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Yamaha XS500B Smokes on right cylinder


William_XS500B
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Hi,

I have been struggling with an issue with my XS500B. The engine has been rebuilt. Re-bore, new seals, gaskets etc. I took it apart because it was smoking from the right cylinder and running very rough. So imagine my frustration when it was still smoking from the same side! So I took it apart again and checked the valve seals, barrels, cylinder head for cracks etc etc etc. I carefully re-assembled it and guess what? The problem is still there.

What am I missing? Is it something other than mechanical? Electrical? Fuel? I have replaced the coils and condenser. I also have  rebuilt the carbs with a re-build kit and kept the standard airbox and filter. The airscrews don't seem to do much though?

 

Please help

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Not a mechanic, but...

The key is to figure out EXACTLY where the smoke is coming from. Try smothering it in soapy water and look for the bubbles, that will give the mechanical guys more to work on!

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Hi there William, welcome to the group, can you just clarify what is smoking.

Are you referring to smoke coming out AROUND the Right cylinder itself?, and as Snake suggests a good smoothering of soapy water whilst the engine is running will help locate any location of a leak. Base gaskets are common source of poor running and smoke.

OR

..are you referring to the Right cylinder as being the source, as its smoking OUT of the exhaust pipe which serves that cylinder?

In which case what colour is the smoke,? white, black?, etc. because then it's either oil from the sump, or unburnt fuel gases getting  past the valves.

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I just found this on the net it states that there are some problems with valve seat arrangements that have been known to cause issues. You might like to think about using the updated heads that they mention. just a thought!

The first models had some problems with warping valve seats, so later cylinder heads were changed to round exhaust ports to help the heat dissipate. Heat remained a problem, frequently causing the head to fracture. The balancer and camchain arrangements needed regular attention.31 Aug 2015
 
Not saying this is the problem but valve seals are a source of smoke if they are old or worn plus valve seats do wear and that might be an easy fix!! Press out the valve seats and put in new round ones plus seals.
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On 6/18/2022 at 12:35 PM, William_XS500B said:

Hi,

I have been struggling with an issue with my XS500B. The engine has been rebuilt. Re-bore, new seals, gaskets etc. I took it apart because it was smoking from the right cylinder and running very rough. So imagine my frustration when it was still smoking from the same side! So I took it apart again and checked the valve seals, barrels, cylinder head for cracks etc etc etc. I carefully re-assembled it and guess what? The problem is still there.

What am I missing? Is it something other than mechanical? Electrical? Fuel? I have replaced the coils and condenser. I also have  rebuilt the carbs with a re-build kit and kept the standard airbox and filter. The airscrews don't seem to do much though?

 

Please help

 

Thank you all for your response.

 

I have checked through the electrical system, all is good. I have found the right cylinder is running rich, very rich. So I am going to take the carb apart and see if the choke is not seating properly. Prior to my assembly of the motor I checked all the valves and seats and gave them a quick lap with fine grinding past to make sure they seated properly. Compression is good.

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On 6/19/2022 at 10:35 AM, slice said:

I just found this on the net it states that there are some problems with valve seat arrangements that have been known to cause issues. You might like to think about using the updated heads that they mention. just a thought!

The first models had some problems with warping valve seats, so later cylinder heads were changed to round exhaust ports to help the heat dissipate. Heat remained a problem, frequently causing the head to fracture. The balancer and camchain arrangements needed regular attention.31 Aug 2015
 
Not saying this is the problem but valve seals are a source of smoke if they are old or worn plus valve seats do wear and that might be an easy fix!! Press out the valve seats and put in new round ones plus seals.

 

After some work on the carburettor (sanding the choke piston/rubber down flat and checking and adjusting the float level again (it was 2mm higher than standard) replacing the new jet kit with the old Keihin CV32 jets all is well.

The jets I was supplied with were quite a bit bigger than the originals which is odd.

Anyway It runs and I have been out on it. It is a bit lumpy on the overrun and a bit gutless until you rev it a bit,  but it is running clean which is what I wanted. The engine is a very low mileage  (2200) as it was chucked in a barn and forgotten about so I am hoping if I take it steady I wont get the valve seat issues others have suffered from. 

 

My thanks to all of the reply's, I know where to go if I need anymore tech info.😃

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Well done William. Glad you got it sorted out and good that you posted your outcome. Some people just come on here for advice, get it and never respond again. Again, cheers and glad you've got it sorted.
Mike.

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