Running issue

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Samuel Hagan JR

Well-Known Member
Joined
Jul 18, 2010
Messages
4,567
I've noticed that after about 5 laps my boat picks up speed and runs good and continues to pick up speed throughout the race.

The first 5 laps it's crap.

Any ideas?

Motor is a VAC 45

Pipe is a CMB Nitro at 10"

Fuel is 50 percent

Plug is ODO 003 Blue

Prop is a 450/2 and does it on others.
 
I've noticed that after about 5 laps my boat picks up speed and runs good and continues to pick up speed throughout the race.

The first 5 laps it's crap.

Any ideas?

Motor is a VAC 45

Pipe is a CMB Nitro at 10"

Fuel is 50 percent

Plug is ODO 003 Blue

Prop is a 450/2 and does it on others.
Samuel

I have seen this happen on a lot of boats over the years when the tanks are separated, one left, one right or one tank lower than the other, suggest U just run 1 tank and run the boat resetting the needle until U get a nice clean sound from the engine and the ad the other tank back into the system with the same needle setting and see what happens, also have seen a few cases of this happening with bad bearings.

JM2CW

Mobydickk
 
That happens in all set ups using large carbs and high nitro, even with a single tank. What you have seen is caused by two things.

#1. The engine is taking a few laps to come up to temp, which helps the fuel burn better.

#2. Tank "head pressure" is reduced over the course of the run. This means continuously less fuel delivery to the carb as the tank empties, meaning the mixture is getting leaner as the run progresses.

There are a few ways to deal with this. Maybe someone will chime in with those details.
 
I've noticed that after about 5 laps my boat picks up speed and runs good and continues to pick up speed throughout the race.

The first 5 laps it's crap.

Any ideas?

Motor is a VAC 45

Pipe is a CMB Nitro at 10"

Fuel is 50 percent

Plug is ODO 003 Blue

Prop is a 450/2 and does it on others.
Samuel

I have seen this happen on a lot of boats over the years when the tanks are separated, one left, one right or one tank lower than the other, suggest U just run 1 tank and run the boat resetting the needle until U get a nice clean sound from the engine and the ad the other tank back into the system with the same needle setting and see what happens, also have seen a few cases of this happening with bad bearings.

JM2CW

Mobydickk
I do have a 2 tank setup.
 
Samuel,

What size fuel line are using and Also brass tube size in the cross over lines in the fuel tanks??? Are the fuel tanks the same ounce size???

Bert Dygert
 
If you have two tanks run two 5/32" fuel transfer (feed) lines form tank 1 to tank 2 . This makes it easier for the pressure to move fuel from one tank to the other . I have also wondered if using a larger dia. pressure fitting would help deliver a little more push to keep the fuel transferring easier . Andy , Dick ?
 
If you have two tanks run two 5/32" fuel transfer (feed) lines form tank 1 to tank 2 . This makes it easier for the pressure to move fuel from one tank to the other . I have also wondered if using a larger dia. pressure fitting would help deliver a little more push to keep the fuel transferring easier . Andy , Dick ?
In our tank systems "Head pressure" has a real effect. The mixture WILL get leaner as the tank empties. No exceptions!

A full tank will exert more pressure at the needle than a 1/4 full tank, regardless of the location of the tank, HIGH , LOW, FORWARD, BACK. The changing head pressure, will ALWAYS change the flow.

A two tank system will go leaner as the first tank empties. Once the first tank empties the mixture will instantly go richer and then gradually go leaner again as the second tank empties. The size of the cross over lines will effect how much richer the engine will run once the first tank empties. The reason is because fuel is moving through the cross over lines when both tanks are full. Once one tank is empty, then only air is moving through the cross over line. And air moves much easier than fuel. The larger cross over line will reduce the amount of change once the the first tank empties.

This is very noticeable if two equal tanks are used and a good portion of the run is made on the second tank. The best situation is to have one Large tank that will not empty during the run and a small header/surge tank, then this instant richness will not happen until very late in the run. I mention this as a matter of record only.

I don't think it is part of Samuel's problem.

