Carb adjustments……… At wit’s end..
 

Background: 540 ci NA motor.. aprox 9.1 comp. Roller motor..Timing locked out @ 34. Digital 6plus MSD box, MSD crank trigger and billet distributor. Rotor is phased in properly..Plugs as advised by both Nickerson AND NGK..(forgot the exact ## off the top of my head).

Cam: 114 Lobe Separation
Intake: 234 duration 572 peak valve lift @.050
Exhaust: 232 Duration 572 peak valve lift #.050

HVH Super Sucker spacer.

Carb: 850 marine demon from Barry grant sent to Nickerson Perf in 2006.. Modified to 980cfm(plus whatever else they do) Carb has been sent back each year since owned for refresh. Great people Brad and Dean.. and great work by the way.

Motor runs great, good acceleration great midrange and top speed is adequate (I would suspect a bigger dominator style carb would be even better top end)

Problem: Idle.. I cannot get this thing to idle correctly to save my live. Out of gear 950 (so so) RPMS.. 4 corner screws 1 to 1 ½ turns out..(all even).. Put in gear drops to 650 ( not bad I guess). Issue is idle starts to drop after 10/20 seconds. Down to 600.. then 550.. always a rough idle in gear.. never quite “right”.. put it back in neutral after a few seconds of idle RPM’s are around 800.. they start to climb.. 850.. then 900.. then 950.. sometimes closer to 1000.. back in gear same thing.. No matter what I adjust.. front butterflies.. rear butterflies.. Idle mixture screws.. nothing help.. closest I can get is if I idle the rear to the point they are off the idle circuit.. then just touch the front butterflies a tad.. but even then.. not the best.. Does this sound normal to anyone? Any ideas at all?? Would I just be better served to run a dominator style carb on this motor?

Any advice would be greatly appreciated..

Have you talked to Nickerson about this problem???????
You do not have anything radical that should keep it from idling nicely.
So is it loading up/rich at idle???? You may need to drill a couple holes in the rear butterflies, but I wouldn't do that until you talk to Nickerson.

Have you taken a vacuum reading? Could be a small vacuum leak or power valve not holding shut .

Oh yeah.. I have spoken with them often on this... Last I sent the carb to them I had a some water in the gas.. (this was obvious). Drained it.. all new 80 gals of fuel put in yesterday before the trial run. The flies are drilled already (from them).. I am sure they did a great job.. and I am sure it runs great on a dyno engine..(which it was done in 06)..

It "feels" as if it is loading up at idle.. But.. no soot on the transom. Plugs are not fouled.. I do get a nice "smell" of fuel though.. I can lean the 4 corner screws in, but then in gear in stumbles.. almost a 500 rpm drop.. I think the carb has a 5.5 power valve.. Just replaced last week ( as done each year part of the refresh). This carb has never idles correctly.. I can try the vacuum gauge again although I have in the past done this as well..

First you need an O2 sensor installed to find out what is going on....ie, is the engine going rich or is it going lean. You also need a vacuum gauge(temporary is fine) to see what the vac, reading is. You need this to properly size the power valve. Get those two things installed and you will find your problem pretty easily. The problem should become pretty obvious. For example, if the engine is going rich after you put it in gear, the power valve is opening to soon. Get some data from those two items and let us know. We can pin it down from there and help you get it right.
Eddie

Thanks Eddie.. # 2 I can do tomorrow.. (vac gauge)..
As far as O2 sensor.. educate me a tiny bit.. give me a starting point.. Where do I buy one? Where to install? Running a CMI E-tops ex is that makes any difference also.

You can either buy or borrow a wide band O2 sensor. You will have to weld an O2 bung in your exhaust. You can either put it in the collector of the header or in the tailpipe just after the collector. This will tell you how much unburned oxygen is in the exhaust. This will let you know if you are running lean or rich. A lot of guys on here use a wide band from Innovate. It is a nice piece and is pretty reasonable in price. I use one from FAST because it can do 2 sensors at a time. You really need to monitor both banks because one will be leaner than the other. You should tune on the lean bank.
Eddie

If you decide that you need an O2 bung installed, it might be easiest to UPS CMI a tail pipe and have them install the bung.

Sounds like it might be a reversion issue. What type of exhaust do you have?

You did not mention what Intake you have, and WOT rpm....I'm guessing carb way too big and your puddling fuel in the intake.

Ben/Eddie: That is a great idea.. Since the season is coming to a close I can easily remove both pipes and ship them.. I will call them 1st thing Monday AM for advice..

Kvot: reversion has crossed my mind.. In the 4 years I have run this motor though I don't think I have found any evidence of this. What would be a perfect tell-tail sign? I have CMI Etops..

Back: Currently I am running a hurricane intake. Actually the only piece on the entire motor I am not very failure/happy with.. The block is a Merlin III and the heads are Canfield.. I would think a 980 CFM modified by Nickerson would not be too big though.. My WOT is only 5200/5300 right now with a Hydro P5 26 pitch prop.. Just got the prop 3 weeks ago and seems to have lost a few RPMs..

An 850 Demon would support 700HP at that rpm.

700hp?? @ 5200/5300?? Interesting.. This 540 dyned @ a tender 622 hp.. closer to the 5600 rpm range.. would the intake really puddle fuel? This is possible? Does open an interesting thought process..But if that was true would it happen at all RPMs? when I start it and warm it put it in gear without even running over 1200 rpms for warm up the problem is present.

