1979 Yamaha Dt125 Troubleshooting

[SeanRides]

Hey guys, so I bought myself a 1979 Yamaha Dr 125 at the beginning of last summer, in a non running condition. It being my first 2 stoke (and admittedly, my first bike) I decided to tear the engine apart so I could get it running as good as possible. I have experience working on cars, engine work and all. So I split the cases, took everything out, cleaned it up, and replaced everything that seemed damaged. In the engine I replaced the:
Piston
Piston rings
Crank bearings
All of the gaskets and seals
And the Ball bearing in the clutch.

I cleaned up both case halves, all of the transmission parts, clutch friction plates, oil pump, absolutely everything pretty much. So I pit the engine back in the bike, and spark was being really wonky. Sometimes there was a spark, other times there wasn't. So then I got into the ignition system. At which point I replaced:

Points
Condenser
Ignition coil
Spark plug

And so now I have a nice blue spark. Awesome. But my bike still wouldn't run so with EVEN MORE sleuthing around, found that there was no fuel getting into the combustion chamber. At this point I figured it must have been the reeds, so I went ahead and replaced those next. (Note that the caurborator was cleaned and is functioning properly, the reeds were wet, so it must be, right?) However I'm confused by the fact that it still doesn't seem like there is much fuel getting to the spark plug.

As you might imagine, still doesn't run. The compression is good (I don't have a compression tester, but if I put my thumb over the spark plug hole, it pushes it off with ease) and it has a really good spark. It doesn't seem like much fuel is getting to the plug, because it's not very wet at all, but it DOES smell like fuel.

So here is my thought: bad timing. I don't know what else it can be.

List of all of the repairs I have done:
Battery
Headlight
Headlight wiring harness
Throttle tube
Rewired all of the factory wiring (checked and double checked, I used a wiring diagram)
Cleaned caurborator
Reeds
Piston
Piston rings
Crank shaft bearings
Cleaned engine internals
Replaced all gaskets
Spark plug
Ignition coil
Points
Condenser
Flasher relay
Cleaned oil pump
Cleaned and lubricated chain
Cleaned sprockets
Fuse
Cleaned flywheel
Replaced magneto woodruff key

Even with all of that replaced, the engine won't sputter, even with starting fluid. One important note is that the end of the crankshaft, where the nut that's holds the flywheel on threads onto goes, is slightly bent. The crankshaft is straight apart from this, but I'm wondering if this could throw the timing off? The flywheel seems to be sitting and rotating the way it should, but I know that the smallest screw up matters.

My question to anyone who has made it this far though reading my motorcycle life autobiography is this: what do YOU think might be wrong with it, and what do you recommend I try? Any help at all would be appreciated so much, even if you recommend something most people check first off. Maybe I missed it. Over this winter, I'm going to RE-RE-build the engine, and see if I missed anything internally, but that's beside the point.

ANY HELP ALL WOULD MEAN THE WORLD TO ME!!

-Sean F.

 

[Deleted member 12676]

clean out the idle jet and then push the bike down a hill and put it in second to see if it will try to run

I assume you replaced the crank seals

blow through the exhaust pipe to make sure it isn't clogged up

 

[SeanRides]

I've already tried all of that exhaust flow is perfect and I even cleaned the carbon build up from the exhaust ports. I didn't try going down a hill pit I pushed it with second gear turning over at a decent speed for about 200 feet and nothing. yes the crank seals were replaced. caurborator is cleaned spotlessly, good flow, nothing in the pilot jet, slide, needed or idle needle. I'm at a loss here..

 

[Deleted member 12676]

if theres gas and compression and it still will not combust even one time then it's the ignition.
There can be spark outside of the combustion chamber but not in it. That is because with compression there needs to be more spark voltage.
So lessen the gap and make sure the electrical connections at the crankcase for the stator coil are clean. Corossion is resistance which drops electrical power.

 

[SeanRides]

Alright I'll definitely try that next. thank
you!

 

[Frankenstein]

Is the freewheel upside-down? Is the timer upside down? Are you sure it's firing when it need to fire? Is the sparkplug wire shorting when its installed for running the engine, did you check to make sure it wasn't loose?

Are you 100% sure the replacement parts for the ignition were the right parts and non-defective ? Carb float is set right? Too little fuel and you get not enough Gas even when choked to start it.

