"Up-propping" and idle adjustment

[HughN]

If "up-propping" is a real word, that is what I am doing - going up an inch and three-quarters in pitch. For the purposes of testing it, am I likely to need to play with the idle speed?

I don't have a 'fast idle' lever to play with and obviously want to avoid the engine stalling when I put in gear.

Its an ex-contract 30 hp Mariner-badged Yamaha (originally fitted to the Ark).

Thanks!

[Nos4r2]

Inch and 3/4 ? That's an odd amount.

No, dont' touch the idle speed.

[HughN]

Originally Posted by Nos4r2

Inch and 3/4 ? That's an odd amount.

It's replacing a Piranha plastic prop that I inherited with the engine. The sizes seem to be based on hat sizes!

[Nos4r2]

In which case, don't expect the plastic prop to be any benchmark for pitch-they slip like mad in my experience.

[HughN]

Uep. Like driving on ice.
The 'new' prop is a 'free' one so it might be a starting point.

[Festinghouse]

on that engine does turning the choke knob not adjust the idle speed? im guessing its a 2stroke? my merc 25 used to have a choke that pulled out but also rotated for idle speed.

[Nos4r2]

Originally Posted by Festinghouse

on that engine does turning the choke knob not adjust the idle speed? im guessing its a 2stroke? my merc 25 used to have a choke that pulled out but also rotated for idle speed.

That'll be idle mixture not speed, and it's a bad idea to mess around with it. Later motors don't hve the feature because people played with it, not knowing what they were doing.

[bartiny]

Might be a starting point, check engine model matches first.

[Dav9790]

Originally Posted by Nos4r2

That'll be idle mixture not speed, and it's a bad idea to mess around with it. Later motors don't hve the feature because people played with it, not knowing what they were doing.

Just to let you know the old merc 25's with that know that pulled out and turned actually adjusted the timing to give the engine more rpm and was only used for starting from cold.

[bartiny]

Sorry missed this bit off

[Nos4r2]

Originally Posted by Dav9790

Just to let you know the old merc 25's with that know that pulled out and turned actually adjusted the timing to give the engine more rpm and was only used for starting from cold.

I stand corrected-thanks

[HughN]

Originally Posted by bartiny

Might be a starting point, check engine model matches first.

Thank you. That was indeed my starting point - it just took a bit of time to find one of the right size and that was going begging.

[bartiny]

Originally Posted by HughN

Thank you. That was indeed my starting point - it just took a bit of time to find one of the right size and that was going begging.

What I meant was check the model number matched on the manual that I posted then you could get an idea as to prop pitch etc against the chart.

[9D280]

Idle speed wonlt change as it;s still just turning the vertical shaft, not the pro[p.

What you might find is when you try to open the throttle it stalls. This is becauss rhe idle mix is too lean to provide enough grunt until the main jet starts doing anything useful.

Easiest bypoass for ta test - blip the cholke as you open the throtlle. That gives you a wee bit more fuel when you need it. If you then stick with that prop, can adjust the idle mix to suit

[uncle al]

with those obms, it is better to run slightly to rich than slightly to lean.Dont forget tickover is usually at a certain timming and revs, also with W.O.T. (wide open throttle) also the propeller is the govener for the engine, to highrevs at W.O.t.is just as damaging as to few ie having a to bigger pitch propeller so that the engine wont reach its proper rev range,good luck and a merry christmas and a happy new year people.

[HughN]

A cunning plan it may have been but the prop doesn't fit - it fits the splines but the hub doesn't touch the thrust washer and there is about 15mm of unthreaded shaft at the other end. Buy cheap, buy twice!

(I think a proper one will be on my Christmas list )