[tanshi]

Ok the issue is this.
Even since i got the LJ50 the motor has had various issues, miss fires, lacking power etc. I know its not a rocket ship but it doesnt feel right.

We picked up a different carbie (non standard) which seemed to fix the misfires but resulted in not as much power.

Basically is there any one out there who can give me a good step by step of how best to tune it, or maybe if in brisbane area can come and give it a going over for me? Happy to Pay you for your services if you can get this beauty running sweetly

[UBZ]

I'm no expert but my mate goes on and on about how his tuned exhaust expansion chamber makes his 50 go so well.

Here's a link to his build thread with pics and info on the exhaust setup.

http://www.offroadexpress.co.nz/Forums/ ... ilit=Fiddy

[3cyl]

Been a bit hectic for spare time lately but I reckon I could take a look. Does it have a decent air filter and fuel filter, cleaned out the tank and pick up? You've swapped out so many bits by now, what could be left?
As well as not feel right it doesn't sound right. You've had a couple of dizzys in it but mine had a topend flatspot at different times due to timing, fuel flow and lack of airfilter flow.

[tanshi]

i honestly dont know what it could be. im pretty much at my wits end. it is getting fuel up easily now where it wasnt a while back. we even had elec ignition on it for a bit and that was no better.

[303zuke]

There were at least 3 crank pulleys I know of with different timing marks on them, and with different thicknesses behind the belt groove. You might need to check what degree the scribed mark on the pulley is before you assume that the timing is spot on. I think the 3 different marks were 5 deg, 6 deg or 8 deg BTDC.

Check angle by finding TDC (take out No1 plug and use a rod or screwdriver on the crown of the piston and rotate fan until piston is at highest point) with a degree wheel fitted to the crank nut.

[tanshi]

thanks, have done that. mine is the 8degrees one.

[JrZook]

Id be pretty keen to have a tinker!! Deffo gotta get it running on all 3cyl again!

[tanshi]

Dan you welcome to have a play, it cant get much worse than it is at the moment. I will PM you the details

[tanshi]

ok so it turns out my second carbie was no good either. I put a third cardie on ( on loan from 3cyl) and its almost perfect. This atleast has provent that there is nothing wrong with the motor or electronics, no i need to get a tacho on it so i know when to stop revving, cos it wont stop on its own now!!!!

[3cyl]

Glad to be of service, oh and you rev them until they stop accellerating then you change gear, repeat until you are either going fast enough or in top gear. (and going fast enough)

[303zuke]

3cyl wrote:

...and you rev them until they stop accellerating then you change gear, repeat until you are either going fast enough or in top gear. (and going fast enough)

That's the technique, all right!

[tanshi]

so it wont just go bang if i rev too high?

[3cyl]

If you stop revving it when it stops producing more power it'll be fine, you know, in a common sense kind of way, also assuming the oil supply is adequate. They sort of run out of air and timing (by design I assume) before the crank flies apart. Bear in mind though the crank is only pressed together. Factory max hp is 33hp at only 5500 RPM, they sound like they're revving so hard because they're firing twice as often as those erm less manly 4 strokes.

[3cyl]

Oh don't forget the 6" length of 6mm fuel hose on the float bowl breather if you want to go up hills.

[JrZook]

3cyl wrote:

If you stop revving it when it stops producing more power it'll be fine, you know, in a common sense kind of way, also assuming the oil supply is adequate. They sort of run out of air and timing (by design I assume) before the crank flies apart. Bear in mind though the crank is only pressed together. Factory max hp is 33hp at only 5500 RPM, they sound like they're revving so hard because they're firing twice as often as those erm less manly 4 strokes.

Think its also a combo of heavy flywheel the peanut carb as well as the timing. Super de-tuned, im sure they could punch a few more ponies out whist still being reliable.

[sideways]

JrZook wrote:

3cyl wrote:

If you stop revving it when it stops producing more power it'll be fine, you know, in a common sense kind of way, also assuming the oil supply is adequate. They sort of run out of air and timing (by design I assume) before the crank flies apart. Bear in mind though the crank is only pressed together. Factory max hp is 33hp at only 5500 RPM, they sound like they're revving so hard because they're firing twice as often as those erm less manly 4 strokes.

Think its also a combo of heavy flywheel the peanut carb as well as the timing. Super de-tuned, im sure they could punch a few more ponies out whist still being reliable.

