Author Topic: Misfires above 4,500  (Read 6714 times)

Offline jon stead

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Re: Misfires above 4,500
« Reply #30 on: September 28, 2017, 10:35:47 PM »
just a thought have you swapped the plugs around just because they are new doesnt mean they are all perfect...
possible duff one

Yes, I swapped the plugs around, no change.
2015 Triumph Bonneville T100 Newchurch

Offline jon stead

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Re: Misfires above 4,500
« Reply #31 on: September 28, 2017, 10:40:17 PM »
Thank you everybody for your suggestions. I appreciate them.

If reverting to the original coils and points then I'm stumped.
2015 Triumph Bonneville T100 Newchurch

Offline kevski

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Re: Misfires above 4,500
« Reply #32 on: September 29, 2017, 07:10:43 AM »
Can you test the compression as it is? I know you won't get a hot/absolute figure for it, but it would makes a valid comparison from one cylinder to the others and see if you have any major discrepancies.

Bike had a rebore, new pistons and rings less than 500 mile ago. I haven't retested the compression as I'm assuming it's good.
One of the first things i would have done, may have broken ring/s ring in upside down valve blow by.
« Last Edit: September 29, 2017, 07:54:40 AM by kevski »

Offline totty

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Re: Misfires above 4,500
« Reply #33 on: September 29, 2017, 09:14:44 AM »
I've just re read it all and I'd advise one further test with the Boyer before swapping back to points, swap parts around so the sooty one runs off both a different lead, coil, cap, plug - ideally having another cylinder run off the suspect set of parts. (they all fire at once and the leads unplug from the coils so this should be easy to setup)
I'd also check the unit has a really good earth and temporarily add an earth to the engine in case it's mounts are isolated by paint - I've seen bad earths act like a rev limiter.

I'd also follow the compression test advice once it's back together, but while the head is off I'd remove the barrels and check the bore and rings on the cylinder with the sooty plug.
The sooty plug should really only be caused by oil buring or a rich mixture and you've rulled out the rich mixture.

What happens at 4,500, does the engine tone go dull like one cylinders stopped firing or does it go erratic and stutter like a typical misfire. How consistent is it, is it always at 4,500 and immediately on hitting it or is in just in that ball park, does it recover immediately when the revs drop?

I wouldn't rule out two independent problems here. More gut feel than anything but I doubt the sooty plug is an ignition problem and swapping parts around will confirm this, however I also doubt that something which would cause a sooty plug would consistently only give symptoms at a set rpm.

Offline jon stead

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Re: Misfires above 4,500
« Reply #34 on: September 29, 2017, 09:45:01 AM »
I've just re read it all and I'd advise one further test with the Boyer before swapping back to points, swap parts around so the sooty one runs off both a different lead, coil, cap, plug - ideally having another cylinder run off the suspect set of parts. (they all fire at once and the leads unplug from the coils so this should be easy to setup)
I'd also check the unit has a really good earth and temporarily add an earth to the engine in case it's mounts are isolated by paint - I've seen bad earths act like a rev limiter.

I'd also follow the compression test advice once it's back together, but while the head is off I'd remove the barrels and check the bore and rings on the cylinder with the sooty plug.
The sooty plug should really only be caused by oil buring or a rich mixture and you've rulled out the rich mixture.

What happens at 4,500, does the engine tone go dull like one cylinders stopped firing or does it go erratic and stutter like a typical misfire. How consistent is it, is it always at 4,500 and immediately on hitting it or is in just in that ball park, does it recover immediately when the revs drop?

I wouldn't rule out two independent problems here. More gut feel than anything but I doubt the sooty plug is an ignition problem and swapping parts around will confirm this, however I also doubt that something which would cause a sooty plug would consistently only give symptoms at a set rpm.

I've already swapped the coils but as yet, untested. As you say, easy enough to swap an ht lead so I can do that. I did try swapping the plug caps from 2 to 3 and vice versa and that made no difference.

Regarding your remaining questions, hard to pin point exactly, but now I think about it, no not consistently at 4500 revs and the recovery is not really noticeable as you reduce revs but bike rides lovely at revs below, say 4500. It's only when you open the throttle full that it bogs down and yes I suppose stutters as you call it.
2015 Triumph Bonneville T100 Newchurch

Offline jon stead

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Re: Misfires above 4,500
« Reply #35 on: September 29, 2017, 10:15:05 AM »
Can you test the compression as it is? I know you won't get a hot/absolute figure for it, but it would makes a valid comparison from one cylinder to the others and see if you have any major discrepancies.

Bike had a rebore, new pistons and rings less than 500 mile ago. I haven't retested the compression as I'm assuming it's good.
One of the first things i would have done, may have broken ring/s ring in upside down valve blow by.
As I say I never considered compression given the recent rebore and new pistons and rings. Surely I'd be burning oil if a ring was broken or in upside down?
2015 Triumph Bonneville T100 Newchurch

Offline AndyH

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Re: Misfires above 4,500
« Reply #36 on: September 29, 2017, 11:03:07 AM »
Stumped again.

Engine still ticks over nice and rides nice at low revs but doesn't pull above 4500 rpm. Number 2 plug was sooty, so I put the original carbs back on, hard to say if better or not, but plug 2 still sooting  up. So unlikely the same fault is with both sets of carbs.

Checked Boyer Branson electronic ignition advance is ok, I.e. Full advance at 4,500 rpm.

