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Starting the bike

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rob75
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Starting the bike

Post by rob75 on Tue 27 Jan 2015, 8:28 pm

Hi All,

I recently purchased a CB 500 (1994 model) and have a question on starting the bike.
When i bought it, as the price was low I paid for it without questions asked, it drove well as expected. Now after two weeks, I noticed that the bike can be started with the choke applied but this has to be turned off after 15 seconds and the bike will run. At the moment, the outside temperatures are approx. between 2 and 6 degrees Celsius.
Driving the bike I suspected that the bike is tuned a bit rich (pilot screws). At the moment I've turned them 1/2 turn inward (leaning the mixture). The bike seems to be running better now.

My questions now are the following:

- is it normal that the bike starts with the choke and the choke can be switched off after 15 seconds of idling? driving after that is fairly ok. Driving with the choke on is fairly rough.
- during driving, it makes a distinct sound like a lawnmower at low revs (<3000 rpm)
- during driving on the motorway (>60 mph) you still keep the sound of a twin with a slight notice of a screaming Japanese four-cilinder.

Are these normal experiences with the bike.

Cheers,
Rob
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teamster1975
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Re: Starting the bike

Post by teamster1975 on Tue 27 Jan 2015, 8:43 pm

@rob75 wrote:
- is it normal that the bike starts with the choke and the choke can be switched off after 15 seconds of idling? driving after that is fairly ok. Driving with the choke on is fairly rough.
It is very rare that you should need the choke apart from in cold weather. I have always found that the engine runs smoother after I close the choke, I would check your air filter though and the colour of the spark plugs for too rich/lean
@rob75 wrote:
- during driving, it makes a distinct sound like a lawnmower at low revs (<3000 rpm)
Keep your revs higher, it's much happier that way. There is a nice power band around 6-8K Wink
@rob75 wrote:
- during driving on the motorway (>60 mph) you still keep the sound of a twin with a slight notice of a screaming Japanese four-cilinder.
I guess a parallel twin is half a 4 pot engine so that would make sense Smile Get yourself a Fuel can (club discount!) or similar, it sounds much better.

sullivj
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Re: Starting the bike

Post by sullivj on Tue 27 Jan 2015, 8:47 pm

Your bike sounds much like mine - I wouldn't be concerned.
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jchesshyre
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Re: Starting the bike

Post by jchesshyre on Tue 27 Jan 2015, 8:51 pm

Likewise, nothing you describe sounds weird.

I'm sure you know this but don't work the engine (full throttle or above about 6000rpm) until it's warmed up (10-15 mins' riding).
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rob75
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Re: Starting the bike

Post by rob75 on Tue 27 Jan 2015, 10:27 pm

Thank you for the quick respones.

It seems my guesses are right. It is running fine now and the choke is hardly needed.

I always drive any kind of vehicle in a moderate way until it warms up. I'm to much a mechanical guy to know about the consequences. BTW, I've driven my whole life Alfa Romeo's which seem to hate revving when cold....

The experience with the bike so far seems to be a very usable powerband between 3500 and 6500 rpm and a joy beyond 7500 rpm. Unfortunatly, I want to be in front of the traffic light queues, manouvering between the line of cars in first or second gear with some just above idle rpm's. At those moments I experience the "lawnmower" sound, but also a good running engine without judder or hesitation.

It seems nothing to worry about. I will be checking the spark plugs soon. And if in doubt I will use my Gunson set to check the mixture. Already checked the caburettor balance and this is OK. A slight difference (+/- 2 cmHg) between the carbs. Only strange thing is that with opening the throttle, one carb stays behind in vacuum. When the throttle is stable, the vacuum difference is also gone. It seems one slide is somewhat slower as the other. Maybe sticking a bit? Added carbcleaner to the fuel to see what is happening.
Cheers,
Rob
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jchesshyre
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Re: Starting the bike

Post by jchesshyre on Tue 27 Jan 2015, 10:42 pm

When did you last check the valve clearances? Could be that. Also, low speed running and throttle response should improve after you've racked a good few miles up if the bike had been sitting around a bit, especially after a good long run.

