Vmax

I have a 454 Mark IV BBC not sure what heads with B&M 174 with small pulley 5 PSI boost a carb from a HP 500 motor. Electric choke is not hooked up. My dilema is getting a good idle that will prevent boat from stalling out in gear. 1100 RPM in neutral delivers 550 to 600 RPM in forward gear with Bravo 1.5 to 1 gears and 27P mirage. Boat is 1989 230 Velocity with zero efforts separate shifter and throttle levers. Trying to eliminate the kerthunk from 1100 RPM engagement. Motor will idle less with adjustment screw but die out in gear. Separate controls make slapping in gear and then providing enough throttle to prevent stall a challenge. Is 1100 RPM too much for cone clutch? I had a guy suggest blip of throttle then watch tach drop to 400 Rpm and drop in gear. Some what a pain in the arse and speed wont drop unless you turn down idle equates to stumbles at dock or trailering. Should I mess with idle mixture. Boat is jetted fine right now and runs like a banshi. Dyno 552 HP 5600 RPM. Prior to the HP 500 carb which is a Holley 830 or 800, I believe, Boat had a 850 Holley carburator similar problems with idle but less throttle response and tired floats and needle seats from years of sitting. Engine has 35 hours since it was built to handle the blower all polished and ported carb that came with built engine was not marine version and had to pull it for obvious reasons.

Anybody ever deal with this type issue before and find a workable solution? Or is this something you just live with?

GEOO

Maybe you can tune the idle better.
Go Fuel Injection...or...
Some people turn engine off and restart in gear.

HiPerf2000

iTrader: (2)

i have the same blower set up on my 454. i use a merc V-6 ignition module. my motor idles around 800 in nuetral and 600 when in gear. only other difference is that i have a nickerson carb that Dean tuned when he dynoed the motor.

my buddy has a couple V-6 modules from his old boat that he would want to sell.

Gary Anderson

I agree with hi-perf. What is your initial and total timing? Are you running a Tbolt IV distributor and module?
Gary

Cord

iTrader: (2)

A lot of the idle issues come from setup. The correct selection of cam and the carb. I wonder as a crutch the alpha's shift interrupter could be Incorporated.

John B

The V-6 timing module made my idle worse, because the timing advanced much more at high idle than low idle speeds. Check your timing in gear and in neutral, it should be about the same.
You should richen the idle enrichment screws on the carb. There is a lot of fuel that rotates around in the blower that sticks to everything unlike the normal manifold that the 500 carb was originally set for.
Ideally the timing at idle should be as high as possible while not exceeding 28 -30 at full throttle.

Griff

You should not loose 500+rpms dropping it into gear.

My 525SC with a 177 idles at 750rpms and only drops 100 rpms putting it into gear.

You may have a vacuum leak that is causing this problem. That or the initial timing is set to low.

RLW

I went through the same dilemma when I first got my boat with a B&M 250 Blower already installed. It prompted many questions to members of OSO (thanks John B for the e-mail at the time). I posted a thread where the question was "To boost reference or not to boost reference". Got a lot of replies where members were adamant about what they thought was the correct answer. Low and behold I received an e-mail from Dean Nickerson to call him. He got wind of my question from somebody as he does not post on OSO and requested I call him. Needless to say, I sent my carb to him and voila', turn key no hassle boating. It idles at the docks, doesn't load up and zero transom soot.
I say leave it to the experts.

Vmax

Correction Bolwer is B&M 177.

The timing marks on the saw tooth were painted over from the rebuild and since I have no manual not sure what the numbers are. If any one knows sequence port to starboard would be helpful in determing where idle timing is set when I put the timing gun to it.
I am not sure what module this motor has. It has a lot of components from the original 365 hp 454 magnum. Since the motor was built for previous owner I have few specifics. The came is a crane last two digits end in 31 I looked it up once and it was not tto radical and appeared to be proper for set up. I can not see a thunderbolt module hanging anywhere on the motor. A previous boat I had with the 330 454 magunum had module mounted on exhaust manifold with stand offs. This motor has a distributor and what appears to be a Merc standard coil. No module to be found. How do I tell if I have the V-6 module. The parts list I get from receipts provided for engine build lists a distributor block which was added. I assume this was to retard timing to prevent detonation. Not to sound too stupid but how due I determine timing advance at full throttle once I determine markings for idle timing?

The post on adjusting idle mixture. Any tried or and true instructions on getting this right. I feel this might be an issue since sometimes a good throttle blip off idle cause a stumble and a pop. Does this indicate a too lean condition?

Gary Anderson

The modules came in 2 types, a square "box" and a triangular "wafer" on a metal plate. Follow the wires ie, green/white & red/wite, from the distributor. They will lead to the module. Get all the numbers off it.
Clean your timing mark on the tab and the balancer. Hook up the timing light to #1 pug wire (left front) and get the initial timing at lowest possible rpm. Rev it to about 3200 rpm and use a variable advance light to get total.
On a SC engines with higher compression total advance will usually be retarded to around 28 degrees total from a normally aspirated 34 degrees. This prevent detonation. If you have a standard Tbolt V8 module, it will have about 24 degrees advance built in. If it's only 28 total, you'll have only 4 initial and poor idle quality.
The V6 distributor module has less advance. 12 initial will give about 28 total and a much better idle.
Get a timing light with variable advance and set your total timing at 3200 rpm. Then check your initial timing.
If that checks out OK, then go into tuning the carb.
Gary