Bajapred

iTrader: (1)

As some of you know I have installed my 250 blower on my HP500..I took it for a test run today... Stock I ran a 24 Bravo1 labbed at 5100rpm about 62mph...I now have a 250 b&m with twin 750 holleys and have a 26P bravo1..I ran about 63mph and 4600rpm..... I am not sure where my problem is yet..I kinda think I am not making any boost...my setup is supposed to be @ 4.5psi..I wonder if I may not have my belt adjusted correctly..I plan on getting a boost gauge on it Saturday....it seems to have something in the mid throttle but it falls off at about 60mph now....also, if I rev up the motor, it has a dead spot before it revs up...I am sure the fuel supply is adequate because I opened it all up....I will know more tomrrow after I get the boost gauge installed..but any ideas..

Anyone have the instructions for adjusting the belt? Thanks

Back4More

What changes did you do or make to the ignition? as in advance curve and timing adjustment.
Also, what size carbs are those and whats in them for power valves, jets on the primary and secondary circuts?

Bajapred

iTrader: (1)

Not sure on the power valves or jets..but the guys at Performance marine..Chip & Jeff..said the carbs are ready to use on my application...the timing was done by my mechanic..the way Chip and Jeff said to..

Griff

That doesn't mean either one of them was correct.

You need to find out what you have now in order to make changes. You should be making 600+hp and be able to spin the 26" prop. I would also get fuel pressure guage to make sure its not falling off in the upper rpms. You need to take plug readings after a WOT run.

nocigarette

I hear that bs all the time....There is no such thing as a ready to run carberator especially in a blown application. You need to have someone who knows what they are doing adjust your timing and tune your carbs....

Pure Energy

Agreed!! You never should have run the boat without a fuel pressure and boost guage. What was done to the fuel system to supply much needed extra fuel? What size are your fuel lines? More important, what size is the pick-up tube in the fuel tank? Not enough and too much fuel both can damage the motor. Timing is also critical

Keep us posted, courious to here what is going on.

AO31

According to Nickerson, adjust the belt tensioner to show about half inch to 5/8 of the chrome idler shaft for correct tension on the blower belt.

Back4More

OK, let me throw more out there....
Boost gauge is a must, you need to know how much boost its making to know if its enough or too much.
I would put the 24's back on and see how much more speed and rpm you get with the new induction...that should at least tell you if your making more power and if so how much more. Changing too much all at once is like trying to hit a moving target, you loose the baseline figure that way.
If you still have your stock 500HP module (P/N 17316A 1) with 20*of advance in the ignition system, then set your total advance to 30*@3200rpm...that will keep it safe for now.
You should be running colder plugs also...The stock AC MR43T's should be replaced with the MR41T's.
Carbs...
What size and model # are they?

BadDog

Sounds like you have something wrong. I have a B&M 250 on my 502, here is my basic setup on my Force 235.

Timing 30 degrees total with a base of 10
Carb by Nickerson, single 1050 reworked to something.
Belt with 5/8 showing on tension rod
AZ 120 thermostat, crossover with small bleed holes to headers when stat closed. Water temp (measured just at port forward fitting of manifold) 120 at cruise 125 WOT. Never varies from 40 to 85 degree water.
Water pressure 15 to 20 depending on water temp and speed
AC MR41 plugs
Holley Black fuel pump, no check valve, 9 psi at WOT
3x21 oil cooler with Mocal T-stat. Temp gauge in pan, 180 at 3000, 200 at 3500, 235 at WOT

Boost gauge generally shows 1 lb. vacuum around 3000 and builds gradually to 4 to 5 from there. If your belt was slipping I think you would smell it. From your numbers I would not run it further until you determine where the power is being lost. Might be lean or else the rotors are not sealing well enough to make any boost. Not sure where you should start checking but get someone to assist that does. I believe you only get one shot to do it wrong with a blower motor.

Keep us posted as to what you find but I would start with doing some plug readings from 3000 up at 500 rpm intervals. Check fuel pressure while running and get that boost gauge on there. Check timing from idle to 3K and up.

You should be running about 76 to 78 with that setup.
Force 235
stock 330 56 to 58
stock 502 415 hp 64 to 66
502 w/headers and single plane dart 67 to 69
502 w/B&M 250 at 5 psi 78 to 80

My 235 did not like the 4 blade prop, lifted the stern too much. The best prop for the 235 seems to be the Mirage Plus. I still have issues with bow lift. The faster you go the more the nose plants. Scrubbing a lot of speed off. BudMan shaved the hooks off his and it did not seem to make much difference but he is only running 60. Once I get over 65 you can fell the nose dropping as you add throttle. You have to over trim a bit to get the bow to carry and then feed some throttle in. Once you get the bow up drop the trim a touch to hook the prop back up and feed it more throttle to 75. At that point over trim a touch and rock the wheel slightly to Starboard and back to straight, this seems to put it up on what little pad the hull has. Once up on the pad it will wind out to 80. That hull was not meant to go over 65 or so. I think I can avoid all that trimming nonsense with the right prop but I have not addressed that yet. Might just have to change the address of the hull to fix it.

Bajapred

iTrader: (1)

Ok guys...here is where I am at now.... I added all the guages and took her for a test...fuel pressure runs about 7 constant, sometimes a bit more or abit less but basically 7..boost is mostly vacuum until wide open then I make about 1 psi...I have the 4" pulley....I am just not making any boost with that pulley setup..I need a 3.34 and I should be around 5-6 psi...here is my problem..my blower is the older model b&m so it has the older shaft in it...The older b&m blowers have a 2" shaft that has about half of it splined, the pulleys I have are not as deep as the earlier b&m pulleys...I need either a 3" or 3.34" older style b&m pulley..I can post a picture later...but anyway, that seems to be my problem..just no boost yet..timing is about 32*..boat runs strong even without boost..Can't wait to get some boost on this bad boy! should be a screamer!...thanks for all the help guys...it will most likely be a few days before I get a pulley but I will let you know how it goes...I may have to replace the shaft if I cannot find an older style pulley..that would be a huge bummer..

also, thanks for the heads up BadDog, I will keep all that in mind when I get her running right