Hi all, so I recently bought a Honda NC29 CBR400RR which doesn't start. Most of the bikes life was sitting in a garage with a few weekend rides here and there but since the last time the previous owner rode it (six months ago), it hasn't started ever since.

So I stripped the bike down, cleaned the air filter, fuel filter, the carbs, and the spark plugs, put in a new battery and removed the old gas and put in fresh gas in it and tried to start it. I engaged the choke and I can hear the engine trying to turn over and occasional sputtering, and a few really loud backfires from the exhaust. I also noticed the rpm goes up and then back down even though the engine hasn't actually turned over but now always, just did it two times if I recall correctly.

So I went out and bought some new NGK spark plugs and replaced the old ones. The bike still didn't start with the same symptoms happening. I tried to bump start it by not giving it any choke, just put it in second, some slight throttle and it started. However, the damn thing wouldn't idle and will just stall as soon as I let go of the throttle. Now it starts without any need for a moving start however it will always need a little bit of throttle to turn over. I started it again and left my hand pulling the throttle and let it sit around 3k revs as maybe I thought it just needed to warm up but it still stalled. I checked the manifold and discovered that two were hot, however the other two were just warm and you could even hold your hand to them for a few seconds.

Do you guys have any suggestions please? I'm thinking maybe the spark plug caps are in the wrong hole, as I left them as they were when I got them from the previous owner so I'm not sure if they're correct or not.

Perished "O" rings on the air fuel screws at the front of the carb underneath. That or they're blocked.

dunkenb wrote:Perished "O" rings on the air fuel screws at the front of the carb underneath. That or they're blocked.

Do you mean the carburetor drain screws?

On the side of the carb nearest the engine near where it goes into the inlet rubbers are the adjusters for the air/fuel ratio. Screw one all the way out and they have an o-ring on them. Also make sure they're all set as per the manual .
Hope that helps.

dunkenb wrote:On the side of the carb nearest the engine near where it goes into the inlet rubbers are the adjusters for the air/fuel ratio. Screw one all the way out and they have an o-ring on them. Also make sure they're all set as per the manual .
Hope that helps.

Ohh, you mean the carb synchronisation screws? Unfortunately I don't have vacuum gauges/calibrated tubes.

http://www.motorcycleinstitute.tk/honda ... s-lso.html The second picture shows the fuel/ air (pilot) screw

dunkenb wrote:http://www.motorcycleinstitute.tk/honda ... s-lso.html The second picture shows the fuel/ air (pilot) screw

Ah, so sorry that took me a while to understand. I'll check that out and see how it goes . Thanks for now :)

dunkenb wrote:http://www.motorcycleinstitute.tk/honda ... s-lso.html The second picture shows the fuel/ air (pilot) screw

So before I remove the carbs to adjust the screws, I tried to start it without the airbox to see if I notice anything unusual. I started the bike and ofcourse it stalled and when I started it again, I heard a pop and saw a tiny flame coming out of Carb 2 and this pipe popped out of the screw looking thing. Anybody has any idea what it is and it's use & the reason the carb pops?

http://imgur.com/a/MRG5R

It's where you attach the vacuum hoses to synch the carbs.

dunkenb wrote:It's where you attach the vacuum hoses to synch the carbs.

Oh nice, any reason on how it could shoot out like that?

So I checked the screws for the air/fuel adjustment and was pretty surprised at what I saw. One of the cylinders which wasn't working properly didn't even have an o-ring, and shockingly enough, one of the good cylinders had no washer or o-ring They were even set at just a 1/4 turn.