Offshoreonly.com - Carb adjustments……… At wit’s end..

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I have not heard many good things about Nickerson. Most of the carbs I have seen from him run very rich. I guess that could be considered safe but..... If you have a friend with a carb that is close I would give it a try.

Are you sure those cam numbers are correct? Most big block cams have more exhaust duration than intake. Is it possibly 234 int, 242 ex. If so, you are getting close to reversion. Depending on your exact set up, it could happen. 7.5 lbs of fuel pressure is a little bit high for that carb. You might be pushing the needle off the seat and allowing excess fuel at idle. No need to use more than 6 lbs. Good luck.

I always had a weird feeling about this carb from day one..Way before I ever heard of Nickerson or had anyone else touch it. Stright from the box it never idled correctly. Back in 06 I did borrow another carb and it worked much better.. I will see if I can get my hands on one again..

Patri: The cam numbers are correct.. Looking at the cam sheet right now.. What is a tell-tail sign of reversion @ idle? I can lower the FP tonight and see what happends.. I have had it @7lbs for a while.. I still wonder if going lower on a PV might help though

Idle the engine for a while then shut it down and shine a mag light up into the tailpipe. See how far up into the pipe you see moisture. If you see moisture anything more than half way up the tail and anywhere near the "bend" of the header I'd be concerned.

I usually run 5-7 lbs WOT and 3-4 lbs at idle with mechanical pumps. Electric I run 5-6 lbs up and down.

Time to lower the fuel pressure and perhaps the floats..
Just spoke to the cam manufacturer and Barry Grant tech support.. General thought is something is wrong in the idle circuit and it is getting WAY too much fuel.. Bottom line.. Time to find a 4150 carb to borrow to test..

Tommy.. Thanks for the chat.. very insightful.. you did make me think of one thing.. The fuel pressure regulator and gauge are located down line from the carb.. right next to the fuel pump which is mounted next to the gas in intake from the tank.. must be a good 2/3 feet away from the carb.. is this an issue? will I get in-accurate readings?

Spoke to dean at nickerson.. Told me the Power Valve would not be the cause of this.. Since even of the motor vacuum IS low and the PV IS open, it will only open the NON idle circuit therefore not effecting idle at all.. He said the only way the PV effects idlea is when you are OFF idle circuit OR it is blown.. perhaps the carb is perfect and something inside the motor is off? Have to find someone who wants a Nickerson 980 carb.. haha

Quote:

Originally Posted by Panther (Post 2961788)

Little Tommy, my friend has a similar problem with a Deamon a few years ago. In the end he took the carb to a local Race and Barry happened to be at the booth and tore down the carb. Turns out one of the bowls was improperly machined and was causing the carb to leak down, no matter where you set the bowl height.

Getting back to the carb. There's no doubt an 02 sensor is the easiest way to check the idle to see what's happening. There's also your eyes, ears, nose and other senses that can work pretty well! ;)

Take the flame arrestor off and look down into the venturies at idle and see if you see fuel dripping from any of the boosters. then put the engine in gear and check again to see if you see fuel dripping from the boosters. this would be one of the first things I'd check for.

All these years I've never actually used an 02 sensor to set my idle mixtures and most of the time don't even need a vacuum gauge. Just ask anyone who's been on my boats how they idle. :)

yep that pretty much covers it. John why don't you try to find a hp950 holley and put it on and try it.

also i thank holley now makes a 4150 carb that is a 1000 cfm carb

This power valve gasket caused me problems for two months, rough rich idle! I found the bowl empty and found this was not sealing.

How are you adjusting your carb?

I have not read where anyone was telling you how to adjust your carb. I was having simular problems until I adjusted the carb in the water in gear with the bow on the beach not letting the boat move foward. You can do the same thing by leaving it on the trailer in the water in gear. Try adjusting your carb at idle this way and see what happens. Some times we over look the obvious.