Having Trouble With Rossi 7.5 Outboard

[DonSoper]

I am still having trouble. I started with a Prather 230 prop, then I went to an x447. I even tried a Prather 220 just to see if I unload it if it will run. It goes about 30' & dies. I am running 60% fuel. I have tried different needle settings from 2 turns all the way to 5 turns in 1/2 turn increments. I have a hyperformance head button, which has less volume, set at.0015" clearance. I have tried Irwin pipes both muffled & un-muffled.

I am getting very frustrated. :angry: Any help would be appreciated.

 

[ZIonOB75]

I am still having trouble. I started with a Prather 230 prop, then I went to an x447. I even tried a Prather 220 just to see if I unload it if it will run. It goes about 30' & dies. I am running 60% fuel. I have tried different needle settings from 2 turns all the way to 5 turns in 1/2 turn increments. I have a hyperformance head button, which has less volume, set at.0015" clearance. I have tried Irwin pipes both muffled & un-muffled.
I am getting very frustrated. :angry: Any help would be appreciated.

check if there is water head O-ring,,,,lower the nitro %,,,i'm running 20% nitro with os 8 glow plug,,engine rans pretty consistent..

 

[jydracing]

Hi Don I had a problem with a rossi 7.5 once look at the water nipples were they go in to the cooling jacket. sometimes they are to long and hit the block and will not let the head button get tight enough and leak. If you do not have trash in the carb than it sounds like you have a air leak. When I was running a rossi engine on my Hornets I was turning a prather 235 stainless prop and running a .392 bore carb. Also look at the boat while it is running watch the pipe. I have seen many as the boat is running the pipe will wabble on the header flange and leak. I made a flange that went on to the exaust nipple and the header bolted on no more wobbling or leaking.

Hope this helps Jimmy

 

[happybradboating]

I am still having trouble. I started with a Prather 230 prop, then I went to an x447. I even tried a Prather 220 just to see if I unload it if it will run. It goes about 30' & dies. I am running 60% fuel. I have tried different needle settings from 2 turns all the way to 5 turns in 1/2 turn increments. I have a hyperformance head button, which has less volume, set at.0015" clearance. I have tried Irwin pipes both muffled & un-muffled.
I am getting very frustrated. :angry: Any help would be appreciated.

Don,

Don't feel to bad I am having the same problems with my new 7.5cc Rossi. I have raised the motor on the transom, cut the spray bar down inside the carb, tried shortening the pipe down, etc. At this point my head is set at .018 and I was told that my be to high. Currently to make more changes my pipe length is at 11 1/4 so I plan on shortening it, raising the motor higher on the transom. In addition, removing the head shim to get the head clearance down to .0145, and possibly trying another plug other than a cold McCoy #9. It was suggested that I try a hotter plug such as the K&B HP plug or K&B 1L.

Stay in touch maybe we can figure out the Rossi motor together?

Brad

 

[DonSoper]

I am still having trouble. I started with a Prather 230 prop, then I went to an x447. I even tried a Prather 220 just to see if I unload it if it will run. It goes about 30' & dies. I am running 60% fuel. I have tried different needle settings from 2 turns all the way to 5 turns in 1/2 turn increments. I have a hyperformance head button, which has less volume, set at.0015" clearance. I have tried Irwin pipes both muffled & un-muffled.
I am getting very frustrated. :angry: Any help would be appreciated.

Don,

Don't feel to bad I am having the same problems with my new 7.5cc Rossi. I have raised the motor on the transom, cut the spray bar down inside the carb, tried shortening the pipe down, etc. At this point my head is set at .018 and I was told that my be to high. Currently to make more changes my pipe length is at 11 1/4 so I plan on shortening it, raising the motor higher on the transom. In addition, removing the head shim to get the head clearance down to .0145, and possibly trying another plug other than a cold McCoy #9. It was suggested that I try a hotter plug such as the K&B HP plug or K&B 1L.

Stay in touch maybe we can figure out the Rossi motor together?

Brad

Thanks for the input guys. If I find out anything, I will post it here.

 

[norm j]

I WOULD BE LOOKING AT THE FUEL LINES AND TANK FOR LEAKS ALSO MAKE SHURE THE FUEL PICK UP TUBE IS ROUTED TO THE LEFT REAR OF THE TANK,I WOULD ALSO MAKE SHURE THAT YOU FILTER THE FUEL BEFORE, IT GOES INTO THE CARB AND I WOULD USE A DIFFERENT CARB,I USE THE K&B RED CARB ON MINE AND IT RUNS GREAT!

