Shilohsam: Good luck with the CDI- I'm intersted to hear how it turns out.
Roads up here in Maine are salty, sandy and wet, and slushy. I last rode two days before the Thanksgiving holiday. I hope it's better where you are!
CDI problems?
Installed the CDI unit. Easily revs. to 8000rpm now. Runs strong 80mph against a head wind 90mph calm or tailwind. Still playing with the Mikuni vm carburator . Get good plug readings with a 250 main jet and the slide needle adjusted next to the leanest setting. The slide cutaway that controlls the 1/8 to 1/4 position seems too rich it has a #2.5 cutaway . It probably needs a #3 or #3.5 . I have file cut the #2.5 to alter it to a larger cutaway so I would not have to purchase a $40 slide with good results. Do you know what number slide cutaway you have in your carburator . I believe you also have instaled a VM on your bike. Thanks for your comments about the CDI , they pointed me in the righr direction.
VM Carb
- I've got a mikuni VM carb on my bike. I measured the bore of the intake on the motor and ordered the closest size for the fit (can't say I knew what I was doing!) from bike-bandit. I got a round slide VM 36mm bore. I installed it the way it came. I don't know how to rejet it- except maybe to move the clip up and down the long jet needle that's hooked to the cable. You know more than I do for that. Standard with mine is #310 main jet, #35 pilot jet, N/J #159, T/V 2.5, AJ 2.0, NV 3.3
It runs well for me so I haven't played with the carb except to clean it. The old cv carb was one solid piece, and of course I soaked it in carb cleaner before reading that you should keep the carb cleaner off the rubber diapraghms- I gave up and got the VM.
Check out Sudco on the web- they have a bunch of info and charts, and specs for the VM carb- and every part for it- and diagrams.
What size is your VM. I think that changes the jet settings- so no two carbs are alike unless they are the same bore.
Good luck- I'm learning from you on this one. Maybe there are some guys on this site who've done this!
Keep me posted.
...I'm thinking of replacing the fork oil this spring- front shocks are a little bouncy!
It runs well for me so I haven't played with the carb except to clean it. The old cv carb was one solid piece, and of course I soaked it in carb cleaner before reading that you should keep the carb cleaner off the rubber diapraghms- I gave up and got the VM.
Check out Sudco on the web- they have a bunch of info and charts, and specs for the VM carb- and every part for it- and diagrams.
What size is your VM. I think that changes the jet settings- so no two carbs are alike unless they are the same bore.
Good luck- I'm learning from you on this one. Maybe there are some guys on this site who've done this!
Keep me posted.
...I'm thinking of replacing the fork oil this spring- front shocks are a little bouncy!
I also got my carburator at Sudco. 36 mm is the right size for the GN 400. However the standard carburator that they sell is jetted for the adverage engine that the 36 mm might go on. Many of the 36mm size go on larger motorcycles , Harley sporters etc. which draw much more air flow than the GN 400. I had mine special jetted for the GN 400 by Sudco. They said they had never jetted one for the GN before but could get it closer than the standard jetting based on engine size and other data. They set it up with a #240 main jet in place of the #310 and replaced the #35 pilot jet with a # 40. They left the #2.5 slide in ( this really needed to be changed and has cause me problems) We have had some 40 to 50 degree days here so I have been able to take so high speed run and do some tuneing. I have change to a #250 main jet dropped the slide needle one down from the top( leaner) changed the pilot jet to a #30 ( leaner) and most important I had to increase the cutaway on the slide by hand fileing quite a bit to lean out the !/8 to 1/4 throttle position. It is probably a #3.5 slide now??
The #40 pilot jet and the 2.5 slide was way to rich causing poor performance high fuel comsumpton in the idle to 1/8 throttle range which is the 30 to 45 mph county road city speed for my bike.
It is now running very clean and crisp set up this way Foam air cleaner, Less restrictive muffler than stock, Vm carb. with #250 main jet, #30 pilot jet, Probably about a#3.5 slide cutaway. New CDI unit.
The #310 standard main jet would seem to be way to rich for this bike however the main jet only comes in to full play at 3/4 to FUll throttle positions and you would not notice it in normaly ridding . However the #2.5 slide cutaway was way to rich for my bike and was the major problem. This causes problems in the idle to 1/4 throttle positon which is used most of the time. It caused my bike to be jerkey when accelerating in the slow ranged and I was only getting about 40MPG when this bike shoule get 55- 70 MPG
If your bike is running fine I would leave it alone but if you notice any of the jetting problem mentioned above I hope this is of help
l
The #40 pilot jet and the 2.5 slide was way to rich causing poor performance high fuel comsumpton in the idle to 1/8 throttle range which is the 30 to 45 mph county road city speed for my bike.
