Author Topic: Misfires above 4,500  (Read 2533 times)

Offline jon stead

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Re: Misfires above 4,500
« Reply #60 on: October 11, 2017, 11:01:27 PM »


   the plug gap should be 27 thou,

  non resistor plugs, and resistor plug caps ,

   

 

I’m using non resistor plugs and 5kohm resistor plug caps. I’m sure I read somewhere on Dynatek site, to set plug gaps between 0.035 and 0.040”
1973 CB 500 K2, 2015 Triumph Bonneville T100, Newchurch

Offline jon stead

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Re: Misfires above 4,500
« Reply #61 on: October 12, 2017, 06:18:10 PM »
Number 3 plug still fouling up. The other three are a beautiful grey/brown colour.

So, it’s not coils, ignition system, plugs or leads. It’s not carburettor or valve clearance.

All four cylinders are showing 100 psi on compression test.

I have found the Cap. Tach Gear, pn 12451323000, to be broken and this had been previously “stuck” back together, by P.O. Since I’ve had the cylinder cover off, this tachometer drive housing is now leaking. When I remove the plugs, clean Number 3, put it back in, the bike runs good for a few miles, then the misfire starts again. Could this oil leaking down into Number 3 spark plug well be causing the misfire and the sooty plug?

If it’s not this then the only other thing that’s specific to Number 3 cylinder is the exhaust.

As can be seen from my previously attached YouTube clip, the bike ticks over lovely and freely revs when in neutral. Out on the road, when it’s struggling to get above 5,000 rpm, if you pull the clutch in, the engine will happily rev right up.
« Last Edit: October 12, 2017, 06:49:22 PM by jon stead »
1973 CB 500 K2, 2015 Triumph Bonneville T100, Newchurch

Offline mike the bike

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Re: Misfires above 4,500
« Reply #62 on: October 12, 2017, 06:30:32 PM »
That's caused by an air leak on the inlet rubbers of thereabouts.   I had the same fault on my 550four.
Why did I get rid of that one

Offline jon stead

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Re: Misfires above 4,500
« Reply #63 on: October 12, 2017, 06:48:04 PM »
That's caused by an air leak on the inlet rubbers of thereabouts.   I had the same fault on my 550four.

I tried the WD40 squirt trick around the rubbers on the intake side and noticed no increase in revs but I’ll certainly look at it again.

I thought an air leak would make it run lean and hot, as opposed to rich?
1973 CB 500 K2, 2015 Triumph Bonneville T100, Newchurch

Offline K2-K6

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Re: Misfires above 4,500
« Reply #64 on: October 12, 2017, 08:11:20 PM »
Are you sure of that compression reading? It looks way too low to be running properly.

Offline jon stead

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Re: Misfires above 4,500
« Reply #65 on: October 12, 2017, 08:29:30 PM »
Are you sure of that compression reading? It looks way too low to be running properly.

I can’t vouch for the accuracy or calibration of the gauge, but as a means of comparing one cylinder to another, they are all the same reading.

#1, 2 and 4 are running great, #3 has the mis fire resulting in the sooty plug.
1973 CB 500 K2, 2015 Triumph Bonneville T100, Newchurch

Offline K2-K6

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Re: Misfires above 4,500
« Reply #66 on: October 12, 2017, 10:36:38 PM »
It doesn't sound logical I agree,  in that one cylinder differs in burn from others that are apparently the same.

That compression overall reading though I wouldn't by able to resist investigating further.  A slightly wide field view perhaps,  but if compression is genuinely that low then it's conceivable that the combustion burn time would be slow and as such it would limit the rpm under load to give the 4500rpm ceiling.

You could try advancing the timing to compensate and see if it would rev higher at all to give you more of a picture.

Offline jon stead

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Re: Misfires above 4,500
« Reply #67 on: October 13, 2017, 07:42:14 AM »
It doesn't sound logical I agree,  in that one cylinder differs in burn from others that are apparently the same.

That compression overall reading though I wouldn't by able to resist investigating further.  A slightly wide field view perhaps,  but if compression is genuinely that low then it's conceivable that the combustion burn time would be slow and as such it would limit the rpm under load to give the 4500rpm ceiling.

