g9 jerking when starting

KFX700#319 · 02-26-2011, 09:23 AM

what type of jets do these use? where is the best place to get them? with gutting the airbox what size of jets should I be looking for I know it will have a lot of different factors in it but where should I start?

Mike Mac · 02-26-2011, 10:08 AM

You jet according to altitude and well as engine modifications.

Before you start, tho. you need a good running car, meaning, you should take care of all maintenance bumper to bumper. Decide if you are gonna keep the stock filter box or go with an open element filter. Open filter will get dirty quicker, and may not perform as well in wet situations. I prefer the stock box and filter, so the only air the filter is exposed to, is the air the motor is gonna use.

I have K&N's on my sand rail, they perform poorly in rain, and "the only thing they stop is rocks and small birds"! But that motor is torn down every season or so. Open element filters will take out rings and valve guides in my experience, with an off road car. Street car, it will just take longer.

In your case, you need to make sure the 4 straps that hold the top on your filter box are gonna do the job, not the zip ties you have on it now.

Search "carb. jetting", there has been alot posted on this subject. Read and understand before you start.

I would enjoy your running car for a couple weeks before you tear into it again, (take that dog for a ride, she looks like she's ready)!! All the while, reading this site for maint. and mod. tricks, (old posts). Read the whole Yamaha site, you will learn tons!!

Your gonna have alot of fun here!! Mike

KFX700#319 · 02-26-2011, 12:13 PM

Thanks Mike yea I am gonna wait till spring to mess with the jetting and everything else...like body work and paint.. it really needs a nice paint job it is pretty ugly right now..lol....someone thought it would be a good idea to spray bomb it **** brown and dark green...trying to camo it?.. seat and all!!! but for now I am just gonna ride it as is..

sho305 · 02-26-2011, 12:26 PM

Glad you got it going, the airbox on these is not a very good design it can be a pain to get sealed.

I can point out one thing I took the silencer off my airbox, the part over the generator. Had to rejet for that and it made a small difference in power but not sure it was worth it or not. Racing another cart it seemed to make a very small difference. Since then I have removed other parts of the airbox and it made no difference. This seems to say that the silencer is the major restriction in the airbox from my experience. The noise difference is not that much. I used a torch tip cleaner to file the jet larger little by little and read the plug until it ran right. Its a little rich the plug is dark brown, but aircooled tend to run the best that way. When I took the rubber hose and baffle out of the airbox I checked the plug and it didn't get any lighter. The smallest part looks to be the exit from the air filter, but that is still larger than the inside of the carb IIRC, so I doubt the airbox itself is very restrictive without the silencer but I could be wrong. Another issue is I ran it with and without the airbox and I get very little power from the last 1/4 of carb opening. It seems like the carb is plenty large, it only seemed to help a tiny bit at top speed only maybe another mph or something. That means increasing intake flow is not going to do much anyway, but note I still have the stock muffler on it. I would guess at top speed the rpm is so far beyond the powerband of the cam, that is why it matters little, in addition to possibly the muffler. All in all I've seen nobody get much in power gains from intake and exhaust work, you have to mod the cam for sure and maybe compression and timing IDK. On the other hand its fun to play with you might get a little more from it.

Mike Mac · 02-26-2011, 12:45 PM

Sho, you and I are pretty close on this. I have done the same thing you have done, and have got the same results. My jet is at .042 I'm at 1200 feet ( but I take it to 6500') during the summer, and it does ok. My muffler is stock as well. No noise!

sho305 · 02-26-2011, 06:33 PM

I'm at about 850' there IIRC, and its relatively flat, some hills but they go back down. I didn't measure my jet in the stock G9, did some filing for sure. The clone I posted the jet size I had. I know with a stock G9 you can get the jet out lol. It runs good but not as good as the clone. I'll be looking forward to this summer with twice the power long as I don't run into another spree of appliances blowing apart on me...and taking over my fun fund.

YouTube - G9 16hp pull

Jitter Bug · 06-14-2012, 05:54 PM

Your starter brushes could be sticking or the battery may be going.

