My first classic bike (70s BMW)
Discussion
Roboticarm said:
So I've been enjoying owning the bike, not used it much as yet but been cleaning it, regular start ups and move arounds.
However yesterday it would start up, put partial choke on and it started fine but cut out, restarted and I managed to keep it idling by holding the throttle open but as soon as I let the throttle off it stalls out.
Tried with and without choke but just won't hold an idle.
It does idle if I hold the throttle but won't once I let go
Any ideas what I should be looking for please?
Sounds very much like the idle jets(and other passageways) are blocked .However yesterday it would start up, put partial choke on and it started fine but cut out, restarted and I managed to keep it idling by holding the throttle open but as soon as I let the throttle off it stalls out.
Tried with and without choke but just won't hold an idle.
It does idle if I hold the throttle but won't once I let go
Any ideas what I should be looking for please?
Strip the carbs and give them a thorough clean, idelaly strip them and pop them in an ultrasonic cleaner.
If you dont intend to actually to ride it for some time, you would be best off draining the tank and carbs rather than these "regular start ups" , they do more harm than good.
podman said:
Sounds very much like the idle jets(and other passageways) are blocked .
Strip the carbs and give them a thorough clean, idelaly strip them and pop them in an ultrasonic cleaner.
If you dont intend to actually to ride it for some time, you would be best off draining the tank and carbs rather than these "regular start ups" , they do more harm than good.
Agreed.Strip the carbs and give them a thorough clean, idelaly strip them and pop them in an ultrasonic cleaner.
If you dont intend to actually to ride it for some time, you would be best off draining the tank and carbs rather than these "regular start ups" , they do more harm than good.
I seem to remember my Dad's old R65LS had the occasional issue with the BING carbs and he didn't like them much - but when running well, they were fine.
If you're going to start it - the whole engine needs to get 'properly' hot - 30+ minutes of running (ie a short ride).
Reason: there's air in them thar crankcases, atmospheric air, with all the pollutants and extras of the air you're breathing.... including our old friend H20 (water).
Running the engine for a a minute or two will heat up the oil, and the metal, but is NOT enough time for the moisture in the air (and in the oil) to be 'burnt off', and pushed out of the crank-case breather valve. But it WILL stir up all the moisture.
Then - as the engine cools down again, the oil runs to the bottom of the engine, pushing the moisture laden air back up to the top of the engine, where the metal is cooling. This means the moisture in the air will condensate onto the cooling metal - which means you have water (with pollutants, acids etc) sitting on the metal bits in your engine.... this leads to corrosion.
If you give the bike a decent length ride, then you're getting the oil up to 'proper' temps and the water and pollutants are burnt off to a greater extent and so you reduce the chance of corrosion within your engine.
A happy engine is a well maintained, and USED engine. I did 52,000 miles on a ZXR400 over 12 years - a lot of that was daily commuting a 40 mile journey (80 miles a day each weekday, then also riding at weekends). When the valves were checked at 40,000 miles there was virtually zero wear on the valve-train, and only 1 valve needed adjustment. It helped that I used good quality fully-synth, but basically, the engine never really got cold, so wear-inducing corrosion never really happened.
Edited by RockBurner on Thursday 26th May 15:36
Edited by RockBurner on Thursday 26th May 15:37
If it's running on both at wider throttle openings then as others say, it's the idle jets.
Don't strip the carbs yet.
Get the bike out of the garage, take it for a spin. Get it hot.
Find a steep hill and rev the engine going down it up to a few thousand revs short of the redline. Hlaf way down the hill snap the throttle shut and leave it there a few seconds. Then speed back up again and do it again. Hopefully the vacuum on the overrun will pull the crap through the idle jets and you're sorted.
As other posters say - either use the bike (get it proper hot) or don't. No inbetweens.
Don't strip the carbs yet.
Get the bike out of the garage, take it for a spin. Get it hot.
Find a steep hill and rev the engine going down it up to a few thousand revs short of the redline. Hlaf way down the hill snap the throttle shut and leave it there a few seconds. Then speed back up again and do it again. Hopefully the vacuum on the overrun will pull the crap through the idle jets and you're sorted.
As other posters say - either use the bike (get it proper hot) or don't. No inbetweens.
Before stripping carbs and going riding there's a couple of obvious things I'd do.
1) Check fuel. Has it got any or have your starts in the garage used it up? On some systems the higher revs will suck through the dregs at the bottom so they'll just about run. Does it have fuel taps and are they turned on? Have you tried reserve?
2) Clean the spark plugs. Some bikes don't like running on choke too much and soot up the plugs leading to poor starting/idle. It's normally much easier to remove plugs than carbs so I'd do that first. While they're out, do they both give a strong spark (adds a couple of minutes before you put them back so might as well check).
