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  #1  
Old 01-15-2018, 07:40 PM
Weekend Warrior
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Default Polaris 400 scrambler running rich through the mid range

Hi all. I was given a seized 2002 Polaris Scrambler. It looks like it was driven right off the showroom floor so I rebuilt it. .025 piston, rings, all new gaskets, crankcase seals, water pump bearing and seals, etc. Had to make the counter balancer puller and buy the special socket for the left handed thread slot nut. Have to love specialized tools but since I have over a significant investment in Snap On tools it was a nice add on to the collection. I'm well versed with Evinrude and Johnson outboards, have raced them for years and been to service school and have worked on two strokes for 50 years or so to give you personal history.

So here's the deal. I am running 32-1 fuel mix (93 octane with Red Line Synthetic oil) and Red line in the oil tank. Since I was unsure that the oil pump caused the seizure I doubled down on oil (mixed fuel and oil injection pump) and will switch to straight fuel once I determine the oil pump is doing its job. As it turned out, 2 head bolts were loose and all the coolant was gone so I'm going to say the seizure came from over heating. The piston was scuffed and cylinder scored on the exhaust port side.

Because of the fuel mix and oil injection shes smoking which is too be expected for the first tank. I'll change the spark plug once I get the engine broken in a little better than where its at now. The machine fires first pull of one revolution of the starter when I crank over and once it warms up idles nice. It runs strong but once you start getting into the throttle ( like 3/8 to maybe 1/2 throttle) the motor is making that ever so familiar 2 stroke running fat sputter. The RPM increases as you open the throttle however, it still sputters like it is running too fat. I took the carb apart, boiled it out in Gunk carb bath then put it back together as per the service manual.

Can any of the experts perhaps tell me where to look and maybe what to do to dial this machine in?

Thank you very much in advance.
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  #2  
Old 01-16-2018, 12:05 AM
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OPT should be around in the morning to help you out. I understand pre-mixing on the first tank but think you overdid the oil a bit. Good luck.
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  #3  
Old 01-16-2018, 04:44 AM
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First off you don't need 93 octane for an engine that only has a 6.9/1 compression ratio in stock condition. Premixing 32/1 is too much also as the pumps are calibrated at 50/1 from the factory. These two combined are probably the reason for the bogging. 87/89 octane is good enough,plus if you premix,40/1 with a good synthetic 2 stroke oil is sufficient even if you do away with the oil pump which on these older models I'd do. Not because they were junk,just from where they are located.Right on the front of the engine to where moisture could corrode the pump wheel and spring. I'd block off the the injector line at the intake manifold with a 6mm bolt and washer. You can go to the trouble of removing the pump and using a block off plate and run a single throttle cable,or as some have done,remove the pump gear and leave the pump in place along with the split cable.You'd just have to keep a check on the pump spring and cable.This final year model Scrambler 400 Polaris jetted way too rich with the 240 main,but a little lean on the 25 pilot jet when all the other year models had a 230 main,35 pilot jet. Same for the final year model Trail Blazer 400 that had the same jetting. Get the tank premixed right,block off the pump and see how it runs. Plug chopping also to make sure the plug is a tan to medium brown in color. Altitude you're at plus this winter's weather may cause you to have a few jets on hand to get it right along with raising and lowering the slide needle may help.Most cycle shops have a good supply of jets or this place has plenty of oem Mikuni and aftermarket jets.https://www.jetsrus.com/a_jet_kit_at..._1997_2002.htm
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Old 01-16-2018, 07:36 AM
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Thank you for the reply. We are at 4400' in Reno Nevada. I've had to re-jet a couple of other quads but they have engines with 2 extra strokes and that is a whole different animal. I suspected doubling the oil may have had an effect, it really doesn't with outboards as they have an open cooling system. Typically they will just smoke a whole lot more.

I know you have suggested blocking the oil pump which if everything is working well I really don't want to do. We don't have the corrosion issues in Nevada that wetter states do and truth is, I'm going to sell this machine and put the money down on a 4x4, Grizzley, Can Am, King Quad or something like that, just haven't found the right one in need of repair and, compared to new prices, the guys selling used are crazy based on age of their equipment.

The type of riding we do are steep rocky mountain trails as well as some well weather ghost town roads.
That said, I've seen that the oil pump is pumping, I'll run it like that and go to the jetting suggestions you have made if I'm still running fat unless you suggest something else considering I'm going to keep the oil pump.

