Riddle me this, Blaster Bros

[royalt67]

I swapped the top end off my 94 (which ran great) on to my 04 this weekend. I moved everything with it, pipe (Toomey), carb (PWK 28), reeds. The only change was I used a clamp on filter with a short tube (4-6 in) instead of my modded stock airtube and UNI,

All logic says this should have been bolt-on and go, but I had no top end. After trying everthing else I decided it had to be jetting, specifically main jet since the low was right there.

Again, logic says if you put on a high flowing intake, it should go lean, so I went up and that made it worse. Long, agonizing story short, I ended up dropping from a 158 to a 135 (!) and it runs great. The other puzzling thing is that it was cold, about 40, and that should have required more fuel too.

Anyone else had this experience going from the stock airtube to a clamp-on? It doesn't make any sense. The only thing I can think of is that the different length of plenum makes a big diff on air scavenging.

 

[98blaster+4]

sounds like you lost all velocity with the clamp on vs. airbox. my setup is about the same and i am running a 165 main and a 52 pilot. only difference is my clamp on doesnt have a tube between it and the carb.
btw i have a dynoport, pwk28, uni clamp on, and boyseen superstock reeds.

maybe you had an airleak in the other one???

 

[royalt67]

The velocity thing is the only thing I can think of too.

It was tight and recently leahdown tested. That's why I "borrowed" it. And that carb used to be on the 04 before the 94. I didn't have to rejet it when I put it on the 94...

 

[99LRDblaster]

I'm a bit confused. You switched the top ends of what for what? Let's put it this way. What was were all the engine related(intake/exhaust) related mods on the 04 and what were they for the 94 when you switched over.

From what I'm seeing now, you switched from you Duncan cylinder to the stock port cylinder and took the 34mm carb off and put the 28PWK on. What was the 158 main in?.....the 34 with the Duncan cylinder, the 28 on your stock port cylinder 94? Was it running with the 158 main with the SAME exact setup on the SAME exact bike before you switched intakes?

 

[98blaster+4]

lrd, hes not looking for a riddle back......he clearly states......"I moved everything with it, pipe (Toomey), carb (PWK 28), reeds. The only change was I used a clamp on filter with a short tube (4-6 in) instead of my modded stock airtube and UNI,"

 

[98blaster+4]

try it wothout the tube in between the filter and carb. then see whats up . maybe you could make another tube and cut it down till its better for ya.

 

[royalt67]

Like 98 said, I moved EVERYTHING. It should have been like swapping motors, including induction and exhaust. They only real diff was a different filter arrangement. The whole point was to move a known setup and not have to make changes. (this was a fast racing related swap)

The weird thing is I thought it would go lean, not rich. I wouldn't have thought the length of the air filter tube would make that big of a difference, but apparently it did.

Any other thoughts, guys? I'm not really looking for solution, it runs fine now that it's jetted right. Call this a learning exercise.

 

[Awk08]

hes not looking for a riddle back......"

baaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaahahahahahahahaaaaaa

 

[brandoz28]

this is odd. few ideas:
what's the difference in the surface area of the filters?


there IS the possibility that there is enough more velocity that its pulling fuel through the main jet harder?

 

[royalt67]

this is odd. few ideas:
what's the difference in the surface area of the filters?


there IS the possibility that there is enough more velocity that its pulling fuel through the main jet harder?

A 6 inch K&N clamp-on with a 6 in long (2 inch diameter) vs. a stock (modded to fit PWK 28) air tube with a stock-style UNI. We all "know" how restrictive the stock tube is, that's why I assumed more airflow through the clamp-on would need more main jet not less.

Maybe you have a point, Brando. Perhaps more airflow also caused an increase in velocity, pulling more fuel, faster, through the smaller 135 jet. I was thinking in terms of finite size, but there is no reason the fuel couldn't flow faster with more negative air pressure "sucking" it out.