I have gotten my Xplorer all finished and I am just running one more tank of premix through it to help the break in of the new motor. What I have done so far is, replaced all the engine gaskets, replaced all the seals along with water pump bearing, new piston and rings with an over bore, new reeds(the old ones had two petals that would not seal all the way) and a rebuilt carb and adjusted the choke. I rebuilt the carb with the same jets it had originally. A 210 main jet, a 30 pilot jet, and a 6DH29 jet needle. After breaking it in and running a tank of gas through it, I warmed it up and found that the machine ran the best with the needle clip set at the 2nd position from the top and the pilot screw turned out 1 1/2 turns. I also checked the float arms for wear and set the float arms to 24 millimeters. It runs awesome, starts very easily and doesnt run hot. The only complaint I have with the rebuild is, there is a choppiness or almost like a miss just off of idle. The machine idles great, and is fairly clean sounding now that I sealed up the exhaust joints because it was so rattley before. When I mean just off idles, I mean like less than an 1/8 open, anything 10 mph and under cruising around. This choppiness goes away for the most part if a load is applied to the engine, such as going up a slight incline. I am not very familiar with two strokes and I know they can be a bit erratic when not under a load. My boss is pretty heavy into snowmobiles and he says that most two strokes just are that way when there is no load on them. I just want to make sure in case there is something I am missing on redoing this machine. To me, it feels like a miss almost but maybe its just me. The plug is burning clean and isnt sooty. Could this be ignition related or is this just a two stroke thing? I would assume I have a good consistent spark if the engine starts good and runs out clean. How would I check if I have a good consistent spark at low speeds? Do I really have a miss or is it all in my head? lol

Thanks,
Mike

 

Nature of the beast on the 400 to load up at low speeds or just putting around,then hesitates/bogs when you throttle up . Down here for the old farmers and ranchers in our summer heat I dropped the main jet that had 200 stock jets down to a 180 and lowered the needle one,sometime two notches(needle clip at top position) to get rid of the bog/choppiness. You have to find that "sweet"spot that suits your riding.Jetting from the factory especially on the main jets were always too rich in my opinion. 1 1/2 to 2 1/2 turns out on the air screw didn't help as much as jetting changes did. Normally after all was said and done after the changes 2 turns out worked pretty good as a general setting.You may not have 100+degree days where you're at in the warmer months,plus you have to be careful in cooler weather and high speed driving. Always check the spark plug color.It'll let you know if the jetting is ok.

 

Thanks OPT,

I think I may have found part of my problem. When I went to my shop yesterday, I noticed a small spot under the fourwheeler that was coming out of the vent hose that goes to the nipple on the fuel bowl on the carb. It was doing this before, so I bought a new carb kit last summer for it and it quit leaking. I also adjusted the float arm at that time but it really wasnt off. It was at the recommended 24 millimeters. Is it common for the needle and seat to wear out that fast? They were installed in July of last year. When I bought my carb kit, I bought one from Moose Racing and I had a hard time finding a kit for the 96 model. Mine had a 210 main jet and a 30 pilot jet. the needle was a 6DH29. I can pick up a set for the 97 on up which uses a 200 main jet and a 30 pilot jet with a 6CEY6 needle. Will this be a leaner set up and why is it different on the 97 on up models? Seems like the 96 is its own animal for carb kits. I also run only premium fuel (91 octane or better) with no ethanol added. I put about an ounce of seafoam in the tank when I fill any of my machines also. The rubber isolator under the carb is in good shape so maybe its just the nature of the beast that these carbs vibrate to the point that they wear out so fast.

Thanks,
Mike

 

Seems like every year jet needles,main jets and occasionally pilot jets would change on the 400 in spite of it being the same engine and using the same old dependable VM34 Mikuni carbs that Polaris has used on all the 350/400s,plus a pair of them were on and old Polaris Storm snowmobile that one guy brought in several times to get ready for Colorado trips. Wouldn't hurt to experiment on jet needles or jets as your model like I mentioned is used on so many different applications.Even the old 96 Scrambler 400 had a 250 stock main jet just because Polaris knew what people were going to do with them. A lot of carbs that went to Colorado I dropped from a 200-210 to a 160 main jet for 13,000 ft or so. That's a pretty big drop. Yes a lot of year specific carb kits may be hard to find,but basically all 400 kits will work. You just have to check the main and pilot jets that are supplied. Everything else is the same for the most part. I've used Moose kits with really no problems,but in my old opinion Shindy makes about as good a kit as you can get as all parts are Japanese,not from Taiwan or mainland China. Plus believe it or not premium fuel is not required or recommended.87/89 is the fuel I'd run. We learned that on the small Ktm race bikes that specified premium. They ran good on premium,but wouldn't run worth a crap on 50/50 or 60/40 premium and VP108 race gas. They'd just stumble and sputter. Problem is the higher the octane,the slower it ignites,especially on lower compression engines.Premium is really for higher compression engines and burns slower and cooler,which those machines definitely needed.http://www.ebay.com/itm/1997-2001-POLARIS-400-SCRAMBLER-2x4-4x4-CARB-CARBURETOR-REPAIR-KIT-03-406-/330806422215?hash=item4d05996ac7&vxp=mtr And yes the 400 engine regardless of what model it was did go through needle and seats quicker than any other machines,just because of the vibration,even with the rubber transmission adapter.

 

The main reason I run the premium is because anything lower than that around here is mixed with 10% ethanol. Most of the small engine repair guys around here say that is the number one cause of fuel problem when people bring their stuff in. Does the main jet affect the off idle operation? I thought the pilot jet was mostly responsible for that and the main jet was for more WOT. I also run the stock NGK plug. Is there any plug that runs better than NGK's?

Thanks,
Mike

 

Pilot jet affects idle to about 1/4-3/8 throttle or so. That along with air screw setting, jet needle position to fine tune this area of operation. Wot is handled by the main jet along with a small amount from the pilot jet even though it's insignificant at wot.I'd still try a tank of lower octane,mixed with a little marine Stabil,Star tron,etc to negate the effects of ethanol and see if there's any difference in performance.Can't beat the stock copper core NGK plug. Older machines really don't benefit from platinum,iridium as much as the newer dci ignition systems do.Stuck some iridiums in my old Honda and ended up fouling two of em.Went back to plain old NGKs.

 

Thanks OPT,

Looks like another carb kit is in order before I start my summer use of the Xplorer. I have always had good luck with NGK plugs. Ran them in my old muscle cars and even in my newer mustang that I had a 150 HP shot of Nitrous on. I always have a couple new plugs in the toolbox of my fourwheelers just in case I foul one out, but I never had one go bad so I just change the two stroke one twice a summer and the four stroke ones yearly.

Thanks,
Mike