Choked OFF

[freddy3]

Is it age or something else that's causing the bike to require ~10 minutes idling with the starter jet lever (choke) ON before it's drivable with the choke OFF?

When cold, the bike usually starts with one kick (or a coupla cycles of the decompression lever) with the starter jet lever (choke) ON. However, it'll stall or misfire if I switch the choke OFF and try to drive it until it's been running (with the choke ON) for at least 10 minutes.

With the choke ON, I can drive right off without any problem and, then, just switch it off after ~8~10 minutes. But, according to the owner's manual, driving with the choke ON is NOT recommended; the manual states that the choke can be turned off within a minute or two and drive fine after that. So I'm stuck sitting around for 10 minutes before I can drive.

If I let the bike warm up for ~10 minutes before switching the choke OFF, the engine runs beautifully after that.

The carbs and petcocks have been rebuilt (multiple times!), the tank cleaned and the timing's spot-on.

What's the reason for the extended warm-up time or is it safe to drive with the choke ON for a few minutes?

 

[XSLeo]

I would say the pilot circuit is a bit on the lean side. Try opening the idle mix screws 1/2 turn. That is if the aircleaner is clean and no air leaks on the intake to cause a lean condition.
Leo

 

[freddy3]

The air cleaner's new and there're no intake leaks. I think I've got the idle mix screw set to 3/4 of a turn now (spark plugs look perfect), but I'll try another 1/2 turn and see if that helps.
Thanks!

 

[blue900]

I use to drive mine all the time after startup with the choke on to get going down the road.
Now I have it tuned really well, its not needed so much.
One time I was having that problem and one of the o-rings on a mix screw was bad (denigrating) and not sealing.
I have the timing retarded per XSjohns Recommended.
Synching the with a homemade nanometer REALLY makes a difference.

I am pretty amazed how well these bikes run when every things right.
It sure took me too many years to figure it all out, but eventually I got it.
It now starts right up even at 30degs with full choke, after a min or so halve choke. I use to have a devil of a time keeping it started.
They run amazingly smooth down the road and it idles great.

 

[XSLeo]

I'm not sure what year your bike is but 3/4 turns out was the spec for 70-75. On my 75 I found 1 1/2 worked better.
Leo

 

[freddy3]

Thanks, Leo. I'll try to get over to the bike in the next coupla days, but the screw's currently at about 1 turn. I'll try adding another 1/2 turn and see if that reduces its required warm-up time.

 

[weekendrider]

The sweet spot won't be found in 1/2 turn increments. It will be somewhere between a titch and a tad more.

 

[freddy3]

I was waiting for someone to say that...

 

[gggGary]

Float level will affect how long the choke needs to be on also. I think that's part of the reason they are fussy about it. Low gas level = leaner idle and taper jet running. Conversely a bike with a leaky float valve often needs no choke at all. And air temp matters, at 50 degrees some choke is needed for a few minutes.

 

[XSLeo]

Yes, to get it tuned properly it can take very small changes to the mix screws, 1/2 turn should have an easily recognizable change. If this makes a difference he can do more tuning by using the dead cylinder method. Which is detailed in his repair manual.
Leo

 

[freddy3]

And air temp matters, at 50 degrees some choke is needed for a few minutes.

The air temp hasn't been below 65 so far, but I'm wondering whether, at 50 degrees, can I drive the bike with the choke ON or do I need to stand there and let it warm up first?

 

[freddy3]

Yes, to get it tuned properly it can take very small changes to the mix screws, 1/2 turn should have an easily recognizable change. If this makes a difference he can do more tuning by using the dead cylinder method. Which is detailed in his repair manual.
Leo

The only "dead cylinder" method I know of in the manual is for setting the idle speed (run on one cylinder while lowering the idle speed until the engine dies, repeat with other cylinder to set proper idle speed). Is there something similar for setting the mixture screw?

Other than the static mixture adjustment in the service manual, the only other method I know of is setting it for the smoothest idle, which is usually one-to-two full turns past the setting specified in the service manual. But I worry that this will result in rich running.
By the way, my carbs are rebuilt and all internal journals were cleared and checked.

 

[weekendrider]

Do what you will, but I ride mine with the choke on. It will tell you when enough is enough.
Might add petes suggestion that if you do ride it cold DON'T run the rpms up till it is warm to save your sump filter from tearing. But if you are on a road with little to no traffic what could be the harm in letting it putt down the road as opposed to letting putt on the yard?

 

[retiredgentleman]

The air temp hasn't been below 65 so far, but I'm wondering whether, at 50 degrees, can I drive the bike with the choke ON or do I need to stand there and let it warm up first?

