Seca 400, K&N filters

[Crusty Snippets]

My 83 Yamaha 400 Seca had running issues at WOT. It revolves around the main jets. I almost have it right, just need a few more jets.
Part of the problem is the air box. The RH side holds the battery which makes the space on that side smaller. So Yamaha runs a smaller main jet on that side. The other problem is installing the boots from the diaphragm Mikunis to the air box. It is rather difficult and not helped by a slight misalignment.
So: I can cut out the front area of the air box and install two K&N filters. Then I could use the same size jets in both carbs.

My question for those that use K&N filters.
Did it require a change in the main jetting?

Thank you. Unkle Crusty

[donebysunday]

My 83 Yamaha 400 Seca had running issues at WOT. It revolves around the main jets. I almost have it right, just need a few more jets.
Part of the problem is the air box. The RH side holds the battery which makes the space on that side smaller. So Yamaha runs a smaller main jet on that side. The other problem is installing the boots from the diaphragm Mikunis to the air box. It is rather difficult and not helped by a slight misalignment.
So: I can cut out the front area of the air box and install two K&N filters. Then I could use the same size jets in both carbs.

My question for those that use K&N filters.
Did it require a change in the main jetting?

Thank you. Unkle Crusty

Funny on the 650 I did not need to change jetting with the K&Ns but needed to run one size smaller mains after putting the 2-2 Mac on. Then after installing the MMM anti reversion cones I went back to stock, worked great.

[Crusty Snippets]

Filters

Thank you Sunday.
My XS11 Yami ran much better with new pipes, and a small change in jetting.

Do you know if those who have changed to K&N or other types of filters, have connected them directly to the carbs, or run some type of velocity stack. I am hearing that the diaphragm carbs need some type of tube / stack, about the same length as the original rubber boots. However I recall seeing photos of bikes with the filters attached directly to the carbs.
Reasoning for the stacks is to enhance the air vent for the diaphragm.
And a further question. What was done with the crank vent hose.

All the above is to get a plan for my 400. I do not think the vent hose has to go in to an air box. And I am not convinced of the need for short stacks.
However I have a plan to build them.

Unkle Crusty

[MaximPhil]

Hi Unkle,
I have seen the vent hose replaced with a small cone filter which is both neat and functional.
Phil

[Crusty Snippets]

Update

The XS400 is running sweet with two foam pod filters mounted directly to the carbs. The carbs required smaller jets than logic would suppose. Stock they ran a 117.5 and a 127.5. I am now using 120 on each side. The exhaust is not original. I can nudge 90 indicated with a bunch of gear installed. Side bags, top box, leg guards, front window. Will check speed with the GPS. Motor can pull 10,000 in the lower gears and around 9000 in top. Tried lower gearing, but it did not improve top speed, and made the gearing too low for rural and town roads. Hits a wind barrier and does not have the horsepower to overcome it.

Yami the XS11 Special is reading over by about 6 mph.
110 kmh on the speedo, 100 on the GPS.

Unkle Crusty*