you guys keep on sharing all these hop up tricks for the stock carb the stock might be alright. I'm trying pushingthe limit trick of 6 coils today. Oldman what size hole did you drill.

 

Well what the vacume slide spring does is just control the tension pushed against it while the throttle is opening. So, if you cut the spring it puts less resisstance against the vacume action of the spring. Meaning it will rev very noticably quicker. And if it revs quicker by just jabbing the throttle, it will be quicker under a load too. Just over all quicker. It doesn't hurt anything if you don't cut more than 6 coils off. If you cut more, at an idle the slide will want to open a little and it will run lean on bottom end. I accidentally went too far and it ran lean from idle to about 1/8 throttle. No big deal if you go too far just stretch the spring out a little and/or adjust feul screw to compensate the difference. The results will put a smile on your face. [img]i/expressions/face-icon-small-happy.gif[/img]

 

so how big are the vaccum ports drilled out to and what exactly does it do for performance?

 

leave it, I got this trick from Mr. Horsepower a while back and it works great.

 

I drill the two vacuum ports out to 1/8 " each.
That is the largest you can go because of size of internal passage.
I would then cut only 4 coils off spring and do not re-lengthen.
Do not run with lid off. Not only does this reduce airbox pressure, but the air is tumbling reducing velocity.
Without velocity the gains at bottom(Torque) will be loss at top(Horsepower).
Always make changes that help in both areas.

My custom direct mount:

Angled Uni-filter attached to Velocity Stack(From Lectron Carb - Fast By Gast)
Velocity Stack attached to rubber adapter(3")
Rubber adapter mounted to carb.
Elbow fitted to middle of rubber attapter and sealed with JB Weld.
New piece of plastic tubing to mount vacuum balance tube to elbow.

Vacuum balance tube is important:
Test - Remove filter from carb.
Start motor. Look into carb.
Hit throttle.
Note slide goes rapidly up and down - dumps fuel unevenly and kills velocity.

Balance tube helps maintain slide movement (transition) at low velocities till higher rpm's.
With motor stopped - blow into the balance tube and note slide go up.
In a 4cycle engine the motor is drawing air only on one revolution and on one revolution, when all valves are closed air movement is stopped. High velocity stops causing backpressure that goes up the balance tube to maintain slide control till draw cycle is restarted.

That is also why, when lid is removed, power gains are not noticable. Balance tube is too close to filter.

 

would you still run the lid with an aftermarket high flow exhaust?

 

Aftermarket exhaust does greatly help with low-in velocity and thus major improvement with torque.
In 300 ' drags have found no improvement removing the lid. Just more noise.


Jetting:
Have a small vise grips available. Screws top and bottom of carb are lock-tited from factory.
Replace with allen head.
Needle should be in the 4 th position from top of needle
175 main jet 0-3000' altitude
Don't get crazy and use a 180 like most do. That is mostly used because they have not reworked their slide and are using excess gas to help launch.
Rotax motors with 2 spark plugs like to be alittle lean on top.
Stock needle is actually more aggressive than a dyno jet needle.
You need to replace the pilot jet to a 47.4 or easier to find 50. I use a 50 since It works better with motors with new CDI's or ignition timing advanced.

 

I run a 185 main with a trinity exhaust, if I put the lid back on how much smaller should I go with the main? I also run a RWR CDI box and my DS is kind of hard starting a bigger pilot will probably help this out.

 

Stockbomb,

Pull out a sparkplug and look at the electrode. Is the burn line at the bend or closer to end(center of plug). If burn line is at middle of bend, your jetting is fine. If closer to center - too rich

What is the color of porcelan- If light tan - OK. If dark tan - lower needle. If white - raise needle.

When you put the lid on you usually go smaller one size - your case 180
Same atmospheric change that makes slide rise faster also draws fuel thru main jet harder. So even though main jet is smaller, fuel delivery is increased.

Changing to a larger pilot jet will help starting. DS's are very cold blooded and even on warm days, if the motor is cold, you still need to use choke.

 

Good stuff Oldmanracing!

JMiller