Misfires above 4,500

[jon stead]

  plugs 2 and 3 share the same ignition system,points,coils,and capacitor,can you swop the plug leads over? are the long enough?

 and then see if the trouble still stays on 3,

 that make it a carb issue,and/or exhaust

 BTW does the 3 exhaust silencer/tailpipe got hot ?or the same as the others ?

I changed the Boyer EI and associated coils plus leads, for a Dyna S with the original coil and leads, the only thing common after the swap was the plug caps and the plugs. The same problem is there on either ignition/coil/lead set up. I’ve swapped plug caps and plugs but fault stays on Number 3.

I have two sets of fully overhauled carburettors and the fault is the same whichever set of carbs is on. (Of course the intake rubbers and inlet manifolds are the same ones in each set up.)

The exhausts don’t look great from the outside, no idea what’s going on inside them, but suspect some serious corrosion. I was thinking maybe some intermittent internal blockage in number three exhaust, or not even intermittent, I guess if not exhausting freely, plug would soot up, then misfire occurs.

Regarding the temperature, I can’t honestly say there’s any noticeable difference, but I haven’t checked it that carefully. I did check when first back together, that all were warming up equally, and they were, but haven’t really checked after a run.

[K2-K6]

Was it running before the rebore? If so,  what was it like?

Getting to more obscure stuff,  have you checked the tdc mark against actual tdc with a wire down cylinder 1 or 4.

[K2-K6]

Just looked back at the thread from beginning,  the problem you said was with no2 plug sooting up,  you changed the caps over from 2 and 3 to see if it transfered,  that's what you have now. Do you have two new caps that you can put on those two cylinders?

Are you using the same caps for both the boyer and the points system by transferring them onto the lead sets?

Also, I think, you get an opposite effect it some circumstances. One coil fires two plugs,  if the resistance fails on one side then that route to earth will fire more easily as it has least resistance to impede it. But the good side with normal resistance may fail to fire at all if all the coil's energy is dissipated via the path of least resistance. So the failure exists of one side but the observable fault is effectively in the "wrong" position.

[jon stead]

Was it running before the rebore? If so,  what was it like?

Getting to more obscure stuff,  have you checked the tdc mark against actual tdc with a wire down cylinder 1 or 4.

It was running before the rebore but not really ridden due to carbs overflowing and severe engine oil leak. The carbs were sent away fir refurbishment and upon return, the bike was sent away to a “restorer” to sort out all the small faults and get it running as it should. We agreed to fit an EI system which he did. He fixed the oil leak and got it mot’d. He then informed me that he couldn’t get it to run right and that there was a serious problem with the carbs that I had had the temerity to pass onto him. Long story short, the bike came back to me in an unridable condition. Having set off down the wrong path of carburettors, which is how I now have two sets of fully overhauled carbs, the engine was rebored and the problem of poor running persisted- swine to start, erratic tickover, unridable. Eventually I found the Boyer coils wired in parallel instead of series. When I sorted that out the bike started on the button and ticked over lovely, as it does now.

I haven’t checked the TDC mark against the actual TDC but I can when I get home.

[jon stead]

Just looked back at the thread from beginning,  the problem you said was with no2 plug sooting up,  you changed the caps over from 2 and 3 to see if it transfered,  that's what you have now. Do you have two new caps that you can put on those two cylinders?

Are you using the same caps for both the boyer and the points system by transferring them onto the lead sets?

Also, I think, you get an opposite effect it some circumstances. One coil fires two plugs,  if the resistance fails on one side then that route to earth will fire more easily as it has least resistance to impede it. But the good side with normal resistance may fail to fire at all if all the coil's energy is dissipated via the path of least resistance. So the failure exists of one side but the observable fault is effectively in the "wrong" position.

Yes, sorry, it’s always been on the same cylinder even after I swapped the plug caps. I was initially calling it number 2 by mistake, senior moment. I should’ve gone back and corrected that. It is on Number 3 and always has been. Again, sorry for confusing you.

Makes sense what you’re saying about the path of least resistance.

[matthewmosse]

I've had a similar issue a long time ago, found one valve rocker eventually discoulored from heat so assumed the valve must be sticking so that engine got pulled, do you have another set of pipes to try, and possibly try new O rings on the inlet manifolds, or a spare set of inlet manifolds and rubbers. I'm just wondering if something is leaking air only when hot and leaning the mixture out on the inlet side, maybe smear silicon over everything - spraying wd40 doesn't always find inlet leaks. Were both sets of carbs overhauled by the same person? Possible if unlikely that perhaps something has been misplaced in a similar way on both sets of carbs, or a partially blocked tap on one fuel line starving one pot of fuel in preference to its neighbour.  I've found on the sidevalve motors I'e been working on recently I was getting counter initiative plug fouling and backfires when it was actually too lean ( air leak in the manifold and head bolts not properly tight, ran perfectly til worked hard then no power and backfires, left for 15 minutes it ran fine again. Whether engine was  hot the head bolts needed a good 1/2 turn to feel about right, they felt tight when it arrived. )
 Its a bit baffling on your bike, it seems you have covered most of the bases, is the battery and wiring good? Last time my 500 was in regular use it had a few issues with not revving out and with not charging, swapping 're then rec units from spares that worked fine when last used didn't resolve it, sadly neither did parking it in a shed.

