Vintage Dirt Bike Q & A

Hello. I'm just getting into the whole dirt bike thing and have a few questions regarding an old bike I just recently picked up. I may come back and edit this topic with further questions as I go along working on it, but for now I can only think of a couple.

One thing I'm need to know is, how abouts do I go mixing the gas and oil to run it, and what kind of oil do I mix it with?

Also, what kind of oil, and how much of it do I pour in the bottom end of the engine with the crank, gears, clutch, etc.?

Could the reason for the engine being in it's current condition (piston cracked, walls scored in one spot, God knows what else.) be because it was previously ran without a proper exhaust system? (I was told the previous owners friend ran it with a rigged up car exhaust. ) I've heared that running it without an exhaust kills the engine very fast, and should NEVER be done.

One thing I'm wondering is, can I rig up the exhaust from another dirtbike and have it work?

Is there any way I can tell if the transmission is good while it's not in any condition to be fired up? I tried turning the engine by hand and running it through all the gears, and it seems to work fine except for a little bit of trouble getting into second sometimes.

I know these are a lot of questions, but I am very new to all of this. And hey, everybodies got to start somewhere!

Bel-Ray 2-stroke oil is popular. I also pick up the Husqvarna 2 stroke oil available at just about every hardware store when I don't feel like driving to the cycle shop. IMO: Don't use regular motor oil as it may have additives that aren't good in a 2 stroke.

I mix my gas right in the can. Pretty easy to dispense exactly two gallons and drop in the correct amount of oil. I like 32:1 or 40:1 ratio gas:oil.

For the crank case you can't go wrong with Castrol 10-40 as that is what the Honda reccomended at the time. Don't get the stuff advertized as extra milage and you should probably run non detergent.

Cracked piston could be from exhaust but not directly related. Something like it was running too lean because of the home brew exhaust and overheated. Putting an exhaust from anything other then another Honda 125 would be a crap shoot since you pretty much have to rejet with every change in exhaust or carburetion.

If the bike came with a spark plug then check the plug color. If it has white flakes/powder on it with metal beads like someone was arc welding near it then it was too lean. Brown or black and it was probably something else like the previous owner forgot to use mix or ran it hard w/o warming it up.

There seems to be a lot of bikes out there that people just trashed. I mean stuff like the slow jet got plugged so it would only run wide open throttle and so that's how the bike spent the last hours of its life before it melted.

I'm of the opinion the only way to test a transmission is on a running bike. It should be a little tough getting from first to 2nd since it has to rotate the shifter drum past neutral. You won't be able to pick up problems like worn clutch and jumping out of gear until you put the bike under a heavy load.

Wow, thanks a bunch for all your help! I really appreciate you taking the time to answer so many questions.

I'm a little dissapointed I can't just use any exhaust. When I asked at the parts department at a local honda store, I was told the cost of the exhaust, not including the end piece, is 500 bucks. Seeing as that is more money than I even HAVE at the moment, it looks like I'm pretty screwed.

However, assuming I can get ANY exhaust from any honda 125, would that suffice for just leisure riding? I'm not gonna run it hard for now, if ever.

The bike did come with a spark plug, but it looks to be nearly brand new with only very little dark stuff (whatever it's called) on it.

The piston isn't TOTALLY destroyed, just a crack down the skirt and a small bit missing along the crack. And a rather large chunk missing from the groove in between the two rings. My thinking is, somebody pulled the engine apart, took the broken bits out, and just threw it back together and ran it like that.

As for the transmission, I believe the clutch may be fine. When I got it, it was apart and the clutch itself looked relatively new actually. Not to mention the clutch springs are really tight.

The gears though, that worries me. I don't want to go pouring a couple hundred dollars into getting it bored out and getting a new piston, only to find out it's shot. Could I maybe put a bit of oil in it then drain it to see if metal filings come out and if not assume it's in fair condition?

Lets try and save you a lot of pain and heartache in the long run. You will need to prepare yourself to drop some coin on this bike, and be pleasantly surprised if things work out cheaper. Firstly if this piston is cracked you will need a top-end rebuild - piston, pin, circlips, rings and bearing. If the cylinder is marked, scratched or whatever you will also need a re-bore or a sleeve put in. That's about $300 or so. 2-stroke competition bikes have carbs, cylinder porting, exhausts etc. that are tuned to work with each other. You can get better after-market parts but they will have been designed specifically for your bike. For around $300 or so you might get a pipe and silencer that will work better than stock (and be lighter and look trick). If you go ahead at this point you need think about the bottom-end - like where did the piece of piston go? Hopefully not into the main bearings which might be worn anyway. Transmission-wise, change the oil and see how you get on. Expect to see some metal in the oil - a magnetic drain plug is a great idea - because the clutch plates wear.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

Ahh hmm. I see. That's a bummer. One thing I should've posted earlier, is that I plan to buy a new piston and rings and have it bored out. I went to the honda place near here and was told it'd be 60 bucks for a new piston, 25 to 30 for the rings, but he had no idea what it'd cost to bore it out. I was, and still am prepared to spend that much on getting that done. I'll also be able to rebuild it myself, so labour costs are not a problem.

