New to bikes, carbon build-up & tuning issues.

[taniknight]

Hi everyone,

My name is Tani and I'm rather new to bike land. I have myself a '78 XS650 that was cafe'd out 2 owners ago and after MUCH time and messing around I have gotten to a point where she is running pretty strong but I'm having richness and carbon build up problems. While with me 3 different workshops have had their hands on it and god knows how many prior to that. Hence I decided to take matters into my own hands despite being time poor (who isn't). Since then I've made a lot of progress. More details on the bike:

Ignition: Pamco with E-advance, 5k caps, 82kV coil (I believe), BP7ES plugs, gaped 0.035, timing checked. Tested resistance of coil and measured good. Spark strong.

Charge: PMA by XSCharge (I think), small battery, kickstart only.

Carbs: BS38, 30 pilots, Z-2 needle jet, SO2 needle at slot 3, 125 main (yes, smaller than standard but I'm suspect about the possibility that a previous owner drilled the jets.... I've ordered replacements). They have been recently reconditioned by a professional and I've had them apart to clean them after tank gunk got back in them. I've since de-rusted and Red-Koted the tank and added inline paper filters. New "XS" brand oval pods filters fitted to replace ill fitting K&N pods. Tuned the mixture screws using dead cylinder method and then sync'd using a manometer.

Engine: Compression ~148psi each side, cam chain tension set (a ~1mm bounce of the pin), valve clearances 5 thou exhausts 3.5 intakes, fresh oil. Other than that I haven't been inside.

Exhaust: Aftermarket pipes with Comando style mufflers.

Ive attached photos of the spark plugs after a half hour ride at 70-100km/h along with a look at the combustion chamber.

The evidence of richness will hopefully be due to someone previously drilling out the jets and will be cured with new ones. I was expecting to find big jets when I opened the carbs as the exhaust and pods generally call for. Smaller than stock main makes me suspect something's up with them.


Now for the questions:

- As for the messy pistons, do I need to pull the head off and clean?
- What might have caused this given that the compression is good?
- Could the carbon build up be causing the plugs to foul rather than rich mixture?
- I have found that an oil leak from the head/jug joint is likely due to a poorly torqued head (I'll be re-torquing tomorrow); could this cause an oil leak into the cylinders but hold up to a compression test?
- Would an oil leak into the cylinders even cause them to look like they do?
- Where do I go from here?

Many, many thanks for your time.
Tani.

 

[kevski]

Your valve guides and seals may be shot causing oil to enter the cylinders.

 

[retiredgentleman]

I strongly suspect the head gasket is passing oil from the camchain tunnel into the cylinders.

Solution.................there is only one thing to do. Its time for a top end re-build.

 

[TwoManyXS1Bs]

The jet sizes should be very close to the orifice opening in tens of microns. You could use some drillbits to measure your 'suspect' jets, and compare to this chart:

