CMB 45 burning plugs

[fun4ej]

Howdy All,

I'm having some trouble with my cmb 45 burning a plug on every run. I'll try to give all the info that is relative to the matter.

I'm running the cmb .45 in a dumas skater hull, 40% nitro, OS-8 and MC-9 plugs, .023" of head shims (it also burned plugs with .012" of head shims.) and a prather 240 prop.

The motor runs really fat on the boat stand then sounds good for half a lap...then seems like it leans a bit on the top end but motor temps never are over 120deg. I'm running a remote needle valve not on a servo, the remote needle assembly is for an OS .46ax plane motor. The needle valve is as close to the carb as I can mount it...about 2" away, with standard size fuel tubing.

The plugs are silver to grey when the element breaks.

Any ideas on what might be going on or what I should do differently?

Thanks!

 

[Tom Foley]

Howdy All,
I'm having some trouble with my cmb 45 burning a plug on every run. I'll try to give all the info that is relative to the matter.

I'm running the cmb .45 in a dumas skater hull, 40% nitro, OS-8 and MC-9 plugs, .023" of head shims (it also burned plugs with .012" of head shims.) and a prather 240 prop.

The motor runs really fat on the boat stand then sounds good for half a lap...then seems like it leans a bit on the top end but motor temps never are over 120deg. I'm running a remote needle valve not on a servo, the remote needle assembly is for an OS .46ax plane motor. The needle valve is as close to the carb as I can mount it...about 2" away, with standard size fuel tubing.

The plugs are silver to grey when the element breaks.

Any ideas on what might be going on or what I should do differently?

Thanks!

What pipe are you using and how big is the stinger ID ? Too small an outlet will cause this to happen , post a pic of the plug and pipe .

 

[Chris Wood]

if this is a cmb 45 rs it sounds like the rotor clearence.. if it is two wide it will do the lean situation as described.

rotor clearence should be .001-.003

chris

 

[steve wood]

yep, rotor clearance, if it's an rs, and head volume is too small. engine acts fat because the rotor won't seal because there is too much clearance. you lean the motor, and zap, too lean and plug gone. head volume needs to be .38 cc. if it's an hr or purple head probably head volume. or bearings. how much nitro?

 

[Norm Doerr]

I have noticed that the rotor clearances are toooooo big. AND the rotor itself is MASSIVE. I am dealing with the same problem. I tightened the rotor clearance and it will pull a big prop BUT it will not rev up like a Picco and it will take a plug while trying

Norm Doerr

 

[Mike Byer]

You guys might be right about the clearance, but a 240 is just too much prop, it has 3.3" of pitch, I'd back up to an x445 or 447, at about 2.5" and work my way up.

mike b

 

[Duck899]

You guys might be right about the clearance, but a 240 is just too much prop, it has 3.3" of pitch, I'd back up to an x445 or 447, at about 2.5" and work my way up.mike b

Ditto on the prop..... One thing not mentioned is; Is this a new set-up or one that has always ran well before? The reason I ask is because if it worked before and now has gotten worse, then you might want to look at bearings.

A 45 cat will need about the same size prop as a 45 size mono. X-450 being about best. Prather 225-230. More load is heat and plug problems. What length is the pipe at? Too short and it will pull the plug and require lots more fuel. Long and lean vs short and fat.

 

[ALLAN YUEN]

which one RS (EVO) or Cam ( Hydro)for CMB45? look sound bad rear bearing cause too hot <_<

 

[Joe Warren]

I have noticed that the rotor clearances are toooooo big. AND the rotor itself is MASSIVE. I am dealing with the same problem. I tightened the rotor clearance and it will pull a big prop BUT it will not rev up like a Picco and it will take a plug while trying
Norm Doerr

Man says it won`t MEOOOOOOOOOOOOOW like a Picco 45........ Its a CMB......... It AINT going to..........

 

[Chris Wood]

lol and it won't blow up like a picco either

 

[fun4ej]

Ok, lots of replies, thanks!

-Tom, I'm not sure the brand of pipes I have run but here are a couple pics. The stinger I.D. of the longer pipe is .37" and .41" on the shorter pipe. The motor really liked the shorter pipe with the prather 240 but again, blew plugs and leaned on the top end even with the needle as rich as it would go.

-Mike, Really 240 is too big of a prop? I was thinking a 447 would be a bit small for this motor (I used to run a 447 on a .32 motor)

-Duck889, this is a new setup for me, I bought the motor and pipe from a guy that ran the same setup in a hydro(as for what props he ran, I don't know). The first prop I started with was a X648, then went to a x450, then down to a x646/3blade and it blew plugs on every prop. These props were used with the longer pipe.

Hmmm, so the bearings could be causing the prob....

Now, this is the biggest nitro motor I've owned and this "rotor clearance" you guys speak of I am not familiar with. The rotor is behind the carb correct? How do you measure and change it? And the head volume...what's the process to measure that? Is it a physical measurement or a mathematical volume calculation?