I have a 42-tooth rear sprocket (+2 from stock) which makes driveability at low speeds in 2nd a bit better (though that's not the reason I changed it – it's the extra perkiness I like). Actually, check the sprockets on there – who knows, the previous owner might have put a smaller rear or larger front on which would certainly make 1st and 2nd more 'chuggy' at low speeds.
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rob75
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Re: Starting the bike

Post by rob75 on Thu 29 Jan 2015, 6:02 am

The valve clearance is another suspect indeed. Unfortunately Honda chose shims instead of the usual method with adjustment screws. So that will have to wait until spring. I don't want to do maintenance that may take more than a day (getting shims).
Changing the chain and sprockets is a bit of a waste at the moment, as these are in gooed condition.

On the other hand, taking it on some longer drives (using some fuel system cleaner) is a good way to start.

Cheers,
Rob
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Celt500
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Re: Starting the bike

Post by Celt500 on Thu 29 Jan 2015, 10:06 am

@rob75 wrote:Unfortunatly, I want to be in front of the traffic light queues, manouvering between the line of cars in first or second gear with some just above idle rpm's. At those moments I experience the "lawnmower" sound, but also a good running engine without judder or hesitation.

More revs and slip the clutch.
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jchesshyre
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Re: Starting the bike

Post by jchesshyre on Thu 29 Jan 2015, 10:18 am

If you say it's without judder or hesitation then I reckon it's fine and that the 'lawnmower sound' could just be that you're not used to hearing the individual explosions of each cylinder, as you do with a twin at low revs (and even more so with a single, which most lawnmowers are).
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rob75
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Re: Starting the bike

Post by rob75 on Thu 29 Jan 2015, 4:06 pm

Normally I drive a Aprilia V60 twin. This makes a completely different sound at low revs. It is possible to hear the individual explosions on that bike, but with a very different experience.

As said, the bike runs OK at low revs and perhaps my mechanical ears are not used to the sound of a parallel twin. During driving lessons I used a Suzuki GS500, which is comparable, but it's to long ago to remember the sound of that machine.

On the other hand, the CB starts good, runs fine and is reacting very prompt to the throttle. I don't know the correct English translation, but in Dutch we say "It is hanging on the throttle like a pittbull".

Cheers,
Rob
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eternally_troubled
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Re: Starting the bike

Post by eternally_troubled on Fri 30 Jan 2015, 12:47 pm

@rob75 wrote:The valve clearance is another suspect indeed. Unfortunately Honda chose shims instead of the usual method with adjustment screws.



Shims are in some ways good thing:  they can't come undone so the interval between inspections should be longer.  Changing them isn't that bad:  it seems bad when you read it in the Haynes manual but it isn't too bad once you start getting on with it.


...in Dutch we say "It is hanging on the throttle like a pittbull".


We get the idea!  Not quite sure there is an English equivalent (that I know), but that doesn't matter. Sounds like the bike is working the way it should!
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rob75
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Re: Starting the bike

Post by rob75 on Wed 04 Mar 2015, 9:41 pm

Well, I've driven the bike for some time now and trying to see what happened. After leaning the mixture there was some progress in running characteristics. Measuring vacuum left a bike with balanced carbs. Adding a fuel system cleaner the engine started to run differently. Still not satisfied with an engine capable of starting (and running) with no (or marginal) choke at below 0 degree Celsius it left me wondering.

Tonight I reset the pilot screws to 1,5 turns out. Taking the spark plug cap of from one cilinder, no change, even though the exhaust gets warms for that cilinder. Disconnecting on the other cilinder, the engine stalls. So there is definitely an ignition problem. Adjusting the pilot screw on the less functioning cilinder helps in smoothing the engine. A test drive leaves a better bike. So for now, that is the solution.

No time this weekend, but try to sort things out next week. Think I need to have a look at the HT lead and/or coil for the less functioning cilinder.

