Two Stroke Bikes

[tris]

Afternoon!

My stepson has bought himself a KTM 300 Exec 2 stroke bike to play about on the hills with and it appears that I have been designated Chief Mechanic despite living 150 miles away 





Looks like fun, but needs a lot of TLC. We decided that if we both rode from the UK to Mandello, he'd have to service it twice on the road, but could go in a straight line so we weren't sure who'd get there first 

So, can any one point me toward a good source of 2 stroke knowledge that explains the peccadilloes of a 2 stroke engine as my 2 stroke knowledge is sadly lacking

Cheers

[Groover]

Be sure you have the right 2-stroke oil mix/ratio? They are fairly simple I think, many here have good 2-stroke experience. For 2-stroke oil, I'd suggest Motul 710 2T Racing. As far as the mixture goes on those, not sure. Could be somewhere between 2% and 4% maybe, for dirt bike I'd say probably 3-4% more likely. See what the manufacturer recommends, could be printed on the tank. Unless it has the automixer, but unsure if Dirt bikes have that typically (Where there is a separate 2T oil tank, and it mixes automatically as it enters the carbs.). As far as intake, that bike likely has a Reed valve, which sometimes go bad. Typically sign of a bad reed valve is a lot of fuel spitting back out from carb making a mess, also poor/no idle and rough low-end. Those are just some starting items. Good luck!

[vintagehoarder]

They are relatively simple bikes, and way too much fun!  We love our old two strokes.



Just about to get this one back on the road after10 plus years, 550 triple!

[Guzzistajohn]

I rode 2 smoke trials bikes since I was knee high to a jackrabbit, no big deal as long as you mix your fuel right. The aroma they omit is nirvana! I got a KTM EXCF (four stroke) a couple of years ago, I miss the "aroma" but I do like the low end GRUNT.

My biggest issue with the KTM has been the brakes. I've found I need to change the brake fluid every 3-4 rides AND use the stuff that's good to 600 degrees. I do ride in a really hilly/rocky area and I work the brakes REALLY hard. The fluid gets hot and the brakes lock up. I've been able to cool them off with my camelback water and still get back to the truck (thankfully)

But the KTM suspension (once set up right)  and power delivery is AWESOME!! It's been great fun. I might even get to ride this weekend!

John in the Missouri OZARKS

[canuck750]

They are relatively simple bikes, and way too much fun!  We love our old two strokes.



Just about to get this one back on the road after10 plus years, 550 triple!

WOW - nice collection, love the Suzuki 

[pyoungbl]

Odd that this would come up so soon after I had a conversation with Leafman60 reguarding 2 stroke marine engines.  Evinrude now builds a new 2 stroke direct injection line of outboard engines.  Leafman60 has a 50 hp unit and was extolling the virtues: less weight, more power, better torque, less maintenance, no smoke and a 10 year warranty (on his, a promotional extra 5 years).   Now, if we could see this spill over to the motorcycle world I think there would be real market for lighter and simpler engines.  I, for one, like the idea of no valve checks or oil changes.

Peter Y.

[usedtobefast]

Good news is a KTM 300 is a very reliable bike.  KTM recommends Motorex oil mixed at 60:1 .  But any good moto 2 stroke oil should do.

for info, ktmtalk.com has more information than anyone could possibly consume.  :) 

I've never had brake issues (currently have a 2011 300, a 2014 250, and 2018 250), just FYI.

As a engine, only tricky thing might be the powervalve.  When doing a top end job you really should take it apart and clean everything but that is a pain and guys tend to skip it.  KTM manuals are excellent, track one down and the work isn't that bad. 

In the US there are a couple of places that sell top end kits with all the parts you need (vs. buying all the various KTM part numbers).  Assuming there is a shop in the UK that does the same.  And just normal stuff, measure bore, figure out if ok, order correct piston, etc.  The cylinder is the plated type, so no boring it out ... either it is good or you need to get it replated.  And before all that, do a compression check and see how it is. 

And the engines do not need to be rebuilt a lot.  Most guys pull them apart at 100 hours of operation ... so figure 2 hours each dirt bike ride ... 50 rides ... even if you rode once a week that is once a year check.  And if you only get out ~20 times a year then you are talking a check every 2.5 years.  And many guys go to 200-300 hours ... so you could ride the bike 5-6 years and never do a top end check. 

[tris]

Cheers Everyone

Apparently I've already been tasked to go and do a clutch sometime, which means I need to load all my tools PLUS those I don't think I'll need PLUS the wife PLUS the dog into the car for a weekend of spannering!!

