Well while waiting for my 1996 scrambler 400 motor to be rebuilt I thought I would take my wifes trailblazer out a few times. After a few times on it I messed hers up too.

The original symptoms were hard to start, low power on takeoff and real finicky to stay running. I took it to the local Polaris dealer thinking carb problems and they told me they put a bigger pilot jet in it to help with the starting. Then they said they had no problems with it. I went to pick it up and it started right up. Loaded in my truck and when I got home I couldnt get it started again.

Ran compession tester and had 70psi cold. Got a cylinder and piston kit from Rick Ritter .040 over and got it all back together. Starts right up now. 135 psi.

Now it has a pinging sound that I believe is detonation. I can romp on the gas and then as soon as I let off the gas it makes a pinging sound. Like a hammer on metal sound.

How do I fix this? Is it lean? Also if anyone knows the stock settings for this carb? Mainly needle clip position, stock size jets, and air screw adjustment. I would like to get back to stock since I don't believe that a stock quad that is 13 years old would all the sudden need a jet change when in fact it had low compression. Now I am afraid to run this until I get this pinging sound gone.

My buddys think I am paranoid but I know what the quad did before it needed rebuilt and it never pinged like this before.

As always any replies are really appreciated.

 

you are correct in thinking you don't need a bigger pilot jet when nothing has changed like cold temps. any ways stock pilot is a #40, and the main is #130. if your hearing metal to metal sound and it's when you let off(not under load where pinging would be heard imo) then there is an issue. maybe even contact rick and tell him about your concerns and ask what he thinks where you bought the parts form him. must a real good dealership that wouldn't even be smart enough to do a compresssion test of a 98' t.blazer w/ hard starting.

 

hope its not piston hitting the head cause of bad rod bearing

 

Plus did you check the clearance between the bottom of piston skirt and the cylinder before it was installed! If its has too much clearance(over .003) could have a pinging noise from the piston to cylinder clearance? Just fishing! PS: plus the engine would not need a carb jet change if it had the stock jets in it and it ran fine before and you haven't changed altitude!! OPT

 

I didn't check the skirt clearance because Rick Ritter gave me a cylinder head and a matching wiseco piston. What is weird is that I only hear if when I let off the throttle. Also it only appears to do it when the engine is hot. My buddy said his trailblazer did too and he took it to a dealer and they told him that was normal . He said high octane gas helped with his pinging, but doesn't seem to help with mine. To me it also smells hot.

Problem I have is both Polaris dealers within 30 miles have tried to screw me over on this quad. I spent $250 in labor and over 6 weeks in and out of both shops for the hard starting only to find out myself that the compression was bad. I finally have the money to pay someone to fix it for me and I don't trust any of them anymore. I guess the good thing is I'm learning alot about my machines. Perhaps more than I wanted too lol.

 

SORRY,got your 400 confused with the wifes 250 Trailblazer that was actually repaired!)!
Still could be when hot piston to cylinder clearance could be cause of pinging? Plus did you make sure there was NO up and down play on the rod before you installed the new parts? The old 300 2-stroke DID ping straight out of the crate ,but not the 250 engines,were always fairly quiet! OPT