Broken valve

[SteveP]

It warmed up enough yesterday. Fitted carbs but still running rich. I have swapped air jets several times, but I'm happy that they are the correct ones.

I tried without air filters. No noticeable difference.

The bike starts with the choke on, but runs without straight away. As the bike warms up, after a few minutes unburned fuel starts coming out of the exhaust. Similar to ticking over with the choke on a vehicle that has warmed up.

I'm wondering if the needle jets are worn. I've fitted new o rings. I think maybe the po had similar problems. I've attached a photo of the piston when I stripped the engine.

I set the timing with a strobe. Full advance was difficult as I had to chase the bike around the garage. It seemed as though full advance was past the mark on the stator. I need to get someone sat on the bike.

I'm thinking maybe condenser or coil. The cost to replace the original ignition components isn't much less than the cost of a Boyer Bransden system.

I think I will be changing to electronic ignition. If that fails I'll rebuild my spare set of 1976 linked carbs, and try them.

Thanks again for all the input, it's really appreciated

 

[SteveP]

I may seem to have given up posting. It's just that I haven't moved forward .

I've ordered a Boyer Bransden ignition. Christmas has delayed delivery.

I'm still working on the carbs. I have a few queries.

The first photo is the 74 carbs with the floats set at 24mm. The needle valve is closed enough to stop the flow of petrol. The floats are actually touching the carb body. The valve isn't closing properly and the carbs seem to be overflowing. The second photo shows 24mm float height on 76 carbs with more clearance.
I've adjusted the float height to around 22mm until the valves stop the petrol flow. Photo three shows the actual petrol level. I think that this will make things leaner rather than rich. Any idea if the carb bodies or floats are incorrect?

Tiggertoo spotted my tickover screw springs almost coilbound as photo three. I think the springs which came with the rebuild kit are formed from thicker wire than standard. It made me think about the butterfly valves. Do they ever close fully? Mine are slightly open at tickover.

I've got a spare pair of 1976 linked carbs. I'm considering cleaning and rebuilding them. I'm not sure if they will fit the 74 rubber inlet manifolds. And more importantly the 74 airbox.

As always sorry for all the questions, and thanks for all the help so far.

 

[Its been a long time]

I had issues over the last year getting my 77 650D going. I concluded that when genuine Yamaha points and condensers cost about 2/3 the price of a new Boyer Bransden ignition system, then it was sensible to convert to the BB. Given it's a complete new ignition system, I think it's a decent deal. The coil I got with mine is a PVL coil, German good quality.

Having spent far too long and far too much on the 1977 BS38 carburettors, I gave up. I have a set of Kawasaki ER5 carbs that I'm preparing to install. Life has got in the way presently, but in the foreseeable future I'll be fitting them. Good luck sorting your bike.

 

[SteveP]

That's just what I've been thinking. I was always thinking about fitting the Boyer Kit. I was just hoping to get it running on the original equipment first. I've fitted Boyer to two bikes previously and was very happy with the results.

I'm getting to the point where I may just cut my losses with the carbs. Life's a bit too short.

Though I don't like to be beaten.

Good luck with your bike and thanks for the encouragement.

 

[Wingedwheel]

The linked carbs will fit. I’m running a pair on a ‘72.

 

[SteveP]

That's great thanks

 

[jetmechmarty]

I've got a spare pair of 1976 linked carbs. I'm considering cleaning and rebuilding them. I'm not sure if they will fit the 74 rubber inlet manifolds. And more importantly the 74 airbox.

I can’t be positive because I haven’t tried it. I expect you’ll find that all that stuff fits. I don’t think there were dimensional changes to the carburetor bodies in that time. The spigots for those years didn’t change. A test fit might be wise, but I’m not sure it’s necessary.

I have a mashup project on hold right now on a 79 Special II. I fitted BS34 carburetors, plastic airbox and battery box all off of an 83. It all fit like they’re made to go together.

 

[SteveP]

I'll try the liked carbs first. A very good idea. I'm getting really good at removing and refitting them.

I should have said I adjusted the float heights to 26mm not 22

 

[bikefreakjon]

I may seem to have given up posting. It's just that I haven't moved forward .

I've ordered a Boyer Bransden ignition. Christmas has delayed delivery.

I'm still working on the carbs. I have a few queries.

