Drastically different spark plug readings

[Nifty650]

Can anyone help point me in the right direction as to why my plugs are looking this different from each other.

1978 Xs650SE
Bs38 Carbs
Iridium plugs
Ignition timing is spot on
Stock pilot @ 27.5 stock main @ 135 all turned 2 1/4 out.

Any more insight would be appreciated.

 

[Jim]

Providing they both have the same amount of time on 'em, the one on the left is in a dead cylinder.
Not enough info beyond that... no spark... no fuel... no compression... who knows.

 

[Nifty650]

Hmmm, exhaust gets just as hot as the right on startup idle, sounds and feels as though it is firing

 

[Jim]

Hmmm, exhaust gets just as hot as the right on startup idle, sounds and feels as though it is firing

Photo is out of focus... slightly blurry, so I can't say 100%, but I see absolutely no signs of combustion taking place. No soot, no discoloration... nothin'.

 

[Nifty650]

There is a light Carmel color

 

[Jim]

If you're using the original points ignition, pull the HT lead off the discolored plug and see if it'll run off the other cylinder.

 

[Nifty650]

Yes original points ignition.
Pulled the wire from each plug while it was running and it fires independently. Cylinder is firing

 

[5twins]

You might have a float issue on that "rich" running side. Maybe it's set wrong (fuel level too high) or it's developed a leak and is slowly sinking. If the fuel level in the bowl is too high, it will cause rich running. Another thing to check would be the needle jet fit into the carb body. It's a snug, push fit with an o-ring on it to seal. If it's loose in the body, the o-ring is shot and it may be sucking fuel around the outside instead of just through the inside of the jet.

 

[Nifty650]

Thanks 5twins, I will check the float heighth. I have inspected the floats and there is no leak in these luckily. I purchased new o rings and have a nice snug fit on the needle emulsion tube. I’ll order a float level gauge and check that next.

 

[Nifty650]

You might have a float issue on that "rich" running side. Maybe it's set wrong (fuel level too high) or it's developed a leak and is slowly sinking. If the fuel level in the bowl is too high, it will cause rich running. Another thing to check would be the needle jet fit into the carb body. It's a snug, push fit with an o-ring on it to seal. If it's loose in the body, the o-ring is shot and it may be sucking fuel around the outside instead of just through the inside of the jet.

If the carburetors are off synchronization would the plugs be this different from each other?

 

[5twins]

I got one of those float level gauges but found it doesn't work that well and isn't very easy to use. It's biggest issue is that you check the float setting by measuring off the gasket surface but most of the time, the gasket remains stuck to the carb body so is in the way. You run the risk of breaking or damaging the gasket if you have to remove it all the time. I've reverted back to my old tried and true method of using a 6" steel rule graduated in MM along one side. These are thin enough to stick down in between the float bowl gasket and the outer lip around the carb body, to get to the gasket surface. With the BS38s, you can (and should) place the rule on the far side, then sight over the tops of both float "bulbs". Adjust your "view" angle so that the tops of both "bulb" align .....

Sight from too high or too low of an angle and the reading will be off. And you'll want to check from both sides. Often, the float is tweaked or twisted on it's bracket and one "bulb" sits higher or lower than the other. You won't catch this unless you check from both sides.

If you want to buy something, get one of these clear tube fittings .....

https://www.ebay.com/itm/274881260720

It will let you check your float setting externally like so ......

 

[Nifty650]

I got one of those float level gauges but found it doesn't work that well and isn't very easy to use. It's biggest issue is that you check the float setting by measuring off the gasket surface but most of the time, the gasket remains stuck to the carb body so is in the way. You run the risk of breaking or damaging the gasket if you have to remove it all the time. I've reverted back to my old tried and true method of using a 6" steel rule graduated in MM along one side. These are thin enough to stick down in between the float bowl gasket and the outer lip around the carb body, to get to the gasket surface. With the BS38s, you can (and should) place the rule on the far side, then sight over the tops of both float "bulbs". Adjust your "view" angle so that the tops of both "bulb" align .....

View attachment 227845

Sight from too high or too low of an angle and the reading will be off. And you'll want to check from both sides. Often, the float is tweaked or twisted on it's bracket and one "bulb" sits higher or lower than the other. You won't catch this unless you check from both sides.

