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Discussion Starter #1
I normally do not check the oil every time we get out our ATV but did today since I had to break out the pliers because we got it too tight to come out by hand.

When I got it out I was confused because oil was running out of the dip stick hole then I realized it was gas so we did a total oil change but only good oil came out at first when we pulled the drain plug. To be on the safe side we drained the oil cooler and it was just nice pure oil with the normal look and feel.

Thankful it was on compression stroke and the starter would not turn it over because it was hydro locked on gas so we pulled the plug and pulled the rope to clean the gas. Then with the plug still out we used the starter for about six 30 second periods over time to help get the ring groves clear of gas and re oiled at least.

Found when we pulled the gas line to the carb off at the fuel pump it did drip from time to time when it was shut off but the carb had been loading up since we got it so we are going to have to rebuild the carb for sure and check out and make sure the float is still floating as it should. Bet it is not. :(

In short had we not checked the oil level and it had started it would have been a big mess or MUCH worse.

Replacing the shut off and rebuilding the carb on a 2002 ATV is the norm I expect anyway but I know I do not trust either to be right after today.
 

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Discussion Starter #4
Thanks guys. Does the physical float fail often in the 325 carbs?

It was where you could get the RPM's up and it would smooth out but yesterday it finally started loading up so bad it would died and would not restart because it was flooded.

The project 2002 325 Magnum (bought knowing the guy blew an oil line and shut it off when he heard it knocking) seems to have a good carb so we will rob it since it will be at least a month or two before we pull its engine to see if the crank is shot.

The reason I think the carb on it is good the guy said it would start and idle fine out of gear but would start to knock and die when put into gear. The owner of the ATV shop that replaced the oil line and refilled with oil and a new filter confirmed all of this and will do any machining we need done plus talk the son (16) and I though the rebuild process.

The shop owner is well known (former racer) and I have known the seller and his dad for about 20 years. The guy really wanted me to hear it run so I said OK for a second. It started when he hit the starter and ran smoothly without knocking for about 3 seconds because I told him to shut it down. We will fix the engine but if we did not it shows little wear compared to our current 2002 325 so it would be a good parts source.

This there one source for the carb rebuild kit that is preferred over other options?

At least we know to check the oil each time we get it out to ride. :)
 

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Discussion Starter #5
The carb rebuild kit came yesterday and I inventoried the parts with the shop manual and I think it is the right one. The shop manual specs 120 size main jet and the kit has a 145 but I expect that will be fine.
 

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I would put the same size that was in it back, evev if you have to clean the old one it will be fine.Change needle and seat , clean pilot jet and main jet good, remove air screw and idle screw and clean with carb cleaner, after you get it back together, turn gas valve off when not in use and new needle and seat will last a long time.
 

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Discussion Starter #7
POLARIS MAGNUM 325 main pilot slow jets kit

While jetsrus.com and others say 145 main jet is typical size that it 10 steps up from the manual. I will have to see what is in it. On top end it was running OK but with the float shut off valve sticking open it was loading up so bad we could not keep it running.

The kit we got is labeled for our ATV and all parts seem to match the manual except the main jet shipped is 145 v 120 per manual. 330 carb calls for 122.5 per manual so it would seem 120 was not a misprint by Polaris for the 2002 325.

Carbs are not something that I yet grasp very well and conflicting info like on this kit does not help. Does the main jet have an adjustment or it is just a hole and you get what you get?
 

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Discussion Starter #9
So a 120 and 140 main carb jet amost equal size?

Carb Jet Size Cross Reference:Keihin/DynoJet/Mikuni - Honda ATV Forum

I think this chart in the first post may be the answer to my question.

The Keihin number for the same size Mikuni main jet seems to run about 20% higher than Mikuni's number for the same physical size jet?

Since Polaris manual calls for a 120 main jet size for our 325 then one would want a 137.5 if using the Keihin main jet it seems. So the 145 in the kit is only 3 sizes up NOT 10 sizes up.

I guess in that light the folks at jetsrus.com know what they are talking about. :)
 

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Discussion Starter #10
Jet sizing by Mikuni and Keihim info.

Mikuni = Measured in flow

Keihin = Measured in size (some formula)


1) Keihin - OEM main jets - Jets are measured using an unknown convention. Measurements are based on orifice diameter size.
2) Mikuni - Made for Mikuni Carburetors. Available in 2.5 increments. Mikuni uses yet another measurement convention - reportedly based on flow rate. The result is that Mikuni's sizes are vastly different from the other makers'.
The different manufacturers' jets will have a slightly different taper to the orifice, which can affect flow. This means that there will most likely be very slight differences between the same diameter jets from different makers.
 

