question about holley carb

[marty722]

I have a 454 indmar eng in my boat and I just bought a new 4150 holley carb. It has a bad miss at mid range and I took it to a marine shop and they are telling my that it's over carbed. It the 750cfm carb to much carb for a 330HP eng? I think they are wrong but then again I have been wrong before. Thanks.
I need to start somewhere......

[FASTRAT]

I have a 454 indmar eng in my boat and I just bought a new 4150 holley carb. It has a bad miss at mid range and I took it to a marine shop and they are telling my that it's over carbed. It the 750cfm carb to much carb for a 330HP eng? I think they are wrong but then again I have been wrong before. Thanks.
I need to start somewhere......
no way is that carb too big...most people run that & bigger (800-850)...i would ck the plugs & make sure they are ok...then ck the ign wires & coil for a short...also...a quick ck of all ur wire connections to be sure they are grounded properly & tight...if the carb is new rite out of the box...it should run fine...just trying to help
fastrat

[HammerDown]

I run a 715 vac secondary on my 468 @ 52-5300...my 850 DP did nothing for it, so on the shelf it sits.

[Cas]

is it a miss or a bog?
if it's a bog-
Did you check the float levels after the install? Maybe a needle is a little kinked in the seat? how's your fuel filters?
a miss is usually something electrical.
and I'm with Hammer on this one, all an 850 did for me was use a whole lot more gas. I went with a 750 dp the last 2 years with decent results but still used quite a bit of gas. My newly redone 750vs will be here this week and as soon as I get itout there, I'll get some numbers on the differences with my set-up.

[SmokinLowriderSS]

No, not overrcarbed. I'm in the group to check the ignition over for a missfire. Running points or electronic? Could be the power valve either not opening early enough and letting it lean out. Should be a primary side PV. Check it for a size # I would run a 6.5. At a vac level of 6.5" it opens and flows fuel to enrich the midrange. If it is blocked or too small (like a 2), it will not do anyhting or only work at or near WOT. Drive it with a Vac gauge on it to see what vac levels are at the various engine RPM's.
Also, do double-check the things like float levels, just to insure they are right. A fuel supply shortfall tho should show up at full roar even worse than part throttle.
I'm running a 700CFM 4150DP, jetted 66/76, 6.5" power valve, otherwise stock, and it runs great. Just a bit lean so will be upping 1 size with the headers this year. Indmar 454 now carries a .565" lift 280* Duration Isky cam (custom grind), a Edelbrock Performer RPM Air Gap manifold, K&N Air Filter/flame arrestor, and Lightning Headers. Should be close to 400 HP, without the nitrous. :crossx:

[marty722]

and I'm running a electronic. If you nail it it will or even just at midrange it starts to miss. While making a run at full throttle I even hear a noise like a backfire pop. Like a firecracker going off. Compression and headgaskets are good. I have a gps and I had it at 59MPH so top end seems to be ok allthough the sound like a backire worries me. I called the marine shop today and he says the timing is good on it and maybe the dist needs to be worked or replaced. He also told me when I picked it up that it seems that it has a weak spark, He wants me to go with the whole MSD package at 800.00.. More more money..... :crossx: :crossx: :crossx:

[Moneypitt]

See if someone local to you has a different dist. you can borrow. Stick it in and see if the problem remains. If it does, don't spend any $$$ for a new one, and look elsewhere for the problem. It is possible to "over gas" an engine and loose a cylinder here and there. If you're doubting your spark, pull a wire, put a phillips screwdriver into the plug clip, hold the shank of the screwdriver about 3/8ths from ground, (block/head etc), and crank the motor. The spark should be blue, not yellow. Yellow being weak. And yes, a weak spark will temporarily foul plugs under the conditions you refer to............MP
PS: hold the screwdriver by the plastic handle, even a weak spark will get your attention........

[GofastRacer]

He wants me to go with the whole MSD package at 800.00.. More more money..... :crossx: :crossx: :crossx:
Want "reliability", pick up an HEI and put an aftermarket coil and module in it and forget about it and save a bundle!..

[FASTRAT]

and I'm running a electronic. If you nail it it will or even just at midrange it starts to miss. While making a run at full throttle I even hear a noise like a backfire pop. Like a firecracker going off. Compression and headgaskets are good. I have a gps and I had it at 59MPH so top end seems to be ok allthough the sound like a backire worries me. I called the marine shop today and he says the timing is good on it and maybe the dist needs to be worked or replaced. He also told me when I picked it up that it seems that it has a weak spark, He wants me to go with the whole MSD package at 800.00.. More more money..... :crossx: :crossx: :crossx:
i wouldnt spend $800 on any kind of ign system...as Smoke says...ck the carb over..."everything"...then ck the plug wires...if there not solid core wires...they gotta be breaking down...start with 1 thing & then go to the next...make a list of what u cked until u find it..."everything"...wires, coil, carb, plugs etc...its there...u just have to find it...save ur $$$ & do the cks
fastrat

[GofastRacer]

i wouldnt spend $800 on any kind of ign system...
Especially MSD, LOL...