twinport on dellorto problems

[stump magnet]

right over here i can run a dellorto carb on the twinport 250 but am having various starting problems, it would start from cold on choke and when warm would start ok ish but occasionaly would not go at all. plug removed and bone dry so a little fuel poured in the plug hole and away she goes. decided to fit next size up pilot jet at the recommendation of dellorto uk and now it gasses up when starting hot i.e. you have to hold the throttle wide open with the fuel off till it clears which can take ages, what causes this? is it the starting circuit or the float height or is the float needle and seat suspect (its the only thing i havnt checked yet) its a new carb a 34mm phbe and ive stripped it and checked it numerous times its driving me mad!! could it be anything to do with the slide? its a #40 which im told is rich any help out there please thanks

[matcho mick]

i'm running a 34PHBE too,on my ossa,starts 2nd/3rd kick on full choke,runs till starts to blubber,choke off,it's sweet from then!(will not start cold without choke)
you havn't nicked/damage/unseated the choke jets "o" ring,that would cause it to not enrichen,mine a #30 choke jet,not sure what my secondary jet is,spare carby has #50,also has #60 slide,K5 needle,wouldn't have changed the pilot (secondary),as you found it's too rich,concentrate on choke jet setup 1st,cheers 

[stump magnet]

think my starting jet is #60 the slide your running is a #60, how does it respond from a closed throttle? think my needle is the same as yours

[Freakshow]

change to a mukuni

[cheapracer]

I would start by checking/lowering your float height, sounds like it's a bit high or you needle and seat isn't seating very well.

Possibility the floats aren't floating very well or getting slightly hooked up somewhere.

Are you using points still?  It's not always the carby that causes "carby" problems.

[matcho mick]

got the magnifying glass out stumpy  ,my start jets actually a #90(was reading as a disfiguered #30),emulsion tubes AB265,K5 needle,(actually spare carbs needle is K5.5??),#50 pilot,with #158 mainjet,cheers

[tony27]

change to a mukuni

He's not allowed to in the UK

[stump magnet]

change to a mukuni

He's not allowed to in the UK

true im not, its got to be a float problem i think because two meetings ago it wouldnt start after it was warm (starts fine on choke from cold with completely dry cleaned carb) and had a dry plug so bit of fuel down the hole and away she went so replace the #50 pilot with a 55 and now when it starts it a case of buuuurrrrrrrrrrrrrr splutter splutter burrrrrrrrrrrr with the throttle wide open and the fuel off until it clears and then fuel back on and away so ive put the #50 back in and no change still loaded up on start up got to be something wrong with the float height or floatneedle/seat, will investigate, on a seperate note would a leaner slide say #50 or 60 clean up a fluffy bottom end?

[matcho mick]

bit unusuall float height probs on a new carby?,(in 3 years i've run mine don't recall even looking at it )seeing as mine runs a #60 slide & carbeurates cleanly down low,you could try one & see,as an aside i'm running ngk7's,kills cold race plugs stonedead!,( mostly sitting on start line too long),

[stump magnet]

stripped carb last night and found burrs on the cross drillings in the float needle seat this may have been holding up the needle? plus float height was a mile out, incredably easy to accidently bend the very soft tab by moving the floats by hand will give it a try + any danger in using a leaner slide? coz its easier to file an extra 1mm of the cutaway and turn the #40 into a #50 than to pay £40 for a new one?

[matcho mick]

stumpy,usuall precautions mate,set & try the float height 1st before trying the slide mod,40quid!!,ouch,

[stump magnet]

right then, carburation now perfect, it was the float tab. it was cracked where its riveted to the plastic float so the float hight was changing at will.
problem now is some busy bodies over here dont like the dellorto phbe being used as it wasnt available till 1977, they arnt doing anything about it this year but the new wording for next years rules are "original carburetor or that which was available before 1965 with the exception of the mk2 amal concentric" doesnt mention anything about no mikunis or any jap carbs for that matter, all you need to do is to provide proof that the carb your using was available pre 65.
any ideas what was around then that is around now? dont want to use an amal as have tried to make it run on one for years and it doesnt suit that engine.
how long have the mikunis been around? what else could i use, cheers

[09.0]

From what I have been told, Mikuni's were around pre 65 but in smaller versions such as 26mm. I don't think there was a 32mm for e.g.

[tony27]

You may need to do some research into what carbs were used on Suzuki T20 race bikes, anything they used would be close to what you're looking for

[stump magnet]

thanks that will give me somewhere to start