02-26-2011, 09:23 AM	#51
KFX700#319 Getting Wild Join Date: Jan 2011 Location: PARKER PA Posts: 105	Re: g9 jerking when starting what type of jets do these use? where is the best place to get them? with gutting the airbox what size of jets should I be looking for I know it will have a lot of different factors in it but where should I start?

02-26-2011, 10:08 AM	#52
Mike Mac G8 Specialist Join Date: Jun 2009 Location: Phoenix Posts: 7,799	Re: g9 jerking when starting You jet according to altitude and well as engine modifications. Before you start, tho. you need a good running car, meaning, you should take care of all maintenance bumper to bumper. Decide if you are gonna keep the stock filter box or go with an open element filter. Open filter will get dirty quicker, and may not perform as well in wet situations. I prefer the stock box and filter, so the only air the filter is exposed to, is the air the motor is gonna use. I have K&N's on my sand rail, they perform poorly in rain, and "the only thing they stop is rocks and small birds"! But that motor is torn down every season or so. Open element filters will take out rings and valve guides in my experience, with an off road car. Street car, it will just take longer. In your case, you need to make sure the 4 straps that hold the top on your filter box are gonna do the job, not the zip ties you have on it now. Search "carb. jetting", there has been alot posted on this subject. Read and understand before you start. I would enjoy your running car for a couple weeks before you tear into it again, (take that dog for a ride, she looks like she's ready)!! All the while, reading this site for maint. and mod. tricks, (old posts). Read the whole Yamaha site, you will learn tons!! Your gonna have alot of fun here!! Mike

02-26-2011, 12:13 PM	#53
KFX700#319 Getting Wild Join Date: Jan 2011 Location: PARKER PA Posts: 105	Re: g9 jerking when starting Thanks Mike yea I am gonna wait till spring to mess with the jetting and everything else...like body work and paint.. it really needs a nice paint job it is pretty ugly right now..lol....someone thought it would be a good idea to spray bomb it **** brown and dark green...trying to camo it?.. seat and all!!! but for now I am just gonna ride it as is..

02-26-2011, 12:26 PM	#54
sho305 Vegas modded 420 Join Date: Jun 2009 Location: West MI Posts: 15,443	Re: g9 jerking when starting Glad you got it going, the airbox on these is not a very good design it can be a pain to get sealed. I can point out one thing I took the silencer off my airbox, the part over the generator. Had to rejet for that and it made a small difference in power but not sure it was worth it or not. Racing another cart it seemed to make a very small difference. Since then I have removed other parts of the airbox and it made no difference. This seems to say that the silencer is the major restriction in the airbox from my experience. The noise difference is not that much. I used a torch tip cleaner to file the jet larger little by little and read the plug until it ran right. Its a little rich the plug is dark brown, but aircooled tend to run the best that way. When I took the rubber hose and baffle out of the airbox I checked the plug and it didn't get any lighter. The smallest part looks to be the exit from the air filter, but that is still larger than the inside of the carb IIRC, so I doubt the airbox itself is very restrictive without the silencer but I could be wrong. Another issue is I ran it with and without the airbox and I get very little power from the last 1/4 of carb opening. It seems like the carb is plenty large, it only seemed to help a tiny bit at top speed only maybe another mph or something. That means increasing intake flow is not going to do much anyway, but note I still have the stock muffler on it. I would guess at top speed the rpm is so far beyond the powerband of the cam, that is why it matters little, in addition to possibly the muffler. All in all I've seen nobody get much in power gains from intake and exhaust work, you have to mod the cam for sure and maybe compression and timing IDK. On the other hand its fun to play with you might get a little more from it.

02-26-2011, 12:45 PM	#55
Mike Mac G8 Specialist Join Date: Jun 2009 Location: Phoenix Posts: 7,799	Re: g9 jerking when starting Sho, you and I are pretty close on this. I have done the same thing you have done, and have got the same results. My jet is at .042 I'm at 1200 feet ( but I take it to 6500') during the summer, and it does ok. My muffler is stock as well. No noise!

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06-14-2012, 05:54 PM	#57
Jitter Bug Not Yet Wild Join Date: Jun 2012 Location: Cape Cod , MA & Englewood, FL Posts: 8	Re: g9 jerking when starting Your starter brushes could be sticking or the battery may be going.

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