Yeah, I'm sure you could get a ton more power out of them. I'm a 2 stroke nut and whilst pulling my LJ50 engine apart I can't help but thinking they have a lot more to give. For example, a Victa lawnmower has more "racey" porting, my Chinese motorbike has bigger carb, the squish is wayyyyy out, the flywheel weighs almost as much as the rest of the engine, the reeds could certainly be better, I imagine the exhaust doesn't help either (I've never seen an LJ50 exhaust system, or an LJ50 for that matter, I've just got an engine from one) ect ect.

That engine has a lot of potential. I couldn't just leave this potential unexplored could I?

Now to just get the LJ50 to go with that engine. That's proving to be the tricky bit.

Thanks

Hayden

[3cyl]

Just as important as how much power though is where the power is produced. I remember as kids we played with a mate's YZ80C and got the timing all radical, thought it was crap until by fluke we got some speed up down his driveway and got it to rev and it almost shot out from under me. The top end was insane and it totally blitzed both his old man's DT250 and his brother's IT175. Was almost impossible to ride in the bush though and amused us for the short time it took to explode. Then we realized how much better it was stock.

[sideways]

3cyl wrote:

Just as important as how much power though is where the power is produced. I remember as kids we played with a mate's YZ80C and got the timing all radical, thought it was crap until by fluke we got some speed up down his driveway and got it to rev and it almost shot out from under me. The top end was insane and it totally blitzed both his old man's DT250 and his brother's IT175. Was almost impossible to ride in the bush though and amused us for the short time it took to explode. Then we realized how much better it was stock.

Very true, I think there's a lot more you could get out of one and have it still off roadable though.

Thanks

Hayden

[tanshi]

well when you figure it out hayden let me know

I will be setting mine up efi in the next six months so im hoping it will make it alot more tunable. as far as port work and stuff i have no idea. but i am tracking down some carbon fiber reeds

[JrZook]

tanshi wrote:

well when you figure it out hayden let me know

I will be setting mine up efi in the next six months so im hoping it will make it alot more tunable. as far as port work and stuff i have no idea. but i am tracking down some carbon fiber reeds

Chop chop!!

[tanshi]

once i get the comp on the weekend out of the way, and the j20 in the sierra, its next on the list

[sideways]

tanshi wrote:

well when you figure it out hayden let me know

I will be setting mine up efi in the next six months so im hoping it will make it alot more tunable. as far as port work and stuff i have no idea. but i am tracking down some carbon fiber reeds

Sure will!

How are you doing the EFI? Megasquirt or ??? I was thinking of trying an AFM based ECU from a 3 cylinder car with an interceptor between the AFM and ECU (because I'm cheap). Always wanted to EFI a 2 stroke...

Thanks

Hayden

[JrZook]

sideways wrote:

tanshi wrote:

well when you figure it out hayden let me know

I will be setting mine up efi in the next six months so im hoping it will make it alot more tunable. as far as port work and stuff i have no idea. but i am tracking down some carbon fiber reeds

Sure will!

How are you doing the EFI? Megasquirt or ??? I was thinking of trying an AFM based ECU from a 3 cylinder car with an interceptor between the AFM and ECU (because I'm cheap). Always wanted to EFI a 2 stroke...

Thanks

Hayden

The only way (or most plausable way) is to go custom ECU such as mega squirt. Just remember a 3 cyl car with EFI will be 4 stroke thus its ECU would think that its reving twice as fast if put on a 2 stroke (dizzy on 4stroke turns half speed of crank). Thus it will pretty much go into rev limiter mode straight away.

Dan

[oozuk]

Grahame from Suzisport in springwood used to own a few lj50's in the early 80's that were pretty tough, the stories I heard and the video I saw he got he's going really well ( sounded like a bike) he changed the reeds, fitted triple carby's and played with the exahust, so either msg losfer or call Grahame, from what I hear the oil injection system on them is prone to screw up

[sideways]

JrZook wrote:

sideways wrote:

tanshi wrote:

well when you figure it out hayden let me know

I will be setting mine up efi in the next six months so im hoping it will make it alot more tunable. as far as port work and stuff i have no idea. but i am tracking down some carbon fiber reeds

Sure will!