Regards,
Rob
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stormbringer
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Re: Starting the bike

Post by stormbringer on Thu 05 Mar 2015, 7:03 am

@rob75 wrote:Well, I've driven the bike for some time now and trying to see what happened. After leaning the mixture there was some progress in running characteristics. Measuring vacuum left a bike with balanced carbs. Adding a fuel system cleaner the engine started to run differently. Still not satisfied with an engine capable of starting (and running) with no (or marginal) choke at below 0 degree Celsius it left me wondering.

Tonight I reset the pilot screws to 1,5 turns out. Taking the spark plug cap of from one cilinder, no change, even though the exhaust gets warms for that cilinder. Disconnecting on the other cilinder, the engine stalls. So there is definitely an ignition problem. Adjusting the pilot screw on the less functioning cilinder helps in smoothing the engine. A test drive leaves a better bike. So for now, that is the solution.

No time this weekend, but try to sort things out next week. Think I need to have a look at the HT lead and/or coil for the less functioning cilinder.

Regards,
Rob
Fuel system cleaner: Nice idea. Getting rid of the gunk.
Almost-no-choke-starting: They all do that, Sir.
Differing outcome, removing plug caps: Hmmm... Is the engine limping along on one cylinder at idle?
Sound: Parallel-twins sound different, depending on crank geometry I learnt yesterday. The CB sports a traditional 180 degree crank, which means it sounds and rides different from your V-twin. A replacement can from Fuel (see advert in right pane --->) will completely renew - and invigorate - your CB's soundscape. It's the one non-essential investment I've made on mine that I'm happiest about.
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eternally_troubled
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Re: Starting the bike

Post by eternally_troubled on Thu 05 Mar 2015, 1:13 pm

It will be interesting to see what you find. I'm not sure my bike will run on one cylinder at at time - it probably should, I will have to test that next time I have the tank off.

It might be worth measuring the resistance of the ignition coils, if you are taking the bike apart again.

I don't *need* the choke to start until it gets really quite cold - most of the time a bit of throttle is enough if you are prepared to stand there and fiddle with it until things warm up a bit.

If I want to 'press the starter and go' then I need choke below (approx) 7 degrees.
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rob75
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Re: Starting the bike

Post by rob75 on Fri 06 Mar 2015, 8:21 pm

Well the choke usage is unchanged, but that was no problem as I read in several answers.

What wonders me, is the left cilinder hardly responding on disconnecting the plug cap. On the right one, it is quite good to hear the spark between plug and cap when the cap is just a few cm's off. Then the engine stalls.
Stage thing is that both exhaust pipes get warm and (feeling with my hand) seem to warm up evenly.

Hopefully I can find a moment to investigate further.

Cheers,
Rob
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stormbringer
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Re: Starting the bike

Post by stormbringer on Mon 09 Mar 2015, 6:20 am

@rob75 wrote:Strange thing is that both exhaust pipes get warm and (feeling with my hand) seem to warm up evenly.

Hopefully I can find a moment to investigate further.
Sounds absolutely weird.

If both pipes get equally hot, we may assume both fire OK. Unless you define 'hot' as no more than what a bicycle pump gets when used vigorously. Still, if the plugs are nicely tan and dry, this would indicate actual combustion taking place.

Limping...
Uneven compression? Burnt valve? Broken piston ring? Head gasket leaking? One of the coils performing below-par? Carb-balance way off?

If unsure whether the cylinder fires, there's a way to find out. A see-through sparkplug lets you observe the flame.
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rob75
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Re: Starting the bike

Post by rob75 on Wed 11 Mar 2015, 11:08 am

It is a weird situation. Even more weird: yesterday I had the opportunity to test the top speed of the bike. It runs easily to a speed of 160 km/h (100 mph) and somewhat slower reached a speed of 170 km/h. This all within a ditance of 1 km. So it seems to develop a good amount of power.

What I noticed when removing the spark plug caps, was that with one cap you could hear the spark between cap and plug before the engine stalls. On the other cap, nothing can be heard. So this leaves me with a weak spark on one cilinder at low revs, which is normal looking at the nature of a CDI. As I remember, the higher the revs, the stronger the spark gets. First thing I will try is to replace the HT lead and have a look at the LT leads.

