Airone 250 Sport

[Phil Macdonald]

Looking for some inspiration/thoughts in trying to find the missing 15 mph on my Airone. It has had new bearings, crank, conrod, piston rings, valve guides, valve springs. Fitted with the correct SS1 25mm carburettor, sport cam (M2544bis) and MCR4E magneto. It's got good compression, is sparking at 39 degres BTDC at full advance but refuses to run faster than 55 mph. It feels like it would rev out in the lower gears but just runs out of go in top gear. I'm running out of things to check. Anyone got any thoughts?

Phil

[Richard Wood]

Hi Phil, my 9.5hp (when new) 1945 model barely reaches 50 mph (accurate GPS speed) with a tail wind. Don"t believe the factory quoted top speeds despite the bigger carb and compression. Top gear is a big step up from 3rd BTW so it will always rev out in the lower gears.

Richard

On Mon, 22 Apr 2024, 12:27 Phil Macdonald, <philmac.c...@gmail.com> wrote:

Looking for some inspiration/thoughts in trying to find the missing 15 mph on my Airone. It has had new bearings, crank, conrod, piston rings, valve guides, valve springs. Fitted with the correct SS1 25mm carburettor, sport cam (M2544bis) and MCR4E magneto. It's got good compression, is sparking at 39 degres BTDC at full advance but refuses to run faster than 55 mph. It feels like it would rev out in the lower gears but just runs out of go in top gear. I'm running out of things to check. Anyone got any thoughts?

Phil

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[Roger Rowland]

A thought, Ducati 900ss bevel advance is 6BFTDC to 38 AFTDC this is two five hundreds with fairly high tune Desmo heads. Should an Airone be 39 ? My GTS went better than many others back in the day partly because I found the cable joint box brass thing to be too long, turning 1mm off the face suddenly the carbs were fully open! Are you sure the slide it wide open right to the stop ? On that issue see many articles about resleeving carb slides on my Falcone the groove on one side is a very slack fit on the other completely open, the cable open fit and no seal on the cap. Once the throttle stop screw fell out and the bike ran fine ie with an open 6 mm hole so that indicated that a precision fit slide was ? Fuel mixture at high speed is it right ?

Regards Roger U.K. 

Sent from my iPhone

On 22 Apr 2024, at 12:27, Phil Macdonald <philmac.c...@gmail.com> wrote:



Looking for some inspiration/thoughts in trying to find the missing 15 mph on my Airone. It has had new bearings, crank, conrod, piston rings, valve guides, valve springs. Fitted with the correct SS1 25mm carburettor, sport cam (M2544bis) and MCR4E magneto. It's got good compression, is sparking at 39 degres BTDC at full advance but refuses to run faster than 55 mph. It feels like it would rev out in the lower gears but just runs out of go in top gear. I'm running out of things to check. Anyone got any thoughts?

Phil

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[Andrew Nahum]

I’ve had two Airones.  One (1955?)  exceeded 70 mph quite easily and would hold that speed without getting bothered.  The second, which I still have, struggles to get past 60.   I cant explain it.  But since I keep it in Suffolk UK for the country back  roads I’m perfectly happy with the performance and I’ve finally reached the age where if a bike starts and goes reliably I’m happy.  Pietro di Marino did tell me to check if silencer was clogged or choked, and he knows a lot.  So far I haven’t tho.  Both had the SS carbs. 

On 22 Apr 2024, at 12:48, Richard Wood <rcw...@gmail.com> wrote:



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[vanuss...@gmail.com]

Did You use a sport piston? (domed)  Have You a copper ring between the head and cylinder? Lower compression ratio will cause loss of power.

Any good Airone sport will do 70 mph easily. I use special pistons giving higher C/R  to get more.

Op maandag 22 april 2024 om 14:49:33 UTC+2 schreef andrew...@googlemail.com:

[Rick Yamane]

In addition to what others have said, it sounds like you just rebuilt the engine. Is it broken in yet? I don't think it would make a 15mph difference but in combination with another factor or two it just might.
Cam timing might be suspect too.

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From: guzzi-...@googlegroups.com <guzzi-...@googlegroups.com> on behalf of Phil Macdonald <philmac.c...@gmail.com>
Sent: Monday, April 22, 2024 4:27 AM
To: Guzzi Singles <guzzi-...@googlegroups.com>
Subject: [guzzi-singles] Airone 250 Sport

 

Looking for some inspiration/thoughts in trying to find the missing 15 mph on my Airone. It has had new bearings, crank, conrod, piston rings, valve guides, valve springs. Fitted with the correct SS1 25mm carburettor, sport cam (M2544bis) and MCR4E magneto. It's got good compression, is sparking at 39 degres BTDC at full advance but refuses to run faster than 55 mph. It feels like it would rev out in the lower gears but just runs out of go in top gear. I'm running out of things to check. Anyone got any thoughts?

Phil

[Phil Macdonald]

Thanks everyone for your thoughts. Some more clarification - I have just rebuilt the motor so there may be an element of 'running in' needed (although I suspect it's only the rings). I set both the cam timing and static ignition from scratch (no timing marks on the cam or mag gear!) as per the manueal 55mm and 20/21mm BTDC respectively. I think it's unlikely that I've got a whole tooth out on either and have both checked several times. I've checked the exhaust and can't see any signs of it being partially blocked. I have been suspicious of the slide not being fully retracted in the carburettor and have removed it once again for checking. To get the very last of the engine side of the the slide to disappear comes up against the spring becoming coil bound. I'll have a further play with it tomorrow. The spark plug looks a reasonable colour (lightish brown) after a decent run. It definitely has a sport piston fitted (the one with valve cutouts) but I did fit the copper head gasket so this may have lowered the comprssion ratio slightly. I'll try everything else before I remove the head and remove the gasket.

Thanks once again. I'll let you know if I get an eureka moment!

Phil

[John Moody]

Mine gets up to 55 mph not to bad but takes a while to creep up to high 60s but took a while to get used to the slow throttle ..you need to get the revs up in each gear ...also had an issue with weak clutch spring and once replaced and adjusted made a lot of difference .

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[Jeff Buick]

Are you running an air filter or is it an open velocity stack? On my V7 sport I had tried to fit an air filter that was too restrictive and it would run out of juice in the higher RPMs. I didn’t notice it in the lower gears as much because I went through that engine speed quickly. Also, make sure your petcock isn’t clogged.  Lastly, have you verified cam timing?  

Good luck!

Jeff Buick

Michigan

On Apr 22, 2024, at 7:27 AM, Phil Macdonald <philmac.c...@gmail.com> wrote:



Looking for some inspiration/thoughts in trying to find the missing 15 mph on my Airone. It has had new bearings, crank, conrod, piston rings, valve guides, valve springs. Fitted with the correct SS1 25mm carburettor, sport cam (M2544bis) and MCR4E magneto. It's got good compression, is sparking at 39 degres BTDC at full advance but refuses to run faster than 55 mph. It feels like it would rev out in the lower gears but just runs out of go in top gear. I'm running out of things to check. Anyone got any thoughts?

Phil

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[Roger Rowland]

Suspect the measurement method has been used since Stonehenge was built, personally I cut a larger hole in a timing disc and stuck it to the flywheel with Blue tack then used a strobe. Think the “sport cam” has significantly different valve timing as you sure it’s a sport cam ? 

Regards Roger U.K. 

Sent from my iPhone

On 22 Apr 2024, at 19:41, Jeff Buick <jeff...@comcast.net> wrote:



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