This is my first post on the forums and involves the first atv I've owned.

I've kicked around the idea of purchasing an atv for a while now for use when hunting deer in the fall. Due to the limited amount of use the atv would get, I didn't want to spend too much money on it.

While browsing classified ads a few weeks back I found what was advertised as a 96 trail blazer for sale for a low price. The owner informed me that the quad was running last season, but needed carb work and he couldn't get it started up this season. The quad was in rough shape (plastics spray painted black, greasy frame/engine, choke lever missing, neutral/reverse lights gone, etc.) but it seemed to fit my needs and the price was right. I had hoped that I could rebuild the carb and have something to take hunting.

I got the bike home and confirmed it wasn't starting. I emptied the old fuel, cleaned the air filter, added a new fuel filter with new gas lines, and did several rounds of degreasing the entire quad with simple green. While cleaning the quad, I found the model# and serial number and to my surprise I had actually purchased a 1990 trail boss 250 2x4. Given the price, and my inteded use, this didn't matter much to me.

The engine did not want to start with new fuel (premixed because the oil tank had been disconnected). I pulled the plug and noticed it was not sparking. Once I disconnected the wire the black wire from the ignition, I was now getting spark to the plug. I put the plug back in, pulled the starter cord, and the quad fired first try. I let it idle as I put the seat and other parts back together, then took it for a few laps around my place. I have no baseline of how it should run, but it seemed fine. It had good throttle response and accelerated well. I ran the quad for about 15-minutes, turned it off, waited 5 or so minutes, and it started up first try again. I repeated this twice more, and then parked the quad back in the shop.

The next day I came out to do some more tinkering, but could not get the quad to start. I confirmed spark and fuel, which led me to check compression. Three pulls of the started cord with WOT yielded about 110 psi according to my cheap compression gauge. I understand this is considered fairly low compression for these engines. I continued to play with the engine trying to get it to run again and discovered that there was a good amount of fuel pooled in the exhaust. This also leads me to believe I have a compression issue.

In an attempt to narrow down the possible causes for the quad not running, I have cleaned the carb and installed a new spark plug. I can occasionally get the quad to start, but it is very difficult to start.

I am thinking I will need to rebuild the engine...a top end kit w/ piston for sure, and possibly replace parts in the lower portion of the engine?

I'm trying to keep this project as low cost as possible, but don't want to sacrifice reliability while trying to save a couple bucks. I'd rather do things properly now, than have the quad break down when I'm wanting to use it. As of now I'm considering the following:

- New ignition and keys
- New choke cable w/ lever
- Carb rebuild kit
- have cylinder machined and replace wiseco piston in appropriate size
- Replace top end engine seals
- new crank oil seals

What else should I add to this list to have a reliable, good running quad when I'm finished? Do you guys think I'm on the right track here?

I'm also curious if I can delete the neutral and reverse lights without issues? Since the oil tank has been capped off, is there a "proper" way to delete the oil mixing system (is there a write up on this?).

Thanks in advance guys, and sorry for the long winded first post.

 

You're thinking right in having the engine rebuilt from the ground up instead of trying to patch it up as many try to do! Why would you want to delete the neutral and reverse lights on the dash? You can though,all you have to do is to remove the headlight housing and disconnect the common ground(brown wire) on the bulb holder for each one OR with a razor blade or something similar just pop out the lens plate and pull the small bulbs out. Disconnecting the black wire(kill circuit) from the cdi to get spark usually means a short in the left control switch or the kill circuit in the cdi itself has shorted out.Another thing is to disconnect the black wire from the reverse limiter module as when it shorts out,can cause the same loss of spark or will limit in forward range. If the oil injector nipple has been properly "capped off" at the cylinder base,then you can run it as is. I'd recommend 40-1 ratio on mix. You can get a oil pump block off plate if you want to remove the pump itself,BUT with the split cable might be hard for the throttle to work properly without changing to a single cable.I'd just leave the pump attached.

 

Thanks for the response Old Polaris Tech.

It sounds like you agree with my thinking that the issue is the compression and the engine will need to be rebuilt. I understand I can buy a kit for the top end rebuild. Is there any sort of kit for the rest of the engine? If not, what parts should I look to replace. If anyone has a link to a write up or a parts list of some sort that would be very helpful.

