Scale quits running

[Neil Boyle]

Hi I'm trying to get my nitro scale boat running without quitting and I would love to get some suggestions. I have 67 MAC, stock carb, Andy Brown Pipe at 11 1/2" (center of cylinder to weld), 86 Squire Shop that weighs about 18lbs., two tanks, 5/32" tubes in tanks, 5/32" large fuel line through out. Here's the problem- Boat will not keep running more than about 3-4 laps and then dies like it gets very lean. The tank closest to the carb is still full the 2nd tank is about half full when it dies. I have replaced the entire fuel system, tanks, lines, etc several times. I have a OS 9B carb that I was thinking about bolting on to maybe solve my problem. The OS 9B will bolt on but I'm not sure if it will work well given the difference in diameter in carb throats: OS carb throat is smaller than the MAC engine intake. Will that cause me other problems? Does anyone haveany experience using a OS 9B carb on a MAC? I am new to boating (and to this international waters - this is my first post ever)and have been working on this problem for quite some time -about 5 months now. Any help would be appreciated. Thanks!

I forgot to mention that I am running a 1455 prop in 60 degree salt water - in the San Diego pond. By the way, thanks for the replies that I already received! It helps me alot. Neil

 

[DickJones]

Hi I'm trying to get my nitro scale boat running without quitting and I would love to get some suggestions. I have 67 MAC, stock carb, Andy Brown Pipe at 11 1/2" (center of cylinder to weld), 86 Squire Shop that weighs about 18lbs., two tanks, 5/32" tubes in tanks, 5/32" large fuel line through out. Here's the problem- Boat will not keep running more than about 3-4 laps and then dies like it gets very lean. The tank closest to the carb is still full the 2nd tank is about half full when it dies. I have replaced the entire fuel system, tanks, lines, etc several times. I have a OS 9B carb that I was thinking about bolting on to maybe solve my problem. The OS 9B will bolt on but I'm not sure if it will work well given the difference in diameter in carb throats: OS carb throat is smaller than the MAC engine intake. Will that cause me other problems? Does anyone haveany experience using a OS 9B carb on a MAC? I am new to boating (and to this international waters - this is my first post ever)and have been working on this problem for quite some time -about 5 months now. Any help would be appreciated. Thanks!

U have a PM

 

[Grimracer]

99.9% sure its water in the carb...

Try some foam blocks (like gun case foam) under or around the carb area..

Grim

 

[P THOMAS]

How about set the pipe at 12-12 1/2 and use a x455/3 prop. Macs dont like 18lb boat if overprop or pipe is too short. The 9b carb work fine on the Mac67, may help you too.

 

[Mike McKnight]

It could be water in the carb but this sounds more like a loss of pressure problem which is common on a multiple tank system. Especially if it is dying after the same number of laps each time. I use a three tank system and have had issues similar to this in the past. What type of tanks are they and how do you have them mounted?

 

[Neil Boyle]

It could be water in the carb but this sounds more like a loss of pressure problem which is common on a multiple tank system. Especially if it is dying after the same number of laps each time. I use a three tank system and have had issues similar to this in the past. What type of tanks are they and how do you have them mounted?

I have two Sullivan 10 ounce Flex Slant tanks mounted into the interior of the hull, forward of the carb (but not interfering with air flow). The hull was built to accommidate the two tanks, but is limited in dimensions - the 10oz flex tanks fit snug, but need to be flex in order to get them in and out of the hull.

 

[Ted buckley]

99.9% sure its water in the carb...

Try some foam blocks (like gun case foam) under or around the carb area..

Grim

I agree with Grim, I used to have a Wing-ding Hydro a long time ago, and everytime I did 3-4 laps it would die. Rear mounted Carb. close to the bottom of the hull.. Water would collect in there and start to dance - due to the vibration.. Put a peice of soft foam underneath the carb throat - problem solved.

