Navigator re-start problems

How do the plugs look after it dies?, dry or wet?.  If wet look at ignition, if dry ,fuel is not getting through.

You may have tried all the following ideas already but I would start along similar methodical lines as Robert and start with the ignition.   Start by checking th battery is fully charged - electronic ignition systems tend to be unforgiving of low voltage and won't work or may default to fully advanced and therefore not start if it the battery isn't well charged.   Ignition timing is critical on the Lightweight twins so I always double checking that - 24 deg BTDC is correct.   Then double check the wiring and condition of the coils - incorrectly wired up or faulty coils may show a spark but it will break down under compression.   With the plugs out check the gap is between .020" and .022" and then kick the engine over to confirm you are getting a strong spark at both plugs when earthed to the engine.   Move on to fuel, the correct Navigator needle position on the Amal 375/48 carb is 4, blow through with carb cleaner and check the Main jet is 170, Needle jet 105, Pilot jet 25, Needle taper B and throttle valve No. 3 1/2.    Check fuel flows freely from the tank, the carb fuel filter is clear and the needle valve is letting fuel fill the float chamber and shuts off at the right height.   Check the top of the carb is screwed tightly on and the free and correct operation of the throttle and the choke.   Finally check the carb manifold gaskets for air leaks and they are all in good condition - I've had mine disintegrate causing air leaks and poor starting / overheating.   With all that done turn the fuel on, tickle the carb until fuel appears but not too much, select full choke and try starting the engine.   Don't use any throttle initially just in case you have got the mixture too rich and you flood it.  If it tries to start but won't continue running try 'catching' the engine with throttle and see if it will keep running then.  If it does adjust the slow running screw until it will maintain a steady tick over before adjusting the air screw.   If it fires but won't keep running check the plugs to see if they are wet or dry - this should point you back to fuel or ignition issues.  Good luck and let us know how you get on - but wear ear defenders and take care with the exhaust flames, a Navigator without exhausts is mighty noisy and presents a fire risk!

Nick    

A compression reading of 75 psi would be a concern. But it would depend on the method used,and the possibility of poor sealing with new rings .

I agree with Robert, I don't know and the maintenance manual doesnt say what a healthy Navigator's compression test reading should be but 75 psi does seem very low.   If my memory is right my 1969 Triumph Vitesse of the same era should be somewhere between 130 and 150 psi with no more than 10 psi difference between cylinders - but of course that is spinning it over on the starter motor.   A combination of dry bores and not being able to spin the engine over fast on the kick start may make accurate readings difficult.  I will see if I can find my compression tester and see what my Navigator produces.   Just a thought, have you checked the tappet clearances?  They should be set cold at Inlet .004" and Exhaust .006" - if they are too tight then compression can suffer resulting in starting and running problems.  Nick    

Have you had the top end stripped down for inspection and know the state of the bores, pistons, rings and valves Steven?   Do you know the history of the bike, when it last ran and if it has had a top end rebuild in the recent past?    Knowing its history can help a huge amount in fault finding. The fact that both cylinders are showing the same compression is encouraging - if there is a big difference it would point to a serious problem on the low compression side.  If the engine hasn't run for a long time I would pour 10 cc's of Redex or other upper cylinder lubricant into the plug holes, let it soak in and then kick the engine over lots of times without the plugs in to make sure the rings and cylinders are well lubricated and blow the excess oil out.   Put a cloth over the plug holes to catch the oil.  Once you are sure you have got all the oil out pop the plugs back in and retest the compression taking care that you haven't left too much oil in which can cause hydraulic locking .   If it has been standing for a long time the rings might be gummed up and are likely to be dry which might account for the low compression and poor starting.    I haven't found my compression tester yet but will report back when I do!   Good luck.  Nick        

Hmmm, given the work you have done on the top end and the miss match of parts in the carb I think you have identified a major source of your starting problems.  The carb body you have got is probably for the Jubilee which has a 375/36 (Standard) or 375/43 (Deluxe with a special tickler) with a choke size of 25/32" which is too small for the Navigator which has a 375/48 with a choke size of 7/8".    In my experience it is rarely cost effective trying to rebuild a carb which is such a mix of parts.   If you Google Amal UK you will find they sell a brand new Monobloc 375/48 with all the correct jets for £204.48 - I know that is a lot but in my opinion it is money well spent on such a vital part of the engine which will give you confidence that your carburation is correct!  

