Hi, I'm new to the forum. Been trollling here for a few few weeks while I've been troubleshooting this 400. Heres what I have. It's a 1996 Sportsman 400 4X4 2 stroke. Here's the issue I'm having. It starts right up, idles fine. I give it a little gas and its loading up, at about half throttle it clears up. The carburetor is spitting gas out the back. I've rebuilt the carb, new needle and seat, jets. Ive replaced the reeds also. Would a bad crank seal cause this issue? When its running I can see a ton of gas hitting the bottom of the slide. Any info will greatly be appreciated.

 

Check compression and see where you stand. Anything less than 100 psi isn't good. Yes leaking crank seals can cause problems also in not allowing the fuel/air/oil mixture to atomize properly for combustion. Especially the one behind the drive clutch.

 

I checked the compression this morning and its sitting at 125 psi. This seems ok. I lowered the needle and seems to run better. Could the Jet needle be worn? The amount I spent on carb kit and jet needle I couldve bought a brand new VM34. How do I check the crank seals? I had the clutches of and the seal seemed ok. Thanks for your help

 

Lowering the needle shuts down the fuel a tad especially off an idle and mid range. You might recheck the float level plus check that the float arm isn't wobbly and worn and the float pin worn down. Can't get these in kits. Plus may help to look over this fuel section from the manual.https://www.google.com/url?sa=t&rct=...U2gGlaHJWSIlbA Plus a couple videos that can help. On this particular seal it would have been easy to have changed it out once you had the clutches and backing plate off.Best way to check for any 2 stroke leakage is with a leak down tester. Can spot any head or base gasket leakage along with engine cases or seals.

 

So, a quick update. The jet needle which I thought was a suspect, was either really worn or someone drilled it out. I got a brand new one and alot of my symptoms went away. It was obvious the old one was way bigger than the new one.
But now it seems I have a intake leak around the top corner of the intake. I put a new gasket on. Is sealer advised on the intake when going back together?

Thanks for the help!!

 

Gasket eliminator or a good rtv around the intake manifold gasket is ok to use. Anything to help stop air leaks as this is an expensive part now if you had to replace it.

 

OK, quick update. Fixed the air leak but this carb is still giving me fits. It idles good now, but when I give it gas it stumbles and then almost dies and the it catches itself and comes back up. Is this a jetting issue? I took the clutch cover back off and sprayed around the crank seal, idle didnt change at all. Sprayed around the base gasket, no change in idle. The jetting is stock at 200 main and 30 pilot. 200 main seems small to me at sea level for a 400. Thanks for the help

 

Down here the stock jetting was a 210 main and 30 pilot on the old 400 Sportsman. For the old farmers that putted around and fouled plugs I had to drop the main to a 190. If it's bogging then picking back up,could possibly still be rich on the top end jetting. Might help to have a few jets larger and smaller than what you have to try out. You can first play with the needle clip position and see if that can help you on determining which way you need to go on jetting changes if needed.Local dealers have these hex head jets or online.https://jetsrus.com/a_jets_by_carbur...2_main_Hex.htm

 

yeah I tried moving the needle, didnt really make a difference. It actually had a 200 main. I have a 190, maybe try that and see if it makes a difference.

I see you're from north texas also....What area?

Thanks for your help.

 

Northeast of Rockwall.