There's a new set of D7 plugs in, gapped correctly. Valve timing is correct and valve clearances are correct.

Now looking at electrics again. Confirmed plug cap resistance is correct and have also exchanged cap 3 and 2 for each other. If number 3 plug soots up then it's the plug cap at fault. Will check tomorrow. Also going to check all electronic ignition wiring tomorrow, coils and ht leads.

I may be repeating other responses Jon, but when you say "Misfires above 4500" are you referring to a jerky popping effect or just a "running out of breath" situation?
Andy

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Offline totty

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Re: Misfires above 4,500
« Reply #37 on: September 29, 2017, 11:08:42 AM »
It's only when you open the throttle full that it bogs down and yes I suppose stutters as you call it.

That (with jetting and carb cleanliness ruled out) would make me think fuel flow, the strainer, hose, pipes between carbs or float needles could have a restriction. Could be as simple as a kinked or internally collapsing fuel hose, that would be a good result, nice cheap and easy fix.


Also yes I'd expect a ring issue to result in burning oil, but it wouldn't take much to make one plug sooty.

Offline jon stead

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Re: Misfires above 4,500
« Reply #38 on: September 29, 2017, 01:33:28 PM »
It's only when you open the throttle full that it bogs down and yes I suppose stutters as you call it.

That (with jetting and carb cleanliness ruled out) would make me think fuel flow, the strainer, hose, pipes between carbs or float needles could have a restriction. Could be as simple as a kinked or internally collapsing fuel hose, that would be a good result, nice cheap and easy fix.


Also yes I'd expect a ring issue to result in burning oil, but it wouldn't take much to make one plug sooty.

I've got two fully refurbished sets of carbs, both with their own fuel pipes, and problem the same whichever set of carbs and associated hoses are on.

The fuel strainer was renewed and a visual check of both tank outlets, with hoses removed, shows a steady uninterrupted flow of fuel.
2015 Triumph Bonneville T100 Newchurch

Offline jon stead

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Re: Misfires above 4,500
« Reply #39 on: September 29, 2017, 01:37:57 PM »
Stumped again.

Engine still ticks over nice and rides nice at low revs but doesn't pull above 4500 rpm. Number 2 plug was sooty, so I put the original carbs back on, hard to say if better or not, but plug 2 still sooting  up. So unlikely the same fault is with both sets of carbs.

Checked Boyer Branson electronic ignition advance is ok, I.e. Full advance at 4,500 rpm.

There's a new set of D7 plugs in, gapped correctly. Valve timing is correct and valve clearances are correct.

Now looking at electrics again. Confirmed plug cap resistance is correct and have also exchanged cap 3 and 2 for each other. If number 3 plug soots up then it's the plug cap at fault. Will check tomorrow. Also going to check all electronic ignition wiring tomorrow, coils and ht leads.

I may be repeating other responses Jon, but when you say "Misfires above 4500" are you referring to a jerky popping effect or just a "running out of breath" situation?

Again hard to say. It's not jerky as in surging back and forth, but runs less smooth and has no get up and go. Sorry I can't be more descriptive.
« Last Edit: September 29, 2017, 04:53:04 PM by jon stead »
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Offline Pangloss

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Re: Misfires above 4,500
« Reply #40 on: September 29, 2017, 01:50:30 PM »
(Checked Boyer Branson electronic ignition advance is ok, I.e. Full advance at 4,500 rpm. )

Did u check that  advance curve beyond 4,500...?  Using a strobe light.... If the motor is not missing at 4500 but just going flat on power , sounds like ignition retard....at 4500

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Re: Misfires above 4,500
« Reply #41 on: September 29, 2017, 02:29:51 PM »
I've been trying to think about that advance as it's electronic on these systems,  I believe. So it must have an internal count for rpm to allow it's logic to be applied. Don't know what internal architecture is or if it gets rpm count from one or both pickups. Could there be a failure to advance but still fire the plugs?

The rings do different things,  top compression obviously tries to work by stopping the pressure leaking download the bores. The oil control rings try to stop the oil going in the other direction. So if you get a compromised top ring you loose compression to the crankcase but won't necessarily get oil going the other way if the lower rings are functioning correctly. So you can get low pressure on one cylinder without appreciable oil loss.

Offline totty

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Re: Misfires above 4,500
« Reply #42 on: September 29, 2017, 04:03:23 PM »

The fuel strainer was renewed and a visual check of both tank outlets, with hoses removed, shows a steady uninterrupted flow of fuel.

That pretty much rules out fuel flow, but since it's one of the few things you can rig up to test while the heads off it might be worth a quick test for a steady flow on each carb drain.

Offline mickwinf

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Re: Misfires above 4,500
« Reply #43 on: September 29, 2017, 04:39:10 PM »
i would also remove valves on the affected cylinder in case one is bent or not seated properly
Love the 500 and 550 have a 500 called Lazarus under restoration

Offline jon stead

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Re: Misfires above 4,500
« Reply #44 on: September 29, 2017, 04:45:47 PM »
(Checked Boyer Branson electronic ignition advance is ok, I.e. Full advance at 4,500 rpm. )

Did u check that  advance curve beyond 4,500...?  Using a strobe light.... If the motor is not missing at 4500 but just going flat on power , sounds like ignition retard....at 4500

I did use a strobe light and it's as Boyer say it should be, I.e. On full advance mark at 4,500 rpm
2015 Triumph Bonneville T100 Newchurch

 

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