This a very common thing on the 425's. I have had to repair these many more times than I could possibly remember.

The slide needle and nozzle wears out very quickly on these. If you ride a lot these have to be replaced about once a year.

If not they will start to run so rich they foul plugs and roll black smoke.

 

Hey fellas i replaced the needle valve on my 425 its a push in valve that the float actually hooks on to. Mine had gotten bad enough that if i left the fuel valve turned on gas would leak out through the carb and empty my tank if left long enough. Thats what i was told to replace by local dealer and by (flthw)(sp) one of the pollsters on here.
GH

 

Hey kerbbirds are you sure about it being the same as carb on 500's not doubting u just asking cause i tried with several places online and local noone offered a carb kit and said the 425 carb was hard to come by. But all said they could get any parts i needed just no kit. i know that as far as ebay the 500's carb is pretty common but have only seen one 425 carb sold there and it brought like 252.00$$ and thats to steep for me.
GH

 

His problem is not with the float needle and seat. It is with the slide needle and nozzle.

Still it would be a good idea to replace the float needle and seat while he was at it. They go bad also.

 

Hey cornbread maybe thats what i need to to replace too. now when u say the slide needle and nozzle are u talking about the diaphram needle and what nozzle? the float needle did fix part of my problem just not all of it.
1577092-001 $3.64
2: E-RING(10) 1577093-001 $1.56
3: JET NEEDLE(5F81-3)
(5F81-3) 1577111-001 $14.55
4: RING 1577292-001 $3.64
5: DIAPHRAGM ASM. 1577091-001 $72.79
6: NEEDLE JET (P-8) 1577092-001 $3.64
2: E-RING(10) 1577093-001 $1.56
3: JET NEEDLE(5F81-3)
(5F81-3) 1577111-001 $14.55
4: RING 1577292-001 $3.64
5: DIAPHRAGM ASM. 1577091-001 $72.79
6: NEEDLE JET (P-8)
(P-8) 1577094-001 $22.87
7: JETBLOCK ASM. 1577089-001 $31.19
8: WASHER (10) 1576847-001 $0.76
9: MAIN JET,#140
(#140) 1577110-001 $3.11
10: SEAL 1577099-001 $3.11
12: E-RING 1577101-001 $1.04
13: CAP 1577102-001 $4.15
14: PIN, FLOAT 1576992-001 $4.82
15: FILTER 1577116-001 $4.68
16: O-RING 1577115-001 $3.64
17: VALVE-NEEDLE,1.5(PUSH IN) 1577746-001 $23.91
18: PLATE 1577167-001 $9.35
19: SCREW(10) 1577166-001 $0.52
20: O-RING 1577114-001 $11.43
21: SCREW 1577103-001 $0.78
22: FLOATBODY ASM. 1577165-001 $62.39
23: SCREW 1577104-001 $6.23
24: FLOAT ASM. 1577112-001 $62.39
25: ADJUSTER 1577107-001 $7.27
26: SPRING 1577108-001 $1.56
27: WASHER(10) 1577106-001 $1.30
28: O-RING 1577105-001 $3.90
29: JET,PILOT,#40
(#40) 1577192-001 $7.27
30: SCREW, ADJ. 1577128-001 $3.90
31: RING 1577127-001 $7.27
32: SPRING 1577126-001 $3.90
33: VALVE,THROTTLE,100
(#100) 1577087-001 $23.91
34: SPRING 1577164-001 $7.27
35: RING 1577098-001 $2.34
36: SCREW 1577086-001 $0.78
37: SHAFT ASM,THROTTLE 1577097-001 $57.19
38: GUIDE,CABLE 1577125-001 $10.39
39: SCREW 1577117-001 $2.34
40: COVER 1577095-001 $14.55
41: O-RING 1577096-001 $11.43
42: HOLDER,GUIDE 1576952-001 $10.14
43: SPRING 1577120-001 $1.56
44: PLUNGER ASM. 1577121-001 $14.55
45: JET,AIR,PILOT,#160
(#160) 1577193-001 $6.23
46: CARBURETOR
(INCL. 1-37- 42-51) 1577272-001 $395.19
47: ASM.,SCREW & WASHER(10) 1574405-001 $0.78
48: WASHER,SPRING 1577122-001 $1.30
49: SCREW 1577123-001 $4.94
50: SPRING 1577090-001 $7.27
51: ASM.,COVER 1577088-001 $36.39
52: SCREW

