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Collection, Preservation and Display of Old Lawn Mowers

Introduction, and a query..

HI. I'm Nigel,  After 35 years of carrying out safety inspections on lifts & lifting equipment, and having had major surgery for Prostate cancer, I took early retirement in 2014. I immediately started volunteering with our local Wildlife Trust and, especially as I was already chainsaw trained, managed to wheedle myself in until I was doing a lot more than just joining a work party once a week. I now get to play with all the toys, including the Ferrari two wheeled tractors, the modern Italian made equivalent of the Allen Scythe (not that fast really, but great fun, I think).

Anyway, earlier this year my father in law asked me to get his old Punch 35S up and running. It had been left in the shed for quite a few years as he'd been using Honda rotary with a roller fitted , but it was getting too heavy for him. I didn't stop at just getting it running and, by the time it went back, it was a pretty smart machine. I posted a few photos on FB and came home one day to find a old, tired looking 35DL stuffed behind the front hedge, left by a friend. My wife wasn't as pleased as I was because we already have two other lawnmowers, 3 brushcutters, chainsaws  & various other stuff.

So the second mower project is now underway. And here's where the query comes in.

The machine has a Zenith carb with a fixed main jet. On the LH side is a small coil spring, anchored at one end to a bracket with the other end looped over the end of the throttle spindle. It doesn't really appear to do anything, except maybe exert a little friction on the rotation of the spindle. I've got what Zenith manuals I can find on t'internet, but can't find out what this is. Can anyone enlighten me? 


wristpin Fri, 11/10/2019

Welcome to OLC.

As you say, all that spring does is to smooth out the movement of the throttle spindle - a throttle damper?  The Zenith carb’ started life with an adjustable main jet and the move to the fixed jet was made to comply with the emission regulations in the 80s. A consequence of this, shared with other engine suppliers,  was that any minor alteration in fuel flow to an already emissions compliant weaker mixture,  resulted in bouts of erratic running - hunting - that could no longer be adjusted out by tweaking an adjustable main jet.  My guess is that the spring was fitted in an attempt  to damp out sudden governor / throttle reactions so caused .

Nigel N Fri, 11/10/2019

Thanks. I was wondering which decade it was from. The speed control on the handlebars is the smaller metal plate version rather the later plastic lever so I may be able to pin it down a bit more than that too.

wristpin Fri, 11/10/2019

Don’t put too much score on my 1980s date as while looking through some old bulletins to see if there was any info on that damper spring it does seem that it could be earlier. I couldn’t find anything on that but I know that I have one regarding the introduction of the fixed jet carb’ , so that will establish a “ can’t be before” date. Always assuming that the machine is as it left the factory.


This suggests that your machine was made later than the introduction of the fixed jet carb' with the damper spring . 1979>. Now I need to find a date for the introduction of the Dellorto carb' that followed on from your Zenith.…


Nigel N Fri, 11/10/2019

Thanks. So 39 is the spring? a bit of artistic license there, but description sounds right.. 

Nigel N Sat, 12/10/2019

Was cruising ebay last night & just happened to buy a 43 (as a non-runner).  Ah, well ......

Nigel N Sun, 10/11/2019

Update, and a query

The DL is now back in one piece & is running quite happily, albeit the plug seems to be getting a bit sooty.

There's no black smoke out of the exhaust (after opening the choke) & tickover & fast running seem to be good to my untrained eyes & ears,

As the Zenith carb is one of those without a main jet, is it likely to always run a bit rich (or even possibly lean) because it can't be adjusted? If the slow running jet is open  a bit too much could this cause it to run rich?. Otherwise the carb seems fine, fuel running freely but no overflow from the bowl unless you tickle it.