g9 jerking when starting

KFX700#319 · 02-13-2011, 08:51 PM

Sorry last post didn't work...here it is take a look shoot me some ideas...this is with a brand new battery

YouTube - 101 0399

yamahag9er · 02-13-2011, 09:14 PM

Did you run this motor at all before you did the exhaust valve? We had a cart in this past summer doing the exact same thing and it wasn't the starter or the battery. I'm drawing a blank at the moment as to what we found. To many carts not enough brain cells. It still seems like the valve timing is off.

Mike Mac · 02-13-2011, 10:02 PM

Oh, man I'm lost as well! I didn't know you had it apart! Is the head milled? could the valves be hitting the piston? These are the easy ones. Probably not happening, you'd hear it, but I'd have ta pull the plug, and look at the top of the piston for valve marks! Then, ya I would be looking at the flywheel next. Did you have it off?

When it does lite off, will it idle down? Or does it stall?

SteveRand · 02-13-2011, 10:26 PM

Just an educated guess here, but it seems like the spark might be too far advanced, igniting the mixture before the piston is at the top of the compression stroke. Your starter/generator is cranking fine.

Have you tried cranking it with the spark plug installed, but disconnected? I bet it cranks fine.

The flywheel key could be sheared, as you suspected. I'm not sure about the G9 ignitor, but my G2 has timing circuitry in it that might cause this if it goes bad. I don't think valve timing or adjustment would cause your problem.

Please keep us posted.

Mike Mac · 02-13-2011, 10:40 PM

Great idea Steve! Pull that wire, and wind er over!
I thought the same thing about the starter. Pull the jack on the TCI. (electric ignition) as an extra precaution.

Also, that kick back is killing that starter!

KFX700#319 · 02-14-2011, 12:17 PM

Come to think of it i dont think it did do it when i did compression test.....i am gonna pull wire and try it tonight and probably pull flywheel and check the key...hopefully that is problem.....thanks for all yhe input i will keep you all posted thanx....

sho305 · 02-14-2011, 01:31 PM

Yeah that looks like a bad ignitor or key. Ignitor is not cheap try to swap one to test. They advance the timing at higher rpm except really they don't, they retard it at low rpm. So if they still work and the advance goes bad it is advanced all the time. If it runs ok at high rpm and not good at low rpm, I would look at the ignition first. If it runs bad at high rpm too (no power/etc) I would look into cam timing/other valve event issues. See my tired G9 would do this sometimes when it got hot, but still starts its not that bad. I think its the ignitor going bad sometimes I can feel it change when running it at slow speeds....however I'm not sure. This spring I will swap it for the one out of the cart I put the clone into and find out before I pull my engine for good. Some carts will do this with a loose gen belt, but not that bad I don't think, that one is turning over pretty fast to stop that quick.

KFX700#319 · 02-14-2011, 06:23 PM

So i disconected the plug wire and it did not do it at all it turns over perfectly fine.....so bad igniter most likely or is sheared key more likely? Will i have to pull engine out to check the flywheel key or can it be done in the cart?.. WOULD A BAD COIL OR PLUG CAP CAUSE THIS AT ALL?

yamahag9er · 02-14-2011, 07:15 PM

If your igniter and coil and all of that worked fine before you installed this engine I would lean towards they are probably ok. Obviously there is a chance, but just playing the odds I would check the flywheel and key first before I started dumping money into ignition parts. Did you double and tripple check ALL of your wire connections. All wire ends/connections and especially grounds are huge on Yamahas. You said this motor had a bad exhaust valve but did it come out of this cart originally or did you get it to replace a motor that was in the cart? As far as checking the key with the motor in the cart I guess it would depend on how easily you can get the fly wheel off. Those motors are so easy to pull anyways it may end up being easyier just to yank it. If you pull the spark plug and check it for spark you could at least see if it has a good strong spark before you rip into the motor.

sho305 · 02-14-2011, 07:26 PM

You could try a new plug, but I doubt it, but its cheap enough to try. Bad plug usually hard start and cuts out. The flywheel is kind of different on these I doubt it sheared but who knows. If you get that side cover off its right there, actually the whole gas tank comes out really easy in these you should be able to get at it. I would check the plug on the ignitor, coil wires and ground, and wires in general though I doubt it would cause this, but wire problems are common you never know. The only way I could think to test the ignitor is put it in the freezer overnight, but that might not fix it.

But you could put a timing light on it and see if its advancing with rpm once you can see the flywheel.

02-13-2011, 09:14 PM	#22
yamahag9er Fry's Golf Carts Join Date: Dec 2006 Location: Central Michigan Posts: 857	Re: g9 jerking when starting Did you run this motor at all before you did the exhaust valve? We had a cart in this past summer doing the exact same thing and it wasn't the starter or the battery. I'm drawing a blank at the moment as to what we found. To many carts not enough brain cells. It still seems like the valve timing is off.

