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just a thought have you swapped the plugs around just because they are new doesnt mean they are all perfect...possible duff one
Quote from: K2-K6 on September 28, 2017, 09:56:56 PMCan 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.
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.
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.
Quote from: jon stead on September 28, 2017, 10:32:13 PMQuote from: K2-K6 on September 28, 2017, 09:56:56 PMCan 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.
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.
It's only when you open the throttle full that it bogs down and yes I suppose stutters as you call it.
Quote from: jon stead on September 29, 2017, 09:45:01 AMIt'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.
Quote from: jon stead on September 24, 2017, 10:48:22 PMStumped 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?
The fuel strainer was renewed and a visual check of both tank outlets, with hoses removed, shows a steady uninterrupted flow of fuel.
(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