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I don't know what kind of manual your looking at but Polaris microfiche for a 2002 Magnum lists a #142 main jet as stock so your #145 would be just fine.

11 3131303 Jet, Main [#142]
26 3131327 Jet, Pilot [#50]
46 3131133 Jet, Air [#175]

Maybe you're mistaking the throttle valve (aka butterfly) which is listed as a 120
34 3131126 Valve, Throttle [120]



Have you looked on the actual old jets? They are marked with the size.
The float valve o ring and/or valve itself (#24 and #25) is what's causing your engine to fill up with gas. Is the overflow vent line stopped up? It should be leaking fuel on the ground when you turn the fuel on and before filling the engine.
 

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Discussion Starter #12
Polman500 thanks for your high info reply.

We have not removed the carb yet. Jetsrus states the same numbers you state for the main jet size but Polaris 2002 Magnum shop manual page 1.4 states the main jet size is 120 for the BST 31 Mikuni carb.

I knew Jetsrus and Polaris should be passing out good info so there must be two different points of references as to sizes. I even downloaded the 2003-2006 325/500 PDF version someone posted in another thread the other day. It states 122 which would be logical since they suck in a bit more mixture.

The Shindy 03-423 carb kit came with a new float valve with a new o-ring so that should fix my most critical issue but will go through the carb while I have it out and install the full kit. I will set if the bowl overflow outlet. Yesterday the new gas tank shut off valve came since it was in the off position when gas flooded the crankcase.

Is disconnecting the two cables to the carb hard or require any non typical tools? I have not looked at how to do that yet but may this weekend.
 

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Here's a link to the Polaris microfiche for future reference.

Browse

For the throttle, just take the plastic cover off and roll the throttle shaft assembly (#38) around with your left thumb to get slack in the cable and then wiggle the cable guide (#39) and cable end free. There is a slot in the guide so that you turn the cable sideways a slip it out. ***Be very careful not to lose the little brass cable guide. They are hard to find when dropped and cost about $12 if you have to order one...don't ask how I know this.
The choke cable/plunger assembly (#43,44,45) will just unscrew and pull out with a 12 or 14mm wrench. I take the carb loose from the intake first before trying to get the cable off for better access.
 

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Discussion Starter #14
Thanks again. We got the carb off before dark just fine thanks to your info and warning about the brass piece.

A few years ago we picked up a 7x14 heavy enclosed trailer with roof AC and inside it wired with two 30 amp circuits that we use as our tool/mini shop since we do not have a real shop yet. It got 'congested' due to just piling stuff in on top of stuff so when we got home about 8pm we tackled that mess and filled up a couple trash cans. Things are semi organized and the work benches are clear. I just got the carb on the bench and cleaned in the throat a bit so hopefully I will it it open tomorrow evening.

A few weeks ago I was in the process of warming it up to adjust the carb when it just flooded out on me when riding. Somehow when we had it apart earlier it was setting outside and covered when not working on it and I guess with the air filter off.

This evening when we took off the carb there was a huge dirt dauber nest sucked again the slide. When riding I guess it came loose from the plastic tube from the breather box to the carb and cut the air flow so it would just load up and not run any longer.

I have read the manual several times to try to insure the rebuild of the carb goes well.

We really want to get this one running again then find time to get into the engine on the other 325 project Magnum with engine issues due to the owner blowing an oil line running down the road and when it started to knock he shut it off. It will start and idle but I only let him run it for like three seconds and it sounded good but he and the shop that fixed the oil line said it will knock then die if put into gear. Since it was ran every day of its life the carb on it may be fine since it was just used on a chicken farm and not off road.

These last days before winter has been busy because we are mounting gates onto the 10x20' horse shed and rerouting the fence that was put up fast before we had any shelter. The ATV would be handy with upkeep of the mini horses.
 

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Discussion Starter #15
Spent some time early this AM going over the parts diagram, looking at the kit and reading the shop manual on how to do a carb rebuild instead of getting into the cold shop and ripping out parts. :)

At first I was planning to remove and replace one part out of the kit at a time. Now I am thinking it would be best to hull it out to keep from moving trash to a new jet, etc. Is removing all old parts in the kit and cleaning well before starting to replace any parts best?

In removing the cover to disconnect the cable I saw it had no gasket so I expect someone has been into the carb before perhaps. Will note the size of the jets when I remove them.
 

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