Once again thank you.
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Old 01-16-2018, 08:04 AM
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So...you didn't say how's it's running at WOT...if it feels crisp there then it could be a simple needle jet adjustment (move the c-clip up one notch to lean it out). As OPT mentioned, do a plug chop after each adjustment. Also, right down your settings after each change. Finally, many folks mistake a lean condition for a fat condition...check your plug color often and don't burn her up!!!
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Old 01-16-2018, 10:59 AM
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Quote:
Originally Posted by Bill Schwab View Post
We don't have the corrosion issues in Nevada that wetter states do and truth is, I'm going to sell this machine and put the money down on a 4x4, Grizzley, Can Am, King Quad or something like that, just haven't found the right one in need of repair and, compared to new prices, the guys selling used are crazy based on age of their equipment.
That said, I've seen that the oil pump is pumping, I'll run it like that and go to the jetting suggestions you have made if I'm still running fat unless you suggest something else considering I'm going to keep the oil pump.
Dry,arid conditions,then I'd keep the pump but still keep an occasional check on the mechanics of it. Polaris was over cautious imo on jetting as they knew what people were going to be using these machines for. Down here in the summers most folks had to drop down from those 230/240 jetting because of the blubbering. Even the old Xplorers that had a 200 main and 30 pilot,for some of the old farmers that putted around, I had to drop them down to a 190 to keep them from fouling plugs.Plus make sure you still have the carb vibration dampener under the carb on the gear case.These have a tendency to dry rot or break off causing the carb to dump fuel into the intake. Item#32 on the parts break down.https://www.partzilla.com/catalog/po...g38ca/gearcase Hope you're able to get a good price for it to put down on the atv you really want.
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Old 01-17-2018, 09:03 PM
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Quote:
Originally Posted by old polaris tech View Post
Dry,arid conditions,then I'd keep the pump but still keep an occasional check on the mechanics of it. Polaris was over cautious imo on jetting as they knew what people were going to be using these machines for. Down here in the summers most folks had to drop down from those 230/240 jetting because of the blubbering. Even the old Xplorers that had a 200 main and 30 pilot,for some of the old farmers that putted around, I had to drop them down to a 190 to keep them from fouling plugs.Plus make sure you still have the carb vibration dampener under the carb on the gear case.These have a tendency to dry rot or break off causing the carb to dump fuel into the intake. Item#32 on the parts break down.https://www.partzilla.com/catalog/po...g38ca/gearcase Hope you're able to get a good price for it to put down on the atv you really want.
Once again, thank you for the help. I got off work later than normal so I put straight gas in the tank. With no load on the machine it runs up nicely without the sputter it had while running heavy oil ratio. With load (in gear) it comes out of the hole hard and strong but once you hit that mid range shes sputtering. It's definitely running fat, the plug was black. Thats as far as I got, tomorrow I'll yank out the carb, check the vibration damper and head to the dealer to get some jets. Because we have mountains and its so dry, dealers carry lots of jets and they are around the same price as the ones you sent the link for.
The plastics, and seat look like they were right off the showroom floor. The tires still have the flashing in the middle and a few tire *******. It was the wrong machine for what she used it for, but she had a cart she pulled around a 5 acre piece of land doing chores. Worst thing on earth for a two stroke but that's how it spent its life.
I think I'll start the price around $2,000 and see what happens. Found a 4x4 that needed wheel bearing close to that price.
Anyhow, thank you. I'll write back when I got her dialed in.
I'll let you know what it runs like when I'm done playing.
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  #8  
Old 01-18-2018, 12:14 AM
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Quote:
Originally Posted by Bill Schwab View Post
It was the wrong machine for what she used it for, but she had a cart she pulled around a 5 acre piece of land doing chores. Worst thing on earth for a two stroke but that's how it spent its life.
Probably never saw more than 1/4 throttle unless it was accidental. I'd get out and open it up just to clear out all the oily crap out of the exhaust that's accumulated over time.That might help it more than anything else.
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Old 01-21-2018, 02:11 PM
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Originally Posted by old polaris tech View Post
Probably never saw more than 1/4 throttle unless it was accidental. I'd get out and open it up just to clear out all the oily crap out of the exhaust that's accumulated over time.That might help it more than anything else.
You are probably right! So, went to the dealer and picked up a 230 and 220 main. Originally stuck in the 230 and ran well but I knew it had more so, I opened the carb up and put in the 220. You have to warm it up full choke for about 15 seconds, and then you can gently give it throttle until it hits operating temperature. Runs like a raped ape! I have one more issue and then I can put it to bed, will post under a different title.
Thank you once again for your wisdom.
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Old 01-21-2018, 02:48 PM
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Remember if a 2 stroke is running fantastic,beware.. Always do a plug chop to check the plug color. Hopefully the 220 jet will show a tan to medium brown color on the plug.
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