Newly Rebuilt Motor Wont Start. 10 common faults?

Well I have not been here for a while, good to be back!

'72 combat I have owned since '94. Second rebuild, this time replaced main and big end bearings, pistons, rings, and had a crack in the barrels furnace welded. I also replaced 20 year old Boyer with a Wassel EI.

Re-assembled by the book, pinion, intermediate gears and cam sprocket alignment double checked. Valve clearances double checked. Old NGK plugs (.025") spark brightly when removed, connected and kicked over. Static timing on lucas rotor set to 28º btdc, verifying position by observation of actual tdc. Single 34mm Mikuni has lots of new high octane fuel, and bike still will not start with ether.

Trying to start this lil monster has been all my spare time for over a week. Wifey says "Can't you ask somebody?" well yes, I can ask the best.

MANY THANKS

All that work and old spark plugs...

May I enquire as to why ???

Probably because they were known good. If they get a good static spark you are usually ok but not always.
If you put a few drops of fuel down each hole and quick put the plugs back in, give it a few kicks, will it at least cough?
Im an Amal man so no need for me go on about the carb. That is up to others.

Suck.

Squeeze.

Bang.

Blow.

Begin basic I.C.E. troubleshooting.
Gas getting IN to the cyls?
Test, don’t guess...

I left my bike standing for about 12 months, then took it to a practice day. It refused to start when normally it starts immediately. I replaced the plugs and it fired up straight away. There seems to be certain conditions where the carbon on the spark plugs can stop them from working.
When I took the old plugs out, they did not look as though they were fuelled. But there was not a peep out of the motor - dead as a maggot.

I’m with Al, if something won’t start the FIRST THING I’d do is change the plugs. Knowing they’re old plugs hardly changes that...!

But, my next focus would be the carb. Is it a known quantity? Or is it new?

If it’s a known quantity cos it’s your old carb, then I’d suspect a blocked pilot jet, or similar.

If it’s new I’d suspect set up error, it doesn’t take much error in carb settings to make a bike not start, and a Mikuni has more opportunity for error than an Amal in this regard.

As has already been said, if cam and ign are timed correctly, the engine and ign is in good condition, and the carb is supplying correctly, it HAS to start. I’m not trying to sound condescending here, on the contrary really cos I know from personal experience just how easy it is to disappear down rabbit holes at times like this!

Could be using the wrong mark on the rotor, try resetting your static timing to the other mark on the alternator rotor.

Best regards

Esme

Fuel level in the float bowl, blocked needle jet!

I’ve seen ether not fire, but a teaspoon of gas in each cylinder made it happen...

If your EI does not fire both plugs simultaneously, you could try reversing the hi tension leads.

I dont know the Wassel EI but most EI units need either a resister plug or plug cap so check.

Definitely use new gapped plugs.

I know you said you checked the timing against TDC but check you havn't had a senior moment and timed it on the wrong side. A very experienced mate did that recently and he was very embarassed.

Your battery is good ? How long was it sitting around while you rebuilt the bike? Just because it measured 12 volts it doesn't mean its good with a load on it.

I agree with the carb suggestions above plus a random one. Check you slide isn't hung up some how. I have seen that happen to.

In leui of further details (does it go bang at all?) I'd think the EI setup may be to blame....I too have the Wassell and it seems to work quite nicely without resistor plugs/caps/wires. check the timing (mech & ignition) and recheck the two 6-volt coil hook up correctly with the EI.

Here's an old thread. Eerily the same problem. It sounds like ignition timing 180 degrees out.

https://www.accessnorton.com/NortonCommando/cannot-start-my-newly-rebuilt-mk3.3843/

~998cc

johnm said:

I know you said you checked the timing against TDC but check you havn't had a senior moment and timed it on the wrong side. A very experienced mate did that recently and he was very embarassed.

Click to expand...

+1

998cc said:

Here's an old thread. Eerily the same problem. It sounds like ignition timing 180 degrees out.

https://www.accessnorton.com/NortonCommando/cannot-start-my-newly-rebuilt-mk3.3843/

~998cc

Click to expand...

As I said I do not know the Wassel unit so my suggestions are based on Boyer and Pazon.

The OP said he checked the static timing was correct by looking for TDC - hopefully by carefully feeling the piston coming up with a screw driver. So that should mean he is not 180 deg out. (or timed at BDC). But it is possible to time AFTER TDC not before if your having a bad day ;-).

He also said he static timed at 28 before TDC which wouldn't be right with a Pazon. 28 deg is about right for the advanced timing not static. The timing should be about 28 to 31 deg when checked with a strobe when the bike is running at about 3000 rpm. But being that much out shouldn't prevent it running at all.

Most EI units fire both sides with a redundant spark so swapping plug leads over shouldn't make a difference.

Sometimes its good to go right back to square one with the wiring and timing set up and carefully check everything word by word, line by line, page by page. A little knowledge can be a dangerous thing and many is the time have glanced over a paragraph thinking I know all that only to discover one little sentence in there that has caught me out.

Id really look at plugs and battery.

A last random thought. If your plugs are crap and you have flooded it. Just crack the throttle wide open when you kick it over. I'm just getting my 850 back together over years overseas and my starting technique is forgotten. I couldnt get the silly thing started a few weeks back and finally opened the throttle fully and away it went.

Pull new plugs after flailing away on kicker to a no start. Wet tips ? Yer getting gas. Rest or fix plugs to headfin then kick away to observe for good sparkage at (new) plugs..one or the other if rebuilt properly.

An old trick for a reluctant motor with wet plugs is to take the plugs out and heat them up (mildly) with a blow torch to burn off any wet fuel / oil. Put ‘em back in and kick whilst they’re hot and (I guess) the heated plug gives things a head start by helping to vaporise fuel.

When I was playing around recently with my newly acquired / newly restored T140 I had a helluva time with it not starting and running rough, very rough in fact.

I ran numerous hypotheses in my head about what must be wrong with it. I’d pretty much convinced myself the engine needed a full tear down again.

Long story short; incorrect carb settings (wrongly specified by Amal), some duff new NGK plugs followed by using the wrong plug heat range (fancy Denso Irridium plugs, that I wasn’t familiar with, incorrectly supplied by the T140 Shop in the U.K) were all that was wrong.

A few simple problems (all caused by suppliers in my case) working together as a team, can conspire to confuse any mechanic!

I got there eventually, the bike now starts and runs like a Swiss watch and NO I didn’t have to tear the engine down !!

Hence my earlier comment about rabbit holes...

Fast Eddie said:

An old trick for a reluctant motor with wet plugs is to take the plugs out and heat them up (mildly) with a blow torch to burn off any wet fuel / oil. Put ‘em back in and kick whilst they’re hot and (I guess) the heated plug gives things a head start by helping to vaporise fuel.

Click to expand...

And with the plugs in, the ignition switched off, fully open the throttle and kick it over a couple of times. Blows out any excess fuel.

Have you tried different throttle openings while starting?