(P-8) 1577094-001 $22.87
7: JETBLOCK ASM. 1577089-001 $31.19
8: WASHER (10) 1576847-001 $0.76
9: MAIN JET,#140
(#140) 1577110-001 $3.11
10: SEAL 1577099-001 $3.11
12: E-RING 1577101-001 $1.04
13: CAP 1577102-001 $4.15
14: PIN, FLOAT 1576992-001 $4.82
15: FILTER 1577116-001 $4.68
16: O-RING 1577115-001 $3.64
17: VALVE-NEEDLE,1.5(PUSH IN) 1577746-001 $23.91
18: PLATE 1577167-001 $9.35
19: SCREW(10) 1577166-001 $0.52
20: O-RING 1577114-001 $11.43
21: SCREW 1577103-001 $0.78
22: FLOATBODY ASM. 1577165-001 $62.39
23: SCREW 1577104-001 $6.23
24: FLOAT ASM. 1577112-001 $62.39
25: ADJUSTER 1577107-001 $7.27
26: SPRING 1577108-001 $1.56
27: WASHER(10) 1577106-001 $1.30
28: O-RING 1577105-001 $3.90
29: JET,PILOT,#40
(#40) 1577192-001 $7.27
30: SCREW, ADJ. 1577128-001 $3.90
31: RING 1577127-001 $7.27
32: SPRING 1577126-001 $3.90
33: VALVE,THROTTLE,100
(#100) 1577087-001 $23.91
34: SPRING 1577164-001 $7.27
35: RING 1577098-001 $2.34
36: SCREW 1577086-001 $0.78
37: SHAFT ASM,THROTTLE 1577097-001 $57.19
38: GUIDE,CABLE 1577125-001 $10.39
39: SCREW 1577117-001 $2.34
40: COVER 1577095-001 $14.55
41: O-RING 1577096-001 $11.43
42: HOLDER,GUIDE 1576952-001 $10.14
43: SPRING 1577120-001 $1.56
44: PLUNGER ASM. 1577121-001 $14.55
45: JET,AIR,PILOT,#160
(#160) 1577193-001 $6.23
46: CARBURETOR
(INCL. 1-37- 42-51) 1577272-001 $395.19
47: ASM.,SCREW & WASHER(10) 1574405-001 $0.78
48: WASHER,SPRING 1577122-001 $1.30
49: SCREW 1577123-001 $4.94
50: SPRING 1577090-001 $7.27
51: ASM.,COVER 1577088-001 $36.39
52: SCREW 1577092-001 $3.64
2: E-RING(10) 1577093-001 $1.56
3: JET NEEDLE(5F81-3)
(5F81-3) 1577111-001 $14.55
4: RING 1577292-001 $3.64
5: DIAPHRAGM ASM. 1577091-001 $72.79
6: NEEDLE JET (P-8)
(P-8) 1577094-001 $22.87
7: JETBLOCK ASM. 1577089-001 $31.19
8: WASHER (10) 1576847-001 $0.76
9: MAIN JET,#140
(#140) 1577110-001 $3.11
10: SEAL 1577099-001 $3.11
12: E-RING 1577101-001 $1.04
13: CAP 1577102-001 $4.15
14: PIN, FLOAT 1576992-001 $4.82
15: FILTER 1577116-001 $4.68
16: O-RING 1577115-001 $3.64
17: VALVE-NEEDLE,1.5(PUSH IN) 1577746-001 $23.91
18: PLATE 1577167-001 $9.35
19: SCREW(10) 1577166-001 $0.52
20: O-RING 1577114-001 $11.43
21: SCREW 1577103-001 $0.78
22: FLOATBODY ASM. 1577165-001 $62.39
23: SCREW 1577104-001 $6.23
24: FLOAT ASM. 1577112-001 $62.39
25: ADJUSTER 1577107-001 $7.27
26: SPRING 1577108-001 $1.56
27: WASHER(10) 1577106-001 $1.30
28: O-RING 1577105-001 $3.90
29: JET,PILOT,#40
(#40) 1577192-001 $7.27
30: SCREW, ADJ. 1577128-001 $3.90
31: RING 1577127-001 $7.27
32: SPRING 1577126-001 $3.90
33: VALVE,THROTTLE,100
(#100) 1577087-001 $23.91
34: SPRING 1577164-001 $7.27
35: RING 1577098-001 $2.34
36: SCREW 1577086-001 $0.78
37: SHAFT ASM,THROTTLE 1577097-001 $57.19
38: GUIDE,CABLE 1577125-001 $10.39
39: SCREW 1577117-001 $2.34
40: COVER 1577095-001 $14.55
41: O-RING 1577096-001 $11.43
42: HOLDER,GUIDE 1576952-001 $10.14
43: SPRING 1577120-001 $1.56
44: PLUNGER ASM. 1577121-001 $14.55
45: JET,AIR,PILOT,#160
(#160) 1577193-001 $6.23
46: CARBURETOR
(INCL. 1-37- 42-51) 1577272-001 $395.19
47: ASM.,SCREW & WASHER(10) 1574405-001 $0.78
48: WASHER,SPRING 1577122-001 $1.30
49: SCREW 1577123-001 $4.94
50: SPRING 1577090-001 $7.27
51: ASM.,COVER 1577088-001 $36.39
52: SCREW

