CMB 28.5 Evo Help

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Steven Kinney

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Anyone have knowledge with the timing?
I have a new 28.5 Evo in my 1:6 scale Hydroplane.
I ran it this weekend for the first time on the water. It ran great for a couple of laps then started to die. I pulled the plug and it had burnt the electrode out of the plug. Figured it was a timing issue. The directions say to line up the make on the crank with the line on the stator but you can’t. I have the stator cocked all the way to the left but it still won’t line up. I know you want the timing advanced but I am not sure how much.
I sent Stu an email just wanted to see if anyone on here might have some insight how the timing and needle setting. I not sure about either. Thanks
 

Buckshot

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The lines on the flywheel and ignition should line up when the piston is 1.2mm - 1.3mm BEFORE TOP DEAD CENTER.
 

rhomodel

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Could also be a lean issue, or pipe too short. Usually if timing is off due to sheared pin it won't run at all...
 

Buckshot

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And like others have said, it must be ran extremely rich and with at least 18% oil or it will die very quickly. If you burned the plug electrode you should probably check the big end rod bearing, just a suggestion from previous personal experience.
 

Wasted wages

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If it burnt the electrode off, I think more advanced timing would be the last thing you would want...
 

Steven Kinney

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Anyone have pipe length and needle setting to start out with? I have the needles richened up a 1:4 of a turn right now.
 

rhomodel

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Not sure what carb you have, length I would do minimum of 13; would even start at 13 1/2 and then start shortening Mauro always say boaters do 3 things wrong with his engines: Pipe too short, too lean and prop too large.. So prop might be another suspect You have any color on your plug or is the ceramic element as white as when it came out of the package?
 

Steven Kinney

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The plug was actually black. I don’t think it was to lean I think I had the timing to far advanced. I believe I had a 6716 or 15 prop on it. Pipe is at 13.5”.
 

rhomodel

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That indeed sounds like you have the rest set well: black sparkplug indicates it's not too lean, the pipelenght also sounds good, prop a bit on the large side but that shouldn't damage the sparkplug so much it burns. So I have to say that indeed timing would be the next thing to look at, though initially I dismissed that.
 

Steven Kinney

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Just so I am clear I am measuring the pipe length from the center of the plug to the weld on the pipe correct?
 

rhomodel

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I measure from exhaust port, so if you do like you do add about an inch.. Have you measured your ignition timing already? I can post a picture how the flywheel - ignition markings should look like with 1.5 mm before TDC measurement. Usually too short a pipe will only make the engine stall or bog, not burn a sparkplug.... You have any detonation marks in the ignition dome or top of cilinder?
 

Steven Kinney

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I just reset the timing to 1.3 before TDC.
If you can post a picture I would appreciate it.
Pulled the head to look at the cylinder everything looks fine.
My pipe length might have been a little short but the boat ran great so I don’t think that had much of an effect.
What kind of boat are you running your engine in?
 

rhomodel

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Good stuff: what I see in your picture is the primary coil is moved out to the max: I would turn it back to the middle position. Though I have no CMB Alpha I am the Dutch dealer of BZM, but also run SG and these have similar ignition systems. As a rule of thumb I advice my customers (but that is what I also run myself) 1.5 mm before TDC. 1.3 I think is too late. I run the engines in rigger and FSR 27 and 35 offshore: not sure you have those last 2 classes, might be called marathon. Heats are 8 minutes, most laps win. Final 12 minutes most lap win.
As I'm in Europe the scene here is small and at races you meet al the guru's, including the SG, CMB and BZM guys.
 

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Steven Kinney

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Sep 25, 2019
Messages
116
That picture was just to show you how far off it was at TDC. I set it to 1.3 mm and moved my pipe out a little. I will fire it up tomorrow and see how it runs if everything seems good I will take if you the pond and give it another go. Thanks
 

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