MY 199cc Cub is fitted with a 22mm Dellorto carb of the type supplied for the Triumph Cub so presumably correctly jetted but I think it runs a bit rich on the pilot jet, with no reference available that I can find I hope someone can suggest the preferred jet and slide combinations please?

Edited June 28, 201511 yr by trialsrfun

Think Black cat cub Tony in Usa runs a Dell on his immaculate Cub. Hopefuly he'll be along in a bit to help you out.

You shouldn't be too far of with this:

40 slide

D40 needle on middle clip

BZ260 atomiser

35 pilot

105 or 110 main

60 choke

I bought mine direct from Eurocarb when Serco went tits up, I just asked them to supply me with what they supplied them!

You shouldn't be too far of with this:

40 slide

D40 needle on middle clip

BZ260 atomiser

35 pilot

105 or 110 main

60 choke

I bought mine direct from Eurocarb when Serco went tits up, I just asked them to supply me with what they supplied them!

Thank you for that.

The carb I have is jetted similarly but the plug is getting a black coating which causes rough running and loss of tick over, fit a new plug and all is good again. Ignition is PVL from Alan Whitton.

Might the carbs we have be jetted to suit the 250 Cub engines that Martin specialised in?

A 35 pilot jet would be a large size if fitted to a Mikuni or Amal Concentric fitted to a 250 2 stroke.

Edited June 29, 201511 yr by trialsrfun

Are you sure there is no oil getting into combustion?

I had similar issues and it turned out the inlet valve guide was shot.

It was odd as it's better known for the exhaust one to go.

BTW, it's a 40 pilot that most supply for cubs.

Edited June 30, 201511 yr by goudrons

If it were worn guides would that produce smoke as it seems to run quite cleanly.

Is there any way of testing for worn valve guides, is both valve and gude replaced as a pair. Are quality replacements readily available?

As mine was leaking from the inlet guide, it spat oily gunk into the inlet track and mouth of the carb, it didn't smoke up either like I expected., just fouled the plug and idled lumpier and lumpier.

 

To repair I bought the largest guide I could and turned it down to fit tightly.

Cut a new valve seat and lapped a new valve in.

Think I might have fitted new springs as well.

 

If you are sure the engine is in good nic and it's still fouling plugs it'll be worth rechecking the timing, methinks I set mine around 3mm before TDC even thought it's always written it should be 5mm.

 

Then perhaps buy a set of jets and spend a bit of time trial and erroring, sets of pattern jets are available quite cheaply.

 

Write down all your starting setting/jets and change one thing at a time.

Time and space are needed, it can be quite frustrating, mine was road legal, well sort of, so it was easy to run it up and down the road while altering things.

 

There are plenty of guides around the net on carb tuning, but remember, chasing perfection can often be futile, tunings carbs is always a bit of a compromise.

 

 

 

Thank you for the above info.

I will check for oil in the inlet as well as the other things suggested.

Having previously stripped the carb without finding a problem I once again dismantled it but this time noticed petrol in the right hand side float, so hopefully when the replacement arrives it will solve the Cub carburation issues.

Thank you for your help.

Just for interest, the float in the carb is made from a cream/grey opaque plastic material, the new ones apparently from closed cell foam black in colour so worth keeping a check on your Dellorto float.