NC29 used to start on 3 cylinders - now won't start at all!

Bonzo · Post by **Bonzo** » Mon Jun 25, 2012 11:14 pm

Hello people. My Nc29 has always struggled to start from cold. It used to start on 3 cylinders and after about 10 seconds or so, clear its throat and fire on 4.

Until this morning! It started on 3 as usual but never cleared its throat and just cut out. No amount of gentle revving would make it fire on all 4. I tried restarting but it just wouldn't have it. It turns over fine, but just won't fire - you do get the odd chug every now and then though so it is trying.

A few weeks ago I decided to take a thermometer to the downpipes when it was running on 3 to find out which one wasn't firing. The far right one as you sit on it was a lot colder than the others. So tonight I get home from work and set about changing the plugs for a spare set I have.

First one I change is the suspect cylinder one. I thought I'd see if it would start - but no - still the same. I whipped the plug back out and it was nice and wet with fuel so I figured that it can't be a fuelling problem. I then checked to see how good the spark was - rubbish! Just a little orangey spark every now and again when turning over the engine.

My first thought is a dodgy coil or bad earth on the coil. The spark on the number 3 cylinder which is fed by the other coil seemed fine - nice and blue.

Any thoughts? Other than checking all connections? I'm a little peed off as it's my birthday tomorrow and fancied going for a birthday blat!

dunkenb · Post by **dunkenb** » Tue Jun 26, 2012 2:21 pm

My 29 was the same, was shit inthe tiny air inlets on the front of the carb , the four small brass ones by the in let trumpet. Try blowing them out with compressed air . Mine were real bad so i attached a small pipe to it and let carb cleaner soak in to it over night . Next day blew through with air. Run spot on ever since.

(Also if you've sprayed wd40 on a carb don't try using a steam cleaner on em after, it turns the wd40 into jelly which blocks everything up) i learned the hard way lol

gullarm · Post by **gullarm** » Tue Jun 26, 2012 10:04 pm

Bad lead and/or coil cap.

The coil fires two plugs at the same time so if one plug fires fine then other must be the lead/cap.

On mine I had 1 bad lead and 1 bad coil cap.

Or it could be a crap plug theres new and theres new!

I would be tempted to get all the plugs out and get them firing on top of the engine to see whats going on with all of them. Do it in the dark to get best effect.

Bonzo · Post by **Bonzo** » Wed Jun 27, 2012 10:27 pm

Thanks for the replies people.

Gonna spend the weekend (depending on the weather) going over the electrics/fuel system with a fine toothcomb and a multimeter, but not a steam cleaner

Bonzo · Post by **Bonzo** » Sat Jun 30, 2012 7:48 pm

Ok - I've removed the coils and cleaned all the contacts up and checked them with a multimeter. They are both within the readings in the Haynes manual.

One question - the fuel pump pulses as soon as I hit the starter button, but that's it. I can hold the starter button for about 10 seconds and it only pulses once. If I release the button and then press it again - still no more pulses. The only way to get it to pulse again is to switch the ignition off and then on again. Should it not pulse more often than this?

I'm going to check the pump and relay tomorrow as per Mr Haynes' instructions. I'm sure I read on here somewhere that the relay effects the spark as well as the fuel pump?

willpisme · Post by **willpisme** » Mon Jul 02, 2012 4:58 pm

good way to check the fuel pump out is disconnect it from the tank and the carbs but leave it connected electrically. Then take the relay out and short out the connection using a bit of wire or something metal and switch the ignition on. Mine wouldn't fire at all (or spark) until i replaced the relay. Also the pump stops pumping when the pressure is up i believe, but i could be wrong about that!
Hope you get it sorted!

Bonzo · Post by **Bonzo** » Thu Jul 05, 2012 7:16 pm

So if I disconnect the fuel pump from the carbs, in theory, it should pump continuously because pressure won't build up?

Bonzo · Post by **Bonzo** » Sun Jul 08, 2012 7:17 pm

Think I've sussed it! I bypassed the fuel pump and ran a hose from the tank to the carbs and it started!

I removed the pump to have a look at it and the 'points' or contacts on it were just about worn out and black.

Gonna get me one of these - http://www.wemoto.com/bikes/honda/cbr_4 ... nt_switch/

Bonzo · Post by **Bonzo** » Thu Jul 12, 2012 8:54 pm

Yeah baby! It runs again! Got my new contacts in the post this morning. Two screws and one wire to solder and we're back in business. Such a relief! Not that we've had much good biking weather.

Bring on the summer!!!

NC29 used to start on 3 cylinders - now won't start at all!

NC29 used to start on 3 cylinders - now won't start at all!

Re: NC29 used to start on 3 cylinders - now won't start at a

Re: NC29 used to start on 3 cylinders - now won't start at a

Re: NC29 used to start on 3 cylinders - now won't start at a

Re: NC29 used to start on 3 cylinders - now won't start at a

Re: NC29 used to start on 3 cylinders - now won't start at a

Re: NC29 used to start on 3 cylinders - now won't start at a

Re: NC29 used to start on 3 cylinders - now won't start at a

Re: NC29 used to start on 3 cylinders - now won't start at a