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Air Box Modifications ???
- WABBMW
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But before cutting into the air box, I decided to try a short ride with no filter and no top collar on the air box. This opens the top of the air box to about 4". The bike ran so lean that it would bog badly after about 1/4 throttle. It ran terrible. No mid or top end power.
I screwed the top collar back on, but without a filter. The bike ran very well. So it appears that the carb tuning is depending on a certain amount of restriction from the air box. I expect that if the air box is modified, then it would be necessary to go considerably richer on the jets and jet needle settings.
Does anybody have any experience with modifying the stock air box? What can be expected regarding performance, and what other tuning is necessary? Thank you so much.
Bill Baker
Houston, Texas
1982 KZ650 CSR
2008 Yamaha FZ1
2006 Yamaha FZ1
1977 Honda Supersport 750 four (sold)
1984 Honda Nighthawk 650 (sold)
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- hocbj23
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- TexasKZ
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1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough
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- mtkawboy
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78-KZ1000/1105, 80 KZ1000, 82 Kawasaki GPZ750, 95 Harley Fatboy, 80 Suzuki GS1100ET, 81 GS1100E parts bike, 83 GS1100SD Katana/1394,78 Yamaha XT500, 81 Yamaha XS650, 78 Yamaha XS650E, 48 Whizzer model J motorbike, 71 Honda CT70H, 71 Honda CT70, 81 IT 250 Yamaha,82 Honda XL100S owned
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- bountyhunter
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That also proves the "restriction" of the air filter has negligible effect. I think if you screw with the airbox and you will have a new hobby that will last a lifetime. The makers are so good at squeezing power out of these engines, there is not much fruit left to pick. You might get a little more power one place at the expense of somewhere else.I read the article here in the KZR site under the KZ Information tab / Articles / Technical Tips / "Making Power With Air". The article recommends building a fitting that allows air to enter the filter from the bottom in addition to the stock set-up, which is only from the top. The inside diameter of my stock top collar is only 1 9/16". I would think that the 4 carbs can probably pull more CFMs than the top collar of the stock air box.
But before cutting into the air box, I decided to try a short ride with no filter and no top collar on the air box. This opens the top of the air box to about 4". The bike ran so lean that it would bog badly after about 1/4 throttle. It ran terrible. No mid or top end power.
I screwed the top collar back on, but without a filter. The bike ran very well. So it appears that the carb tuning is depending on a certain amount of restriction from the air box. .
1979 KZ-750 Twin
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- spudbudy
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On the high end depending on exactly how much you mod your airbox needle clip to #4 or #5 and main jet 120 or bigger.
With only the top of the airbox opened up to the max, main jet 115 needle clip#3.Both top and bottom of airbox fully open you will need at least a 120 main jet and the needle clip to #4 with the stock air filter. No need to spend $$$ for a K&N when a stock filter works just fine.Good luck!
78 KZ 650B2. Vetter faring, Dyna S, Dyna Green coils, WG coil mod,AGM Battery, VM26SS carbs, Pilot jet 15, mains 110, jet clip #2 shimmed position, Modified stock air box, stock air filter, Kerker 4 into 1 with stock baffle. currently 48,785 miles. and climbing daily.
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