Idle mixture

Lean · Post by **Lean** » Tue Jun 03, 2008 3:58 pm

Hi all. I have trouble starting my superfour. Most of the time it starts without choke and without throttle. When it doesnt start like this, it will not start off the starter motor at all no matter what combination of throttle and choke I give it. I have tried starting it with choke and 9/10 the engine just does not start.

When it does start up with no choke, it will stay running no problems which makes me think it could be idling slightly rich?

I was thinking about having a play with the idle mixture screws to see if starting can be improved, but I dont know where they are or what they look like? Is it one screw for all 4 carbs or 1 screw per carb?

All input appreciated cheers

DerSchlang · Post by **DerSchlang** » Wed Jun 04, 2008 7:39 pm

There is 1 screw per carb. They are located under carbs, so you have to take them off or use a 90 degree or flexible shaft screwdriver. Tighteen them and rotate 2 turns.

alexibrow · Post by **alexibrow** » Wed Jun 04, 2008 8:52 pm

As you say: it sounds like it's running rich. Using the choke will flood the engine immediately if it's too rich to start with. Is it harder to start on warmer days?

Lean · Post by **Lean** » Wed Jun 04, 2008 9:42 pm

Ive got the russian translation manual and felt like throwing my monitor through the window after tryingto use it to find the mixture screws. Some of the direct translations are laughable, and most dont make sense.

alexibrow wrote:As you say: it sounds like it's running rich. Using the choke will flood the engine immediately if it's too rich to start with. Is it harder to start on warmer days?

I wouldnt say harder to start no, but has been known to refuse to start on hot days.

DerSchlang wrote:There is 1 screw per carb. They are located under carbs, so you have to take them off or use a 90 degree or flexible shaft screwdriver. Tighteen them and rotate 2 turns.

Thanks derschlang I will have a look tomorrow and have a poke about. Im reluctant about removing the fuel tank, let alone the carbs. I dont have any of those fancy screwdrivers either.

alexibrow · Post by **alexibrow** » Wed Jun 04, 2008 9:51 pm

When was the last time you replaced or cleaned the air filter? A clogged filter would have the effect of richening the mixture by virtue of reducing the airflow!

Lean · Post by **Lean** » Wed Jun 04, 2008 9:57 pm

I gave it a bit of a service in feb. It is 33bhp restricted: washers in the carbs. In theory it should not make a difference though, since the amount of petrol that gets pulled through depends on the amount of air passing through the carbs? Thats how I understand it anyway....

alexibrow · Post by **alexibrow** » Wed Jun 04, 2008 10:10 pm

Sorry, can't help you with that one I'm afraid, as I don't know enough about the carbs on the SF. Someone else must know though!

cbr900rrider · Post by **cbr900rrider** » Wed Jun 04, 2008 11:08 pm

The restrictor washers shouldn't be a problem.

If you arn't having any luck with it, and you want to know if its definatly a rich mixture.
Take the plugs out, and have a look see if they are wet, or oily, smelling badly of fuel.
This means your bike is running rich.
(if its not then this isnt your problem)

so clean the plugs up, clean out the air filter, ajust the air/fuel mixture.
If you still have problems, check the float heights.

---------------------------------
Maybe yours is like mine.
my superfour likes to be started in a particular way.

It has a mind of its own im sure.

Press the starter,
blip the throttle so she fires,
then get the choke on full,
keep the throttle open until the she picks up on the choke.
once warm, take off choke and ride.
(even in summer, unless the engine is warm already in which case dont worry about the choke)

Idle mixture

Idle mixture

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