On my bike the choke is only on for about 10 seconds. If you need to have the choke on for any longer than 15 or 20 seconds, it means your carbs are not adjusted correctly. Low speed pilot circuit is starving for fuel and choke is adding the extra richness required. That's how it works on my 78 with just an On or Off choke. If you have a choke with several steps, perhaps you can leave a partial choke on for longer periods.

Yes, its a good idea to let the engine warm up................prevent ripping the sump filter as weekendrider mentioned.

 

[freddy3]

The choke on the XS2 is an ON/OFF affair; there're no steps or partial settings. Also, the sump filter's a metal screened filter frame that sits under a two inch diameter cover in the right side cover. I don't get the connection between driving the bike with the choke on and ripping or damaging that metal sump filter?? Can you explain that? I thought the reason for not driving with the choke on is because the engine's running rich and may foul the spark plugs. Did I get that wrong?

 

[weekendrider]

If you have a choke with several steps, perhaps you can leave a partial choke on for longer periods.

I should have taken that into consideration. I rarely have to use full choke, my choke rod (34's) is modified with two extra steps.

 

[retiredgentleman]

The choke on the XS2 is an ON/OFF affair; there're no steps or partial settings. Also, the sump filter's a metal screened filter frame that sits under a two inch diameter cover in the right side cover. I don't get the connection between driving the bike with the choke on and ripping or damaging that metal sump filter?? Can you explain that? I thought the reason for not driving with the choke on is because the engine's running rich and may foul the spark plugs. Did I get that wrong?

Your bike has 2 filters (strainers actually). The one in the sump of the engine, is easily torn if you rev the engine while the oil is thick (cold engine). The filter on the right side cover does not normally tear with cold oil.

The connection between choke and sump filter damage is the fact that if the choke is on it means the engine is cold and the oil viscosity is heavy.

Its not normal to drive with the choke on with a bike or with a car/truck. In fact with proper adjusted carbs, the engine will bog down very quickly if the choke is left on. The choke is adding extra fuel, but within 15 or 20 seconds your engine is happy to run with the normal 14 to 1 air/fuel ratio.

 

[freddy3]

Your bike has 2 filters (strainers actually). The one in the sump of the engine, is easily torn if you rev the engine while the oil is thick (cold engine). The filter on the right side cover does not normally tear with cold oil.
The connection between choke and sump filter damage is the fact that if the choke is on it means the engine is cold and the oil viscosity is heavy.

Got it!

Its not normal to drive with the choke on with a bike or with a car/truck. In fact with proper adjusted carbs, the engine will bog down very quickly if the choke is left on. The choke is adding extra fuel, but within 15 or 20 seconds your engine is happy to run with the normal 14 to 1 air/fuel ratio.

Well, then there's definitely something amiss on my bike, because it takes at least 10 minutes (ambient temp above 70) before the bike's drivable without the choke.
Could it be the idle mixture screw (currently set at ~one turn) needs to be opened further or is it the float level height or something else? Again, the carbs have been rebuilt and that had no affect whatsoever on the choke status.

 

[weekendrider]

What is your rpm idle speed when the bike is warm?
With the 38's(on/off choke only) I've always had to play with the throttle a little between the choked positon and off choke position till it is fully warm. Just part of it.
You could raise your idle speed till it warms to avoid this but then your have to lower it or the idle races. Use a cruise control to keep it open a little more. Or there may be some obstruction, clean the carbs again. I don't think I'm the only one to experience this and seems to be what you are describing. One of the reasons I like the 34's better.

 

[freddy3]

What is your rpm idle speed when the bike is warm?

~1200rpm

With the 38's(on/off choke only) I've always had to play with the throttle a little between the choked positon and off choke position till it is fully warm. Just part of it.

Can you clarify this a bit?
When starting from cold, the bike'll sit, idling with the choke on at ~2000rpm, without any problem for ~10 minutes. The problem is that if I take the choke OFF and try to ride the bike before then, it'll sputter, backfire and generally run poorly. After it's fully warmed up (usually about 10 minutes), I can then switch the choke OFF and drive away without any problem.
Just to be clear, the bike'll idle more or less fine with the choke OFF after about a minute. But if I turn the throttle or try to drive it before it's fully warm, it'll sputter, backfire and just run without any power.

Or there may be some obstruction, clean the carbs again.

The thing is that the carbs've been rebuilt three times, once by two different shops and the last time by me. In each case, the journals were cleaned and blown clear and all new internal gaskets and valves have been fitted. The engine runs swell, but only after it's fully warmed up. The only thing I haven't tried is boosting the idle mixture screw past it's current one-turn setting. So I'll try that.