79 xs650 Special - No Spark... But 12v. help?

[XSLeo]

Following the carb guide using a good spray can carb cleaner will get most of the crud out of the carbs. Compressed air sure speeds things up. On some of the tiny holes that may be plugged, I use a twist tie from a loaf of bread. Strip about 1/2 from one end. This leaves a fine soft wire. Use this wire to carefully probe the holes. This will get a hole through the blockage. This will let the carb cleaner get to more of the blockage.
I recommend you do it your self, you will learn a lot about the carbs.
If you can't get them clean enough then send them to your friend.
Leo

 

[Pabeye]

Thanks Leo........for your continued advice and patience.

I cleaned both carbs yesterday following the cab guide instructions and today hooked everything back up using my "Tropicana test bottle"

She sure seems to be firing on both cylinders now, so I think my cleaning job was successful.

I am having a bit of trouble understanding the relationship of throttle stops on the two carbs and the one in the middle that seems to adjust them both at the same time.

Even though the throttle shutter fly was closed when I installed the carbs i can't seem to get the RPM below about 3000 at "idle". The throttle lever adjustment screw on both carbs is barely touching the stop.......very confusing to me....I will have to read the carb guide some more! I guess it's one step at a time

 

[XSLeo]

Ok, where the throttle cable hooks is the adjustment for the idle speed.
The adjuster screw in the middle adjusts the right throttle to match the left side.
This is called carb sync.
With the carbs off I use a 1/4 inch wide strip of paper. Use it as a feeler gauge, start with the left carb, open the throttle, insert the paper under the throttle plate. Close the throttle. Adjust the idle speed screw to get a slip fit on the paper.
Now on the right insert the paper and use the sync screw, the one between the carbs to ad just the right throttle so it has the same grip on the paper as the left.
You now just did a bench sync.
Install the carbs on the bike. It should start and run ok. Adjust the idle speed screw to get a 1200 to 1500 rpm idle speed.
If you have a manometer made up you can hook it up and fine tune the carb sync.
Use the screw between the carbs to adjust the fluid level in the lines so they are even.
A bit of research on carb syncing will find you plenty of how to.
Leo

 

[Pabeye]

Ahhh, tomorrow's project! THANKS LEO!!

One more thing. My carb holders have these little barbs that had a thin tubing attaching them to the petcock of the gas tank. I'm not using the gas tank right now, so, what should I do with these little brass tubes? Leave them open or plug them?? As always.......Thanks

 

[XSLeo]

Those are vacuum ports. One was used to control the petcock, the other was plugged. If you are not using a vacuum petcock plug both.
Unplugged you will have a massive air leak. This will make that side run very lean.
Leo

 

[Pabeye]

THANKS! Maybe that's why I have high RPM

 

[Pabeye]

One other little issue popped up along the way. I had the big acorn nut / cover removed from the cam chain tensioner to facilitate installing the carbs and I noticed quite a bit of oil coming out from the tensioner rod hole. Is ther a "O" ring or something to prevent that or is that "normal. I put the cover back and for now at least it has contained the oil.

 

[retiredgentleman]

One other little issue popped up along the way. I had the big acorn nut / cover removed from the cam chain tensioner to facilitate installing the carbs and I noticed quite a bit of oil coming out from the tensioner rod hole. Is ther a "O" ring or something to prevent that or is that "normal. I put the cover back and for now at least it has contained the oil.

With the cap off and engine running, you will get some oil coming out.

The cap has a groove around the outer edge; that's where there should be an O ring. With a good O ring, should be no oil leakage.

 

[Pabeye]

Thanks RG.........you are right. ( as usual ) put the cap on and all waas OK

Gotta say thought I spent about 4 hours on 'er today and I'm gettin frustrated. Before I started the old beast I clipped one ring off the ATU springs ( as per someone's suggestion ) as it seemed to me that they were not pulling the weights in enough. Then I took off the carbs AGAIN ..did a bench sync using the piece of paper and re installed them with new hose clamps on the intake manifold. as I noticed the old ones did not really tighten enough.

After that I cranker 'er up and I thought all was good...took the choke off and she seemed to idle at about 1200 rpm which I thought was pretty good.

All of a sudden ( at least that is the way it seemed ) she jumped up to 3000, so I shut her down and decided to check the timing again and adjust again as I thought maybe my mixed up wires had me adjusting the timing wrong. Also checked the points gap by the way. All this time the carb mixture adjustment screws were turned out 2 1/4 turns as per recpmmendation. All seemed OK.

I fired it up again and noted the following......as I pulled the plug wires:

left side firing it idled at 2000
right side firing it idled at 3000

both firing jumped to almost 4000 RPM

Adjusting the mixture screw on the left carb changed the idle a bit as i could slow it down to 1200 by turning the screw in

Adjusting the mixture screw on the right card did not seem to do anything.

Mind you this is without touching the idle screw which is barely touching.

On a positive note, while it was turning 4000 RPM or so I blipped the throttle and and she picked up RPM very nicely and did not die. Another small step?
Thanks as always for your help.

BTW all this "testing" is going on with no air filters of any kind on the carbs..don't know if that is important or not.

Thanks as always

 

[retiredgentleman]

Have you looked at the needle jet O-ring on each carb (BS38 carbs)? If they are hard or cracked, etc. , they will pass extra fuel/air and cause a high idle. They need to be soft and supple to seal properly.

 

[Pabeye]

RG...BS 38 carbs.....YES ...I have NOT inspected the "O" ring on either side............

