Dolmar engine racing...any ideas?

[Magooligan]

Hi

I have a old Dolmar 116si, amongst others, which I bought as a job-lot. So I cleaned it and checked out the obvious, fuel delivery and spark. It took a bit of work but got it fired and ran but over a few seconds it's revs built, to say half throttle speed.  Its now warm, not on half throttle, both mixture screws are within the correct range and when I wound the tickover screw right off it was still racing. I fitted an identical carb of a nice running saw (Dolmar 120si) which did exactly the same (and obviously it doesn't do that on the 120si.  So I think I've eliminated the carb as the problem.  Do you think I'm looking at air-leaks, ignition timing, both or something else....what do you say?  At least it gives me a distraction from trying to fathom out how this 2 rope thing is going to go!!

Thanks folks! ?

[htb]

Air leak. Get it vac and pressure tested.

[Magooligan]

Thanks....I did wonder!

[spudulike]

Yup, it does sound like it has a big air leak. Possibly seals, impulse line if of rubber tube construction, cylinder gasket failed etc. Best to pressure and vac check it otherwise you may get away with it by changing the seals but would get it checked.