450 and Grey cam question

[graeme]

A question.
I have a 1974 450 Scrambler that has had a bad vibration over 4000 revs in all gears and wasn't very powerful and leaked badly from the centre case gasket.
I bought this bike as a non runner 4 years ago.
Fixed the wiring and sorted the 32mm PHF carb and used it as daily transport.
It started easily and was easy to ride and very reliable. (apart from the above faults)

I dismantled the engine and static balanced the crank
Honed the cylinder which could do with a rebore and a new piston but good enough to last a few years yet.
I had a grey (Gray) cam from a Mach 1 I believe? and swapped that with the standard cam.
Dew-Cat-Tea Bob had suggested the Grey cam should work well with a 450.
It's very hard to start on first start.
All I can get is a put, put, put. But it doesn't start easily like it used to.
I think I have a carb problem so will work through that.
Should I have timed the Grey cam differently to the standard Scrambler cam?
Like an offset bevel key? Or should it just be a swap for the original cam and be a carb fault like I think the problem is?

Regards
Graeme

[double diamond]

The only info I have on the 450 SCR is timing as follows:
Intake open 27 btc, close 75 abc, exhaust open 70 bbc, close 48 atc in. lift:8.2, ex. lift: 8.05

This is identified as a “white” cam and appears to be the same timing as the 250 WC SCR

The grey cam specs are as follows:
Intake open 62 btc, close 76 abc, exhaust open 60 bbc, close 32 atc in. lift:9.05, ex. lift: 8.45

As you can see, the opening point on the grey cam is quite a bit earlier than the stock cam and closing quite a bit later. Did you check for piston/valve clearance? Valve to valve clearance? After determining that the valves are ok, perhaps verify the opening/closing points. You may need to adjust the mixture strength of the starting circuit on your PHF.

Matt

[graeme]

Hello Matt,
Valve clearance is ok.
There is some fuel evident at the carb inlet suggesting that the idle is too rich with choke just on. (float level is about 20mm)
With the same carb settings (I didn't disturb the carb settings from previous) there is evidence that it is way too rich.
Before the engine would fire with half choke then shut the choke and the engine would idle from cold.
Now with the same starting procedure I can only get it to fire after I have shut the choke off but it won't carry on running. Just put, put, put then stop.
Kicking after that no fire. Choke 1/4 on, two kicks, choke off and put, put again.
It feels as if the choke is too rich and with no choke it's too lean?

Ta for your help
Graeme

[double diamond]

HI Graeme,

The PHF doesn’t have a “choke” as such that blocks the venturi of the carb which makes the engine draw more fuel when a richer mixture is required for starting. A true choke can be adjusted to half position, quarter, etc. and affect the fuel mixture. The PHF has a starting circuit, an air passage that is blocked by a piston when closed or opens the starting circuit when the piston is raised, either by a lever on the carb or by a cable arrangement. The starting circuit is either open or closed ; there isn’t a “half” or “quarter” position. Either the starting circuit fuel port is exposed or it’s blocked. The starting circuit fuel mixture is determined by a metering jet in the starting circuit. Dellorto actually has different size jets for this purpose to allow adjustment of the starting circuit mixture. You may need to adjust the mixture provided when the starting circuit is open. But, before you get into that, your PHF has an accelerator pump (providing you still have it installed) that squirts fuel into the intake tract whenever the throttle slide is lifted. If you’re having difficulty getting the engine to start and you’ve been opening the throttle, the result is a very rich condition that worstens with each twist of the throttle. You may wish to disable the accelerator pump while you sort out this starting issue in order to eliminate the rich mixture from the pump complicating your tuning efforts.

Regards,
Matt

[graeme]

Hello Matt,
The carb has a starting system (choke here in the lower colonies) is as you say.
Cable operated piston that opens and allows fuel to be drawn into the inlet.
This can be adjusted to open fully or partially depending on how much the piston is lifted. (to a point)
Pump is disconnected, so not that.

I've had two fires in the exhaust yesterday (backfire) when I tried again to start the engine. I'll check the timing before trying again.
This has the red box and the feeble spark associated with these ignition systems and I haven't checked the timing.

I also admit that I hurt my right knee some months ago and have been kicking with my left leg. So I'm pretty sure my girly kicks don't help.

Graeme

[graeme]

Got it running
The ignition timing was retarded.
Advance the timing and it ran second kick.
Thanks for your help.

Is there any way to static time the ignition with the red box ignition?
I can time it to 28 degrees using a timing light now that it runs. But it seems like trial and error if the engine isn't rotating?
Doesn't seem to be any marks in the pick up at all?

Graeme

[ducwiz]

Good morning, Greame,

ignition timing for the electronic CDI systems from DUCATI and Motoplat is described in the Haynes manual, along with fotos. This manual seems to be still on sale. Both types of pickups are depicted on page 78, and on both have adjustment marks are engraved. Which system is mounted in your SCR?
My 350M3D came with a DUCATI CDI. I haven't adjusted her timing for a long time, but remember the timing marks were only useful as a starting point, final timing had to be done with a stroboscopic lamp and a dial attached to the crankshaft. The markings on the primary cover were unprecise, too. Have you checked yours against a dial?
The timing procedure for the CDIs is also described in the 1974 user manual. If you don't have it, I can send a download link. But unfortunately, it is in italian language.

cheers Hans

[graeme]

Greetings Hans,

I have the Haynes manual, but, there are no marks on either of my 1974 450's that use the red box and electronic ignition.
Once running it's not hard to use a degree wheel and strobe light to set full advance and check that the ignition advances.
Where is the mark on the casing ?

Graeme

[graeme]

Neither of my '74 bikes have the dots as shown in the picture in the manual.

[ducwiz]

Greetings Hans,

I have the Haynes manual, but, there are no marks on either of my 1974 450's that use the red box and electronic ignition.
Once running it's not hard to use a degree wheel and strobe light to set full advance and check that the ignition advances.
Where is the mark on the casing ?

Graeme

The left cover has an embossed dash, as well a point, near the threaded plug covering the crankshaft end, see Haynes manual p. 79. Ducati made a special pointer tool, which could be screwed into the crankshaft's M8 thread (in a position aligned to TDC by a small key fitting into the slot in the crankshaft). At firing moment, the pointer tip for the 450 should should just concide with the dash on the cover. But as mentioned, the tool and markings lacked precision, at least on my engine.

Hans

user manual dl link: http://renato2.bplaced.net/DUCATI/Ducati_2-3-450_M3-D-SCR_CUM.pdf