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+--- Thread: Engine misfire - I doubt this is the first thread! (/showthread.php?tid=78678)
Engine misfire - I doubt this is the first thread! - Unionjack30 - 25-08-17
Evening all!
I have developed a Miss fire on cylinder 3 under 3k -3.5k.
The exhaust pipe on cylinder 3 is cold untill above 3k.
I have changed all the plugs and checked the ht leads, all seem to be sparking fine. But this is as far as I have got, as not sure what to check next!!
Thanks in advance
Re: Engine misfire - I doubt this is the first thread! - darrsi - 26-08-17
Probably easier for you to put 'misfire' in the search box (above left) and have a good read.
Re: Engine misfire - I doubt this is the first thread! - Disorderlypunk - 26-08-17
when you say missfire there are so many meanings and i dont think any of them are applying here
a pop and a bang through your exhaust every so often is a missfire (missplaced firing)
but below 3000 rpm no bang, above 3000rpm a bang things are a little different
this is where things get interesting and somewhat difficult to identify through here (but have before)
starting with easiest to get access etc
can you smell petrol in your oil (take filler cap off and get your nose in there)
(if you can then blown gasket or piston rings kaput)
are you able to perform a compression test ??? check all 4 and write them down you will see if something is wrong
(below 3k rpm pressure could just leak into crank through a couple of routes gasket/piss rings or even badly seated valves [size=78%])[/size]
(above 3k rpm its still leaking but not fast enough so still ignites)
these are only the two i would start with here because this has popped up a few times but described differently and has turned out as 2 blown gaskets (including my own) and one badly seated exhaust valve - thankfully both of these are relatively easy to fix if you have the time, patience and a little know how (or this forum to be pointed in right direction)
and in tommorows lesson we shall be looking at fuelling issues
THE FIXES
Blown gasket - REPLACE GASKET (bet you couldnt have guessed that :lol [/size][size=78%])[/size]
[/size]Non seating valve - Valve lapping then check clearances - its easy its basic its like being in the scouts before we had lighters (some might get that joke)[size=78%]
[/size]piston rings - pray that it isnt them (it is the least likely to be a problem)[size=78%]
Re: Engine misfire - I doubt this is the first thread! - pointer2null - 28-08-17
On the fazer there are two coils, each fires a pair of cyclinders, so normally if a coil fails then both cylinders will play up.
Take the plug out on #3. If dry maybe carb issue (no fuel), if wet then that shows you have fuel.
Re: Engine misfire - I doubt this is the first thread! - storm - 28-08-17
can only be the pilot jet on number three cylinder, make sure its clean
Re: Engine misfire - I doubt this is the first thread! - Disorderlypunk - 28-08-17
(28-08-17, 11:41 AM)storm link Wrote: can only be the pilot jet on number three cylinder, make sure its clean
damn you beet me to the carb section - was leaving this till second as can be a bastard to get in there
- i have a pilot issue on mine at moment on 1+2 and ticks over like a lump just aint got the time to rip them out at the moment
Re: Engine misfire - I doubt this is the first thread! - Bretty - 29-08-17
Someone needs to find a good misfire diagnostics thread and make it a sticky!!
Swap the caps and plugs over between cylinder 2&3. They both spark at the same time (although only one fires, as it's on its compression stroke while the other is on exhaust stroke), so if the issue changes cylinder with the swap you know its the plug/cap/coil, or if the problem stays with cylinder 3 you know it's a carb issue (air/fuel).
Issues with cylinder 3 - I tend to lean towards a plug/cap issue as if the bike is left outside on the side stand, water sits around the top of that plug and corrodes it.
Also don't always assume that problems that change with rev range are always the result of a carb issue. The carbs do change the air/fuel mixture through the rev range, but this also changes the resistance of the mixture in the cylinder and will create a misfire at certain revs if you have a weak spark / electrical fault.
It may very well be the carbs. But it's not the first job I would be rushing to do with a misfire.
Re: Engine misfire - I doubt this is the first thread! - pointer2null - 29-08-17
(29-08-17, 10:14 AM)Bretty link Wrote: It may very well be the carbs. But it's not the first job I would be rushing to do with a misfire.
Totally agree - hence advised to take out #3 plug and inspect it. Swapping leads is another good one.
Re: Engine misfire - I doubt this is the first thread! - Disorderlypunk - 29-08-17
he has said everything is sparking fine though
Re: Engine misfire - I doubt this is the first thread! - pointer2null - 29-08-17
It maybe at tickover, but a crack in the plug cap may not show up until higher rpm or under load.
If you swap leads and the fault follows it's electrical - a simple and easy tests. Same for removing the plug and looking at it. As every Haynes manual used to point out, you could tell the mixture by the spark plug colour. Block jet or air leak = weak mixture . Electrical fault means unburned fuel.
I'd start with stuff like that before pulling the carbs.