basic 454 with a demon 650, holley elec fuel pump... it see's 7-8 psi all day long no problems.  it idles fine but on acceleration i have a studder... also previously i had the choke plate secured open since i didnt have a torx bit at the time to remove it... then when i did remove it my studder got worse.  so i put it back and its back to "normal"...   you can hear it in the exhaust tone, no backfires just kinda like a "thud" sound when accelerating.  when im on plane and just cruising it goes away. 


any tips on getting this damn thing dialed in?  it runs GREAT at WOT, the vacuum sec's open up and it perks right up to 5-5200 rpms no problems.  its just inbetween idle/WOT that sucks.

Hows the spark plugs look? First thing I'd check

Could be a slight timing issue, vacuum leak. Vacuum or mechanical dizzy? Start with the plugs though.

Ray

also the idle screws were turned in like 1.5 and then backed out as i ran it until the black on the transom went away. 

heres a plug



pulled one from each side and they're equally beautiful.  im stumped.

Looks lean to me. Is that a front or rear plug?

Ya, you're lean. The porcelain on those plugs should be a light to medium mocha color. If the front and rear plugs look that way, a jet size increase is in order. Start off by increasing the primary and secondary side by 2 sizes then run the boat.

ok thanks for the help!  im assuming demon jets are similar to holley?

I'm almost certain that they are the same. Demon and Holley are very similiar. Good luck

You could always go more than two sizes at a time, but everyone that I've spoken to about carbs always recommends two. When I first got my boat going again I startedout with 74/80 and my plugs looked just like yours. Im at 78/83 and now the plugs have a nice light mocha color to them. Every motor setup is different though and there no guide that says exactly what a jet size should be for a particular application  It's all trial and error. You'll figure it out.

VERY lean. The guys are right. Check them all to be sure about distribution. If that's from #7, it's primarily fed from the secondaries, etc. You want them all to look they were dipped in coffee.

As white as that is, I might consider going 4 sizes if it were me, and upping the accelerator pumps. Depends on what the rest look like and how often you were into the secondaries, etc.

You might want to invest in a Holley Jet kit. Cheaper over the long haul, and you get a box full of jet sizes to play with. Removing your choke probably helped the engine more than anything.

Ray

i have a holley jet kit plate with pretty much everything thats why i was asking originally.  i just gotta get a set of gaskets for the bowls. 

as far as how much i was on it, i gave it maybe 2 wot runs for 10 seconds or so.  i pretty much babied it to the beach, left it there all day, then babied it back to the trailer last time i was out.  everytime it comes home i tear a bunch of stuff apart so everytime i go to the river its something new.  heh.  by the time i get everything iron'ed out, it'll be time to sell it. 

The more that I look at those pics, the more I tend to agree with you that he should go up four sizes to start. The accelerator pumps may not have to be changed, but depending on camshaft/engine vacuum he may have to change the power valve(s).

Exactly where I.m reading that plug at. BUT IT's one plug. not the rest. What ntake, etc?  I'm guesing a dual plane intake, probably an Edelbrock. Seen this before, fronts fine, rears lean as hell. These forums exist for this reason.

Ray

you should look at all the plugs as a whole anyway. it will show how your engine is running. if it was running well with the the choke plate on put it back on. unless you plan to cut the whole horn off and cleaning it up. just an oppion but you will gain nothing by just removing the choke plate.

Late to post, but...

Timing should be "all-in" by 2500 RPM, try two jet sizes to start. Do you have a fuel pressure gauge? 

Also too, did you ever get the water situation worked out in the exhaust. Your water volume in the exhaust can lessen as the pressure in the exhaust system builds up. A little less water into the tail pipes can cause a false lean by allowing the amount of exhaust gasses to escape to increase. This was why I was trying to push you toward running your water lines differently (different thread)..

Also again, do you know what power valve your carb. has?

Just questions at this point....

GT

Yeah the exhaust situation is all overwith. It was due to my welder guy chopping off the part of the riser that holds the water in so the water went straight to the bottom and the top saw nothing. 

Fuel pressure is between 7-8.  I had someone watch it while I was wot.  So not too worried about that.

Power valve not sure.  I've read that I should get a vacuum gauuge and then get the appropriate valve?  I guess I can start it up before I tear the carb off and get that reading.

If the plugs are that light after idling around and back to trailer and stuff,, you are probably leaner than you think.  To get a better reading, you want to take a plug wrench in the boat with you,, make a pass, and then as quickly as it is safely possible, slow down and get the engine shut off.  No idling if possible.  If you want to go back to the beach or trailer to swap the jets, no problem, but take the reading without the idling first.

Not only that, but water will clean the plugs too...Reversion cannot be ruled out. Of course this depends on what camshaft, idle speed and so on.

I have really never been and advocate for plug reading, with today's fuels it is a "best guess". Exhaust temperatures at the manifolds/headers is a more ideal way to go..

Just my personal preference.

Unfortunately it is not easy to do...

You have to be aware that exhaust temps can be "high" when rich and lean and timing plays a big part in the equation as well.

I typically use a spark plug mounted thermocouple on each head and set the timing at a known safe number (almost always about 35*BTDC) and start rich (again, safer).

Once a reading has been established, the jets get dropped by two orifice sizes and readings are analyzed at mid throttle and WOT. Once the EGT temps stop dropping, notes are made, then drop jet sizes by one.  I keep dropping jet sizes until the temps begin to rise (indicating lean) then split the difference between the two (the point where they started to drop and the point where they began to rise).

Bear in mind that this is by no means an exact science, but I have had pretty reasonable success doing it this way for decades. A wide band O2 sensor is the ultimate (while still checking EGT's) but not real practical on a marine engine...

By auto mechanic friend has a portable exhaust gas analyzer that is super killer for tuning, but again, not real practical on a marine dealio.

These are what I have...  http://www.isspro.com/installation/IS013.pdf    I have type K plugs on them and I use a dual input Fluke thermometer (I am in the HVAC business so this was easy)....

Good hunting.

GT

picked up the jets today from my pop.  now i just need to find out what bowl gaskets i need...





does anyone tune with a wideband and an O2 sensor?  that seems like the BEST way to go about reaching stoich.  ive done a lot of tuning on my old mustangs and such... it seems like pulling plugs and guessing works, but theres gotta be a more accurate way?

I have a dash gauge wide band O2, but never came up with a good way to run it on a boat, I use it for the motor home..(open loop EFI)..

GT