CR85RB new to me...question

I haven't had a two stroke bike since the late 1950's, so I don't remember much; any help is appreciated.


I traded for a 2003 CR85RB that has been raced quite a bit, and then left to sit for several months. The guy I got it from said it wouldn't start for him, but that the previous owner (the racer) said it was okay when he quit riding it. I found a bad spark plug cap, and replaced that along with a new spark plug and fresh 32:1 fuel and got it started today. It revs fine, but doesn't idle, which I can probably sort out.


My primary question is, now that it cranks, what are the steps I should take in terms of getting it ready to ride? I don't want to ruin something out of ignorance. If you assume I don't know anything about 2 strokes, especially water cooled 2 strokes with hydraulic brakes, you won't be far from correct. It seems to me the chain is really tight, the snorkel to the air box is loose, but beyond that, I don't see anything wrong.


Thanks for your suggestions.

I'd pull the carb off, and clean it. Pull the jets out, everything, such as air screw, choke knob, idle screw, etc... and make sure all passages are clear. They may have gummed up while sitting. I'd go ahead and change the crankcase oil, clean the air filter or replace it. Make sure to get the snorkel issue fixed, so no air bypasses the filter, and wipe the engine out. Maybe pull the chain off, and soak it in kerosene awhile. Then when reinstalling it, adjust it to spec.

Sounds like the carburetor needs a thorough cleaning.  When you have the carburetor off you should complete a leak down test.  There are many sources on here that will show you how to build one for cheap (under 20 dollars.)  A compression test is also a good test.  This will help you achieve a idea of how the engine is but only an idea.  For an example a leak down test will tell you that the crank seals are good, the head gasket and so on.  But what it will NOT tell you is if the crank bearings are good or not.  Typically if the seals are good the bearing will be good though, the bearings cause the crank seals to fail.  I would strongly advise buying new top end and installing it or at minimum take apart the top end and inspecting it.  The reason for this is that if a piston skirt goes it makes a mess out of everything and causes great expense.  When the top end is off an inspection of the crank can be done.  Next item up is the chain.  On a 2000 cr250 there should be 25-35mm of slack.  It might be different on your bike, you should refer to your shop manual.  Hydraulic brakes, should probably have its fluid replaced with new clean fluid.  Check your wheel bearings by having someone balancing the bike under its own weight.  Then you shake the front wheel then the rear.  There should be no side to side movement at all.  Then check linkage and swing bar bearings and bushings.  Put the bike on a stand with the rear wheel off the ground.  Then just lift up on the rear wheel.  There should be no slack.  Then grab the swing arm and try to wiggle it left to right up and down and so on, there should be no play in that.  Next up go to the handle bars with the front wheel off the ground and turn side to side to check those bearings.  They should just turn smoothly with no binding.  That's about it.  Other then making sure all bolts and connections are tight.  I can't stress the engine enough.  I am currently rebuilding my engine on my cr250 that was running very very very strong.  My crank bearing on the right side was burnt up and I had NO idea.  I did a compression test and that was in spec.  The only reason why I started a rebuild was because my leak down test indicated I had an issue with my right crank seal,  I have had other cr250 blow up with good compression.  So a new top end for 120 dollars or so is cheap insurance compared to a full on rebuild.


Hope this helps,



Thanks to you both for your input. I have found another issue: the choke won't stay up. I took it out and cleaned it, but it still pops down immediately when released. An OEM choke is more than $40, but there is an aftermarket one for about $13. Would the aftermarket choke be okay, or should I spring for the big bucks?



It's a choke... Oem is always the best option but this part is easy enough to install and wont leave you stranded on a trail. Save yourself a few bucks and get the aftermarket. Worst case it goes out and you buy the oem one and your out 13 bucks. Buts it's a pretty safe bet that the aftermarket will work just fine. Are you completely sure you reassembled your carb correctly. I have rebuilt my carb a few times and for the life of me I'm trying to remember how that part goes together and what could have failed. Seems like a pretty simple system.

Today, I took the airbox off, washed it inside and out, and put in a new air filter.


I also took the carb off and took it apart, cleaned it insided and out, and put it back together. I noticed on the slide where the idle screw makes contact, there seems to be quite a bit of damage. In a XR100 carb, that slanted area is smooth, but I don't know what it's supposed to look like on the CR85RB carb slide. Does it come from the factory with a dimple or something in the slanted area? Anyway, I was able to adjust the idle with the idle screw, but the setting was erratic. I am thinking that I need to somehow smooth off that damage on the slide. Comments or suggestions?


I was able to ride the bike for the first time today. It seemed to shift okay through the gears, although I only went through them twice (I was riding on the residential street where I live, and didn't want to annoy my neighbors.) The engine seemed kind of boggy, and the clutch seems to be slipping. Comments or suggestions?



Edited by tracecom

Here's a picture of a CR80 slide that's for sale on e-bay.


What is that round spot in the slanted area where the idle screw makes contact? Is that normal?


Would this slide work in the carb for my CR85RB?




Thats normal. Screw is made of brass and is softer than aluminium.

I REALLY suggest you do that top end and the clutch packs/hubs.

Thats normal. Screw is made of brass and is softer than aluminium.

I REALLY suggest you do that top end and the clutch packs/hubs.

Thanks for the reply; I was beginning to lose hope that anyone would answer.


The slide in my bike is quite damaged. My guess is that someone used a steel screw as an idle screw, and the steel screw damaged the aluminum slide.


So, I really need a slide for my carb. Would a slide from a 1980 CR80 be a good replacement?


As to the top end and clutch, I want to be sure the engine runs before I spend more money. Once the engine is running well, then, I will rebuild the clutch, and then if that functions well, I will tackle the top end.


Thanks for your input.

it wount be running well anyways if it needed top end.


look, i know you dont want to spend money (who does) but ask yourself. do you want to keep the bike? if you want to keep the bike as a play bike then ATLEAST do a top end. and that clutch. owners tend to neglect  small bikes because they are small and not worth taking to the track and its not the "big ole 500" that ppl are intersted in getting into threads these days. i just want to help you out because i also have a CR80 and that bike HAULS after a topend and clutch change. all my friends are scaredof the wicked powerband these little montsers do when they scream.

forget about the mark on the slide. all old bikes have these marks same depth and yet runs great.

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