Starting on one cylinder

[bazz]

My xs650 fitted with bs34 carbs will only start on the left cylinder
Both enrichment plungers are opening
The rubber tips on the plungers are fine
It starts immediately on the left and right won't cut in until I've turned the choke off and revved it a bit
As it starts to warm up it pops and bangs and the right cylinder comes to life
What should I be checking?
Cheers

 

[Raymond]

Just exploring this further, you said as it warms up the right cylinder comes to life - does it behave itself after that? Is it like the r/h cyl is cold-blooded? Almost sounds like pilot on the r/h carb is blocked or part blocked. Other things - carb synch, float height/fuel height, dodgy plug, Others will list more things to investigate.

 

[mike in idaho]

How does the spark plug, on that side, look?

 

[YamadudeXS650C]

The popping and banging is typically, but not always, a lean condition. sometimes it's a flooding issue.
Likely source of the issue is the float needle/seat. They can stick closed (lean) or open (flood).
Inject some Gummout in that carb thru the fuel feed line could free it up, or pull the carb and clean the needle/seat.
If it's really old, buy a new OEM needle/seat for both carbs.

While you're at it, double check your float setting; this could be a variable.




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[Charles13]

Mine did that once, I cleaned and reset the points and it was fine

 

[bazz]

Mine did that once, I cleaned and reset the points and it was fine

Sorry
Should have said it has a Boyer so waisted spark on both cylinders

 

[bazz]

How does the spark plug, on that side, look?

I'll take a look at it when the engine has started but not yet fired on right
See if it's wet or dry at that point

 

[bazz]

Just exploring this further, you said as it warms up the right cylinder comes to life - does it behave itself after that? Is it like the r/h cyl is cold-blooded? Almost sounds like pilot on the r/h carb is blocked or part blocked. Other things - carb synch, float height/fuel height, dodgy plug, Others will list more things to investigate.

No it's pretty even but not perfect once warmed up

 

[bazz]

The popping and banging is typically, but not always, a lean condition. sometimes it's a flooding issue.
Likely source of the issue is the float needle/seat. They can stick closed (lean) or open (flood).
Inject some Gummout in that carb thru the fuel feed line could free it up, or pull the carb and clean the needle/seat.
If it's really old, buy a new OEM needle/seat for both carbs.

While you're at it, double check your float setting; this could be a variable.




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I have had these carbs completely stripped more times than I could count recently
I've cleaned every where I can think of
All jets are clear the float heights are set
New O rings on the pilot air adjusting screws and new inlet manifolds etc

 

[Jim]

I have had these carbs completely stripped more times than I could count recently
I've cleaned every where I can think of
All jets are clear the float heights are set
New O rings on the pilot air adjusting screws and new inlet manifolds etc

Have you sync'd them? I don't mean a bench sync, I mean a proper engine running sync.

 

[bazz]

Have you sync'd them? I don't mean a bench sync, I mean a proper engine running sync.

Yep they are 100% in sync with vacuum guages

 

[Jan_P]

I would inspect the sparks both sides .. Plugs out grounded against the cylinder IMPORTANT .. and kick it over check so the spark looks the same on both sides

 

[bazz]

Ok I've been out and started it
It starts straight away with the enrichment knob all the way out running on the left only
I ran it a little more than a minute,I turned the enrichment off and the right side still hadn't fired
I pulled the plug and it just looked normal
Not soaking wet but not bone dry
I laid it on the head and it's sparking well
I tried to turn the float bowls screw on the right carb just to make sure it had fuel but the screw is buggered
I put the plug back in and started it and as it warmed the right cylinder cut in and ran happily

 

[bazz]

I would inspect the sparks both sides .. Plugs out grounded against the cylinder IMPORTANT .. and kick it over check so the spark looks the same on both sides

I'll try swapping the leads from one side to the other as it's waisted spark
I've changed the plugs many times

 

[Its been a long time]

I'll try swapping the leads from one side to the other as it's waisted spark
I've changed the plugs many times

Good idea, that's the definitive test for your sparks.

 

[gggGary]

This is my best guess,
Spray carb cleaner should blow right out in your face.
I sharpen a piece of safety wire poke from the top, the hole is quite small.

 

[bazz]

This is my best guess,
Spray carb cleaner should blow right out in your face.
I sharpen a piece of safety wire poke from the top, the hole is quite small.
View attachment 344297View attachment 344298View attachment 344299

I'll check this out
Cheers

 

[bazz]

I swapped the leads from one side to the other with the same result
After that I swapped the plugs too just for the hell of it but still the same
I cleaned the float bowls as gggGary suggested and bang it fired right up on two

 

[bazz]

This is my best guess,
Spray carb cleaner should blow right out in your face.
I sharpen a piece of safety wire poke from the top, the hole is quite small.
View attachment 344297View attachment 344298View attachment 344299

You were bang on the money mate
It fired straight away on two
I'll try it again tomorrow from dead cold to make sure it's not a fluke
Can't thank you enough

 

[YamadudeXS650C]

You were bang on the money mate
It fired straight away on two
I'll try it again tomorrow from dead cold to make sure it's not a fluke
Can't thank you enough

Good to hear!

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