All Things Moto! Dirtbike Forums

Go Back   All Things Moto! Dirtbike Forums > Dirt Bike - ATV - Suspension Forums > 2-Stroke Dirt Bike Forums

Reply
 
LinkBack Thread Tools
  #1  
Old 02-24-2013, 07:17 PM
Young Gun, But A risky One
 
Join Date: Dec 2012
Last Online: 05-23-2013 09:30 AM
Location: Carlton, tx
Posts: 52
Default Rebuilt engine, new gas, good compression, good spark... but no!!

     

91 CR 250R

Heres it to you straight...

Brand new over bored cylinder and new piston (MAYBE 2 HOURS ON IT)
new gas mixed at 32-40ish:1
New spark plug today

Rebuilt the engine like yesterday and it ran good but leaked coolant out of the head gasket... fixed that and today got fresh oil in the trans and a new spark plug. Ran great from 3-about 6:30 pm then it did its usual runs decent and get on the throttle and bogs out as in... i am at half throttle then i open it up and it will struggle to gain rpms and then just eventually sputter its self out...

So this means good compression, what i think is good fuel, and a spark that looks fabulous but it still does this!!

Could it just be something simple as not riding it hard enough or could it be something like antifreeze finding its way into the cylinder?? All i know is that if i were to put a new plug in it right now it would take 2 kicks tops to start the dang thing!!! Please respond, thanks
Also i ride it as a putter but then more often then not i get on it and normally it will run ok until this happens...
Reply With Quote
  #2  
Old 02-24-2013, 07:56 PM
stevo450's Avatar
ATM! Pro Class
 
Join Date: Aug 2012
Last Online: 01-31-2017 07:35 AM
Location: South Australia
Posts: 3,709
Default

Ok a good starting pointing in my opinion is find out how you are sure coolant is not still getting into the cylinder? If you suspect the head is warped then I'd suggest getting the cylinder and head checked. Next thing I would ask for is a plug reading. My cousins bike had similar problems ( along with others ) a bad float height, incorrect jetting, not riding hard enough, are so things that contribute to a bike fouling and dying out like you state.
Reply With Quote
  #3  
Old 02-25-2013, 04:27 AM
arnego2's Avatar
Expert Class
 
Join Date: Mar 2008
Last Online: 01-09-2018 02:14 PM
Location: Porlamar
Posts: 762
Default

If you just lugged it around you could have a lot of premix in the crankcase accumulated.

Normally if you loose coolant your level would drop in your radiators, does it?

Something not running more than half or 2/3 of throttle would make me check, swap the coil.
Reply With Quote
  #4  
Old 02-25-2013, 05:21 AM
Expert Class
 
Join Date: Jan 2010
Last Online: 02-20-2016 01:21 PM
Location: North Carolina
Posts: 651
Default

Don't get mad but I noticed something in your post.
32-40ish?
Could your rebuild be "ish"?
Could that attitude perhaps gone into your build?
I mean, do it right and know what you have.
Reply With Quote
  #5  
Old 02-25-2013, 09:09 AM
Young Gun, But A risky One
 
Join Date: Dec 2012
Last Online: 05-23-2013 09:30 AM
Location: Carlton, tx
Posts: 52
Default

32-40ish as in it depends on how i ride... 32 for hard riding wich i dont normally do and 40 for just riding in the trails

I wouldnt rebore my cylinder and put over 10 hours of work in a bike i dont care about

---------- Post added at 09:09 AM ---------- Previous post was at 08:24 AM ----------

The plug reading is a little black with a back ground of brown on it... signaling a slight richness. But if i let it sit for like 20 minutes after riding i try and ride again but i cant get passed 1/2 throttle before i bog out and have to put a new plug in...