Are you trying to make it FOUR for four my friend?............will chekc and let ya sone how it goes...thanks!

 

[Pabeye]

Another bump in the road. I was going to replace the "O" rings on the mixture screws. Of course one broke taking it off for a sample.

I went to no less than 5 stores today all with a GOOD supply of "O" rings.......NO ONE had a ring that tiny

No problem thought I...... I will get it at Mikes.......only to find this:

"Fuel Idle Mixture Screw with O-Ring - Fits: XS650E/SE/F/SF/2F(1978-79) Stock
Mikuni BS38 CV Carbs.

Beware!
Carb idle mixture screw O-Rings included may or may not fit correctly in your
Mikuni BS38 CV stock carburetor. The O-Ring in the carb as originally supplied by
Mikuni/Yamaha varies in fit and size and we have found it impossible to match
or guarantee a proper fit. No alternatives can or will be supplied. The mixture
screw and matching O-ring was never sold or supplied by Yamaha or Mikuni. "

HUMMM..

 

[retiredgentleman]

Another bump in the road. I was going to replace the "O" rings on the mixture screws. Of course one broke taking it off for a sample.

I went to no less than 5 stores today all with a GOOD supply of "O" rings.......NO ONE had a ring that tiny

No problem thought I...... I will get it at Mikes.......only to find this:

"Fuel Idle Mixture Screw with O-Ring - Fits: XS650E/SE/F/SF/2F(1978-79) Stock
Mikuni BS38 CV Carbs.

Beware!
Carb idle mixture screw O-Rings included may or may not fit correctly in your
Mikuni BS38 CV stock carburetor. The O-Ring in the carb as originally supplied by
Mikuni/Yamaha varies in fit and size and we have found it impossible to match
or guarantee a proper fit. No alternatives can or will be supplied. The mixture
screw and matching O-ring was never sold or supplied by Yamaha or Mikuni. "

HUMMM..

I recommended you look at the needle jet O-ring.

Well, with old carbs, you should replace both needle jet O-rings and mixture screw O-rings.

McMaster Carr sells both:
Viton 1 mm thick X 4 mm ID for the needle jet
Viton 1.5 mm thick X 3 mm ID for the mixture screws

Inexpensive and come in packs of 25.

Edit: The sizing and the source of these O-rings comes from 5twins.

 

[Pabeye]

Thanks RG will order them today!

DONE..What nice folks out there on CA!...........

Once again I am indebted to 5Twins AND you RG.

 

[Pabeye]

WOW, got those "O" rings TODAY!.....Two day delivery! AWESOME..........along with some stuff from Mikes like new carb clamps to make sure there was no air leaks at the intake manifold.

Took the carbs apart AGAIN..went over everything AGAIN........made an adjustment on one of the floats and blew everything out with compressed air.........

Now the BAD news........while blowing everything out with air...I managed to break this thing.......(see pix )

I can't fined it on the schematic of the carb. PLEASE tell me it can be fixed or replaced!

I also put the carbs back on in spite of the broken "thing" It was not completely broken so I pushed it back into place.

Still trying to get the thing to idle at 1200 as per manual. When I bench synched the carbs I put the butterflies completely closed just to try it. Mixture screws set to 2 1/4 turns out. After she warmed up it was still doing 2000 rpm with idle screw totally out.

I did notice if i mess with the mixture screws and turn them out ( a richer mix I think) I can get the idle lower...maybe 1500 or so. I also noticed the plugs are getting a lot of black soot I assume from the rich mix

As always, help appreciated.......ESPECIALLY about that broken brass tube in the carb!

 

[weekendrider]

That is the choke pick up with the small jet the posters have been talking about.
You have screwed the pooch.

 

[Pabeye]

Ahhh, yes......found it mentioned in the "carb guide" with your help Rider........so, no fix?

 

[weekendrider]

I the past I've read about corrosion/ cracking where it joins the carb body.
I can't think of anyone posting a fix for this other than replacing the carbs.
But hey you could put what I know in a thimble and it roll around like a bb in a box car.
One of the more knowledgeable may help.

 

[Pabeye]

Thanks Weekendrider....It broke about 1/2 way up the tube. I might be able to solder it.......in any case I just bought two BS 3 carbs on ebay. Maybe I can use one of the bodies to replace the one on mine. I appreciate your input and your modesty. Thanks!


UPDATE:

I just bout a pair of carbs on ebay .....hopefully that choke feed pipe is intact on them!..

About the fuel situation/high RPM situation.........I know almost everyone blames an air leak.......if there any way ( with throttle closed ) that fuel can get into the carb like through the choke ( primer ) system. I just noticed that there are several holes at the top of the carb throat that are visible with the throttle butterfly closed. I have to check the "carb bible" before Griz scolds me again, but I was wondering if fuel were passing by the choke plunger even with the choke off, would it somehow end up there. I think it interesting the the bike always starts immediately even with no choke in cool weather........Ahhh the hunt continues.

A few other notes ...there is not throttle cable attached , so there is no issue there. I've had these carbs apart 4 times already and the diaphragms are fine. The slides move up and down nicely and VERY slowly when that hole is covered. I had the choke /" primer" plunger assemble apart and it at least LOOKS ok. I have sprayed starter fluid all around the carbs while the engine is running with no increase in RPM...........I'll be dammed.....the search continues!

 

[Pabeye]

My home made "nifty" (LOL ).........enricher pick up tube............

AND my "NEW" 35 year old carbs.........soon to be rebuilt and tried on the bike just for fun!