Hey guys!
Im wondering if you have an idea for my problem with my enduro bike.
Its a yamaha Dt 250 1978

I bought it after it had sat for several years.
Cleaned the carb and got it running.
It hasnt got a battery yet
It smoked a bit so i replaced the right side crank seal.
Now its better and the spark plug always look perfect.

But, the issue is that the spark plugs usually last for 3/4 hours of running.
I use NGK BR8ES
Sometimes the bike just dies on me and i replace the spark plug and it goes again.
Sometimes when i try to start it, it starts for 1 second then it dies with no spark.
I then have to replace the spark plug to get it running again.
Ive looked into the head and the piston and rings are in perfect condition with a OEM yamaha piston.
The rad valves are in good condition as well
I didnt run a compression test yet, but im assuming its good since the bike usually starts in 1 kick and has good power.
Ive also tryed a Bosh spark plug, it lasted a bit longer but ive got the same issue.
My Rm 250 had the same problem before i dit a complete rebuild of the engine.
Now i dont have to replace the spark plugs in my Rm anymore.

So im wondering if my Yamaha also need engine repairs or if my problem could be related to something else including the fact i dont have a battery yet.

Any idea would be appreciated.
Thanks
Ben.

Hi, nice bike
A couple things come to mind.....is your spark strong or kinda weak? I had a YZ80 recently in the shop that did almost exactly same thing and it was solved by replacing the source coil in the magneto. Fairly simple fix but what a difference....the spark went from a yellowy whisker to a white/blue zap that would jump 5mm...lol.
Next, try a normal NGK plug and not an R or resistor plug.....also, this goes doubly true if the bike already has a resistor type plug cap since with a resistor plug you now have two sources of bottleneck for the spark energy to get through. I don't run resistor plugs in ANY of my points type ignitions, no matter what the specs may say....I'm a rebel like that..lol.
Also, all of my Enduro's ran one step hotter plug, B7es from B8es since I never really ran them WFO for too awfully long. You have to be aware of how the bike is running and any pinging or heating BUT the plugs do burn a little cleaner around town.
Of course check all of your electrical connections around and at the magneto, clean and gap your points just to be sure you aren't making something of just dirty contacts
Good Luck,
--Ray

Thanks Ray
The spark is very strong, considerably stronger then my Rm 250 and my Rm dont have spark plug problems.
What do you mean by a normal NGK ? I was convinced the BR8ES was the recommended plug for this engine ? Should i try B8ES like you said ?
I never touched the ignition system on this bike since it worked fine, i was thinking that the spark plug problem wasnt related to the ignition system since my Rm had the same problem before i did my engine overhaul and i didnt touch the ignition system on the RM either and its fixed now.
Im thinking it has the original plug cap since the entire bike looks original.
To be completly honest ive never worked with such old ignition system before, ive done many engine overhaul but on newer 2 stroke motorcycles with CDI ignition systems.
Thats why im asking the question because there might be something i dont know with these older ignition systems that could cause the problem.
The fact that i dont have a battery dont have anything to do with it i suppose ?

I shall mention as well that i dont run the OEM oil pump since i dont trust it. It didnt seem to work when i got the bike since the oil level wasnt going down ! All the parts of the pump looked good and it turns freely but it didnt seem to suck any oil. Maybe my oil was too thick ? I dont want to blow the engine to smithereens and dont have an engine anymore since they are quite hard to find here in quebec/canada.
I run Klotz 38:1 syntec with no oil pump gear now.

Hi Ben....If the spark is that good then half the battle is won Haha sorry for the code talk, normal for me is back in the dark ages before resistor plugs were so popular......try using a B7ES or even a BP7ES (projected nose, burns a little hotter) and see what that does for your problem. The BP I would only use to test a theory, to rule out any ignition related problems (since this type burns cleaner).
When you pull the plug from the bike after it quits is the plug clean/dry or wet looking??
It's not advised to run your bike without it's battery since it's possible to overload the electrical system and blow every bulb without it, but the battery isn't part of the ignition so it's not affecting anything we are discussing.

such usefull informations comming out of this forum.
Best forum ever without a doubt.

Im willing to buy a new battery for the bike, but since my Yamaha isnt used very much these days because my RM 250 runs like a dream. The dirt trails around my home are hard for the old enduro and its not registered for the street yet because its got this spark plug problem which makes the bike not very reliable for the streets yet.

SO, im going to try the B7ES. Now that you mention it, im pretty sure that the bike had this plug when i got it and i was convinced it wasnt the right plug so i installed a Br8es instead. (ill mention that the bike did started with the plug it came with but after 150 feet on the street it died with no spark so thats when i installed the BR8ES with not much more succes)
The plugs do last considerably longer since ive replaced the right side crank seal so thats why im thinking it might be related to engine problems.

The plugs always look perfect, no matter if it has spark or its dead.

Ive updated the previous comment so maybe you didnt see it but any idea about the oil pump too ?
Id like to make it work because its gonna be easier to live with on the streets with an oil pump.

.

Quote: "Now its better and the spark plug always look perfect."

I don't want to make any assumptions or recommendations, until I can see how your plug looks when it quits you.

Can you post a few picture of the spark plug .... both flash enhanced, and under natural lighting?

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PS . . . while you're at it, if you still have that original B7ES plug, post up a picture of it as well.

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i can indeed but im at work right now so it will have to wait for tomorow.

But im not sure that you will be able to tell anything from the spark plug because it looks perfect.
It stops working because i think something goes wrong into the plug for some reasons since its not black or white just a perfect tan.

The b7es is probably long gone, but i can look in my toolbox if i can find it !

SOMETIMES, two or three opinions can be better then one . . . Your concept of perfect may differ from mine, but the fact that it's tan sound promising !

The fact that you said it now runs a bit better .... or longer ???? since replacing the crank seal, indicates it was/is experiencing a lean condition.

If so, you might want to hold off on trying a B7 spark plug until we can verify what's going on mixture wise . . .you don't want to end up with a hole in your piston!

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You're very welcome
I'm still wondering about the condition of the plug when the engine quits...lemme know.
Yeah the oil pumps are a nice feature.....to check operation first be sure the oil tank is full, unscrew the bleeder from the oil pump and observe there is oil coming out steadily without bubbles or start stop. Then when the engine's idling, manually pull the oil pump cable to it's maximum and observe the output line (going from the pump to your engine/carb) should have a steady flow with no bubbles or start stops. You are running premix so this is the right time to check all this. Last thing to check would be that the oil pump is "timed" right.....there is a paint mark or some sorta marking on the rotating pulley assy where the oil pump cable connects and that mark should line up with a mark or marker on the oil pump body at wide open throttle. There may be a few little details I'm not remembering but you get the jist of it.
I'm sure we have a service manual on here somewhere that describes it better (and maybe with pictures..lol). Almost all of the two strokes Yamaha ever made (no YZ's) from '64 on had this pump on them and their operation is essentially the same, they are very reliable.
Your current premix is fine, the ratio isn't the prob

Absolutely! This is why Forums like the Enduro Forum are so useful......we can ALL always learn something from each other