There should not be any reversion with that cam. Many people, including me, have run much larger cams with no issues. I ran a Crane 731 which is 226/236, .587/.610 on a 112 lob sep without a hint of reversion in a 454ci.

I have almost the same set up as you. 540 with AFR heads cam 236/[email protected] 112 lc. Nickerson also did my carb. My carb. is a 1050 domminator and it idles perfect at 750 rpm so i dont think your carb. is too big. When i set my idle i make sure my throtle plates front and rear are set the same. I also use a 4.5 power valve front and rear.

I think Dean said I have a 5.5 PV?? Have to verify tomorrow when I talk to him..Are you @ 750 in gear or neutral? My front and rear are also set the same.. But it does seems to like being off the idle circuit in the rear.. I know Nickerson does great work.. This carb runs awesome other then the idle.. And I know several people who have had Dean work on their stuff.. Always top quality.. but if it is NOT the carb what the heck is it? Guess I will have to try and borrow a 4150 style carb and put this issue to bed once and for all..

That is in gear i keep abuot 850 out of gear.Did you degree the cam in?do you have any valves too tight? What kind of fuel pressure are you running and are the floats set correct?

The cam was "supposed" to be degreed.. But since I was not present for the assembly up till the heads I am not 100% sure it was actually done.. Anyway to check without removing the motor??
I just went through the valves while the carb was at nickerson. Hydrollic roller. tighten nut by hand till tight then 3/4 turn right? Also have a stud girdle but I am sure that makes no difference. 7 1/2 PSI fuel pressure and yes floats are good..

I set mine at 1/2 a turn. Make sure you are on the heel of the cam. there are sevral whays of doing that. I use cranes method there web site explains how to do it. Set the push rod to zero then tighten the nut. Make sure there are no bent studs if there is when you tighten the stud girtle it could change your setting.

When I adjusted them last summer I did half.. Wanted to try something different.. went to 3/4. I adjust them in fire order 1-8-4-3-6-5-7-2 each a 90 degree turn on the crank starting at TDC..

Going to go with a VAC gauge in an hour or so to check idle vac.

John cranes method works pretty good also i always set hyd rollers at 1/2 turn but 3/4 should be fine as long as you were on the heel of the cam. what kind of exhaust you got on the motor

ok i have reread the thread have you checked the floot leavel if it is to high it can cause the carb to drip at low rpm and load the motor up with fuel. bottom line i am with Eddie you will find it with the vacum gage and o2. i would try the vacum gage first and see where the vacum goes in gear you may want to pick up some 4.5 power valves to try something tells me the vacum is falling to where the power valve may be starting to open

Thanks Mike.. Just waitng for the wife to get back and I am off to Kings Point to look.. I will post the VAC in and OUT of gear when done..

Vac at idle (900 RPMS) was 12-14.. in gear at 650 @8 or so.. then started to drop as the rpms started to drop.. but it back into neutral rpms went back to 800.. sounds like it is loading up.. running rough.. then rpms climb to 850.. then 900.. back into gear same thing over and over.. no matter what I do with idle mixture screws.. is 8 a normal vac in gear??

John check the float level and make sure it is good if you have 5.5 power valves you should be ok. has the motor ever backfired throiugh the carb

The way i understand power valves is if your showing 8 on the gauge you would need a #4 power valve. I think the most imporant thing would be to keep the power valve shut at idle.

The motor never fire back through the carb.. and this carb just came back from Nickerson last week.. Just ran it once.. on friday for tuning.. it HAS been to Nickerson each year for the last 3 or 4 years.. Always a great carb.. NEVER idled right.. never. not even before it went to Nickerson..
I think they put in a 5 power valve.. looks like it is stamped 50 on the side of it.. what exactly does that mean? Also the vac flickers up and down a bit on the gauge at idle.. never a solid reading.. I had always thought this was normal though.. 8 is about the highest I get in gear. @ 650.. I can get it closer to 9 if I adjust the mixture screw in to only 1 turn BUT the idle jumps to 700-750 in gear.. then comes closer to 1000/1100 in neutral..Should I try a #4 or a #3.5?

Dude, I feel your pain!!! I have an extensive history working with Carbs from Drag racing to Marine applications.
I have motors very similuar to yours with even more cam shaft. I had bought two new 1050 Demons, ran them on the dyno and made excellent power..They ideled great, pulled strong numbers and I was thrilled..
I put the motors in the boat at Riggs Marine. We went out to sea trial and we could not get the motors to idle with the Demon carbourators. Neither motor would idle properly. So knowing what I know about Carbs I began fine tuning them. I spent numerous hours on the phone with Demon on a daily basis.
The end result??? We could not make them work.
I promised Demon that I would not bad mouth them on the web, but this happened 1 1/2 years ago and I hate to see anyone go through the headaches I went thru..What is weird about this is that I know several people that have the marine carburators and have not had a wink of problems -- Go figure!!
So the rest of the story?? I sent the carbs back and they (Barry grant) agreed to give me a fulll refund. I now run Holley Marine 1050 Dominators. All I did was change the power valve and contoured the idle airbleeds. I am going on 2 years of flawless running - Now go figure that one...LT

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. :)

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

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.