Liberator21

I'm with PatriYacht on that one.

stinger390

Another day at the office....(slip). Changed all 8 plugs again. (I should buy stock in NGK) I think things are getting better. The plugs were dark but clean on Cyl 1 & 2. 3&4 a little darker with some carbon, 5&6 Darker still with lots of carbon caked on and slightly damp, 7&8 carbon caked. It seems the front bank is leaner and the back... far richer.

I re-checked the timing and set it at 10 Deg base. At 3300 RPM that advances to 32 degrees or so, about the most that I should want I think. (89 octane pump gas and a heavy boat) I checked both engines and set the timing the same. I would like to advance a little more thinking it would lean things out, but I don't want too much total advance. (V8-HP module and Thunderbolt IV) I re-checked the idle setting with my vacuum gauge, and it seems to be running fine at the dock.

Bad fuel should not be a problem soon since I am now on fumes and any left over nasty fuel should be run out. I'm thinking about letting it run out completely and adding fuel at my dock to get any old crud out of there. Then change the fuel filters etc. This baby is burning a serious amount of fuel in the limited time I have run it, especially since 100% of the fuel burned (about 160 gallons) was with some kind of problem. 14 hours on the motors now and only about 2.0 or so on plane.

I'll get new gas tomorrow and take her for a spin to see if anything is better. It is wierd to me that the plugs are fouling so un-evenly though. Could that be a limitation with the intake that I have. It is a power plus "hurricane" high rise aluminum single plane. Totally square open throat with no square bore passages to direct the fuel, outside of the square bore spacer. Could fuel distribution also be a problem here?

blue thunder

I would buy a new carb and start there. You are running a real risk of ruining a near new engine. Switching carbs from engine to engine pointed directly to the carb as the problem, no?

BT

Linster

Always check plug 6 for fuel, Its the leanest cylinder

MILD THUNDER

you should buy one of those plug sandblasters. Im no carb guru, but could it be possible that your fuel pump has too much psi, blowing the needle of the seat? Or a pin hole in the float causing it to sink?

You said it ran better when you swapped the carbs, but you also said you werent positive. So, Im assuming the crappy carb was originally on the port motor. You swapped it to the starboard and the problem followed to the starboard? Am I correct? I just want you to be 100% that its the carb.

I only say this because I had similiar problems. i started fooling with the carbs, took them apart, got rebuild kits, went thru them, put them back on, and still the same. Turned out to be ignition. My motor wouldnt rev past 3500, puked when I put it in gear, didnt pull under load, smelled super rich, but yet idled in nuetral and revved in nuetral to 5k with no problem.


I agree with blue thunder. You want to solve this problem asap especially being that you have a new engine that has spent its most crucial part of its life(break in) running bad, missing, idling, and probably has a lot of gas mixed in the oil.

Not that your intakes are an ideal setup, but I doubt fuel distribution is your problem, or clogged fuel lines, etc. Its clear that you are getting plenty of fuel, its just that you need to be able to burn it. Which either means a better a/f ratio, or better spark, assuming the compression is good.

Maybe you can sell those carbs on ebay, and buy some smaller carbs like 800's. Id look into it, cause when I had my 540 with the 1050 dominator it was good on the top end but on the low end it was lazy. Several carb guys told me to go to a 950 4150 stlye and I would get better low end response.

stinger390

You have me thinking about the ignition now MT since my problem seems to immitate yours. I'm trying to think about the entire package here, and not just that the problem seemed to follow the carb, but that there could be another problem here with the engine as well.

When I pulled the wire off the coil yesterday to brighten up my timing marks I noticed a light orange colored oil where the ignition wire plugs in. The coil lead wire hole was full of it. I think the coil is housed in a light oil and this is making me wonder if the coil is bad as well. The port coil lead wire plug was dry.

This is an older MSD Blaster coil sparking the Thunderbolt IV. This part was not replaced and came with my boat when I purchased it with the old engines. The mechanic re-used this part and it could possibly be bad, which certainly would not be helping things and I'm thinking creating a weak spark.

MILD THUNDER

could be a bad coil. I beieve the oil keeps the coil cool, and maybe its overheating. Also, change the cap and rotor for the hell of it. Throw some locktite on the rotor shaft before you put the new one on.

stinger390

Changed the coil with another MSD Blaster2, put on a fuel pressure gauge, reading 9-9.5 psi. Ordered 2 Holley fuel pressure regulators to try tomorrow to correct that down to 6-7 psi. Need to change the oil, add fuel, change fuel filters, and see what happens. I'm thinking if the fuel pressure is too high, I can't correctly adjust the float levels, since I am adjusting against the pressure of incoming fuel. This could also add to my extremely poor economy I'm thinking, coupled with a bad spark, and possibly timing that was off some. After I get the regulators installed I'll re-adjust the carbs and see if I can get a better vacuum reading adjustment and lean them out some more, at that point I'll re-evaluate the correct power valve to use based on that vacuum, and see if I can get this baby running right finally. If it all comes down to excess fuel pressure I will have to laugh. I had asked the guy if I would need regulators with the fuel pumps that he installed and he said no, and not to worry about it. The Holley literature for this pump 12-454-130 (130 GPH) I just found out specifically states that a fuel pressure regulator is required with the use of that pump. It is also an automotive pump, and if excess pressure is the problem, I'll break down and buy a couple of 110 GPH marine pumps with the dual diaphrams, and the sight tube and put them in over the winter.

More tomorrow after a test run....too much wind howling out there today to take the chance of having a dead engine on return.

MILD THUNDER

yeah, 9psi seems high, I think holleys can only handle about 7 psi before the needle blows off the seat. Im anxiuos to hear the outcome!!!

amer3

fuel pump for 500hp carb is 130gph to. buy a regulator