Alternative Carburettors

[tankstraddler]

Has anyone successfully fitted non-standard carburettors to an early Strada? Mine give me a variety of challenges and I am sure that new, simple and unworn replacements would be an improvement; even a single carburettor serving both cylinders looks feasible and would avoid the dreaded synchronisation problems even if at the (to me unimportant) cost of a small loss of performance. Warming to the topic, does anyone know why the early metal cylinder head stubs were replaced by rubbers? I have heard it suggested that the standard carburettors were unchanged as a result of this modification and were actually designed to fit over stubs rather than fit inside rubbers. Thanks as always to you knowledgeable people.

[EVguru]

Has anyone successfully fitted non-standard carburettors to an early Strada? Mine give me a variety of challenges and I am sure that new, simple and unworn replacements would be an improvement; even a single carburettor serving both cylinders looks feasible and would avoid the dreaded synchronisation problems even if at the (to me unimportant) cost of a small loss of performance. Warming to the topic, does anyone know why the early metal cylinder head stubs were replaced by rubbers? I have heard it suggested that the standard carburettors were unchanged as a result of this modification and were actually designed to fit over stubs rather than fit inside rubbers. Thanks as always to you knowledgeable people.

Alternative carbs have been used. I think the Italian Morini club site has jetting for one of the later round slide Dellortos.

What's wrong with your carbs? Mine are pretty worn but the bike runs very well.

A single carb apparently doesn't work well with wide angle vees due to the firing angle.

The rubber manifolds were used to isolate the carbs from vibration which wears the slide faster than would be ideal. I think the metal manifolds almost certainly flow better and want to modify a set with the insulator plate replaced with a resilient spacer. Early carbs were VHB whilst later were VHBZ with a different manifold fitting. I think NLM have an adaptor for the early carb to match the rubber manifolds.

I'm fussy about synchronisation, but have never found it very difficult and I don't find it drifts if you have one piece throttle cables (or good tight inline adjusters).

[George 350]

Further to what Paul has said,

The 'metal' manifolds were made of aluminium, and the piece that screwed into the head is/was very thin. The result is that the manifold can shear off where it threads into the head. (The threads make excellent stress locations) Mine did this in the middle of France when the bike was less than 15 months/20,000miles old. Fortunately there was just enough thread left on the stub for me to screw it in without the lock ring and get back home.
This was in 1979. My then dealer (Jon Green of Elbymoto) said that he had seen several fail just as mine did, and bizarrely it was always on the front cylinder.(Angle that carb sits at ?) The 'fix' was to fit the rubber manifolds that had been introduced to the electric start models, and they have been on there ever since. These came with a black plastic 'top hat' shaped tube to install in the inside of the carb stub to take up the space where the old manifold used to sit.

As for the carbs wearing out, mine made it to 92,000 miles before I replaced them, with only 3 sets of slides including the original ones. But as I said, the last 70,000 were with rubber manifolds, so Paul could well be right with that.
I thought the rubber manifolds were to aid carbutation by having the float chamber isolatesd from too much vibration, (and being much cheaper to make and assemble) but that is just my thoughts, not a fact.

George.

[tankstraddler]

Thanks for your posts and suggestions, chaps. I will see what I can come up with.