I may try the aftermarket pipe route, 300 isn't too bad. And if I can get it used, all the better for me.

I think some day soon I may tear the engine apart completely and have a look for the broken piece of the piston, although it is so small it was probably crunched up then came out when the oil was drained.

I don't think the bearings are gone as even in the engines current condition, it turns over real smoothly, and I even got it to start twice, although I didn't run it for too long at all as that would have been really bad for it. It only ran for at the very most 10 seconds each time.

I just remembered, there's a line that for some reason goes from the bottom of the carb to the crank case or transmission or whatever. Is it supposed to go there? I believe the other two on the left and right side higher up on the carb are vents, but I don't know where the bottom one should go.

One really important thing I should have asked before is, are there any good, reputable parts dealers that ship to Canada that you know of?

A lot depends on what tools you have, how many hours you want to ride, and how lucky you are. Just a for instance, I use one of those ~$25 cylinder hones you put on the end of a drill to clean up light scratches. If your cylinder isn't to badly scarred you could probably get away with that. You need a micrometer/calipers to get the piston size and get lucky enough to find the right size piston.

Even at that I have had some bad luck. One piston I bought on eBay listed the over size in mm but he was apparently measure it in inches/mils. $40 down the drain.

I do a lot of shopping on eBay which is a crap shoot. Sometimes you will find an engine for ~$10-$20 plus shipping and it will be near perfect. Other times you get in a bidding war and end up spending over $100 for a couple of cracked cases, melted piston, and broken gear box.

eBay is probably where you want to look if you want to keep the cost down. Usually people will sell piston and sleeve together if they are good so you get a usable fit. You may even be able to find a pipe there. If you have access to another pipe from a different model I wouldn't worry to much about using it, just make sure it isn't running to lean! There is the ricortes rule that says: Immediately after spending dozens of hours and dollars making something work the right part you need will become available for $10. This never fails.

I don't race, warm my bikes up before I ride, use fresh gas, can read a plug, and only spend maybe 40 hours a year getting handle bar time betwen my different bikes. With a formula like this even a worn bike lasts years for me. I've had my 350XL since ~1991 and it still runs fine. Even a two stroke, if it is well maintained and not beat, will go 2,000-7,000 miles w/o needing a rebuild.

I've been looking on ebay alot actually, and it seems like a good place to go for the nonspecific parts that I need like clutch and brake handles, throttle, and the cables for all those. But for things like the piston... Unless I could get a combo deal on a cylinder and piston in great condition, I wouldn't wanna bother trying my luck and would sooner pay the 60 bucks at the dealership. That way I can even bring it in and have them inspect it and tell me how bad it looks, and exactly the right parts I need.

Personally I don't think it's TOO bad. Maybe honing it out might do the trick. I'll have to talk with a few people my Dad mentioned who know alot about these things.

Question though, what's a sleeve? Is that just like basically replacment walls for in a cylinder or somthing that you slide in?

As for the pipe, I'll just keep looking. Saw one for a 1979, but dissapointingly that's the first year for this model (I think) that had the exhaust go up under the seat rather than out by the rear swingarm.

Just have to ask, but you're positive that if I use a different exhaust it won't melt the piston all to hell? I'd hate to spend money like that to have it ruined a few rides later.

And ahh, just because I like to make extra sure, is there any trick to tuning the carb on a two stroke? I've tuned em on mowers before (that's pretty well where I learned everything :p) and was told that a good rule of thumb is to turn it all the way in then one and one quarter turn out. Start it, and tune it till you get it where it's idling the smoothest/fastest. But once I'm there I'm lost, as you can turn it quite a bit in both directions before it finally starts to sound different. How do you know what the right spot is if you can't hear the difference while fine tuning?

I plan on making this old beast last quite a while if and when I get 'er running. I'm usually very carefull with the things I own, and I enjoy and take pride in taking good care of them, whatever it may be. Even my computer for instance, every once in a while I'll take the side panel off, blow all the dust out of the fans and heatsinks to make sure it stays running cool. And I never like to push things to their limits, so I definately won't be racing this bike. I can see myself occasionally running it fast, but I definately won't be going full throttle in 6th for 100 miles.

Question though, what's a sleeve? Is that just like basically replacment walls for in a cylinder or somthing that you slide in?

Right. Old one has to be pressed or cut out and new one pressed in.

Just have to ask, but you're positive that if I use a different exhaust it won't melt the piston all to hell? I'd hate to spend money like that to have it ruined a few rides later.

You said ~the plug looked like it had some dark deposits on it which probably means it wasn't a lean condition that caused the piston to break. => Could of been the bike wasn't warmed up, old gas/low octane causing detonation, or maybe running flat out in 100 degree weather with a 300lb rider. No matter what pipe you put on it, watch out for running hot and detonation when you get it going. Check the plug condition to make sure it is jetted right and use the factory recomended plug before you beat it. It is impossible to do anything but guessimate what happened. Sometimes you get a series of events that end in disaster. For instance previous owner may not have rev'ed it and only used it for slow trail riding which caused the plug to foul so they put in a higher heat range plug. They then happened to take it to where they could run it flat out. Hotter plug, cheap gas, WOT, pinging like an machine gun => busted piston.

