Gremlins are back

When I suffered such things on my Mk 3, it evntually turned out to be an internal break in the wiring to the ignition sensor. Took a fair while to suss that one out. Try fiddling with wires with the engine running. Highly technical I know, but it might just show something up.

The lumpy running might be the clue here. It suggests to me the appearance of an electrical problem. I would be looking for a loose wire or another electrically driven chunk that has come adrift and is causing a short.

Top of my check list would be .......is the horn still in p;lace and not waving at passing traffic. If this is ok I would then look at the wires in the handlebar switches. On my Commando, the white wire that powers the indicators has twiceparted company from its soldered position.Both of the aforementioned have shorted out the battery and caused grotty engine performance.

It might be worth checking the leads to the Pazon gear. The connections to the trigger plate strike me as a bit flimsy compared to the rest of it. There was a problem with the first Boyer gear when the Commando enginesvibes caused internal breakages in the pick-up wires. Could this be a repeat???

Check out your coil terminals. These suffer greatly from muck chucked off the road and do need a clean up now and then. Is one of the terminals or spades a bit loose?

I was quite surprised at the green contentsinside my ignition switch when I fitted my Pazon a few years ago. A good clean-up made all the lights suddenly go much brighter. Check the terminals on this switch for loose bits. Some new ones, recentlybeing sold by a BIG NAME supplier,had rivitted terminals which came loose as soon as a spade was pushed in place. Cheap imported junk sold for big bucks......shame on them.

Hello And After You have Done all this it will turn out to be a earth wire from the battery to frame thats at fault Yours Anna J

PS have you tryed out a SU carburettor conversion yet these carbs are more relivable and give a better MPG , with very little of the top speed to contact AMAL Carburettors On the Interweb Yours Anna J

Previously steve_elston wrote:

Commando slowed to a halt just as we'd entered an underpass on the A3 over the bank holiday

Bloody frightening to say the least, not a good place to breakdown.

My initial thought was petrol starvation as the engine didn't suddenly stop but ran lumpy for a hundred yards or so, straight on with the reserve tap but she still died

I'm running a VM36 Mikuni which I jetted back to standard with settings I got from Allens Performance,with Pazon Sure-Fire ignition, when the bikes warmed up she runs very well

This has happened twice before when I was running on a Boyer ignition with a single Amal

I thought these were the problem ,and so changed both for more modern alternatives (as above)

I've checked the petrol tank cap breather, clear, I'd only done forty miles on a full tank of fresh fuel so I've discounted that, oil levels OK.

The bike restarted after a few kicks, these intermittent breakdowns are bloody annoying as well as dangerous

Any ideas for what to look for would be appreciated

Steve

Have you discounted icing up of the carburettor? This seems more prone now with ethanol added to fuel (which increases the dissolved moisture content) Kawasaki had a real problem with this on their 900 four - a factory recall included fittiing manifold heaters Mike

Previously steve_elston wrote:

Thank you all for your ideas, Anna I will check the major earth cable first off as it's the easiest to access, the coils are brand new from the club so I'm ruling them out

The bike has only done roughly twenty thousand miles from new(1977) rebuilt by myself back in 1998 ( I'm a engineer specializing on vintage / veteran car engines) so I'm confident nothing is breaking down mechanically causing partial seizures.

I will take a look at the petrol taps, though relatively new they may be partially blocked as I'd sealed the tank with Wasselâs tank sealant, maybe the ethanol's causing it to come adrift.

I took the main power feed to the Pazon from the white wire near the kill switch (which doesn't seem to work anymore) but that can't explain the two breakdowns on my earlier set-up ie Boyer / Amal where the Boyer box had a direct feed via an isolation switch straight from the battery.

I like Gordon's idea of fiddling with the wires.

I'll report any findings next weekend

Cheers Steve

Hello Steve It looks like you may have more than one problem . I would check out the kill switch and earth wires and there is little trick if you run the bike in the dark you see if there any thing aching any where . the other thing with be that Wassel tank sealer . you need to get the Harley Davidson tank sealer , they been making it longer than anyone else , as they Had Ethanol way longer than us in the UK

. yours anna j

I had a 750 with Mikuni which used to ice up occasionally, very disconcerting. Like your bike it just coasted to a halt and would restart after 20 or so seconds. Never did find a cure.

sam

You certainly have a short or a damaged lead that is earthing your coils. Check your ignition switch these have a tendency to short especially if moist or have a hair line crack in the insulation.