The first photo is the 74 carbs with the floats set at 24mm. The needle valve is closed enough to stop the flow of petrol. The floats are actually touching the carb body. The valve isn't closing properly and the carbs seem to be overflowing. The second photo shows 24mm float height on 76 carbs with more clearance.
I've adjusted the float height to around 22mm until the valves stop the petrol flow. Photo three shows the actual petrol level. I think that this will make things leaner rather than rich. Any idea if the carb bodies or floats are incorrect?

Tiggertoo spotted my tickover screw springs almost coilbound as photo three. I think the springs which came with the rebuild kit are formed from thicker wire than standard. It made me think about the butterfly valves. Do they ever close fully? Mine are slightly open at tickover.

I've got a spare pair of 1976 linked carbs. I'm considering cleaning and rebuilding them. I'm not sure if they will fit the 74 rubber inlet manifolds. And more importantly the 74 airbox.

As always sorry for all the questions, and thanks for all the help so far.

The float height with the clear piece of tubing attached looks good.
It needs to be below the level of the paper float bowl gasket.
You will know it's too low if it acts like it's running out of gas on a hard pull up a hill on the highway, but it absolutely cannot be above the level of the float bowl gasket.

Aside from Worn or improperly fitting float valves, the only other place fuel will leak from is if there is a crack in the overflow tube. That can happen if water got in there and froze sometimes and the crack can be very very small.

The thing about the idle screw being coil-bound is one reason I don't use those replacement parts out of a cheap kit.
***More likely though: something in your idle circuit is out of adjustment or your timing is off, causing the need to run off the main jet at idle.

I would say install your electronic ignition first and then try and readjust your idle mixture to a place where you can close the main throttle plates more.

I'll bet if this bike does idle when you blip the throttle it hangs at high RPM for a while before settling back down and that's a symptom of a messed up mixture.

The ignition timing does affect the fuel demand for the engine.


Jon

 

[SteveP]

Thanks for that Jon. I'm hoping that changing the ignition will help.
And thanks for taking the time to help

 

[bikefreakjon]

Thanks for that Jon. I'm hoping that changing the ignition will help.
And thanks for taking the time to help

You were saying how the advance did not look right with the timing light, the advance mechanism is prone to wear and corrosion as well as the springs becoming weak and I think that the electronic ignition is really the way to go unless you enjoy messing with points.

I used the electronic ignition and TCI box out of an 81 on my 75

 

[SteveP]

The advance sorta worked. But I think it advanced too far.
At least I'll know it's working properly with an electronic ignition kit.
I must admit to not enjoying working with points. At fifty years old there seems to be lots to go wrong.

 

[bikefreakjon]

I've been away for a while and now I'm going to have to go back and read this whole thread because I really enjoy the forensics of broken valves LOL.

Without reading it I'll bet the person downshifted into too low gear and the 50-year-old valve springs couldn't keep the valves away from the piston.

Most more modern vehicles have a rev limiter (that isn't just the points or the valves floating) so it's not really possible to crash a valve under acceleration but it can be done by accidentally shifting down too many times on the highway.

I've hooked a dirt bike electronic tach to my bike and with the Ninja 500 carbs the power seems to level off around 7,500 RPM. That's as high as I dare rev this design of motor with its terrible vibration and super heavy valves.

Little side note: I tried five different used tachometers, stock tachs, and they were all wildly off! Too high, too low, wouldn't go past a certain RPM... So I confirmed the drop off in power below factory Red line with an electronic tach and now I just run a speedo.


Jon

 

[SteveP]

Hi thought it was about time to post an update. I haven't disappeared.

Over Christmas I was talking to a friend who lives a distance away, so I don't see him very often. He had the same problem with his XS. It turned out to be a dodgy capacitor not working correctly, as it warmed up. Confirming what gggGary suggested way back in post 120.

I've fitted a Boyer Bransden electronic ignition. It took weeks to arrive and then the weather turned very cold. Instead of fitting a relay as suggested by Mailman in his post; https://www.xs650.com/threads/boyer-bransden-ignition-installation-on-my-xs2.60740/.
I've fitted a voltmeter after the kill switch, to monitor the voltage to the ignition and at the same time check the alternator output. I've posted a photo.

I've timed the ignition slightly retarded.
To check the carbs I acquired a Gunsons Colortune. Everything looks fine .

