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Discussion Starter #1
Alright all hear me out.

Back in my day of pit bikes and honda horizontal carbed motors, you could get a couple of degrees of advance by moving the CDI pickup forward (opposite) on the rotation of the flywheel.

On my grom i would like to RETARD timing a couple degrees to see if it helps pinging issue i get under a small window of load / rpm. From what i can tell if there is room i could move the pickup a bit with the rotation to retard the timing a bit. Do yall think that would work?


assuming a 6in diameter flywheel (which i think is probably too big) an 1/8th of an inch move of the pickup would net 2.3* of timing change. So it might very be possible to do it.


I do have to take off my stator cover to replace my cam chain tensioner so when im in there i will see if its going to be possible to move the pickup. What i really wanna know is if its going to change the ignition timing at all.
 

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It should... ha I have moved the pickup on my old crf50 engines too. I've not looked closely at the pickup on the Grom to see if it can be moved easily. Keep in mind it will also affect the timing of the fuel injection.
 

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Idk if it makes a difference but note the Groms fly doesn't have one big pickup, it has multiple small ones.. do the other marks provide information to the ecu for other things? Does it determine when the injector fires? If so then by regarding the pickup you would essentially retard the injector timing?

icould be way off, just thinking out loud since the only angle position sensor the engine has is the ignition pickup
 

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According to Finbro, there ecu is already about 3 degrees retarded timing from what stock would be. You really still have knock?
 

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Idk if it makes a difference but note the Groms fly doesn't have one big pickup, it has multiple small ones.. do the other marks provide information to the ecu for other things? Does it determine when the injector fires? If so then by regarding the pickup you would essentially retard the injector timing?

icould be way off, just thinking out loud since the only angle position sensor the engine has is the ignition pickup
^^^

Being EFI its a little diffrent than mag pickups/whatever. While I cant speak for the grom, as I have never examined it closely... Going off of Kohler EFI engines, Their blower/flywheel was toothed, and used a missing tooth (and hall sensor) to determine TDC (i think). Additionally if it was a 2 cylinder, could tell which stroke it was on when coupled with a MAP sensor.
Im making a metal idler gear setup, with some hardware coming in today, so maybe ill pull the cover off early and take a look at the flywheel to see how it actually is.


But basically, since its EFI, rotating it probably wont work, unless you were to move rotate the entire flywheel.
 

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Discussion Starter #7
the grom has the same sensor as like a CRF50 but yes it does have some extra little spots on the flywheel for more sensing of whatever.

But yes that would affect injector timing as well hmmmmmm.


It pings (or possibly piston slap) around 7k rpms under high load (going up a hill in 3rd or 4th) at 90+% throttle. Reason why i think its pinging is if i flip my cold start switch which alters injector opening it goes away.

It does not ping if i am on flat ground running through the rpms / gears.


Well when i get the stator off to do my cam chain tensioner ill have a look and see if its possible to move the pickup.
 

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the grom has the same sensor as like a CRF50 but yes it does have some extra little spots on the flywheel for more sensing of whatever.

But yes that would affect injector timing as well hmmmmmm.


It pings (or possibly piston slap) around 7k rpms under high load (going up a hill in 3rd or 4th) at 90+% throttle. Reason why i think its pinging is if i flip my cold start switch which alters injector opening it goes away.

It does not ping if i am on flat ground running through the rpms / gears.


Well when i get the stator off to do my cam chain tensioner ill have a look and see if its possible to move the pickup.
Do you have an AFR gauge on it? Maybe it is going lean.
 

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annnywayy. took the flywheel cover off, there are 9 raised spots, split by 30 degrees each (patterned for 12). Is it possible? Maybe, if you move the speed pickup. But how will that be accomplished? Its not like theres tons of room there to re-position the sensor.

If you wanted to make it easy, you could grind out the keyway on one side or the other, and then grind out the opposing side on the flywheel, along with a larger key to re-position it. Or you could grind just 1 out, and make an offset type woodruff key.


Orr... It turns out they already make these, without the need to increase the size of the slot. Not sure how small they go. ex https://www.summitracing.com/parts/mrg-988g?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-mr-gasket&gclid=Cj0KEQiA4JnCBRDQ5be3nKCPhpwBEiQAjwN1bgrZxq8inVF3W4fbwk6LTfvQvi_nk4rIxY-VA_miHBQaAqH88P8HAQ
 

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Serious question here...
What plug are you running in the bije currently? What fuel? And I assume by reading it's the finbro ECU?
 

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Discussion Starter #17
annnywayy. took the flywheel cover off, there are 9 raised spots, split by 30 degrees each (patterned for 12). Is it possible? Maybe, if you move the speed pickup. But how will that be accomplished? Its not like theres tons of room there to re-position the sensor.

If you wanted to make it easy, you could grind out the keyway on one side or the other, and then grind out the opposing side on the flywheel, along with a larger key to re-position it. Or you could grind just 1 out, and make an offset type woodruff key.


Orr... It turns out they already make these, without the need to increase the size of the slot. Not sure how small they go. ex https://www.summitracing.com/parts/mrg-988g?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-mr-gasket&gclid=Cj0KEQiA4JnCBRDQ5be3nKCPhpwBEiQAjwN1bgrZxq8inVF3W4fbwk6LTfvQvi_nk4rIxY-VA_miHBQaAqH88P8HAQ

Rather than moving the flywheel, id end up moving the pickup, accomplishes the same thing. like stated 1/8th of an inch move of the pick up is right around a 2.4* change in timing.



Running a 9 plug of the right style (forget the exact model, but stock model in a 9 heat rating - NGK) premium fuel, i literally take a 5 gallon jug to the gas station, fill the truck up with premium so the line is clear of regular (impossible to find a 3 handeled pump around here) then fill up my jug and use that to fill up the grom over the next month or so.
 

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You say 9 but there are two types of 9s boss. I run a non-projected tip because of this exact scenario and my aggressive timing curves. Projected tips will
Act is flame throwers and duplicate this scenario more times than not. CR9E is my current plug in a stock bore setup and many degrees advanced timing. I do watch the plug often and replace it frequently in heavy weather swings here in TX and time my bike accordingly. Colder drier air gets a few degrees retard to keep the piston happy.
 
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