Won’t start

This bike is old tech .  It needs a rich mixture to fire up from cold. If after some attempts to start the plugs are still dry then its likely there is the problem. Close the choke fully ( slack cable) ,tickle the carb a few tomes and your finger should be wet with fuel . The fueling is now likely to be a bit too rich and it may need a little throttle to fire up.  The carb has not been tuned yet  to allow an idle so you will have to keep it running with the throttle , As the choke is on full within a couple of seconds the engine will choke on a too rich mixture so you will need to open the choke a little or the motor will stop . Its a balancing act till the motor warms up . Once warm you can adjust the carb for a tickover.    A Norton that ticks over well and starts easily from warm is often a poor starter from cold and the reverse is also often the case. Welcome to our world.  E10 fuel is not a help either.

“If you are convinced it’s carb it’s probably ignition….”

Depending on your set up get some fresh fuel into the cylinders.  A syringe, teaspoon, rubber tube…. Just a small amount.  Once in there if all else is correct it should react. Partially fire, kick back or run.  Once it’s breathing it will draw the fuel through on the throttle.   Should it remain unresponsive, check your ignition timing, spark generation. plug lead orientation…  

 Monoblock with an an “O” ring is not a favourite mounting solution for me.  If it’s been over tightened to flatten the ring it may be distorted. Check the flange on a flat surface….    I use paper gaskets on all but concentric.

Burlen Ltd have overhaul kits for monos, Martin Bratby  01543572583 services carbs.

good luck  

Jon

If the spark plugs are dry, the carb is not doing its job and the jets may/will be blocked.

Dismantle the carb and ensure its clean and all the jets are clear.

Put a small amount of oil down each cylinder to lubricate (& seal) the piston rings.

Create a (removable) choke across the carb inlet (do not use a mates hand, as it might burn if there is a backfire). See if that gets the plugs wet.

As I wrote in Roadholder this month: If there is compression, If there is fuel, If there is a spark, & its at the right time - it WILL run.

If the  bike has not run since the 70's I would try another carb. I might have one for you to borrow. I found all sorts of crud in my original carb that required some effort to clean such as boiling in vinegar! Nowadays, sonic baths do a good job but even they may not clean out the fine passageways. 

I flood my carb and use choke to start the engine but it soon settles to tick-over after 30 Seconds and i can back off the choke.

Send me a PM if you want to borrow a carb.

Dennis 

If the engine starts using starting fluid, you will be fairly certain that it's a carburettor issue.

  A Norton that ticks over well and starts easily from warm is often a poor starter from cold and the reverse is also often the case.   Not the whole story, the statement above is correct BUT any engines on carburettors that is set up correctly ie correct mixture. Bear in mind with petrol the engine can run on quite a range of mixtures ie week/rich. But if set 'correctly' it WILL need choke to start. Any machine that starts without choke is running too rich!

As I wrote in Roadholder this month: If there is compression, If there is fuel, If there is a spark, & its at the right time - it WILL run. Correct ANDY, In the original problem there was no mention of closing the air slide. ALSO Jonathan says 'plug lead orientation' -Boyer ignition!

One other point I didn't mention when trying to start a recalcitrant engine. If a rebuild and you think you have compression, kicking, whirring on starter, you might find that the 'compression' is  resistance in the bore. Not real compression. The answer then is a squirt of oil around the top of the piston to 'seal' it, during/after building. Perhaps a 'squirty' can through the plug hole.

I once had to go out to rescue my son who's MG Midget had died  on Chiselhurst Common . We spent a few hours determining that there was plenty of fuel and  an enormous spark from the coil . We knew the timing etc was fine as it had run well before the stop. We eventually tired of it and left the car in the drive of a very friendly couple . Next day after a fruitless couple of hours we found that the spark was shorting out  invisibly through the center of an otherwise perfect rotor arm. So fuel and a spark are not enough ,it also has to be where its needed. On a lighter note , on the way out the friendly couples wife pinched my bum !!  , Those were the days.

I would add that I haven’t had an old bike that’s didn’t run better with a new carb - the mono blocks are available from Surrey Cycles/Burlen and prob others!

Dan

As far as I know - Surrey Cycles/Burlen/Amal do not produce a 25/32" choke size Monobloc carb to suit the Jubilee.

"As far as I know - Surrey Cycles/Burlen/Amal do not produce a 25/32" choke size Monobloc carb to suit the Jubilee."

They claim to sell the basic body but they are: "Temporarily out of stock."

I have one that is for another motorcycle (25/32" choke) that has been kitted out with Jubilee spec parts to act as a spare for my Jubilee.

Burlen's comment reminds me of an old joke. A man goes into a green grocers to buy a pound of potatoes. The shopkeeper says the price is £3. The man says the grocer down the road sells them for £2 but he is out of stock. The grocer replies that when he is out of stock he also sells them for £2!

