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 Post subject: Re: MR250 gas/oil issue
PostPosted: Thu Mar 31, 2016 8:27 am 
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Joined: Sun Mar 13, 2016 6:18 pm
Posts: 13
Well, I should have known that "dark light" meant "dim"! That makes a difference! I just received the carb kit Ray suggested--no more leak down of gas in the clear line to the carb overnight after I installed the float seat and needle. Also I checked the spark plug cap, it looked a little worse for wear where the wire connects to the cap, so I replaced it. Swapped the condenser for a new Yamaha 6 volt version as well. Big difference after two 5 mile rides is that there is NO oily black goop dripping from anywhere on the bike and less smoke too. It starts easily and runs pretty well except for missing and jerking at different rpm ranges, sounds like electrical from what little I know. Seems to clear up and kicks in again.
I still need to try the timing light, haven't had a chance to borrow one yet. Would the ignition coil or the stator source coil make it act this way? Another thing--the idle screw to set idle rpms doesn't affect the bike at all, the screw barely touches the slide and doesn't move it at all--this from looking into the carb throat... If anyone wants the left over carb kit parts let me know and I'll drop them in the mail to you, no charge. They fit CR250 and CR250M, gaskets and #55 slow jet, #148 main jet, and needle.
Thanks again for helping with my problems!
Steve


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Thu Mar 31, 2016 2:15 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
It's great the bike's starting and running a little better, but if it's still four-stroking and loading up (that's what I assume the 'missing and jerking' is), I wouldn't give away those carb-tuning parts just yet. Also, it's quite likely there's still a bunch of crap in the crankcase that hasn't been blown out yet (IME that's going to take at least six 30-second WOT runs to clear out, maybe more). Until that's cleaned out, the plug may be partially fouling on oily crankcase fuel in addition to the carb being rich, causing the missing and intermittent operation.

If it were my bike, I would

a) make sure the correct idle-speed screw is in it (33mm OAL, 15.5mm of threads, 13.5mm of unthreaded 'nose' - it only lifts the slide maybe 2-3mm)
NOTE: the smaller air screw has the same-diameter threads; I've seen carbs with the air & idle-speed screws swapped
b) put in an NGK B6ES plug for now, then a BP7EVX (the plug I use) once the jetting is right
c) set the timing to 21° BTDC (slightly more advanced than stock)
d) at least try the carb-kit needle, clip at the #2 (2nd from top) position

The carb will likely also benefit from smaller main and pilot jets, and also a leaner slide (Honda P/N 16022-357-425) if you can find one.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Sat Apr 02, 2016 5:37 pm 
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Joined: Sun Mar 13, 2016 6:18 pm
Posts: 13
Well, getting a LOT closer! Put carb kit needle in carb, set in 2nd notch from top and took it for a ride. Ran ok but really breaks up under load and higher rpm's. I did 3 of the wide open bursts, it sounded like a war going on in the engine. So I got a B6ES and put the air screw out 2 full turns. What a difference, it ran great at idle on up through 1/2 throttle. Maybe not optimum power, but really smooth and a pleasure to ride for 15 miles. However above 1/2 throttle it begins to get erratic and skips and misses. There's less smoke too, I think the hotter plug is helping out. The new needle is #D43, the old one was #271006. Still need to set the timing--maybe tomorrow...
I'm using 32:1 synthetic 2 stroke oil.
Appreciate all the help!
Steve


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Sat Apr 02, 2016 6:46 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
That's great it's running better! I went back over this thread and noticed the carb has a richer 110 main jet (stock is 100). You can try moving the needle clip to the top #1 position which should help a bit more, but I think what's really needed now is a 45 pilot jet, 95 main jet, and ideally a 130 power jet too, which affects mixture from 1/2 throttle up. I would also keep going with the WOT bursts until the engine pulls fairly normally; the new jets will make this happen sooner. I guess it's idling normally now?

Main jets are here (if it were me, I'd get 90, 95, and 100): http://jetsrus.com/a_jets_by_carburetor ... 25-xxx.htm

... and the pilots are here (a 42 and 45 should do it): http://jetsrus.com/a_jets_by_carburetor ... 29-xxx.htm

And as long as you're getting jets, how about a 130 power jet, which may actually make it run right at full throttle? http://jetsrus.com/a_jets_by_carburetor ... _leak.html

If the compression is low that'll make it run richer and a lot less crisp, obviously the timing will affect that as well.
I think it's pretty cool you're making the effort to tune this thing. Back in the day, I don't think many people did.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Tue Apr 05, 2016 9:04 am 
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Joined: Sat Jan 18, 2014 11:47 am
Posts: 3
Location: Georgetown Ontario Canada
Hi,
I have been fighting this issue for years, been through stators and coils until I found the spark plug cap was a 5K resistor cap! Changed that and the bike would start, but then I was into this excessive fuel issue. i'll go through the ignition and replace the condensor, the carb has been gone through I don't know how many times. If someone could send me a picture of the jets in the air filter side of the carb, not sure what is supposed to be there.

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Thanks, The Mad Mechanic
'05 FJR '76 KZ900 '76 MR250

Old road racers adage:
Stay in the gas until you see God or Elvis, then brake hard.


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Tue Apr 05, 2016 10:40 am 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
There should be only one jet in the air filter side (mouth) of the carb - the #200 air jet, inside the tunnel to the needle area. This jet shouldn't need replacement, but make sure it's clear or the carb will run mega-rich everywhere.

