I have a 2003 polaris 700 sportsman carb. I started bogging over half throttle. I rebuilt the carb and replaced the torn intake boot thinking I solved the problem. Now it still boggs down but only over 3/4 throttle. I then replaced the spark plugs and found 120psi of compression on the left cylinder and 160psi on the right one. Do you think the top end needs to be replaced?

 

General rule on twin cylinder compression is within 10% of each other...although 160 sounds on the high side...but OPT can confirm...


Can it be run for some distance while bogging? Curious if you can do a plug chop while bogging and pull/read the plugs. Might be fuel starvation...

 

Compression should be between 150-200 psi according to the manuals. You are low on one cylinder,getting close on the other one and it's probably time to replace the pistons and rings. Namura make a stock size "A" kit for bores that are still showing 80 mm along with group B and C kits that compensate a little for the plated bores that are worn past the stock 80mm. Bore size would need to be checked before you ordered any kit.https://www.ebay.com/sch/i.html?_odk...+kits&_sacat=0 There is one other lurking problem that could be causing some of the bogging and that is if you still have the original Ducati ignition system and not the updated Kokusan ignition. Not being able to take throttle,back firing,rich fuel smell were a few of the symptoms. Not all Ducati ignitions failed,but I would keep that in mind as the kits are around $ 500 or so and changes out the whole ignition like shown in this video.

 

The engine boggs when cold or hot but only at full throttle

The ignition coil part# is 4010898 that is currently on the atv. I think this means the ignition system has been updated. It has good power at half throttle and runs rich at wide open. Adding choke doesnt help either and I can smell fuel when its bogging. I am amazed at how much compression these atv's should have.

The carb kit had two main jets in it, 152.5 and 155. The original was 155 so I put the 155 in it after rebuild. The diaphragm slide in the carb seemed to have alot more slop when inserted into the jet block then I am used to.

I think its time for a top end. I am guessing the engine was run for a long time with the intake boot leaking and prematurely wore out the engine. Do the 700's have camshaft issues like the 500's? Thanks for the quick responses.

 

Appears you have the late model 2003 that had the 2004 updated ignition which is good to know. If it's really worn,you can get the jet block for around 34 bucks. If the diaphragm and slide are still ok that's the way I'd go before I bought a cheap Chinese knock off carb that may or may not work right.Cams weren't normally a problem on the 700 as they were in the center of the engine.Has a push rod system similar to auto engines. For tear down and assembly can't beat a good manual that has pics,step by step instructions and torque specs. Namura is the only piston I know of that does have oversize pistons for these plated cylinders.2003 Polaris Sportsman 700 Service Manual PDF Download

 

I have rebuilt many carbs and I never cam across a worn out jet block. The bike only has 800 miles. Do you know the symptoms of a worn jet block? Also, where is the best place to buy parts?

 

Dirt mainly is the culprit. If the slide itself is scratched up look at the jet block areas where the slide rides.If worn enough they can cause cv slides to stick.Not a common thing to replace but I've had to replace slides along with jet blocks. Cycle Parts Warehouse,Partzilla,etc are a couple good places for oem parts.