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Collection, Preservation and Display of Old Lawn Mowers

Suffolk Colt 75G14 Hunting

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Hi,

I've got a suffolk colt with a 75g14 engine, I cant get it to idle, usually it is running too fast and then it will slow and if I open the throttle fully it wont pick up revs. I am constantly adjusting the throttle to keep it running. I have tried to adjust the mixture screws but cant get it to idle so i can adjust them properly. I think my mixture is too rich but i dont know which way to turn which screw.

If anyone can give some advice that would be much appreciated.

 

Thanks,

Henry

Forums

hillsider Thu, 23/08/2012

Hello Henry,

Re your carb problem the basic settings for the jets are 3/4 to 1 turn open (anticlockwise from the closed position) for the idling jet and 1and a 1/2 turns open for the main jet. The engine should run at these settings allowing you to warm the engine before fine tuning if required. When closing the jets be very careful not to over tighten them as the tips of the jet screws are very fine and can easily be damaged.

If the fault remains the same then you may need to remove the adjusting screws to inspect them for previous damage also to check that the jets are clear, WD40 or similar and an extension tube is useful for this operation. 

If you visit the technical section/operator manuals section of this forum there is a copy of a manual for the Suffolk Punch this contains a good section on how the carb works including adjustment.

Ray

wristpin Thu, 23/08/2012

The three cutaway drawings will give you a good idea of how the carb works. The right hand of the three shows the idle adj screw. Note the little orifice into the manifold  (6) When machines with this carb were still regular workshop jobs we often found this orifice blocked - easily accessed if the carb is removed from the manifold. Remove the idle screw removed poke a piece of fine wire through it (usual disclaimer!) until you can see it down through the screw hole and give it a good squirt of WD with the thin injector tube. Also check the slow running tube (11) - early ones screwed in, later were just a push fit. Hold it up to the light and see that it is clear and again give it a squirt through with WD or carb cleaner..

Hopefully this will solve your problem but as with any engine , particularly small single cylinder ones, no amount of ignition or carb fiddling will will work unless the basics of valves and compression are good.

Hope that this helps.

 

Difficult to read - try this link

https://www.dropbox.com/s/smgavyf7tw1a3si/Zenith%20carburettor0001.pdf

 

HenryB Fri, 24/08/2012

Hi,

What is the best way to slow the engine down, it is revving fast when throttle is set to a slow position.

Thanks

wristpin Sat, 25/08/2012

Richening the idle mixture a little may slow it a bit. However I seem to remember from the days when they were common in the  workshop that the arm to which the throttle cable fixes has two or three holes for the governor spring so make sure that it is in the "slackest" position.  Also is it the correct spring -  remember there being a few different springs used across all the variants if the 75 and 98cc engines. Also make sure that the spring is lying at a natural angle when not tensioned and is not twisted. Finally, some of the governor vanes had two holes for the throttle rod to locate in  - is yours in the right hole?

Another thing worth checking, particularly if you have had the throttle shaft out, is that the butterfly is correctly positioned on the shaft. a - the right way up so that the chamfers meat the carb throat correctly and ,b- that it is nor rotated slightly preventing it being a snug fit in the throat when completely closed with the stop screw backed right off.

If all else fails you may need to "fettle" the linkage a bit to ensure that the idle stop screw does return to the fully closed position against the lug on the carb