Rebuild was successful the compression is excellent with a 195 reading.
Im assuming i am just to easy on it.
Does anyone want a cr 250 in texas
Reply With Quote
  #6  
Old 02-25-2013, 09:31 AM
ATM! Addict
 
Join Date: Oct 2003
Last Online: 04-14-2014 08:07 AM
Location: alaska
Posts: 10,344
Default

why dont you fix the overly rich condition? if you are coming back to it and having trouble getting it started and being able to take throttle it sounds like it is flooding, float needle and setting usually fixes that.
Reply With Quote
  #7  
Old 02-25-2013, 11:44 AM
Young Gun, But A risky One
 
Join Date: Dec 2012
Last Online: 05-23-2013 09:30 AM
Location: Carlton, tx
Posts: 52
Default

Ok when i take the carb off and take it apart how do i set the float hight... i know how to fix the jetting... Just go down on the main right
Reply With Quote
  #8  
Old 02-25-2013, 12:02 PM
ATM! Addict
 
Join Date: Oct 2003
Last Online: 04-14-2014 08:07 AM
Location: alaska
Posts: 10,344
Default

there is a good pictorial in the knowledge base here on ATM by faded on setting the float. while you are at it, screw the enrichenor (choke) down all the way, it wont idle but that causes flooding too on the pj carburetor as they age. 16mm should be the float setting and just do it as his pictorial shows and test that it is shutting off. this will eleminate that as a problem.
Reply With Quote
  #9  
Old 02-25-2013, 02:26 PM
Expert Class
 
Join Date: Jan 2010
Last Online: 02-20-2016 01:21 PM
Location: North Carolina
Posts: 651
Default

Sorry you took my comments personal, just pointing out what I read.
btw-the main jet is but one component of jetting a carb.
Should be a manual floating around somewhere or someone could give you the stock settings.
Also, rejetting should be done when you change ratios.
I suggest pick one and stick with it.
My personal preference is 32:1 Klotz.
My 2001 CR250 is a shredder.

Your problem could be something simple.
Get the manual and check the stock settings.
If your bike is stock start there.
Question, did you check all the tolerances before you buttoned it up?
Reply With Quote
  #10  
Old 02-25-2013, 06:41 PM
Young Gun, But A risky One
 
Join Date: Dec 2012
Last Online: 05-23-2013 09:30 AM
Location: Carlton, tx
Posts: 52
Default

Tolerances? Explain... i am still quite a newby when it comes to fine mechanical work with dirt bikes

---------- Post added at 06:41 PM ---------- Previous post was at 06:35 PM ----------

So basically setting the float is checking for wear on the inlet needle pin and if it is out of spec bend the float assembly in the direction needed?
Reply With Quote
  #11  
Old 02-25-2013, 06:59 PM
ATM! Addict
 
Join Date: Oct 2003
Last Online: 04-14-2014 08:07 AM
Location: alaska
Posts: 10,344
Default

It isn't so much of a wear correcting but yeah. You ptobably need e new needle tho. The spring sacks out in them.
Reply With Quote
  #12  
Old 02-25-2013, 07:08 PM
Young Gun, But A risky One
 
Join Date: Dec 2012
Last Online: 05-23-2013 09:30 AM
Location: Carlton, tx
Posts: 52
Default

Got it... thanks ill try the float

and ill stick with a 42:1 ratio from now on...

I will post up again for an update
Reply With Quote
  #13  
Old 02-25-2013, 07:15 PM
ATM! Pro Class
 
Join Date: Jul 2011
Last Online: Today 12:16 PM
Location: Benton, LA
Posts: 4,911
Default ?????

Quote:
Originally Posted by 2StrokeBrapster View Post
Got it... thanks ill try the float

and ill stick with a 42:1 ratio from now on...

I will post up again for an update
You do understand that a 42:1 mixture is much richer than the recomended 32:1 mixture, right? I would get back to the 32: 1 before changing any jetting.

Paw Paw
Reply With Quote
  #14  
Old 02-26-2013, 05:01 AM
Expert Class
 
Join Date: Jan 2010
Last Online: 02-20-2016 01:21 PM
Location: North Carolina
Posts: 651
Default

Whenever you put a new part in like a top end or such, always check the tolerances.
A good machine shop will do that for you when you have it bored if you give them the rings and ask.
The ring end gap is critical.
Honda for example sells an "A" and "B" cylinder and pistons that match those cylinders.
Don't forget, these bikes ran great out of the box, stock.
Sometimes they run a little rich brand new but not enough to foul plugs.
I would get back to stock and get it running good from there before I made any changes.
Otherwise you'll be chasing down gremlins and won't know where to start.
Reply With Quote
  #15  
Old 02-26-2013, 07:15 AM
dogger315's Avatar
ATM! Pro Class
 
Join Date: May 2009
Last Online: 05-18-2018 01:08 PM
Location: CA
Posts: 2,514
Default

