CR250: Jetting & mix ratio?

[englee1]

CR250: Spooge, jetting & mix ratio?

Hi Folks, looking for a little advice. I have searched the forums & have found some info, but I'm still not 100% clear.

Last year I purchased a '95 CR250 that is in great shape for its age. I ran it all summer without any issues at all. It seemed to run strong & was perfectly reliable. This spring I decided to be proactive re-do the top end in prep for this summer.

Upon disassembly I found that the piston was OEM & stock size 66.4 MM & the cylinder was in great shape. P.S. the piston had a small crack on the inlet side...so yup I was glad that I took it apart.
I now have a Wiseco Pro-lite piston ordered for the rebuild & am awaiting its arrival. So I decided to remove & clean the exhaust valve....WOW spooge city!! Not just carbon but lots of tarry gunk.

So I decided to check the carb. Main is 170, slow is 55, needle is standard. This bike is supposed to have a 175 main with a 55 slow. Could the 170 be the cause of the spooge?

The only performance mods the bike has is Boysen reeds & a FMF gold pipe. The previous owner ran Ipone samurai synthetic premix. (I run Amsoil synthetic). We both run / ran 32:1.

I would love to hear your thoughts on the spooge + suggestions on proper jetting for my locale:

0 - 1000 ft sea level, 65 - 80 degrees (during riding season).
Right on the coast so salt air (if it makes any difference?).


Thanks in advance.

 

[Matt90GT]

So they leaned out the main jet. You should leave the jetting stock until you learn more about it. You shound like a novice here. For sure do more reading on the subject - TONS of info out there on jetting.

Spooge, well here is the deal. you jet the bike with the mixture ratio to lubricate the crank and piston at WOT (since we dont have oil injection to varry the ratio). So knowing this, you can fix the problem by running WOT all the time. If you dont, you will have excess oil that is not burned/needed/used to lubricate.

So what happens if you change the oil ratio? Well then you have to rejet. So if you run a 50:1 oil mixture, you will have an OVERLY rich mixture coming from a 32:1 mixture. Gas:oil Make sense yet? If you do not rejet, you will be overly rich and may not have enough oil to lubricate the engine at WOT.

I personally run 50:1 on all my 2 strokes with the amsoil, but I have also rejetted the carb for this.

But cleaning the power valves on a 2 stroke is a NORMAL maintenance item. You should do this YEARLY.

 

[2strokerfun]

Bottom line: The dropping from a 175 to 170 is fairly normal jetting procedure and is not contributing to your spooge. If anything, it is probably lessening spooge compared to running a bigger mainjet. Lack of routine cleaning of the powervalve is why you have a city of spooge there. See how it runs after you rebuild the top end. Might have to rejet a little. Might not. Pick one oil/gas ratio (32:1 is widely considered a safe choice by many--I run 28:1 personally) and stick with it. Clean the exhaust valve periodically. Good luck. Sounds like you pulled the cylinder just in time to save yourself from a costly grenaded piston!

 

[englee1]

Thanks for the responses guys;

I think I will set it to stock jetting (55 & 175) & keep my mix @ 32:1.
That way when I have the top end finished, it will give me a good baseline to do some plug chops.

Matt90GT: Yup not to hard to tell I'm a newbie :nod: this forum sure is a great place to learn though...

2strokerfun: I was not happy to find the piston cracked, but sure was glad that at least I FOUND it... you know what I mean :whoa: