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Discussion Starter #1 (Edited)
The 2001 325 Magnum we got last summer would load up and not idle or idle very very rich.

We rebuilt the carb and the same story. We put the carb of the 2002 325 with the spun bearing that would still idle well and that carb would load up. We did the in the crankcase hand dressing of the crankshaft (knocking again but running well) in the project 2002 325 Magnum. We put rebuilt carb from the 2001 on the 2002 and it idled and ran fine.

Shut the gas off on the 2001 and it went to idling well. By passed the fuel pump and it idles well with good power when hitting the throttle.

We just shut down for the evening and wanted to get some feed back because I really do not get this one.

We can swap out the fuel pump with the other 325 but really do not see how a 1-3 PSI fuel pump is causing the 325 engine to load up with gas.

Any experiences similar to this issue?

We had be trying to set the fuel/air mix but that was not the issue it seems now because the carb that was loading up ran fine on the 2002
 

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Discussion Starter #2
Short version:

Carb loads up really bad unless we by-pass the fuel pump and go gravity feed only then it idles, has good power and throttle response.

2001 325 Magnum machine.
 

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Carb loading

Thanks for the post. My 2001 magnum 325 does the same thing. Only mine seems to occur only after riding for some time. I simply turn off the engine when we stop riding. Then restart when we get going. Probably would work if I just shut off the gas while idling.

I think you have it isolated to the fuel pump. My next step is to go to gravity feed and see how it runs. My theory is it really doesn't need a pump. I have 2 yamahas, 2 Hondas and a Suzuki dual sport MC, and they are all gravity fed. Polaris makes snowmobiles which do need a pump because the fuel tank is under the seat in back of the engine and carbs. Also snowmobiles consume tremendous amounts of fuel compared to a quad. I think Polaris just brought there snowmobile experience to making quads. The pump looks like a snowmobile pump. What regulates the 1-3 psi?

These fuel pumps work off vacillating crankcase pressure, which I understand on a two stroke since the crankcase is part of the fuel intake system. I suppose it works the same in a four stroke.

You saved me a lot of time. Now I don't have to consider rebuilding the carb. Maybe the float system in a Mikuni carb can't handle the 3 psi. I bet it is designed for a gravity feed system.

I'll let you know how it works out.
 

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Discussion Starter #4
Poko2 I think you are correct about gravity feed working but we have not been out riding on it yet. Going back into Deep Freeze weather starting in a few hours.

I have researched this a lot the last few days and some have been fine with just gravity feed. What gets me is how can the fuel pump make it run rich?

After the carb that worked fine on the 2002 but would start loading up when put on the 2001 made me think it much needed rebuilding so I tore into the carb but never opened the kit.

If the bowl gasket and diaphragm are not leaking I see no reason for jet replacement. Now if the float shut off valve is failing it must be replaced.

Since you are in a warm place let us know how riding without fuel pump works for you.

If the fuel pump failed I can see it not running but still clueless is how the fuel pump can cause the carb to start loading up. It has to be causing the carb to suck in more gas but HOW I can not figure out?
 

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I had the needle and seat go bad on my 400 a few years back. It would flood out at idle sometimes but not all the time.
 

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Discussion Starter #6
That happened on the 2001 and lead to stuck rings when a gallon of Sea Foam treated gas traveled to the cylinder and crankcase washing the piston top carbon down into the ring groves. We did not run it with gas in the oil but the heat after we started it baked the carbon that had flowed into the ring groves.

Before we installed it on the good idling 2002 we checked the float level after we had put it back together per the Polaris shop manual. We attached a new clear carb overflow hose with the drain screw open enough to pass gas out the drain and let the carb fill and the float shut off valve stopped it at just about the bowl gasket line per specs.
 

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I have researched this a lot the last few days and some have been fine with just gravity feed. What gets me is how can the fuel pump make it run rich?

If the fuel pump failed I can see it not running but still clueless is how the fuel pump can cause the carb to start loading up. It has to be causing the carb to suck in more gas but HOW I can not figure out?
In order for the fuel pump to be the problem it would have to be producing a fuel pressure strong enough to overcome the float valve system. I don't believe this carb has an overflow so the excess fuel is forced up into the Venturi and into the engine.

I believe that is possible with this type of pump. As an engine gets older there is more compression "blow by" which will create more pressure in the crankcase. Especially at lower rpm. This higher pressure could translate to higher pump pressure. Just my theory. If you want to feel the crankcase pressure remove the airbox, start the engine and feel the air coming out of the tube which was connected to the front left of the airbox. It pulses slower and stronger at idle. This is the crankcase pressure that runs the pump.