And ahh, just because I like to make extra sure, is there any trick to tuning the carb on a two stroke?

That's right, but that is only for the idle mixture. Soon as you crack the throttle open the mix is determined by the slow jet. If it runs right with the idle screw anywhere from 3/4 to 2 turns out it kind of implies the slow jet is the right size. When you get to ~1/2 throttle the needle mounted on the slide taper determines the mix and at 3/4-WOT the main jets orifice size sets the mix. Once again, from your plug observations you are probably good to go. Just check the plug after you've been running a while to make sure it is right.

That's true, exactly what I was thinking. I don't want to spend all that money then have it ruined. I'll just keep my eyes out then, checking on ebay every once in a while and asking around town. I'm bound to eventually run into the right exhaust sooner or later!

You mention running low octane gas causing the piston to break. Does this mean I'm going to be filling up with the high octane stuff only then? Also, how to you check for detonation? I'm pretty sure I know what it is and does, but is there any particular sound I should be listening for? And lastly, what IS the factory reccomended plug for this bike?

Also, thanks for explaining about the carb there. I appreciate you both spending some of your time to teach me so much.

The stock spark plug is a NGK B9ES. Run the bike on 91 or higher pump gas, with a high-quality synthetic 2-stroke oil mixed at between 32:1 and 40:1.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

I have a 76 CR125M and have recently been going through the same things you are now with your bike. I am not a mechanic in any sense of the word so I had a somebody up near my cabin do the work for me.

Anyways, I had problems with low end bogging down on my bike so he rebuilt the original Keihin carb with Honda NOS parts from Western Hills Honda in Ohio, cost: $139.00 (inc. shipping). Probably should have gotten a new Mikuni carb but the circumstances didn't work out. Once that was done, the bike still had low end bogging issues and he measured real low compression. Piston scored pretty bad. New Wiseco piston kit, cost: $109.00. He also did a once over, put a fuel filter in, and cleaned out the exhaust system. He charged me $125.00 for all the labor. I put in a new air filter obtained from Vintage Elsinore. The bike runs like a champ now with all the bottom end I'll ever need. Louder than hell so I'm looking for the silencer. So I spent about $400.00 getting the bike up and running properly. Use hi test fuel/motor oil and change the tranny oil often, lube the chain, and we should have all kinds of fun on the weekends. If you look frequent enough, you'll find a used exhaust system on Ebay, if that's the way you want to go. Anyways, that's what happened with my bike-so far. Good luck. It's pretty awesome riding around on an old Honda Elsinore.

Thanks man, I'll have to check n see if that's what was in it when I got it.


Yeah I check ebay every so often for an exhaust for mine. That's the main issue right now, cause I mean, it already ran! Just needs a few parts so it can be driven.

Try E-Bay company called Dirtoverstock item#4570223406 they have new DG pipes for $124.99+$18 shipping! These pipes are for the 74-75 so you will need to switch over to the 74-75 exhaust manifold. Bolts right up. Take your Kehin Carb & toss it as far you can. Buy a Mikuni! My opinion. Stock plug is a NGK B9EV right from the owners Manuel. Check your timing! Take Mike Stiles advice you might want to rebuild that motor. Don't take the chance of any old pieces in the bottom end!

Good Luck.

Dude, thank you SO MUCH! How can I ever repay you? You migh have just saved me at LEAST a hundred dollars not to mention weeks of my time spent looking for an exhaust system. The manifold though, might be a bit more difficult to find. But patience is the key. Do I need a silencer for it as well? I don't mind with putting up with the noise, but if it's going to damage my engine in any way or reduce my engines performance by alot, I think I may as well get one as well.

The carb... ahh I dunno about that. Maybe if I've got it running great and still have a bit of cash left over, I'll try and pick one up.

I also need to pick up an intake manifold cause the rubber on mines cracked all to bits. And an air filter... anyone know what I could use on my bike? This one didn't come with an air box or anything. Just the carb, then nothing.

Hmm, how do I check the timing and set it so it's running right? I think I might have messed that up on accident.

I think I'm going to rebuild it then just for good measure. At least it'll give me somthing to do while I wait to find out if the guy my Dad knows found any parts. Are there any tricks for pulling the whole thing apart? I really don't want to screw up the gearbox as I've seen the inside of one and it looks really complicated.

Lastly, which plug is it? redrocket190 suggested the NGK B9ES, and you suggested the NGK B9EV. Gotta make sure here, I don't want to screw anything up.

You can inter-change the B9ES and B9EV plugs. The V is a more modern, better and a little more expensive. I use a B9EV in my 1979 Honda. Just don't use a plug with a different number (i.e. B8EV) because this will affect how hot the engine runs...

_________________
Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF