What are your jet settings? Most interested in the needle as that generally moves from one carb to another...to fat a condition (clip on lowest position) will cause the symptom you described off idle.


I also didn't see that you verified jets...I'm curious what you're running for a main...that could explain your full throttle symptom as at full throttle you are only on the main...


Was this thing modified or is it stock? If stock betting a baseline will be easy...if not then you'll need to do a plug chop at as much WOT as possible to see how you're running on the main...

 

Adjusted valves to spec. They were too tight to start so I figured that was the problem. Got them all at 0.15mm and guess what? No change. runs exactly the same as before.

I dont know man...I just put the carb on there as it came out of the box. Stock machine except a pipe.
It doesn't puff any smoke like i would expect out of a rich condition. It just dies as if you shut the fuel off. Above mid throttle it stutters and will die if you don't let out of it.
I adjusted the valves as suggested above and thought that would help but it did not even though they were too tight by a good margin.

 

Are you sure your replacement carb is a BST40 not the older BST34. This is the carb you should have. 155 main jet,40 pilot jet. 2000 Polaris SCRAMBLER 500 (A00BG50AA) Carburetor | Cycle Parts Warehouse Plus here's a good article on this carb and how to set the float level correctly.The BST-40 Bible | Adventure Rider Plus here's a pdf fuel section from the manual on carbs that can help also.https://www.google.com/url?sa=t&rct=...U2gGlaHJWSIlbA

 

well, it looks exactly like the one that came out of it. How do I know what jets are in it? I'm carb dumb so bear with me.

 

Jet sizes are marked on the top of the round main jets. Pilot jets are marked on the side. Magnifying glass helps on older jets.

 

Thanks...
I noticed something interesting while messing with it, that I should have noticed earlier. It appears that the flywheel timing mark doesn't line up with the inspection hole when the camgear dots are in the proper position in relation to the head, i.e. parallel. It seems the timing mark is about 3 teeth too far advanced on the flywheel, past the mark in the inspection hole.
It also looks like someone had the head off somewhat recently becuase it's spotless under the valve cover and the bolts have the usual marks on them that comes from having tools on them.
I was going to pull the flywheel and stator and verify the timing chain settings but cant' get the damn flywheel off!
The question is, that timing mark is supposed to line up with the mark in the hole in the cover right?

Bad cam timing will certainly cause issues like I"m having!

 

Yes it would.. You need a good harmonic balancer puller to pull the flywheel. Sometimes they may be a little tough. Heat helps on the crank shaft. 1/2" impact gun is a must! Here's what timing looks like using the plated links for a guide courtesy of another member.https://atvconnection.com/forums/pol...ml#post3305250 Plus a pic from the manual.

 

I"ll go "rent" a puller from the parts store. I tried heat with a little 2 jaw puller but it wasn't budging. I didn't want to put too much on it though for fear of messing up the stator.
I found the entire manual online free .pdf download so that helps a lot!

 

Manual..

 

if the flywheel is still being stubborn when you get a good puller, just give the end of the crank a little love tap