I've had my 4rt for 2 months now and think it's absolutely fantastic, but I'm now having my first problem in the shape of a misfire when I open the throttle looking for a bit of power when climbing or getting up a step etc.

Basically what happens is, I open the throttle and at low revs / low throttle openings the engine is OK, anything more than 1/4 throttle or so, then I get a misfire which feels like the engine is dying and then it comes back in with a bang (a bit like a 2-stroke when it '4-strokes', or like a bike with a warm engine and the choke partly on). When I ease off the throttle a touch it starts running cleanly again

When I take the plug out it's dry and sooty and cleaning it doesn't make any difference to the running

The bike starts well from either cold or hot

I recently gave the bike an oil change and cleaned and re-oiled the filter (I didn't have a new plug, but this is on order and should be here tomorrow hopefully)

I did wonder if I had over-oiled the air filter, so I tried it without the filter and flame arrestor grill - the plug still soots up

The plug gap is correct as per the manual

The plug generates an intense small white spark when I earth it on the cylinder head (and a plug from my pals GasGas gives a fat blue spark

I have read that the bike has a "get you home safe mode" which kicks in if the engine overheats, but the fan appears to be working and switches on and off as I'd expect

Can anyone out there give me some pointers as to where to start looking ?????

I have a friend over here in Squamish, B.C. Canada that Has experienced the same problem when he removed the restricter plate from the throttle body. The bike that he has is a 2008 and more than likely a Euro-spec bike. The local distributor has not been able to offer any advice except to say that "The electronic fuel injection takes care of everything so it shouldn't do that".

Any advice would be helpfull to all.

Spencer

I'd try a new plug. Plugs can fail as the compression builds up under more throttle, but spark fine at idle. It's rare, but new plug is a quick and easy way to rule it out.

Rich

Make sure the head pipe collar is tight. (don't over tighten) If it is loose it can cause a mis-fire.

Art

Did you buy it from new?

If not and it's been running fine till now look back through the forums, someone had a misfire and it turned out to be the fuel pump.

What fuel do you run the bike on? I found using std unleaded the plug tended to blacken up quickly and the bike wouldn't run properly. I use super unleaded and the bike runs fine.

Hi there,

Are all the restrictors removed throttle body, 2x exhaust, and electrical (green wire) ?

Lots of things to look at here - thanks for this everyone........... and here's some more info which these answers have raised

The bike was running fine until recently and it still has the exhaust and throttle body restrictors in place

I havent touched the green wire - what do I do with it and what does it change on the bike ?

I've tried the bike on unleaded and super unleaded and it doesn't seem to make any difference to how it runs (although I can't vouch for any differences in the plug condition)

A new fuel pump sounds expensive... surely Montesa (Honda) design them to last more than a year !!!!!! Is there a method for testing them ?

I'll check over the things that have been listed here over the weekend and post my results as soon as I have any

ask gizza5 about about a fuel pump. He replaced his at about 300 pund. Think it was to do with cuttin out though. Yes your right it shouldnt go on a mont so new but its like anything i guess can break. Regarding plug i would change first. Mine soots up. When changed its spot on. I do get the occasional miss but it dont worry me. I have an 08 and changed plug 5 times this year so far, but i do a fair bit of riding. Good luck and hope you solve the problem. JUST A THOUGHT. Have you rang the importer?

I agree with the new plug suggestion. My "07" did the same thing once and a plug fixed it. They always appear sooty no mater what but you might try something I found elsewhere on this forum. Don't touch the throttle for the first five minutes after starting from cold - just let it idle. I have no idea why but plugs seem to last forever if you do this.

Before doing anything drastic, get the new plug and let it idle until the fan comes on before riding. This cured all starting/running problems with my 07. Good luck! - Bob

Definately try as said above waiting untill the fan kicks in before touching the throttle, if i dont on mine it instantly fouls a plug or runs abit ****e, no idea why it works but it does.

Wait 5 minutes!

What happens if you turn up late for a trial?

k its that rumour ,every one adds a bit .

k its that rumour ,every one adds a bit .

Ah, I see. The same rumours that state every 1 in 2 Beta stators fail, all Sherco mains fall out, most Gassers fall in bits and all Scorpas are ****e

Complete B*****ks then! Well, apart from the last one obviously