Use of choke

Issues with balancing, jets, filters, etc

Use of choke

Postby Freddy » 14 Nov 2020, 02:56

A post just for the sake of it, seeing nothing much is happening at the moment on the forum.

Whenever I've parked the bike up for a period, say 5 or 6 weeks, I've often found it hard to start. This is after turning the tap to prime, and using choke. Just doesn't want to fire. Thsi si odd as it always fires first time when used regularly. Eventually get it going, runs a little rough for 10-15 seconds or so, and then all back to normal. Starting first go from then on, no choke when cold needed.

Bikes been again sitting for a while as I've been caught up working on the house. Couldn't get it out from the back shed even if I'd wanted to go for a ride. Job now finished so today I decided to try something that I know is required to start my XT250 which also has a CV type carby. And that is to open the choke, and DO NOT touch the throttle at all. Primed the carbies, full choke, and it started first spin. Still ran a little rough initially till it came good.

What I think happens is while sitting for a while all the petrol evaporates out of the carbies. Priming them puts petrol into the fuel bowls, but doesn't put it up inside the emulsion tube. So it won't start after sitting like it normally with no choke due to no fuel in the emulsion tubes. You must use the full choke circuit to get it started, and it doesn't run 100% right until the fuel is drawn up. Touching the throttle when using the choke actually negates the choke circuit exactly as my XT250 handbook says, that's why it is hard to start if you 'rap' the throttle.

Basically its prime the carbies, full choke, DON'T touch the throttle till its fired up and running.
Freddy
 
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Re: Use of choke

Postby hugojose » 14 Nov 2020, 14:30

Freddy, that's good information.

OK, nothing is happening here so I'll write some....I'll relate my experience on this, and of course, not all bikes, even same models are exactly same.

As well known, the CVK32s have enrichening plungers, not 'chokes' as in choking the air. For many years I considered the Zephyr 750 difficult to start when cold...and the 'choke' very difficult to modulate, as in, racing to 3000 RPM or nothing, and struggled for year starting when cold. I also used similar technique as Freddie described, giving it about 1/3 'choke" and no throttle, then fiddling with 'choke' trying to achieve 1500 rpms.

But what finally worked for me was raising the bowls fuel levels aiming for richest values. 1.5mm fuel level ABOVE the seam, and 15 mm bowl free floating height, upside down. Am not saying I achieved exactly that, that's hard, but that was my aim. I also run 38 pilots, instead of 35.

..I live in Florida and is mild to hot (getting worse, of course, as anywhere else by our doing), but even after 7 days, I can cold start it with a flip of the throttle and no "choke", then hold throttle slightly open, and adjust 'choke'(mix) to sustain 1500 rpms by itsel, ...while I perform the rituals of fitting ear plugs, helmets, gloves and such.....then close 'choke' and bike idles by itself, ready to go.
hugojose
 
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Re: Use of choke

Postby Freddy » 15 Nov 2020, 06:41

hugojose wrote: I can cold start it with a flip of the throttle and no "choke", then hold throttle slightly open, and adjust 'choke'(mix) to sustain 1500 rpms by itsel, ...while I perform the rituals of fitting ear plugs, helmets, gloves and such.....then close 'choke' and bike idles by itself, ready to go.


I ALWAYS put my ear plugs in and helmet on before starting the bike. Find all the rattles and bangs WAY to distressing otherwise, lol.
Freddy
 
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Re: Use of choke

Postby hugojose » 15 Nov 2020, 12:49

I know what you mean,..... when cold sounds a bit rattily (no water jacket to muffle it),....... but I'd rather face any estrange new noise before starting to move. The ear plugs are really to minimize any damage of wind noise, but they do make the engine sound a lot 'smoother', as everything is more quiet and peaceful-.
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Re: Use of choke

Postby Shedman » 15 Nov 2020, 21:24

Hi guy's, mine starts fine if used regular but this time of year in the UK that is highly unlikely. Anything longer than a week lay up and she just doesn't want to start unless I get the exact sweet spot on the choke which is about 2/3rds closed without touching the throttle and the tap on Prime. Even then its only on a couple of cylinders for what seems like a half a minute which amplifies the clunkiness of a cold 750 Zephyr engine, how the Hell am I ever gonna sell this bike and convince a new owner that the rattle bang wallop noise is normal for a Zephyr. I may as well just bury it in concrete now and forget about it :lol:
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Re: Use of choke

Postby Freddy » 15 Nov 2020, 22:52

Shedman wrote:Hell am I ever gonna sell this bike and convince a new owner that the rattle bang wallop noise is normal for a Zephyr. I may as well just bury it in concrete now and forget about it :lol:


Tell them to go listen to a dry clutch Ducati, especially one with an open clutch cover. Some people pay a LOT of money for noise.
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Re: Use of choke

Postby 550 Dunc » 18 Nov 2020, 18:37

Shedman wrote:Hi guy's, mine starts fine if used regular but this time of year in the UK that is highly unlikely. Anything longer than a week lay up and she just doesn't want to start unless I get the exact sweet spot on the choke which is about 2/3rds closed without touching the throttle and the tap on Prime. Even then its only on a couple of cylinders for what seems like a half a minute which amplifies the clunkiness of a cold 750 Zephyr engine, how the Hell am I ever gonna sell this bike and convince a new owner that the rattle bang wallop noise is normal for a Zephyr. I may as well just bury it in concrete now and forget about it :lol:

Sell it in the summer
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