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Tue Apr 05, 2016 5:29 pm 
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Joined: Sun Mar 13, 2016 6:18 pm
Posts: 13
I ordered new jets fromJets R Us yesterday, should have them by Friday. They didn't have the 130 power jet though...
I'm pleased that Ray has such knowledge of these old bikes, as well as the other folks input too. I'd be even more lost without the help!
I have 7 other motorcycles from the early to mid '70's, all have required minor to major adjustments and repairs which I really enjoy getting involved with, right now all are in great operating condition. This MR250 is a little more of a challenge though!
BMW R50/5, BMW R100/7, Moto Guzzi Ambassador, Guzzi 850T, Yamaha CT-1 175 Enduro, Norton 850, and a Honda XL250.
Steve


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Fri Apr 08, 2016 5:56 pm 
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Joined: Sun Mar 13, 2016 6:18 pm
Posts: 13
New jets came in yesterday, tried 95 main and 45 idle jets. Ran awful so I went with the #100 main and back to the 48 idle jet. This is the best it's run since I got the bike, it idles and runs smoothly up to higher rpm's, where it breaks up some with an odd like backfire sound from the engine. I still haven't gotten the nerve to run it wide open and try to clear it out--sounds like it might come apart.
Another curious occurrence is when wound out pretty good in third or fourth gear and gas off, clutch in for an upshift, the engine revs way up by itself, ending when I let the clutch out in the next gear...
It's got to be pretty close to being right and is certainly enjoyable to ride around the area near my house, but I still want to make it a little better. Hopefully tomorrow I can put the timing light on it, this may show something else that's a bit off!
Thanks again! Steve


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Fri Apr 08, 2016 6:19 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
It's best to change only one jet at a time, and then test-run the bike bike only for the performance of that jet. I realize it's more work, but it's the only way to really get the jetting right. For instance, the #45 pilot may have been an improvement, but since it was tested with the #95 main - which apparently was not - it was assumed both jets were wrong, so both were removed when only the #95 may have been wrong. I test pilot-jet changes only from idle to 1/4 throttle, which is the range they mainly affect.

I'd suggest putting the needle clip back in the #3 position; now that the main jet is closer to being right, the needle clip at #1 may have been too lean. I would also try it in the #5 (bottom / richest) position to see what effect that has on the revs rising during shifting, which sounds like severe needle leanness to me. It's also possible the power jet is too lean.

When my ignition was double-sparking, it was a very definite backfire-like sound, only it was coming from inside the motor and not the exhaust. If you think your motor is doing this, I would not run it again until the ignition problem is fixed; you can blow out the crankshaft seals or possible the center case gasket, which is a nightmare to replace.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Sun Apr 10, 2016 9:48 am 
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Joined: Sun Mar 13, 2016 6:18 pm
Posts: 13
Still haven't gotten the timing light yet. I did remove the carb again, I'd taken out all the jets and cleaned everything before, except the power jet--it was clean and I didn't want to ruin the rubber o-ring that fits over the jet. Decided to risk damaging the o-ring, took out the jet which is a #140. This is probably affects the richness I've been troubled with, I'd think.
Jets R Us doesn't have the #130, any idea where I might find one? Good thing I'm retired, otherwise I'd have to quit my job so I can fiddle with this bike all the time!

Steve


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Sun Apr 10, 2016 11:50 am 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
Here's a 130

Here's a 135

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Tue Apr 12, 2016 4:19 pm 
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Joined: Tue Jan 27, 2004 8:51 pm
Posts: 136
Location: Gilbert, AZ
When I used that carb kit I used every piece that I possibly could. My main problem was the O-ring around the needle's seat but wow, that was only part of my problem.
I also used that new idle screw as I liked it better because of the large head. It's much easier to adjust sitting at a stoplight and not needing a tool.
I even used the large o-ring seal for the bowl even though it was a pita to install.
With every part utilized that I could it went from surging at idle to running totally awesome but when I hit a little over 7000 RPM it's like the motor power hits a wall. I have not fine-tuned my new points adjustment but I think that limitation is more in the carburetor than anything else. I am trying to keep this baby as stock as I can and would gladly give up a couple horses on the top end in order to have that low and grunt that I have now because I'm going to be riding mostly from 7000 to 9000 feet altitude.

I wonder if you may have a leak around your left crank seal? I did and I found a replacement on eBay so I bought both but only replaced the left seal. BIG DIFFERENCE. With the engine idling and the Magneto cover off, spray some carburetor cleaner in the area and see if your RPMs change. If so the seal is leaking.
Rick


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Tue Apr 19, 2016 3:34 pm 
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Joined: Sun Mar 13, 2016 6:18 pm
Posts: 13
Back in town again and installed the #130 power jet. Finally checked the timing and got it set correctly as best I can tell. The compression is over 130#. Starts pretty easily, but haven't ridden it over half mile yet. I'll try that carb cleaner trick tomorrow, thanks.
On timing, the light dims when the marks align and stays dim for 180 degrees rotation, then is bright all the way to alignment again. Is this normal? One of the coils under the flywheel rubs the f'wheel when turning by hand. You can hear a scraping sound and see them touching through the openings. Could this be part of the misfiring issue at higher rpm"s? With 3 coils, which is the ignition, the lights, and the third?
Appreciate your interest in helping me get this classic running at its best!


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Tue Apr 19, 2016 4:19 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
130 psi is fairly low - when new it would've had at least 150. Low compression makes for easy starting without kickback, but it also makes the motor run rich and a bit weak.

If the light is staying dim for 180°, it sounds like your points gap is excessive. Max gap at 20° BTDC is .024".

I would definitely fix the stator scraping, before it fixes itself (violently). The MR250 only requires 2 stator coils (ignition and lighting), so maybe Kokusan used an MT250 stator with no cable connection to the charging coil - I really don't know.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric


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