Heavy Motoplat Flywheel - Spooky 400

[KJDonovan]

I saw the for sale post marsattacks had on the heavier motoplat flywheels and rather than glomming onto a for sale post I figured I would start another as I have some questions on these larger flywheels.

I am working on dialing in a 74 400 I picked up this spring and I have 2 questions; the first were these flywheels matched to the stators?  I ask because the bike came the heavy flywheel but the stator with it had lousy spark at low rpm's so I swapped out the stator and heavy flywheel with rebuilt stator and regular flywheel I had.  I would like to switch back to the larger flywheel but I have not sent off the stator that came with for rebuild yet.  So can I mix and match the heavy flywheel with any other same size motoplat stator?  
Next question, will the heavier flywheel make this bike a little less spooky?  I say spooky because this thing winds up quick which is great, but when I back off on the throttle it seems to take a second or two for it to respond and back off.   That's the spooky part that I don't care for.  Ideas?

Thanks,

Kevin

[SouthRider]

The flywheel is not matched to the stator.

As long as it fits the crankshaft end you are good to go. Make sure that you lap it in before installing, and it wouldn't hurt to put a dab of blue loctite on the shaft (not the threads).

Check the torque at least 3 times - initially, after warm up, and again after a 20 minute or so ride. Then check it after every ride. Those motors & that big flywheel can shake themselves loose if not properly set up.

The flywheel will tame the savage beast. A lot of riders will also slightly retard the timing, and slightly richen the jetting to turn that bike into a tractor with unbelievable torque - ride all day in 3rd or fourth gear type of torque.

It may be that your bike is surging a little, either from lean jetting or a small air leak. Sounds like a separate issue.

_____________________________________________________________________________________

"We the willing, led by the unknowing, are doing the impossible, for the ungrateful. We have done so much, for so long, with so little, that we are now qualified to do almost anything, with nothing."

1972 Penton Berkshire 100
1983 Husqvarna 250 XC
2011 Jayco 31.5 RLDS
2009 Chevy 2500 HD Duramax

[Kip Kern]

2.4 BTDC for the 400,  Have had mine for several years and no issues.  Send the stator and flywheel as a set along with the coil to be tested.  Dane used to re magnetize the flywheel for better spark.  Bosch W3AC plug at .022.  Have fun!

[KJDonovan]

Clark / Kip,

Thanks for the responses.  I will check for an air leak, plug tells me the jetting is on.  As for timing and correct plug I have that covered.  I will ping Jerry to see if he can re magnetize the heavy flywheel though as that's probably the weak spark at low rpm problem I was initially having.  I noticed when I set that big flywheel on the bench it did not really magnetize itself to the bench as strongly as most other motoplat flywheels do.

Thanks,

Kevin

[KJDonovan]

Just circling back on this as I was finally able to exorcise the spookiness from the 400 [:0].  The problem was new a slide I had just purchased from Bing.  At some point Bing stopped making the #1 38MM slides so Charlie had some made up by a local machine shop which fit a little snug.  

I didn't realize it when I originally posted this but after I rebuilt the carb with the new slide I snapped the throttle a few times and could hear the slide hitting the bottom.  What I didn't check (lesson learned ) was when I backed off the throttle slowly did the slide hit the bottom....not!  There was a 1 to 2 second delay before it fully seated.  Took a trials rider to find this issue, thanks Gord.  Anyway I called Bing and when I explained the problem Charlie stated that some of these homemade slides "may be a little out of round" and sent me a new heavier gauge spring that drops the slide like a guillotine!  That and a little steel wool on the high spots on the slide did the trick.  Just figured I would post this in case anyone else purchases one of these slides and runs into the same issue.

Thanks,

Kevin


Kevin J. Donovan
Foster, Rhode Island
72 Jack Piner
72 Six Day
74ish Mint 400
74 Hare Scrambler
71 Suzuki TS125
72 Montesa Cota 123

[SouthRider]

Great news Kevin - you'll be better off in the long run as Bing slides are notoriously soft.

After you get a few miles on it you will be able to return to the standard spring.

Are you still going to try the heavier flywheel?

_____________________________________________________________________________________

"We the willing, led by the unknowing, are doing the impossible, for the ungrateful. We have done so much, for so long, with so little, that we are now qualified to do almost anything, with nothing."

1972 Penton Berkshire 100
1983 Husqvarna 250 XC
2011 Jayco 31.5 RLDS
2009 Chevy 2500 HD Duramax

[KJDonovan]

Clark,

Yes, I will be going back to the heavy flywheel but I need to get it re-magnetized first.  I called Penton Imports, but they no longer offer this service so I will see if Vance Smith can do it for me.

Thanks,

Kevin

Kevin J. Donovan
Foster, Rhode Island
72 Jack Piner
72 Six Day
74ish Mint 400
74 Hare Scrambler
71 Suzuki TS125
72 Montesa Cota 123