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 Post subject: MR250 gas/oil issue
PostPosted: Thu Mar 17, 2016 5:48 pm 
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Joined: Sun Mar 13, 2016 6:18 pm
Posts: 13
Recently I acquired a really nice MR250 with only one problem. It blows black oil/gas goo out the cylinder to exhaust pipe connection and even has it dripping out the spark arrestor. Plus it smokes quite a bit, even with 32:1 ratio and synthetic 2 stroke low smoke oil. After riding a few miles there is raw gas oil that drips out of the carb to air filter rubber connection.
I've gone through the carb and set the timing and points. I cleaned the exhaust system too. Very good compression also.
If anyone has any ideas I'd sure like to hear them, this is quite frustrating!
Thanks! Steve


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Thu Mar 17, 2016 6:11 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
My MR175 did the same thing when I first got it. Here's a simple test: start the motor and warm it up a little, then turn off the petcock and let it idle until it stalls. Post back with the results, which will help with further troubleshooting.

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: Thu Mar 17, 2016 6:32 pm 
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Joined: Sun Mar 13, 2016 6:18 pm
Posts: 13
Thanks, Ray, I'll try your suggestion in the morning and post the result.
Very interesting that you had the same problem!
Steve


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Fri Mar 18, 2016 9:30 am 
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Joined: Sun Mar 13, 2016 6:18 pm
Posts: 13
Well, warmed it up, shut off the gas and it idled for a bit, then rpms increased, then went up and down for 20 seconds or so, then died.
It still had gas in the clear line to the carb when it died.
I did notice that when I parked it yesterday the gas level in the clear hose was almost up to the petcock and this morning-no visible gas.
Maybe this will help with a diagnosis!

Thanks, Steve


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Fri Mar 18, 2016 12:01 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
Does your bike have the stock carb, with 073A stamped on it? If your revs only climbed a small amount with the fuel shut off (less than @ 2K rpm), then your pilot jet's probably fine (stock is #48) - you might want to turn your air screw out maybe 1/2 turn for testing, & see if it runs a bit better at low throttle. You might want to pull the carb off again, set the float level (20mm), write down all the jet numbers, and maybe change out the float valve as well. I would also check the small O-ring around the power jet, which is in the float bowl gasket surface area.

Just for grins - try sniffing the oil fill in the clutch cover (you do not want to smell gas). I'd want to see at least 140psi compression, too.

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 Mar 19, 2016 4:00 pm 
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Joined: Sun Mar 13, 2016 6:18 pm
Posts: 13
No gas odor in the oil, thankfully. 110 main, 48 idle, 073A carb. Float is set at 20mm.
The power jet o-ring is there and intact. Blew out all the jets again, all seems clear.
The float needle looks new, no rough spot or worn area. I'll pick up a new one Tuesday at the Honda shop just to be sure. Hopefully they'll have one in stock.
Thanks again!


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Sat Mar 19, 2016 5:53 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
No problem, Steve - seems like we've eliminated a few things. Regarding the dripppage at the air boot & exhaust manifold - I've seen this before in an MT250, which turned out to have a crankcase half full of 2t oil and unburned gas from running super rich for years on end (something MR250's are famous for too). By the way... my MR175's problem turned out to be mainly a worn needle jet and very low compression, though the ignition was surely to blame as well.

Does your MR need the choke to start, or will it start fine without it? Another thing, before I forget - the 073A carb has a power air jet opening in the carb mouth, on the LH side opposite the choke-circuit air inlet (normally no air jet is screwed into this opening, although the threads are there). I'd suggest blowing some cleaner through it if you haven't already - if this passage is plugged the engine can pull excessive fuel through the power jet, even at low throttle openings.

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 Mar 20, 2016 6:11 am 
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Joined: Sun Mar 13, 2016 6:18 pm
Posts: 13
Thanks, I'll follow up on the suggestions when I put the carb back on in a couple of days.
If, by chance, there is oil/gas in the crankcase, how best to remove it?
Steve


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Sun Mar 20, 2016 7:43 am 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
The easiest way is to run the bike at max power/rpm in 4th or 5th for maybe 30 seconds or so, then repeat as needed until the motor clears out. I did this recently with a KTM 200 that was horribly loaded up after months of use at 1/8 throttle, and even after five long full-power runs in top gear it was still running a little oily (although much better than before).

