Ducati 450power delivery problems.

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TerryH
Cucciolo - the Lil Pup
Posts: 1
Joined: Sat Nov 07, 2009 5:41 pm

Ducati 450power delivery problems.

Post by TerryH » Sat Nov 07, 2009 6:27 pm

My 450 desmo doesn't like cruising easily unless it is doing at least 5000 revs in top gear. It runs smoothly everywhere through the rev range in lower gears but won't maintain speed easily until it reaches at least 5000 rpm. The problem is only noticable in 4th. and top gear with the longer gearing and 5th. with the std. gearing. The carburation seems fine and the plug colour indicates the mixture is ok. The final drive gearing has recently been changed to 13/32 from 12/32(std. gearing). Even wth the std. gearing fitted it prefers running at 5000 rpm or better. Obviously this would tend to exaggerate this problem,but over 5000 rpm it seems to pull the taller gearing ok. The engine is fitted with a light aluminium alternator rotor. I am wondering if I am experiencing this problem because of the lighter flywheel. Are the 450's more susceptible to loosing momemtum as a result of using this flywheel over the std. heavier steel item?
The engine is fitted with a 87mm, 10.25:1 wiseco piston and a VEE TWO Desmo cam. The head has been slightly ported and has a 36mmDel Orto carby and a free flowing megaphone exhaust. Can you advise on this problem. Thanks TerryH.

wdietz186
Cagiva Alazzura
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Joined: Sun Sep 10, 2006 5:40 pm

Post by wdietz186 » Sun Nov 08, 2009 9:15 am

Terry, I'm no expert on the big singles but the symptoms you describe seem to point to the cam timing and exhaust tuning.Putting a cam in that has higher lift and more overlap will give you more power but that usually comes at the expense of lower speed tractability.Adding a megaphone exhaust or a system that is shorter/larger dia. will also affect the power output and delivery due to its changing the pressure waves in the system which somewhat control the cylinder filling.It sounds like the changes you have made have biased the power curve to the upper end of the rev range and lowering the overall gearing to keep the revs up is needed

Nick
Diana
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Joined: Wed May 10, 2006 3:40 pm
Location: On da Rock

Post by Nick » Sun Nov 15, 2009 3:18 pm

Most likely the low-speed circuits in the carb are plugged. Disassemble carb, soak in lacquer thinner (not paint thinner, not gasoline, lacquer thinner) for about 30 min. then blow out with high-pressure air. while it's apart, confirm that the jetting is what the manual calls for.
From probably the only person in the world who rides a Ducati 350 Sebring for daily transportation.

bobnorton
860 GT / GTS
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Joined: Wed Jan 16, 2008 2:18 am
Location: bromley kent

Post by bobnorton » Mon Nov 30, 2009 12:54 pm

The 450 was always thought to be a bit under flywheeled, and any tuning is likely to worsen the tractability.

Nick
Diana
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Joined: Wed May 10, 2006 3:40 pm
Location: On da Rock

Post by Nick » Mon Nov 30, 2009 7:41 pm

Putting a 'dam' in the exhaust pipe just downstream of where the header pipe enters the head may improve your lower-end performance considerably. Assuming the carb and timing, etc. are within spec., you probably have a negative pressure wave traveling back up the pipe, arriving at valve overlap and messing up the flow through the head at lower rpm. This problem is so common on tuned 4-strokes that it has a name: 'megaphonitis.' This refers to stumbling performance at low rpm and then a hard hit as the engine comes 'on the cam' at high rpm. Hard to explain without a drawing, but you need to weld a small lip around the lower half of the header pipe just downstream of the exhaust port. Another way is to cut the pipe, then push the cut section inwards, then weld a small plate in there to fill up the whole. This is also standard practice on racing Ducatis and BSA Gold Stars, etc. but you can't see it from the outside. That innocent-looking weld on the header pipe often conceals a very sophisticated bit of technology.
Your other alternative is to use a milder (stock) camshaft and smaller-bore carburetor. The milder cam will reduce valve overlap, and the smaller bore carb will increase intake velocity at lower rpm, improving low-rpm performance.
I remember riding a very pretty and very noisy 450 a long time ago and being astonished at what a dog it was. My mildly modified Sebring had far more performance. Cured me forever of wanting a 450.
You might just try a smaller bore carb and see what happens. Another easy test would be to put a temporary 6" extension in the exhaust pipe, as this will change the timing of the negative pressure wave, perhaps causing it to arrive at the exhaust port after the exhaust valve has closed.
From probably the only person in the world who rides a Ducati 350 Sebring for daily transportation.

Ray O'Donohue
Parallel Twin
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Joined: Tue Oct 13, 2009 8:11 am

Post by Ray O'Donohue » Tue May 04, 2010 1:00 pm

To all the above suggestions,I would add: You may be way too rich at early throttle openings;that is,the slide cutaway size,and the needle/needle jet settings.The first and easiest thing to try is to drop the needle down to full lean and see what happens.You have a huge cylinder,and a (fairly)small carb,so your vacuum signal is very strong at part throttle.

maurice
Cucciolo - the Lil Pup
Posts: 5
Joined: Mon Jun 14, 2010 8:18 am
Location: UK

450 issue

Post by maurice » Fri Sep 03, 2010 6:21 am

I run a 450 desmo with 40mm pumper, conti mega, flowed and twin plugged and the V2 cam, Lucas Rita as ducati ignition is crap and the advance is inconsistant!, (could be part of the issue) 86.6mm 900 desmo piston, also 18/36 narrow chain gearing.
Mine carburates perfectly with no step, lots of torque-all down to lots of carb tuning time!

bobnorton
860 GT / GTS
Posts: 281
Joined: Wed Jan 16, 2008 2:18 am
Location: bromley kent

Post by bobnorton » Fri Sep 03, 2010 9:50 pm

It could be worthwhile (after alterations) putting the bike on a dyno for emission checks at various throttle positions, If you mark the twistgrip with the carb phases it will help set up the fueling..

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