The cheater MX85 argument. I might be changing my mind.

[F5 Dave]

Yeah I know, I’ve always been the biggest opponent. But I’ve had a rethink in line with the changing times.

Well we had the first outing of the cheating weasel that shall remain nameless. But it’s Sketchy.

The idea was to power a bike with an MX85 in this case a dirty Suzuki that came for just about nix & treated to a new piston & see how it goes for giggles at our non championship club days.

Well he pretty much mostly won from memory (I was pedalling further back on the 50), but there wasn’t that much in it, & lets face it he’d do ok on a CT110.

But to be honest Rich would have cleaned him up, there were no real fast buckets there that day.

Apparently in fresh form with std pipe & carb etc it puts out a fairly peaky 17hp. That surprised me. I’d always assumed about 22hp. In the old days I'd cleaned up quite a few races on a 17hp H100. Times have changed & you'd get no where on that ol H100.

My argument against these engines is that they are competition engines & they would make all the MBs, TSs, KEs, GPs etc obsolete. We’d also enter an escalating arms race that would increase costs.

Little Johnny would get beat on his old YZ & his dad would buy him a late model CR & then Franks Dad would buy a 2014 RM, pull the engine out & insert it into a road chassis & yer away.


But time has moved on. If indeed the power of these things aren’t as high as I’d suspected perhaps it is time to have another look. MX85s haven’t evolved for over a decade. They're just changing decals & pumping out the same thing while they can still sell them to a decreasing market. Heck they still run round slide carbs from the early 80s.

You can buy a complete going less than 10yr old bike for under $2k without really trying & downhill (or uphill) from there. A blown engine is peanuts and can use the carb, rad, ignition & even redo the pipe (Sketchy fit a std one in an RGV frame).

A top end refresh costs less than a hundy & a full engine rebuild can be done for a few hundred. Try that on your popped FXR.

Now that there are very few 30yr ol aircooled 2 stroke engines (ie: me) about we are talking compatibility with FXRs. It appears that there isn’t a big advantage over a std FXR.

So what do they offer & why should we even consider changing the rules that ‘aren’t broken’ ?

I’d offer FXR availability. When were they last sold? The last of the roadbikes are being converted to buckets as they get smashed up & unregistered.

MX85 offer reliable racing on a sensible budget with another stream of motors that are going to be increasingly dumped on the market as 150 4 stroke MX bikes take over.


Preparing to be smacked down by people such as myself.


Go.

[Skunk]

I favour updating the rules. We need sources of new engines without going power and cost hungry.


If it ain't smokin', it's broken.

[Crasherfromwayback]

I'm surprised you guys haven't agreed to use them before now mate.

[scott411]

the latest model KX85 (2014 on) and esp the KTM 85 (2013 on) put out more than 24 hp std, the RM/YZ have not been updated for a while but i would be suprised if they are under 20hp std anyway,

although i agree with your theory that they will be way cheaper to run than a FXR150, they will make everything else obsolete pretty quick,

[mr bucketracer]

it will start standard then you can do this and that. then out to a hunderd ..

[Skunk]

it will start standard then you can do this and that. then out to a hunderd ..

It's only 4 stokes that have done that. 2 strokes aren't broken apparently.


If it ain't smokin', it's broken.

[F5 Dave]

the latest model KX85 (2014 on) and esp the KTM 85 (2013 on) put out more than 24 hp std, the RM/YZ have not been updated for a while but i would be suprised if they are under 20hp std anyway,

although i agree with your theory that they will be way cheaper to run than a FXR150, they will make everything else obsolete pretty quick,

Yes more dyno comparrisions are in order, but claimed hp & what one actually measures are often poles apart.

Clearly as MrBucket mentions we would have to consider ultimate potentual. But a set of restrictions such as below could keep that inline perhaps?

85cc, I'm guessing they are plated so keep them that way (Scott411 might know). barrels are cheap & available. So I'm told.
std carb
and the kicker if required; std ignition cdi. They don't rev high & have a pretty mean curve to stop little johny holding them open & revving to a million, which will happen to every bike. This will stop you building a pipe to rev them to 13 & produce serious power. It will restrict you to about 11,000. This has to restrict hp. Maybe too much to be competitive with one of the GPR 'lightly over' builds, let alone the hotrods they make for themselves.


Just to keep things in perspective a 1/2 opened FXR does about 16hp. A hot FXR does early to mid 20s. My old MB100 does about 27 and so do a few FXRs. I won't claim my MB is reliable, or anywhere near std.