Or... you could pull off the intake manifold and move the piston just past TDC to get the rod out of the way, then slide a length of small flexible tubing down the intake tract & between the crankwheels as deep as you can get, then close the end off with your finger and pull it back out to see if anything's in there. Once the carb's running right any oil buildup should eventually get sucked out of the crankcase, although it may take a while.

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 Mar 20, 2016 3:31 pm 
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Joined: Sun Mar 13, 2016 6:18 pm
Posts: 13
Power jet opening was clear. I did try the plastic hose trick down into the engine, no black goop but there was fresh oil/gas mixture down there. Don't know how much since none came up with the finger on the end method, but the hose was wet about 2" from the end on down. Makes me think the float needle valve may be the culprit, never really closing correctly and allowing too much fuel to flow when riding. Does this sound feasible? I love these little thought provoking problems!
Thanks again


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Sun Mar 20, 2016 4:38 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
Wow - 2" !? Definitely thought-provoking. :) That means the crankcase is nearly filled with fuel droplets while the engine's running, and no doubt the mixture that makes it into the cylinder is super rich.

The MT250 I mentioned had issues with its float valve too, but nothing ever got resolved (wasn't my bike). You could try filling a long fuel hose with water and testing the float valve over a bucket on the bench, especially at lean angles similar to the kickstand angle (which was a prime suspect for me, since the MT's carb didn't overflow on another bike). There also have been instances of the brass bowl-overflow tubes cracking and screwing up the fuel level in the bowl.

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: Fri Mar 25, 2016 4:03 pm 
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Joined: Tue Jan 27, 2004 8:51 pm
Posts: 136
Location: Gilbert, AZ
I was going to suggest the crankshaft right side seal but liquid in the crankcase points back to the carb.

On my MT250 the seat and needle were slightly pitted.
Some toothpaste and patience can polish those up or a carb rebuild kit off fleabay comes with the parts needed, at least for a FL250 and MT250.
Someone on here gave me a link to that carb kit. Thanks to whoever it was.

Rick


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Fri Mar 25, 2016 6:25 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
That might have been me - but at any rate, glad it worked out for you.

This carb kit will probably work fine for the MR250 carb, which shares a lot of parts with the later ('74-'78) CR250M one:

http://www.ebay.com/itm/Honda-CR250-CR2 ... aQ&vxp=mtr

I doubt a different power jet will be needed, but if so, these can be made to work pretty easily:

https://www.jetsrus.com/a_jets_by_carbu ... _leak.html

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: Sat Mar 26, 2016 1:22 pm 
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Joined: Sun Mar 13, 2016 6:18 pm
Posts: 13
Thanks for all the good info! I haven't had the opportunity to check the compression and leak down on the cylinder yet but will soon. I did replace the o-ring on the float valve seat, it was a little rough, then polished the valve seat. No leaks at all when full of water and tilted at any angle. I finally got the flywheel off to check things out under there--the spark didn't seem too hot to me. It was a little grubby around the coils but was all intact, I cleaned things up with electrical cleaner. Trying to set the points and timing per the manual I just printed is a bit troublesome--the book says the test light should stay on through the flywheel rotation and turn off as "F" lines up with the mark on the case. Mine dims when it's lined up but doesn't go out, and the brightness varies as the flywheel goes around. Putting it back together shows a weak spark (to me), nothing bright blue or yellow at all. I'm wondering if the weak spark is failing to burn all the gas and that's causing the richness, smoke, and black goop.
Steve


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 Post subject: Re: MR250 gas/oil issue
PostPosted: Sat Mar 26, 2016 5:07 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
Steve,

The MR250 shop manual (p. 4) states "lamp should be dark light" (i.e., dim) when the points open (and the stator source coil drops the bulb voltage), and bright when they're closed (with the source coil shorted out by the points). A weak spark could be a partially-shorted source coil, condensor issues, wiring, ignition coil, plug cap (sometimes they have resistors inside that can fail), etc.

My MR's points ignition was horrible - at one point it started sparking at BDC and setting off explosions in the crankcase. :( I replaced it with a CR125M ignition which wasn't hard and made a huge difference in low end, starting, acceleration, you name it. I believe the '75-'77 CR250M ignition will fit your motor and PVL makes an analog CDI unit without a lighting coil, but I don't know how much you want to put into the bike or if you need lights for night riding.

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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