Skip to main content
Collection, Preservation and Display of Old Lawn Mowers

Qualcast SPP 17 S Carburetter problemI

Enter a word or two to search the forum section and click the Search Forum button.

I decided to give my Qualcast Suffolk Punch a run as it has been stood up for some time. I thought it best to clean out the carb and give it some fresh fuel. After a few tries it started but cut out withing two or three seconds. I now have it running but even after it has been running for a while, as soon as choke is turned off, the engine stops, so I am guessing that the choke is giving it a normal running mixture but  when choke is turned off it goes weak.Is there any way of adjusting the mixture  ? I am wondering if it is drawing in air somewhere, so when choke is in operation, the air leak is not so obvious.

Model isSPP 17 S. No idea what the engine is,but carb is very small. I will take a photo later. I will add that I have cleaned the main jet and blown through all the minute holes I could find.



sparkymike Thu, 06/06/2024

I changed the carb gaskets on each end of the right angle inlet manifold and tried it again and could then run it without choke, but it is hunting like mad, much worse and it would shake the machine apart in time, so pulled the carb off once more and had another look at all the internals. Blew penetrating oil through the small holes and made sure they were all clear. I also cleaned the threads on the tube that holds the main jet and I think that it now scres in a bit deeper. Not much more I can do here but give it another go and see if there is any improvement. Carb is a Del'orto FHC 20 (Does the FHC stand for flippin horrible contraption I wonder ?    By the way, I also had to clean up the gasket surfaces on the manifold. They were none too clever from the factory by the look of things.( Emery on a sheet of glass.)


wristpin Thu, 06/06/2024

Make sure that you have thoroughly cleaned the small drillings in the emulsion tube and that the 3 progression drillings in the Venturi each side of the butterfly are clear . If neads be they can be accessed from outside by removing the welch plug.

sparkymike Fri, 07/06/2024

Hi Wristpin, thanks yet again for more useful tips. Yes the emulsion tube holes are all clear. I was wondering re. the welch plug . I have blown penetrating fluid and compressed air through but not sure if all those progressive just holes are clear. Is there any way to remove that welch plug without damaging it? If not, I suppose you have to drill a jole in the middle and insert a selftapper screw and then slide hammer it out. Can't think of any other way, unless you could block both ends of the carb and then pump it out with a HP wanner grease gun through grease nipple in one of the tempory end caps ? Have to put my brain into gear. Can you buy those welch plugs ? By the way, mower is running a little better each time I fiddle with the carb. At least it is not getting worse.!!  I removed the mower belt side cover as there is a problem . You can pull mower backwards ok but it is very jerky if you try to hand push the mower in a forward direction. I know what it happening, but how to cure it is the problem. The belt although slack is grabbing the bottom large pulley wheel rim and putting the brake on ,so to speak. 


wristpin Fri, 07/06/2024

If you pressurise the slow running system with an aerosol of carb cleaner you a usually see sprays of cleaner from the tiny orifices in the venturi just where the throttle butterfly touches . Welch plugs can be purchased in boxes of assorted sizes or from repair shops dealing with chainsaws or other small hand held kit. When aerosols of carb cleaner and the ultra sonic tank fail I drill a small diameter hole and lever them out. Can often reuse them by filling the hole with Araldite and seal around the circumference with Loctite or JB Weld.

Assuming that your Qualcast uses a final drive pinion driving a ring gear inside the rear roller, the symptoms such as you describe are often caused wear in the pinion, its bearing bushes, or wear in the roller bearing bushes causing intermittent mismatch of mesh between piñon and ring gear.

sparkymike Sat, 08/06/2024

Worth a try checking those extra fine holes. At least I can get the carb off in under five minutes now !!  This mower was given to me by my next door neighbours son, when his father passed away. Poor old Alan (the father) was deaf as a post and always had the cylinder rubbing hard against the bottom blade. I could hear it grinding away from a distance. Whenever I had to repair it for him, I used to re-set the cylinder to blade clearance, but as soon as he got it back , he re-adjusted it to zero again !!          The slow running black screw makes no difference to the running, so I think there must be a problem with those holes that you mention above. Re. the free-wheeling problem, I still think it is the belt sticking in the pulley in one direction. There is a belt guide at the bottom, so will check if that is too close to the pulley. The pulley had surface rust in the V but I have cleaned that off now. Will have a play later. Going to the next village garage sale today. Maybe an old mower lurking about in one of the houses !!


chirpy999 Sat, 08/06/2024

If you find the answer to the freewheeling problem let us know, I have one and have had new belt and pinion made no difference.



wristpin Sat, 08/06/2024

I’ve done several where the cure has been new bushes in the rollers where they run on the dead shaft that runs across the chassis. There have been a couple of different types, plain nylon and plastic with oilite inserts. Some machines use the bevel gear ones even though they have not got a split roller with a diff.

sparkymike Sat, 08/06/2024

Have now removed the welch plug from the carb and the minute middle jet hole was possibly blocked but now ok. It is back together now but no time today to run it yet. I will fit a fuel filter in the line as the slighted bit of dirt could block that minute hole again.


sparkymike Sun, 09/06/2024

Now running better than ever, I found another problem with the speed governor linkage. The long lever was bent outwards which had the efect of shortening the rod link which goes to the carb throtttle so that the carb lever was not going back to the slow running screw. Now the black headed screw on the carb  makes a difference when it is screwed in or out.                            Re. the lack of freewheel when pushing the mower forwards, I have improved it a bit. I found that the belt jockey wheel was not moving away enough from the belt when in disengaged (loose belt) position. In addition, the land roll belt is one of those toothed type, so may not be as good as a normal V section belt and may be gripping the pulley too much. I will change it and see if it improves things. I enclosed two photos with the hope that someone can identify the make.model etc. of the engine.        One other update, I gave it an oil change. Old oil came out very black indeed. It took around one and a quarter pints of oil to refill. 

wristpin Mon, 10/06/2024

I think that you will find that the engine is known as an AQ148 ( Atco Qualcast 148cc) of Tecumseh origin . I may even have a parts manual , but with Tecumseh being no more , I’m not sure about the availability of parts.

sparkymike Tue, 11/06/2024

I have found a 123 page pdf on Tecumseh engine manual on line, but it is a generalised issue. It gives all the models it covers on front page, but as the AQ engine designation it Atco/Qualcast's own number, no way of telling which is which, unless I can locate a number on the engine , which so far unable to find. All the same it is a useful data pdf and handy to have on file. If I can find it again i will post a link. By the way, it now starts on second pull, so must be close to where it should be. Re freewheeling problem, I am going to remove the belt tension wheel bracket and make sure it has some lube. behind it.


sparkymike Sat, 15/06/2024

Re. the freewheeling problem. I removed the belts and pulleys again and had another look see. The jockey wheel was not retracting far enough. I gave the jockey wheel pivot area a good oiling and it seems a bit better. I don't think the jockey bracket front spring has quite enough tension, and which I have made an improvement, I will change that spring if thing go bad again.