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Hi

Giving my carbs a rinse through prior to ordering some bits and noticed that one carb has an O ring on the idle needle, the other doesn't. I then checked on a set i pulled off a Laverda (fitted Mikuni's) and no O rings?

Am I right in thinking it's a go buy an O ring answer, the idle screw is the one with a shoulder.

Regards

Kevin

I've run them with and run them without the O-ring.

I've not found it to make any noticeable difference. Probably best to run both sides the same though.

Hi, there should a washer between the O ring and the spring (idle and pilot jet screws). Sometimes they both stick in the hole and it looks like there is no O ring or washer in there.
There are problems with the running if the O rings are old and hard (as with the starter jet O ring) and need to be replaced from time to time.
Trust this helps

Hi, yes they were hidden in the hole behind the washer! they look pretty old so will replace along with the choke ones, thanks for the replies

And here is a picture! Not sure about the gold wheels and black exhausts with the paint scheme, it came as an import some time back, i have since removed the Tarozzi risers and replaced with black 35mm clip ons, risers available if anyone wants them

I think the colour scheme is fine - it's of its era.

Looks very nice to me, have fun.
Regards Pete.

What I meant about the colour is that I had one of these new in 1984 from Jack Lilley in Shepperton, it had grey wheels and chrome pipes - never saw one like this

kainsworth wrote:What I meant about the colour is that I had one of these new in 1984 from Jack Lilley in Shepperton, it had grey wheels and chrome pipes - never saw one like this

... perhaps that was a Wednesday model?

'It must be a .....' wrote:There are problems with the running if the O rings are old and hard (as with the starter jet O ring) and need to be replaced from time to time.

The majority of Dellortos I've serviced have not had an O-ring fitted to the mixture screws and ran perfectly fine.

I've done ABA testing, that is test condition A, test condition B and then revert to condition A.

The simple act of removing a mixture screw to replace an old O-ring may fix a fault. Only by re-fitting an old O-ring and having the fault come back, can you demonstrate that it was actually the cause.

As far as I've been able to tell, the only purpose of the starter jet O-ring is to hold the float bowl in place when the main jet holder is removed. The jet is fed from the lowest point in the float bowl, so having the O-ring seal the jet to a length of submerged passage is unlikely to have any effect. I've left the O-ring out on a number of occasions with no apparent difference.

Hi Paul, my experience with Dellortos is primarily with 26/28 mm PHBH carbs fitted to 500/507 engines and they have all (11 bikes) had O rings fitted. I've found some starting and running issues are often due to hard/old O rings; but mostly due to the pilot/air screw O ring.

I agree that the starter jet helps to locate the float bowl and I replace the O rings when they are no longer tight in the float bowl; I appreciate your logic yet from experience they do have an effect on the efficiency of cold starting.

Surely as the O rings are not much money it is best to replace them once they get hard and no longer provide any real function?

Take care, regards Ian

'It must be a .....' wrote:Hi Paul, my experience with Dellortos is primarily with 26/28 mm PHBH carbs fitted to 500/507 engines and they have all (11 bikes) had O rings fitted. I've found some starting and running issues are often due to hard/old O rings; but mostly due to the pilot/air screw O ring.

That's called conflation.

You changed the O-rings, which required removing the idle screws and the problem was solved. Was it changing the O-rings that cured the problem, or simply removing and replacing the screws? Have you ever put the screws back in without O-rings?

Yes, the O-rings are cheap, but what I'm trying to get across is a methodical system based on evidence and not a Cargo Cult approach. Often this replacing of parts gets really confused and expensive.