Vintage Dirt Bike Q & A

ok, so i am working on getting my 1975 Elsinore MR175 back to life... it has 130 compression, so thats good... i ve been first dealing with electrical gremlins, now i finally am getting good strong blue spark... coil has been checked out, has new .20mf condenser, all wires are new, points came from a spare engine and look recently replaced... the plug has been gapped to .028 and the points have been set to open .012 when the T-mark lines up with the timing mark... oh, and i found one of the last original air filters in existance to replace the old sock that was wrapped inside of the air box...

it definitely wants to start... i think it might have actually started for a second a few times... it kicked me back a few times... backfired a few times... i cleaned the exhaust, but to no avail... took it off for now, can see the flames shooting out on occasion, but still no start... definitely trying to combust something... i tried pouring a little gas mixture and even carb cleaner down the spark plug hole, no change...

so it sounds like a fuel issue

aparantly, the PO soaked the carburator in carb cleaner and rust remover without taking it all apart completely... could that have hurt the rubber parts inside of it? may anything need adjusting? it ran before i got it, but died easily...

any ideas? my leg is about to fall off from all the kicking today...

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2000 XR600R
1979 XR200R
1975 MR175 Elsinore
1987 Husqvarna 510TE

Check that the flywheel hasn't slipped on the end of the crankshaft. The Woodruff key can shear if the nut was not tight enough. To check this take off the ignition cover, take out the spark plug, hold a piece of wire down the spark plug hole so you can feel the top of the piston (but don't drop it). Slowly turn the crankshaft and make sure that the piston is at top dead center when the T mark is aligned.

i did take the flywheel on and off a few times, the little key deal is a be-atch to deal with, so i just superglued it into the slot, the flywheel goes on and off a lot easier now... i dont think it's sheared, but i will check the alignment here in a little while... good idea, thanks!!!

i also replaced the original MR175 flywheel with the one from my nice MT125 spare engine - it looked identical in all dimensions, including the position of the slot... that couldnt be it, could it?

i still have a feeling that its fuel related... like the carb...

but why does it not start with gas or carbcleaner in the hole? how much exactly do i want to use?

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2000 XR600R
1979 XR200R
1975 MR175 Elsinore
1987 Husqvarna 510TE

It should start with the fuel you put in the plug hole unless you have flooded it,you don't need much.Here's what I'd do- put in a fresh plug and a little gas after I put the original flywheel back on, the part #'s do not match between the two bikes so there is a difference.Stators are different numbers also, if you changed them. MR 175 flywheel part# is 31141-373-003. The middle numbers are the product code, 373 tells you it's a MR 175 part.MT 125 is 31121-361-003,the 361 means it's a MT 125 part. That middle code tells you what bike that part was originally designed for. For example a MR 250's product code is 395,but the exhaust springs are part # 18332-357-010. The 357 code is for the 73,74 CR250m,so in this case the springs from a CR are the correct parts for the MR. Hope this helps.

i will try again with the original 175 flywheel... its just a bit beaten up...

thanks for the explanation of how the part #'s work... appreciate it!
however, just cuz its a different number, does it certainly mean it wont work???
i will compare them again when i take this one off, but they did look very similar...
i wunder if the points gap will be different...

i guess i ll find out when i switch them and try again...

all good ideas, keep em coming!

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2000 XR600R
1979 XR200R
1975 MR175 Elsinore
1987 Husqvarna 510TE

Have you worked the carb over? Float needles do some strange things. I just bought a bike and the guy had the floats in upside down, flipped them over and it ran fine...just had to shake my head.
If I have spark, I always go straight to the carb....seems carbs are generally the weak link. You said it started then died made me think sticking float needle.
One more past experience that caused me great pains.....take some compressed air and clean around the points....I had the smallest little metal shaving touching the points one time that was causing some intermittent grounding problem. Had spark but the metal shaving was stealing the gap on the points after it started..go figure.
I found it, pulled it off with tweezers and it ran fine.
Good luck, be patient and report back.

