Carb Butterfly damage

[GsBike]

O.k. Here's a strange one..

I took the carbs off of my new 79'F soon after I got her for a thorough cleaning and noticed something. Apparently, a PO drilled out the bottom center of each carb near the neck (at the end where they go into the engine) and in doing so slightly drilled through the leading lower edge of the butterfly valves (the brass round valves that the throttle opens). The holes that were drilled in the carb bodies were plugged, however the butterfly valves still have a half-moon shaped divot cut out of each of them (because they sit against the carb body at an angle). - I know it's hard to imagine, and describe. The bottom of the valves where the damage is does sit snugly against the carbs when the valves are fully closed...but, of course, they are thinner in those locations due to the damage.

I didn't think it would effect the performance much since the 4-small jet holes are at the top of the carb neck not at the bottom where the damage is. My bike does run good - minor stutter around 4K in 3rd & 4th at cruising throttle.

Would anyone know why these holes were drilled in the first place (then plugged) or if the damage to the butterfly valves could be effecting my performance?

Any chance someone has seen new ones for sale?

[Redbaron]

carb butterfly damage

Have no idea why holes may been drilled in this location. But, for sure any holes drilled in the butterfly valves will affect your performance. How does the bike idle, how bad is the stutter, and have you checked carb synch? Pull the plugs, what color are they? this is the best way to read your engine. there are better ways to test performance, but for now i'd start there to see how the engine is performing overall.

[skids]

Re: Carb Butterfly damage

If the leading upwind edge is undamaged, I don't think there could be much effect in performance. If you take a good look at the No. 2 carb throttle plate, you'll notice a slot cut in the top, down-wind side of the plate to provide for the ignition vacuum.

Originally posted by GsBike
O.k. Here's a strange one..

(snip)The bottom of the valves where the damage is does sit snugly against the carbs when the valves are fully closed...but, of course, they are thinner in those locations due to the damage.

Would anyone know why these holes were drilled in the first place (then plugged) or if the damage to the butterfly valves could be effecting my performance?

Any chance someone has seen new ones for sale?

[GsBike]

I did notice the notch in the #2 butterfly valve.

The bike idles well - takes about 30 seconds on full & 1/2 choke to warm up. The shutter is noticeable most in 3rd and 4th between 3.5K and 4K RPM when the trottle is in the first 1/8 (cruising). It feels like it's studdering a bit. The top and low end RPM pull good. The plugs are mostly white...2 of them are darker on one side of the insulator (think it's the side facing the carbs). I did syc the carbs and just finished a valve adjustment and tightened the cam chain.

I'm planning on pulling the carbs and doing another full cleaning. After I will run a test with the bike in this 'shutter' zone (if it's still present) and take a look at the plugs.

[ratbyk]

I chased the stutter between 3700 &4000 for a long time. Finally disappered when I changed pilot jets from 42.5 to 45. In fact not only did the stutter go away but the whole engine seemed to run freer and stronger over entire RPM range.
Ken/Sooke
78E Ratbyk

[GsBike]

Pilot jet change

Ken, do you have aftermarket exhaust or air filters on your bike?

I have stock air box and exhaust (although exhaust is rotting on muffler bottom).

[ratbyk]

Stock exhaust and stock air box. I have run it with the air box off and the ram tubes from the air box fitted to the carbs with a fine mesh stainless steel screen over the air intakes. Found no improvement in power or in the engines running. All I got was a lot more intake air roar. Some people like this and it gives them a sense that they are going faster but really think all that I was doing was making more noise. Also this noise can mask other engine noises that could be important to detact ASP.
ken/Sooke
78E Ratbyk

[GsBike]

Good info...

I'll try the pilot increase if the shutter persists after the cleaning. I have to say being new to the workings of the XS...it has an intersting array of noises.

[Snow]

Also be mindful that 78 Carbs took 45 pilots while the later bikes starting in 79 took 42.5 by default.

[skids]

Re: Pilot jet change

If the pipes have holes in them or if your baffles are shot, you are "chasing ghosts" by trying to adjust poor performance with the carbs. The Cherry Bomb actually started getting metal deposits on the spark plug when her baffles were shot. James Ho pointed that out (the metal) at the Gillette rally a few years ago. I don't know how bad your exhaust system is, but you might want to give that some thought.

Sid

Originally posted by GsBike

I have stock air box and exhaust (although exhaust is rotting on muffler bottom).

[GsBike]

Thanks Skids, My exhaust is in decent shape except for the dime size rust hole just at the back of the mufler - I am in the market for a new exhaust.

I plan to start with the simple stuff first when chasing down the shutter - carb clean, new exhaust...