This may very well be a dumb question but does reving a motor to 8000 rpms with no load create the same vacume demand as a motor reved to 8000 with a load?? What would deform the boot? Has anyone watched the boot on a dyno??

 

It would be a load, but probably not the same load. Since it would take more fuel to push 8000 RPMs up a hill, it would also take more air, thus more load on the boot. However seeing what it does with no load would be a start. I guess if I was really interested in seeing the results I could get on a flat road, hit 7900 RPMs in first gear with the seat off and take a look. The carburetor wont care what gear your in, just throttle position - meaning first gear is at least safer to be looking down under your butt while trying to drive in a straight line. Shouldn't be THAT hard assuming the area is wide open.

 

hey this is all great guys, I appreciate everybody's input.

The TM45, with accelerator pump, has great throttle response with the carb mount, due to the pump. Not to sound like a broken record, I know I always preach the pump, but that's because its the ultimate![img]i/expressions/face-icon-small-happy.gif[/img]

I do see the oscilation that Ironrod speaks of - its very obvious when reving in neutral past 8,000rpms. today I pulled the air box and installed the filter directly on the boot with no airbox and still got the same result.
Mudstud has a good question - to what extent would it oscilate under load? Whether more or less, it would still indeed do it.
I frequently break 9K, so the partial collapsing of the boot is undesirable, but also as mentioned before I really haven't felt a difference in power between carb mount or lidless box.

Now MisterHP brings up a new thought for me to play with jetting more, perhaps I was just too fat when I was carb mount and never saw the real significance. When I first installed the carb I tuned with boot on, later went carb mount, and back again. I didn't spend a lot of time fine tuning the carb mount jetting. I plan to clamp up the boot as recommended, and also play more with the carb mount jetting in the future.

 

The hose clamp trick is very effective. It made a 3HP difference on the dyno. Thats back to back runs with out clamp then with clamp. Watching it on the dyno the tube seemed to suck itself together about 3 or 4 inches behind the carb, closing off air flow. I just snugged the clamp down right there and it held the shape of the air tube through the next dyno run. 3HP with a .69 cent hose clamp now that good HP per dollar!



MrHorsepower

 

Now that is truly amazing - you bet your bottom dollar I'll be hitting the hardware store first thing in the morning for some hose clamps.

Hey, where was the 3hp increase - at peak hp, and if so what rpm was peak - or was it a 3hp increase at the rpm where the collapsing begins, which is probably after peak has begun dropping off?
Thanks!

 

I made this tube to adapt the carb mount filter. It has a barb fitting to attach the vacuum line from the carb. It also pushed my filter back far enough to remove all the seat contact.


I made a couple extra and gave them away to a few people in the forum. Don't know if they're still using it or not.

I like it, and works real well for me. I'm running a 192.5 mikuni main jet with it.. and it still seems a little lean in the top end.

K&N Adapter Tube

 

This was at peak HP 7500-8000 range. The motor was basically a stage 2.


MrHorsepower

 

Hightower,
Sorry for the late response, I just got back in town. No I haven’t had any evidence of what you described. It is possible but it seems unlikely with the routing I used. I used a piece of 5/16” steel line and bent it to go from the crankcase vent outlet straight over to the radiator support following the angle of the outlet nipple. Then it runs straight up the radiator support to the upper frame tube, turns and follows the upper tube all the way back until the frame starts to dip down around the sub-frame mount area. From there it is rubber hose to the boot nipple. So, the oil liquid has to overcome a significant amount of gravity to get to the carb.


I too have observed the high RPM oscillation on the dyno with the seat removed during tuning. But I was unable to create a collapse.

 

I now have my crankcase breather ducted into the grommet on the left side of the intake boot where the stock carb breather used to connect, I'm burning emmisions and evacuating any positive crankcase pressure much more efficiently now too, like KenDS. So far, no adverse effects, no mess.

I got the hose clamps, one between every other rib, with all the clamp screws turned down so its all nice looking when you pull the seat off, and there is no more oscilation or partial collapse at all when reved past 9K. First chance I get, I will see If I get back the 300rpm's I lost at the top of 5th, and eventually I plan a dyno trip to see actual #'s with all the different intake setups I've tried.

Hey thanks guys, this is all fun stuff.