Yamaha XJ750 Seca Airbox

In frustration I made a decision to take out the airbox with the sawzall and replace it with those cool looking airpods. It is a real PITA to pull the carbs in and out with the airbox in there. The airpods would make is so much easier to pull the carbs for adjustments to the floats and cleaning.

Trouble is I don’t know how exactly to jet the carbs for the new airpods. The carbs were not working with the shared atmosphere airbox. I think I should first get the bike running good with the airbox.

I bought a used airbox from ebay. Now to put it back in. Well you can’t do that without pulling the engine out. I don’t have time for that.

Here how I modified the airbox to get it back in the bike.

There isn’t much room


too big to fit
It is NOT going to fit


The airbox uncut


Sliced .
I cut the air-cleaner box off of the carb-boot part. I then added the aluminum flange and weather stripping to the carb-boot part.
test fitting after slice
Sliced and Test fitting. Test both the carb-boot part and the aircleaner part. You will need to know how to get these back into the bike.
I then drilled and tapped the aluminum flange so the two parts could be screwed together after they are in the bike.
side view
Side view of finished slice


Back in the bike.


Now we can put the rubber boots and carbs back in.


BMW F650 Transmission

BMW F650 with engine out
With the engine removed

It is a 1999 BMW F650. The transmission was slipping out of 2nd gear. This is the process of replacing the gears.

Step 1. Remove the engine. Use the instructions from http://faq.f650.com/main.html

This is the document I wrote about Splitting the engine case_(pdf) Download this document for detailed descriptions of my process for splitting the cases

BMW F650 with engine out
Removing the exhaust and the airbox seemed to be the easiest way to get the carbs out.
BMW F650 with engine out
There isn’t much left after the engine is out.










Engine on the table
Here is the engine out and on the helpful wooden jig described on the F650.com website.
Engine on table. Right side view
I think it would be a real PITA without the jig.












The valve cover off
The valve cover off






Cam Shaft view
Top view of those cam shafts.






Remember to mark those valves
Remember to mark those valves






cam chain
Remember to keep the cam chain facing the same way. Use some twist ties to keep in together with the sprockets.





Ouch! That can be welded. It broke off when the bolt was loosened. It welded up fine in the end.
Ouch! It broke off when the bolt was loosened. That can be welded.








welded jug
The bolt hole welded up fine. A little time with a file and a counter bore, it is good as new.







Top of piston
The top of the Piston and Jug


Buy a new head gasket.



Case is split
Read my document before you do this.


Spend some good time learning how it works before tearing it all apart. It will help when it comes time to put it all back together.

Case split
My opinion is this is the wrong side to open up. You want to keep all that shifter stuff in place in the right side of the case.
snap rings
removing the snap rings
This is both new and old gears. Can you tell the difference? Very little to make me think this is the cause of the slipping but the new gears fit much more sound. It might just work.
Tools for Transmission.
The type of tools you need to take off those gears.
Snap rings are not easy
without the shifter
The gears without the shifter in place
A work of art
The case won’t go back together without the counter balancer being in alignment.
All together and ready for the other half.