GOOD LUCK!

NORM J

 

[happybradboating]

I WOULD BE LOOKING AT THE FUEL LINES AND TANK FOR LEAKS ALSO MAKE SHURE THE FUEL PICK UP TUBE IS ROUTED TO THE LEFT REAR OF THE TANK,I WOULD ALSO MAKE SHURE THAT YOU FILTER THE FUEL BEFORE, IT GOES INTO THE CARB AND I WOULD USE A DIFFERENT CARB,I USE THE K&B RED CARB ON MINE AND IT RUNS GREAT!GOOD LUCK!

NORM J

Hey everyone.

The 7.5 Aerotech boat I am using with the 7.5 Rossi had a 7.5 K&B on it last year and it at least came up on step but wasn't real fast at the 2008 Nats. I have already checked my tanks and everything looks good.

Thanks for suggesting the K&B red carb, I was wondering if there would possibly be a better choice?! I assume it the 7.5cc Red carb?

Brad

 

[norm j]

THE RED CARB IS ACTUALLY MADE FOR A 40 SIZED ENG. I HAVE A AREOTECH HULL

AS WELL AND I'M SOMEWHERE AROUND 50MPH, WITH THIS SET UP,THERE ARE SOME BETTER SET UPS TO RUN OUT HERE BUT THIS IS WHAT I GOT GOING NOW,ITS VERY CONSISTANT AND SMOOTH RUNNING, ALSO, YOU MIGHT WANT TO RESTRICT THE WATER OUTLET ON THE COOLING JACKET,TO LET THE MOTOR HEAT UP SOME MORE,

THE OCTURA 447,547 AND 647 ARE GOOD PROPS FOR THAT BOAT,IF YOU HAVE THE SET UP INSTRUCTIONS FOR IT FOLLOW THEM AS DIRECTED AND YOU SHOULD BE GOOD

GOOD LUCK

NORM J

 

[LarryConrad]

THE RED CARB IS ACTUALLY MADE FOR A 40 SIZED ENG. I HAVE A AREOTECH HULLAS WELL AND I'M SOMEWHERE AROUND 50MPH, WITH THIS SET UP,THERE ARE SOME BETTER SET UPS TO RUN OUT HERE BUT THIS IS WHAT I GOT GOING NOW,ITS VERY CONSISTANT AND SMOOTH RUNNING, ALSO, YOU MIGHT WANT TO RESTRICT THE WATER OUTLET ON THE COOLING JACKET,TO LET THE MOTOR HEAT UP SOME MORE,

THE OCTURA 447,547 AND 647 ARE GOOD PROPS FOR THAT BOAT,IF YOU HAVE THE SET UP INSTRUCTIONS FOR IT FOLLOW THEM AS DIRECTED AND YOU SHOULD BE GOOD

GOOD LUCK

NORM J

The K&B red carb is a 3.5 carb.

 

[HTV Boats]

The red carb I believe came from K&B in a 45 inboard and 45 outboard. I have not seen it in any factory .21 from K&B's. Only as an aftermarket carb. Call it what you may but it has a .340 bore with a small spray nipple an it works very well in a .45 outboard. I have used them very succesfully in K&B's,Rossi's and currently on all our Nelsons. Simple easy to tune and a great heat race set-up. Now if your running straightaway trials only there may be faster carbs out there. My son and I have won many internat heats and trophy's in Charleston. Jay holds the D-tunnel US-1 with a "red carb". Rod Geraghty approved also.

Mic

 

[LarryConrad]

The red carb I believe came from K&B in a 45 inboard and 45 outboard. I have not seen it in any factory .21 from K&B's. Only as an aftermarket carb. Call it what you may but it has a .340 bore with a small spray nipple an it works very well in a .45 outboard. I have used them very succesfully in K&B's,Rossi's and currently on all our Nelsons. Simple easy to tune and a great heat race set-up. Now if your running straightaway trials only there may be faster carbs out there. My son and I have won many internat heats and trophy's in Charleston. Jay holds the D-tunnel US-1 with a "red carb". Rod Geraghty approved also.Mic

Hi Mic,

I was just going by K&B's parts listing on their web site,they list it as a 3.5 carb. I run one on my 7.5 Rossi with an adapter that Rod G. made. The two that I have are the same physical size as a 3.5 gold carb, and wouldn't fit any of my 7.5 K&B's without an adapter.

