Help diagnose engine choke-start issue

[mrt6644]

So my current issue is regarding the choke.

The engine will pretty much never start unless the choke is on 1st or 2nd position.  No matter how long it's ben running.
When the engine is warm, it runs perfectly and doesn't stall when in neutral or with clutch pulled in.

But its strange that even when hot, the engine needs the choke to be on to start again.

[mrt6644]

I picked up my used 94 K75 this summer.  It ran rough but always started quickly.
After changing fuel pump, cleaning injectors, changing plugs and running fuel system cleaner through it, the engine runs very well.

It always starts immediately with the choke on.

However, the engine will not start without the choke on, no matter how long its been running or how hot the engine is.

Is this normal?  That the engine always needs the choke on to start?
the engine idles and runs perfectly once warm.
Does this condition point to any particular issue?

[Past-my-Prime]

Once your machine is running, can you turn the "choke" off?  -- As you may already know, it isn't really a choke, which applies to carburetor engines and restricts air entry in those, effectively enriching the mixture.

My K75 will start even when cold without the throttle boost which is what I understand the 'choke" does in these fuel injected engines.

Although it will start, it will not continue to run when cold, so it immediately stalls out.  Once it's warm, however, I can turn the "choke' down and then off, it runs fine. And starting once warm does not require me to use the choke to start (or run).

Not sure if another K75 owner's experience is particularly helpful, but I believe that my performance is normal.

[mrt6644]

Once your machine is running, can you turn the "choke" off?  -- As you may already know, it isn't really a choke, which applies to carburetor engines and restricts air entry in those, effectively enriching the mixture.

My K75 will start even when cold without the throttle boost which is what I understand the 'choke" does in these fuel injected engines.

Although it will start, it will not continue to run when cold, so it immediately stalls out.  Once it's warm, however, I can turn the "choke' down and then off, it runs fine. And starting once warm does not require me to use the choke to start (or run).

Not sure if another K75 owner's experience is particularly helpful, but I believe that my performance is normal.

Yes, after a few minutes of running the engine with the 'choke' on, I can remove the choke and the engine will run without stalling.  It just seems strange that the engine not start when hot, without the 'choke.'.

There are still a few service procedures I haven't gotten to which might affect this?
I have to check the throttle body sync and also check the valve clearances.
Im also wondering if I need to check or clean the mass air flow sensor.

My bike seems to idle at a high rpm.  Im wondering if maybe a previous owner just increased the idle instead of checking the sync/valve clearance, dirty injectors or other issues.

[Laitch]

My bike seems to idle at a high rpm.  Im wondering if maybe a previous owner just increased the idle instead of checking the sync/valve clearance, dirty injectors or other issues.

That is definitely a possibility.

[mrt6644]

I was able to perform the throttle body synchronization.
I bought the vacuum tool from Beemer Boneyard and I followed the instructions or procedure in the YouTube video by Chris Harris.
I also reduced the engine idle as it was set too high by the previous owner.

I cannot say that the "issue" is fixed.  I did have to use the 'choke' to start the engine at least once in the 20 mile test ride after.

But during the test ride after, the engine felt great and ran better than it ever did in my short life as its owner.
This "feeling" could be completely false as there is no science or data to an engine feeling good. 
But the acceleration feels great, it idles great.  Not even sure if synchronizing the throttle bodies can make a noticeable difference in the perception of the performance of the engine.
But I am checking off boxes of things I need to do and confirm.

Now, this so called issue I am having is very low priority in the scheme of things.  Every other aspect of the engine's performance feels great.  I have no history iwith K75 engines to compare it to.  But I can compare it to the way it works from the moment I bought this 30 year old bike with nearly 70k miles.

I guess the next step is checking valve clearances, regardless of whether there is an issue to address.

Im also wondering if there is some procedure or check I need to do with the cold start 'choke' linkage.  and also the mass air flow sensor.

[Laitch]

Check the valve clearances.

If each intake valve clearance is from 0.15mm–0.20mm and each exhaust clearance is from 0.25mm–0.30mm, the valve is in specification. Correct those that aren't and re-synch the throttle bodies when finished. The necessary valve shims can be purchased here at much less cost than BMW shims. This is a must-do task.

[mrt6644]

Check the valve clearances.

If each intake valve clearance is from 0.15mm–0.20mm and each exhaust clearance is from 0.25mm–0.30mm, the valve is in specification. Correct those that aren't and re-synch the throttle bodies when finished. The necessary valve shims can be purchased here at much less cost than BMW shims. This is a must-do task.

Thanks!!!

Will do and I'll report back.

[mrt6644]

I checked the valve clearances. I followed the procedures in Chis Harris's video as well as another. (below)
They all seem too tight.
I suppose the next step is to measure the existing shims?  So I know what size to order?
What tools or procedure should I use to remove the shims?
The video I watched used a special tool to depress the bucket, and another to hold it there.

