2001 RM250 Coolant Into Carb

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7/28/2018 7:07 PM

What's up guys, I have a 2001 RM250 that I completely tore down two years ago and restored. When I put it back together, the crank didn't have too much play in it so I left the bottom end alone. I put a new top end in it and ran it for 13 hours. At that time, I had some tapping going on and tore everything down. The crank bearing was on the verge of going so I tore the bike completely down and put a new crank in it. Rebuilt the bike with a new top end... which leads me to now.

I put coolant in the bike and coolant proceeds to go through the carb into the airbox once it fills up enough in the radiator to go over to the other side (near the top). I drained all the coolant and cleaned the carb. Then I pulled the oil drain bolt and there was no coolant in there. I assumed the inner o ring for the top of the cylinder was a bad o ring, because its the only way I can think coolant went into the intake. The piston wasn't at TDC when I put coolant in and I'm assuming it was just below the intake opening, allowing it to drain into the carb and also probably into the exhaust.

Anyways, I just replaced both of the o rings with OEM o-rings and I still have coolant going through the carb into the airbox when I put coolant into the radiator...

Why is this happening? No coolant is leaking around the bottom of the head. No coolant leaks anywhere outside of the head either. I'm kind of at a loss right now for how to fix this thing....What's killing me is the bike ran great (not burning or losing any coolant) before I tore it down. What am I missing here?

Bottom gasket is a cometic (brand new). Top o rings are both OEM suzuki (brand new). Thanks!

-Colton

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7/29/2018 8:01 AM

Is there a water pump seal?

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7/29/2018 9:00 AM

There is yes. When I rebuilt the motor I changed every seal out, to include the water pump seal. But the water pump is below the intake and there isn’t any coolant coming out when I pull the oil drain plug (there’s no oil in the bike right now).

If it was a bad water pump seal, wouldn’t the coolant be in the oil? Not coming through the air box?

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7/30/2018 7:11 AM

Some coolant seal is leaking. Are there o rings between center case gasket?

What kind of sealing bond did you use?

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7/30/2018 7:36 AM

I suspected the top o rings leaking and I changed them before the original post. The Suzuki cases use a gasket instead of something like yamabond. I used a cosmetic gasket.

After further research, I read a thread about a CR250 where the guy had installed the water pump seal backwards. The manual I have is for an 06 (since I can’t find an 01 manual). After comparing the micro fishes Online, it looks like the 01-02 pump seal is installed with the flat side facing the impeller. 03 and up is flat side facing inboard towards the motor. I ordered up a new seal and hope to have it installed by the end of the week. I’ll post the result in a few days. Thanks for the suggestions guys!

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7/30/2018 10:13 PM

Your head might be warped or damaged in some way that it's allowing coolant to enter the combustion chamber.

If you take your subframe including the airbox and filter off ( obviously only in a clean garage environment with a perfectly clean bike for a very brief time) and start it up then put your hand near the entrance to the carb you should feel very brief puffs of air and atomized fuel coming backwards through the carb.

The first time I noticed this I was concerned it was issue with my bike and reeds not sealing etc. but after researching it a bit came to understand its normal on a two stroke due to a very brief moment before all intake type ports.....IE boost, transfer etc. are completely closed off by the piston. If you've got any coolant making its way into the combustion chamber it might be getting blown backwards and into the carb with the rest that i mentioned.

The only other way I could fathom coolant making it into the carb would be something ridiculous like running the overflow vent from your radiator directly into one of the carbs overflow vent openings.

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7/30/2018 10:22 PM
Edited Date/Time: 7/30/2018 10:35 PM

I can also imagine a scenario where if you don't have the vent tube connected to your radiator overflow port that coolant might possibly be coming out of that overflow opening and if the tubing isn't there to run it down the frame could possibly be making its way to the outside of your gas tank and migrating down to its lowest point which is where yout petcock will be and then following down the fuel line to the carb but just the outside of the carb unless you have vent tubes missing from the carb as well.....but your saying the coolant is inside the carb correct? Again this is far fetched if even possible. I would check that radiator overflow vent to make sure it's going where it should be though.

If im not mistaken your water pump seal would only allow coolant into the transmission cavity not the carb and milky oil would be the tell tale sign.