 

[u60]

Hi I'm trying to get my nitro scale boat running without quitting and I would love to get some suggestions. I have 67 MAC, stock carb, Andy Brown Pipe at 11 1/2" (center of cylinder to weld), 86 Squire Shop that weighs about 18lbs., two tanks, 5/32" tubes in tanks, 5/32" large fuel line through out. Here's the problem- Boat will not keep running more than about 3-4 laps and then dies like it gets very lean. The tank closest to the carb is still full the 2nd tank is about half full when it dies. I have replaced the entire fuel system, tanks, lines, etc several times. I have a OS 9B carb that I was thinking about bolting on to maybe solve my problem. The OS 9B will bolt on but I'm not sure if it will work well given the difference in diameter in carb throats: OS carb throat is smaller than the MAC engine intake. Will that cause me other problems? Does anyone haveany experience using a OS 9B carb on a MAC? I am new to boating (and to this international waters - this is my first post ever)and have been working on this problem for quite some time -about 5 months now. Any help would be appreciated. Thanks!

I forgot to mention that I am running a 1455 prop in 60 degree salt water - in the San Diego pond. By the way, thanks for the replies that I already received! It helps me alot. Neil

 

You are running the pressure line from the pipe to the tank, correct? If so, and you don;t have any leaks in the fuel system it could be sucking in some water. I would check for leaks in fuel system, if that's good try the foam under the carb. The OS9B carbs work well by the way. They provide fine adjustment on the low end and high end needle.

 

Fred

 

[Rokieboater]

What's the plug look like when you get it back? If the plug is good chances are its not starving for fuel or going lean. You can try running it on one tank and see if you get more laps out of it. Try one tank at a time individually and see if it changes any results.

Let us know what your findings are.

Robert

 

[SayMikey]

Get a 90 degree ruber from the hobby shop for. It put it on the carb inlet pointing straight up. If that don't help. Try new engine bearings

 

[Grimracer]

I put a rubber ding dong who ha on the carby and it STILL took on water.. I could not find it for almost a full season of racing.. then one day AH HA.. water on the plug.. after a full year of racing it finally showed a drop on the plug.. Installed the foam and its never done it again..

Frustrating as H E double toothpicks

BTY.. its a direct mimic of what you are saying.. it would NEVER finish 4 or 5 laps..

Grim

 

[Neil Boyle]

I put a rubber ding dong who ha on the carby and it STILL took on water.. I could not find it for almost a full season of racing.. then one day AH HA.. water on the plug.. after a full year of racing it finally showed a drop on the plug.. Installed the foam and its never done it again..

Frustrating as H E double toothpicks

BTY.. its a direct mimic of what you are saying.. it would NEVER finish 4 or 5 laps..

Grim

To Grim and everyone, I'm am going to try all of your suggestions: more leak testing, soft foam under the carb, OS 9B carb, lenghten the pipe, test with one tank at a time. Thank you very much for the suggestions - I really appreciate it! I will let you know what I find out. Neil

 

[DON MAHER]

I would say Grim is on it with the water thing. Pressure test the complete water system. One small leak can put a large amount of water in the boat in 2-3 laps,

Don

 

[P THOMAS]

I would say Grim is on it with the water thing. Pressure test the complete water system. One small leak can put a large amount of water in the boat in 2-3 laps,

Don

In addition to the water lines leaking, check the strut opening thru the hull and seal it up with clay or silicone sealer, a lot of water can be shooting into the engine well and killing the motor after a few laps.

 

[Dan Kramer]

might also check cooling water as it may not be getting enough and getting hot .

could also be loss of pipe pressure causing a lack of fuel.

read plug , it will tell a lot .

 

[Ken Hildreth]

Well, water sucking from a mac with its carb sticking at the angle it does is a lot less likely than the cmb I run, You said you run multiple tanks, I still think it could be pressure, I know Phils mac loves fuel. Your lines are large all the way to the carb, What pipe are you running? How big is your pressure outlet? Just like everyone else. I would really like to see that plug after a run, it will tell a lot, usually, a motor that sucks water, even a little, will have problems starting the next run. A motor with lack of pressure will just start once it gets fuel to the carb again. Hope this helps, Ken

 

[Mike McKnight]

