Theory as to why you cant run a K&N filter on a spree

[Kenny_McCormic]

I got to thinking, maybe the filter is so free flowing the motor cant make the vacuum needed to suck the fuel into the motor.

[Dac]

this makes since, but if this was the case how would people make elites run open filters?

are you saying you think the problem is with the intake? or with the petcock?

[mousewheels]

Keithw had a post after de-restricting his Spree intake where he had a problem at WOT, where it would sag, then take off again. I don't know if his petcock is an oddball, but it was interesting.

http://www.hondaspree.net/phpBB2/viewto ... 8&start=15

Found the fuel problem. I teed into the vacuum line going to the petcock with a vacuum gauge. At WOT there isn't enough vacuum to keep the petcock open. I'll pick up a vacuum check valve today to put in the line. I guess the derestricted air box and intake was just a little much for it.

He also was experimenting with an open airbox, and had to upjet from a 68-70 to 85-90 to get it running correctly. The plots he gave showed no speed improvement. Don't know how close this is to the K&N filter, but like you guys have said, Spree is sensitive to airbox and filter changes.

http://www.hondaspree.net/phpBB2/viewto ... 0&start=30

[tru72]

jetting......

[PimpinSpree]

I got to thinking, maybe the filter is so free flowing the motor cant make the vacuum needed to suck the fuel into the motor.

i don't get why it doesn't work, isn't the elite motor pretty similar to the spree, just with a variator?

[Bear45-70]

jetting......

I agree. The K&N filter lets more air in and leans out the motor. Needs a fatter main jet and then air screw enriched. The no vacuum theory wont' fly because at WOT there is next to no vacuum anyway.

[Dac]

I got to thinking, maybe the filter is so free flowing the motor cant make the vacuum needed to suck the fuel into the motor.

i don't get why it doesn't work, isn't the elite motor pretty similar to the spree, just with a variator?

i run a UNI pod on my all stock 92 back in the day. no problems there. i didn't even rejet. I now run a oko filter on my 96.

I dont know why a spree dont like open filters.


i think tomorrow pending on weather im going to put a UNI single stage pod filter on my SB50 (same as a spree) and see what happens.

[Bear45-70]

I got to thinking, maybe the filter is so free flowing the motor cant make the vacuum needed to suck the fuel into the motor.

i don't get why it doesn't work, isn't the elite motor pretty similar to the spree, just with a variator?

i run a UNI pod on my all stock 92 back in the day. no problems there. i didn't even rejet. I now run a oko filter on my 96.

I dont know why a spree dont like open filters.


i think tomorrow pending on weather im going to put a UNI single stage pod filter on my SB50 (same as a spree) and see what happens.

I would suspect that the intake system is "tuned" (just like the exhaust) from the air box opening to the reeds. On the newer 2 stoke outboards done this way, with even the top off the air box they won't run above idle. You have to totally rejet to make them run.

[tru72]

lol I jus did a ruckus the other day at the shop. put on a really nice exhaust, variator and a K& N filter.. It ran like crap LOL why...?
No jet kit, I didnt want to drillout the customers stuff, so I put back on the original airbox and restricted it to richen it up, ran fine. had almost no difference in the top end because of the lack of a CDI. When he get the CDI and jet kit ill retune it for him.

[noiseguy]

Bottom line on Spree is that you're not going to get a performance improvement from a pod filter and an upjet, so why bother? The engine is too plugged-up in other areas for it to be limited by the filter in stock form. Even with a tuned pipe on mine the stock filter is more than adequate (as is the jetting!)

Most noobs throw pod filters on without upjets or any other mods, lean out the motors (with no performance benefit) and end up burning up the engine. Pod filters are the last thing to mess with on the engine, after you've made other changes.

[noiseguy]

I would suspect that the intake system is "tuned" (just like the exhaust) from the air box opening to the reeds. On the newer 2 stoke outboards done this way, with even the top off the air box they won't run above idle. You have to totally rejet to make them run.

BTW, you're exactly right, the intake has a "tuned" length just like an exhaust. If you put the pod filter on an extension of the same length as the intake tract, it works just fine. I did this once as an experiment; it neither helped nor hurt. Check out this ghetto filter I put together using a stock spree intake tube. Yes, that's a baby food lid, the un-oiled paper element was from a new lawn mower filter and flowed fine. Certainly less restrictive than the stock system, and required no upjetting to run properly:



My takeaway was that upjetting for a short pod filter is only compensating for a mis-designed intake system, and that it's a form of inefficiency. The stock intake seems to be tuned to about 4000 RPM. Shortening it up raises the tuned RPM, but let's face it, how much higher RPM does one want to set the peak intake at for a street bike?

[mousewheels]

Noiseguy and Bear,
Good one on the intake tuning. Easy to overlook the importance of that little tube. Wow <shaking> that's tuned for 4k.

Like that mower/baby food filter too, why spend $$$ to run an experiment.

[Bear45-70]

Noiseguy and Bear,
Good one on the intake tuning. Easy to overlook the importance of that little tube. Wow <shaking> that's tuned for 4k.

The length has to do with how long (in time) for the pulse created when the reeds close to travel from the reeds to the end of the intake system, in this case the opening of the air box to the atmosphere. The shorter the length the faster it happens and the higher the rpm for that tune length.

[Dac]

do you have a theory as how to fix this Bear?

[Bear45-70]

do you have a theory as how to fix this Bear?

There is a formula to figure it out but I lost all that stuff when my XP computer got the virus from *. It has to do with the length of the runner and the cross section of the runner. I could ask my engineer buddy when I get over to Seattle next time, if he isn't in New Zealand at his winter home already.