GN400 flat spot

littlehop · 09-06-2010, 11:55 PM

Hey all,
I've been working on this bike for a few weekends and its kick starting and running smoothly now, but at 4000 rpm it just drops off and almost dies. this occurs without a load and with a load on engine. So far the tank has been cleaned, carb completely gone through three times, adjusted valves which were spot on when checked. ?? There is alot of carbon on the piston face and I can see some on the exhaust valve. Not sure were to go from here.
Will the carbon build up cause this and can it be removed without disasambly?

littlehop · 09-14-2010, 12:39 AM

This bike is a suzuki gn400 1980-81 and I still havnt found a suitable air cleaner huosing, its just runnuning with a screen right now. Any recommendations on an aftermarket replacement instead of stock. Maybe this will help the problem.

Massoodk · 09-14-2010, 08:35 PM

Hey, i have a similar problem with my 1980 GN400. It struggles when getting to about 4,000 rpms and doesnt want to go any higher. If i hold the throttle open mine will also stuggle really bad and start to die out. I found some others with similar problems to ours and their problem was the CDI unit. Im still not positive what is going on with mine. Ill let you know if i found anything else out. Heres the link to the other forum.

http://www.totalmotorcycle.com/BBS/viewtopic.php?t=6714

O and im running a UNI Filter on mine instead of the stock air cleaner.

littlehop · 09-14-2010, 09:03 PM

Thanks Massoodk, I have a second cdi I'll try out and see if that changes anything. I have not seen many cdi's for this bike out there for sale, I wonder if another brand cdi could be subbed, say maybe a honda in the same class size? The voltage may be the biggest issue.

Massoodk · 09-14-2010, 09:33 PM

Yea, no problem. Let me know if it foxes your problem. I found two listed on ebay for like 100 and then the oem is nearly 300 off bikebandit.com.

littlehop · 09-14-2010, 09:48 PM

Yeah I saw the ebay ones but I'm nervous to spend that kind of money on electric parts that look just like the old ones I have, I'll be more likely to go stock on this part from bike bandit.

09-06-2010, 11:55 PM	#1
littlehop Verified Join Date: Aug 2010 Location: Port Townsend,Washington,USA Posts: 26	GN400 flat spot Hey all, I've been working on this bike for a few weekends and its kick starting and running smoothly now, but at 4000 rpm it just drops off and almost dies. this occurs without a load and with a load on engine. So far the tank has been cleaned, carb completely gone through three times, adjusted valves which were spot on when checked. ?? There is alot of carbon on the piston face and I can see some on the exhaust valve. Not sure were to go from here. Will the carbon build up cause this and can it be removed without disasambly?

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09-14-2010, 12:39 AM	#2
littlehop Verified Join Date: Aug 2010 Location: Port Townsend,Washington,USA Posts: 26	This bike is a suzuki gn400 1980-81 and I still havnt found a suitable air cleaner huosing, its just runnuning with a screen right now. Any recommendations on an aftermarket replacement instead of stock. Maybe this will help the problem.

09-14-2010, 08:35 PM	#3
Massoodk Verified Join Date: Jun 2010 Posts: 24	Hey, i have a similar problem with my 1980 GN400. It struggles when getting to about 4,000 rpms and doesnt want to go any higher. If i hold the throttle open mine will also stuggle really bad and start to die out. I found some others with similar problems to ours and their problem was the CDI unit. Im still not positive what is going on with mine. Ill let you know if i found anything else out. Heres the link to the other forum. http://www.totalmotorcycle.com/BBS/viewtopic.php?t=6714 O and im running a UNI Filter on mine instead of the stock air cleaner.

09-14-2010, 09:03 PM	#4
littlehop Verified Join Date: Aug 2010 Location: Port Townsend,Washington,USA Posts: 26	Thanks Massoodk, I have a second cdi I'll try out and see if that changes anything. I have not seen many cdi's for this bike out there for sale, I wonder if another brand cdi could be subbed, say maybe a honda in the same class size? The voltage may be the biggest issue.

09-14-2010, 09:33 PM	#5
Massoodk Verified Join Date: Jun 2010 Posts: 24	Yea, no problem. Let me know if it foxes your problem. I found two listed on ebay for like 100 and then the oem is nearly 300 off bikebandit.com.

09-14-2010, 09:48 PM	#6
littlehop Verified Join Date: Aug 2010 Location: Port Townsend,Washington,USA Posts: 26	Yeah I saw the ebay ones but I'm nervous to spend that kind of money on electric parts that look just like the old ones I have, I'll be more likely to go stock on this part from bike bandit.