1985 CR125 making me crazy

benclimbing
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Georgetown, TX US
8/2/2016 6:47am
I have a 1985 CR125 that I’ve completely rebuilt. All new bottom end seals and bearings, rebuilt crank, new Hot Rods con-rod, Wiseco piston, properly gapped ring, resurfaced head, new reeds, rebuilt carb, new stator, new coil, good cdi, good compression, passed leakdown test great (held 6lbs for 20 min). It will fire but once it starts it won’t rev at all (see video link below), it will just sit and idle. It seems to dump fuel too, both during starting and idling, so much that I had to empty the crankcase at one point. The ATAC chamber even fills up some and starts to leak. The carb has been completely cleaned multiple times, fuel passages blown out with compressor, floats work, level is correct, needle stops flow properly (I bench tested), jets are new, and tank petcock flows good. No rags in airbox etc, all the basics have been checked. It’s got fuel, spark, air, and good spark timing, or else it wouldn’t even run. It just won’t rev, only bogs every time you crack the throttle. I can’t figure out what the hell is going on here, so I’m looking for help. Any opinions appreciated. Thanks

https://youtu.be/RYsDvZEuaso

Build pics: https://drive.google.com/open?id=0B64HLi9uAU6edTNQcWI4aWZ4VUk
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sandman768
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Saratoga Springs, NY US
8/2/2016 7:02am
My 88 rm 250 did same thing, I had the carb off 100 times! Try turning the petcock off when it's running, see if it starts to run better, my rm would clean right out when I turned gas off, that isolated the problem to carb/ gas flow. After rebuilding carb it still flowed too much fuel, out of desperation I tried another carb I had laying around....problem solved..I never did figure out what was wrong with the stock carb..but after taking it on & off so many times I did not care!
mxracer666
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NE Iowa, IA US
8/2/2016 7:18am
I have a 1983 CR480 that had a similar problem. You could start it up fine, would run great on the stand, but once out on the track it would not rev past 1/3 throttle. Sounded like the jetting was horribly rich. Had that carb off and changing jets/needle so many times I was crazy! I finally realized it should at least run OK with the stock jets, right? I traced the problem to a bad CDI box. I found one on eBay (it looked all beat up and crappy) plugged it in and the bike ran perfectly!!! You can also check the Stator with an ohm meter and compare to specs in the manual...I do not know of a test procedure for the CDI box tho.
benclimbing
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Georgetown, TX US
8/2/2016 7:33am
mxracer666 wrote:
I have a 1983 CR480 that had a similar problem. You could start it up fine, would run great on the stand, but once out on...
I have a 1983 CR480 that had a similar problem. You could start it up fine, would run great on the stand, but once out on the track it would not rev past 1/3 throttle. Sounded like the jetting was horribly rich. Had that carb off and changing jets/needle so many times I was crazy! I finally realized it should at least run OK with the stock jets, right? I traced the problem to a bad CDI box. I found one on eBay (it looked all beat up and crappy) plugged it in and the bike ran perfectly!!! You can also check the Stator with an ohm meter and compare to specs in the manual...I do not know of a test procedure for the CDI box tho.
Thanks for the replies.

I need to find a loaner carb to try, don't have an extra for that bike. I just don't understand how it could dump fuel if the needle seat is new and works fine on the bench. I even leaned it out quite a bit via float, needle and jet adjustments, no change. I understand orifice obstructions causing lean, but a lack of obstructions causing rich, I don't get it.

The cdi is one I just bought off ebay ($80), thinking the old one might be suspect. Same outcome.

Stator and pickup are brand new too ($90). Getting tired of throwing money at this thing; I've built a lot of bikes/motors and just can't bring myself to take it to a repair shop.

sandman768
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Saratoga Springs, NY US
8/2/2016 7:46am
If it cleans out & revs nice after gas being turned off, for 30 seconds or so, it tells you it's not the electronics, but all carb related. Process of elimination at this point. was it a running bike before you rebuilt it? Did the carb sit outside at some point? My rm carb sat in a shed for years with mice living in the airbox, the carb was full of mice debris, I"ve since disassembled all carbs for rebuild & soaked them in Chem-dip carb cleaner bucket for a few days before rebuilding them.