[mr bucketracer]

It's only 4 stokes that have done that. 2 strokes aren't broken apparently.


If it ain't smokin', it's broken.

2 strokes are always broken unless its ricks

[scott411]

Yes more dyno comparrisions are in order, but claimed hp & what one actually measures are often poles apart.

Clearly as MrBucket mentions we would have to consider ultimate potentual. But a set of restrictions such as below could keep that inline perhaps?

85cc, I'm guessing they are plated so keep them that way (Scott411 might know). barrels are cheap & available. So I'm told.
std carb
and the kicker if required; std ignition cdi. They don't rev high & have a pretty mean curve to stop little johny holding them open & revving to a million, which will happen to every bike. This will stop you building a pipe to rev them to 13 & produce serious power. It will restrict you to about 11,000. This has to restrict hp. Maybe too much to be competitive with one of the GPR 'lightly over' builds, let alone the hotrods they make for themselves.


Just to keep things in perspective a 1/2 opened FXR does about 16hp. A hot FXR does early to mid 20s. My old MB100 does about 27 and so do a few FXRs. I won't claim my MB is reliable, or anywhere near std.

yes all the modern ones are plated cylinders, Barrells are available, but I am not sure what you call cheap,

What about the CRF150 (the air cooled one) and KLX140 (which are 144cc) motors, both these models have been out for a while now, and should be coming up second hand cheap, both are not race bikes, and should be similar performance to a FXR

[quallman1234]

Its pretty easy if you think about it to get some rules which will work ok.

Limit it to 80cc MX engines, with a pipe only.
They haven't been 85's for that long. Before then they were 80's.
80's are still super easy to get parts for and i've seen whole bikes which look all good, for 800$.
You have to remember that you won't ever get crazy numbers out of an 80.
As after all they are 80cc.
Say you get it to a standard of a stock Honda RS125 engine.
They are 40hp.... 40*8 = 320hp / Litre

320hp / Litre Divide by 12.5 (to get to 80cc) is Only 25hp, which is a very high state of tune.

I was the other one who rode it that day (as i helped build it with him).
Its seriously not quick at all, and requires a very aggressive racing style compared to my FXR.
Has very little torque and your using all 6 gears at kaitoke to get it moving.
Oh and it vibrates like hell! (But thats more our fault than the engines).


Scott have you had a new KX or KTM on the dyno?
http://www.scalvinipipes.com/KAWA852014.JPG

[quallman1234]

yes all the modern ones are plated cylinders, Barrells are available, but I am not sure what you call cheap,

What about the CRF150 (the air cooled one) and KLX140 (which are 144cc) motors, both these models have been out for a while now, and should be coming up second hand cheap, both are not race bikes, and should be similar performance to a FXR

Both of those are 2 valvers by the way.

[Bert]

Well the easiest way if for a few of us to build a few and test the waters.

Personally I've always supported the idea due to the price and it would also move us closer to the rules across the ditch (who cares about that you may say!!)

Simplistic solution is the dorna controlled ECU and 10 motors a year.... Just kidding.

Standard pipe/28mm carb/stock ignition. Everything else open.



This would encourage a new range of tuners and developments.

[mr bucketracer]

i think now , do what you want with a 80cc competition engine but no competition frames, forks, wheels etc ....buld it your self !! .you can have one without the other

[Skunk]

MX85 in an RS125 frame.


If it ain't smokin', it's broken.

[Bert]

i think now , do what you want with a 80cc competition engine but no competition frames, forks, wheels etc ....buld it your self !! .you can have one without the other

Humm yea that's quite fair, I quite like that idea.
The advantage is weight and gearbox ratios, not max power. As far as I see it.
So weight advantage can be nullified by not allowing competition frames to be used.
We could get an extension to the current rules and make it un available for the GP titles for the next two years and do a full analysis on the effects before changing the rules completely...

Something like this needs to be submitted.

Formula 4.b
Provisional class (non-GP). <85cc competition derived engines.
Stock CDI. limited to maximum 28mm carb.
No aftermarket cylinder kits.
None competition frame, suspension and wheels.
Race tires open.
Note: to be reviewed 2016.


It offers a good starting point for any Jonny to join in.
Maybe we should build a conversion kit...

Also offers up something to do with all the rolling FXR frames sitting in the back of your shed...