 

[skyash]

Is the fuel Line or tank clear no blocks .you said you got spark but do you have a wet plug ??? From trying to start it ....I have herd of sticky Reeds .Is there any way to see them when you start the bike ? So you can see them open...I don't know enough about ignition to say anything about it . good luck

 

[Frankenstein]

Is the fuel Line or tank clear no blocks .you said you got spark but do you have a wet plug ??? From trying to start it ....I have herd of sticky Reeds .Is there any way to see them when you start the bike ? So you can see them open...I don't know enough about ignition to say anything about it . good luck

He said it gets good fuel flow, and even then a horrible flow would still fill a bowl eventually enough to get the bike running for a few moments, he can't even get it to start yet. I have a feeling he got the right parts and smartly got them together perfectly, I am thinking float level is wrong, second thought is wonky wires whipping up wet gremlins. I've on occasion had flip-the-atv-over-a-cliff mess ups on wires that frustrated me to no end because I looked at the wiring a thousand times and SAW nothing wrong whatsoever yet somehow knew it was the wiring but still explored other avenues to no success . Eventually I run across a single wire that either got yanked at one point or are a very terrible (meaning easy to detect ) quality control guy,and find that the wire has a break internally, so while the shielding looks perfectly fine, the wire inside is yhe equivalent of an open circuit .

Now its unlikely that's a problem, he's got a spark, if he can determine if it is happening just after TDC then it has to be very much something else. The only real way he could get a badly timed spark is if one of the components is faulty, or something is installed wrong. There is a possibility his bent magneto/flywheel is either an indicator or a perpetrator. He said it's bent a bit, so it's possible it's grounding something a bit, unlikely if it's spinning freely, but still possible . It might also be twisted, if twisted enough the timing will be off so as to prevent anything from happening . Then it could even indicate that the magnet/flywheel were removed at one point, and possibly replaced with a bad one, or a wrong one even. For all we know it could have been put back on upside down (wrong way out) and that could just be effing the whole thing out to bits.

He's getting a spark, he should have enough mechanical knowledge to determine between a healthy gap and spark and something sub par , even a bad gap can run a motor it will just run like poopoo . So brings you back to spark, a correctly timed spark. So too much resistance from mag to ignition coils will lead to bad sparks or , depending on the design, badly timed sparks. Probably not there, these bikes I believe have a timing unit, waits for a particular magnet to pass the sensor to tell it to spark. If the mag is not positioned right, it will spark at the wrong time, and of wired badly, could also result in bad timing. He said sometimes it would spark in the beginning of the efforts. He also replaced the Woodruff key for the mag, why was is missing or damaged in the first place?

Seems sketchy how many issues can be caused by a specific part being wrong, while he has those exact problems,and had to replace physical parts close to the problem. Maybe it's a replacement mag, the key could have been missing or damaged if it didn't fit right with the new mag, heck they might have beat it on with a hammer (dents happen when you do that) so's it would fit like a misshapen glove.

So of the mag is right and good then it might be float level. Possible old owners might of screwed with it in an attempt to get it running, or replaced it with a new one and found they couldn't get it running (possibly because of a bad float level) then took it apart because they didn't know what else to do (bent crank arm) then messed up the electrical system as a last resort , or just let the environment kill the wire harness because why disconnect the battery when you can let it rot the bike from the inside out since you can't get it started anyways.

Wet reeds are probably the result of minute bits of oil and gas building up after multiple attempts to start it. Wouldn't bet they are evidence of a sufficient amount of fuel, rather just means that fuel can get from the tank to the inside of the motor enough to wet an object in a very enclosed space that's somewhere between the two.

My 3 cents.

 

[skyash]

No he Siad its not getting much fuel he thinks .if it's got fuel and a spark it should Fire even if timing out one Fire half a fire because of fuel mixing with that s**t spark .Just because there is fuel in the caby bole don't mean its getting to the motor if you block the tank. then evon with full lines and carby of petrol it won't come out .or not enough to start it or Fire .

 

[Frankenstein]

No he Siad its not getting much fuel he thinks .if it's got fuel and a spark it should Fire even if timing out one Fire half a fire because of fuel mixing with that s**t spark .Just because there is fuel in the caby bole don't mean its getting to the motor if you block the tank. then evon with full lines and carby of petrol it won't come out .or not enough to start it or Fire .

He also said its flowing good, I can only assume he did check it flow-wise then. Not enough fuel however is lean, and too lean is not going to start with much ease. Low floats will make that happen.

If the timing is off then it MIGHT fire once and a while, but equally so it will not fire at all. That spark needs to have enough fuel and air in the vicinity of the spark to actually get an explosion to begin. Compression does help, ever try to start a motor with a blown head gasket? You can do it but it will probably take a good long while, and that's with a correctly timed spark, but with a bunch of fuel being blown out and air brought in, making it lean, it creates a bad environment for a motor to start.

So brings us back to square one, not enough gas to make a bang, so why? Probably not fuel flow, if the carb is filled with gas, and it's been cleaned correctly, with the BREATHERS opened as a byproduct of good cleaning, then the bike should start at least for a few moments , then cut out as the fuel level drops too far.

Where does that leave us? Not enough Gas, 2 ways this is happening in this situation, bad float level, or very lean jet, I can only presume that the jets are fine but for all I know. .