Engine cutting out from full throttle to idle

[Paul1098]

Yes, I'm finding that out.
It's good to learn and do stuff yourself which is slightly easier on older bikes compared to the modern stuff where you need software to talk to the various ecu's.
I'm scrabbling round the garage looking for tools that i've not used for the last 30 years ever since I stopped playing with mini engines.

[Jordan]

Royal Enfield big singles used the same type of decompressor valve as on Ducati R/T 450.
They were also popular as aftermarket fitments on two stroke trail bike in the 1970s, where they were used for engine braking effect.
Some of these bikes, especially from Spain, had a 2nd spark plug hole.

[Duccout]

Hi Paul,

You do not need to use a degree wheel to set the piston back to the correct position; as Ian say's, turn the crank until the piston is at the bottom of the stroke, NOTING WHICH WAY YOU TURN THE CRANK, then rotate the crank the opposite way to bring the piston back to the starting point. If you do lose the timing it is not the end of the world, you would need to take off the timing cover and realign the lower timing gear dots.

I would say that a fuel additive is essential - when I bought my 250 from Spain both valves had the seats eroded away and were so thin they were like knife edges, which I believe was caused by running with unleaded fuel.

Colin

[Paul1098]

Hi Colin,

What additive do you use?

Photo's of the exhaust valve, is the pitting normal as I've not seen that before but I've only dealt with SS valves.

20240723_172004.jpg

20240723_171907.jpg

Cheers
Paul

[Duccout]

Hi Paul,

I'm not an expert, but I would say that the pitting is not normal and is possibly the result of excessive heat. No valve in an engine of mine has looked like that and I am wondering if the valve has been held off its seat, possibly by the inaccurate grinding of the desmo camshaft? The early desmo cams were notoriously poorly ground and I have read of NCR cams fitted to the belt drive engines that held the valves off the seats. It is important to check both opening and closing clearances all of the way around the cam lobes in case there are tight spots.

Eldert, are you around? What is your opinion?

I have always used Castrol Valvemaster Plus as it came top in a comparison carried out by the Federation of Historic Vehicle Clubs. It seems to work, but all three of my old Ducatis produce strange deposits in the inlet port these days which I blame on modern fuels.

Keep us informed,

Colin

[Paul1098]

Hi Colin,

I'll look at getting some Castrol Valvemaster plus.

I didn't think the pitting looked normal, be interesting to hear what a bevel expert thinks.

Cheers
Paul

[blethermaskite]

That valve looks pretty over heated to me, and is not in a normal condition, not to be controversial but I don't use any additives just straight super unleaded, there is 50 years and 50ish thousand miles on my mk3 350 its been thrashed most of its life and my ex valve does not look like that. I think the last ex valve I dealt with like that came out of a 1940s Morris 8 side valve lump with many many un serviced miles of neglect on it.
Cheers,
George

[Paul1098]

Hi George,

You've corroborated what Colin has said so this might be the time for me to step away from doing anymore and hand engine over to an expert for a top end refresh as I can also feel movement in the guides and don't have facility to replace guides and re-cut seats.
Haven't managed to measure side play between valve and guide but I assume if you can see movement then it's probably too much?

I was hoping for a quick turnaround and get the bike back on the road for the rest of the summer and sort it in winter but that's looking less likely and I suppose that could maybe cause more problems.

Cheers
Paul

[Duccout]

Hi Paul,

Guide wear is one of those areas which an experience mechanic can assess by feel - there will be some movement with the valve off its seat, but not much. Whereabouts in the country are you? There are a few good engineering shops around who can handle this work, but actual Ducati repairers are almost extinct now, although I suppose a modern Ducati mechanic should be able to do the work.

The old experts are retiring - I think that Richard Walker is long gone, as is Anthony Ainslie, and Paul Klat has retired; and I think that I recall that Nigel Lacey is not doing much head work now, or perhaps only racing work.

Colin

[Paul1098]

Hi Colin,

I'm in North Yorkshire but close to Middlesbrough. This area is a bit like a desert when it comes to bike or Ducati related places.
I do know of one bloke that could do it but he's in Europe for 2 months so not much use now.
Craig at CMR is probably the closest Ducati Bevel man to me but he's 120 miles away although I bet they get post even in Lincolnshire so I could send the head to him.

Cheers
Paul