Larry

 

[Geraghty]

The K&B red carb is a 3.5 carb.

Larry,

The "Red" carb was never designed by K&B for use on any K&B 3.5 motor.

The "Red" carb was designed for the 7.5 inboard "disc rotor" motor.

The "Red" carb is a great 7.5 outboard carb. B)

MECOA has got it all screwed up.......

If you want a miserable day at the pond just put a K&B "Red" on a 3.5 O/B and try to run it :blink: ....Hint:Make sure your chase boat doesn't leak.

Rod Geraghty

 

[topfuel443]

If you want a miserable day at the pond just put a K&B "Red" on a 3.5 O/B and try to run it :blink: Rod Geraghty

Well said Rod!

~James

 

[HTV Boats]

Well that seems to cover the red carb so back to Don's original problem. Setting up a new engine combination on your tunnel if you can go with the same parameters as someone who has a good running setup on the same boat. Staring from scratch #1 stay with a light prop load until you feel your boat runs well enough to need stiffer. On a 45 OB a X447 should work. Next start with the propshaft centerline even on slightly above the plane across the bottom of the sponsons.

As for the engine your Rossi carb at .308 with a full spray bar will tune easier than a larger carb and is capable of 50 mph. Maybe dial the low speed full rich and just work with the high speed needle. Sounds like you have the correct head button and .015 should be good to start but I would go to .012 at some point. Head clearance is mechanical and measureable much like checking for air leaks and water flow. Once your confident those are good you need to work on the PIPE. Until you find a performance range on your pipe most "mods" are secondary. Exhaust timming will dictate your length somewhat but starting around 10 1/2 inches on a 45 and working in a 1/4 inch at a time till you don't see an improvement. I find when the engine runs well and turns good revs in a straightaway but lags out of a turn your a tad too sort. The pipe and head clearance will give you your greatest percentage of HP and until its right your other mods may get you going to down a lot of dead ends. Another thing I have seen is too large an outlet on a pipe that may not give enough back pressure and will be hard to tune. Shimming down the outlet you may find you pick up speed and reliability. Not like 454 that needs big breathing your working with a tunning system that need a fine balance over big flow. A shim can easily be removed if you go too far.Now you play with bigger carbs. Keep us posted on your progress.

Mic

 

[DonSoper]

Thanks for all the info. I'm sending the whole setup to Rod G. I will keep posting with progress.

 

[LarryConrad]

Thanks for straightening me out Rod! I should know better than to believe everything I read on the internet!

Don,

You have two of the best guys in the country helping you with your boat, Rod is a wizard when it comes to making motors run the way they should, and Mic knows what it takes to set up a tunnel to be fast and consistent, and he can drive!

 

[DonSoper]

Glad to hear it & I really appreciate all the help. Sending it out to Rod tomorrow.

 

[moparbarn]

sure not gonna argue with rod about the red carb being designed for a 3.5, BUT, it may have been added to one. mecoa's web site shows the watercooled 3.5 sx with a red carb now.........that is just a picture on a website, & a RECENT CHANGE. 3 or 4 months ago, it showed a gold carb.

 

[JSCARPINO]

I am about to give up on this brand new Rossi.....

I have been reading this thread and trying to get my tunnel to run....

but no success.

Anyone have a brand new Nelson or CMB they want to part with.

Joe

 

[HTV Boats]

I am about to give up on this brand new Rossi.....I have been reading this thread and trying to get my tunnel to run....

but no success.

Anyone have a brand new Nelson or CMB they want to part with.

Joe

Joe,

From what I see you have a Leecraft/Rossi45 with a silver bullet? Did you get Dave's head button from Hyperformance? Whats your head clearance,pipe lenght,what carb/fuel, and what prop? Not running at all or up to your race standards? A couple years back our first outing with a 45 Rossi yielded 39 MPH. Getting parameters in tune it went into the mid 50's.

A CMB is arguably the best 45 you can buy and not cheap. I am not a fan of the extra weight up that high but they have plenty of torque. The Nelson is fast right off the shelf and not all that expensive. No need to modify as timing is where it needs to be from the factory. John Otto or Gary Pruesse can set you up there. Not sure if Henry is selling his newest motor with carb but I would recomend asking for one that way.

Before you give up on the Rossi let the guys here know your specific problems so you get guided in the right direction.

Mic