At tickover it's a nice bunson blue flame see photo

Slowly opening throttle nice bunson blue flame

Blipping throttle yellow flame showing rich, just as it should be.

I just need a test run. Unfortunately it's just above freezing here. The roads are wet and covered in salt and grit. Maybe after this weekends storm (you are sending us from the US) the roads will be cleaner.

I'll post after a test run

 

[SteveP]

Quick update.
Managed a few miles near home a couple of weeks back. Fully warmed up the bike on old plugs. Fitted brand new ones. Still getting bogged down between 1500 and 2000 revs in first gear.
This this is how the plugs looked

Decided to have a break from the bike. Try to get the brain cells working, and let the weather warm up a bit.

Yesterday I adjusted the float heights to 25mm, which is still within tolerance.
Warmed up the bike today then fitted new plugs. Went for the same ride. Bike felt nearly right. This is how the plugs looked.

I think I'm finally getting somewhere. Maybe I'll set the left hand float height to 26mm.

It doesn't seem the right way to tune carbs. But it seems to be working. Has anyone done anything similar .

All thoughts as usual would be really appreciated.

 

[Paul Sutton]

We agree the left carb is running rich. This could be too high a fuel level in the carb bowl or the mixture screw is out too far: I have assumed the choke is working correctly. If you can, use a clear plastic tube to make sure the fuel level is correct in the bowls. Then check the mixture screw is correctly set: If screwed in too far that cylinder will stumble and die at idle. If screwed out too far the cylinder will run too rich, blacken the plugs and stumble especially when the engine has warmed up a little. You can have a little fun listening to the engine idling while turning the mixture screw in until it stumbles, then out until it stumbles and then listen for the smooth spot in the middle.

With some carburetors (e.g. BS34) you can easily attach a clear piece of plastic tubing to the bottom of the fuel bowl to check just how high the fuel level is. I never measured the float heights, just adjusted the tang on the floats until I could see the fuel at the correct level. I made up a metal plate so I could attach the carbs to the vice and used an auxiliary plastic fuel tank - Saved taking the carbs in and out for adjusting the tang. Once this was correct I set the mixture screw for 3 - 3.5% Carbon Monoxide with the Gunson G4125 Gas Tester. The G4125 is not too expensive, about £145 in UK, but takes a lot of guess work out of setting the mixture screws.

Notes:
1. When using a plastic tube to check the fuel level there must be no bubbles trapped in the tube or you get a false reading.
2. I have tried the Gunson Colortune see through plugs but found them no better than using your ears to find where the mixture screw made the idle run smoothest.

 

[SteveP]

I've used a clear tube to check the fuel level. It seemed about right when the floats were set at 24mm as per spec.
I adjusted the mixture screws by ear. Both ended up .75 turns out as per spec.
I adjusted the mixture screws using the colortune. Again. 75 turns out was best.
My problem seems to be too much fuel is being sucked in as I open the throttle.
Interestingly the float was set at 31mm high when I got the bike.
Thanks for the input. I'll try to get my head working.

 

[SteveP]

So I increased the float height on the rich left pside carb to 26mm. Didn't touch the sorted right carb.
Took the bike for a run.
Both plugs really sooty.
Threw in the towel.
Borrowed an ultrasonic cleaner. Stripped, cleaned and re-jetted a pair of linked carbs from a 1976 XS.
Went for the usual run.
No real hesitation, nice clean plugs.

I'm ready for summer. Just need to get the speedo working

 

[SteveP]

Another question
The speedometer for my TX650A 1974 isn't working correctly. The trim and mileage digits seem to be functioning. The needle only occasionally gets up to 25mph, and no higher.

I've been reading through as much information on this site, and elsewhere and think I may be able to rebuild the speedo. I'm just wanting to get some miles in through summer.
I've found a speedometer for a 1974 RD350 at a reasonable price. It's in Kmph though. As anybody any experience of fitting one of these to an XS? The max. Speed is 200 not 220. I'm just wanting to fill the hole in the gauge bracket through summer with something that'll give me an idea how fast I'm going, and not concern the police.

 

[AUTOMAN]

Most speedo's are a set ratio, cable speed/indicated speed.
Wheel circumference dictates how close it's supposed to be.

I'll look up the common ratio. 37/1