02-13-2011, 10:02 PM	#23
Mike Mac G8 Specialist Join Date: Jun 2009 Location: Phoenix Posts: 7,799	Re: g9 jerking when starting Oh, man I'm lost as well! I didn't know you had it apart! Is the head milled? could the valves be hitting the piston? These are the easy ones. Probably not happening, you'd hear it, but I'd have ta pull the plug, and look at the top of the piston for valve marks! Then, ya I would be looking at the flywheel next. Did you have it off? When it does lite off, will it idle down? Or does it stall?

02-13-2011, 10:26 PM	#24
SteveRand Yamahaulin' CC Rider Join Date: Jul 2010 Location: Altadena, CA Posts: 684	Re: g9 jerking when starting Just an educated guess here, but it seems like the spark might be too far advanced, igniting the mixture before the piston is at the top of the compression stroke. Your starter/generator is cranking fine. Have you tried cranking it with the spark plug installed, but disconnected? I bet it cranks fine. The flywheel key could be sheared, as you suspected. I'm not sure about the G9 ignitor, but my G2 has timing circuitry in it that might cause this if it goes bad. I don't think valve timing or adjustment would cause your problem. Please keep us posted.

02-13-2011, 10:40 PM	#25
Mike Mac G8 Specialist Join Date: Jun 2009 Location: Phoenix Posts: 7,799	Re: g9 jerking when starting Great idea Steve! Pull that wire, and wind er over! I thought the same thing about the starter. Pull the jack on the TCI. (electric ignition) as an extra precaution. Also, that kick back is killing that starter!

02-14-2011, 12:17 PM	#26
KFX700#319 Getting Wild Join Date: Jan 2011 Location: PARKER PA Posts: 105	Re: g9 jerking when starting Come to think of it i dont think it did do it when i did compression test.....i am gonna pull wire and try it tonight and probably pull flywheel and check the key...hopefully that is problem.....thanks for all yhe input i will keep you all posted thanx....

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02-14-2011, 01:31 PM	#27
sho305 Vegas modded 420 Join Date: Jun 2009 Location: West MI Posts: 15,445	Re: g9 jerking when starting Yeah that looks like a bad ignitor or key. Ignitor is not cheap try to swap one to test. They advance the timing at higher rpm except really they don't, they retard it at low rpm. So if they still work and the advance goes bad it is advanced all the time. If it runs ok at high rpm and not good at low rpm, I would look at the ignition first. If it runs bad at high rpm too (no power/etc) I would look into cam timing/other valve event issues. See my tired G9 would do this sometimes when it got hot, but still starts its not that bad. I think its the ignitor going bad sometimes I can feel it change when running it at slow speeds....however I'm not sure. This spring I will swap it for the one out of the cart I put the clone into and find out before I pull my engine for good. Some carts will do this with a loose gen belt, but not that bad I don't think, that one is turning over pretty fast to stop that quick.

02-14-2011, 06:23 PM	#28
KFX700#319 Getting Wild Join Date: Jan 2011 Location: PARKER PA Posts: 105	Re: g9 jerking when starting So i disconected the plug wire and it did not do it at all it turns over perfectly fine.....so bad igniter most likely or is sheared key more likely? Will i have to pull engine out to check the flywheel key or can it be done in the cart?.. WOULD A BAD COIL OR PLUG CAP CAUSE THIS AT ALL?

02-14-2011, 07:15 PM	#29
yamahag9er Fry's Golf Carts Join Date: Dec 2006 Location: Central Michigan Posts: 857	Re: g9 jerking when starting If your igniter and coil and all of that worked fine before you installed this engine I would lean towards they are probably ok. Obviously there is a chance, but just playing the odds I would check the flywheel and key first before I started dumping money into ignition parts. Did you double and tripple check ALL of your wire connections. All wire ends/connections and especially grounds are huge on Yamahas. You said this motor had a bad exhaust valve but did it come out of this cart originally or did you get it to replace a motor that was in the cart? As far as checking the key with the motor in the cart I guess it would depend on how easily you can get the fly wheel off. Those motors are so easy to pull anyways it may end up being easyier just to yank it. If you pull the spark plug and check it for spark you could at least see if it has a good strong spark before you rip into the motor.

02-14-2011, 07:26 PM	#30
sho305 Vegas modded 420 Join Date: Jun 2009 Location: West MI Posts: 15,445	Re: g9 jerking when starting You could try a new plug, but I doubt it, but its cheap enough to try. Bad plug usually hard start and cuts out. The flywheel is kind of different on these I doubt it sheared but who knows. If you get that side cover off its right there, actually the whole gas tank comes out really easy in these you should be able to get at it. I would check the plug on the ignitor, coil wires and ground, and wires in general though I doubt it would cause this, but wire problems are common you never know. The only way I could think to test the ignitor is put it in the freezer overnight, but that might not fix it. But you could put a timing light on it and see if its advancing with rpm once you can see the flywheel.

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