If you want to buy something, get one of these clear tube fittings .....

https://www.ebay.com/itm/274881260720

It will let you check your float setting externally like so ......

View attachment 227846

Awesome! I placed an order for the float bowl fitting. I like your idea on the floats being tweaked, that could very well be the case I have a steel graduated ruler on my feeler gauges I will use to check instead of the gauge. Thank you for the heads up and alternate method of checking.
I will plan on taking the carbs off later this evening and check the float heights tomorrow and get back on the readings of the 4 floats.

 

[bosco659]

Yikes! What happened to the spark plug gasket on the right?

 

[Nifty650]

Yikes! What happened to the spark plug gasket on the right?

Was hoping nobody would notice
When I had to retap my spark plug hole the tap went in at a very slight angle causing the seat to be off, it does not leak any compression luckily. But I am reminded of that every time I pull my plugs and it bothers the sh** out of me.

Thanks for noticing

 

[gggGary]

spit balling.
Intake air leak on the lean cylinder? while running spritz a bit of carb cleaner around front of carb any changes in how it runs?
air filters off do both slides rise at the same time, amount?
Usually if carbs are badly out of synch there will be lots of backfiring on deceleration.
Did you check timing on BOTH sides? With a timing light; at idle and for smooth up and down advance through RPM changes?
strong bright spark on both sides?
Wipe a finger inside both muffler ends what do you see?
Compression tests done?

 

[Nifty650]

Hey Gary. I checked for leaks with carb cleaner and the only leak I was getting was around the air intake boot, I noticed in my Clymer with the foam element air filter there is actually a clamp that goes around air filter side onto the carburetor. Was thinking maybe it’s sucking in more air from around that boot? So I ordered some clamps and will see if that makes any difference.

I just set the timing, and yes with a timing gun. Got the timing spot on and smooth through the advance. I’m leaning towards checking the floats, I remember a few days ago I left the fuel ON for about 2 minutes with the bike off and it was leaking fuel from the right carb.. I’m thinking 5 twins is on to something. I’m getting strong bright spark yes. I will check for proper slide operation and equalization with air filters off.

With the timing set correctly my motorcycle is running much better and I’m enjoying it much more I just want to get to the bottom of all this little stuff.

 

[bosco659]

Was hoping nobody would notice
When I had to retap my spark plug hole the tap went in at a very slight angle causing the seat to be off, it does not leak any compression luckily. But I am reminded of that every time I pull my plugs and it bothers the sh** out of me.

Thanks for noticing

No problem. It’s my job. Lol.

 

[gggGary]

Take along gloves and your plug wrench, go out do a full throttle run, pull in clutch, kill motor, pull and compare plugs see what they look like from running on the mains.

 

[gggGary]

Will a full throttle run be enough to get the black plug lightened up enough to notice a difference?

I would think so.
I take the propane torch and heat my plugs HOT, lightly brush off with a stainless steel brush. LIGHTLY!

 

[Nifty650]

I got one of those float level gauges but found it doesn't work that well and isn't very easy to use. It's biggest issue is that you check the float setting by measuring off the gasket surface but most of the time, the gasket remains stuck to the carb body so is in the way. You run the risk of breaking or damaging the gasket if you have to remove it all the time. I've reverted back to my old tried and true method of using a 6" steel rule graduated in MM along one side. These are thin enough to stick down in between the float bowl gasket and the outer lip around the carb body, to get to the gasket surface. With the BS38s, you can (and should) place the rule on the far side, then sight over the tops of both float "bulbs". Adjust your "view" angle so that the tops of both "bulb" align .....

View attachment 227845

Sight from too high or too low of an angle and the reading will be off. And you'll want to check from both sides. Often, the float is tweaked or twisted on it's bracket and one "bulb" sits higher or lower than the other. You won't catch this unless you check from both sides.

If you want to buy something, get one of these clear tube fittings .....

https://www.ebay.com/itm/274881260720

It will let you check your float setting externally like so ......

View attachment 227846

I measured the resting float height. These photos are only from the suspected carb that had carbon fouled plug. When I sighted down the floats they all seemed to sit at the same height, no tweaking on them.

The last photo shows a repair I did to the float which had a leak, I used a small amount of tank weld to repair the holes which worked well… but do you think that this could be causing some sort of issue?

Thanks again for your time and helpful knowledge.