What am I missing?

[5twins]

If you installed an aftermarket float needle and seat assembly from some rebuild kit, it may be no good. My dealer told me he won't even use them because he's had so many problems with them leaking.

 

[hotrdd]

GREASYC- I had the throttle cranked open when I did the compression test but the bike only has a few hundred Kim's on it since rebuild so maybe the rings need to seat.

5TWins - where are you getting your rebuild kits from if that aftermarket ones are crap?

 

[5twins]

Generally, I don't use rebuild kits, I just buy the individual parts needed. Rebuild kits are a waste of money for the most part. You don't need to replace most of the stuff they come with and many times the jets included are the wrong sizes anyway. If someone brings me a rebuild kit with their carbs, I will try any needed parts. If they work, fine, if not I get genuine Mikuni replacements. That would mean either the Yamaha shop or someplace that deals in Sudco parts (the Mikuni distributor).

Before replacing, follow the advice given in prior posts. Carefully clean the float needle seat and carefully check the float level from both sides. Insure the float moves freely on the pivot pin.

 

[hotrdd]

Pulled the carbs and cleaned them out with carb cleaner and the other recommendations here. Checked the floats for leaking and for height. They were both exactly 24mm. Should I move the to 25mm?

The carbs are clean and the floats move very easy. Thanks for the advice on the carb parts 5twins.

 

[hotrdd]

Set the floats to 25mm and got everything back together and took it out for a run. Also went up on the mains from 132.5 to 135. There was a lot more popping on deceleration, bike pulled hard from 4K and higher but wasn't quite right in the mid range. I haven't done any playing with the mix screws to see if it will help yet. Otherwise I'll step the mains down to 132.5 again and try the ride and mix screw adjust method.

So far things are running better

 

[5twins]

If you haven't increased the pilots one size from the stock 25s to 27.5s, you'll need to do so. These bikes pretty much always require changing the pilots AND mains for mods. If you're still running the stock pilots, that's probably why it's popping so bad on decel.

The 25mm setting will give a slightly lower fuel level than 24mm. This will be less prone to leaking but will also run a bit leaner. That's probably why the popping increased. 25mm is the proper setting for the '76-'77 carb set so I would stick with that and change the pilots. Also, you'll want the needles leaned one step from stock for the larger mains.

 

[hotrdd]

Thanks I'm currently running
- 135 mains
- 27.5 pilots
- needle one step down

Things are getting very close and it's rideable, I'll need to do some playing around to seeif the pilots need to go up one more. Question though, should I be tryingto do the ride and adjust for the mix screws or at this points it worthless until I jet the pilot and main selected? Will adjusting them help me?

 

[5twins]

You probably don't need to get the mix screws exact yet. Set them at the factory spec (1.5 turns out) and maybe try 1/4 to 1/2 turn in and out from there right in your driveway. That should indicate if you're rich or lean depending on which setting works best. Final setting should be within a half turn either way or I'd say you need to change the pilots again. Two sizes up on the pilots usually isn't needed but with an open exhaust, maybe you will.

 

[hotrdd]

So I'm sure the bike is still running lean so I'm going to get a few sets of pilots. I realize I should keep going up on the mains until I get stumbling in the upper range but I'm concerned that I'm already at 135, am I crazy to keep going up further? The plugs aren't black or showing carbon, they appear lean to me as well.