Set it up with Champion plugs they are a lot more forgiving to engines running rich than ngk, I've had ngks only last on starting once then had to replace them from memory it' n6yc or n7yc but you would need to check
-
Enjoy XS650.com? Consider making a donation to help support the site.
XS650.com receives a small share of sales from some links on this page, but direct donations have a much greater impact on keeping this site going.
Left cylinder not firing on 2 XS’s
- Thread starter voelser
- Start date
voelser
XS650 Addict
Right, update time. I had to amend the subject as I think I solved the sparkplug failure, but not the fact the left cylinder doesn’t (always) fire.
Following my previous posts here is what I did in the order I did it in:
1. Changed the spark plug caps to 5kOhm resistor ones. Bike fired up second kick. But left cylider cold, no ignition.
2. Used new HT leads. Bike fired up, but again left cylinder didn’t fire.
3. Put the old leads back on (as a working baseline), swapped the coils. Still the left cylinder would not fire.
By now I am starting the clutch at straws: i have spark, i have fuel, maybe air?
4. Swapped carbs around. Same result.
5. And here is where it gets weird: for lack of any other ideas i swapped the ht leads around at both ends, so in a way nothing changed other than that the left lead is now the right lead and vice versa (to clarify, I also swapped them round at the coil ends). So should really not make a difference, right? Well, it fired up, on both cyliders. Although the left one not quite that happily, but it ran. Three times in a row. Go figure. Still don’t know what the issue is though.
One observation I madeis that there is a small hole in the left cylinder exhaust pipe, just beyond the engine. Although it doesn’t help, it should not prevent the cylinder from firing, right?
Anyway, obviously I need to get that hole fixed and the only other thing I can think off is timing? Now that it kinda runs, maybe I can manage to look at that. But again, that should not just put one cylinder out surely?
I’m open to suggestions!
Following my previous posts here is what I did in the order I did it in:
1. Changed the spark plug caps to 5kOhm resistor ones. Bike fired up second kick. But left cylider cold, no ignition.
2. Used new HT leads. Bike fired up, but again left cylinder didn’t fire.
3. Put the old leads back on (as a working baseline), swapped the coils. Still the left cylinder would not fire.
By now I am starting the clutch at straws: i have spark, i have fuel, maybe air?
4. Swapped carbs around. Same result.
5. And here is where it gets weird: for lack of any other ideas i swapped the ht leads around at both ends, so in a way nothing changed other than that the left lead is now the right lead and vice versa (to clarify, I also swapped them round at the coil ends). So should really not make a difference, right? Well, it fired up, on both cyliders. Although the left one not quite that happily, but it ran. Three times in a row. Go figure. Still don’t know what the issue is though.
One observation I madeis that there is a small hole in the left cylinder exhaust pipe, just beyond the engine. Although it doesn’t help, it should not prevent the cylinder from firing, right?
Anyway, obviously I need to get that hole fixed and the only other thing I can think off is timing? Now that it kinda runs, maybe I can manage to look at that. But again, that should not just put one cylinder out surely?
I’m open to suggestions!
Post #16?
voelser
XS650 Addict
Hmm...yes, not tried that yet. Been using brand new plugs and keep thinking this should not be needed as they work on the other side. But then again, running out of ideas...
thats a good diagnostic 2M suggested.
If you have a weak spark then closing the plug gap will improve the spark due to less resistance.
We don't know much about the rest of the engine and electrics.
My inclination at this stage would be to start again and check everything through systematically so that you can eliminate all the other little variables that could be adding to this cold cylinder fault like carb sync and idle mixture and inlet air leaks, battery voltage drops valve settings , cam chain tension etc etc
Start with a compression test of both cylinders
Until you can test and eliminate more,... you will be continuously floating from one thing to another replacing things until you strike lucky.
I notice that we share the same profession (albeit I have now retired ). Where did you study ?
If you have a weak spark then closing the plug gap will improve the spark due to less resistance.
We don't know much about the rest of the engine and electrics.
My inclination at this stage would be to start again and check everything through systematically so that you can eliminate all the other little variables that could be adding to this cold cylinder fault like carb sync and idle mixture and inlet air leaks, battery voltage drops valve settings , cam chain tension etc etc
Start with a compression test of both cylinders
Until you can test and eliminate more,... you will be continuously floating from one thing to another replacing things until you strike lucky.
I notice that we share the same profession (albeit I have now retired ). Where did you study ?
I think 2m is suggesting it as a diagnostic. The plug gap determines how high the voltage in the entire secondary goes. Any high voltage leak upstream of the spark plug may be (temporarily) stopped by keeping the total voltage lower. A smaller plug gap might prevent it from sneaking out through an alternate (fault) path.
Have you done a compression test recently? then try a leakdown test. And yes even small exhaust holes can create some surprisingly big running problems. Though I've fired and run an XS motor for a few seconds with NO exhaust a time or two. Always fun to watch the flame from the exhaust ports.
Cross post with peanut, great minds, LOL.
Cross post with peanut, great minds, LOL.
Last edited:
voelser
XS650 Addict
Thanks guys. A compression test had actually crossed my mind as well. The engine had been rebuild by Howard Smedley (before I bougjt it) and not run, so I was assuming it to be fine. But when it did fire on both cylinders yesterday there was a difference between pressures from either exhaust pipe. But this could also be because of the exhaust leak of course.
