Sounds rich....blows plug

Trying to resolve a problem with my daughter's scale boat. We've been fighting the same problem at the last 2 races. At the pond tonight, she was just doing laps at half throttle and there was lots of smoke in the air which made me think it's rich. Then it dies after 4 laps with a blown plug. Tried it again...same thing. We're using 50% fuel in a CMB 67 with new bearings and using a CMB black belly 67/80 pipe at 11 3/4" (c/l engine to weld on pipe). We've also tried different fuels and the results are the same.

We tried a different engine and although it still seemed to 4 cycle, it didn't quit nor did it blow a plug. All I can come up with is that the first engine is leaning out but I can't find out where.

Anyone got some ideas???

Mike Hallam said:

Trying to resolve a problem with my daughter's scale boat. We've been fighting the same problem at the last 2 races. At the pond tonight, she was just doing laps at half throttle and there was lots of smoke in the air which made me think it's rich. Then it dies after 4 laps with a blown plug. Tried it again...same thing. We're using 50% fuel in a CMB 67 with new bearings and using a CMB black belly 67/80 pipe at 11 3/4" (c/l engine to weld on pipe). We've also tried different fuels and the results are the same.We tried a different engine and although it still seemed to 4 cycle, it didn't quit nor did it blow a plug. All I can come up with is that the first engine is leaning out but I can't find out where.

Anyone got some ideas???

Click to expand...

Mike Are you burning the wire or blowing the seal ? ERNIE

I'm blowing the coil, not the seal.

Mike Hallam said:

Trying to resolve a problem with my daughter's scale boat. We've been fighting the same problem at the last 2 races. At the pond tonight, she was just doing laps at half throttle and there was lots of smoke in the air which made me think it's rich. Then it dies after 4 laps with a blown plug. Tried it again...same thing. We're using 50% fuel in a CMB 67 with new bearings and using a CMB black belly 67/80 pipe at 11 3/4" (c/l engine to weld on pipe). We've also tried different fuels and the results are the same.We tried a different engine and although it still seemed to 4 cycle, it didn't quit nor did it blow a plug. All I can come up with is that the first engine is leaning out but I can't find out where.

Anyone got some ideas???

Click to expand...

Bet the motor is hott try to prop down and lessen the load. Whats the squish band at? make it close to .020

We are only testing with a X457/2. Head clearance is at .013. Think that's too tight??

Mike Hallam said:

We are only testing with a X457/2. Head clearance is at .013. Think that's too tight??

Click to expand...

Is it hot there? id open it up some and just fot giggles try a x455 and see if it helps. Here its 100 and humid as all get out

Mike, You may actually not have enough load on the motor by running a small prop, therefore leaning the needle till it blows the plug. With a proper load it may clean out under more load. The other issue maybe the volume of the head. Gary

What is the head space of the engine that does not blow plugs? Head button CC, squish band the same? Sound like detonation or shake could be blowing the element.

Head buttons on both engines are the same. Volume is 64 in the button. I think the total is 72 when you include the dish in the top of the piston.

We were getting lots of rpm's so I also thought that loading the engine with a larger prop might help. I'll try that tomorrow.

The additional load may help or fix it, but it does not explain why the other engine does not blow plugs. Are the squish bands and head clearance the same?

Mike put the head clearance .018 .020 and pull the coil out a bit on the plug. It sounds like the first engine runs rich on the low end and lean on the top end. I would also decrease the size of the stinger so that you could get a little more fuel pressure.

Nick

I know head clearances are the same but I'll have to check the squish bands.

An angled squish band is typically easier on plugs than a square squish band. The difference in squish bands has a very noticeable affect on shake.

