T20 Filter Box/Elemet 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 Filter Box/Elemet 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 and the air box hooked up to the carbs 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.

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

Re: T20 Filter Box/Elemet Problem

Post by ettore »

I just took the top of the air box off and installed the filter then went for a ride and it worked great. So I am figuring the problem is with the round air opening that passes air into the box to be filtered. The inside of the box that has the air opening looks like something was glued to the inside of the case. Any chance these air boxes had a rubber(?) venturi tube that went thru the air opening into the box to increase and improve air flow? My parts manual shows nothing?
Vintageman
Expert racer
Posts: 1474
Joined: Tue May 18, 2010 5:38 pm
Country: USA
Suzuki 2-Strokes: Suz, Yam, Honda, Kaw.
Location: New Hampshire

Re: T20 Filter Box/Elemet Problem

Post by Vintageman »

Did you ever solve this?

Is this an example of your air box?

https://www.ebay.com/itm/294155225244?h ... SwwQxgjqex


I don't own t20. I have t305/t350/GT250. This air box is different then what I attached for t20. Importantly, they all have openings for air intake as round hole possibly followed by length of tubes top and/or bottom side of meatal cover and "scoop" opening on side of cover. The openings are different sizes if GT250 vs T350 for example and change thought the model years (more restrictive usually). The Y boot may have open plenum or added tube lengths (effect top end, may more mid range boost). To my point

The design of the Air Box and Y boot greatly impacts jetting as then engine needs to bring in more air/fuel as you noticed as you try to climb rpms.


I general mfg has carb jetted nominally or centered so the bike can still run ok if a little hotter or cooler one day to the next for example.
In your case you seam to have migrated to the rich side. You take cover off and runs OK and cover on may be too rich.

Your T20 box just has one round air intake snorkel opening? If not blocked or baffled then best flow possible when using cover. However, it is still
much more restrictive then running with cover off. So if you truly run OK with cover off, then you are jetted too rich for when cover on.


Main Jet
Float Heights
Worn eroded needle jet (Inside where it meters against jet needle).
Needle jet worn.

Or timing off (too retarted for example)

Or engine worn - Top end/crank



Curios if you solved this
Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400 (Daytona Cyls),
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