 

From partsland.com you need the following parts:

http://www.partsland.com/index.cgi?N...4X4-CARBURETOR

#1
3130507
1
RING 3.82
3.82

#2
3130508
1
E-RING(10) 1.64
1.64

#3
3130528
1
JET NEEDLE(5F81-3) 15.28
15.28

#4
3130752
1
RING 3.82
3.82


#6
3130510
1
NEEDLE JET (P-8) 24.01
24.01

And this to keep from having this problem again,

http://www.partsland.com/index.cgi?N...NGINE-MOUNTING

#14
5240609-067
1
BRKT, CARB.MT. 7.10
7.10

The two links will have diagrams with the parts shown.

Be careful as some things may be locktited on the carb, if you havent replaced the float needle this would be the time to to that as well.

Good luck, your dealer should also have these parts as it was a VERY common problem with the 1995 425 Magnum

 

Not saying its not a carb issue, but cams were bad to wear down the exhaust lobe and make it run rough. Also, If the prefilter is not over the snorkal they may not run correctly. You say the plug is black so its most likely not that. If you are running out of options and you most likely have the gas tank sitting off to the side anway, Pull the valve cover off and make sure the cam lobes arn't wore down. The center lobe would be the suspect. Watch the rocker arms and make sure the exhaust arms are moving just as far as the intake arms. You can see the cam in there too but it's kinda hard to get a great look at. I'll take my finger and hold against the exhaust lobe and slowly pull crank it. Just a thought. Hope it's simple though.

 

Right out of the service manual, 1997 425 had a mikuni BST 34 ID# 42plo1b carb. main jet 140, pilot jet 40, pilot air jet160, jet needle P-8 Throttle4 valve #100 pilot screw 2.5 turns out. 1997 sportsman, explorer had a muikuni BST34 ID#42pl01b carb Main jet 142.5, Pilot jet 42.5, Pilot air jet 160, jet needle 5D78-3, Needle jet P-1, Throttle valve #100, Pilot screw 2.0 turns out.