Italian Tune up suitable revs for my 4108

[pcatterall]

Thanks all for the hints on clearing the engine out via the ,Italian tune up method' ( apt as we are in Sardinia)

Our cruising revs over the last 2 years have been 1500 to 1700 revs which give us 5 to 6 knots on a calm sea. We get around 0.4 gallons per hour. Perhaps this has been too low and that 1800 to 2000 would have been better.

Anyway question is what sort of revs do I need for this 'tune up' Reading your previous replies I reckon this would be 15 to 30 minutes.

Does the engine need to be under load for this.

Many thanks

 

[sailorman]

Wide Open Throttle underway, that should be around 3k RPM if it is like the one i had

 

[Tranona]

Sounds like you are grossly over propped. The 4 108 had different ratings, so you need to find out what yours is rated at and at what max revs. The "tune up" is running at max revs under load - so get in some clear water and open the throttle wide and see what revs you get. don't do it without load as it will just rev to whatever the maximum is set by the governor.

The optimum cruising speed should be at around 65-70% maximum power. Your engine is probably rated at max 3000 rpm so you should be running nearer 2000 than 1700 for your 6 knots and should be able to get just over 7 at about 2800. Note - these are sort of guesses, but won't be far out.

 

[prv]

How many revs?

All of them!

Pete

 

[Marsupial]

Sounds like you are grossly over propped. The 4 108 had different ratings, so you need to find out what yours is rated at and at what max revs. The "tune up" is running at max revs under load - so get in some clear water and open the throttle wide and see what revs you get. don't do it without load as it will just rev to whatever the maximum is set by the governor.

The optimum cruising speed should be at around 65-70% maximum power. Your engine is probably rated at max 3000 rpm so you should be running nearer 2000 than 1700 for your 6 knots and should be able to get just over 7 at about 2800. Note - these are sort of guesses, but won't be far out.

+1 Italian tune up is reckoned to be 75 - 80% of maximum rpm but for a long period - at least a couple of hours

4/108 max revs is 3600 so @80% 2880rpm, very important: keep monitoring exhaust temperature if you don't normally use the engine like this.

 

[sailorman]

+1 Italian tune up is reckoned to be 75 - 80% of maximum rpm but for a long period - at least a couple of hours

4/108 max revs is 3600 so @80% 2880rpm, very important: keep monitoring exhaust temperature if you don't normally use the engine like this.

No, over 4k when rated @ 48hp

 

[prv]

+1 Italian tune up is reckoned to be 75 - 80% of maximum rpm but for a long period - at least a couple of hours

That's not how I understand it.

Indeed, 80% of max was the recommended cruise for our last boat.

The one time she needed it, I gave 20 minutes at the maximum revs the engine would offer under way (ie, pushed the throttle to the stop and kept it there). A fair bit of black smoke to begin with as the carbon burnt off, then the smoke reduced and disappeared and the engine ran smoother and cleaner thereafter.

Pete

 

[Buck Turgidson]

Agree with prv. Max chat for half an hour keeping an eye on temps. If you aren't getting max rpm you are either over propped or have friction problems. The idea is to blow out the carbon at the expense of some high wear.

 

[macd]

I'm pretty sure Vyv Cox, who's written a fair bit about this, suggests 15 minutes at max available revs. Regardless, to use prv's experience in post #7, once the smoke's gone, the tune has done it's job so you can resume pottering with a glass of chianti. (Unless, of course, the engine's over-fuelling, in which case it'd smoke forever.)