Nick       

hello  now have you timed this engine the right way as  all twins are timed from the left-hand cylinder all valves closed and on compression, for the left-hand side   the lower set of points should for the left-hand side and the upper set for the right-hand side,  so recheck  and try again  if this is not the case then its a case of elimination  one by one until you find the fault    yours  anna j

Anna it has Boyer ignition so no points and it has a wasted spark! 

…..but not nasty, it seems to be doing the job and cuts down a little on induction roar without effecting performance.  

Sounds reasonable Steve and it looks like you are homing in on the solution to your starting problem!   Probably worth waiting for the new carb and the exhaust headers before trying to start it again.   If my memory serves me right Amal provide the carb with the slow speed and air adjustments at a good base line setting which should allow the engine to start - they include instructions on how to then adjust it for optimum running.  Good luck and let us know how you get on!   Nick      

I’ve never regretted buying a new carb! 

Hi All,

The xx in 375/xx is the finished build of the carb.

In our case:
375/43 was for the Jubilee STD model
375/36 was for the Jubilee D/L model
Both were identical in bore size (25/32") & jetting - just a stronger tickler spring on D/L

375/48 was for the Navigator STD model
375/47 was for the Navigator D/L model
Both were identical in bore size (7/8") & jetting - just a stronger tickler spring on D/L

375/48 was also specified for the Electra - identical to Navigator except 190 main jet (instead of 170)

I had trouble with a 'bitsa' carb on a Jubilee once - turned out that the Jet Block 375/059 was from a Navigator & screwed it right up.

Other tips from experiece:
1) The ignition timing has to be spot on.
When you get it running, you MUST time it with a timing light to ensure accuracy. As stated before, the fully advanced reading is 24deg BTDC. So for starting, it could be more like 2deg BTDC. With Boyer its hard to tell - thus they advise you how to line up the plate.

2) Did you check the plate underneath (once fitted), to see if there is enough clearance to the rotating magnets? sometimes, they have been known to touch.

3) When setting the timing - there is no easy way to accurately determine TDC. The only accurate system is by using a piston stopper as advised in the manual. I use an old detacheable spark plug with a bolt inside it. Once having set up a timing disc with a pointer - make your best guess at TDC and set your pointer. Then slowly rotate the engine (using 4th gear & back wheel) one way until the piston stops against the 'stopper' and note the reading on your disc (for example - 36). Now rotate the engine in the reverse direction until it again stops - note the reading (could be 32, say). Now you know there is 4deg difference between the two readings, bend your pointer by 2deg toards the lower reading side. check again, until you read the same both ways. Viola - you now have TDC marked spot on!

4) On a points system, if having difficlty starting - swap the plug leads over. Oh, the number of times I've done that! Timed it on the exhaust stroke, rather than compression. Boyer does away with that issue, firing both at once.

PS - never run an ignition coil with a dangling lead - always make sure the spark has somewhere to go. It will damage your coil otherwise.

5) Your compressions sound low. Dribble a bit of oil (half a teaspoon?) into one cylinder, with both plugs out & ignition off, kick it over a few times and check the compressions both sides again. If the side with the oil has improved, its your piston rings at fault (the oil makes a temporary seal). If still no differece, your valves are at fault.

Good Luck!

Its a brave man who admits, I c***ed up, so congrats Steve for not burying the fault.

Nevertheless, loads of sound info in this thread, well done all who have contributed. It's why I keep coming back to these Forums

Nice!

Dennis