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7/30/2018 10:59 PM

The way you describe it the coolant runs into the carb without you even starting the bike???? Are you sure you're not missing a radiator hose someplace? If it's like a cr there should be a hose coming off your head that Ys off to the top of each radiator and there should be a hose way up top connecting the 2 radiators together and one at the bottom connecting the 2 radiators together just above your exhaust port and 1 or maybe 2 hoses coming off your water pump .... again im not sure about RMs.

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8/1/2018 9:11 AM

A cracked cylinder or bad base gasket can cause this as well as the head gasket.

Paw Paw

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8/1/2018 9:14 AM

Paw Paw 271 wrote:

A cracked cylinder or bad base gasket can cause this as well as the head gasket.

Paw Paw

Thanks!. I'm crossing my fingers hoping its just a bad base gasket or there's some type of interference. Can't imagine a head for an 01 RM250 are easy to come by. Pulling the head off this weekend!

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8/5/2018 12:25 PM
Edited Date/Time: 8/5/2018 12:32 PM

Pulled the head off. Don't see anything wrong with it. Put a new OEM base gasket on it and installed a new water pump seal. Put the head back on the bike and proceeded to fill the radiators with coolant. Coolant continued to fill up in the bottom of the crank and up into the cylinder head. The cylinder is a stock cylinder and hasn't been sleeved. At this point, I'm getting pretty pissed because I didn't have any issues with the bike holding coolant before I split the cases and put a new crank in it. Before I pull the motor out of the bike and split the cases again...is there anything else should check?

I don't think the cylinder is cracked because it was never dropped or anything like that during the rebuild. At this point, the only think I can think is that one of the coolant passages in the cases is cracked, the case gasket isn't sealing properly in one area, or there is some internal coolant seal missing that I am unaware of. The rate of the coolant filling up in the bottom is pretty quick, so whatever it is, it is not a small leak point. Any advice would be greatly appreciated.

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8/5/2018 12:36 PM

At the rate it sounds like you’re describing the coolant filling up there’s a sizable leak.... can you take the cylinder off and fill the passages in that case to see if you can possibly visually watch it fill the crank cavity???

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8/5/2018 12:43 PM

Paul_Pitzonka wrote:

At the rate it sounds like you’re describing the coolant filling up there’s a sizable leak.... can you take the cylinder off ...more

Good idea! I'll give that a try. That would 100% rule out the cylinder head cap o-rings not sealing at the top as well.

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8/5/2018 3:42 PM

Sounds to me like you got the gasket between the cases messed up or something is not completely flat and allowing the cases to mate flushly together. Coolant is passing from the passage in the cases behind the pump, through the wall at the front of the crank into the crank cavity.

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Powerband in every gear !

8/5/2018 4:19 PM

FGR01 wrote:

Sounds to me like you got the gasket between the cases messed up or something is not completely flat and allowing the cases to ...more

FGR01 has it correct....you'll have to revisit your crank case assembly procedure.

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8/8/2018 11:22 AM
Edited Date/Time: 8/8/2018 3:51 PM

Does it have an internal water passage in the cases at the seam that’s supposed to have an o-ring? My 02 Honda has an oval shaped o-ring behind the front motor mount that joins a water passage between the pump and cylinder (so they don’t have to use an external hose) . If it got left out I could see this happening.

Edit:
On the Honda I realized it has a weep hole so you’d see it leaking out the bottom. Guessing others would be the same.

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8/12/2018 12:10 PM

FGR01 wrote:

Sounds to me like you got the gasket between the cases messed up or something is not completely flat and allowing the cases to ...more

Thanks for the advice man. This was the problem.

Photo


The gasket wasn't really sealing in this area. I ditched the cometic gasket for an OEM one. Both the OEM head base gasket and the case gaskets have little, kind of like o rings, embedded in the gasket around the coolant passages. I used a little bit of yamabond with the new gasket as well. Threw the motor in the bike this morning and poured in some coolant and looks like were good! Now just gotta put everything else back together and we'll be in business. Thanks everyone for the help!

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8/12/2018 1:05 PM

Nice! Good deal.

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Powerband in every gear !