Hi. New member to 400 grey bike, site looks really helpful.
I have recently purchased a 1991 NC29 and am turning into a track bike so i dont have to use my road bike.
i have a problems with the bike not reving past 8000rpm. Has anyone had this problem before? I have put in brand new plugs, new HT coils, checked all electrics and wiring and all checks out. Removed and cleaned the carbs, new o rings, checked jets standard jetting etc... all air screws set to 2.5 turns (has race pipe) fuel pump working, all connectors replaced.

I havent ballanced the carbs as I dont have any gauges and would prefer someone with greater knowledge to have a go. Last week I got the bike to start and idle fine, open the throttle and it warbles then runs smooth until 8000 ish. No smoke. Above this the power dies. Is it changing over onto the main jet??

It also revs higher not at full throttle as full throttle seems to over fuel it and it dies off. The plates within the carbs seem to worble. Iassuem this is a ballancing issue.

The bike pops, farts and backfires at first which would suggest air/mixture screws but I have tried every setting possible from fully in to fully out. Just at my wits end.
Apart from that the bike is amazing and is coming on really well. Cant wait to get her running and get on the track. I will post some photos as and when.

Hopefully someone will be able to help.

cheers Dangerman

Did you check compression before you bought the bike ?

havent checked the compression. seems to rev without problems to 8k. how can you check the compression?

cheers

dangerman13 wrote:havent checked the compression. seems to rev without problems to 8k. how can you check the compression?

cheers

There is only one way. You need such tool to do this - should be not expensive and recomended to have it to check condition of any bike. That generally what we do before buying any bike to check the condition of the engine. Or go to nearest service - they easy able to do this. If the compression is fine 10 - 11.1 by manual, check the fuel supply system. It's difficult to give advice never saw vehicle.

Did you saw bike rune over 8K ?

Thanks for the advice.

was not able to warm the bike up as it was just popping and farting. taking the cylinders as No 1-4 from left hand side as sitting on the bike. i removed the plugs and were as follows.
1 - looked normal
2 - didnt look to have been firing clean
3 - carboned up - asume mixture off
4 - slight black sign, connectoin to ht lead bent.

checked the spark from each coil with the good spark plug and all had good sparks.

tested the compression for each cylinders.
1- 150psi
2- 148psi
3- 150 psi
4- 148psi

the haynes manual lists PSI pressures between 1556-213. i assume that these are slightly lower due to not being able to warm her up properly.

put a drop of oil in each cylinder and the readings are as follows
1 - 220psi
2 - 275 psi
3 - 220 psi
4 - 270 psi

would this sugget new piston and rings?? i hope not. are these very pricey to have done through a garage. i dont think that my garage is the best site to carry this out for the first time and wit my limited tools.

can anyone recommend a good mechanic near leeds uk??

cheers Dangerman.

Sorted it.

Put a new set of plugs in. just checked the ht connection order before reattaching. previously i had thes on as i got them from the previous owner. LH coil 1 & 2 cylinder, RH coil 3 & 4. Checked the wiring diagram in the back of the manual and it details LH 1&4 LH coil 2&3.
Bike started straight away and ideld smooth. i had been told that with the type of carbs on the 400 they require a restricted air flow to enable the slides to mopperate correctly. Put the air filter back on and it worked like new.

revs through the full range. will get her on the track soon. hope this helps someone.

cheers Dangerman

dangerman13 wrote:
hope this helps someone.

cheers Dangerman

After reading through here and reading the bold above, I had a thought. It would be useful for future reference if thread titles were changed to add "solved" at the end, this would help people using the search function to find the answers they're looking for more easily.

May be something for us users to consider.

angry_rob wrote:After reading through here and reading the bold above, I had a thought. It would be useful for future reference if thread titles were changed to add "solved" at the end, this would help people using the search function to find the answers they're looking for more easily.

May be something for us users to consider.

I agree, but would also love the poster to actually add how he fixed it as theres nothing worse than following a thread only to have the poster to say something like "fixed it now, thanks" and you never find out what he/she done to fix it. Of course this does not apply to the above which was explained nicely.