Fouling plugs within hours

[cmsoard]

Just finished refreshing a 95xp a few weeks ago, carb rebuild, new fuel lines, oil lines, all the basic stuff... Primed the oil injection system, but still premixed for the first tank to be safe even considering I may sacrifice a set of plugs.

First time out two weeks ago she ran like a champ for 3 hours or so. Checked my oil levels and could see it was consuming so refueled with just gas. Then back out on Saturday ran great for like 5-6 hours. Once warmed up I did notice it would sometimes have to crank for a few seconds before turning over, but would and then run great, figured maybe running a little rich. Then needed to refuel so zipped over to marina and she took about a full 9 gal fill up. Fired it back up and idled back out, went to get into it and bogging and barely running so limped it back to ramp and took home. Out of water it did start up and rev for me some. I pulled the plugs and they were black and carbon covered. Put in new plugs and she fired right up well. Then we went back to the lake Sunday. She ran good for maybe 3 hrs, doing the same slow start up thing, so I thought maybe running rich a bit. And then one time I couldn’t get it going just a boggy idle that wouldn’t go anywhere. Pulled plugs and they are black and gas wet, but not carbon covered again.

Coincidence that this happened immediately after refuel, or could this tank of gas be somehow to blame? Just running rich in general and I need to make an adjustment to stop fouling plugs?

 

[mikidymac]

When were your carbs rebuilt last?

 

[cmsoard]

Less than a month ago, did it on July 4th. Mikuni rebuilt kits, used the rebuild thread here as a guide, and did pop off test to check that was in spec. Put high and low idle screws back exactly as they were as described by process in thread.

 

[mikidymac]

Did you replace the needle and seat as well as pressure testing them when finally assembled?

 

[cmsoard]

Did not replace as new ones didn’t come in kits, but yes did pressure test both carbs and they both were in spec.

 

[mikidymac]

I would start by replacing the needle and seats.

 

[cmsoard]

Why do you think this? If I was only able to achieve low pop off pressure this would make sense to me as that would lead to rich conditions (which granted I’m having). However, I pressure tested within spec just weeks ago.

 

[mikidymac]

THe hard starting and running rich makes me think your needle and seats might be leaking. The pressure test is different than the pop off. FOr the pressure test you get the diaphragm and cover and cover on like the carb is ready to install then block the return line and put 10 psi into the inlet and it should hold it indefinitely to make sure the needle and seat aren't leaking.

 

[cmsoard]

Okay yes, now I follow, and yes I did pressure test also when following through the carb rebuild procedure. I let them sit for maybe 5 minutes and pressure held.

 

[cmsoard]

Could this be something as simple as adjusting my low speed idle screws in some? Correct me if I’m wrong, but that would lean the mixture I think.

 

[mikidymac]

Yes but that only leans out the idle and if you have to mess with the factory settings there is a good chance something else is wrong.

 

[cmsoard]

Well, I didn’t put it to factory settings, I followed the procedure to turn in until they stopped while counting the turns, then recorded and pulled out. In my reading now I’m seeing they need to be identical on both carbs. I don’t still have the paper I wrote my numbers down on, but I do remember they were slightly different which I thought was odd. Maybe I need to turn both to factory settings and start from there. Looks like that should be 1.5 turns? I know they aren’t far from there, but I’m sure I need them equivalent.

 

[mikidymac]

Yes, try that first.