Don't rule out the coils as even new ones can break down. Also check the leads (just buy cable and make your own 100% copper ones its better) oh and plug caps as I believe your bike should not have plug caps with resistors in, check these as modern bought ones usually have resistors in...not good!

Another little tip get a small plant sprayer, put some redex in and spray a very fine mist into the carbs when running at mid power. We we used to do it to clean out carbs prior to racing.

It smokes like hell and coughs a bit but worked for us cleans them out as gumming up is a real problem with our old bikes due to the bloody dreaded methanol.

No one has yet mentioned the arch gremlin, the dreaded lucas ignition switch. Hot wire the entire ignition loom, battery to ignition supply. This counts out the loom problems. Have you tried swearing at it yet? That allways works!

Happy Huntig,

Boo.

Hi, in addition to Boo's comments I had similar on my 72 750...Interpol / police part of the loom with purple/white wire ( belive a kill switch option ) with an intermittent short to frame near the 2MC capacitor...random event till I found it. Defo think ignition issue...good luck.

Hi Steve, I think that a gradual lose of power is more likely to be a lack of fuel than an ignition problem. You are unlikely to get carb icing if you are running an air filter particularly in the current dry-ish weather. Carb icing will manifest itself as a stuck throttle after a period of open throttle work. I would borrow another carb to try and isolate the problem. You could have a reduced flow of fuel into the float chamber, enough for poodling around but not enough for open throttle work. Try this, remove the float bowl drain plug, place a measuring jug under it, open the petrol tap and measure how much flows in say one minute. Now lets say a Commando does 60 MPG at 60 MPH you need to see a sixty'th of a gallon in the jug in one minute 1hour = 1 gall, 15 minutes = 2 pints, 7.5 minutes = 1 pint, 3 minutes 45 seconds = half a pint etc. Any less than that and you are not getting enough fuel at large throttle openings.

When the bike has died on you, you will have to wait until the float bowl has filled again before it will start. Measure the feed rate with one tap open and then with both. You could measure the flow through the taps first if you want. If that is satis then the fault may lie with the float needle mechanism.

My money is on lack of fuel supply

Yours

Gripper

I would be extremely surprised if it were carb icing. My 99 is very prone to icing, but the conditions required are air temp at or below freezing and damp or wet conditions. The symptoms are running rich, loss of power, black smoke and sticking throttle. The sticking throttle is such fun on icy twisty roads... It clears if you stop the bike and kill the engine and wait for a few minutes for the engine heat to melt the carb ice.

Your symptoms do sound much more like fuel starvation. We have mentioned the fuel tank breather, haven't we?

Gordon.

Fuel lines are very suspect. I fitted a nice new stainless braided one and it quietly dissolved then poured petrol everywhere. Back to the boring black Halfords fuel injection pipe - works a treat. If your fuel line feels spongy, I would change it sooner rather then later. Gordon.

glad we got to the bottom of that one. I use "TYGON" fuel pipe normally used in the light aircraft world it's clear, though a yellow colour and does not go hard with use as does normal plastic tubing. Not cheap, 2 metres cost me about 18 quid but I reckon it should see me out, available from a small outfit near coventry airport Google reveals all

Even light aircraft have been having fuel problems, despite expensive aircraft quality components... You should see pictures of Gypsy Major carbs pretty much eaten away with modern fuel.

Glad you got the problem fixed. It's astonishing how current petrol dissolves fuel lines. Your old one looked like it was made from rat intestines- which would probably have done a better job. The cheapy Halfords fuel injector black flexible tubing has been on my bikes for years now and I have had no problems at all, other than the brief interlude with the nice braided stainless pipe that failed. At least it didn't cost me - it was a gift from a well-meaning friend.

Could it be that your bike is objecting to that Italian made cable you are using?