AIR TIME

I have a 509 9/5 to 1 comp, the carb is a BG 850 WITH 84'S ALL AROUND FOR JETTING. IN THE boat it seams to run out of rpm5100 26p lab b1 4000lb baja it makes 601hp at 5050rpm goes to 637 at 5700 at 6000 it hits 647hp tq is 628 at 4800rpm I was thinking the jets are too small?? also it made about 15 more hp with a 1050dom on it should I try a new bg king demon marine or send this out to nickersons or some one else I HAVE A 1/2'' FUEL LINE SET UP ON IT ALSO TOOK CHECK VALVE OFF THE GAS TANK TO GET MORE VOLUME PRESSURE IS 7 TO8LBS WITH CP HP PUMP ALSO HAVE A BLACK ELEC HOLLEY PUMP I CAN USE ANY THOUGHTS THE BOAT SHOULD RUN 5800RPMS ART ps my buddy runs 92's in his for jetting and all the stock merc fuel lines its a 502 some where a around 525hp he has a 79 superboat24 with trs drive 25p 5400rpms 74mph help please

Lofty

The carb sounds like it should be fine on a 509. If you go bigger it'll be hard to make it idle. The jets sound real small. What do your plug reads look like? That'll tell you what you need to do.

CcanDo

There are more variables than the carburetor.In fact,the carb is often the last place to look for dependable performance.Included in the menu is exhaust system,timing,ignition system,cam,cam timing,flame arrester,spark plugs and prop......of course,there are other variables.However, a prop change or smaller prop may be a simple test.Any time the engine won't easily gain RPM to a predetermined speed,it is "lugging".Lugging causes detonation,heat and imbalanced fuel to air ratio....If your engine is designed to live at 6,000 and it will get there without lugging you should expect more speed with a smaller prop.

AIR TIME

it has MSD FULL set up, plugs are NGK same as a hp500 I tried my old 25p m prop it would do the same. plugs are hard to read right, a little color but that can come from slowing down you just do't shut off your boat at 5000rpm in the ocean the motor was built good balanced and so flame arrester is a BIG K/N ISKY CAM 114 LOBE CENTER /It was dino when built maybe bigger jets , timing was 37 so now what do you think jets how big do most guys run with 600hp in the end I want to run the motor at 5400 to 5600rpm. thanks again I will be gone for 3 days I will check back on thursday.

TC

AIR TIME, I think you could fatten it up a bit. I use a BG 850 Mighty Demon on a 496 with 83's and 91's in it. I did not get to test and tune the carb as much as would have liked by the end of the season last year but I am not showing any signs of being overly rich.

AIR TIME

Ttt

RumRunner

Airtime,

Which 850 do you have? What size PV are you running? Have you tried going up on the jets yet? How did the engine dyno?

nordic95

AIR TIME,

I just had twin 502s built for my Fountain just recently.9.8 to 1 comp. 651 Comp Cams cam.Aluminum Edelbrock heads and 850 BG Speed demon carb on a Hardin Marine single plane intake.When we dynoed these motors we ended up pulling timing down to 28 degrees total advance at 3000.We also had to fatten the jets up seven sizes over stock.I am running 101 in the secondaries and 92 in the primaries.We made 634 HP at 6000 rpms with that combo.I feel you may have way to much timing and not enough fuel.Let me know how you make out.

Thanks Nordic95

RumRunner

Nordic95,

It sounds like your 850's a touch big for your combination. Probably would have recommended using annular booster carburetors which would have been able to pull more fuel with less jet. As long as your plugs are burning OK, and the engine runs fine I wouldn't worry about the big jets.

nordic95

You and I spoke via e-mail.Roccard built the motors.I only have dyno time,about 50 minutes of total run time.I pulled the plugs and they have just the smallest tan color on them.When I get them in the boat I will run O2 sensor to finale tune.

PS: I ment my last reply to AIRTIME,Sorry Rum Runner