Mike Hallam said:

Trying to resolve a problem with my daughter's scale boat. We've been fighting the same problem at the last 2 races. At the pond tonight, she was just doing laps at half throttle and there was lots of smoke in the air which made me think it's rich. Then it dies after 4 laps with a blown plug. Tried it again...same thing. We're using 50% fuel in a CMB 67 with new bearings and using a CMB black belly 67/80 pipe at 11 3/4" (c/l engine to weld on pipe). We've also tried different fuels and the results are the same.We tried a different engine and although it still seemed to 4 cycle, it didn't quit nor did it blow a plug. All I can come up with is that the first engine is leaning out but I can't find out where.

Anyone got some ideas???

Click to expand...

Head Volume too large? Squish clearence too high? If the plug is dark brown or black around the outer ring, Too much load......too hot. Burning the oil in the fuel...... Got to get rid of some of the load. If it is clean? hardley any color & it sounds rich & is boiling the element either the head volume to excessive or the squish band is excessive. Too much total vloume.... excessive total volume will require you to pinch the wire right of the plug trying to get the engine to clean out, & it will take the element before it ever cleans out on the stinger or on your ear..... These type problems the ring will have hardly no color & the element will look like you were pinching the needle to death.... The wire tells all...... The wire is the fuel Mixture. the color of the ring on the plug is the load. Have you tried a different pipe if all of this is correct?? Throw a long 13cc pipe on it to see if all changes. After you know the engine is right. If all else fails.......... Put a Picco in it...... You know it will run then ..... jw. p.s that paticular pipe you are running comes with a tiny stinger too.... if the engine is right ????I would 1st put a different pipe on it......

That big belly pipe needs some fine tuning to work right. In outriggers, the pipe would really haul but would lean out at the end of the straights. There were several solutions such as drilling 1/8" holed in the converget cone near the stinger to relieve pressure.

I'm sure the Woods can chine in on this.

I tried the CMB big belly pipe on my scale boats a few years back. When you get everything just right it is fast BUT was a pain in the you know what to keep consistent & the needle range of adjustment from too lean to too rich was about 3 or 4 clicks total. It is not really a good pipe for a heavier boat like a scale, very unforgiving and a bigger prop is only going to make it worse. :blink: The 13cc pipe like Joe suggested is a good choice, that one always worked for us. Start at about 12" with a X457/3 and keep shortening the pipe until it falls off in the corners then go back out 1/8" or so, you'll probably wind up about 11 1/4" to 11 1/2". What carb is on the motor? We always run the OS 9B on the CMB's in the scales.

Anyone not happy with there CMB Fay Belly pipes.

Believe they are not a good scale boat pipe!

You can send them my way, I'll take them off you hands!!!

Rick Bellinger

Mike:

I can't understand why people would tell you to raise the squish clearance????

If you do that, you are in effect reducing the Horsepower/Torque output of the engine and it will have to work harder to pull ANY prop. The squish should be about where you are or even lower .012" and the engine will produce all of it's available power.

Jow Warren has MANY great tips that you can study to find which one will help you. If you don't have enough pressure to the tank via the pipe pressure fitting, you will not have adequate fuel flow at any speed. Reducing the stinger like he suggests might be all you need. If you have a prop that is loading the engine a lot, it could be the problem. Another thing that you might overlook is that on 1/8 Scale boats, it is necessary to have some shaft angle to help the prop lift the back of the boat. If you are not running as much as possible (without the boat hopping) you are missing a ton of performance.

The only reason that you are blowing plugs is that you are not getting enough cooling via fuel to the engine. Look at your fuel delivery system FIRST.

If you will send me the specs for the engine, I will check to see what the SQUISH VELOCITY is and tell you the exact squish clearance the you need to get you where you need to be.

DON'T raise the squish clearance....

Marty Davis

I'll have to go with Marty on this one..............check the fuel system out. Check to make sure that the pressure fitting in the pipe isn't stopped up. I've seen these stopped up with oil from sitting for a period of time and you'll be lucky to get 4 laps before it quits. Listen to the Scale guys about the fat pipe, too.

Dick Tyndall

And the bearings ?? Are they still okay ?