I wish I had a good fuel gauge to attach to the output of the pump, but I don't. I'm going to do some testing tomorrow and see what happens.
 

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Discussion Starter #8
I agree it is not the fuel pump PSI dumping all of the gas into the engine. The carbs do have an overflow it the bowl over fills but that pin hole would not deal with more than a slow leak at the shut off valve from gravity feed.

One time when I pulled the carb switching out to the known good carb based on its performance on the other Magnum the intake side was completely filled with raw gas just from trying to start it.

Something is causing the gas to suck in at a fast rate from the gas tank.

The fuel pump is related because when by-passed the idle and and heavy throttle becomes perfect.

As noted before we checked the flow level after the carb was back together and the shut off was working perfect under gravity feed. The gas tank was setting on a table. We have not done a dynamic float level with the ATV and do not plan to. I do not want any more raw gas dumping in on the new set of rings.

There is an answer as to the roll a 1-3 PSI fuel pump is playing in causing the excessive gas flow into the intake valve. Finding it however has escaped me.
 

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One other possibility is a leaking diaphragm in the pump. This would allow fuel to be sucked into the crankcase and when the engine is hot it would be vaporized and flow into the airbox thru the breather tube. Now you would have fuel rich air coming in mixing with more fuel giving a very rich mixture. It would be easy to check this. Disconnect the crankcase breather tube at the air box front left and vent it to the atmosphere and see if this makes a difference.

I actually had this problem with my motorcycle. I left the fuel on while it set for several months and a slow leak around the needle seat allowed fuel to leak into the cylinder and eventually into the crankcase. As soon as it warmed up it would sputter and die and would not start. When it cooled down it would start find. Took awhile to figure out, but an oil change fixed the problem. Now I make double sure I turn off the fuel when done riding. Actually the MC is supposed to have a vacuum operated fuel switch. It will only come on when the engine is running. It has no off position. I have one ready to install.
 

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So much for that theory. The pulse to run the pump comes from the carburetor not the crankcase. Disconnecting the crankcase breather won't test the pump. I tested the diaphragm as outlined in the book and mine is not leaking. Holds a vacuum fine.

I have disconnected the fuel pump and will try running on gravity feed only for awhile.

Also the fuel pump has a regulator to keep the pressure down to 1-3 psi. It's basically a spring on the inlet. I'm going to take the pump apart and check it out and clean it.
 

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Discussion Starter #11
The other day we cut off the fuel (on Magnum that does not load up) and it idled for four minutes before dying so there is a lot of gas in the bowl at all times it seems.
 

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It just seems your problem is the fuel pump. If your diaphragm had a small leak it would dump fuel directly into the intake manifold and flood instantly. My fuel pump checks out fine, but my problem doesn't occur until a couple hours riding. I'm beginning to think I have a marginal float needle and seat seal. I have bypassed the fuel pump and on gravity feed it runs and idles great. In the next couple days I will take it out for a days ride. If it runs ok I will just leave it that way.

Check your pump by applying a vacuum on the "p" pulse inlet. It should hold indefinitely.
 

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Found my problem

My fuel pump checks out fine. Still flooded even with gravity feed. In checking my carb I found out my pilot screw was 4.5 turns out! It's supposed to be 2 turns +/-. I don't remember what I had set it to but it wasn't 4.5. It must have vibrated out over time?

I plan on retuning then dabbing some silicon adhesive on the screw end to hold it. I hope this is the end to it. I am going to reconnect my fuel pump also.

I don't think this is your problem as your carb worked fine on another machine. You might check it though.
 

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Discussion Starter #14
Not the same but similar happened with us on Sat.

The air time was up a bit so I ran the one that has the OK engine some without the fuel pump at about 1200 RPM and after about 30 minutes it started loading up.

Pulled the lid off of the air box and there was some milky oil splatter coming from the hose from the top of the engine to the air box. A guy came by so I just went out and talked with him and have not messed with it and with 6F air temps forecast for later this week it can wait to warmer weather.

My guess at this point with the very cold weather and idling the moisture in the oil increased and the oil is blocking the air flow into the box from the head so it starts running richer.

Will check it out in time and will try to order some of the $5 fuel pump rebuild kits. I had to pressurize the tank to get it started the other day.
 
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