Dyno Puzzle for you guys!

After 3 months of my mechanic trying to cure my unaltered '81 750 Seca with a hesitation that occurs between 2,500-4,500 rpms (under load). He adjusted the valves and rejetted carbs, put in a new CDI unit and new coils, and I finally broke down and took it into my local mc dyno shop, and what it showed, was that idling, air/fuel mix is good (about 13 to 1) but as it gets above 2,500, the air/fuel goes up above 18/1 and continues off the chart (literally!), until at about 5,000, it drops back to where it should be (and runs smoothly), and then goes a bit rich. Obviously, it is running out of gas, and this leaves me & the dyno guy scratching our heads, so I thought I'd run it by you guys. Any suggestions or guess what the problem might be? Thanks in advance!

 

clunk test ?

See if the carb sliders glide smoothly, with the slightest force.
Do you have the airbox, and stock mufflers?

 

Yep, TTR; the sliders are smooth, and the airbox and mufflers are stock, and there's a brand new air filter. . .

 

The Emulsion Tubes are partially clogged.

Remove the Emulsion Tubes and look through them at a light.
You should be able to see light through all the holes.

Additionally, Check to see that you have the Main AIR Jet and Pilot AIR Jets in their correct positions.





ALL the Metering Ports in the Emulsion Tubbe need to be open.
Twist together 3 Pipe Cleaners and scrub the Inside Diameter.
Welders Tip Cleaning Tool Set Ideal for opening Ports on the E-Tube.

 

How do you get the emulsion tubes out to check?

 

Pull the Main Jet.
Take off the washer.
Bottom of Emulsion Tube is exposed.

Screw a Cap Screw with the same thread pitch as the Main Jet into the Bottom of the Emulsion Tube.
Drive it out through the Top of the Carb after removing the Diaphragm Piston Assy.

The Emulsion Tube on Hitachi is Not "Keyed" like Mikuni. Replacement is done by inserting the Emulsion Tube through the top of the carb.
Screwing-in the Cap Screw.
Pulling the Emulsion Tube down until it seats.

Don't try to seat it with the Main Jet and washer tightening.
You can pull-off the Main Jets threads that way ... they're brass.

 

Expanding on what Rick said: Pull the slide before you try to tap the emulsion tube out.