Hi everyone,

Picked up a Qualcast Suffolk Punch 30 a couple of weeks ago off Facebook Marketplace. Can't find any builders plates or info anywhere on the mower, apart from the grass box having a green sticker that says "Qualcast Suffolk Punch 30" on it. I assume this is the grass box it had from new but I've attached photos in case this isn't correct and it needs identifying. However, the petrol tank is on the handlebars, with the Zenith carburettor.

When I went to pick the mower up the owner showed me it starting up etc, and it ran really nicely. However, it was running as fast as you'd ever want to run it with the throttle lever on the handlebars barely cracked open, and there was no way to get it to idle.

So, having stripped, cleaned, and adjusted the carburettor to the manual's instructions (3/4 turn out from fully seated for main running speed screw and 1 turn out from fully seated for the idle speed screw) it will now idle, however, full speed now sounds inconsistent and not smooth at all. It's not revving up and down / surging, but the tone of the engine and the exhaust just sounds, well, awful to me.

The exhaust sounds quite loud and makes 'putt' noises sometimes, feeling the exhaust, the blast of the exhaust gasses against my hand is consistent, but the engine doesn't sound smooth at full speed. It just doesn't sound happy, consistent or how an engine should sound to me. It sounds rough.

I know these engines run beautifully when all tuned up as per dozens of YouTube videos but mine won't seem to be consistent at full speed (a sensible 'full speed', not revving the engine as far as it will go, may I add).


Some things I would like some answers to are (in addition of course to any suggestions and advice you have to get the mower running better):

1) How should the throttle tensioner be set?

2) There is a small arm with a screw and spring that touches the carburettor and then swings away when the throttle is opened. This hasn't been mentioned in any manuals I've read or any videos online. How should this be adjusted?

3) The spark plug on the mower turns very black and carbon-y after a short period of running (was clean before today and a half-hour of running has it looking like a piece of coal!) I understand this is due to the mower running rich, but how do I adjust this (without the mower revving too high?)


I'm ordering new gaskets for the cylinder head, carburettor and exhaust and I'll be changing the oil and spark plug as well. I doubt this will help much as they're not damaged, just very old, and like the rear roller drive belt, look to have been on there for donkeys years!


There's my plea for help, and thanks in advance for all your help. Let's get this beautiful old machine working right again!

Hi suffolkpunchman, and welcome to TGMF.

I haven't touched one of these in years.  The grassbox looks like it came off a later model with the aluminium engine. Is it a Punch or a Colt? https://m1.secondhandapp.at/2.0/5d5abe602e2b7656841fd0b3?height=1024&width=1024

Your machine has a cast iron engine with points ignition system. As long as the points are clean and set correctly and carburettor is in good clean condition and set correctly it should run smooth as a sowing machine.

The engine speed is governed by a air vane under the engine cowl just above the flywheel it's about as basic as it gets, so as long as it has the correct governor spring fitted all should be good.

Popping could be any off those these things, Valves moving around in their guides and not seating occasionally, points dirty or failing, or carb out of adjustment. 

Always set high speed screw first (the lower one) and then set the idle screw (top) afterwards. Then balance the idle speed using the throttle stop screw on the throttle arm itself.  Also check that arm hasn't come loose on the shaft, they have a habit of coming loose.

And a tip if you ever spin the flywheel by hand to check the spark, please slide the governor vane off first, it'll save you from cutting your thumb open on the sharp corner of it. (I wonder just how many people have done that over the years). 

Thanks very much for the tips Mick. I'll whip off the engine cowling and make sure everything is moving freely. I'll send some photos as well so you can see if everything looks to be set ok (and is original!)

I think I'll have a go at whipping off the flywheel and cleaning the points with some contact cleaner I've got. How would I go about setting them (how would I know if they need to be set?) Toolstation / Screwfix have feeler gauges very cheaply so I can buy one if necessary.

Also, how do I set the throttle cable adjustment? I can turn the nut that will pull the governor arm closer to the operator or push it away, where should this be set?

Thanks for your help

Just a quick note before you attempt a flywheel removal, you might already be aware of this, but the nut that holds it on is a left hand threaded nut, so clockwise to undo it.

Seen many people hit this with a impact the wrong way and shear the end of the crank off. Once the nut is undone you should also use an appropriate flywheel puller to prevent causing any damage. 

There's a manual here which might help you with some of the adjustments, https://oldlawnmowerclub.co.uk/sites/default/files/opmanual/Suffolk%20Super%20Colt%2075G14-25A.pdf

Points gap from memory is cast onto the front of the flywheel, if not around 18 thou should be good.

Think we could be (more than) half way to sorting this out!

Noticed on removing the cowling that the governor spring that goes to the governor arm was in the hole closest to the governor flap - most of the photos I've seen have it in the middle hole so I relocated this when all the work was done.

Removed the pull start mechanism and removed the flywheel by prying behind it with a crowbar, and threading the flywheel nut flush with the end of the crankshaft, giving it a sharp whack with a hammer and off the flywheel popped. No damage done!

