Carb needle and seat issue

[Scootertrash]

I'm posting here for best traffic and also this could be encountered with any carbed vehicle. If mods feel the need to move it that's cool:cool:

Machine is an '04 Arctic Cat 400 4X4

Carb was all gunked up with old gelled fuel, etc, etc.

Ran the carb thru the ultrasonic, checked every jet and orifice out. Used a q-tip to clean the seat for the needle. It's clean.

Float is set according to Factory Service Manual- Just touching the tip of the spring loaded plunger on the needle. Yes, I'm quite certain it's properly set, I've verified it multiple times, trust me.

I cannot for the life of me get this needle to seal up. I have never had this issue before and I've been wrenching a long time.

I can attach a hose to the carb, turn the carb upside down and blow thru the hose and the needle will seal. Unfortunately that's not the position the carb operates in.

I set up a bowl of water and I sink the carb into the water until the needle seats and I also check the float height at the point the needle first seats. Gently blow thru the hose and I get air bubbles.

Sink the carb deeper into the water to the bottom of the carb throat, my attempt at trying to induce as much pressure on the spring loaded plunger as possible to seal the needle. Still get air bubbles.

I'm thinking that the crappy fuel sitting in the carb for an extended time damaged the seat by corrosion. The machine has sat for an extended period, over a year. Very hard to get a good close look at the seat area, even using a magnifer headband.

Have any of you guys tried "dressing up" the seat of a carb needle? Used to have a neighbor who would "touch up" the seat lightly with a sharp drill bit.

Seems like it might solve the problem, but I've never tried it.

A new carb is $400. No, I will not try one of the cheap Chinesium carbs off of ebay. Used carbs on the 'bay run 125 and up.

I would like to salvage this carb for the owner. Give me some ideas over and above basic carb cleaning..........:wondering


ETA-Rubber tipped needle

[Shep1970]

I’ve read on here and other places you can put valve grinding/lapping compound on a q-tip and spin away on the seat, couldn’t hurt to try.

Shep

[Scootertrash]

I’ve read on here and other places you can put valve grinding/lapping compound on a q-tip and spin away on the seat, couldn’t hurt to try.

Shep

Thanks for the tip ;):lol:

Yup, I've done that lightly but it hasn't helped yet. I don't want to get too aggressive. I figure very light dressing can be offset by minor adjustment on the float. I have one of those bore scopes, gonna try today and see if it fits and I can get a better look at the seat.

[El Camexican]

Drill bit = NO!

Lapping compound might work, but it would need to be very fine.

I’ve cut high quality Q-Tips in half an put them in a variable speed drill before dunking them in metal polish and spinning them in the seat. You’ll likely go thru a few tips before you brake the surface of the seat and start smoothening it out.

Is your needle steel or rubber tipped? If steel, maybe you can find an equivalent rubber unit that might be a little more forgiving of a pitted surface?

Also make sure that the needle is loose enough in the bore that it can self-center.

Curious to see if you can fix this, I’ve given up on a couple, but the sets were replaceable, so it wasn’t a big deal.

[Scootertrash]

Rubber tipped needle, that's what makes it so frustrating. Needle has plenty of play in it's bore. Float and needle assembly moves freely.

I've ordered a second needle to try, that should get here today.


So here's a question: Does the seat have a squared edge where the needle sits ? is it chamfered to match the angle of the needle? Is it slightly rounded? Like just enough to eliminate any sharpness that may damage the needle?:confused::wondering

[El Camexican]

If it’s rubber tipped and NOT new I’m banking on that being the problem. I suspect they dry out and get hard, or distort.

I’ve had what looked like perfectly good rubber needles that wouldn’t seat.

I’d still clean the seat with a Qtip, but don’t use anything aggressive on it. Toothpaste works if you don’t have brass polish.

[Scootertrash]

Needle is new, figgered trying another won't hurt. I have some gun bore paste that's very fine, probably try the toothpaste first if the new needle gets here today and that doesn't do it

[plastikosmd]

I’m not sure I can help but would love to see pics of the hose/water/bowl test at some point!

[Scootertrash]

I'll set it back up and take some pics in the next couple days:beer;)