Thanks everyone! Just for poops and giggles, here's pics of the plugs and the remote needle

 

[shann harrison]

Sounding like a fuel delivery problem check your fuel tanks for leaks or broken brass tubing.,also check for pin holes in the fuel lines doesn't matter how new they seem to be,Check fuel filter for crap,the needle is an O.S which is the same as I run it is very touchy one click in either way will throw a flow meter a good tenth off,take it a part see if theres junk in it.check all bolts ,also check the gasket from what I see from the pictures on the plugs looks to me like shes sucking air somewheres seen this myself before specially from the black one But given the historyI have had with the purple head check the drive as well push & pull on the flex cable see if the flywheel moves alot in and out I have had this with my purple head which does mean the front bearing housing is screwed meaning New case.pipe is a little long 10.5 would be in range.That forty muck pipe would be the best pipe with a add on muff Just throwing my experience with my purple head which is now junk out there..head volume with these motors is to small.go through every nook and cranny. like everyone else mentioned check bearings for binding You'll find the problem...shann

 

[Buckshot]

Your motor has a drum valve and not a rotor disk.

Check fuel tank(s) for broken brass tubes and fuel lines for pin holes.

Check needle valve for trash as well as filter if equipped.

Bearings could be the problem. Do they feel smoooooooth?

-Buck-

 

[lundahl]

Hello.

That needle isent it a bit small for that engine? change it to a bigger one that can handle the fule amount the engine needs.

Fredrik.L

 

[Duck899]

Remove the fuel line from the carb and pinch the pressure line to the pipe. Blow in the fuel line from the carb. It must hold pressure. If this is ok, it may be a head volume or clearance problem (if the engine feels smooth in the bearings). You could add shims between the liner and head button for a quick fix. This will help with the plug issue but ultimately its probably a head volume issue.

 

[FloridaScaleBoater]

Duck, you method of pressurinzing the fuel system will only tell you if you have an external leak.

If one of the brass tubes inside the tank has a crack, it won't tell you that

Rick

 

[Mike Byer]

smaller prop and run it richer, that's kind of a heavy boat and needs a smaller prop than you would think.

mike b

 

[Dan_Cousin]

A couple of things to test or sure up.

1) With the tanks in the boat just like it is when running, pump your tanks full of fuel then draw the fuel out. Watch the fuel line going back to the pump as you pull the fuel out. There should be NO bubbles in the fuel line as you pull the fuel out until the tank is empty. If you see bubbles early woul have a tank plumbing leak (cracked tube)

2) take the tanks out and put a long (new) piece of fuel line on the vent side and plug the fuel side. Puch the tank underwater and blow into the vent side to put pressure inside the tank. There should be on bubbles form the tank.

3) I can't tell if you haven't already done so but add a tie wrap around that needle valve. Where it is, it will see lots of vibration and will spin if it is easily adjustable. it should be very hard to click when the tie wrap is set right.

4) You pipe length is very long for a 45 boat. Most 40 rigger are running close to 9" from plug to weld. Monos should not be too far longer that this. try 10.5" and prop accordingly.

5) That carb is going to sound rich on the shore since there is no low end needle. you'll have to keep working the throttle to keep it forn loading up on the beach. soo how rich you can run it before it stops getting on the pipe at all.

6) All of your plugs look like too lean and too much compression or load. Anytime the plug melts or moves its because there is too much heat being generated or held in the combustion chamber. You can cool this off by increasing the fuel, decreasing the compession (opening the head bubble) and reducing the prop.

7) set that motor for between .008 and .012" head clearance and forget it. Any adjustments should come from change the bubble. I'd start at .012 and get it running reliabily then drop the .008 and see if I can get it running reliably with the tigherter clearance nd higher compression (usually with more torque)

8) How old is your fuel? Moisture in old fuel can drive you nuts with this kind of stuff.

 

[tnrcboatracer]

It appears that the needle is plumbed backwards. It looks like the fuel line from the tank comes in the bottom and out the side. The fuel should flow down the needle from the fat end to the tip. Also, this motor is the CAM, not the RS. The RS has a disk rotor, the CAM a drum rotor, as previously mentioned. Another possiblity that was previously mentioned is bad bearings. Bad bearings allow the crank to break the oil seal at the front of the crank. If the bearing is too loose, the crank will hit the housing, and damage the seal bore, causing an air leak. If the crank has hit the seal bore, the case will need to be replaced or sleeved with a bushing.

 

[Duck899]

Duck, you method of pressurinzing the fuel system will only tell you if you have an external leak.If one of the brass tubes inside the tank has a crack, it won't tell you that

Rick

Sure...I know that.... Been there done that.... The best way to check for a crack in a tubing inside the tank is to fill the tanks and then reverse and empty them. If you cannot get all the fuel out, then you have a crack or broken tubing problem provided that the tanks were plumbed correctly in the first place. At the same time, by pressurizing the fuel system, its a quick way to check for leaks which may be causing a fuel draw problem and a lean condition that the original post suggests. Kinda hard to suggest any immediate remedy to the problem without being present to see the boat up close and in person.

What about a small 2 ounce sump tank? Are you drawing off a sump tank first so that it always remains full as your other tanks empty?