rotated and I did not check. Also don’t over tighten clamps. I can see from other post here this is pain for others too.


Stock is best. Those engineers spent a lot of time getting it right!

[BassCliff]

I still would like to know how you guys adjust the Pilot mixture screw while running. That is how you get access to Pilot screws due to Gas Tank in the way. Please let me know.

Hi,

You'll need a temporary tank. Some folks buy a manufactured auxiliary tank, others use a washer fluid tank from a car, still others use a lawn mower tank or similar. I went really low-tech and used a gear oil bottle, a length of fuel hose, and a barbed connector.



You'll find lots of information on my little website that may help you. Feel free to stop by. There's a link in my signature file.

Thank you for your indulgence,

BassCliff

[Vintageman]

BassCliff.

That is simple and perfectt! I have an empty gear oil jug just like that, some hose, and couplings. I don't have the I-V stand, but will rig something up. I'll give it a go tomorrow.

Thanks everyone!

[Vintageman]

Conclusion,

I did the adjustment. I lifted the back side of gas tank about 6 inches and allowed me access to the screws with a short driver just fine. The first one carb I did I found that I had it at the best spot to start. However, two of the others were too lean.

The method I used-> I turned 1/2 turn at a time. When I went in-lean direction, there was a definite drop off point in the idle. On the rich extreme it took quite a few turns to have the Idle drop and was not as pronounced. So, I used the drop off point lean then backed off until the RPMs maxed and add 1/4 turn out. My settings are between 1.5 and 2 turns. so there is variation between carbs. Also since it drops of on both end the 45 pilots look OK, but probably why I am about 1 turn lean then others using 42.5.

Took the bike out for about 30 miles runs well no stumbles.

Thanks everyone for your help

[BassCliff]

Hi,

Nice work.

When you get around to performing a vacuum sync on the carbs you will have to remove the tank. That's where a temporary tank comes in handy. You'll find lots of pictures of the procedure in the carb synchronization guide (PDF file) on my little website. There's another guide on Mr. bwringer's site HERE.

Thank you for your indulgence,

BassCliff