OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Tecumseh / Kirby Engines SB45 Kirby hunting

Hi, what a fantastic resource this forum is.

I'm restoring a deceased estate SB45 from about 1973 (restoring as in getting it running nice and selling it!). Its has a Kirby/Tecumseh HK30 H4-5A W3 engine and it hadn’t been run for 20 years. I cleaned it up with lots of degreaser and WD40. Drained and replaced oil with Classic Light engine oil. Oiled chains and shafts with 80-140 vintage gear oil. Replaced foam air cleaner with new one. Cleaned fuel tank with Evaporust. Cleaned carburettor with Repco Carby Cleaner. Replaced carburettor rubber primer with working original second-hand unit. Replaced muffler with an almost new original. Replaced NGK B6S spark plug. Cables and other small parts lubricated with Inox. The compression seemed very good, and measured 110PSI with my old compression gauge. The clutch was professionally rebuilt after a tragic discovery, and the blades sharpened.

It started first half-pull after 20 years. Initially idling perfectly but running a little rough, then improved and seemed to improve even more when the engine was under load. It idled pretty well but runs rough and smoked with the throttle open. It ran better with the air cleaner off so I checked the main jet and dropped the float level; it ran pretty well, but still lumpy. It starts at idle with barely a pull on the starter.

I tried the governor spring in a couple of different holes but it ran worse. The governor spring looks pretty misshapen, So I was thinking of trying a new one, but doesn't that extra tension mean even more throttle opening? At 1/2 throttle its ok but at 3/4 throttle the governor seems to take over and open wide.

Pretty hard to describe in text. Does anybody have some suggestions?

Thanks.

It is a carby problem and even with putting carbys through my ultrasonic cleaner I still get about a 50% failure rate with the hunting

Hi remery and Norm,

Probably a few things that need checking.

Adjust Mixture Screw: Start by slightly adjusting the mixture screw on the carburetor. Typically, turning them clockwise leans the mixture and counterclockwise enriches it. Make small adjustments and observe the change in throttle response.

Check Main Jet Size: If you have access to the original specifications for the main jet, ensure it is the right size. An incorrectly sized jet can contribute to rough running.
Inspect the Needle: Make sure the needle and seat in the carburetor are clean and functioning correctly; they can cause rich running if they are not sealing properly.

Adjust float level to correct specification.

Ensure the ignition timing is correct. If it’s off, it can lead to poor running characteristics, especially under load.

A weak spark can cause rough running.

You might want to inspect the ignition components:

A weak governor spring can cause instability in throttle response

Cheers
Max.

Thank you.

Hmm, the governor spring does look misshapen. I figure a new one would have more tension and make things worse... but there is no harm in trying. On the governor shaft it is in the bottom hole, I tried the middle one and the hunting got worse. As I increase revs slightly its all good, but by about half throttle the governor swing the butterfly wide open and it misses and blows black smoke out the muffler. I suppose the previous owner could have drilled the jet. I was trying to avoid checking the timing because I feel like something might break when I pull it apart!

Check out this video of a cold start:

https://photos.app.goo.gl/7ELe2LLVZU8eSvRs8

It does sound like a carby that is running too rich or too lean remery, you haven't mentioned if the main jet and emulsion tube were removed for cleaning ,sometimes I drain the fuel from the tank and run the motor by spraying fuel into the carby or use starter fluid and if the motor revs out fine and runs fine you know it's a carby problem ,l would also check there isn't a vacuum leak ,like a loose intake manifold or an old damaged gasket on the intake side, l usually tighten the head bolts on old motors as they can come loose when they haven't been checked for decades.

Cheers
Max.