The Shop

benclimbing
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Georgetown, TX US
8/2/2016 8:08am
I bought it blown up. They seized it and parked it and then I took it for next to nothing. Famous last words: "How bad could it be, right?" So yes, it was running to some extent. I found a pinhole in one of the rads so I suspect they just overheated it. Rebuilt the whole thing and here I am, ready to push it off a cliff. I'll play with it again tonight and report back. Thanks for the advice.
pete24
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Marlborough, MA US
8/2/2016 9:39am
back in the day my buddy had the same problem with a 85 rm125 it was exactly what you are describing, it ended up he had the wrong piston it in dome/no dome or something
are you 100 percent sure its got the rite one?
benclimbing
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Georgetown, TX US
8/2/2016 9:50am
pete24 wrote:
back in the day my buddy had the same problem with a 85 rm125 it was exactly what you are describing, it ended up he had...
back in the day my buddy had the same problem with a 85 rm125 it was exactly what you are describing, it ended up he had the wrong piston it in dome/no dome or something
are you 100 percent sure its got the rite one?
Yeah, piston is good, not many piston options for that year other than overbore sizes, and it's installed correctly too...
wolfy0067
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Wernersville, PA US
8/2/2016 10:18am
If it's loading up with gas it a carb issue, was the needle /seat and float replaced, if the needle/veer has an oring type get the new oring, I have seen this be the case with an 83 250
evomx244
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Mason, OH US
8/3/2016 4:18am
Anytime I rebuild a bike I replace the needle seat assy, for peace of mind. I did have an issue with my 82 YZ250 last year at a race. With the petcock in the on position fuel would pour out the overflow, I had replaced the needle and set when I rebuilt the bike. With the float bowl off, I could push the float in the up position and the fuel would stop, So I knew it wasn't the needle/seat assy. I got home took the float off put in it a bowl of fuel and one side dropped down. I had never had float leak before but that's exactly what it turned out to be.
8/3/2016 4:23am
I rebuilt an 1983 YZ125K and had some of the problems you describe. I didn't rebuild the carb, but fitted a brand new Mikuni. However, even though i set the float as per specs, it was still wrong and filled the crankcase after i forgot to turn the fuel tap off. I just lowered the float level a whisker at a time until all was good. You may have multiple problems, but re-check your float level... She is an old girl and part of the fun of the rebuild is ironing out all the bugs...
benclimbing
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Georgetown, TX US
8/3/2016 11:03am
Yeah, needle and seat are new, and I learned years ago to submerge the floats before assembling old carbs to make sure they weren't taking on fuel. This one floats well. I'll play with the float level some more and see how that goes. I love building these old bikes but this one has been a real pain, though I do think the challenge is very therapeutic in some twisted way... Thanks for responses.
RyanLester761
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El Dorado Hills, CA US
8/3/2016 11:22am
Do you have any pictures of your bike? I'd love to see it.

As far as the carb issue; My buddy had a similar problem on his '98 YZ250. He finally replaced the carb and it solved the problem. He could only assume the casting had a hairline crack somewhere inside and the gas was being sucked through while the bike was running.

Good luck ben.
benclimbing
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Georgetown, TX US
8/3/2016 11:33am Edited Date/Time 8/3/2016 11:35am
I might go to the local track/shop and see if someone has a loaner carb I can try. At least I could eliminate one more thing.

Pics of my 1985 CR125:
https://drive.google.com/open?id=0B64HLi9uAU6edTNQcWI4aWZ4VUk