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Garry Mainer
#33m (retired)
Honda Cr250r 1980
Honda Cr250r 1980
Yamaha TY250C 1976
Arctic Cat 650 H1 2007

You have to remember that an MT is a lower performance bike than the MR and that a CR is the top. It's possible that the timing is different,which I believe is fixed on these bikes.My old CR250m you would adjust with a dial indicater and a moveable points base.My MR 250 you can only change point gap which by changing you can adjust the timing ,but by very little,compaired to a CR.By using a flywheel not for your bike you could by changing those fixed settings.

If you have a timing light it will work with the MT. Just hook the timing light's power leads up to a car battery and put the inductive pickup on the MT plug wire.

I just pull the plug and lay it on top of the head so I get a good spin. I don't think you need to ground the MT to the car frame but it couldn't hurt.

Rick

well, swapped the old flywheel back in... it does look identical though, the gap stayed the same too, but i readjusted it again just to be sure... still the same story... this time it started for about 1-2 seconds a couple of times, but then it was either getting not enough gas, or getting flooded... i messed with the adjusting screw on the carb, got it 3 turns out - is that about right? i took the bottom of the carb apart and looked at the floats - they looked like floats, i dunno what i am looking for i guess... but its pretty old in there, and the gasket is falling apart... it really seems like the carb problem - i dont know much about carbs, how and what can i adjust? what does the rebuild kit include?

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2000 XR600R
1979 XR200R
1975 MR175 Elsinore
1987 Husqvarna 510TE

Usually, the only thing you need to replace on a carb is the needle and seat--and even those can sometimes last a loooong time with a cleaning. The most important part is just a thorough cleaning. Make sure you clean out the jets especially good. On an old carb, I take it apart-including the jets--and let parts soak overnight in carb cleaner---you don't won't to soak your rubber parts. Blow them out with air and put back together. Measure your float height. It's not rocket science, these carbs are pretty straightforward. Done correctly, that should get you going, but it might need some jetting adjustments once its running.
Also, make sure you are running fresh pre-mix. I'd clean out the gas tank while your at it. And a brand new plug always seems to help.

go take the carb apart again and move the float up and down and see if the float needle is moving, if its stuck in the up position its not letting gas into the carb. If you have a piece of fuel line, put it on the carb like you would for gas and blow in it with the needle( the float needle) out....got air going through??? Need to take the jets out and make sure they are not clogged. Sometimes it don't take much to clogged a jet or if you got crud on the end of the float needle or the seat.
Do what Mitchie said and clean it out real good, compressed air sure helps.

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Garry Mainer
#33m (retired)
Honda Cr250r 1980
Honda Cr250r 1980
Yamaha TY250C 1976
Arctic Cat 650 H1 2007

Well at least your now on the right track- now once you get it going then you can try the better flywheel and see if it works,change too many things at once you don't know what worked or didn't.

the float needle was moving up and down (although can i "adjust" the float too somehow?)... how do i take the jets out? as i said, i am pretty new to working on carbs... thanx guys

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2000 XR600R
1979 XR200R
1975 MR175 Elsinore
1987 Husqvarna 510TE

You really need to find a manual for this bike. In the worst kind of way.
For the main jet, a brass piece at the bottom of the stem in the lower carburetor, I like to use a small socket. Be careful putting it back in: a little too tight and it will break the threads off up in the carb. If you use a socket, don't put a ratchet on it, just use one of those screwdriver-like handles for the socket. The pilot jet is brass and takes a screwdriver to remove.

Go back to your timing, " T " means top dead center, there will be a " F " also it means "fire" set your timing to the " F " most of these bikes are 20 degrees or more before "T" Top dead center, which should be the "F"

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Al Carr
73-74 CR250M Elsinore
78 CR250 Elsinore
2003 CR250R