This one is tough to describe, but here goes:


Also, since it is tough to describe, here is a video I took trying to show what happens.
The popping noises you hear in the video are not me hitting something with the camera, it's backfiring:

https://youtu.be/ep6jQg_Z48c



It will drag behind the throttle quite a lot. I know it has an exhaust leak, but it also backfires fairly consistently. It also has a dead-spot around 3-4k RPM. I'll turn the throttle enough to get it to 5-6k RPM and hold it there. It will slowly get up to 3-4k RPM, and then chuff around in there for a little bit. Then it feels like it breaks past it and finally revs up to 5-6k RPM. I'm a bit (very) stuck on this one. And based on my previous experiences with mechanics, I'll post here before I take it there!

It IS running on all 4 cylinders.
Compression on all 4 cylinders is good.
Spark plugs are clean and sparking.
Hall sensor is a known-good.

Have you checked the TPS?

I would hazard a guess and say its a timing problem.
Certainly sounds like it.

R

I'll check the throttle position sensor asap

I was also thinking it could have to do with mixture, for example, if one of those butterfly things was stuck open??

Also, as far as it being a timing problem, I agree that that's what it sounds like, but isn't timing done automatically by the hall sensor, which is as I understand it, the crank position sensor?

Rabidchiwawa007 wrote:I was also thinking it could have to do with mixture,

A 4V relies much on the TPS signal for calculating the mix.

Also check for intake leaks below TB`s....first check spark plugs for differences in colour.
(If a leak causing it, it have to a be rather big one.......)

Check these links: #1 #2

I would check for vacume leaks, also I had a similar problem, and found the air flow sensor flap was hanging up, at 18-2400rpm, after you are sure there are no leaks, do you have a air flow meter you can borrow?

yankeeone wrote:, and found the air flow sensor flap was hanging up, at 18-2400rpm, after you are sure there are no leaks, do you have a air flow meter you can borrow?

A 4V don`t have an AFM.

have a look at all the vacume lines along the throttle bodies and whereever they all join up etc ...sounds like something has become unstuck or broken , cracks in the rubber are notorious for hiding

on the 2 valve its pretty simple ....but on the 4 valve a little more complex

but check the tps connector for corrosion etc

good luck

Cool, thanks again everyone! I've got some work to do in the next day or two, and I'll post what happens.

It's lean from leaks in the inlet track somewhere quite possibly after the butterflys.

Does the 4v have that crappy tube from the crankcase to the air box that always rots and splits also causes a bad air leak? I think it's more a air leak than timing.
Also when I did the K100 that I had I could only see one intake tube that looked questionable but when I pulled the TB's 3 were split.

The 16v has a tube that splits and it goes to an oil extractor in the top section of the air box and then to the TBs via more tubes that split and the oil returns to the crankcase via more tubes that split. It may pay to remove the lower section of the air box, then you can see more of this wonderful setup.

Sounds like an ingenious design!

Anyways, I messed with the TPS. I didn't set it exactly, but the bike revs MUCH smoother in neutral. I was actually able to ride it today, so we're making progress!
It also takes awhile to rev back down as well.

So for example, if I rev it up to 5k RPM, it takes maybe 3-5sec to get back down to idle. This screams pretty big air leaks to me, can anyone confirm?



When I'm riding it, I can't turn the throttle too much or the bike just chokes, loses power, feels like it's been flooded or something, and just feels like it stops pulling all together. If I turn the throttle bit by bit, however, very slowly, it stays pulling fairly consistently.

So for example, if I'm in first running at 2.5k RPM and I grab enough throttle to get to 5k RPM, it'll just choke and lose power.

But, If i'm in first running at 2.5k RPM and just slightly turn the throttle enough to get to, say, 2.6k rpm, and then when I'm at 2.6k, I'll turn it a little more to get to 2.7k, for a gradual and slow increase in RPM and speed, it seems to not choke nearly as bad and pulls more consistently.

Does this also scream major air leaks?

Sure does. When you touch the starter button as well as engaging the starter it sends a signal to the ECU to enrich the mixture for an easy start, hot or cold it does it. when the engine is running also the starter wont engage due to the ECU removing the Earth for the starter relay. So when it bogs down press the start button and see if it makes a difference. If it does go better then it is a leak for sure.
Also there is a tube at the back of the TBs that connects to all 4 TBs and joins into one tube then goes to the oil whirly gig that seperates the oil from the air from the crankcase vent. If it has come of the TBs and on my K11 it was off when I got it, that could also cause the leak.
Once again you need to get at the back of the TBs by removing all of the airbox that you can easily do.
My K11 was running so poorly that the PO was told by some guru BMW idiot mechanic to sell it to the wreckers because the engine was shagged. All it was was leaks that I fixed before I even started it and it is now a sweet bike.

Fantastic, such a wealth of knowledge on here.
So glad I found this site.

My second thought was "air leak", hence the popping.
However as I am not totally or even in any small way familiar with my own machine...yet, I too will look to other's for guidance.

Every little helps !....now who says that ?

bcnu

R

Just a thought....and a question to those who knows a loit more than I do

Could it be a malfunctioning fuel pressure regulator, making the bike act up like this?

Again, just a thought...

So here's what I've done:
_____________________________

Replaced all components underneath the butterflies, meaning:
-The intake manifolds and the O-rings under them
-The rubber hoses that connect the intake manifolds to the throttle body.

Checked the split hose system for air and oil behind the air box, all seems to be okay.

Adjusted the TPS to 0.375v with the throttle completely closed. This means I adjusted it with the idle screw all the way out to ensure the butterflies were closed. Was this the right way to do it?

Cleaned air filter (which wasn't too bad to begin with) and put it back in

Replaced cracked fuel line with new high pressure line
_________________________________

I think that's about it. So here's the thing.. the same issue is still there, but it's not NEARLY as bad. At this point, I would ride the bike the 4 miles to school and back, but I wouldn't take it on a road trip or anything.

There is still an exhaust leak, which I believe I have narrowed down to being one of the copper gaskets in the exhaust port that needs replacing. Could this cause actual running issues?

Here's the other thing: The bike seems to run and rev better with the TPS set to around ~.600v instead of .375v. In fact, it was better to the point that the issue with it bogging down upon twisting the throttle seemed to not be there any more. Does this mean anything?

Thanks in advance!

In the previous post FPR is mentioned...not a bad idea...
have the fuel pressure checked, should be 2,5 bar.

I personally would set up the idle screw before I set the TPS, loosen off both screws on the TPS, balance your throttle bodies, set the idle at 950 and only when that is all done then set the TPS.

cool cool, i'll take a look at retuning that TPS then.

also, "bar"? what is 2,5 bar? Is there a certain PSI I'm looking for? I'll most likely split off the fuel rail with a T connector and put a fuel pressure gauge on one side.

Rabidchiwawa007 wrote:what is 2,5 bar?

36PSI

What is a bar?.... Click here to see

ungaas wrote:I personally would set up the idle screw before I set the TPS, loosen off both screws on the TPS, balance your throttle bodies, set the idle at 950 and only when that is all done then set the TPS.

My only question with that is: The position of the TPS has an effect on the idle speed. So I could set the idle to 950, then change the position of the TPS, and the idle could raise or lower depending on which way I move it. So setting the idle before setting the TPS seems out of order to me. Does that make sense at all, or am I missing something else?