Keihin, Dynojet, Mikuni Jet Size Cross Reference

All Hole Diameters Are in Inches

Hole Dia"---Keihin # -- DynoJet # -- Mikuni #
0.0350---- 92.5--------- 92----------- 86.3
0.0360---- 95----------- 94----------- 88.1
0.0370---- 97.5--------- 96----------- 90
0.0380---- 100---------- 98----------- 91.9
0.0390---- 102.5------- 100---------- 93.8
0.0400---- 105--------- 102---------- 95.6
0.0410---- 107.5------- 104---------- 97.5
0.0420---- 110--------- 106---------- 99.4
0.0430---- 112.5------- 108--------- 101.3
0.0440---- 115--------- 110--------- 103.1
0.0450---- 117.5------- 112--------- 105
0.0460---- 120--------- 114--------- 106.9
0.0470---- 122.5------- 116--------- 108.8
0.0480---- 125--------- 118--------- 110.6
0.0490---- 127.5------- 120--------- 112.5
0.0500---- 130--------- 122--------- 114.4
0.0510---- 132.5------- 124--------- 116.3
0.0520---- 135--------- 126--------- 118.1
0.0530---- 137.5------- 128--------- 120
0.0540---- 140--------- 130--------- 121.9
0.0550---- 142.5------- 132--------- 123.8
0.0560---- 145--------- 134--------- 125.6
0.0570---- 147.5------- 136--------- 127.5
0.0580---- 150--------- 138--------- 129.4
0.0590---- 152.5------- 140--------- 131.3
0.0600---- 155--------- 142--------- 133.1
0.0610---- 157.5------- 144--------- 135
0.0620---- 160--------- 146--------- 136.9
0.0630---- 162.5------- 148--------- 138.8
0.0640---- 165--------- 150--------- 140.6
0.0650---- 167.5------- 152--------- 142.5
0.0660---- 170--------- 154--------- 144.4
0.0670---- 172.5------- 156--------- 146.3
0.0680---- 175--------- 158--------- 148.1
0.0690---- 177.5------- 160--------- 150
0.0700---- 180--------- 162--------- 151.9
0.0710---- 182.5------- 164--------- 153.8
0.0720---- 185--------- 166--------- 155.6
0.0730---- 187.5------- 168--------- 1575
0.0740---- 190--------- 170--------- 159.4
0.0750---- 192.5------- 172--------- 161.3
0.0760---- 195--------- 174--------- 163.1
0.0770---- 197.5------- 176--------- 165
0.0780---- 200--------- 178--------- 166.9
0.0790---- 202.5------- 180--------- 168.8
0.0800---- 205--------- 182--------- 170.6
0.0810---- 207.5------- 184--------- 172.5
0.0820---- 210--------- 186--------- 174.4
0.0830---- 212.5------- 188--------- 176.3
0.0840---- 215--------- 190--------- 178.1
0.0850---- 217.5------- 192--------- 180
0.0860---- 220--------- 194--------- 181.9
0.0870---- 222.5------- 196--------- 183.7
0.0880---- 225--------- 198--------- 185.6
0.0890---- 227.5------- 200--------- 187.5

 

[angus67]

nice looking bike. get this sorted, and your good to go. check the oring around the emulsion tubes. I will send you a pair for free if you need them

 

[5twins]

If your 125 jets really are drilled and bigger than stock, you should have the needles leaned a step to slot #2. Running the midrange too rich really blackens plugs because that's the range you run in most of the time. Your choice of pod filter style may be contributing to the richness as well. The pleated K&N type just don't work very well on a CV type carb. Get UNI foam pods.

 

[taniknight]

Excellent replies, thank you.

I'm ordering a micro drill set for some other projects so I'll use them to check jets. Thanks for the chart TwoMany.

Thanks angus67, I've had the tubes out and the o-rings weren't the freshest but not destroyed either. They were a very firm fit when replacing them. Should I replace regardless? I'm over in Melbourne, Australia... I'm assuming Shelton Wa is in Washington, not Western Australia . Thanks for your offer, perhaps I should look locally first.

I'm going to check the head torque today as I know at the least one acorn nut I check was not tight enough. I'd rather not do a top end build until the weather turns shitty. If torquing slows/stops the external leak it may help with the oily pistons too. I'll know what that problem was and I'll start preparing for a top build while enjoying some time on the bike.

I'll report back.
Cheers.

 

[angus67]

if they fit snug, they are fine

 

[retiredgentleman]

I think you will find that cleaning the spark plugs, is a never ending task. You should monitor the dip stick level carefully. Go for a 200 km ride and see how much the oil level has dropped..................it may be a considerable drop. Are the insides of your exhaust pipes as black as the ace of spades?

 

[taniknight]

Exhausts are pretty dark but not black and not with a heavy coating either. I've see worse in cars that are running rich for sure.

As for cleaning the plugs, I've just been using a wire brush (though the ones pictured in my first post were new). I'm probably going to get a cheap soda blaster... I've heard that's good for plugs too. Any thoughts?