Ethanol, heat soak and poor hot starting

For by tank and fuel line deterioration (ethanol is only added to fuel in the tankers)can ethanol vaporise in fuel on a hot engine causing difficulty in starting while the engine is warm. Apparently ethanol carries 35% oxygen and is more volatile than petrol so the more ethanol in the fuel the leaner the mix? Is this crap ?

J

Wes and I on basic Miki carb or dual Amals and 10% spiked gas have no issues for 1st kick starts in hot summer days creeping 30-40 mph in lower gears climbing Gravel steeps getting hot as can be to stop and share a high at the top then one kick to get next leg of joy done. We both have got stuck trying to start away from home d/t mostly electrics but sometimes a carb fastener loose so we flash a nod or hint of grin when they fire right up with just a step on em to carry on the joy together. Check timing and float level etc but gasoline old or new will tarnish fuel hoses over time. Hope its not fiberglass tank resin messing with ya. My lawn mowers and chain saws sit up 6+ mo at a time with boozed gas but start fine even in cold damp weather. My SV650 sat up 2 yr in the fella yard who dropped it miles away but I got it home and charged up and after some hit/miss stalls cleared up to normal starts and got to fresh fuel station. Always worth while to stick in new plugs just to feel like a mechanic and eliminate that possible issue.

I have no idea if any of that is true in theory but in reality I have not encountered any difficulty starting an already warm motor

the technique is what matters

my experience continues to be that with a warm motor one should still tickle a bit, not as much as cold motor, but one must open the throttle about half way while kicking, versus not opening the throttle while kicking with a cold motor but more fully tickled

this works on every commando I have owned or ridden owned by others

auldblue said:

For by tank and fuel line deterioration (ethanol is only added to fuel in the tankers)can ethanol vaporise in fuel on a hot engine causing difficulty in starting while the engine is warm. Apparently ethanol carries 35% oxygen and is more volatile than petrol so the more ethanol in the fuel the leaner the mix? Is this crap ?

J

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It's crap. However, you are correct, that as EtOH content of petrol increases, in a petrol fueled engine this results in mixture leaning. The stoichiometric A/F ratio for petrol is ~ 15/1 whereas the stoichiometric A/F ratio for EtOH is ~ 9/1. Thus you can see how enriching a petrol/EtOH fuel blend in EtOH content results in creating an ever leaner mixture as the carb continues feeding at A/F ratio of 15/1.

Although EtOH has a slightly higher vapor pressure than petrol, I doubt this would cause the sort of issues suggested in your inquiry above. I live in MN and 99% of the regular grade petrol here contains 10% EtOH. It's not the best fuel for sure, but it does not cause the sorts of issues you inquired about above.

The plot below shows how EtOH added to petrol changes the stoichiometry, so at 10% it definitely affects mixture strength.

When I say difficult on hot start after a petrol stop one kick , after cigarette toilet etc flood carbs kick a bit flood again kick a bit , pull plugs and they are dry and don't smell of petrol. Let her sit for an hour or so and she starts no prob. Twin 50k plus Amals , no choke n7yc plugs or NGK equivalent. When you pull the plugs the spark is good. It's no the fuel cos I empty my tanks from bike to bike. My single mikuni starts first or second cold on enricher and one kick when hot using fuel from other bike. It has to be something simple.

J

Its always possible to get real layer of water in bowls by magic occasionally. Booze gasoline runs leaner cleaner than the original tuning advice was for the leaded gasoline so not unusal to have to richen up a dash to compensate. When right should take a mere one or two carb tickle then a closed throttle one kick start, or if in a sloppy kicker mood that day, crack throttle and step down a bit faster. If no joy check key, fuel taps, fuse potato in mufflers as there is a distinct issue to solve if they don't fire first or rarely 2nd kick on cold day wake up call. After that unless as cold as over night should only need to step down on closed throttle then catch throttle and off ya go no wearing down but an energy life from the bit of muscle firing. This is state my Combat spoiled me on and also Wes'st '71 with Amals and now Miki single. My best start timing was backing off slight back firing till just didn't. Slide bore leaks can be checked with slather of grease but mostly just won't idle down well, but would aggravate a slightly lean state beyond expected. A fully fettered Cdo may be easiest to KS as often mine fire right as foot starts decent so kicker beats foot speed so doesn't feel like a kick. Lots and lots of little shared satisfied hi's with Wes either alone or in cycle gatherings all eyes/ears on the dinosaurs, Varroommmm, varrooommMM we putter off with cheese eating grins. Wes is sedate rider so let him pitter patter so pleasantly away then I leave with a bark of sharp swing as rear spins a fish hook manevour then nail peashooter SNorton's back at em. Most pleasant but not good for engine starts I do is close throttle hands off so just turns on at dead slow idle steady as can be. Cam/lifters don't like low rpm much as everyone else does.

auldblue said:

When I say difficult on hot start after a petrol stop one kick , after cigarette toilet etc flood carbs kick a bit flood again kick a bit , pull plugs and they are dry and don't smell of petrol. Let her sit for an hour or so and she starts no prob. Twin 50k plus Amals , no choke n7yc plugs or NGK equivalent. When you pull the plugs the spark is good. It's no the fuel cos I empty my tanks from bike to bike. My single mikuni starts first or second cold on enricher and one kick when hot using fuel from other bike. It has to be something simple.

J

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This is really strange based on your description. Are you opening the throttle after you flood carbs? Dry plugs if your priming doesn't make sense.

