81 Special Project

[TopCatGr58]

Brant already told you about the JETS. As to the tach not working....could be the charging system not working properly, so get it running above 2500 rpm....DOH....1/4 throttle and test the Voltage at the battery, should be ~14+ volts, if so, charging is working, if only 12V or less, charging not working which could explain tach not working.

Tach gets it's signal from the ALT, but if it's not charging, then it may not be sending the required signal to the tach. There are other reasons why the charging system won't charge, ie. Voltage Regular/rectifier, no voltage to the field coil, etc.. There is a large ALT harness plug BEHIND the fuse panel that can corrode, even MELT, and it has the wire for the tach signal with the other 3 white wires, check it, clean it, etc..

IS the headlight coming on? If not, that's another device that uses a signal from the ALT to throw the headlight relay to turn on the headlight...won't throw if not charging.

T.C.

[mschor]

Ok, I looked at Jetsrus for needles and pilots. They go by the carb type (BS36, VM, etc). Do you know what would be on this bike? 99% sure it's original...or how to identify it? Or a better source for these parts? Thanks for the suggestion on soda blasting the plugs, will definitely do that.
I'll start testing the electrical tonight or tomorrow

[motoman]

Ok, I looked at Jetsrus for needles and pilots. They go by the carb type (BS36, VM, etc). Do you know what would be on this bike? 99% sure it's original...or how to identify it? Or a better source for these parts? Thanks for the suggestion on soda blasting the plugs, will definitely do that.
I'll start testing the electrical tonight or tomorrow

BS34 type......81Special main jet size:110 across all four
" " pilot jet size: 42.5 " " "
Again, Genuine Mikuni......no aftermarket.

[mschor]

So I pulled the K&L needles out and they match what was in there exactly, just the spring tab on top sticks up a hair taller, which seems to me could be because they're 30 years younger. When you say the needles are taller are you including the spring tab? The body matches exactly. Not being cheap but if I can not spend $100 on needles and seats, it would help, as the little things are adding up to big numbers over time. I can see the difference in the pilots pretty easy just looking at them

[motoman]

So I pulled the K&L needles out and they match what was in there exactly, just the spring tab on top sticks up a hair taller, which seems to me could be because they're 30 years younger. When you say the needles are taller are you including the spring tab? The body matches exactly. Not being cheap but if I can not spend $100 on needles and seats, it would help, as the little things are adding up to big numbers over time. I can see the difference in the pilots pretty easy just looking at them

Float needles referring to is overall length compared to Genuine Mikuni float needles. Jet hole differences is pretty obvious.
FWIW, I'm using K&L float needles with no issues for some five yrs. now. Having to bend that float tang a bit more wasn't my favorite choice, since figuring the tang could cause a wedge scwnario between float tang and float needle when floats are all the way down. Hasn't been an issue as of yet anyways.

[mschor]

Ok, cool, well I ordered the pilots I need from the dealer, and I'll use the needles I have and clear tube the levels--actually they were pretty much right on before I pulled the jets out again today. Thanks for all the helpful info

[motoman]

Ok, cool, well I ordered the pilots I need from the dealer, and I'll use the needles I have and clear tube the levels--actually they were pretty much right on before I pulled the jets out again today. Thanks for all the helpful info

Fuel bowl levels to be checked with bike idling(careful of the hot exhaust muffs). Fuel level while idling is 3mm down from where fuel bowl and carb body meet.

[motoman]

Key to excessively smooth running motor is initially, get all four bowl fuel levels identical. Plus, it makes for good practice for quicker removal/installation of carbs a few times to make that happen. Normally, the static setting of the floats rarely have any two fuel bowls the same running fuel level just because of the spring loaded float needles.

[mschor]

Ok, all the floats are at 23mm, but one looks a little different than the others. It goes up at a steeper angle from the float pin, because I had to bend where it wraps around the float pin to remove it the first time. I made up for it with the tang adjustment, but not sure if it matters that the angle' s a little different. Kind of hard to explain, but maybe you can picture it.

[motoman]

Ok, all the floats are at 23mm, but one looks a little different than the others. It goes up at a steeper angle from the float pin, because I had to bend where it wraps around the float pin to remove it the first time. I made up for it with the tang adjustment, but not sure if it matters that the angle' s a little different. Kind of hard to explain, but maybe you can picture it.

For a final fuel level check while idling, just gonna have to 'clear tube' those carbs.

[mschor]

Still waiting on pilot jets, so I'm going through the electrical. I tested the ohms and volts for the brown and green, and the 3 white wires at the connections behind the fuse box and they look fine. Waiting to be able to start the bike to check the running voltage at the battery. Now I'm at the brake light. Front brake works fine but rear brake doesn't flip it on. Checked voltage at the yellow wires to the light and no voltage. I opened the connector and tested by applying the rear brake and checking voltage at the yellow wires. Front brake sends voltage to the blue wires no problem. Any thoughts where to start looking for a solution? About to open up the rear brake switch

[mschor]

Got it. Not sure what was going on, I messed with connections a little and ended up shortening the spring from the pedal. I think that was the problem, not pulling the switch out far enough. From now on I demand all things will be this simple.

[FranksBMW]

Don't we all. Good luck going forward with this project!

[3Phase]

The rear brake light switch is adjustable. Loosen the plastic locknut and position the switch body until it works On/Off, then tighten the locknut.

Shortening the spring works too....

[mschor]

Thanks Scott, I'll remember that for my next XS, should be getting the pilots tomorrow, then we'll see if she's getting close.