And pics of my 1986 CR500:
https://drive.google.com/open?id=0B64HLi9uAU6efll2QTJkbnZ2ZHVQdExjUGk3V…



wolfy0067
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8/4/2016 5:02am
I would perform what called a pop-off pressure test to the needle/ceet, use soapy water, I have seen a few that leak around the brass ceet where it's pressed into the carb body, the oring may be bad. I have used the oring from Suzuki's part# 13374-35C00. You can adj. the floats all day, however if it's leaking around the valve body there is no shutting fuel off.
benclimbing
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Georgetown, TX US
8/4/2016 7:23am
wolfy0067 wrote:
I would perform what called a pop-off pressure test to the needle/ceet, use soapy water, I have seen a few that leak around the brass ceet...
I would perform what called a pop-off pressure test to the needle/ceet, use soapy water, I have seen a few that leak around the brass ceet where it's pressed into the carb body, the oring may be bad. I have used the oring from Suzuki's part# 13374-35C00. You can adj. the floats all day, however if it's leaking around the valve body there is no shutting fuel off.
If that were the case wouldn't gas continue to run out the overflow?
riv187
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Lakeland, FL US
8/9/2016 8:20am
2 more ideas , the orfices from back of carb. A small spec of dirt or silicone in these will cause raw fuel to siphon from bowl. Also, I've had rewound stator coils that where soldered backwards. Study pictures and make sure not flipped over or backwards. I have a stock 1985 cr125 carb I could loan as last resort, you pay shipping.
riv187
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8/9/2016 8:27am
Or, I'm interested in buying it. I have a rough one with Mugen top end I'd use best from both and make a trick one.
benclimbing
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Georgetown, TX US
8/9/2016 8:33am
riv187 wrote:
2 more ideas , the orfices from back of carb. A small spec of dirt or silicone in these will cause raw fuel to siphon from...
2 more ideas , the orfices from back of carb. A small spec of dirt or silicone in these will cause raw fuel to siphon from bowl. Also, I've had rewound stator coils that where soldered backwards. Study pictures and make sure not flipped over or backwards. I have a stock 1985 cr125 carb I could loan as last resort, you pay shipping.
Ok, I'll look into the stator. It's new, bought from here, and it checks out good. Would it even run if it were backwards? I've cleaned and checked and rechecked all the carb openings.
benclimbing
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Georgetown, TX US
8/9/2016 8:34am
riv187 wrote:
Or, I'm interested in buying it. I have a rough one with Mugen top end I'd use best from both and make a trick one.
I might take you up on the carb. All I'm trying to do at this point is get it running so I can sell it, so if you're interested let's talk. Thanks
benclimbing
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Georgetown, TX US
8/15/2016 3:27pm
riv187 wrote:
2 more ideas , the orfices from back of carb. A small spec of dirt or silicone in these will cause raw fuel to siphon from...
2 more ideas , the orfices from back of carb. A small spec of dirt or silicone in these will cause raw fuel to siphon from bowl. Also, I've had rewound stator coils that where soldered backwards. Study pictures and make sure not flipped over or backwards. I have a stock 1985 cr125 carb I could loan as last resort, you pay shipping.
I'm interested in the loaner carb if it's still on offer, let me know how I can contact you to discuss. Thanks
riv187
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8/26/2016 5:25am
PM message sent,
Brian riv187
8/26/2016 12:26pm Edited Date/Time 8/26/2016 12:28pm
I have a Pro-Circuit Pipe (removes ATAC) and a prestine matched carb, if you are interested in going in that direction. I really don't want /expect a lot for either. Message me if interested
riv187
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Lakeland, FL US
9/24/2016 1:24pm Edited Date/Time 9/24/2016 1:31pm
Hi
The problem is solved. I bought the bike from Ben. When I got it, it tried to run when kicked but died immediately. I suspected timing. Bright blue spark easily seen in daylight. I checked pulsar gap first,,noticed it was new aftermarket and gapped a little wide. I tightened gap, but only minor improvement.. Then I checked flywheel part number, also that crank had a key. I saw the aftermarket stator too. Ben was thinking on right line. Double checked wires. Then swapped stock stator plate with stock pulsar off my bike. Started and ran 1st kick ! Yippeee. I was believing the Pulsar was culprit,, so I put the aftermarket one on my stock stator plate...and back to not running more than 1-2 seconds.
I know these aftermarket places,,many with Chinese import stuff, say one size fits all...but they are wrong. The Pulsar can effect timing and did on this one.
There are now several ruts and turfs stripes up and down my yard Smile
This bike will receive this Mugen top end from a rusty crusty swap meet Cr I have. The crusty chassis wasn't worth fixing with all the bad stuff. Thanks to Ben, I have a nice bike to marry my top end too...





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