ok, this situation is getting a bit frustrating. I have merlin 540's
mild power. About 650hp, completely fresh. My carbs are 4150 based pro systems, built by patrick. I am completely lean on the top end and cannot rev under load over 5100. These carbs came with 86 jets all around, and we gained almost no difference going from 86 all the way to 99's all around, plugs are still dangerously white. Any ideas? Patrick says the j-tubes can be creating negative vacuum which holds the fuel in the bowl and will not let it pass, ever heard of that happening? Running 7lbs. pressure

I'm using their 850 on my procharged 572's (one per Motor) making almost 1200hp. 79 on primary 92 on secondary 12AFR. No powervalve on secondary.

Randy

Is your fuel pump big enough to feed the motor and are the pick ups in the fuel tank large enough to flow the fuel? If your jetting up with no changes then I don't think your getting enough fuel.

I had a 540 with 600 hp and had 84s all around.

how are you reading the plugs? wot and stut the motoes off and read plugs

we have been reading the plugs, and they are ghost white. The boat had 540's with 10-71's last year and flowed plenty of fuel so I would think we should be good. Same fuel pumps, I am at a loss right now, patrick seems set that it is the j-tubes causing the problem, but I have never seen that as a problem. Seems like the 86's that came in them were pretty close judging by your guy's numbers. Any more input?

Patrick did some split doms for me years ago, he is a pretty knowledgeable fella, he might be right?

Michael

i hope so, we will find out this weekend, its just getting a bit old hauling this thing an hour and a half to the lake

Are you getting any black on the transom after a run, with the 99s?

no black on the transom, definately very lean. Even bent a valve last weekend, that was fun

I think I would step it up to a 1050. If you do not have air flow you won't have fuel flow. 850 might support a 502 fine, but anything after 510" I step up to a 1050. Thats just me.