Engine spluttering like hell from 7000 RPM

[Anton17]

Right, a few days ago I went to top up my oil and realised the bloke from my garage gave me scooter oil. It was green, and being unfamiliar with different oils I went back to him to check if it was okay to use it - he said it was fine so no worries.

When I topped it up I started it up and let the engine tick over for a little bit to let the new oil work through and the revs started to mount up a tiny bit without the choke on. The oil temperature gauge worked itself up to half way and it's never been that hot before. But no worries, all fine.

Last night coming back from work I started the bike up then got called in for a few minutes so I turned it back off. When I went back to it, after revving it a few times in neutral to warm it up, I realised I'd left the choke on but turned it off before I went off, i.e. had only revved it in neutral with choke on (could it have been this that caused it?). As I was going home it started spluttering in third gear only from 7000-10000 revs, a little like riding a horse or a kangaroo, coming and going quite badly. I thought maybe it would be the fuel since that's the kind of description people have given with low fuel but I've never let it get that low (fuel level seemed fine). Just sounding and feeling like the engine was about to stall then coming back and repeating in short gasps.

Today it did the same thing but in every gear above first, so not just third.

I've done about 700 miles since the last service so was wondering if it could just be in need of a new spark plug? The only thing that's changed in the past few days is the fuel and the oil so I'm thinking it's probably this new oil, but not sure. Would it be a good idea to drain the oil and top it up with what I was using before?

Was just wondering if anyone knew what was going on. Still new to the technical aspects so I'm no bike doctor just yet. Going to take it down the garage tomorrow for his verdict but was wondering if anyone could help out until then?

[Guest]

the problem with different oils is some dont get on with others, some are like sheets under a microscope others are like balls, so they make problems when mixed.. balls rub against each other, sheets slide over each other, balls and sheets is like paper/rock, (paper/rock/scissors....) not good..

an example is mineral oil or synthetic..

i would drain and replace with the right, usual stuff..

[Colin the Bear]

It would help if you put what bike we're dealing with. Scooter oil? Oil temperature guage? It's all a bit vague.

[Anton17]

the problem with different oils is some dont get on with others, some are like sheets under a microscope others are like balls, so they make problems when mixed.. balls rub against each other, sheets slide over each other, balls and sheets is like paper/rock, (paper/rock/scissors....) not good..

an example is mineral oil or synthetic..

i would drain and replace with the right, usual stuff..

 

Cheers, I thought it might have something to do with that, that's why I tried to run the bike in a bit with the new mix but didn't anticipate it causing this. I'll probably just get it all drained like you said.

 

It would help if you put what bike we're dealing with. Scooter oil? Oil temperature guage? It's all a bit vague.

 

Sorry, it's a Honda NSR 125, used 2-stroke Motul oil designed for scooters.

I think I could just use with draining and replacing oil, replacing spark and topping up transmission oil for luck. Will update tomorrow.

[Colin the Bear]

From what I can gather they recommend a fully synthetic 2 stroke oil. The lower spec scooter oil may well have fouled the plug. 10w/40 fully synthetic for the gear box. (Not car oil/ clutch slip)

Seems like you're on the right lines.

[Anton17]

Yep, well I took it to a tech today and he seemed to think it was not the new oil but the carb . He didn't take a look but said it could be that and that it needed draining and cleaning etc. He then moved on to say it could even be a problem with the gears.

I don't think it was wise to completely rule out the oil and treat it as a coincidence like he did and jump to conclusions.

Anyway, I've went and grabbed some full synthetic oil and a new spark plug from the Honda garage (different tech) and they agreed that draining the oil and replacing it would be my best bet. Will get on that later tonight and update.

[Colin the Bear]

Could be water in the petrol I suppose. There should be a little screw / drain plug on the bottom of the carb to drain it out. It seems to coincidental to not be the oil. A new plug is always a good idea.

[Anton17]

Think we've got it. Drained the oil tonight with the old tube 'n' suck technique and replaced the spark plug and now she's raring for it. I like this fully synth oil, I don't think I'll go back to using anything else now. Going to get some transmission oil tomorrow and all's good.

[Chrissb6]

Hi, as you first said you ran the bike on choke, it could well be something simple that you have gone and wet - fowled the spark plug. This would be my first port of call, very easy to check. Tempreture gauge will be reading the coolant - water not the oil. Also check the manual as to what spec of 2 stroke oil you should run on and see if that might cause the problem. l would be surprised if it did to be honest.

[Colin the Bear]

A less tastey way of removing fluid is to use the top off a household pump spray. Stick the pipe in and use the trigger to pump it out.

Easy fix eh?

[Anton17]

Hi, as you first said you ran the bike on choke, it could well be something simple that you have gone and wet - fowled the spark plug. This would be my first port of call, very easy to check. Tempreture gauge will be reading the coolant - water not the oil. Also check the manual as to what spec of 2 stroke oil you should run on and see if that might cause the problem. l would be surprised if it did to be honest.

 

Yep, we took the old spark plug out and it was pretty black, I wouldn't be surprised if it was just that which was causing the problem. And sorry, I meant the coolant temperature.

I was cautious of this new oil from the get go but I trusted the technician and he gave the all okay. Then after it causing problems and him still being adamant about it not being the oil, and giving me quotes for replacing the carb and gear faults... I'm a bit pissed off he was so stubborn it wasn't the oil, then after a quick job and draining and replacing it, no problems... I thought he was an alright guy, too.

[Chrissb6]

Happy to hear your sorted, It payes big time to do some investigating, no need to jump in the deep end keep it simple. Spare spark plugs was always part of the tool kit in the old days on 2 strokes, new oils suppose to rid plugs of fowling, but all said and done your burning oil! Trust is a big ask of a machanic the work carried out no matter what price you pay is only as good as the guy doing it. I heared a real horror story the other day, where a good friend of my daughter was quoted over £2,000 to change a head gasget on a ford kia

[Colin the Bear]

I think it's what's known in the trade as "Job Creation"