Poor tickover and bottom end power

[fimlimbimjim]

Hi Everyone,
I have recently bought a 251 Kanuni, it's a nice bike in overall good condition but has a bit of an issue at low engine speeds only.
I would like any ideas about what it may be.
1: Starts fine from cold or warm.
2: always runs and pulls ok with the choke on
3: once rolling along the road it runs fine. But if stopping low rev throttle response is appalling.
4: I have thoroughly cleaned the carb, pilot jet etc. all are clear.

now the funny part

at low revs upto about 1/4 throttle it feels like the engine is on a rubber band, it lags dreadfully behind the throttle
like it's running very lean or its a very peaky 2 stroke out of the power band.

The carb responds very little to adjustments of throttle slide tickover screw or air bypass screw (Bing 84 carb)
it just about ticks over at less than 800 rpm but only when warm.

Could this be due to worn crank seals ?

thanks for any ideas.

Regards
jim

[radiograf]

Just a few thoughts, check theres no air leak where the carburettor is connected, and that the air filter is correctly seated. Check that the intake rubbers are not perished, and that the rubber boot over the carb cable is ok. Also check that the carb jets are of the correct size.

[TSiarz]

I would say it may be alternator side crank seal

[Old Dog]

Start with the obvious as advised, unless you know the filter to be clean I would change it. I don't know if you have had one before but they are best on the throttle. At low throttle they are a 2T out of the powerband and I have known there to be a lag between closed throttle and engine recovering itself to idle. Check that you have the correct plug as well B7HS or B8HS
Check the cable routing and lube for both throttle and pump you should hear a clack as the slide snaps back.
As for crank seals these can be changed with the engine in the frame, to check, there will be more smoke (white), starting can be a problem ( so what you describe suggests otherwise) and the gearbox oil will smell of petrol for obvious reasons. You can look easily at the alternator side and see if there is any oil seep.

[fimlimbimjim]

Thanks for the replies.
I have a reasonable Knowledge of 2 strokes but mainly jap twins or mx bikes (old piston port KTM's).
I will have a good look at the air filter side of things but in my experience so far
the air filter side doesn't affect the low speed running or tickover to much.
I will whip the side case off and look for weeping of the seal as well,
Are any special tools required to change the crank seal ?

Thanks again
Jim

[Old Dog]

Which side?

[fimlimbimjim]

I guess I will do both ?
I have had a look round and believe I need the alternator and clutch pullers,
any tips on the procedure or suggestions where to get the tools ?

Happy new year to everyone.

Jim

[fimlimbimjim]

Continuing this little saga, Burwins sent me some seals and a clutch puller very promptly.

I have just done the alternator side seal (which looked quite worn).
This has made little difference to the tickover situation
but the bike "seems" to pull a bit more cleanly.

I am now starting on the clutch side but have come to a halt.
My bike has an electronic tacho and oil pump.

I have taken off the gear lever, removed the oil pipes and taken out the 5 clutch casing screws.
I am now trying to remove the casing. It comes off about 4-5mm then makes a noise
as if its hitting something and won't come any further.

Have I forgotten to take something out ?

suggestions gratefully received.

Jim

[djsbriscoe]

Go to this link

http://www.youtube.com/watch?v=5jdypzaM ... V8WWSEQpoU

and watch the MZ service films.

HTH.

David.

[Old Dog]

Have I forgotten to take something out ?

suggestions gratefully received.

Jim[/quote]

You have removed the nit on the end of the crank - Depending on the model it may have the tacho drive - you will need to block the crank or use a impact driver

[fimlimbimjim]

Hi
A litlle update. I have now undone the crank nut and replaced the crank seal.
The bike again seems to run a bit better but the tickover is still dreadful.

I then replaced the spark plug, another slight improvement.

I have now tweaked the float height and raised the needle so it is second from the bottom this seems to
have improved the tickover and low throttle opening performance. I will live with this for a while and see how it goes.

I have also had a chat with a friend who has a 301 (87+k miles). He has fitted a Burwins conversion Mikuni, his bike
ticks over fine and has much quicker pick up on throttle opening.

Maybe this is the way to go when I have some money

Jim

[fimlimbimjim]

Hi

This is I think the final state of play.

1: new crank seals
2: raised needle 1 slot
3: tweeked float height to make it slightly more fuel in the bowl.
4: B7HS spark plug (on friends recommendation)
5: removed a strange aluminium slug with (approx) 1mm hole in it from the fuel line ???????
6: disconnected and cleaned most of the electrical connections.

As I did these things the bike gradually improved. The bike now starts really well and ticks over smoothly
and reliably. The only down side is I get a little more surging on closed throttle overrun.

Hope this is useful to someone.

Jim

[DAVID THOMPSON]

watch about getting ticks over (idle) to slow as this can load up the bottom end causing surging and other problems
on a 2 smoker ..
dave

[fimlimbimjim]

Hi David,
The tickover is now at what the rev counter calls 1200 RPM (which feels about right). When I started
it was much more like 800. I will continue to fiddle and report on my progress.

regards
Jim

[DAVID THOMPSON]

sounds about right do not have the book on that one ....

over the years have bought several mid 60's bmw bikes where the fellows thought it was
cool to idle them down so slow it was hard to tell they were running
my father was a Machinist and seemed very good at fixing the BMW cranks
he did about 5 of them for me
over the years
dave