Measured in mm

                      Cyl1             Cyl2             Cyl3
Intake             0.127           0.102          0.102
Exhaust           0.229           0.229          0.229

[mrt6644]

I ordered the shims and installed them.  I tried the store that was linked above, but they had some glitch and weak communications issues.  So I canceled and ordered from Rocky Mountain ATV/MC.  Th shims were about $6.75 each with $7 for USPS Priority mail.  They shipped immediately.

I ended up changing 5 shims.  I re-measured Exhaust valve #2 and it was within spec. (0.254).

The engine started right up, no oil leaks.  I got it nice and warm and checked and adjusted the throttle body sync again.

Engine runs great. Again, not sure if it's better or not.  Temp was cold (39) so maybe the difference in temps between running makes it different.
I shut the engine off a couple times and it restarted without the 'choke' lever.  But later on, with more time off, the engine required the lever.
This isn't a big issue and I don't even know it is an issue.  Bike runs amazing on rides, and it sounds great.

Not sure what other things I should check/do with the engine as a new owner of a 69k bike.
Are there other engine related procedures/checks I should do?  Not for any performance issue, but just to make sure all is good with this engine.

[Kaos]

After all the works and still needing to choke when hot, could point to a faulty coolant temperature sensor.
Would it be possible to Test its  resistance: Cold (~20°C): 2–3kΩ;
Have you also checked if your injectors have a decent spray pattern?

[mrt6644]

Where is the temp sensor?  I thoroughly cleaned the injectors recently. And verified the spray

[Laitch]

I thoroughly cleaned the injectors recently. And verified the spray

Did you re-balance the throttle bodies after correcting the valve clearances?

[mrt6644]

Did you re-balance the throttle bodies after correcting the valve clearances?

yes

[Laitch]

If your Brick runs well in town and on the highway, starting it with the choke is no big deal. Some Bricks are just a little cold-blooded. Just ride off after you start it and shut the choke down after 30 seconds or so. Check the mileage your brick is getting. It should be around 40–50 mpg in mixed driving that is not too mountainous, high speed or moping around in the lower gears. If the fuel is clean, if the spark plugs are the correct range, and if the air filter is relatively unobstructed, I suggest you end your quest for perfection and enjoy the ride.

To understand how your Brick operates and what a coolant temperature sensor is, consult the LE Jetronic Training Manual to be found in the list at this link. The coolant temperature sensor is explained on p. 22.

[mrt6644]

If your Brick runs well in town and on the highway, starting it with the choke is no big deal. Some Bricks are just a little cold-blooded. Just ride off after you start it and shut the choke down after 30 seconds or so. Check the mileage your brick is getting. It should be around 40–50 mpg in mixed driving that is not too mountainous, high speed or moping around in the lower gears. If the fuel is clean, if the spark plugs are the correct range, and if the air filter is relatively unobstructed, I suggest you end your quest for perfection and enjoy the ride.

To understand how your Brick operates and what a coolant temperature sensor is, consult the LE Jetronic Training Manual to be found in the list at this link. The coolant temperature sensor is explained on p. 22.

Good advice.  It’s not that this so called issue bothers me. I just want to make sure I’ve checked any possible issues the engine has.  Once I’ve done that I’ll be happy knowing I didn’t neglect anything.

[Kaos]

Good advice.  It’s not that this so called issue bothers me. I just want to make sure I’ve checked any possible issues the engine has.  Once I’ve done that I’ll be happy knowing I didn’t neglect anything.

By what Ive read, i think you've done more than average.
And as long as she rides well, choking is just a minor inconvenience.

[mrt6644]

Thanks.  I haven’t addressed the throttle position sensor and I probably need to set the idle now that I’m
Done
With the valves and the throttle
Position sync.

[stokester]

Slow warm-up is a good sign of the need to check valve clearances.


Keep in mind that your local motorsports dealer of Kawasaki and Yamaha will probably have those 29mm shims.  My local shop just exchanged them for mine at no charge.

[mrt6644]

I checked the valve clearances and most were out of spec.
I ended up ordering the shims from Rocky Mountain ATV/MC Accessories.

After installing the shims I did the throttle body sync procedure again.
Not sure if the issue is fixed or not.  The weather turned pretty cold and it was hard to compare the performance to the last time.
I haven't ridden the bike much since then due to snow/ice/salt, and I have been away.

[Scott_]

Something you haven't mentioned is checking for a vacuum leak after the Air Flow Metering device. A small leak can present itself as needing an extra fuel boost to start.
There are probably some tube videos out there you can reference using an unlit propane torch for finding leaks. The unlit gas will be drawn in thru the leaking spot and give you an rpm increase.

[mrt6644]

I did try the leak test a couple times.
I think I will go through all the checks again and see if I missed anything.
It’s likely that the bike is running as well as it can given the age and condition.
But I enjoy working on it so it’s no bother to keep looking.

[Laitch]

How many miles are on the odometer?

[mrt6644]

Just under 70k
The engine pulls very strong and feels very solid.  For what it’s worth

But this is my first k75 so I have nothing to compare it to.

[Laitch]

I haven't ridden the bike much since then due to snow/ice/salt, and I have been away.

Where in Florida is there enough snow and ice to use salt this winter?