How are you doing the EFI? Megasquirt or ??? I was thinking of trying an AFM based ECU from a 3 cylinder car with an interceptor between the AFM and ECU (because I'm cheap). Always wanted to EFI a 2 stroke...

Thanks

Hayden

The only way (or most plausable way) is to go custom ECU such as mega squirt. Just remember a 3 cyl car with EFI will be 4 stroke thus its ECU would think that its reving twice as fast if put on a 2 stroke (dizzy on 4stroke turns half speed of crank). Thus it will pretty much go into rev limiter mode straight away.

Dan

I think it'd be easy enough to fool it into 2 stroking, but yes the rev limiter thing could be an issue. Perhaps a 6 cylinder ecu? One with sequential firing instead of bank firing would probably be easier, still be a nightmare to tune though. But yeah, Megasquirt or similar would make your life sooooo much easier.

oozuk wrote:

Grahame from Suzisport in springwood used to own a few lj50's in the early 80's that were pretty tough, the stories I heard and the video I saw he got he's going really well ( sounded like a bike) he changed the reeds, fitted triple carby's and played with the exahust, so either msg losfer or call Grahame, from what I hear the oil injection system on them is prone to screw up

That is basically what I was planning to do! GT550 carbs, carbon fiber reeds and mess with the exhaust! Perhaps we need a proper LJ50 modifications discussion thread? I shall start one tomorrow if no one beats me to it.

BTW: ignore those attached pics, super picture attaching fail, I don't even know how I did that.

Thanks

Hayden

[tanshi]

happy for you to use this thread hayden!

[billrogers]

From my LJ50 days, A few yers ago now.. I created a little flyer. Bored motor,new pistons,rings .1.0 os.
50mm exhaust sysem with a standard 50mm muffler, just noisey enough ! Stock carb but played with the jetting. Found some reeds possibly from a carry, with bigger openings but not as many, these proved to be a great improve. run 10 degrees advance, played a lot with the auto advance springs in the dizzy. 3.00mm off the head, had to chamfer the hemi dome in the head as clearance became too close, even then slow driving for a period used to build up carbon and cause a knock, a quick thrash out the road always fixed that!! All in all a lot of trial and error, but great fun, even found enough power to up the transfer box gearings. Jimny days now!!
ding....ding ding.....ding,ding ding,,,, Oh for another one to play with !!!

[JrZook]

sideways wrote:

JrZook wrote:

sideways wrote:

tanshi wrote:

well when you figure it out hayden let me know

I will be setting mine up efi in the next six months so im hoping it will make it alot more tunable. as far as port work and stuff i have no idea. but i am tracking down some carbon fiber reeds

Sure will!

How are you doing the EFI? Megasquirt or ??? I was thinking of trying an AFM based ECU from a 3 cylinder car with an interceptor between the AFM and ECU (because I'm cheap). Always wanted to EFI a 2 stroke...

Thanks

Hayden

The only way (or most plausable way) is to go custom ECU such as mega squirt. Just remember a 3 cyl car with EFI will be 4 stroke thus its ECU would think that its reving twice as fast if put on a 2 stroke (dizzy on 4stroke turns half speed of crank). Thus it will pretty much go into rev limiter mode straight away.

Dan

I think it'd be easy enough to fool it into 2 stroking, but yes the rev limiter thing could be an issue. Perhaps a 6 cylinder ecu? One with sequential firing instead of bank firing would probably be easier, still be a nightmare to tune though. But yeah, Megasquirt or similar would make your life sooooo much easier.

You have pretty much summed it up there. It is possible for a 6 cylinder ECU to work in terms of reading the correct RPM but absolutely everything else will be out. Much more hassle than its worth

Dan

[3cyl]

LJ50s kind of have a 6cyl dizzy, the shaft has 6 cam lobes to open the points and the rotor is double ended so that even though the rotor turns clockwise the dizzy fires anticlockwise as in alternately firing at each end of the rotor.
I try to be happy if I can keep the thing running properly and even if it's worked to the point of being undriveable I doubt it would be any faster than if it had a 1 litre in it, just that it'd be cool.

[3cyl]

Spoke to the local bike shop guy today about reeds, even brought one down there to show him, hoping to match something up. He had a box full of random reed petals but he reckoned it'd be crap to use fibre ones even if there WERE some that fit as they'd be too flexy, causing them to open too early, a bad thing he assures me.