fuel octane

[Fiat48]

Maybe not because you have those .125 holes in the throttle plates. You have to look and see where they are now.
PS: you can do the projected tip plug also which will help plug wise.
2000 rpm seems awful high to idle.

[Moneypitt]

To answer a few questions....no power valves......1 small hole in each butterfly, about 1/8 inch (.125). With reference to the plugs I'm using, Bob brought up a good point about heat range. I was beat dead tired at work last night and wrote the incorrect plug on the thread. I'm running a NGK B8ES. For WOT heat range may is okay...discoloration in the middle of the strap...maybe a 6 range would serve better for warm ups, like bob said.
Now , say I turn the idle screws back down a turn, turn and a half.....idle speed drops too much. Trying to stay at 2000. If I turn my IDLE set screws up this will start to expose the transfer slots won't it?
At 2K you should be well into the main jets, and the idle circuit is doing nothing. Now you're battling the overlap and vacuum signal at a relatively low RPM...........And your scoop is doing nothing on the trailer to add additional air to the mix...........Ray

[BDMar]

At 2K you should be well into the main jets, and the idle circuit is doing nothing. Now you're battling the overlap and vacuum signal at a relatively low RPM...........And your scoop is doing nothing on the trailer to add additional air to the mix...........Ray
You beat me to the punch. Exactly what I was typing as you posted this. Makes me wonder what your combination is and exactly what carb(s) you are running....

[Fiat48]

I don't know about you guys but what I always did was make the motor idle as slow as possible (throttle plate wise)....then set the air screws and then set my throttle plates to desired idle speed. With big camshafts I purposely did dist curves to have the advance all in the moment it started for better idle control and leave. I kept the idle low to save the V drive when putting it in gear.
In the rolling start days I actually rigged up a fast idle solenoid (like a Q jet had on it) so after going in gear...my approach speed was always the same.
Just some info.

[steelcomp]

I'm not sure I agree that you're "well into" the main circuit @ 2000, but you're definately at the transition stage. Are you seeing fuel drip from the booster venturi's at idle? That's a sure sign you're into the main circuit. Do these carbs have an intermediate? Have you tried playing with air bleeds? You can delay the main circuit slightly with a change in air bleed. If you have an intermediate, you can do the same there.
Try turning the AFR screws in a little, maybe to 1 3/4 - 2 turns, and then opening the throttle a little to increase idle. Then go a little more, and see what happens. Idealy, you shouldn't be more than 1 1/2 - 1 3/4. If you get into the transfer slots, you'll know it, but if your idle stays clean, my guess is that you'll have better throttle response, and a crisper sounding idle. Last resort, you might have to go a few thou bigger on the holes in the butterflys, but I wouldn't start messing with that yet.
Why so high on the idle?

[Fired Up]

Carb is a #9375 1050, air bleeds are fixed. It has a soft progressive linkage. Timing is locked out at 38. At 1400rpm's when I drop it in gear the idle drops a bit much, at 16-1800 rpm's it stays up, burns the prop a little better and the boat takes a better set as I pass the lights.
Didn't get a chance to pull her out tonight. Thursday morning I will have some time in the AM before I pack for the races and I'll try some of your (plural) suggestions. For starters a set of hotter warm up plugs.
Steelcomp, how will I "know it" when I'm into the slots, aside from seeing them?
Bob, tell me about the single cylinder pyrometer...easy set up or expensive sensors,data recorders ,laptops..etc?

[Fiat48]

http://www.computechracing.com/egtsystems.html
They make a clamp on probe that only requires you to drill a small hole in the header pipe. I make all the blown guys put them on. Generally I do #6 as with a blown motor that seems to be the hottest cylinder. I see the new units can now read 2 cylinders. One has always been good enough for me.
The unit has a memory and will record the highest EGT and the lowest. It's a great tuning aid especially when combined with plug readings.
LOL....think I have had mine a long time? I paid $195 way back when.
On that rpm fall off...put a timing light on the thing and you will probably see the timing drop back....a double hit on your idle. A faster curve can help...if you can....you want it all in when the motor starts...light springs.

[Jetboatguru]

Scott,
Flatbottoms leaving from a dead stop have a hard time taking the throttle. They need to have lots of fuel at the hit as the prop hooks and tugs the motor down. 2 1/2 turns out is pretty normal for us and in PHX, it might be 3.

[steelcomp]

Scott,
Flatbottoms leaving from a dead stop have a hard time taking the throttle. They need to have lots of fuel at the hit as the prop hooks and tugs the motor down. 2 1/2 turns out is pretty normal for us and in PHX, it might be 3.
Thanks for that input Tony.
To me, it seems that "hit" should be a function of the acc. pump. As soon as you open the throttle, regardless of rpm, you're off the idle circuit. I understand the need for fuel at the hit, but what you're saying dosen't make sense to me. Now mind you, I have zero prop boat experience, but I've been around enough cars with big ass slicks to know what can load an engine. May be apples and oranges...I don't know.
Just as an observation, I've heard some guys bring their engines up before launch...there's a trick with the acc. pump adjustment for that style of leaving. Here's the deal...If you've got the throttle open 1/4 or so before you leave, you've wasted that much travel of your acc. pump, and lost that much of the pump shot when you mash the gas. That's all I'll say on that.
At 2 1/2 - 3 turns on the AFR screws, you some how should be adding more air to that much more fuel. The engine really dosen't care where it get's it's idle fuel...just as long as it has enough air with it, and it can transition to the main circuit smoothly.

[steelcomp]

Steelcomp, how will I "know it" when I'm into the slots, aside from seeing them?At that point you'll be pulling fuel out of the main well, the AFR screws will become in-effective, the idle quality will go away, and it's likely to be way rich.