Samuel, I would say that your speed gain is caused by the engine/pipe temp increase and head pressure reduction during the course of the run. This happens in every boat. Some a lesser change, some more change. I suspect you are running one large tank and one small tank, correct?

Now that I explained the WHY, maybe someone can give ideas on how Samuel can improve the situation. This is obviously a Sport 45 hydro.
 
I think Andy's got it.

Are you running full water cooling?
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I think Andy's got it.

Are you running full water cooling?
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10thou_004.jpg
Terry is asking the right question. If it takes 5 laps to come up to temp, then it has too much cooling. It should take two laps at most. One lap at full throttle would be best.
 
A little tangent to Samuel's specific problem, but I have always wondered about trying an IV bag (like gas boats) to solve the air problem and a Perry pump instead of pipe pressure. It seems like a problem with this might be that once you had the needle set for top end, you would get too much fuel at lower speeds, unless you used the low speed needle feature. Any thoughts?

Here is what the Perrry Pump does:

The VP-30 regulating pump is capable of performing like no other fuel delivery system. It delivers an ideal .25 PSI to any model carburetor from a .15 to a 3.0 cu.in. engine. The pressure remains constant throughout the entire speed range, making the carburetor adjustment easy and simple. Once the needle valve is adjusted, the mixture will not vary regardless of how low the fuel or the attitude of the airplane, thus eliminating rich/lean runs altogether.
 
I've noticed that after about 5 laps my boat picks up speed and runs good and continues to pick up speed throughout the race.

The first 5 laps it's crap.

Any ideas?

Motor is a VAC 45

Pipe is a CMB Nitro at 10"

Fuel is 50 percent

Plug is ODO 003 Blue

Prop is a 450/2 and does it on others.
Have you tried changing plugs to a say an OD 99 (289 now I think ) ,
 
Fuel tanks are 8oz on both sides.

5/32 transfer lines until the it gets to the needle.

After the initial 3 to 5 laps the boat runs fine. Picks up a little speed. I've been noticing it more when I test by myself. During the last few races I've noticed it.

After the race the exhaust pipe seems unusually hot to me but could be normal. My water lines are pretty small. Not sure on the size.

The tanks where custom made by Walt Barney.

I don't have a transfer problem it's just the initial 3 to 5 laps.

I have tried the ODO 89 and 88 and the motor does not like them.

Yes Sport 40
 
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Fuel tanks are 8oz on both sides.

5/32 transfer lines until the it gets to the needle.

After the initial 3 to 5 laps the boat runs fine. Picks up a little speed. I've been noticing it more when I test by myself. During the last few races I've noticed it.

After the race the exhaust pipe seems unusually hot to me but could be normal. My water lines are pretty small. Not sure on the size.

The tanks where custom made by Walt Barney.

I don't have a transfer problem it's just the initial 3 to 5 laps.

I have tried the ODO 89 and 88 and the motor does not like them.

Yes Sport 40
The OD 003 is a hotter plug than the 88 an 89? If so, that would further indicate the engine (head) is too cold. Use one of the many methods to restrict water flow until the engine comes up to speed sooner. Be aware that you may very well need to richen the needle. It would be a good idea to do that as soon as you restrict the water. If it is too rich, you can always lean it, but normally the hotter head will burn the rich mixture which will in turn give more power. If it then pulls the prop easier, shorten the pipe and richen the needle a little more when you do that. In the end you should have a faster boat that gets up to full speed within one or two laps.
 
OD99 work really nice in my 45RS.

May be it is time we take note to the guys over seas and try a float controlled hoper tank.

This will maintain a even head pressure in the fuel system in front of the needle.

I started to make a setup for my 1.01 to get a handle on the fuel delivery problems with my new pipe.

The only thing that stopped me was the room in the rigger for the tank.

I know that Jack Sinclair uses no pressure to the tank with his Scale boat and that thing rocks................................no hopper just pulls of the main tank.

Use the pipe pressure to the main tanks to feed the float tank and pull from that with the needle.

You may have to make adjustments to the spray bar size to get a good vacuum and flow relation ship on high nitro.

Not a easy solution but with testing it should pay off.
 
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I'm more then sure it's not a pressure issue or a tank issue.

I'm going to restrict the water line and see what it does.
 
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