Carb problem has me stumped?!?!

[SkiDaddy]

In the past couple weeks my SJ was running kinda rich off idle, & I noticed it was dribbling when revving down to idle. So I replaced the needles & seats, went out today & it ran great the first session. 25 minutes into the second session the richness off idle was back. It got progressively worse, at anything above idle, to the point where it would barely run at 2500 RPM or so even at WOT. Went to shore, spark looked weak in the bright noonday sun, so I changed plugs. Same problem, felt like it was still running on only one cylinder. Problem exists in & out of the water.

Got home, flushed, tried pulling the rear plug wire & grounding it w/an old plug. It started & idled on the front cylinder, but immediately ran super rich at anything above idle. Put the wire on just the rear cylinder, ran strong & crispy, it actually ran better on the just the rear cylinder than both.:bigeyes: . Switch plug wires, plugs, same thing. Definately a front carb (stock 38mm) issue.

I've pulled the carb apart, checked the fuel filter, needle & seat, sprayed carb cleaner through the jets, visually looked for a perforated diaphragm, or fuel valve disks. Saw nothing unusual. I also felt the reed petals, they're all intact & sealing well as best I can tell; plus, the front cylinder alone will start & idle just fine. Reassemble, exact same behavior. Front plug is quite wet w/fuel. Rear plug is fine.

At this point I'm stumped.:frown: Any ideas guys? Cracked carb body?

 

[SJ/XPBri]

Did you check the pop off after replacing the needle and seat? Possible that the needle pivot bent when replacing it, making the pop-off too low on that carb.
Bri

 

[SkiDaddy]

Possible, but it ran great for a 40 minute session, then started acting up 25 minutes into the second session. I don't think it would change from use.

I also visually checked the pivot arms, they looked identical - flush w/the carb body/kidney piece. It's not just a little rich - it's waaay rich.

 

[surfjetlouie]

Ok this may help. I have brand new 38 mm mikuni for $80 ship each
Louie

 

[SJ/XPBri]

Should have read a little bit more closely that it ran ok, for the first run, and pop off wouldn't affect the ski at the RPM you are having the problem with. Did you check the check valve that leads into the high speed jet chamber, also make sure the high speed jet didn't vibrate loose, and is still tight.
Bri

 

[SkiDaddy]

Jets are still screwed in, didn't check how tight. The check valve looked OK, no obvious tears or anything. I blew through it fine, & it held pressure from the other side when trying to blow through it.

 

[ketsair]

is the front plug firing strong?

 

[keefer]

Check the resistance between the plug caps. If you are running the stock wires with stock or non resistor caps the the reading should be about 4.7k ohms. With resistor caps you should read somewhere around 15k ohms. If you do not get a reading then you probably have a broken wire. Try wiggling the front plug cap while on the meter and see if you can get it to read. I have had to trim wires back to get them to read good. Worst case if the wire is broken too far back you can have new wires installed on a stock coil. Good luck.:banghead: :banghead:

 

[SkiDaddy]

I thought it might be the plug wires, but running both cylinders off the front wire (one at a time) has the back cylinder strong & crispy, front cylinder misfiring. I'll still check it though.

 

[SkiDaddy]

Plug wire resistance is 4.3K Ohms, and doesn't waver if I wiggle the wires all around. So maybe the wires are OK?

The problem is getting worse; now it runs itermittently on either or both cylinders. I blew back thru the fuel filter & it seems fine. Tried removing the fuel tank vent, disconnecting the kill switch wires, no change,

Spark is now itermittent, so I'm calling it an electrical problem. I switched out the MSD w/the stock CDI; no difference.

John at JSS told me to check the AC voltage at the brown/white wire coming from the ignition cover into the electrical box; it should be around 37 volts or so when cranking w/plugs in. Mine's 21 w/plugs out. So off go the stator, coil, MSD, stock CDI, & little black box in the electrical box (start/stop wires go to it?) to JSS to get fixed.:banghead: :banghead: :banghead: :banghead:

Thanks for the replies guys. BTW, does anyone have an electrical box wiring diagram to help me get this all back together? :biggrin: