Fuel Mix MX250A/MX360A

[Nathan S]

I've been running Motul M800 at 20:1 in my Yamaha 125s + DT1, and have no dramas with fouling plugs. Not all of them are jetted all that well either...
Certainly no dramas with wearing stuff out, or blow-ups either.

I was always a bit of a fence sitter WRT the ratio debate. The Lozza pointed out that ALL of the reasons for lean oil:fuel ratios were about convinence and cost, and NONE of them were about performance or longevity. I jumped on board the 20:1 boat, and haven't had a moment's regret. Also worth noting that the leaner your oil:fuel mix is, the greater the consequences will be if you make  a slight miscalculation when mixing...

Generally speaking, the larger the engine, the lower it will rev - so the leaner you can safely run the oil mix.


What brand of fuel are you using? The 98 octane Shell fuels have a known tendency to foul plugs in carb'd engines - something to do with trailing throttle/idle, and the way the EFI cuts the fuel right back in those conditions (carbies do not).

[JohnnyO]

I've run Motul 800 at 40:1 in all my bikes with no problems, any more oil than that and it spits out everywhere. What Lozza says is the opposite to what Mr Belray says.. who do you believe? I think i'll go with the guy that gets paid to know and promote oils. I run BP ultimate fuel and have had great results.

[Nathan S]

I've run Motul 800 at 40:1 in all my bikes with no problems, any more oil than that and it spits out everywhere. What Lozza says is the opposite to what Mr Belray says.. who do you believe? I think i'll go with the guy that gets paid to know and promote oils. I run BP ultimate fuel and have had great results.

I've been using the 98 Octane Caltex petrol, simply because its the only 98 octane available local to me. I have no complaints with it.

When Mr BelRay can tell me (over the phone) how to port an otherwise standard DT1 so that it is consistantly 3rd or 4th into the first corner against the pre-70 big guns, then I'll listen to him over Uncle Loz. ...

Like I said, the thing that convinced me was that all of the arguments for lean oil ratios were for things like "low carbon build up", "less smoke", "less money spent on oil" and the like.
None of which has any relevance to an MX bike, at least not when compared to "maximum power" and "doesn't go boom".

[firko]

I spent a day at the farm earlier in the year with my old square barrel, my ex '81 490 my mates IT465 and another mates '02 360 Husky. In the past I always use Castrol TTS @30:1 with no problems but had changed to Motul @ 40:1 in recent times because that's what my mates were using. All of the other bikes used Motul except my mate with the IT who used Silkolene @40:1 (because he got 10 litres of it for free!). Anyway, we decided to do some chopping and changing of petrol/oil ratios and plug chops to see what was going on within. In the end, I found that my bike ran a little nicer with BP 98 fuel and Motul @30:1 and most of the more modern bikes were happy on Motul 40:1.

I'm not one to experiment too much after an early seventies disaster using some evil stuff called Gary Jones Racing Oil that seperated in the fuel and blew up three of our Maicos at Woodstock short circuit. It'd been reccomended by Maico importer Blair Harley who coincidentally imported the shite. He didn't tell us we had to keep shaking the can to keep it suspended in the fuel. It was safe old Castrol TT and later TTS after that. It now appears that Motul is the oil of choice so I'll stick to my 30:1. 

[DJRacing]

I use Motul 800 at 35:1 and never had a problem.

[holeshot buddy]

i am with johhny o and dj
i have run motul 800 at 40 to 1
in everything from pre75 to pre78 evo
up to modern never a problem
never change my plugs
it can be run down at 30 to 1 with no problem as well
must use bp ultimate at all times

[DJRacing]

i am with johhny o and dj
i have run motul 800 at 40 to 1
in everything from pre75 to pre78 evo
up to modern never a problem
never change my plugs
it can be run down at 30 to 1 with no problem as well
must use bp ultimate at all times

Yes the old BP ultimate 98 and I aslo mix it 50/50 with avgas. The other guys I ride with mix Motul 800 at 32:1 and we will share the fuel and I havnt had a problem with fouling at 32:1 on up to 40:1

[BJJ]

I'll run anything I can get from K-Mart or Big-W that is 2 stroke racing oil,  and mix it at 40:1 .  I run B8eS plugs.  Haven't looked at the carburetor yet.  I would rather leave that tuning stuff to the professionals. 

[BJJ]

ok,  yeah,  I always just try and buy 98 octane BP as a rule.

[Freakshow]

i dont think its got anything to do with your oil, il'd say either your not running on the pipe, your spark plugs are a shit batch, or most likely your coil or electrics are weak, i have had the same plugs in both my MX250a, 360a for 3 season's and there still the same NGK plugs in there.

THe jetting numbers seam a bit light if anything to me i think im on 270 and 300 respectively, so id say if its oil fouling start looking at you plug and the power getting to it, maybe the black box or the  coil is shite,

 its an A model right , not the 73 model ?

[Tossa]

i dont think its got anything to do with your oil, il'd say either your not running on the pipe, your spark plugs are a shit batch, or most likely your coil or electrics are weak, i have had the same plugs in both my MX250a, 360a for 3 season's and there still the same NGK plugs in there.

THe jetting numbers seam a bit light if anything to me i think im on 270 and 300 respectively, so id say if its oil fouling start looking at you plug and the power getting to it, maybe the black box or the  coil is shite,

 its an A model right , not the 73 model ?

Running both the 360 and 250 on the standard jetting.  Ran the 360 all last season with very few probs.  But been doing plugs on it this season after changing oil   The 250 will run great on the pipe for first lap and then start 4 stroking or loading up.  Went through three plugs at last meeting.

[mx250]

 The 250 will run great on the pipe for first lap and then start 4 stroking or loading up.  Went through three plugs at last meeting.

You have a prob - that aint normal . Four stroking and loading up suggests carb although it could be a compound prob.

Unless of course someone slipped in a Bully motor when you weren't looking .

[Tossa]

 You have a prob - that aint normal . Four stroking and loading up suggests carb although it could be a compound prob.
Unless of course someone slipped in a Bully motor when you weren't looking .
[/quote]



Now I'm starting to worry, think I'll get the electrics checked out

[Freakshow]

I wouldnt worry it can only be 2 things petrol or spark.

YOU have an issue, what you describe isnt right.

MY money is on the spark it might be failing away after the bike gets warmed up, and as its breaking down its struggling to keep the oil alight, can you try a new coil ? At $20 its a cheap way to check.

IF i Motorcross a 360 and over rev it like on the line or overrun oin the straight, it can kill a plug ,  in my case i searioulsy think its somthing in the way it advances and spikes out the  plug, but im prity sure its not carby related as i can leave it on the pipe in the DT frame and never misses a beat.

IF you have clean jets and pilots, my suggestion is go down the hot path, when it gets hot your getting a breakdown in there sowhere, put you 360 electrics on the 250, and see what happens when it get up to temp, still does it, also try swapping over the stator plates, if it still does it and you have ALL the known working electics on it, then report back.

[jimg1au]

before you do anything check that your drive side crankcase seal is not leaking.i had 1 blow off on a 360 once and the motor still ran but oild up plugs.the best way to check is to drain the oil from the motor and check how much came out.if real low you can say 1 seal is gone 2 (poor mainance)
anyway buy some castrol r30 2t oil fill the gearbox with the corect amount of oil.start motor run for a while,with the motor runing smell exhurst.r30 has its own smell and if you can smell the r30 burning you have a brown drive side seal,as the only way it can get in the engine is through the drive side seal.
if blown change both seals
good luck