Always step back and think of a plan that start's with the easiest stuff. I'm another that won't start a bike unless I have time to ride it, it causes more hassle than it saves in my opinion.
1) Check fuel. Has it got any or have your starts in the garage used it up? On some systems the higher revs will suck through the dregs at the bottom so they'll just about run. Does it have fuel taps and are they turned on? Have you tried reserve?
2) Clean the spark plugs. Some bikes don't like running on choke too much and soot up the plugs leading to poor starting/idle. It's normally much easier to remove plugs than carbs so I'd do that first. While they're out, do they both give a strong spark (adds a couple of minutes before you put them back so might as well check).
Always step back and think of a plan that start's with the easiest stuff. I'm another that won't start a bike unless I have time to ride it, it causes more hassle than it saves in my opinion.
There seems to be a total focus on the carbs when there are a number of other things it could (and in my experience of owning a number of airhead BMWs) are more likely to be the problem.
1. Confirm both cylinders are firing.
2. Take out each plug and confirm spark on both sides when turning over
3. If one isn’t, check the coil/lead combination by swapping left for right.
4. Check the tank is full and both fuel tabs are on main feed, not reserve
5. Check the fuel flow to the carbs by removing the float bowls and seeing that a “reasonable” amount of fuel flows.
Only when these have been done, and you’re sure there is a strong spark and a good feed of fuel to the carbs do you then need to look at the possibility of blocked jets.
1. Confirm both cylinders are firing.
2. Take out each plug and confirm spark on both sides when turning over
3. If one isn’t, check the coil/lead combination by swapping left for right.
4. Check the tank is full and both fuel tabs are on main feed, not reserve
5. Check the fuel flow to the carbs by removing the float bowls and seeing that a “reasonable” amount of fuel flows.
Only when these have been done, and you’re sure there is a strong spark and a good feed of fuel to the carbs do you then need to look at the possibility of blocked jets.
Thank you all for the feedback.
I took a quick look yesterday and can confirm that a) the fuel tap was on, there only one on this which feeds both sides, tried it on "on" and "Res" which made no difference, checked the tank via the filler and there's plenty of fuel
B) both cylinders appears to be running although the left bank got very hot whilst right was only Luke warm, there was visible output from both exhausts c) bike revs smoothly throughout the range just refuses to idle without throttle input
I guess the next step is to check the plugs but I'll have to watch some YouTube videos 1st as not something I've done before, very much an amateur with this stuff
Based on the above though sounds like a blocked idle jet ?
I took a quick look yesterday and can confirm that a) the fuel tap was on, there only one on this which feeds both sides, tried it on "on" and "Res" which made no difference, checked the tank via the filler and there's plenty of fuel
B) both cylinders appears to be running although the left bank got very hot whilst right was only Luke warm, there was visible output from both exhausts c) bike revs smoothly throughout the range just refuses to idle without throttle input
I guess the next step is to check the plugs but I'll have to watch some YouTube videos 1st as not something I've done before, very much an amateur with this stuff
Based on the above though sounds like a blocked idle jet ?
Roboticarm said:
Thank you all for the feedback.
I took a quick look yesterday and can confirm that a) the fuel tap was on, there only one on this which feeds both sides, tried it on "on" and "Res" which made no difference, checked the tank via the filler and there's plenty of fuel
B) both cylinders appears to be running although the left bank got very hot whilst right was only Luke warm, there was visible output from both exhausts c) bike revs smoothly throughout the range just refuses to idle without throttle input
I guess the next step is to check the plugs but I'll have to watch some YouTube videos 1st as not something I've done before, very much an amateur with this stuff
Based on the above though sounds like a blocked idle jet ?
The answer is above. It's running on one only. That's the problem! The exhaust has a connector pipe at the front of the engine (visible in pictures) so both silencers will give a hot output, but it's from the same cylinder. I took a quick look yesterday and can confirm that a) the fuel tap was on, there only one on this which feeds both sides, tried it on "on" and "Res" which made no difference, checked the tank via the filler and there's plenty of fuel
B) both cylinders appears to be running although the left bank got very hot whilst right was only Luke warm, there was visible output from both exhausts c) bike revs smoothly throughout the range just refuses to idle without throttle input
I guess the next step is to check the plugs but I'll have to watch some YouTube videos 1st as not something I've done before, very much an amateur with this stuff
Based on the above though sounds like a blocked idle jet ?
Next step - take out the spark plug on the right side, earth it to the cylinder fins and turn the bike over. Confirm you’ve got a good strong spark.
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