dan williams

I suspect your problem is a missing ground. The kill switch wire comes from the trigger circuit of the CDI and shorting it to ground stops the sparks. The fan drive circuit comes from the lighting coils through a rectifier (changes ac to dc) and I think a voltage regulator (zener diode that clamps voltage at a certain level) The two circuits should be completely separated. What can happen is the two share a common ground point. If this ground point is lifted because of a loose screw or paint/anodizing/corrosion on the frame then the two circuits become connected through the common ground point. So if you have a defective kill switch (not uncommon on a Beta actually sorta expected on a Beta) it could short out when the thermostat comes on and it will stay shorted until the thermostat switches off. It's also possible you have inadvertently connected the hot side of the kill switch into the hot side of the fan. This could blow your CDI up so it's important to fix this immediately. First thing you need to do is make sure the circuits are separate. Find the hot wire for the kill switch which is typically black/white and make sure it only goes to the kill switch. Take the return wire from the kill switch and attach it to a hard ground on its own. I run mine back through the harness to a mounting screw on the ignition coil. Next make sure the ground connection for the fan circuit is making a good ground contact. Scrape paint/anodizing to get down to bare aluminum if you have to. I'll usually add a drop of silver filled thermal paste used for CPU coolers just to prevent corrosion and silver is the most conductive metal (mini geek-out there). A high resistance ground on the fan circuit can mimic all kinds of issues including a weak fan or a bad thermostat. Once you do this I think your problems will be fixed. At least with your thermal kill switch.

Hmmm, usually not a good sign when somebody replaces critical bolts with non-standard items and they aren't stainless or titanium.

Ok I just looked at the Sherco manual. Definately not the stock bolts. Here's the problem, by not using stock bolts which may be stainless steel or at least a better grade of corrosion resistant steel you may have caused corrosion in your water jacket. Using tap water or non-premixed coolant will accelerate corrosion. Sorry to say this but you might want to pull the engine out of the frame for a proper tear down. Radiator flush is probably in order too. Good call Beta_Blocker

Are those the stock head bolts?

Yup thought of that too but I figured that has a lot to do with air in the system absorbing some of the travel of a fully pressurized/purged system. When all the air is purged the system should have sufficient displacement to move the pucks past the elastic flex of the seals so they return to a new rest position. Once I got the last bit of air (assumed) burped the pads set up properly. I'm just not keen on using the regular banjo bolt as a purge point but it is the highest point on the system. it's all good now. At least until I fall off again

Only place I see that would work is on stop adjuster bolt on pedal. Switch would hit frame above pedal. Switch would have to be normally closed type opening when pedal Is up and switch hits frame.

I retried cracking the hose connection at the top of the master cylinder and it pushed out air and pedal firmed up. I'll still put the bleeder on when it arrives. I did notice the clutch slave cylinder bleeder is the same style. Rear pads are screaming and not biting so I probably contaminated them. Easy to replace. Not a fan of the full metallic pads anyway. A bit too abrupt for my style (or lack of). Besides the rear brake it's been a good day to sort a few front end maintenance issues, replace the chain etc. I could buy a new bike but this one just feels so good I can't justify it.

Did that. I suspect there is still space on top of the banjo bolt for air to hide in. Already ordered Ti goodies so..... You know I can't just let it go if I think I can fix it.

Not asking for anything but just venting. Stuck rear caliper, rebuilt. Can't get rear brakes to bleed properly so disassemble master cylinder and chase bubbles and install rebuild kit in master cylinder. Bleed by disassembling master cylinder worked but new piston in master cylinder stuck. Remove piston and polish inside of master cylinder with Dremel and polishing compound. Clean and refit piston and attempt to bleed regular way. No luck. Who designed this system? Stared at bike for good half hour and figured obvious place for bubbles is top of master cylinder. If the banjo bolt has any space above hose holes it'll never properly bleed. So I ordered some titanium banjo bolts with bleeders on top. I'll try screwing one of those bad boys into the top of the master cylinder brake line mount and try bleeding it from the high point in the system. Let's see if that works.

Nice work. I think you'll like the 3mm of preload relief. It's not obvious at the start of the day but you'll really appreciate it by the end of an event.

This would work. The key is just for alignment. It isn't what holds the flywheel in position. Ask anyone who didn't use a proper torque wrench to reinstall the flywheel.

Bonkers, that sounds like a missing ground. Beta have been known to have some odd wiring including getting lazy with how they attach ground leads.

Not sure if Andy will let me upload this but it's worth a shot. It may be useful to you. Beta_wiring.pdf

Like I've said before the best way to kill a bad rule is to enforce it. Arbitrary or partial enforcement not only makes a bad rule difficult to get rid of but allows it to become an instrument for abuse.

