Alpino Idle

R

Rob7

Senior member
Location
Perth, Oz
Just finished rebuilding an Alpino and now trying to get the idle to work. Seen a few posts which seem to indicate this isnt easy!

When dropping to idle the engine exhibits odd characteristics - it first drops to the around 1400 - and then after a short period - maybe 30 seconds or so - drops further to around 900 - 1000 where it sits for about another 30 seconds before stalling (often with a "spit" back through one of the carbs). This is consistent. Otherwise runs fine.

Idle jets set up as normal (both about 1.75 turns out), but what is also odd is that the above happens with the slides fully down - ie - the idle screws are fully disengaged.

Any thoughts?

R7
 
Assuming you're using the stock ignition system.

You need to get the pick-up to rotor gaps as close to equal as you can.  Although the overall timing can hardly be adjusted, the pick-up gap influences the step from retard to advance.  I suspect this is happening first on one cylinder, then the other, then the idle is so slow that the engine eventually stalls.  The pick-ups allow a slight amount of "up-down" adjustment in their locating slots.

An unequal gap will have next to no effect on timing at higher revs, hence the good running.

If using stock pistons and cams, a steady idle should be attainable at around 950-1000rpm.  Engine has too little flywheel to support a slower idle.  Lumpy cams and hi-comp pistons will need around 1200rpm.

Once the ignition side is seen to, you can turn your attention to the carbs.

piet
 
Hi Rob,
From a carburetor angle it could be running too lean.

What size pilot jets are in? Cams? Exhaust fitted?
Turn the mixture screws 3 turns out and see what happens.

Andy
 
Once you've followed Piet's recommendations, set the idle mixture. Your 1.75 turns is just a starting point. There'll be some detailed info on this somewhere on the Forum - Dell's are pretty straightforward to set up.

With regard to mixture the motor must be at op temp. Turning the mixture screw out richens it, turning in leans it. If you have to go more than around 2 1/4 turns I'd be looking at larger pilot jets. A healthy range would be 1 1/4 to 1 3/4 turns out. Sometimes you need to go a further 1/8 or 1/4 turn out beyond highest idle speed setting in order to obtain a clean drop from revs back to idle and also to aid pick up off idle - and eliminate the popping and stalling.
 
Get Mark Muir to come over.. he just loves Dellorto tuning.. :LOL:
Joking of course..
Balance hose fitted..? stops carbies 'fighting' against each other I have found.. buggers to get right, takes a patient hand.

8)
 
No - no balance pipe and nowhere to fit one. Main pain is the non linked slides and having to adjust them individually. After recleaning the carbs, and fitting new plugs, got it to idle around 1100. Pick ups were way to close (almost touching) - bit of a mission to get the clearance.

Idle screws now around 2.25 - i think manual says 2.5 - seems high but works.

Here it is.....OK..... colour is not "correct" - but better completely different than "not quite right"..... :)

Rob


 

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Rob7 said:
No - no balance pipe and nowhere to fit one. Main pain is the non linked slides and having to adjust them individually. After recleaning the carbs, and fitting new plugs, got it to idle around 1100. Pick ups were way to close (almost touching) - bit of a mission to get the clearance.

Idle screws now around 2.25 - i think manual says 2.5 - seems high but works.

Here it is.....OK..... colour is not "correct" - but better completely different than "not quite right"..... :)

Rob
Click to expand...

My parts book shows a blanking screw as standard fitment. Check your carbs, just forward of the mixing chamber on the LH side, accessable from above.  Either a brass spigot or a blanking screw.  If you find only blanking screws, it's a good idea to retro-fit the spigots and connect them with a hose.  Helps a bit with the erratic idling attitude these motors have by ironing out minor discrepancies between the carbs.  Spigots are then the take-offs for vacuum balancing equipment.

Use the slide stop screws to set a fast idle and synchronise that for a start.  Then move on to synchronising throttle movement with the cable adjusters.  When all that is set up, you can fiddle with mixture adjustment.  More than 2.5 turns out from closed calls for a larger pilot jet, less than maybe 1 turn out, a smaller jet.

Setting up Dellortos is a doddle, provided they're not totally clapped out and you have half-decent balancing equipment.  Don't attempt to do it by "feel" or "ear", that will get you only half-way there and can at best, only be considered as a starting point.

Compression OK and even for both cylinders?  Are the valve clearances within spec?  These engines are very fickle in regard to clearances/valve timing.  The more even these are, the better.  I don't bother with carbs until I'm certain the valves are gas tight and set correctly. 

I generally don't like red, but that's nice. (bigthumb)

piet
 
If you rotate that front axle about 30 degrees forward it will idle properly. Great looking bike, I have loved the 500s since my first ever test ride after a service when they first came out, I could easily downsize from the huge SF when I get too old and frail. In my experience with PHF Dells on any bike, they like to be just a tad richer than fastest idle (normally regarded as ideal setting), maybe 1/8 turn more out.
 
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