To answer Peanuts question: I got an Architectural Engineering degree at the Technical University of Eindhoven and then was lucky enough to receive a full scholarship to a Masters of Architecture at the Architectural Association in London. But that was a long time ago! Haha
To answer Peanuts question: I got an Architectural Engineering degree at the Technical University of Eindhoven and then was lucky enough to receive a full scholarship to a Masters of Architecture at the Architectural Association in London. But that was a long time ago! Haha
.........maybe not as long ago as me lol(1982 Oxford) 
back then we got generous Government grants in the UK I even received an additional 'Mature student' grant If the engine was rebuilt by Howard it will be exceptionally good but I would still do the compression test and check your valve settings . Howard advocates looser settings for all models .His tests in the technical section are a 'must read' for anyone interested in improving xs650 engine performance
http://www.smedspeed.co.uk/tech.html
voelser
XS650 Addict
Hey guys. Not a lot of progress as I've been away for a bit. I did however take the exhausts off after finding one pinhole to find they are riddled. In all fairness the guy who built them has apologised and offered to fix them. However I am re-thinking the design. At 44mm OD I may have gone overboard on the size, so I am thinking I may use smaller diameter pipe and also using some baffles. So, some research required and may start a separate thread for that.
In the meantime I have a list of things to check for my initial problem. Obviously I can't do a compression test or timing check until I have exhausts back on, but I will indeed check the valve clearances.
In the meantime I have a list of things to check for my initial problem. Obviously I can't do a compression test or timing check until I have exhausts back on, but I will indeed check the valve clearances.
I don't see why you cannot do both checks ?
The exhaust has no bearing on setting the timing as you do the test with the engine not running .With a compression test you are measuring the seal of the combustion chamber .ie the head gasket, the valves and their seats ,rings,piston , head and cylinders. The exhaust or inlets for that matter have no bearing on that check
If you need to check the dynamic timing with a timing light , I'm pretty sure you can do that without the engine running using a
drill/socket adaptor . With the plugs out you should be able to spin the engine at sufficient speed. We do this with 2 strokes so I see no reason why it shouldn't work but I have not tried it with a xs650
The exhaust has no bearing on setting the timing as you do the test with the engine not running .With a compression test you are measuring the seal of the combustion chamber .ie the head gasket, the valves and their seats ,rings,piston , head and cylinders. The exhaust or inlets for that matter have no bearing on that check
If you need to check the dynamic timing with a timing light , I'm pretty sure you can do that without the engine running using a
drill/socket adaptor . With the plugs out you should be able to spin the engine at sufficient speed. We do this with 2 strokes so I see no reason why it shouldn't work but I have not tried it with a xs650
voelser
XS650 Addict
well, I'm obviously not as experienced as I've never done a compression test and in the research I've done it says that for the compression test you'll need to run the engine first. Although I was not quite clear why, I assumed the engine needs to be at temperature so you measure compression at operating temperature.
When I said checking the timeg I meant dynamic with a timing light. I like the idea, but not sure my feeble drill could handle it. But will have a look at that..
Sure you can do compression hot, but cold is fine to determine if your engine is capable of supporting reliable combustion. I do cold compression checks to see if a motor is a candidate to run all the time
compression testing can be carried out with the engine cold or warmed up. There will be a slight improvement with a hot engine due to expansion and lubrication but not enough difference to matter significantly if you are testing for leaks .
I generally use a wide open throttle for maximum air intake and turn the engine over 8-10 times each cylinder or until I'm sure maximum pressure has been reached .
If you have a electronic ignition system with electronic advance then these are not timed dynamically they are timed statically because the correct advance is preset
I generally use a wide open throttle for maximum air intake and turn the engine over 8-10 times each cylinder or until I'm sure maximum pressure has been reached .
If you have a electronic ignition system with electronic advance then these are not timed dynamically they are timed statically because the correct advance is preset
Last edited:
voelser
XS650 Addict
Cheers guys. Learned something new today...!
voelser
XS650 Addict
Are you going to do the Distinquished Gentlemens Ride this year ? it would make a good target date
haha..well, actually I wanted to ride this last year. Didn't quite make it. I am taking part again, but really hope it will be done way before then. Besides, I have options...lol
ahhh so you've more than the one steed .....a stable perhaps
I missed last year too so I am all the more determined to do it this year . Nearest for me is Bristol or Exeter some 50 miles distant so the old gal is going to have to be reliable .
I missed last year too so I am all the more determined to do it this year . Nearest for me is Bristol or Exeter some 50 miles distant so the old gal is going to have to be reliable .
voelser
XS650 Addict
ahhh so you've more than the one steed .....a stable perhaps
I missed last year too so I am all the more determined to do it this year . Nearest for me is Bristol or Exeter some 50 miles distant so the old gal is going to have to be reliable .
Ahem...A 2011 Harley Iron, heavily customised (its been on 2 DGR's), a 1978 XS650 cafe Racer Bratt (been on 1 DGR), a 1985 ex Dutch army Moto Guzzi V50 NATO in full military getup (been on 1 DGR), a 1978 BMW R80 in bits (yet to ride again) and of course this one....
I've been involved with the London DGR since the second one here (I think). I have pre registerred, but may go to the Amsterdam one. Will take the Harley for that trip...lol
Sorry, this was Off Topic...
Similar threads