The SS has the basic tools but lacks the confidence for some of these jobs - still, I'll gain a new skill I didn't know I needed

He wants me to ride it too but I suspect with my 29" legs and 58 YO body the only way I'll get off once I get going it is to fall off

[Fontain25]

KTM has shorter bolts than average machines to save weight. It's a very good idea to go by the shop manual when torgueing fasteners to keep from stripping them out. That is really the only problem that I've had with KTM. Also barkbusters to protect the undersized brake and clutch master-cylinders - if they get dumped upon they can just stop working.

[vintagehoarder]

WOW - nice collection, love the Suzuki 

Thanks!

[fossil]

Odd that this would come up so soon after I had a conversation with Leafman60 reguarding 2 stroke marine engines.  Evinrude now builds a new 2 stroke direct injection line of outboard engines.  Leafman60 has a 50 hp unit and was extolling the virtues: less weight, more power, better torque, less maintenance, no smoke and a 10 year warranty (on his, a promotional extra 5 years).   Now, if we could see this spill over to the motorcycle world I think there would be real market for lighter and simpler engines.  I, for one, like the idea of no valve checks or oil changes.

Peter Y.

Now? Evinrude builds these things for about 15 years now! And they are direct descendants from the pre-Bombardier - era´s Ficht Direct Injection engines from the nineties.

In the moment I hate two-stroke - bikes as I am in my holiday flat in southern Spain. And each evening young morons think it is funny to perform wheelies in the narrow streets between 19:00h and 22:00h on two-stroke Motocross - bikes....

[Ronkom]

My little two-stroke....a "Tuttoterreno" 125
ronkom

[Knuckle Dragger]

It's always useful to have a spare set of rings & a couple of spark plugs on hand.  These in particular seem to be the most prevalent 'consumables' for high performance 2-stroke motors.  More so even than rear knobbie tyres (unless used extensively on asphalt) & chains.

[usedtobefast]

Cheers Everyone

Apparently I've already been tasked to go and do a clutch sometime, which means I need to load all my tools PLUS those I don't think I'll need PLUS the wife PLUS the dog into the car for a weekend of spannering!!

Not sure of the year model, but lots of times "clutch" problems are the master cylinder or slave issues vs. clutch plates.  Many years of KTMs had mineral oil on the clutch side vs. normal "brake or clutch" fluid ... the reservoir cover will tell you what should be in there.  From folks I know, seems ~70% of issues are not actual worn out clutch plates.  And a really bad thing is when guys put normal "brake/clutch" fluid into a mineral oil system, all the seals top and bottom aren't meant for that and get messed up ... so master & slave rebuild time if that happened. 

[usedtobefast]

It's always useful to have a spare set of rings & a couple of spark plugs on hand.  These in particular seem to be the most prevalent 'consumables' for high performance 2-stroke motors.  More so even than rear knobbie tyres (unless used extensively on asphalt) & chains.

Not sure what years KTMs you are used to ... but on my 2011, I bought it new, still running on original piston, rings.  Probably on spark plug #3 or so because I change them every other year or so.  Loss count of tires, been through bunches. 

[brider]

Apparently I've already been tasked to go and do a clutch sometime,

He wants me to ride it too but I suspect with my 29" legs and 58 YO body the only way I'll get off once I get going it is to fall off

I had a Gas Gas EC 300, extremely similar engine. 2-stroke singles are stupid-simple and easy to figure out even if you don't have a manual, but anything to service your SS's Katoom should be on-line. Clutches can be re-built by removing a sidecover, master and slave cyls are tiny and rebuild kits are available. My GG needed mineral oil for the clutch system.

My heydays of racing 2-strokes ended when I was in my early 30's on a CR250, and I bought the GG when I was 55. Admittedly, it was set up for cross-country racing in Texas, and my muscle memory was from motocross tracks in Michigan. It felt like it was ripping my arms out from my shoulders while I was trying to dodge the trees here in CT, as there are no open motocross tracks that I could find. Low-end torque was astounding, right off idle. Still, I'd be VERY careful if I were you that you don't grab too much throttle in the wrong place, and avoid arm-pump if you ride it a while off-road, nothing like being unable to shut down the throttle or grab the front brake because your arms are pumped up solid.

[Groover]

If it has a wet clutch, then you need to use the properly rated oil for wet clutches. It's JASO something, not sure which.

https://www.oilspecifications.org/jaso.php

[lrutt]

Pretty much the std 2 stroke trans oil is ATF. That's what I've always run and continue to run in my 3 2 stroke bikes I have.