Mixture screws and intake boots

[xs650newb]

Hello everyone,
As I said in a previous post I have had trouble getting my 1981 XS650 Special running. It will idle ok, however, when I give it throttle it sputters and dies.

I have
1) Adjusted cam chain
2) Adjusted valvles
3) Cleaned carburetor (multiple times)

I am running a 45 pilot and 135 main jet, with a heiden tuning kit needle in position 3, and the mixture screws backed out 3 turns. The richer profile is because I am running drag pipes (with internal baffles) and mikes performance pod filters.

When left to idle for a while the plugs appear white. I tested for air leaks and that atleast one of my throttle shaft seals is leaking.

In the course of replacing the throttle shaft screws I noticed that the o-ring for the mixture screw was destroyed. I have ordered new ones from MikesXS (along with Canadian needles and needle jets).

QUESTION #1
When I installed the old mixture screws there was quite a bit of resistance. It appears that the o-ring was slightly bigger than the hole and I had to force it to go in. I am pretty sure this is what destroyed it. Is this normal? Once I pushed down deep enough, where the screw first became threaded the resistance went away and I didn't meet resistance again until the screw was bottomed.

Question #2
Since my plugs are so white I am afraid of more air leaks. I can't check right now, but I also suspect my intake boots. They have a metal guard around them. Do I boot a clamp around the metal guard? How tight should the clamp be?

Thanks,
Adam

 

[littlebill31]

The o-ring will do that. I usually bottom it out, then go back, then bottom, ect, to make sure it seats correctly. It can bottom out then you turn it back, then again and you will notice you get a 1/2, maybe a whole, extra turn out of it due to it not seating. It's a seal, it'll be tight.

The plugs won't really tell you much from just idling. You need to run it through different rpm ranges to really get a good test.
The jet needle won' effect idle either. That's more 1/4 to 3/4 throttle position.
You need a clamp. The clamp on the carb boot should be tight enough for it to meet together.

I will say I never used canadian needles. I see no use for them and they just ad to tuning problems.
Are your floats set correctly?
Did you replace the float valve O-ring?

 

[gggGary]

Lube the o-ring with a little grease or silicone. Helps to ease it in place.

 

[xs650newb]

- In regards to float height, I have heard of two ways to measure it.
Method 1) Set petcock to prime, put clear tube on overflow nipple and allow gas to fill the tube. Make sure the height of fuel in the float bowl is within 2mm of where the float bowl mates with the carb surface
Method 2) Set floats to 24 mm, IIRC.

I have chosen method 1 and I believe it is correct.

- Yes, I replaced all parts that come standard in MikesXS rebuild kit for the BS34.

- I am aware that the needles wont affect idle, however, I have heard they make tuning easier so I went ahead and got them. Hopefully they werent a waste of money.


Adam

 

[5twins]

Actually, I think the custom needles will make tuning harder for most. Playing with different needle profiles is very advanced and not something the rookie carb tuner would probably have much luck with.

It's true that the needles won't have much effect on idle but they will effect the idle to midrange transition, which is where your problem seems to be.

There are some baseline jetting set-ups that do work for most people on the 650 carbs. For the BS34s, one or two up on the pilots, one to three up on the mains, and about 3 turns out on the mix screws is the set-up. You add a custom needle though and that set-up is out the window, putting you back at square one. So, put the stock jets back in and start over - stock jets and custom needle. The way it dies when you try to give it gas indicates you're either way too rich or way too lean. With a size up on the pilots, it shouldn't be too lean but the plugs indicate a lean condition. See what I mean about a custom needle making things difficult?

 

[xs650newb]

Ok. That make sense.

So I will stick with #45 pilot, #135 main, 3 turns out.

My understanding is that if everything else is working, this jetting setup will probably not be ideal, however,the bike should certainly be able to rev without dying. Is that correct?


Also, any thoughts on my two methods for setting float height?

Adam

 

[5twins]

The Canadian needle and needle jet combo is much richer than the stock set-up. You may not be able to run a 45 pilot with it, you may need to go back to the stock 42.5. You may not need the 3 turns out on your mix screws either. Somewhere between 2 and 3 may be needed now. That's how you do carb jetting, you experiment. I can suggest things to try but only testing by you will tell you if they will work with your bike.

I've used both methods for float setting. I usually measure them but will use the sight tube afterward if there are problems or I want to verify the setting. If the floats are measured and set correctly but the fuel level still reads high, that would point you towards a faulty float needle or seat.

 

[littlebill31]

1981 with plastic floats is 22mm +/- 1mm.

 

[xs650newb]

Thanks littlebil for the correction. Does this correspond to a fuel level within 2 mm of the mating surface between float bowl ad carburetor body?

 

[5twins]

Yes, it should when checked with the sight tube. You wouldn't think so but just a MM or 2 in height can make a real difference in the way the bike runs. Basically, if you don't have the float levels right, you won't be able to tune the rest of the carb. All the jets and all the circuits feed off the fuel level determined by the float setting. If it's too high or too low (too rich or too lean), it throws everything else off.