Mikuni HSR42 and breather system.

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colmj2

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Hello. I have just bought a mikuni HSR42 kit for my 1992 FXRS and am a bit puzzled as to what to do with the breather kit that came with it. The problem is that for my bike you just plug up the holes in the rocker box lid with the supplied bolts, but my engine is brand new so technically being a later model you are supposed to use the breather kit.
If I bolt in the banjo bolts and hose's to the rocker box lid where do they connect to?? or can I just blank the holes off like the earlier models??
Hope this makes sense to someone.

Jamie.
 
Re: Mikuni HSR42 and breather system.

I think I am with you Jamie.

In 1992 the Evo motor changed from being a crankcase breather (hose carrying excess oily gases from crankcase went into air cleaner, 99% of owners re-routed into a little filter clamped to bottom of motor or frame rail) to a head breather (umbrella valves in the head area discharge same gases direct into air cleaner through hollow lines/bolts.

I believe some bikes were fitted with the late style rocker box set-up but were in fact still using the crankcase breather system. It was a matter of production-line availability. I **think**

So I am guessing you would follow the rules for an 84-91 Mikuni set-up.
 
Re: Mikuni HSR42 and breather system.

Thanks for the reply, although I am still a bit confused. I thought the crankcase breather nipple next to the oil pump connected to the oil tank? so if I connect that up does that mean I can just plug up the holes in the rocker box cover with the supplied bolts? or if I also use the breather connections from the rocker box cover, there doesn't seem to be any fittings to connect those hoses to the air filter.
Sorry if i'm being a bit thick....

Jamie.
 
Re: Mikuni HSR42 and breather system.

OK, I found a manual for your kit online....

http://www.mikuni.com/pdf/tkmanual012302.PDF

You are trying to fit Mikuni breather kit KHS 020?


**IF YOU HAVE THE ORIGINAL MOTOR**


Simple question: up until now do the rocker box bolts on your bike purely HOLD the air cleaner assembly on?

If the answer is YES (and I bet it is), forget about the Mikuni breather kit. It does not apply to your bike.

In fact, the instructions state it fits 1993-1999, but I believe many late 1992 bikes could use them as well

(If your bike was a late-type head breather ...and I am sure it is NOT.. with stock carb it would have a short L-shaped section of ''chrome piping'' from each rocker box bolthole to the air cleaner assembly, feeding muck into mix for burn-off. Mikuni do a slightly different version as you will see in the sheet.)

If you read the online instructions (above) you will see there at the very top of page 3 (TK-3) is a special dispensation for 1992 Big Twins: the ones that have the ''late'' rocker box boltholes but are still crankcase breather bikes just slightly bigger bolts.

You haven't really got the wrong kit, you've just got a bit extra you don't need. Should be able to use your existing bolts, but if not the specs are there for you to take to fastener shop.

Of course, you will need to use their other little Z-brackets and stuff as per directions.

BTW, the crankcase breather line does not go to oil tank. Stock, it went into air cleaner. Not a good move. Just route it to frame rail or mount on a bolt somewhere (brake pedal assembly, exhaust pipe support, etc) and place one of those little ?6 filters on the end. Look at any 84-92 Evo, you'll see.



***IF YOUR BIKE NOW HAS A BRAND NEW CRATE EVO WITH HEAD BREATHER ROCKER BOXES****

Follow the instructions as for 93-99 bike. USE the breather kit.

Hope this helps. Pretty tricky scenario!
 
Re: Mikuni HSR42 and breather system.

colmj2 said:
Hello. I have just bought a mikuni HSR42 kit for my 1992 FXRS and am a bit puzzled as to what to do with the breather kit that came with it. The problem is that for my bike you just plug up the holes in the rocker box lid with the supplied bolts, but my engine is brand new so technically being a later model you are supposed to use the breather kit.
If I bolt in the banjo bolts and hose's to the rocker box lid where do they connect to?? or can I just blank the holes off like the earlier models??
Hope this makes sense to someone.

Jamie.
Click to expand...
If you have a new model reman motor, them do as Kiwi Dave says and use the head breather set up.
If your heads have small 5/16 holes then: No head breather. If it has large 1/2 inch holes then: Head breather.
 
Re: Mikuni HSR42 and breather system.

Thanks for that guys. Yes I have got a new evo engine so I will use the head breather setup.The problem is I have the workshop manual for my bike, but as the engine is a new evo it has some different bits on it.

Thanks again,

Jamie.
 
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