For the neutral/reverse light...there is more missing than is there. I essentially have the wires, which are starting to get brittle and crack. Rather than get the bulbs and lense to put it all back together, I figured I would just tidy them up and tuck them away under the plastics maybe.

It sounds like I have some shorts in the left control switch or the cdi itself. Would it be best to replace these? Or just run with the wires unplugged?

For the oil system, I haven't dug into it much, but it looks like the line from the oil tank has been double backed and wired shut. It sounds like the correct way is to cap the oil injector nipple at the cylinder base and leave the rest of the oil system in place.

Thanks again for the response, appreciate the advice.

 

Wiseco top end kit is the best.http://www.ebay.com/itm/Wiseco-Piston-Kit-Polaris-250-Trailboss-blazer-/251358348777?pt=Motors_ATV_Parts_Accessories&hash=item3a862005e9&vxp=mtr(2) 3082162 crank seals easiest just to get from your dealer. The three crank bearings you can take the universal number (3083805) and match them up at any bearing house or auto supply.Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse
Hot rods are the best rod kits.https://www.denniskirk.com/hot-rods/....prd/CR168.sku

 

That helps out a lot for knowing what I am doing. Will it be easiest to remove the entire engine if I'm planning on doing the rod kit and bearings?

 

You have to remove the engine and split the cases. Crank shaft has to be separated,new crank pin installed,spacer washers and rod. Crank halves are then pressed together and trued using a truing stand and dial indicator. This job along with cylinder boring best left to a machine shop if you don't have 20 ton press,dial indicator and stand and cylinder boring bar. Sounds like you need a manual to look over the engine section.Here's a pdf service manual you can look at. http://gh-ftp.com/ORV%20Manuals/Pola...e%20Manual.pdf

 

OPT -

I had a busy summer and slowly got the work done on the 250 trail boss.

I had a local mechanic rebuild the lower end (bearings, rod, seals) and machine the cylinder and install a new piston (wiseco). I finally had a chance this weekend to get things put back together and try to start the bike up.

I installed the engine back in the quad, but have yet to hook up the intake or the exhaust. I then proceeded to rebuild the carb (cleaned and used a kit). With the intake and exhaust off, I put the carb back on and tried to pull start it...nothing.

I can confirm spark (and am assuming compression is there after the rebuild), but I must not be getting fuel to the engine? I have had the carb apart at least a dozen times and have thoroughly checked everything...it all looks fine. I have fresh gas in the tank, and it pours freely from the fuel tube.

As a test, I poured a small amount of fuel directly through the spark plug hole and the quad fired the first pull and ran until the fuel ran out.

Im really at a loss of what to try next? Any suggestions?

 

If you have good fuel flow from the petcock and fuel line to the carb,just check that you have the float needle and float set right if you think fuel isn't getting into the carb.Plus on the choke lever,flip it all the way over to make sure the choke circuit is taking fuel then try to crank it.Also anytime if you think the engine may be flooded(check the plug) Just have the choke off,pull the plug and crank it over with the throttle wide open to clear the crank case of any excess fuel.Then instal the plug and crank it. Should be a simple reason on this "IF" every thing from the stator plate timing,cylinder bore and piston,new bottom end including crank seals have been done right,fuel flow from the tank to the carb is good and you have good spark. Simple engine,but everything has to be right for it to run.

 

How would I check timing to rule out that being the issue?

I did have the stator plate off when replacing crank seals, but believe it was reinstalled in the same position.

Would the fact that the bike runs (rough) when gas is manually added to the cylinder, mean that the timing is close enough to start?

Thanks for all your help.

 

I always made a mark if the stator plate and engine case didn't have timing marks,but if you put it close to the original spot shouldn't be a problem on cranking. To check/adjust timing you have to have it running to adjust timing spot on,most people don't. You have to have a timing light hooked up to the plug wire and battery,a rpm gauge,then pull the plug on the recoil cover. Crank the engine,quickly get it to 3000 rpm and timing sets at the 23.5 degree mark on the flywheel. If it's off a little you have to remove the flywheel and turn the stator plate clock wise to advance timing,counter clock wise to retard it. Then replace the flywheel and check timing again.. That's why most people don't do this. Again if the plate is close to where it was originally set,shouldn't affect starting/running. Just eliminate all the other things that could be the problem as long as you have good spark and good compression from the new top end.