Spluttery TE20

The carb that you have is a Zeinth 24T-2 , (if your tractor is a TEA 20). The small upper slotted screw is the "Slow running adjustment". Screw it in the mixture gets leaner, back it out the mixture gets richer. The usual setting is about one complete turn open from the fully closed position. Never less than one turn as the fuel is used to cool the valves. The lower large screw is the main jet adjuster. Standard adjustment is out one turn. Again never less than one turn due to valve cooling. If you plan on doing "heavy" work with your tractor then you'll need to open the main jet more. Good luck!

About the only other thing that would cause backfiring through the intake side of the engine is valves! Basic engine timing, incorrectly adjusted valves (they don't close properly, particularly when hot as the valve clearances disappear when the engine warms up), and worst of all(for your wallet anyways) one or more valves are burnt. I'd suggest a compression test. The manual reccommends a figure of around 100psi as normal. I've recently completed a valve job on my TEA20. I brought the compression from 60psi to 105psi just by replacing a few valves and grinding the seats and valves. Let me know what yours is...

Bernie

However Iam not convinced that this is the only problem. As you said, if an inlet valve was not completly closing then this would explain by backfire through the air filter. My valves are completetly closing but are not openning far enough. I took your advice and performed a compression test, I had good even readings on all cylinders of around 90 p.s.i. This confirmed that my valves are closing and sealing correctly.

So do you think excesive valve clearence explains my problems, or should I be looking at anything else before I reasemble?
Many thanks Mike

Glad that you pulled the cover... It's possible??? that one or more of your pushrods were moving slightly out of position due to the excessive valve clearance thereby causing the valve(s) to stay open... A guess... With the cover off I'd remove the distributor cap noting the position of the #1 cylinder with regards to the rotor position and the #1 spark plug lead on the cap... I'd then turn the engine through its rotation watching each valve open then close in sequence ie: intake open then close, then rotor aligned with #1 position on distributor, then exhaust valve opens etc. Do that for all 4 cylinbers. If all looks well replace the valve cover and distributor cap and give her a whirl... Please let me know what you find/happens.

Bernie