'00 Xplorer 250 lethargic- stumped! - Polaris ATV Forum
ATV Repair and Maintenance Having problems? Doing a rebuild? All Repair/Maintenance Discussions here.

 
LinkBack Thread Tools Display Modes
post #1 of 6 (permalink) Old 05-28-2019, 07:16 PM Thread Starter
Junior Member
 
04Preddy's Avatar
 
Join Date: Jun 2016
Location: Provo, UT
Posts: 10
'00 Xplorer 250 lethargic- stumped!

I'm stumped, looking for some help here. Some background information for you: Last fall, I found a 2000 Xplorer 250. Thought it was a cool machine, and something that my son could learn to ride on, and could do some chores around the yard. Went and looked at it, made an offer, and took the machine home. With it being the end of the season, I took it out one time, noticed some things I wanted to work on, but ultimately winterized it and parked it until a few weeks ago.

It initially was not back shifting, so I tore the secondary apart. The buttons were worn, and the helix was scarred, so in went a new helix and buttons. Backshifting fixed. Set the clutch with the Red spring on 1 on the moveable sheave, and 2 on the helix. Did not spend any time with the primary, but did notice that it has the blue spring in it. Before final reassembly, I started it in neutral and the clutches seemed to function fine, though it did seem to take a while to get the primary to slide all the way back out completely.

I live at 4500' and took it for a ride at 6200' at 40*F on Memorial Day and the machine was very lethargic. Engine fires up quickly, only needing the choke at or below freezing for 10-20 seconds. On the trip the machine would move under its own power, but struggled getting it on the pipe, and would bog at 2/3 throttle to WOT in high range. At times it was really struggling, so I put it in low range, and it seemed to cruise around better, and would actually get into the power band, but still didn't seem to run as good as my '98 Trail Boss. Chalked it up to be jetting. Tore the carb apart tonight, and its got a 120 main, and 40 pilot which looks to match factory jetting specs for the elevation.

Pulled the plug to do a compression test, the plug is black, and has a lot of carbon build up on it. Did the compression test and got between 95-110 PSI depending on 1 of 3 gauges used.

Not sure where to go next. Would low compression manifest itself more at elevation? What else should I look for?

Last edited by 04Preddy; 05-28-2019 at 07:18 PM.
04Preddy is offline  
Sponsored Links
Advertisement
 
post #2 of 6 (permalink) Old 05-29-2019, 05:32 AM
Premium Member
 
stave7119's Avatar
 
Join Date: Oct 2013
Location: Lena, IL
Posts: 3,346
I would say yes elevation would effect compression. 95 is on the low side for a 2 stroke anyway. They usually say they need 100 to run right. But you said it starts ok which is a sign that it has enough. Low compression would cause a hard starting issue. Your black plug says it is running rich. Did you try it with the air box lid open?

Mine: 2018 Sportsman 850SP - 26" Bear Claw HTRs on OEM steel wheels(I really don't like the Aluminum ones)
Polaris Hand warmers, Mirrors.
Hers: 2019 Sportsman 450. 26" Bear Claw HTRs on Moose 427X Wheels.

2007 Sportsman 500 EFI, Polaris Winch, 25" Bear Claws QSC Clutch Kit, Hand Warmers
2001 Magnum 325 MOSE 12" rear wheel conversion. 25" Sedona Coyote tires
2017 Polaris Ranger 1000XP - Roof and front glass
2018 Kawasaki KLR650
2001 Magnum 325 Warn winch and Moose 60" plow-Sent to Daughter and Son-In-Law since his blew up
SOLD 2004 Sportsman 600 Twin
stave7119 is offline  
post #3 of 6 (permalink) Old 05-29-2019, 10:29 AM
Polaris ATV Legend
 
latebird's Avatar
 
Join Date: May 2014
Location: Illinois
Posts: 4,351
Low compression will let a two stroke start and idle fine, but lack power - I had an old Suzuki 100 with 90 PSI compression - it would start on the first kick and idle fine, but you could push it faster than it would run - it was kinda OK in low gear, but in any other gear it run, but lose speed - put some new rings in it and immediately noticed the idle was about 2000 RPM higher - ran fine after that - rings can do funny things - I think the compression should be about 120 to 150 psi and altitude will drop compression, by about 3% for every 1000 feet above sea level. Here's a chart to figure how to compensate for altitude reduction of compression: 150 psi at sea level will test 125 at 6000 feet

1000 .9711
2000 .9428
3000 .9151
4000 .8881
5000 .8617
6000 .8359
7000 .8106
8000 .7860