Quote:
You do understand that a 42:1 mixture is much richer than the recomended 32:1 mixture, right?
I'm assuming these were typos on both of your parts. Brapster meant
32:1, and Paw meant to say leaner as in 42 parts gas to one part oil
is leaner than 32 parts gas and one part oil.

dogger
Reply With Quote
  #16  
Old 02-26-2013, 07:41 AM
Pro Class
 
Join Date: Nov 2011
Last Online: 09-03-2018 07:40 PM
Location: Cincinnati, Ohio
Posts: 1,237
Default

Quote:
Originally Posted by dogger315 View Post
I'm assuming these were typos on both of your parts. Brapster meant
32:1, and Paw meant to say leaner as in 42 parts gas to one part oil
is leaner than 32 parts gas and one part oil.

dogger
42:1 is a richer air/fuel ratio, but a leaner fuel/oil ratio. As far as 42:1 being "much" richer than 32:1, I would have to disagree. You are talking about ".7 percent" more fuel. One step up or down in main jet size would change the air/fuel ratio more than that.
Reply With Quote
  #17  
Old 02-26-2013, 07:45 AM
ATM! Addict
 
Join Date: Oct 2003
Last Online: 04-14-2014 08:07 AM
Location: alaska
Posts: 10,344
Default

Measuring for 42-1 isnt near as much fun as 40-1 or 32-1 :-)

I am not sure about tearing it back down to check tolerances at this point, but a look through the exhaust port for seize marks on the piston may be in order. Putting one back to stock for me if i walked in on the middle of this one would start at the float and go from there. The "bogging" of course can be a partial seizure.
Reply With Quote
  #18  
Old 02-26-2013, 08:02 AM
Young Gun, But A risky One
 
Join Date: Dec 2012
Last Online: 05-23-2013 09:30 AM
Location: Carlton, tx
Posts: 52
Default

Wait i thought 32:! was four ounces to 1 gal of gas
so then i went on ma calculator and 42:1 says it is 3.046745789321754 ounces for a gal of gas, thus making it leaner right?
Reply With Quote
  #19  
Old 02-26-2013, 09:52 AM
ATM! Addict
 
Join Date: Oct 2003
Last Online: 04-14-2014 08:07 AM
Location: alaska
Posts: 10,344
Default

leaner in OIL, richer in fuel, thus making the fuel to air ratio RICHER.
Reply With Quote
  #20  
Old 02-27-2013, 09:27 AM
Expert Class
 
Join Date: Jan 2010
Last Online: 02-20-2016 01:21 PM
Location: North Carolina
Posts: 651
Default

Spend a couple of bucks and buy a ratio right.
Takes most of the thinking out of mixing.
I probably have 6 or 7 of them around here.

Also, just to stir the pot a little more.......
I was told that more oil without changing jets actually makes it leaner because the oil molecules take up more space.
I'm not the cleanest wrench in the toolbox or sharpest knife in the drawer but it kinda makes sense to me.
We need a friggin engineer

We're gonna mess this guy up good if we get too technical.
And so, here we go

http://en.wikipedia.org/wiki/Air-fuel_ratio

Last edited by Tharrell; 02-27-2013 at 09:32 AM.
Reply With Quote
Reply

  All Things Moto! Dirtbike Forums > Dirt Bike - ATV - Suspension Forums > 2-Stroke Dirt Bike Forums


Bookmarks

Thread Tools


Similar Threads for: Rebuilt engine, new gas, good compression, good spark... but no!!
Thread Thread Starter Forum Replies Last Post
Looking for a Good Cheap Compression Tester Honda-Dirt-Rider General Discussion 13 01-17-2013 04:13 PM
I need my cylinder head rebuilt and looking for a good company that I can send my hea skos 4-Stroke Dirt Bike Bike Forums 1 01-17-2011 12:38 PM
Good engine oil for a DT175 Shadow175 2-Stroke Dirt Bikes - Yamaha 0 05-21-2009 03:46 PM
Good compression gauge Roostman General Discussion 10 09-13-2004 09:52 PM
Determining a good spark cosmo12550 2-Stroke Dirt Bike Forums 2 07-22-2004 08:01 AM


All times are GMT -6. The time now is 03:22 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright ©2002-2017, JDub Consulting, Inc. All Right Reserved.