You could try advancing the timing to compensate and see if it would rev higher at all to give you more of a picture.

I did advance the timing previously, and it made no difference. I agree that if the compression is low it would affect available engine power, but my problem seems to be on Number 3 only. Plus, the engine starts easily and ticks over lovely, revving freely under no load.

As stated previously, I now think that oil leaking from the tacho drive is affecting the quality of the spark on Number 3. I base this assumption on the fact that immediately after replacing the plugs, all cleaned up, the engine runs reasonably well, not perfect but good. Then, after say 5 miles, the misfire above 4500 rpm starts. I think this is when cylinder 3 stops firing, or not firing well, due to the fouled plug.

I have araldited the tacho drive in place whilst I source an intact drive, in the hope that this will stop the oil leak, and stop oil leaking onto Number 3 spark plug cap and HT lead.
1973 CB 500 K2, 2015 Triumph Bonneville T100, Newchurch

Offline totty

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Re: Misfires above 4,500
« Reply #68 on: October 13, 2017, 04:07:16 PM »
I still think no 3 sooting is a separate problem, these bikes will rev higher than 4500 on 3 cylinders.

Offline mike the bike

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Re: Misfires above 4,500
« Reply #69 on: October 13, 2017, 05:17:36 PM »
I do too.  The fact that there's power to be found when the choke is operated suggests that it's running too lean (inlet airleak) and operating the choke enriches the mixture back to what it should be.
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Offline K2-K6

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Re: Misfires above 4,500
« Reply #70 on: October 13, 2017, 05:44:36 PM »
It looks like the number 3 problem could be a symptom rather that cause. The plug caps if they are NGK in good condition are reasonably well protected against ingress and run without problems in rain conditions.

The problem with lower cylinder pressure is not necessarily one of outright power failing to pull the weight along but more of burn time of the mixture. It ultimately,  if too slow,  acts as a speed governor above which a loaded engine will not gain revs. It usually gives a very gentle and smooth tickover though.

Offline jon stead

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Re: Misfires above 4,500
« Reply #71 on: October 13, 2017, 05:47:51 PM »
I do too.  The fact that there's power to be found when the choke is operated suggests that it's running too lean (inlet airleak) and operating the choke enriches the mixture back to what it should be.

Thanks Totty and Mike the Bike. Excuse my ignorance, but running lean wouldn’t cause the plug to soot up, would it? Also, there’s no evidence of overheating and as I say, I squirted WD40 on the intake manifold rubbers and there was no noticeable increase in engine revs.

Edit: Sorry, forgot to ask, where did I say it had power when the choke is operated? I have tried the choke in various positions whilst riding and there is no improvement in performance. All that happens is it bogs down as expected.
« Last Edit: October 13, 2017, 07:17:05 PM by jon stead »
1973 CB 500 K2, 2015 Triumph Bonneville T100, Newchurch

Offline Johnwebley

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Re: Misfires above 4,500
« Reply #72 on: October 13, 2017, 05:48:33 PM »

  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 ?
lifelong motorcycle rider,and fan

Offline jon stead

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Re: Misfires above 4,500
« Reply #73 on: October 13, 2017, 05:51:28 PM »
It looks like the number 3 problem could be a symptom rather that cause. The plug caps if they are NGK in good condition are reasonably well protected against ingress and run without problems in rain conditions.

The problem with lower cylinder pressure is not necessarily one of outright power failing to pull the weight along but more of burn time of the mixture. It ultimately,  if too slow,  acts as a speed governor above which a loaded engine will not gain revs. It usually gives a very gentle and smooth tickover though.

Thanks K2-K6. I’m hearing what you’re saying but do not understand why only Number 3 would be sooting up.

1973 CB 500 K2, 2015 Triumph Bonneville T100, Newchurch

Offline K2-K6

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Re: Misfires above 4,500
« Reply #74 on: October 13, 2017, 06:08:02 PM »
Yes,  I don't understand that either but you seem to have worked through many of the things that would affect the cylinder individually.

It's certainly giving you a bit of a run around,  something very peculiar going on with it.

Looks a great bike in the video though.