T20 Airflow Problem

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ettore
On the street
Posts: 29
Joined: Wed Sep 30, 2020 6:52 pm
Country: USA
Suzuki 2-Strokes: 1966 T20

T20 Airflow Problem

Post by ettore »

Greetings, I just got my T20 running and am using a Kohler Air Filter (32 883 06 S1) recommended on the Facebook T20 scrambler forum site. The problem is I could not get the engine above 4500RPM in 4th, 5th or 6th gear. Ran like it was starving for gas/air. Tried my original filter (very old, stiff and discolored), slightly better performance but still hits a wall around 5000RPMs and surges a little when it gets there.

With the filter box removed (bare open carbs), it goes like a scalded dog, got it up to 80MPH, approx 7000RPMs with at least a 1000RPMs left. So I then ran it without any filter element installed in the air box just to make sure there is no obstruction in the box or rubber boots to the carbs. A very slight increase in performance but it still hits a wall at approx 5000RPMs in 4th, 5th or 6th gear just like when the element is installed. Just removed everything again and it performs very strongly.

LASTLY, I installed the air box bottom with a new filter and the top part totally remove, it ran wonderfully. I am suspecting an airflow problem thru the 1 1/4" opening into the filter box. Has anyone else experienced this problem. The boot is in great shape, no cracks or tears. What am I missing? Any thoughts on individual filters, using foam, wire screens etc. The bike is completely stock no modifications. Thanks for any help.

ettore
sportston
Expert racer
Posts: 1119
Joined: Wed Jul 10, 2013 12:04 pm
Country: England, UK
Suzuki 2-Strokes: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S

Re: T20 Airflow Problem

Post by sportston »

Have you made sure that it isn't sucking anything into the inlet of the airbox? E.g. an old rag stuffed under the seat for wiping oil off when filling up, loose tape from old wiring, incorrectly routed pipework etc.
If nothing is impeding the airflow into the airbox, then there are two possible likely options. Either you have the wrong airbox (unlikely) or you have the wrong mixture.
Have you checked the float height in the carbs? It may sound weird but if the float height is slightly wrong you can have an over-fuelling problem, which may be disguised by the increased airflow of removing the airbox. Are your main jets the correct size? Have your needles got the c-clip on the correct groove?
How sure are you that your bike has not been modified? If someone has changed your port dimensions you may find the jetting would need changing to suit.

Hopefully, this has given you a few things to check and you will find the problem.
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