Strange , I'll say . It's like a window of non opportunity ,leave it half an hour and starts ok.but ten mins and it's about twenty odd kicks, does not even want to start then fires and away no prob not missing or spluttering, but it did show an intermittent electric fault on the dyno at about 5k so I was going to tidy the wires up.
I can start a motorbike anywhere and in front of anyone and think I've got a fair bit of technique , what I haven't got is sufficient nonce to figure out why this bike won't start easy after I have a smoke. It's no bugging me too much but I would like to know why it does it.

J

If it were an electrical problem...why are the plugs dry? Your not getting fuel...but why?

[. Although EtOH has a slightly higher vapor pressure than petrol,


The last I heard, Ethanol has got a lower vapour pressure than petrol. May be wrong, but that is why ethanol engine run better when the fuel is heated prior to going into the engine to raise the vapour pressure. It is also my understanding that the need for petrol to start the engine is more important for the same engine when running 100% ethanol.
Ethanol is thicker than petrol, so is another reason why bigger jets are required as well as the above mentioned . Ethanol has a lower calorific value so to get the same power, you need more fuel. Ethanol has a very much higher octane rating than petrol, and it burns much cleaner.

Got this information from David Blume when he came to Northland. Anyone heard of him.[ alcohol can be a gas ]


Dereck

Could be both state of carbs and intermittent electrics. Heat makes insulation softer to move more. Had that fool me checking while cold then misery at next start up till cold again and me worn down. Ethanol is a rather small orgainic molecules less vicous than water and the hydro carbon chains of gasoline. Part the reason it evaporates faster than plain gas and a good fuel additive in cold conditions as well as wiper fluid if not methanol. Check manifold cross over tube if got one just for fun.

Steve , had this problem for quite some time and I don't want to bugger about with the carbs since it starts easy cold and runs , pretty well otherwise. If it wasn't for dry plugs you would think it's not switched on. Yes Dennis it's a strange one for me. Derek , ethanol vaporises more readily than petrol as it is more volatile, more than half the US Fire services don't have the necessary equipment to fight ethanol fires as the foam used for petrol fires does not work on ethanol. I'm just clutching at straws I have no idea what is up with the old bike.

J

J,

If I hear you correctly it won't start hot, but after allowing ample time to cool then starts and runs well. Sounds electrical to me, and just because you see spark in open air doesn’t necessarily mean you can generate good spark under compression. Seems like it would be easy to prove or disprove the fuel supply issue. When it's in a funk and won't start, intentionally introduce fuel (remove spark plug put a squirt in, spray air cleaner with ether, etc). If it subsequently fires with fuel present then it's a fuel supply issue. If there is no fire, spark must be absent.

When you have the issue and tickle it is it upright (not on side stand) and do you give it a good soaking? In hindsight these all seem like silly questions since you know how to start it in all scenarios but one!

Last time I had one that did this it was weak spark. The spark looked fine but it would not fire a plug under compression. You had to work hard to get it to catch after it was shut off for a few minutes. A new coil was the cure in my case.

You might want to reduce your plug gap to about .012 to test the theory. Jim

PS, It is really tough to get wet looking plugs on an engine that is near operating temperature.

For kix start up at night in dark area and rev up and also jiggle jerk flick leads watching for hints of flashes, some almost imaginary till focusing in. Its a Commando so many things cause same symptoms. Peel pissed me off for a couple mo's starting fine cold but bugger till cold again then misfires ridding but could not reprodue in on road side or home. Finally riding pasture to reach driveway she stumbled and quite but had felt the bumps in yard misfiring just prior. Forget what made me check tail lens, maybe because was easiest like looking for key lost in dark home out under street light, I found the uninsulated earth braid lead had frayed apart and was bouncing on the brake power lead shorting to kill power but so light a contact didn't blow fuse. None of us should be wasting any typing on this if you've a boyah with factory trigger leads, ya desevre the lesion and remember I told ya so if it turns out to be so. In meantime let me count a few more to check off.
Softening fuse holder contacts, fuse internal contact decaying but filiment just fine, coil shorts with heat inside or to case to mount outside and its connections too, heat clearance issue of magnet/coil trigger distances opening too much, dang ole bar kill toggle terminals getting tired on rides, some big wing bug or a fend dropped rag in gas tank. Yoose more experienced guys can expand form here.

Cheers Men , a tidy up of wires and a new set of coils was probably on the cards anyway. The wiring on this old bike is basic 69 with the addition of a podtronics unit, no idea how old the Boyer is. But the old girl has never embarrassed me in public with a non start, even when parked up with competitors at a national Motocross meeting on a cold wet day she started first wallop.
Logic says it must be difficult to wet a plug when it's that hot you've got to juggle , maybe she's not running as well as I think!

Cheers J


The guys at dyno tech said they had an other commando on the books and it was 42hp

If not the fuel causing the starting problem, this is my experience on my '72 combat engine. From warm give it one or two kicks. If it hasn't started, tickle the carbs. Still no start after two kicks it could be flooded. My Lucas RITA ignition sparks after pushing and releasing the kill button. Excess fuel ignites with a pop. Usually will start after that. If not hold the throttle wide open for one or two more kicks...success.

Amal pilot mixing chamber fills up a bit before tickler over flows and designed to send a rich slug of mixture with closed throttle for very predicable starts. Slide cut out can spoil that sweetness too. Poor combustion can only be from poor mixture, poor spark/timing, poor electric conduction, poor plugs, poor air and oil sealing and mis degree'd cam, in any combination or priority. A thinking man's motorcycle that makes me feel more immature reactive infantile that already am.

Steve , poor spark ,poor carbs. that could be the cause , coz it's poor me , frightening the kids from all the kicking and possible cardiac arrest, even my eleven year old girl shouts at me "I thinK you need to tickle it again ,or do you need an ambulance" and I don't think she was kidding about either! Cheaper to buy a complete mk3 with a good lecky start, than to trust NHS to rewire me!

J