[jon stead]

I've had a similar issue a long time ago, found one valve rocker eventually discoulored from heat so assumed the valve must be sticking so that engine got pulled, do you have another set of pipes to try, and possibly try new O rings on the inlet manifolds, or a spare set of inlet manifolds and rubbers. I'm just wondering if something is leaking air only when hot and leaning the mixture out on the inlet side, maybe smear silicon over everything - spraying wd40 doesn't always find inlet leaks. Were both sets of carbs overhauled by the same person? Possible if unlikely that perhaps something has been misplaced in a similar way on both sets of carbs, or a partially blocked tap on one fuel line starving one pot of fuel in preference to its neighbour.  I've found on the sidevalve motors I'e been working on recently I was getting counter initiative plug fouling and backfires when it was actually too lean ( air leak in the manifold and head bolts not properly tight, ran perfectly til worked hard then no power and backfires, left for 15 minutes it ran fine again. Whether engine was  hot the head bolts needed a good 1/2 turn to feel about right, they felt tight when it arrived. )
 Its a bit baffling on your bike, it seems you have covered most of the bases, is the battery and wiring good? Last time my 500 was in regular use it had a few issues with not revving out and with not charging, swapping 're then rec units from spares that worked fine when last used didn't resolve it, sadly neither did parking it in a shed.

Carbs were overhauled by different people, don’t believe it can be a sticking valve as the head was done by an engine race tuner with impeccable credentials. New o rings were used on the intake manifolds when the overhauled head was refitted. Battery is good, wired ng in parts is sketchy but the supply to the coils is good.

I don’t have another set of exhaust pipes to try, but I intend to get a pattern set.

I haven’t paid too much attention to the inlet side of things, other than checking the rubbers are intact and everything slotted together correct.

Thanks for your input, it is appreciated. I’m sure I’ll find it eventually, the problem is I work away and have big periods where I can’t work on the bike. Still this gives me time to postulate and return home full of new ideas and vigor.

[K2-K6]

It sounds like you've brought it quite a long way already Jon and hopefully you'll get this problem sorted as well.

Just a couple more things to throw in the pot, have you tried it with the air filter removed from the air box?

Also,  a really odd one. Years ago a friend had a bike doing something similar revs wise,  turned out that it had a twist grip that was incorrect fitted into the bike's original switchgear that wouldn't open the carbs more that about half way,  it wasn't until looking for something else in carbs that it was spotted.

[Johnwebley]

just seen this thread

  http://www.sohc.co.uk/index.php?topic=9583.msg67421;topicseen#new

  his bike wouldn't runn above 4K

  see if anything helps

[jon stead]

just seen this thread

  http://www.sohc.co.uk/index.php?topic=9583.msg67421;topicseen#new

  his bike wouldn't runn above 4K

  see if anything helps

Yes I’d seen that thread previously. I know I’ve got 100 mains in both sets of carbs and also I only have the fouling of plug #3

[jon stead]

It sounds like you've brought it quite a long way already Jon and hopefully you'll get this problem sorted as well.

Just a couple more things to throw in the pot, have you tried it with the air filter removed from the air box?

Also,  a really odd one. Years ago a friend had a bike doing something similar revs wise,  turned out that it had a twist grip that was incorrect fitted into the bike's original switchgear that wouldn't open the carbs more that about half way,  it wasn't until looking for something else in carbs that it was spotted.

I’ve tried it without air filter, no difference.

I’ve also checked the throttle movement and the carbs open fully when the twist grip is operated. Thanks for the thought though, appreciate it.

[jon stead]

Hello All, the saga continues after my 5 weeks away.

Decided the exhausts had to be checked, especially Number 3 that has been having the sooty plug problem. I’d bought a cheap boriscope, to use with my phone, to stick down the exhaust and hopefully see something amiss.

I removed the exhausts, set up the biriscope, and stuck my probe down my number 3 exhaust down pipe. I didn’t get very far. I tried it down one of the other exhaust pipes and it went down easily. There is a partial blockage just on the first bend of Number 3 down pipe. I can see it when I look down the pipe. It looks like the inner pipe is indented, quite a bit, more than half the diameter, but there is no visible damage to the outer pipe.

This restriction is more than likely the cause of my lack of power problems, especially as everything else seems to have been ruled out. Has anybody any experience of anything like this and has anybody got a number 3 exhaust they want to sell?

Edit: I’ve added a picture below and found a right lower exhaust on eBay that I’ve made an offer on.

[jon stead]

Hopefully you can see the issue here

[hairygit]

Genuine or replica pipes?

[jon stead]

Genuine or replica pipes?

Genuine as far as I know.