7 replies to this topic

[Mini-Hazel-Nut]

Ello all and happy newish year. My classic hot rod is now 99.99999% finished and will take to the tracks on March 3rd. I fitted the race head last week and had to buy a hi-torque starter as the standard job couldn`t handle the comp ratio. As soon as I did that it whizzed round and started and runs lovely but - but on the pick-up it sometimes hesitates and spits back violently through the Dellorto carb. Bearing in mind that it hasn`t been on a rolling road yet what is the most likely cause of the spitting please?  PC311745 resize.jpg   55.14K   0 downloads

[hhhh]

Most likely lean. When I put a 12G295 on my 998 I had the same issue with my HS4. You can try pulling the enrichener to see if it stops it.

[Mini-Hazel-Nut]

Thank you for that. When I bought the carb it was described as being "sensibly jetted for a 1275" but I found it to be a bit rich with the 190 jets. I bought 150 and 170 jets and fitted the former. I`ve gone from rich to lean it seems so I`ll try the 170s as a compromise. Thanks again.

[hhhh]

Dellortos have replaceable idle jets and emulsion tubes like Webers right? If so, I'd try changing out those, assuming the numbers above are referring to main jets.

[minimans]

Save your money buying jets you may not need and get to the dyno, there are many things that could cause hesitation and spitback. your problem is at "tip in" probably not mains anyway.

[hhhh]

I was reading the scriptures last night (Vizard) and he gives guidelines for choosing starting point main jets for chosen venturis. I would suggest that approach. Going from 190 down to 150 represents around a 6 or 7 mm change in corresponding venturi if I remember right and is quite drastic.

[Mini-Hazel-Nut]

I put the 170 jets in and retarded the ignition just a tad and the pick-up is much better and healthier sounding. I now there are many more things to consider within a Dellorto (same as Weber) but the dyno types will sort them for me.

[mikal]

Get on the Ausmini website and chat to DrMini (doc). He runs a Dellorto and has probably forgotten more than most people will ever know...