Shop Owner and Mechanic with over 50 years experience
latebird is offline  
Sponsored Links
Advertisement
 
post #4 of 6 (permalink) Old 05-29-2019, 11:32 AM
ATV Enthusiast
 
pigseye's Avatar
 
Join Date: May 2015
Location: Minneapolis, MN
Posts: 45
Quote:
Originally Posted by latebird View Post
Low compression will let a two stroke start and idle fine, but lack power - I had an old Suzuki 100 with 90 PSI compression - it would start on the first kick and idle fine, but you could push it faster than it would run - it was kinda OK in low gear, but in any other gear it run, but lose speed - put some new rings in it and immediately noticed the idle was about 2000 RPM higher - ran fine after that - rings can do funny things - I think the compression should be about 120 to 150 psi and altitude will drop compression, by about 3% for every 1000 feet above sea level. Here's a chart to figure how to compensate for altitude reduction of compression: 150 psi at sea level will test 125 at 6000 feet

1000 .9711
2000 .9428
3000 .9151
4000 .8881
5000 .8617
6000 .8359
7000 .8106
8000 .7860
Hi Latebird,
I do not mean to hijack the thread but I need some clarification. My presumption here is that there is nothing you can reasonably do to increase compression beyond stock. In other words, if the max compression is 150psi at sea level, then the most you can get in compression at 6000ft elevation is 125 psi. Yes, I do understand you could gain compression with a longer rod or different crank but I do not consider that type of change to be reasonable.

In addition, if stock compression is 150 psi but there is enough wear in the engine so compression is only 115 psi and the engine runs fine at sea level, it would probably not run great at an elevation of 6000 ft because the elevation based compression is only 96 psi.

Note: The values used in this example are pulled from the air for discussion purposes only.

Is this a fairly accurate way to look at it?

Another question, if the air is "thinner" (less oxygen) I would also guess having less compression and less available oxygen would also be a factor. The engine would run richer at elevation and this would also contribute to not running as well as it would at sea level.

Is this true as well?

Thanks
pigseye is offline  
post #5 of 6 (permalink) Old 05-29-2019, 03:13 PM
Polaris ATV Legend
 
latebird's Avatar
 
Join Date: May 2014
Location: Illinois
Posts: 4,351
@pigseye - that is exactly right - as you go up in altitude the air gets thinner and the engine runs rich so jetting down will restore power and performance - also (especially with a two stroke) compression rises with an increase of engine speed, but there are ways to raise the compression without major engine work. The cylinder head or top of the cylinder may be shaved or the combustion chamber welded up and reshaped. Personally I prefer shaving the cylinder head.

Back in my days of racing two strokes, I had an assortment of cylinders and heads - each was marked as to the preferred place of use - timber, motocross, hare scrambles, flat track and divided into categories - short track, long track, groomed, natural terrain and elevations - most were for mid-west, but I had a couple for Colorado and Tennessee and Nevada. Damn, that was a long time ago; 1970 to 76.

If a vehicle is going to be used primarily at an altitude above 4000 feet, the performance may be improved by having the cylinder head shaved about .050" to permanently raise compression. If the vehicle was going to be part time at sea level to 2000' feet above, the compression could be dropped by installing two head gaskets (you don't to remove and replace base gaskets because that will affect port timing) or having one cylinder head for below 4000' and another for above 4000' or you could just leave the shaved head on the engine and use 87 octane fuel above 4000' and 91 to 93 octane below 4000'.

Regardless, the jetting may have to be changed from seal level to high altitude.

Shop Owner and Mechanic with over 50 years experience
latebird is offline  
post #6 of 6 (permalink) Old 05-30-2019, 07:46 AM
ATV Enthusiast
 
pigseye's Avatar
 
Join Date: May 2015
Location: Minneapolis, MN
Posts: 45
Quote:
Originally Posted by latebird View Post
@pigseye - that is exactly right - as you go up in altitude the air gets thinner and the engine runs rich so jetting down will restore power and performance - also (especially with a two stroke) compression rises with an increase of engine speed, but there are ways to raise the compression without major engine work. The cylinder head or top of the cylinder may be shaved or the combustion chamber welded up and reshaped. Personally I prefer shaving the cylinder head.

Back in my days of racing two strokes, I had an assortment of cylinders and heads - each was marked as to the preferred place of use - timber, motocross, hare scrambles, flat track and divided into categories - short track, long track, groomed, natural terrain and elevations - most were for mid-west, but I had a couple for Colorado and Tennessee and Nevada. Damn, that was a long time ago; 1970 to 76.

If a vehicle is going to be used primarily at an altitude above 4000 feet, the performance may be improved by having the cylinder head shaved about .050" to permanently raise compression. If the vehicle was going to be part time at sea level to 2000' feet above, the compression could be dropped by installing two head gaskets (you don't to remove and replace base gaskets because that will affect port timing) or having one cylinder head for below 4000' and another for above 4000' or you could just leave the shaved head on the engine and use 87 octane fuel above 4000' and 91 to 93 octane below 4000'.

Regardless, the jetting may have to be changed from seal level to high altitude.
Hey Latebird,
This is an awesome explanation with relevant experience. And duh! shaving the head is really not that big a deal to raise compression for consistent use at elevation. Using different octane fuels at different levels is a great idea too.

Thanks so much!
pigseye is offline  
Reply

  Lower Navigation
Go Back   Polaris ATV Forum > Polaris ATV Technical Discussions > ATV Repair and Maintenance

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Polaris ATV Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome