JohnSchiavarelli

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..

Griff

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.

fbc25el

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

JohnSchiavarelli

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..

Young Performance

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

JohnSchiavarelli

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.

Young Performance

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

BenPerfected

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.

kvogt

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

Back4More

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.