Small problem with my 400

[shaunc]

Just got this 400 4 at Christmas and took it to a motorcycle dealers just to check it out.  They said it was running a bit rich and adjusted something.  Anyway since it's come back the engine seems to stutter as you rev it.  Once the revs are on it really runs well.  It just makes it a little difficult starting off as I have to have a few revs on slip the clutch a bit more.  Also going round roundabouts when you shut the revs off and want to put them back on again. Any thoughts what it could be?  Is it a normal Honda 400 thing?  Wondered whether it was something I could tinker with but I'm a bit of a novice.

Also, does anybody have any thoughts on repairing the bike seat?  Mine has a split along it.  It seems to be an original one with studs etc.  I know I can get it replaced but I'd rather keep this original slightly well-worn one if possible.

Shaun

[florence]

I am sorry but I do not know what is wrong with your carbs but it sounds like the garage haven't got it quite right.  Have the carbs set up again and then balanced, I would suggest.

With regard to the saddle, I always used to mend mine with gaffer tape but eventually the glue would melt and it would end up sticking to my trousers.  Another option I have tried is sewing, use thick cotton and don't go too near to the edges or it will pull out.  When I was a rather foolish young man I thought it sensible to cover my saddle with sheepskin; shocking in the rain. 

Nowadays, I just live with the splits and tears, it all adds character.

[shaunc]

Thanks Florence.  Think I will try and stick to my original seat as long as I can. You're right I think there's more character than in a new one. I had tried superglue and a strip of vinyl underneath to try and stop the padding showing through and it's lasted for 9 months.  I just wondered if there was any more permanent fix.

Regarding the engine it's not major, just a little annoying.  I may look into it some time when I feel up to it, but I haven't really got a clue what I'm doing.

Shaun

[K2-K6]

If the garage didn't take the carbs apart then I'd guess that it could be adjustment of the idle screw which is fairly simple to do, have you asked them what they changed?

The idle screw changes the very low rev mixture and can be felt at closed throttle and also very small amounts of throttle before the main jets get fully running when the carbs are opened more, this may tally with what you are feeling. If you try pulling the choke out slightly and the response improves then this indicates the motor needs to run slightly richer (more fuel added).

Idle screws are usaully set with a screwdriver and gently turned in until they stop (don't use much force to avoid any damage) then unscrewed one and a half to two turns out as a start setting. Further adjustment is normally in half turn increments, out giving more fuel and in giving less.

Post more questions if you need any further help.

[shaunc]

Hi K2-K6

That sounds like it.  I think they said it was running a bit rich and adjusted it.  This tallies with what my brother was saying about different jets in the carburettor.  He was wondering whether they'd got blocked and wanted me to take them apart and clean them.  But yes as soon as it gets over its little stutter the engine flies along.  One question though is how do I know if the mixture is right?  Do I have to take the spark plugs out and check them or just see if the engine is running right?  Sounds simple if I can get it right!!!

Thanks
Shaun

[K2-K6]

Hi Shaun

Yes general mixture check would be to get it properly warmed up and then check the plug colour, it should look like a slightly pale milk chocolate colour going whiter is too lean and likely to get too hot, going blacker would be too rich.

If it revs and runs ok at wider throttle opening then it seems like it's not far out as unless someone has previously changed them then it's probable that the jets are standard.

The size of the main jet controls max fuel demand, the needle progressively shuts this off to give less fuel as the throttle is closed toward lower speed.

In addition there is an idle circuit that is more accurate than the above to control the very slow running, hence the questions to try and isolate a particular area of the problem.

They should all work in a linear fashion from clsoe to full throttle but if one parameter has been shifted too much away from ideal you end up with a stepped feel as you've described.

The idle screws should be visible to you, one on each carb a small flat blade brass screw in a casting recess. they are not hard to adjust yourself.

[Yoshi823]

The tips of the idle mixture screws used to have a habit of getting coated with fuel residue...something to be aware of when attempting to get the tickover to idle correctly once the float heights had been properly set.

[shaunc]

Don't know what I've done now but I decided to have a go at adjusting the idle screw before I went out for a ride this afternoon.  I had a quick look in my Haynes manual for anything that looked like an idle screw but couldn't find anything.  I had a look at the right hand carburettor and saw a black plastic adjuster and something in a similar position on the inside carburettor but metal. Confident these were the idle screws I started to turn the outside one out by half a turn.  Unfortunately, I didn't get to unscrew it half a turn before it stopped.  I then noticed that this black cap had a little thing on it to stop it being turned too far.  Panicking I tried to turn it back to where I thought it came from.

I don't what it was I adjusted but it seems to have made the bike slightly better at picking up when the throttle's closed.   Do you think it is it the idle screw I've adjusted and how come I can't unscrew it any more?

Thanks
Shaun 

[PatM]

Shaun- sounds like the mixture screw for idle- the black cap comes off and you can remove the screw- that

[K2-K6]

The black cap you speak of is as far as I can tell is to limit the range over which you can adjust the screw.

The method "I think" is to set them up as PatM says and then you'd put the caps back on to effectively give you a small adjustment range that could be used to tweak them when out on a run without having to go and count turns etc again. I think this would be more relevant in coping with altitude to trim the low response just enough to improve running at extremes, don't think it's so useful in the flatlands of UK but central Europe and USA may be a more normal situation with big elevation shifts throughout a trip.

If you do them as PatM says you should be somewhere in the middle of their range and I would expect to see 1/2 turn in either direction to get it as you need if it still didn't feel quite right.

If you find that they need to be very far away from stock it would indicate that something else is influencing it.

[shaunc]

Well it is a left-hand drive Italian model so may be that explains it.    

Thanks for all your help.  I'll go and have a closer look now.

Shaun