The "see-through" plug is in my tool set, so if necessary...

Cheers,
Rob
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rob75
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Re: Starting the bike

Post by rob75 on Sat 14 Mar 2015, 4:43 pm

Made some progress today. took the tank off and removed one spark plug. This was a bit wet, leaving the impression of poor iginition. On the other hand, the electrode was nice coffee with milk brown, so the mixture seems to be allright. Replaced the HT-lead.
Now when disconnecting either spark plug cap, the bike slightly drops in idle rpm, but keeps running idle.
Characteristics are still not really smooth, but I think some tuning may help now in getting the low revs (<3000 rpm) smoother.
Checking carb sync and perhaps adjusting the mixture starting from scratch.

Cheers,
Rob
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Celt500
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Re: Starting the bike

Post by Celt500 on Sat 14 Mar 2015, 5:11 pm

@rob75 wrote:Characteristics are still not really smooth, but I think some tuning may help now in getting the low revs (<3000 rpm) smoother.

If you mean riding along at low revs, it won't. Don't even try.

In the process of adapting to this bike (coming from cars) I've had to keep reminding myself over and over; 
"Change down below 4k. Change down below 4k."
3500 rpm is sort of ok if you're rolling downhill. If you search there is a dyno readout somewhere that makes sense of it - there is NO POWER below 3.5k. The bike will just judder and be horrible and you'll put stress on the engine & drivetrain. Keep it spinning happily above 4k and slip the clutch if you need to go slower.
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jchesshyre
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Re: Starting the bike

Post by jchesshyre on Sat 14 Mar 2015, 8:07 pm

Hmmm...no power below 3.5k? Mine pulls fine from idle in first gear. I don't do that often, but there's certainly useable power below 3.5k in 1st and 2nd gear.
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stormbringer
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Re: Starting the bike

Post by stormbringer on Mon 16 Mar 2015, 12:34 pm

@Celt500 wrote:If you search there is a dyno readout somewhere that makes sense of it - there is NO POWER below 3.5k.

You're possibly referring to this one:


And I concur - no grunt below 3.5k. Somewhere past 6k is much more fun. Especially if you've exchanged your OE can for eg a Fuel. This little bike is able to deliver quite a diverse soundscape if you let it.
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alvamiga
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Re: Starting the bike

Post by alvamiga on Tue 17 Mar 2015, 9:05 pm

I will dip mine below 4k if I'm expecting to go back up very soon after, but it definitely hates getting to 3k! I've also found myself sitting, waiting on an overtake, at 6k as it seems to give a nice run of power for getting past, without having to mess with gears during the move.
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Beresford
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Re: Starting the bike

Post by Beresford on Tue 17 Mar 2015, 10:26 pm

Today, as an experiment, I dawdled along as slowly as possible to see what my bike would do. It would trickle along smoothly just below 3k without complaint - but there was NO power or torque to accelerate away without dropping several gears. Any attempt to speed up in a high gear at those revs just caused severe unhappiness within the engine and transmission - much shunting and gnashing of teeth. Evil or Very Mad
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rob75
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Re: Starting the bike

Post by rob75 on Tue 24 Mar 2015, 8:59 pm

Had some time to fiddle on the bike. After changing the HT lead, I adjusted the idle mixture screws to 2.5 turns out. The result:

- starting is easy. cold with a little choke (temperature now is around 0 Celcius), warm just hit the button no throttle necessary.
- driving in 1st and 2nd gear below 3k is no problem.
- in 3rd gear low revvs are possible

So the initial problem is over. My experience now is a bike running like it should. The noise from the exhaust is also normal. A bass sound below 6k and then turning into a scream. More important, the engine runs evenly.

What may be better: there are still vibrations that are not normal. Accelerating form standstill has a light shudder.hesitation. It looks like a sync problem or still a slight lean mixture. Trouble is, that I ran into the stuck bolt on the air filter.

Maybe I'm a bit stubborn, but this bike should be able to run at low speed in a low gear. Why else is this a prefferded bike at driving schools?

Cheers,
Rob

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