It is now running very clean and crisp set up this way Foam air cleaner, Less restrictive muffler than stock, Vm carb. with #250 main jet, #30 pilot jet, Probably about a#3.5 slide cutaway. New CDI unit.
The #310 standard main jet would seem to be way to rich for this bike however the main jet only comes in to full play at 3/4 to FUll throttle positions and you would not notice it in normaly ridding . However the #2.5 slide cutaway was way to rich for my bike and was the major problem. This causes problems in the idle to 1/4 throttle positon which is used most of the time. It caused my bike to be jerkey when accelerating in the slow ranged and I was only getting about 40MPG when this bike shoule get 55- 70 MPG
If your bike is running fine I would leave it alone but if you notice any of the jetting problem mentioned above I hope this is of help
l
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Masssoodk
- Rookie
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- Joined: Tue Sep 14, 2010 1:06 pm
- Real Name: Massood
- Sex: Male
- Years Riding: 0
- My Motorcycle: 1980 Suzuki GN400
Re: CDI problems?
Hey All,
Im having the same problem on my 1980 GN400. It doesnt want to go above 4,000 rpms, but runs decently well at lower rpms. It has never shut off on me while cruising around or anything like that, but when a open up the throttle it tends to kinda bog down and begins to struggle around the 4,000 rpm mark. I noticed the others did some preliminary checking before changing out the CDI. What should i look for before spending the nearly $300 on a new CDI unit? Should i even bother checking other stuff seeing that this was the problem for two others already? Any info will be greatly appreciated. Also, sorry for posting in your thread but i figured this was the best place for some good knowledgeable info.
thanks,
Massood
Im having the same problem on my 1980 GN400. It doesnt want to go above 4,000 rpms, but runs decently well at lower rpms. It has never shut off on me while cruising around or anything like that, but when a open up the throttle it tends to kinda bog down and begins to struggle around the 4,000 rpm mark. I noticed the others did some preliminary checking before changing out the CDI. What should i look for before spending the nearly $300 on a new CDI unit? Should i even bother checking other stuff seeing that this was the problem for two others already? Any info will be greatly appreciated. Also, sorry for posting in your thread but i figured this was the best place for some good knowledgeable info.
thanks,
Massood
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BuzZz
- Site Supporter - Platinum
- Posts: 4726
- Joined: Sat Mar 20, 2004 12:02 am
- Real Name: Never Used Here
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- Years Riding: 47
- My Motorcycle: makes my 'nads tingle
- Location: Buttfluck Nowhere, Manitoba
Re: CDI problems?
Hey Massood.
Your problem sounds more fuel related than spark. I'd check the mainjets for correct size or plugging, as well, make sure the airfilter is clean.
Your problem sounds more fuel related than spark. I'd check the mainjets for correct size or plugging, as well, make sure the airfilter is clean.
No Witnesses.... 
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Masssoodk
- Rookie
- Posts: 2
- Joined: Tue Sep 14, 2010 1:06 pm
- Real Name: Massood
- Sex: Male
- Years Riding: 0
- My Motorcycle: 1980 Suzuki GN400
Re: CDI problems?
Hey, okay ill check it out. Regarding the main jets, is there a DIY manual anywhere on this forum? I have basic knowledge and can work off directions but i dont really want to start messing around with stuff without a sense of direction. What is the correct size and plugging? Also, im running an aftermarket UNI filter which i just installed not too long ago.
Thanks,
Massood
Thanks,
Massood
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BuzZz
- Site Supporter - Platinum
- Posts: 4726
- Joined: Sat Mar 20, 2004 12:02 am
- Real Name: Never Used Here
- Sex: Male
- Years Riding: 47
- My Motorcycle: makes my 'nads tingle
- Location: Buttfluck Nowhere, Manitoba
Re: CDI problems?
The correct jet size will depend on the elevation and temperature at your location. Re-jetting is a matter of knowledgeable guesswork and fine tuning, so you may want to have a shop or mechanic do it for you. If that's the problem.
If the bike sat for an extended period, it could have gummed up or deposited varnish in the carb, effectively reducing the jet's size. Or the needle could be worn, or it could have worn the jet orifice.
A new pod filter could be flowing more air than the stock one did, and would require a larger mainjet to compensate.
If the bike sat for an extended period, it could have gummed up or deposited varnish in the carb, effectively reducing the jet's size. Or the needle could be worn, or it could have worn the jet orifice.
A new pod filter could be flowing more air than the stock one did, and would require a larger mainjet to compensate.
No Witnesses....