I've got a 2015 Montesa 4rt that I bought new , it's been maintained above and beyond, but I've recently been suffering from what appears to be a rich mixture. I replaced the plug four events ago for an NGK iridium one which has become sooty, as did the last one.

It also smells rich when it's on tick over and uses more fuel than other riders that I ride with that have similar bikes.

The bike rides and performs well and I assumed with fuel injection that there would be no mixture issues.

The air filter is a TwinAir and it's cleaned after each event

It also seemed to boil the fuel, for want of a better phrase, at last weekends event.

The bike still ran fine but I opened the fuel filler to check and it was ariated and bubbled out of the tank then settled down. I checked the breather, not original, the small cap with ball bearing inside type, it appeared fine.

Ran it for another half hour or so checked it again and the fuel bubbled out the cap as I unscrewed it under quite a bit of pressure.

Open to sensible suggestions of how to cure. Both issues do not affect the running of the bike.

Thanks guys.

I'd take the aftermarket breather off and try without it.

The 4rt will soot plugs if it's not warmed up properly and the throttle blipped too much.

As far as I know NGK don't make a cr6eh9 iridium equivalent, they do a 7 and a 5.

I've been using the 7 iridium for a while, purely for the Scot as it tends to misfire when it's thrashed to within an inch of its life.

When we rode abroad for the Europeans the factory lads would give us cr5eh9's.

I use a cr5 in my 2015 and never have an issue.

I think i have a spare if you want to try one and are local to blackburn

Thanks for the reply, the plug I use is a NGK IR CR6EIA9 , which I was told was the IR equivalent of the standard plug.

Already put the original overflow pipe back on to monitor at the Trial on Monday.

I am mechanically sympathetic ( being a mature 57 year old rider ) and will always leave it ticking over whilst I get my gear on, so it's running for 3or 4 minutes before it's ridden off. I'm not a throttle blipper , as 4 strokes don't need it like a 2 stroke does to clear its throat.

Probably need to give it a good thrashing over the Lakeland Fells on Monday rather than mothering it !!!!!!

 

Thanks Teddybattye, see how it goes on Monday and may try a 5, thanks for the offer of the plug.

Are you two gents on the standard petrol cap breather or an aftermarket one??

I only ever have seen this when I over oiled my filter... maybe try getting the bike nice an hot then letting it idle without the filter for a nice bit.  Then check the plug and see what you get?  if it isn't as bad as it was before then that could explain it? 

Best of luck.

That's the correct iridium. It may be worth trying the 5 if it doesn't get to stretch it's legs very often. I'm using the std filler cap with an open tube to vent.

Thanks Jonny, definitely worth a try, thinking about it I use to use engine oil then rung it out and let it drain.

Ive recently used an oil filter aerosol spray oil, may go back to old oil and ringing out method.

Might be guilty of molly coddling it , I'll give it a thrash on Monday see if that clears its head. ??

Try an iun oiled filter and let it tick over for 10 mins 

i think the efi is more clever than looking at the plug colour unless you do s plug chop once its warm

1 hour ago, chappo said:

Might be guilty of molly coddling it , I'll give it a thrash on Monday see if that clears its head. ??

The EFI ECU should adjust the mixture to accommodate gentle running and correct the mixture accordingly. Cold weather may be causing an extended warm up (rich fuelling) period. I think the 4rt will have the following sensors:

1) MAP  Manifold absolute pressure - this sensor should tell ECU to correct for an over or under oiled or clogged air filter

2) IAT   Intake Air Temperature - in conjunction with MAP (and other parameters) enables the ECU to calculate the mass of air entering the engine and hence the mass (Injector open time) of fuel needed to give correct combustion

3) CTS - Coolant Temp Sensor - Its input to the ECU gives longer Injector open duration when engine is cold / during warm up. It may also control fan on / off but this is often a separate sensor.

A fault in any one of the above sensors or a fault (poor connection) changing the voltage across it can give rich running. From my experience on cars the CTS would be the most likely to give a faulty output.

Injector - if it has a fault, typically a weak or broken spring or a piece of minute dirt on the seat it does not close properly resulting in "injector dribble" and an over rich mixture. In this case the over richness will be more prominent during gentle use.

An ignition fault (typically HT coil failing) can give rich running symptoms including plug sutting because the ignition is not sufficient to give complete fuel burn.

EFI injection pressure is typically MAP plus 3 Bar irrespective of tank pressure, therefore a few PSI in the tank due to breather pipe should not have any effect. Cars tend to have an accurately regulated fuel pressure mechanism or a fuel pressure sensor that enables the ECU to calculate injector duration. I do not know which is used on the 4RT. If it has neither then excess pressure in the tank would enrichen the mixture

9 hours ago, chappo said:

Are you two gents on the standard petrol cap breather or an aftermarket one??

I'm on the standard cap with the breather pipe tucked up in the headstock

Thanks for all the help guys, especially the comprehensive dadof2 reply which was like an exam answer.

Ive reverted back to original breather and extracted most of the oil out of the filter, see how Monday goes.

I have the single and dual map software for reading the throttle body if you need to look down that route.

Ive just changed the map on mine