1988 BFN - PCM 454 tune up

No reason to replace floats unless they're broken and nonfunctional. Notice the flat on the top, that's what you're looking at to hang parallel with the top of the bowl when upside down.

Any chance 8.5 is too high a number for the power valve? I know it was mentioned that it should be ok, but you went up a couple points during the rebuild, right?

Rebuilt Carb after spending 8 hours working on it :)

cphase wrote: Tom have you checked for any vacuum leaks?

Ahh, good point.

Spay a little bit of carb cleaner around the base, and if you get a change in RPMS, you most likely have a vacuum leak.

Vacuum leak would be my best guess- that would explain the rough idle as well as the lower vacuum reading. Did you replace the gaskets under the carb and spacer? Sometimes the cheap paper ones dont hold a great seal.

Once thats solved, then report back if your idle screws become responsive... if not, then make sure your idle speed adjustment isnt adjusted so high that the butterflies are remaining open a little bit.

Well thats not good... that would explain why the idle mixture screws arent working. Sounds like you may have a needle/seat problem.

That would explain the black smoke. I've seen a lot of carbs leaking fuel from the front boosters causing run problems. A lot of times you can diagnose that without even taking the flame arrestor off by listening to the carb and hearing the drips be sucked by the butterflies every few seconds.

At idle it should have a smooth suction sound with no breaks in the sound if you get what I mean.

I have another carb off a boat that ran properly other than leaking fuel from the boosters. I am going to go through that one and see if the idle circuits work better than the one on my carb. Could be something plugged up in the body too. I paid a shop to rebuild it back when I was younger and not confident if I kenw what I was doing inside of a carb.

Did you lower or raise the float?

There have been reports of bad Holley needle/seat combos right out of the box- both in rebuild kits and brand new carbs. You may have gotten one of them. If your old one didnt drip, you have the option to throw it back in there and see if it corrects the issue. I'd be on the horn with whoever sold the rebuild kit if it does!

I had to swap out an old needle and seat on an 86 we had in the shop with a new one because it was just flooding fuel out of the boosters when the engine would run.

I have also found many times rebuilding snowmobile carbs that the new needle and seats were faulty. I got to the point of if they weren't leakin from the bowl vents I would re use the old needle and seats because I was tired of taking fresh carbs apart again and cleaning fuel out of the belly pans.

Yep, thats how I'd proceed.

Easier to just change float level I would think, running a wedge or not?

phatsat67 wrote: Usually if you flip the bowl upside down with no float on it and you can't physically blow through the needle and seat it's ok but if you can blow through it at all with just pressure from your mouth than it't for sure bad.

Man I am glad to know I am not the only one to do that.

TRBenj wrote: There have been reports of bad Holley needle/seat combos right out of the box- both in rebuild kits and brand new carbs. You may have gotten one of them. If your old one didnt drip, you have the option to throw it back in there and see if it corrects the issue. I'd be on the horn with whoever sold the rebuild kit if it does!

Chalk me up for one who had a bad one right from the rebuild kit. I took it apart and recleaned it but it still dripped out the primary. I ended up doing just what Tim said, and put the old needle/seat back into the carb and the issue went away.

Installed the old needle and seat and boat runs like a new one. Unbeliveable.......Thanks to everyone for providng support.