Yeah sometimes I'm late to the party

You can make it softer by decreasing the preload on the springs by flipping the red spacers under the spring retaining bolts so the smaller diameter faces (sits inside) the spring. After that you have to go to custom spacers to unload the springs more. See the clutch thread on top of the forum. The throw is determined by the ratio of the diameter of the master cylinder on the bars and the slave cylinder on the engine. You can't change it without changing the bore of either of those cylinders and changing the stroke changes the lever pull. Longer stroke equals easier pull. as for how fast the plates engage oil choice can affect that. Typically a thinner oil will hit quicker with a lot of guys using ATF.

Remember Toni was a sleeper until he suddenly became the monster he is. No one predicted the dominance he would have over the sport. Same for Jordi and Dougie. It does point to one thing though and that is the lack of young riders being fed into the sport and staying with it. For the same commitment you can make many millions thowing a baseball or kicking a football. Not to mention the difficulty of finding training ground that isn't highly regulated or illegal. In the state I live in it's illegal for any rider under 10 years old. So much for the land of the free. Oh yeah you can still put a toddler on a Clydsdale though.

I don't believe the Mikuni uses a stand pipe like the Keihin. If I remember correctly a bore in the float bowl lines up with a hole in the bottom of the carb body and there is an overflow hole into the top of the float chamber.

Fair enough. Wanted to keep it simple in practice.

No I think you checked your floats and they were good so not the floats. Your float level is pretty good now too. Only happening at 3/4 throttle is the odd thing that still points to vibration in my mind. Possibly a casting defect. This is a tricky one. I will give you credit for being persistent and patient with this. It's the hallmark of a good mechanic.

Ok that's a lot closer to correct though the travel is a bit less than optimum. Perhaps it's time to look elsewhere than the floats. Is your float bowl gasket in good shape?

Nope, angle of the carb slightly affects the pilot mixture on a Beta which is why they tend to stall on downhills. If you look at the main/needle jet tower it is in the center of the float bowl. The pilot is also close to the middle but still on the centerline. Pour yourself a glass of water and stick a straw in the middle. No matter how you tip the glass the water level in the center where the straw is stays the same. So with a concentric carb no matter how you tip the bike the main/needle jet combination always sees the average level of fuel in the bowl. Keeping the pilot circuit on the centerline means the pilot circuit is unaffected by leaning the bike side to side. Your adjustment is way off. When you hold the carb as shown the float arms should be level. Flat. Parallel with the float bowl seam. You should then be able to lift the float arms up to where they are stopped by the stop tang pointing to the right angle where the pilot jet platform meets the main/needle jet tower.

Whoa! That adjustment is really wrong. Pointing to that angle bit on the jet tower should be the limit of travel with the valve open. Resting upside down like that the float arms should be level when the valve closes. Parallel to the float bowl. Are your floats upside down?

Hi James, I know you already mentioned some of this but I'm going to run stream of consciousness for a bit so bear with me. Yes the floats only need to move a tiny amount to open up the float valve to full. It's a conical seat so more than a mm or so doesn't flow fuel any faster. When you pull the carb out and take the float bowl off the seat should close when the floats are level or parallel to the float bowl sealing gasket. Don't be fooled by the difference between a closed valve and compressing the spring in the valve plunger past the closing point. The two adjustment tabs for the floats are the tab the spring clip for the valve plunger attaches to (sets float height) and the little tab that hits the side of the tower the float pivot goes through (limits float travel). There are three tubes coming out of the Mikuni. One on the bottom of the float bowl is the actual overflow. The two that come out of the sides are the atmospheric vents for the float chamber. The usual problem with the Mikuni is the atmospheric vents get fuel splashed up into them and because Beta made the tubes too long they act like siphons and pee fuel until the tank is empty. Usually this only happens when the bike is parked. Someone must have had that happen with your bike and figured they'd cure it by looping the tubes up over the carb. The easiest way to cure it is to put the tubes back where they belong down the side of the carb and nip a small hole in the tube above the float bowl. Inspect your floats for leaks. That can mess up a perfectly float adjustment. Also make sure the floats aren't rubbing on the bowl gasket. If they are trim the gasket with an X-Acto or similar knife. Billy's adjustments and fixes are really the gold standard and work perfectly unless something weird is going on. One other thing I just thought of, make sure there's nothing making the carb vibrate like a fuel line that is hitting the exhaust or the carb hitting a part of the engine. A vibrating carb is an unhappy carb. At this point I think you might have tweaked too much at once and should stop and go back to basics. Straighten the float arms. Set the float level. Set the float travel. Check the floats for leaks and rubbing. Let the atmospheric vents go back to the bottom of the carb and nip a hole just under the bend where they come out of the carb. Make sure the carb isn't hitting anything on frame or motor. Report back here what happens. You and I must be extremely diligent. Ninja Billy is watching!

3D puts on good fun events. Gotta try to make it out there this year.