BLOWING PLUGS!!!

[billy]

Im running a CMB purple head with Cooper quiet pipe in my .45 rigger and i can only get about 2 laps then i lose the plug (mcoy 9) i tried another head shim and im on the long side of the pipe measurement i think its about 10.5". The boat is running very rich still lose the plug and if i lean it out it will run about 1 lap and the plug is gone and when when i say i lose the plug i mean the element is totally gone. Can anyone tell me what i may be able to do more head clearance, shorten up the pipe etc...... getting very frustrated when the plug goes after 2 laps if im lucky and would like to straighten this out

thanks guys!!!

 

[shoboat]

Billy,

I would send your motor to Rod Geraghty or Steve Wood to measure

your bowl volume in cc's. I think you have other problems in your set up.

What pipe are you running? And what fuel & % are you riunning? What is

the head clearance right now in the motor? We could use some more information.

Thanks,

Mark Sholund

 

[Grimracer]

Try to get more water to the motor.

Grim

 

[Bert Dygert]

Billy,

Check the flow of the carb after the boat comes back in. You maybe picking junk up in the needle. Also what needle valve are you using you may not have enough volume of fuel to the motor?

Your head clearance should be around 0.010 -0.012 depending on fuel . Also take and break the edge of the bowl of the head where the squish band and the bowl meet. I use a razor knife and then polish with 400 sand paper. I've seen this problem with a parabolic 45 pipe.

Good Luck!!!

Bert

 

[DaveyK]

Billy,

I had the same problem with a CMB 45 last year. I was using the CMB needle valve which mounted directly onto the carb. As I eventually found out, the o ring seal on that needle had disintegrated and I had way too much air getting in. Blew the plug every time. Talk about frustration! Got it solved by the last race and then I had a good running boat (just took me 3/4 of the year to figure that one out).

Good luck,

Dave

 

[FCM Racing]

My 45 did the same thing replaced the bearings and the problem was gone

 

[Nitro]

Billy

Remove the head and visually inspect the piston and head button for damaged. As someone else already mentioned you might need bearings. I have had bearings shead crome which in turn gets to the combustion camber and takes out the plug.

Nitro Nub

 

[Ed Knudsen]

Billy'

I'm running a CMB .45 RS with Cooper pipe. 60% Otto nitro

* bearings going bad definetly could cause this but Typically when the bearings are bad the motor just won't run - may start -

may launch but won't rev up.

* head clearance = .010/.012

* pull the head per Nubs suggestion.

* if your running the CMB stock head bowl CC volumn should not be a cause for leaning out and blowing plugs

* Pipe lenght should not result in blown plug - run mine at about 9 1/2 (case center to pipe band weld)

* check all fuel lines, tank and the needle(s) for leaks.

* follow Daves suggestion about the needle valve "O" ring seal

* make sure your getting sufficient water thru the head though probably wouldn't blow the plug as you describe whats

happening.

* If you are running the "stock" CMB carb with the low end needle - GET RID OF IT! Take out the needle, cut off the tip

and screw it all the way back in. Make sure the "O" ring is okay. The low end needle causes more trouble then it helps.

Hope this helps

Ed

 

[Michael Costanzo]

hi, one last sugestion, if these are new style mccoy's,check that were the wire is welded to the bottom of the plug that it is not too long(sticking out passed the normal lenth),

spoke to my club pres and he told me he had the same problem. fixed the problem by gently filing the wire shorter to weld and problem solved. the plug was accually

shorting out. good luck,mike.

 

[Norm Doerr]

Everybody here has great suggestions. All which you should look at, in any order you like. The FIRST thing I would look at is the FUEL. Run fuel out of a differernt jug, batch.. whatever; eliminate that first. A long time ago I spent three weekends chasing the dragon on the same thing. The rest is a long story.

 

[taber]

I also had the exact same problem using the exact engine and pipe you have. I was using a 3rd ch needle which got ingested with dirt and caused engine to always lean out. Removed and cleaned it now it goes like hell. Pipe @ 9 1/4"[ ab parabolic] , a beautiful Mark Sholund 1457 prop and 50% nitro, timing 185 deg on exh and 135 on trans and boost.[you can locate this info on Dave Marles website [cmb specs for purple head 45 ect]also head clearance @ 11 thou.

 

[billy]

thanks for all the great suggestions guys as for the bearings they should be ok the i got the engine new and still havn't used a gallon yet, the problem with the plugs started the first time i threw the boat in the water i will try some of these things and hope to sort this out...

thanks again guys