carb jetting
 

i installed 850 sea demons out of the box, was running holley w, 88 frt jets and 95 in rear ran 5200-5400 rpm. now with the demons it turn 5000 feels like its running out of gas on the big end,midrange feels strong to 4800
do i need to jet the deamons like the holleys were.:confused:

What were the holley carbs cfm you replaced?
Why did you replace them?
What were the power valves in them?

There are alot of factors that come into play.
power valves, float level,also main jets

I would make a high speed run then as safely as possible shut the engine down quickly and pull a plug and look inside the insulator. You are looking for a tan
brownish color.


Good luck
Gerry

johnnyboatman
Do not perform a plug check in a marine engine as you would in an automotive application IE by killing the ignition @ WOT. You can leave yourself open to very serious problems.
Bob

one of the old carbs had a mid range problem that we never could get out. there the same cfm.
like i said the holleys had 94 in rear, 85 in frt
im fixing to put 94 in the rear of demons and try it like that. float levels are correct, fuel pressure fine.
i would have changed them before the install but people said stick them on and try it first.

t.t.t

That sounds like alot of jet.Im guessing no power valves? If so whats the numbers.My old 454 hydrolic cam made 475hp with 850 holleys jetting was 84 front 86 rear both sides having powervalves the numbers I really dont remember.poss 6.5

just curious
 

why sort of problems are you talking about in shutting the marine engine down from WOT. are you talking safety or potential engine probs.

just want to clarify that.

boatn70
Mechanical problems.
Bob

Specifically sucking water back in, someone that can explain cam overlap and reversion could chime in. Just bring it back from WOT as quickly as possible and avoid and idling and then shut it down. A lot of the hazard involves exhaust type and cam profile.

makes sense
 

glad to have been informed because ive had people tell me to do that before. id still like to hear details if anyone has the time or patience.

sorry to borrow the carb thread!!!

thanks

Allow me to elaborate on " Quickly shut down engine safely as possible" We take the boat out on the bay and run engine to 5000 rpm for approx 60 seconds
roughly 90 mph in this case. Water permitting. Then we quickly bring the boat down to just before loosing plane. of course not swamping the transom Then Allowing minimal engine Idle we shut one engine down. Then allow the wake to settle. kill the last engine. this point we remove a plug from #1 cylinder (usually the lean one) and check the insulator color. Looking also for any small aluminum particles or balls. Depending on the age of the plugs This may take several runs to get a color on the insulator.


This may not be the preferred manor or the text book method of checking pugs in a marine environment. However it is the way that works for me.

Sometimes I forget how literally things are taken.

Gerry

PS
This it what your boat may look like when shutting down to quickly or slamming it in reverse with some good throttle. Some Mechanical problems here.

Wait this just in these are the three that were running the boat above.

I like power valves 5.5 front and rear 84 front 88 rear unless it has a very large cam and some compression it will get you in the ballpark set your secondaries to open later that will help with throttle response.