CR80 cold carb

[bigboss_an]

Hello everyone,

I consider myself pretty handy with two strokes, but this one's got me stumped. I just got my son this '00 CR80. Engine will run but will not rev out all the way. Very hard to start, usually have to drag it behind ATV to get it started. Once tipped over (when he crashes in a turn) problem starts all over again. I suspected bad reeds and the cage itself was missing the plastic insert so I replaced the whole cage with new stock item; problem identical. Checked, cleaned carb and jets (all stock).
Fuel is fresh, mixture is good (40:1), spark plug is good, my kid is desperate so he runs it every weekend as is but I know it can run much better.
Now here's something that might help; I have never seen this but if and when the engine's running, the carb will actually get cold! As is there's a little refrigerator running in there. I'm guessing this is due to the fuel expansion once it gets sucked up in the carb but I have never seen this one any other 2 stroke I have worked on.
My only guess is a bad float level or float itself. Any ideas?
Thanks for your help.
Marc

 

[Patman]

Done a compression check on it?

 

[bigboss_an]

No, not an official compression check. I did the 'finger-on-spark-plug-hole' test :-). It appears normal. Would low compression explain the cold carb?

 

[Patman]

Think about it for a second. Air being sucked through a piece of aluminum at a decent velocity... then you are hot you fan yourself to cool off right? Well you are just moving the air at a higher velocity. Throw in a liquid being atomized and it becomes much like what is known as a swamp cooler. The "cold" carb is far from your problem anyway so don't worry about it right now. Sticking a finger over the hole? Unless your fingers are calibrated much better than mine I doubt you can tell the difference between 135psi and 80psi. Check the compression with the proper tool and I bet you will find it is well out of range.

 

[helio lucas]

+1 on the compression test... note also that inside the bowl you have gas and it´s pretty cold...
check your spark plug also... when you are trying to start the bike after some time take the plug and if it´s not wet the fuel is not getting in the combustion chamber...
could also be an air leak or blocked exhaust...
by the way, since you just bought the bike, and is missing some parts you should look over the bike, with a service manual in hand to see if everything is ok...

 

[bigboss_an]

Well I tried to do the compression test, but the tester hose was too long and it would hit against the frame so I decided to tear the cylinder down. I don't see any abnormal wear on the cylinder or piston but I have ordered a new wiseco piston kit & gaskets just to be safe.
If you don't see any new follow up posts on this...problem will be solved. Thanks for the input gentlemen.

 

[Patman]

I believe CR80/85's have an issue with the head sealing up properly so you may also want to check everything for true flat surfaces and be very precise on your torque values as well as using top shelf gaskets.

 

[bigboss_an]

Thanks for the info. I will recheck especially the top of the cylinder and the head. I will have these resurfaced just in case. As I said I could not get an accurate compression reading but the head gasket and the head showed signs of a leak and while cranking the engine I think I even heard the hiss. Anyway, I ordered a Wiseco piston and gasket set and should have everything up and running pretty soon.
I don't have the shop manual for the 80cc. Do you have the torque values for cylinder and head nuts?
Thanks again Patman.

 

[Patman]

I'd really suggest picking up a factory manual they are about the best bang for the buck you can get on a dirt bike. Service Honda has them for very reasonable prices, just click the link to the left and you are on your way! I think they even have a specific link for the manuals on the site. I get one for every bike and have never sold them for less than 80% of what I bought them for so that's a pretty smokin deal.

 

[bigboss_an]

While I'm waiting for the parts to get in; what do you think about the carburator that's getting so cold? I have never seen it before but it makes sense when you consider the atomization that takes place, but it's cold to the touch while the engine is hot! Is this common or could I have a problem with the jets or the float?

 

[helio lucas]

i have a cr 80 and going to check if mine do it... maybe today or tomorow i´ll post it...

 

[helio lucas]

yes the carb will be a little cold, maybe colder than ambient... i was riding hard and in a very slow pace track i do not use more than 4...

 

[Patman]

While I'm waiting for the parts to get in; what do you think about the carburator that's getting so cold? I have never seen it before but it makes sense when you consider the atomization that takes place, but it's cold to the touch while the engine is hot! Is this common or could I have a problem with the jets or the float?

Think about it for a second. Air being sucked through a piece of aluminum at a decent velocity... then you are hot you fan yourself to cool off right? Well you are just moving the air at a higher velocity. Throw in a liquid being atomized and it becomes much like what is known as a swamp cooler. The "cold" carb is far from your problem anyway so don't worry about it right now. Sticking a finger over the hole? Unless your fingers are calibrated much better than mine I doubt you can tell the difference between 135psi and 80psi. Check the compression with the proper tool and I bet you will find it is well out of range.

 

[bigboss]

Well, problem is solved. Besides a few minor hickups, which I'm sure can be cured with carb adjustments, engine runs strong again.
I did not replace the piston as it measured and looked excellent. So I have a spare Wiseco piston.
A new top end gasket set basically solved all my problems. Most of all I suspect the head gasket which was probably reused in the past by previous owner. There's a lesson to be learned there.
Anyway, thanks to all, especially Patman.