carburation - off/on

[Harry44]

Incorrect mixture has the effect of slowing combustion, so in a way mimics retarded ignition timing.

Myself and several others have had problems with new carbs that are jetted for leaded fuel and run too lean on modern ethanol fuels.

I suspect that older carbs have worn jets that may balance out the effects of modern fuel.

[StephenG80]

Thanks for that Harry44! and yes the symptom is similar to timing being fully retarded now I think of it - OK, got my head round that and now understand the "why".

Mick D - Engine is fine when accelerating - just "stutters" or not smooth when feathered and A/R is manual- thanks .

AJScomboman - well what can I say - if you have to ask, you'll never understand -

Happy riding everyone.

Stephen

[Mick D]

Hi

OK, so feathering in my head means closing the throttle, and in your case I guess you mean slightly - if this is the case then your problem is more likely to be a weak mixture. Closing the throttle weakens the mixture even further and the engine speed has to reduce before reliable combustion can take place, hence the 'stutter'.

Regards Mick

[StephenG80]

Hi Mick,

It may mean different things in different circles but I was meaning just keeping the engine at the point of still pulling, very very slightly, as opposed to the engine de-accelerating, so human "cruise control" with very light, ie "feather light" throttle adjustments if you like ie "feathering". However due to the "stuttering" it means I either have to be slowing down or speeding up slightly, ie opening or closing the throttle but larger amounts, which is a bit tiring ie on or off and no inbetween.

As when the throttle is closed fully there is no popping at all, makes me think the mixture is too rich, which after Harry44 advice, makes me think this causes the flame front to accelerate slower (ie less O2 in the mix than optimum) which has the same effect of retarded ignition.

I'll have a play and let folk know how that goes. Thanks for your further contribution to this thread - are you going out on your bike today ?

S

[Janet]

Just drop it down a gear and rev the nuts off. It'll be fine.


This is a public service announcement: That may not be good advice but it should show up the cause of the problem. Then you'll need to know where to get the replacement parts.

[Mick D]

Hi

Sounds as if your mixture may be too weak - try raising the needle a couple of notches an see what effect that has.

If the mixture was rich grabbing handfuls of throttle would cause the faltering you describe - ie the opposite to what you have..

Regards Mick

[StephenG80]

The "grabbing handfuls of throttle" was referring to what I can do at 60 plus- not problems at that end - she flies, sweeps past 70pmh with gusto! - The issues I am trying to resolve is when in "pottering/taking it easy" mode.

S

[dave16mct]

Do you have an SR1 mag with auto advance?
Dave.

[StephenG80]

Hi Dave16mct,

No, its NI manual A/R, all timed up properly, points gapped properly and "sparkvada" also gapped properly

[g80csp11]

Mark up your throttle to see what % throttle the problem occurs
Then read and understand the tuning instructions
it's most likely that cut out may need adjustment from standard

As you rightly say , ignition correct and generally running well points to a set up problem


http://www.britcycle.com/Manuals/MonoblocTuning.pdf