Got the quite black-looking points all cleaned up, bought a feeler gauge from Screwfix (https://www.screwfix.com/p/hilka-pro-craft-12700132-32-blade-feeler-gauge/4406r) for just £4.29 and set the points to 0.018" / 18 thou. The measurement was set into the plastic insert in the flywheel (which I later realised that I could've removed instead of taking the entire flywheel off, but I often like to take them off for better access and to clean it all out, so it wasn't really an issue, didn't take me long at all). Reset the spark plug to 0.020" / 20 thou too whilst I was at it, although I shall be changing for a new one (which again I will re-gap of necessary).

Reassembled and did a very quick test fire. Seemed to be running decent and started much better than it ever has done before. Not too sure on the smoothness / exhaust noise issue yet though as I didn't have time to do an extended run.

Awaiting all the new gaskets and plug, so I'll fit these and adjust the carburettor too I'll update you on how that all goes when I get chance.

Sound like you're making progress.   

I would have mentioned the removable cover but to be fair I always remove the flywheel rather than doing micro surgery, it enables you to check everything properly.

you mentioned in your first post above that the exhaust is quite loud, so wondering if the round gasket has broken up and fallen off, it should have a thick ring shaped gasket between the back of the silencer and the exhaust stub.

You know I think you might be right. I knew I needed an exhaust gasket from the various manuals I've looked at, but on inspection of the mower this morning, there isn't actually one there, it's just the exhaust stub going straight into the muffler / silencer.

This might just be the cause! Even if it wasn't the points causing the noise I'm happy they've been checked and the start-up ignition is better.

Like a sewing machine it now runs!

New gaskets arrived and fitted for the exhaust, carburettor and cylinder head.

Oil changed for SAE-30, was deciding between this and 10W-30, but research showed that SAE-30 was better for old engines so this is what my Suffolk got. When I had drained the old oil out there was frighteningly little (I hadn't bothered to check the dipstick previouslt as the owner had said it was all checked and ready to go). I think the lack of oil could've been restricting the engine causing due to the friction and causing a lack of power, part of the reason why the exhaust sounded really heavy and noisy. The general noise of the engine (exclusing the exhaust) is also now much, much quieter and smoother, probably because there's less banging and clanging now the correct amount of oil is in!

Spark plug changed for a new NGK B2-LM (which is what was in originally but it looked knackered). Not too sure of the black plug issue yet, I'll check and report back after a couple of mows, but with the points / ignition sorted and the engine running so much better and much more consistently I am sure this is an issue of the past. Start-up is now achieved within 2 pulls, mostly just 1, and without choke, so I'm really pleased with this too.

Exhaust gasket changed and seals excellently between the exhaust outlet stub and the muffler / silencer, can't feel any exhaust "wind" from around the joint, so this is brilliant. Exhaust now sounds smooth, doesn't pop, doesn't "putt", doesn't sound rough - it's absolutely brilliant. The entire machine sounds happier, healthier, smoother, quieter, and stronger.

However, once all these replacements had been carried out, I ran into a problem. A terrible scraping and rattling noise coming from the clutch, even when the engine was idling and the clutch shouldn't have been engaged. Great, I thought, I've fixed one noise and now another's started.

So, I unbolted the engine and slid it back, to find one of the clutch shoes stuck open. I could just about shift it back closed, but I couldn't get it to move as freely as the other shoe. Presumably this show was not getting enough grip on the clutch drum to spin it over properly and instead it lost and gained grip repeatedly, causing the horrific noise.

I soaked the gap where the clutch slid onto the pivot pin on the clutch casting itself in WD-40, and wiggled the shoe back and forth as best I could. Eventually it began to free up. So I then began removing the circlip and the spring, and sliding off the clutch shoe. Lots of rust on the pivot pin and inside the mounting hole of the clutch shoe itself. Sprayed it all out thoroughly with cleaner and WD-40, little dab of oil on the pivot pin, and reassembled it all. Degreased it all with some spray and cleaned all residue of oil and grease out. I repeated these steps for the other clutch shoe as well - thought I might as well since I was in there rather than it become a problem in the future. Again, lots of rust on the pin, so I was glad to be able to see to it.

Started it up, works absolutely brilliantly, no bad noise whatsoever. I can let it idle and bring the throttle up, clutch grabs, and the blades spin and the drive can be engaged. I've noticed now as well that when the drive is engaged, the engine no longer slows / bogs down, which was a problem I had had previously - again I imagine the lack of oil and lubrication was the cause of this issue!

It's the sewing machine you said it would be and all the videos on YouTube show it to be. Total cost to purchase and for parts / tools comes to around £60. I am well chuffed and beaming as I write this report up.

Thanks ever so much Mick for all your help, advice and patience - you're an absolute star! 🌟

Quote from: suffolkpunchman on June 29, 2023, 05:36:16 PMThanks ever so much Mick for all your help, advice and patience - you're an absolute star! 🌟

You're very welcome, that's what I put this site up for.    You did all the work and I'm so pleased you got it running nicely. Sounds like you enjoyed the challenge as well..

Nice job. 
 

Cheers, yes, it has been a very enjoyable process. Looking forward to repairing some other lawnmowers this summer.

New plug turned black after approx. 45mins of mowing. Not overly concerned as long as it will continue to spark! However I will try to back off the main running screw next time I come to mow and see if that makes a difference.