Dennis

hello,

i had similar problem with a monobloc, i could get my bike (not jubilee) going. by bumping it down the road, but it just cut out straight away. on inspection i found that there was no fuel in the idle circuit tube/feed, number 1 in the attatched photo it was blocked solid. letting no fuel through to the fixed jet number 2 in photo. 3 is a cap over the fixed jet. after cleaning it all out it solved the problem

Barry

Hi Michael,

From the info I have the 375/36 was for a Norton 250cc 1958-63; Jubilee Twin De-Luxe; 25/32" bore, with 25 pilot jet, 3.5 cutaway, 130 main jet; 0.1065 needle jet and needle in the 3 position (from the top). Also 0.781" is 25/32", the bore size for the Jubilee. The standard Jubilee uses the 375/43, and the only difference, I believe, is the tickler type because of the panel work.

The 375/47 is for a Norton 350cc 1961-63; Navigator Twin De-Luxe; 7/8" bore.

Hope this helps,

Stan

After reading through some of this saga two things are noted. 'The needled jet was blocked' how can it be? It has a needle going through it on the end of the throttle cable! Second point -if the carburation is anywhere near right, then there must be a choke fitted/used to make the initial start.

Hi,

I forgot to mention that the correct needle for the 375 carb is stamped with a B. I believe the Part No is  RK5/063 (B).

Might be best with RKC/375 375 Repair kit - This kit includes all gaskets and seals, Float needle, filter, air screw and spring, main jet, needle jet, pilot jet, main needle and clip but no slide or Float. Select your jet sizes on the Amal site in your basket.

Stan

Sounds like its backfiring thro the carb, hence smoke under tank.  Could be you have the leads on the wrong plugs?.

The Boyer fires both plugs together so it does not matter which one is which. But if the best you get is a bang and smoke out the carbs, it suggests to me the timing is way out, even firing at the bottom of the stroke.

That's what the wife said the other day, timing is everything........

Have you resorted to Bradex Easy Start? If it's still available....

Plenty of old worn out engines still manage to start without resorting to dropping oil into the bores.  But you certainly don't need to remove the cylinder heads.  

Are the plugs in good condition? They can be faulty (but not very often...)

Also...you say you cleaned the carbs.  Did you include the tiny passages in the pilot circuit?  If you are kick starting on small throttle, the engine is only fed through the pilot circuit.  This can be blocked after a long layoff. That can end up with sporadic firing and then, if it does start, it will only run (roughly) on wide throttle and full choke...

Michael,

It sounds like you are close with the ignition set up hence the backfire. I found, with my Pazon unit, that despite setting up the advance carefully with a timing disc, it was still out when checked with a strobe. The timing was good enough to start the engine but out by about 5 degrees. With the Pazon you can adjust the spark point by rotating the backing disc (that holds the magnets) either way by a few degrees and that sorted out the timing when checked with a strobe. Not sure if you can do that with the Boyer set up.

A squirt of oil down the plug hole is fine to seal the bores temporarily - not too much oil!

Dennis

... if it'll start and run even if just for a few seconds with easy start then it's a carb problem. I've had a tin on the shelf for many years and recently used it to start a Villiers 9E that had been silent for a long time.

I'm wondering if you haven't put too much petrol down the plug holes and washed off the oil from the sides of the pistons.  This loses the compression required to get a proper start-all you get is pops and bangs.  It takes a bit of oil in the plug holes and turn the engine over without plugs a few times, then try the Easy Start.

And...are you absolutely sure the timing advance is being set when the auto advance is fully advanced? With a Boyer ignition, it might not be relevant, but is there a possibility that the ignition you have is incorrect?

It's all to easy to set after TDC instead of before...you won't be the first person who's done it...and it will certainly pop as the spark meets the gas...

Yes I did that. Set after TDC not before. Corrected it after I discovered my mistake. A timing disc on the crank outboard of the alternator rotor with a pointer is the best way to set the timing and then check the accuracy of the electronic set up with a strobe when the engine is running.

Dennis

Michael, are you making the initail setting of the timing on the right stroke?  The compression stroke.

Sorry if I'm repeating previous advice or barking up the wrong tree.

Incidentally, when I set up the boyer system on my Navigator, the initial setting was miles off, 5degrees+ from where it should be fully advanced.  Needed strobing to get it right.  Started easily before and after strobing.  Could be that it was a system intended for BSA singles!

Following John's comment above - only this afternoon my new Roadholder arrived.  Page 10 has a note by Mark Woodward where he repeats a conversation with one of the electronic system providers (Trispark).  Since you must set an electronic system at full advance, you rely on the fact that Lucas auto-advance was typically 12 degrees (24 crank angle).  But yours probably left the factory with Wipac...who knows what its autoadvance total angle change was?

Having said that - if I try to fire up a manual advance single set on full advance, it will either start fine and run or, far more likely, savagely kick back.  But although they can tick over on nearly full retard, they don't like starting when fully retarded.  So if yours has not yet bruised your foot, it might well need a good deal more advance until it does.

Advance your ignition until it kicks back when using the kickstarter, then retard it a little and you should be in the ball park. 

Personally, I never use a degree disc, I set the final timing to what the engine is telling me by the way of pinking, or not.