Hi

I have recently purchased a 1989 Tr34 Campionato. The carb has been changed from the original dellorto PHBH26TD to a Mikuni VM26 (I'm unsure if it genuine or a copy). The bike runs ok at low speeds through sections but when the throttle is opened up for a climb or the tackle a larger obstacle it seems to bog down. Checked the plug and it is black and sooty.I have stripped the Mikuni and checked it over, the plan was to put a rebuild kit in it but soon found that the pilot and main jets have been messed with. For example the main jet said it was a #87.5 but it was way bigger than that. like wise the pilot has been increased in size over the stated #20. This was done by comparing with new jets I had.

I believe in or around 1990/91 Beta fitted a Mikuni VM26-208 carb to the bikes instead of the Dellorto so i would like to know if the VM26-208 carb is available (I can only find a VM26-606)and what is the difference between the 606 and the 208? Or would I be better off getting a new Dellorto PHBH 26SD as an alternative?

Thanks in advance

i have found that sizes can be different in between different manufacturers when the number is the same ,but someone could of filled them bigger ,, it could be running rich at low revs blackening the plug and lean top end causing the bogging down unless fuel level is low in bowl , i would start with some new jets in the mikuni of correct size maybe see what sizes are used on later bikes with mikuni like a zero or techno , a faulty stator could give similar problems ie if low speed coil ok and hi speed coil is faulty this would also cause black plug as fuel will not burn correctly ,,does it rev up ok stationary ? does the choke make any difference

Beta used the same VM26-208 carb up to 2007 with a brief experiment in '95 using the DelOrto. Any dealer should be able to hook you up with a new one but they are not cheap. Stock jets on the later bikes were 30 pilot and I believe a 145 main. Your needle/jet slide may be different too if this was pulled off some other bike and "retuned" for the Beta.

i have found that sizes can be different in between different manufacturers when the number is the same ,but someone could of filled them bigger ,, it could be running rich at low revs blackening the plug and lean top end causing the bogging down unless fuel level is low in bowl , i would start with some new jets in the mikuni of correct size maybe see what sizes are used on later bikes with mikuni like a zero or techno , a faulty stator could give similar problems ie if low speed coil ok and hi speed coil is faulty this would also cause black plug as fuel will not burn correctly ,,does it rev up ok stationary ? does the choke make any difference

Thanks for the reply. Your comment about the ignition has been in the back of my mind too. The bike has the original Motoplat system fitted and I have read that its a good idea to change it to the later Ducati ignition. The bike does seem to rev out while stationary albeit a bit slowly and with a little smoke but only what i would expect from a bike of this age. The choke doesn't seem to make to make a great deal of difference when operated while running. I think I will get the correct jets and go from there.

Beta used the same VM26-208 carb up to 2007 with a brief experiment in '95 using the DelOrto. Any dealer should be able to hook you up with a new one but they are not cheap. Stock jets on the later bikes were 30 pilot and I believe a 145 main. Your needle/jet slide may be different too if this was pulled off some other bike and "retuned" for the Beta.

Hi Dan

Thanks for the info on the jets, I'm going to order some today:-)