‘750 Start gremlin.

[Lobo]

If not run for 2+ weeks, the K2 will fire up on the button (full choke), but then quickly die - no amount of nursing it on the throttle will work. It’s as though the ignition has failed - which I am 99.9% certain isn’t the case. Typically after 3 or 4 similar such cycles we’ll be successful and get on the road.

Everything about this K2 has been fully restored in the last year, but tbh it did this occasionally before the major overhaul. Once running, the bike runs faultlessly.

Engine totally stock, carb settings by the book, plugs look OK. Boyer Electronic IGN, DR8-ESL plugs. (with resistive caps as unable to source non-resistor plugs). Basically, the bike is as showroom new in every aspect.

[Martin6]

Do you keep the bike on a maintenance battery charger? Some electronic ignitions are finicky when voltage drops.

[Trigger]

Wrong spark plugs and NGK are known to have a lot of copy plugs about. Try Denso plugs 

[Pauarc]

Which dense plug fit in place of the ngk

[Nurse Julie]

Which dense plug fit in place of the ngk

Denso X24ES-U = NGK D8EA

[Lobo]

Thanks all - will try different plugs…

[Skoti]

Similar happened to me after a 4 week layoff.
Turned out to be water in the carb float bowls.
Put it down to E10 petrol.

Always use super plus E5 now.

[Lobo]

Thanks Skoti - appreciated. Tbh though, I’m in the habit of selecting the fuel OFF a mile out from home, and running the ‘bowls dry < putting the K2 to bed. This, I guess, would negate water in the carbs? (also stay away from Ethanol additive fuel)

Martin - apologies, didn’t reply. The bike has all new loom, as new electrical components, clean connectors / earthings etc, and a new LiFe battery - whose characteristics include minimal voltage drop over time (a year at least). And given the very energetic cranking witnessed, I’m confident the battery voltage is just fine.

A suggestion has been made to open the ‘plug gaps up slightly (have electronic ignition) in an effort to provide a ‘better’ spark which might hopefully offset the rich start mixture / cold engine otherwise extinguishing it. Makes sense, and certainly worth a shot; it’ll take a few weeks to verify and I’ll obviously report back.

Cheers…

[McCabe-Thiele (Ted)]

This E10 fuel that has been forced upon us is very Hygroscopic so virtually impossible for it to not absorb water even from the air inside/above  the fuel tank.

Thank goodness for SUL that varies between E0 & E5 max at the moment & Wynns Dry fuel.

For the first time in 20 years our Merc that is only used in the summer months developed a misfire this May on its first outing  - when it went for Mot dealer confirmed it was old fuel - we used to brim the tank for winter now I am running it down so the reserve fuel light is on as well as adding Octane booster in the spring.

[taysidedragon]

I agree with Ted. If water is absorbed in the fuel in the tank it will tend to lie at the bottom because it is heavier than petrol. As soon as you open the fuel tap the carb bowls fill with any water laying at the bottom, giving a watery, petrol mix. Not good for starting or running.

[Lobo]

Cheers Gareth,

I’d argue though that 2 weeks is insufficient to pool any substantial amount of water, but more pertinent is the fact that on Normal (vs Reserve) you’re taking (good) fuel from a couple of inches up.

If a fortnight was enough to cause grief suppliers would have done something about it surely?

Appreciate the thought though.

[McCabe-Thiele (Ted)]

I am of the view that the moisture absorption & general deterioration of petrol is not something that immediately settles in the petrol tank as a nice separate layer like in the old glass bowl fuel filters. The vibration of a running engine would soon start to disperse the water droplets so they can move into the float bowl.

If you leave a jar of petrol to evaporate it will leave an almost film like layer of lacquer behind this will block jets quite easily. I had the fuel filter on my Merc replaced as two tanks if SUL were needed before the misfire went on a fuel injected engine.

It might not be the cause of your particular  problem but this E5/E10 petrol does not like sitting in tanks imho

[K2-K6]

I habitually run tanks out to absolute minimal content (much to my wider family consternation) cars and bikes, initially do a practical check of runout from start of "reserve" light or tap, just so I know how far it will reasonably go, then operate within that for normal use.

Yes i do always fill completely for critical journey logistics 

Posted before, with reasoning I think ? use of castor oil for dosing petrol @ 100:1 ratio to (my speculative theory) bind with the E and hopefully prevent or mitigate separation and drop out. Long history of being used with methanol burning motors.

Ad hoc testing.  A mixed jar variously opened with this mix, now about two years old and absolutely clear with no change in homogeneous attributes. 

Work on a lot of small garden machinery, with tiny , tiny carb flows, again with consistent reliability and notable lack of gumming, blocking, decay.
As already mentioned, this is anecdotal and limited to the things I can try.

I look after an old +30 yes V8 with injection, recently starting from 3 month layup and running this mix, sometimes 2mll per 100ml as it smalls nice  it started on all 8  on very first try, not even a hesitation, also on really old NGK BPR6ES plugs too  it runs impeccably by any measure and @ closing on 170,000 miles total. It had roughly 25 ltrs in a 80+ tank during storage.

I emphasise, this is anecdotal, my experience, which you’d need to think if it has any benefits if considering trying anything similar. All fuel is straight from cheapest local supermarket and lowest grade.

[McCabe-Thiele (Ted)]

I know it's been mentioned before about Castor Oil (CO) but had forgotten about it.

Is CO expensive to buy I'm thinking there are loads of grades/purity on the market. I've used Wynn's Dry fuel  in the past but even E5 SUL has now caused problems in our V8. Might have been under dosed.

[Johnny4428]

Interesting findings indeed Nigel. Thanks to you I run 100 to 1 castor oil in the 750 with a bit of exhaust pipe preservation in mind also. Haven’t tried 100 to 2. Maybe no need. Castor oil cheap by the gallon as well. I run Frost’s ethomix in the 550. (Just because I have some) I will probably run castors oil in it too when it’s finished.