MILD THUNDER

Have you put a vaccuum gauge on it? Try that, and see what your numbers are. I would check the distributor caps. This time of year, cold nights, warming up, you may have some corrosion and or moisture in them. Ive had a brand new cap malfuction and it would only fire 7 out of 8 cylinders.

It seems like you have pretty much gone thru the carbs, power valves, jets, etc. At this point, I may try looking into the ignition. When I first bought my hawk, it had the old points distributors. One motor would cough, die, as soon as i put it in gear. Also would not go over 3000. Swapped it for a new mallory breakerless and ran geat. Might not be a bad idea to put new coils in, you can get a msd blaster 2 for about 30 bucks at pep boys or advance auto. Weak spark will foul plugs too.

MILD THUNDER

Make sure you are setting the idle mixture screws when the carb is on its idle circuit. Meaning, if you have the idle speed screw set too high, the idle mixture screws will have little affect. Back out the screws about 3 full turns, and lower the speed screw, turn screws in till idle lowers(or highest vacuum on a gauge), then out a 1/4 turn. Then if you need to, turn the speed scew so it idles in nuetral about 900 and about 700 in gear.

baja36ft

Why Don't You Jet It Like A Hp 500 Lf-81 Rf-75
Lr-93 Rr-89 And This Maybe To Big What Plugs Are You Using?

Liberator21

Have you contacted BG to see what they recommend as an initial setup (Jets, Idle screws, etc)? Everything you're saying sounds like it's running way rich. I would bring the carbs back to where they were when you first started, and then start making your jet changes from there, otherwise you'll be chasing your tail! Also, don't make big jumps when changing jet sizes, maybe only two sizes at a time (like 83 to 81). You'll also have to make sure everything else in the carb is functioning properly. Changing jets all day won't help if there's another underlying problem. It's frustrating, and time consuming, but you'll get there. I personally don't think it's an ignition problem. I think it's all a result of the carbs.
I've been there. You say you run in the sound. Where are you located?
I run out of Hempstead Harbor, and Manhasset Bay.

stinger390

Running out of Mystic, CT (actually idleing out of Mystic right now )

Changed jets to 79 front, 83 rear. (83 was what was in there from the start in the rear.) Changed gaskets on stbd carb, raised float level to the upper mark on the sight gauge, checked #7 plug, way black from yesterday. Plugged in my vacuum gauge started and warmed for a while. Put the boat in gear at the dock and adjusted idle screws to vacuum. In gear, max vacuum was about 11 - 12. Set each screw for max vacuum then 1/4 turn rich. Reved good, idled good at 700 in gear, and about 800 to 850 in neutral. Adjusted both engines exactly the same.

Put stbd engine in gear again, tied to the dock, advanced the power slowly, motor started stumbling and coughing and sounding like it was missing badly, same thing it did on the water the last several times out. When returned to idle it will idle right where I set it perfectly, try to advance the power and she stumbles and coughs but will run up to about 1300 rpm and no more. If I go back to neutral I can rev it right up and it sounds smooth.

Shut it down, closed the hatch, here I am home with the first of many beers gone!

It is only on this carb. The other is fine. It must be the transition circuit or something. Perhaps a crack somewhere or bad metering blocks. I have not done anything with the squirters or the venturi's. I'm going to swop them again engine to engine to make absolutely certain the problem will follow the carb, (and keep the right eng. as the good one for steering's sake) I'm also thinking of connecting a remote fuel tank to rule out fuel, but if it were fuel the other engine would do the same. Perhaps the fuel pressure is a problem, both engines have the same pump though, Holley 130 GPH with no regulators. No flooding is occuring with the carb and the bowl level is holding the same so I doubt it is that.

I feel like yanking off these older Demons and changing to a 750 holley or 800 - 9022 holley or somthing, out of sheer frustration. Who is to say that a new or rebuilt carb will work any better though.

What about smaller power valves? Perhaps a 5.5 (if they make it) or 4.5. Since idle vac was around 10-11 average perhaps that would lean the engine out enough to stop costing me $23.00 in plugs every day, cut the smoke, and the transom soot, and get a little more economy out of the liquid gold? What are the thoughts on this idea?

waybomb

I would take the carb completely apart. I would clean out every pasage, and ensure that the all passages are not blocked in any way. Make sure all the correct gaskets are used, and are installed correctly. Get an assembly diagram / manual for the carb just to make sure.

Do both carbs have a 6.5 PV? Can you hook up a vacuum gage to the good engine under load and see how much vacuum you have? Your PV should be about 2" less than whatever that steady engine speed/steady load vacuum is.

You said earlier you have the float set at the highest mark? I'm not familiar with your carbs, but raising the level of gas in a Holley bowl will enrichen, if anything.

Just curious - have you sprayed any carb cleaner down the carb while idling? Did the idle speed go up or down? What about around the carb base?

Lastly, you should be able to salvage those almost new plugs with a plug sandblaster. Just make sure you get all the sand out after you blast them.

rbtnt

It sounds like you have it isolated to the carb. Have you tried swapping the metering blocks one at a time?

stinger390

I did spray carb cleaner around the base of the carb, around gaskets, everywhere that I thought there could be a leak and found no leaks. Idle vacuum is the same on both engines.

Perhaps it's getting all the fuel it needs but not enough air. I doubt the flame arrestor is clogged enough to cause this but I'll clean it anyway. I have not tried swoping metering blocks but I will this morning.

What is the best power valve for my idle vacuum of 10-11? 6, 5, 4 ? I thought power valve 1/2 the idle vacuum is the right formula for figuring what size. I would think that 2" less than idle vacuum would cause the valve to be opening constantly making it really really rich at the low end. Would a smaller power valve than the 6.5 that is in there make any difference?

Todd

MILD THUNDER

I guess you could try a smaller pv, but if that was causing the problem, why wouldnt the other carb do the same considering they are the same now? I would sell those bg carbs, and look for some holley 9022 800cfm double pumpers. Jet them 79f, 90r, 6.5 pv, then you will have "OE" 420Hp carbs.

When you are on plane, say at 2500 rpm, and you mash the throttles, does the one good engine gain rpm while the other bogs, or do both only max out at the same rpm?

PatriYacht

With your vacuum, those power valves are fine. Changing them would be a waste of time and money. Dropping jet size didn't help. The problem follows the carb from engine to engine so the problem has to be in the carb. Send it back to BG for a rebuild.