I have a Mikuni 45, I own a carb mount filter but I mostly run filter in air box with stock intake boot and no lid due to woods trails, creeks, and ease of washing the bike by simply throwing the lid back on.

there is a difference between the two, it seems I can rev out higher in fifth with the carb mount filter on, probably due to the slight intake boot collapsing at this very high rpm, but 100 yrd. drag race results don't really seem any different at all so it really doesn't seem worth the bother of dealing with all the hastles involved with carb mount.

But I'm curious to what dyno results have said the difference is between the two, and what other people's experiences have been. Is it worth putting the carb mount filter on when I hit the dunes, and what jetting difference is there - seems my jetting can stay the same either way, perhaps due to increased air velocity with the intake boot in place, even though there is this slight collapse at rpm's past 8500?

please share experiences.....I know there are past threads on this, but I think there's been a lot of new testing by others since the last one.

 

I moved away from the carb mount last year for the reasons you stated. I felt a seat of the pants increase in bottom end response with the tube on vs. the carb mount. I ride exclusively in the dunes and have not noticed any difference in top end. I also tried real hard on the dyno to make the tube collapse but it never happened even at 9700 rpm. Most likely reason is the lack of an air box on my set-up, there isn't enough of a restriction to cause a low pressure situation strong enough to collapse the tube.

I sure don’t miss the BS that comes with the carb mount.
[img]i/expressions/face-icon-small-smile.gif[/img]

 

funny you mention yours doesn't collapse, I've never witnessed it either, but I've never reved high enough watching it either, not been on a dyno with it yet, and I won't rev it that high in neutral. I see what you mean by the airbox ellimination though, If I was dunes only I may consider the same. elliminates the hastles of filters hitting the frame and under side seat, and provides a more reliable carb mount that cannot pop off, nice.

I don't miss the BS either, but still wonder about the potential dyno difference - I mean why do so many people run carb mount, there has to be a reason greater than a tiny percentile of a hp? or does there?

 

I have seen many posts that say that the carb mount is worth 1-2 HP, but that is compared to an open air box. I have also seen many posts talking about the collapse potential for the tube. I am not saying that either of those statements are incorrect, but I’m not convinced that there is a significant difference in HP when the tube is used without the air box restriction. The same could be said about the collapse.

I just think that many people on this forum (certainly not all) are working with a limited understanding of the dynamics involved. If there is no restriction of flow, a vacuum cannot be created. You could use a wet piece of pasta as an intake boot if there was no vacuum. I have seen many times over the positive effects of straightening out air flow on the intake tract to produce more torque and HP. That’s why years ago hot rodders used velocity stacks and tunnel ram manifolds to make power, it worked.

For what it’s worth, the other reason I chose to go back to the tube was I wanted an easy connection to the intake flow to vent my blowby. I never liked the Uni filter method for a crankcase vent, I like the upper cylinder lubrication that I get from the oil vapor and it’s much cleaner.

 

is there any significant mess inside your intake boot or carb as a result of the crankcase vent being ducted into it? like if you ever sit on a hill sideways with the right side of the bike facing downhill, does any oil get coughed into it that you have ever noticed? this may sound like a silly question to some, but not if you think about it.

 

We dyno tested the clamp on vs air box @ the Superbike shop in Evansville In. while working on the Predator engine deveopment. The Airbox and Snorkle will outperform the clamp-on. The clamp on filter loses low end velocity. I think Forum member MisterHP has also done extensive testing on this same subject with similar results as we got. I also verified these results on the 1/8 mile strip. ET's were off just a couple of hundreth's and MPH with the clamp on droped off 2 mph. The seat of pants feeling you get is because the low end velocity cause you to actually drop power down low the as the velocity starts to increase you feel the surge as the power picks up.

 

I was wondering the same thing. My 45 is in the mail and was thinking should I get the clamp on filter. But now I am going to save that money and get somthing else real nice. [img]i/expressions/face-icon-small-smile.gif[/img]

Rob

 

not an exact comparison since the predator has the same bsr carb stock as the DS, which operate on vacuum slide apposed to a flat slide directly actuated by throttle lever as the TM45 I and Ken have.

but the same principals of velocity do apply.

 

I have a 2000 DS and I did in fact notice the collapse of the air tube around 7800-8000 rpm. Mind you, it wasn't so much as a collapse, but rather a vibration. This was done in a garage simply by removing the seat and listening to the motor and observing the air tube. The tube oscillated rapidily and you could tell with an unlimited rev box that the motor would struggle at that RPM range. I removed the tube and inserted the direct mount and found the motor ran through the 7800-8000 rpm range with no difficulty.

It's possible that there has been some strengthening of the stock tube over the last several years. This problem was so evident 2 years ago here on the forums that several people dynoed the results, including Don Knetzger and Ron Wood Racing. Both, if memory serves, talked about an increase in the top end of 3-5 horsepower.

I have not re-ordered a new stock airbox or connecting tube to try it out. I would be very curious to test another DS (that has the connecting tube) in my garage again.

As far as issues with the direct mount. I really don't have any issues anymore. It's simply a matter of making a little extra room for the filter/pre-filter.

Marky

 

I have happened to recently put the stock boot on the 720 with no airbox and bigger K&N[just to try it], i figured the seat and the frame was restricting flow and smothering it along with pulling more heat from engine, so i put boot on and took it for a spin and felt a loss of power, even on bottom end, so i now have the direct carb mount filter back on..i heard it was something to do with cfm, but i think direct is the way to go...