back firing

[lachie]

I've put an irk on my bike
it makes it run so much better but it also splutters a little and does a few small back fires every now and then
what could be the problem
it has a new iridium plug and stuff so its not dirty or anything could it be that i might have the idle up to high to prevent it from stalling easily? or wouldn't that effect it?

 

[coolmodee01]

you might be running her a bit to rich
try leaning it off a bit see how you go

 

[lachie]

okay
its weird though because the plug is like a browny sort of colour on top bordering on lean
and then before the thread underneath the gap bit
its black like it is running ritch?
ill give it a shot anyway

 

[coolmodee01]

maybe put your old plug in and see what that does to
if it fixes the problem them your new plug is not the correct one for the bike but thats a bit far fetched but it wont hert to try

 

[Cactus Jack]

Your advice is sound coolmodee1 - don't doubt yourself ...... I once bought an entire box of brand new NGK C7HSA plugs and they were ALL faulty except for a few ....... the stuffed ones were black and sooty with a weak spark making me think it was either the ignition or the carb ......... I wasted heaps of time messing with it , swapping jets , altering the float level etc and checking , testing and resetting the ignition timing which I KNEW was perfect before I finally discovered it was the plugs ........ micro cracks in the porcelain from faulty manufacture .

Whenever something goes wrong , you should ALWAYS work backwards (last alteration first) towards stock until you find the fault ........ I'd try a stock plug first ......then try the stock ignition ..... Of course the absolute mandatory thing that should be done as a matter of course is to check for crap in the float bowl and fuel system ........

 

[coolmodee01]

it's the only thing i could think of that would have left unburnt fuel in the zorst
but maybe carb is woeth a look also

i dont think valves would be an issue

 

[Cactus Jack]

could it be that i might have the idle up to high to prevent it from stalling easily? or wouldn't that effect it?

One way to find out is to back the idle right off and go for a ride ...... if the symptoms go way , then you've diagnosed your own problem without even realising it .......

They WILL burble on deceleration with the idle set too high ......... and fuel in the pipe could cause back firing ........

There was a thread on Thumpertalk a while back where people were talking about how the quicker rev up of IRK's can exceed the carbs ability to keep up ...... resulting in a flat spot or bog ...... that's why most 4 stroke MX'ers have accelerator pump carbs ...... they mechanically overcome any lag time in fuel delivery response when the throttle is suddenly snapped open .......

 

[Cactus Jack]

it's the only thing i could think of that would have left unburnt fuel in the zorst
but maybe carb is woeth a look also

i dont think valves would be an issue

If it were valves ..... it'd be hiccing and popping and carrying on when warming up ...... who knows , he might be a throttle jockey .... one of those people who blip the throttle suddenly all the time ...

I've seen throttle jockeys making new YZF's cough , fart and splutter and most people who ride my worked XR make it do it ........ then I get on it and it runs crisp and clean without missing a beat ....

IF a motor doesn't stall in neutral when you rev it and back off with an IRK fitted ..... then there's no sense in turning up the idle speed ........ you're ONLY doing it to make up for poor throttling , clutching and shifting coordination skills . The ANSWER is to either control the engine stall speed better with your right hand and control the clutch better with your left hand OR fit a heavier flywheel back on ...... accepting that you simply can't ride effectively with an IRK .......

 

[Fabio]

yeah ive had the same problem with my 08 140XR (with IRK), i found that adjusting the idle fixed the problem as it was backfiring on deceleration, took me ages to get the idle right though haha but now its crisp as

 

[mad man]

Is there fuel in the exhaust? If there is your needle in your carby is most probably stuck a tad, try cleaning it out, poking fine bits of metal through out the holes, take the idle screws out and poke wire down that hole too, remember how many turns it is out tho. Install a fuel filter also if you don't already have one.

Back firing is common with four stroke engines, how often is occuring and how bad is it? The timing some how could be out a tad? Or the exhaust valve might be out?

 

[lachie]

I've seen throttle jockeys making new YZF's cough , fart and splutter and most people who ride my worked XR make it do it ........ then I get on it and it runs crisp and clean without missing a beat ....

It is missing a beat though haha it was happening with the old flywheel just not as much
it would idle and then every 10 seconds or so it would splutter just a little i think its just gotten worse it splutters ever 4 seconds or so now..
it runs really rough when you ride it because its spluttering its not that its choking cause it cant keep up with the throttle maybe the timing or something?
but i have no idea about that sort of stuff

 

[lachie]

its basically a new bike so i don't think that the carb would be dirty or anything

 

[Cactus Jack]

Sounds like it's either something to do with the electrics ....... poor coil or ignition earth to frame (make sure there's no paint under earth points) , intermittent shorting , or the plug has a cracked insulator (inside below the electrode) .

Or there's crap in the fuel system or a blocked breather causing intermittent fuel delivery ........ for instance , water in the float bowl can cause missing , crackling and popping ......

To check your plug it's best to remove a lead from one plug on a car , plug your bike plug in ....... and while grounding the plug body ...... watch what the spark is doing while the cars engine is running ..... try to wedge the plug somewhere or hold it with insulated pliers to avoid getting zapped ......

The spark should be a constant and steady pulse between the centre electrode and outside one ...... if the plug is faulty , it'll be jumping the gap sometimes .... then jumping to the thread part or jumping across down inside the guts of the plug ......

I had a box of new plugs ...... I'd put a new one in and the bike would start and run great ....... then it wouldn't start after being turned off ....... I'd put another new plug in and the same thing would happen ........ I found out what the problem was by checking the plugs as above ..... trying to do it on a bike is hopeless ........

You can use a power timing light with an inductive pickup clipped over your plug lead while the bike is running to check if the misfire is electrical or not .... you simply pull the trigger and watch the light to see if it's pulsing at a steady and constant rate ......... but it won't tell you what's going on at the electrode end of the plug .......

If the ignition and plug checks out OK ...... then it's time to go over the carb and fuel system . NEW bikes can most definitely have fine plastic particles from inside the tank floating around in the fuel line or float bowl causing weird intermittent misses , bogs etc .........

It's all trial by elimination ....... there's no magical single answer .........