After re-reading this I am convinced more than ever this is a pressure problem. First you are using a MAC with an elevated carb throat. It's possible you may be getting water if the strut isn't sealed or of you have another leak where water is under pressure coming in. The water issue would be more likely if you were using a CMB with a 9B. But you mentioned you are using Flex Tanks and they are fitting snug and you have to flex them to get them in and out. I used flex tanks in the first scale I ever had and got rid of them. If you are having to flex them to get them in you are creating a problem right there with your pressure. Switch them out for the solid white tanks. I've even had pressure problems with the white tanks fitting in too snug. The boat would quit as soon as I transferred from one tank to the other even though I had a surge tank. I had to relieve outside pressure on the tanks and make sure they were not being squeezed in any way. The other thing was that I bored out my pressure fitting and used a medium line from the pipe to the first tank in the system (a suggestion from Mark Grim that worked well).

Another thing to look out for is your vent tubes in each tank. You may have a sudden shut off in fuel if the end of the tube inside the tank gets blocked by a flexing sidewall of the tank. Just make sure you angle the tips so that they cannot be easily occluded. It's been known to happen using the slant ovals.

 

[Dougwk]

I have to agree with many of these suggestions. I have seen water filling the hull with water shooting up from the strut opening! I have never had luck with flex tanks, as soon as I went to the sullivan hard plastic the problem was solved, also protect the carb as much as you can with foam.

After re-reading this I am convinced more than ever this is a pressure problem. First you are using a MAC with an elevated carb throat. It's possible you may be getting water if the strut isn't sealed or of you have another leak where water is under pressure coming in. The water issue would be more likely if you were using a CMB with a 9B. But you mentioned you are using Flex Tanks and they are fitting snug and you have to flex them to get them in and out. I used flex tanks in the first scale I ever had and got rid of them. If you are having to flex them to get them in you are creating a problem right there with your pressure. Switch them out for the solid white tanks. I've even had pressure problems with the white tanks fitting in too snug. The boat would quit as soon as I transferred from one tank to the other even though I had a surge tank. I had to relieve outside pressure on the tanks and make sure they were not being squeezed in any way. The other thing was that I bored out my pressure fitting and used a medium line from the pipe to the first tank in the system (a suggestion from Mark Grim that worked well).

Another thing to look out for is your vent tubes in each tank. You may have a sudden shut off in fuel if the end of the tube inside the tank gets blocked by a flexing sidewall of the tank. Just make sure you angle the tips so that they cannot be easily occluded. It's been known to happen using the slant ovals.

 

[Pat Bristol]

I agree it's most likely a fuel tank issue.

Just throwing this out there, on rare occasions I have seen scale boats get starved for air at the carb, after 3 or 4 laps they die. then during a run the cowl comes off and the boat takes off and runs fine. Also make sure your not pinching a water or fuel line when placing the cowl on the boat.

 

[moe1117]

Hi I'm trying to get my nitro scale boat running without quitting and I would love to get some suggestions. I have 67 MAC, stock carb, Andy Brown Pipe at 11 1/2" (center of cylinder to weld), 86 Squire Shop that weighs about 18lbs., two tanks, 5/32" tubes in tanks, 5/32" large fuel line through out. Here's the problem- Boat will not keep running more than about 3-4 laps and then dies like it gets very lean. The tank closest to the carb is still full the 2nd tank is about half full when it dies. I have replaced the entire fuel system, tanks, lines, etc several times. I have a OS 9B carb that I was thinking about bolting on to maybe solve my problem. The OS 9B will bolt on but I'm not sure if it will work well given the difference in diameter in carb throats: OS carb throat is smaller than the MAC engine intake. Will that cause me other problems? Does anyone haveany experience using a OS 9B carb on a MAC? I am new to boating (and to this international waters - this is my first post ever)and have been working on this problem for quite some time -about 5 months now. Any help would be appreciated. Thanks!

I forgot to mention that I am running a 1455 prop in 60 degree salt water - in the San Diego pond. By the way, thanks for the replies that I already received! It helps me alot. Neil

Neil, Welcome to modle boating and IW, Just a thought as with all the other great suggestions. How is your fuel pick-up situated using the flex tanks and with them being snug as mentioed you could be sucking the tank down to the pick-up and leaning out Just a thought

Mark