Rough running

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Firestarter · #1 Post by **Firestarter** » Tue Jun 23, 2015 7:12 pm

Looking for some advice. Spoke to Alad at the weekend, but bits have developed since

I've had problems with the Falco recently, running rough, not smooth at the bottom end, lots of popping when dropping through the revs. This is new, not had this before. Started developing after a tune up(Griff), but wasn't immediately obvious and has gotten worse over time. At about 3.5k to 4.5k rpm, it's rough and surges. Had a 2nd tune up, and was told everything has gone lean. Mix reset, which has improved things but not fixed, although I might be a bit hypersensitive to it now.

While taking various bits off to investigate (including the airbox base which I've previously cracked and repaired around the velocity stack), I've noticed that, looking down the throttle bodies, one of the valves is quite black and gungy, the others seem clean including the second which is visible down that body. I do seem to be losing oil, but I've also got an ongoing leak somewhere on the left side so may be unrelated.

Griff is out the shop until Thursday, and I'm impatient. Anyone got any thoughts or suggestions?

Thanks in advance

Firestarter · #2 Post by **Firestarter** » Tue Jun 23, 2015 7:30 pm

Dalemac · #3 Post by **Dalemac** » Tue Jun 23, 2015 9:00 pm

What do you mean by a mix reset?

If the valves looks black and gungy then it could be the valve seats leaking, might explain the oil usage and the rough running.

Have you done a compression test? Should at the very least indicate you have a leak somewhere. What about smoke? Do you have any blue smoke? If so, does it only happen on startup and go away with riding or does it happen constantly?

Have you removes a spark plug and looked at the condition of the barrel and piston? If you know anyone with an inspection camera it will be particularly useful here. Otherwise the only real way to tell is going to be vale cover off, cams off and head off.

There is a lot to consider when removing cylinder heads (finding TDC, cam position/removal, valve removal (if valve seats need replacing), etc). Have you done any it before?

What mileage is on the motor, out of interest?

#4 Post by **mangocrazy** » Tue Jun 23, 2015 10:52 pm

It's hard to tell based on just one picture, but that would indicate that the inlet valve in the picture is leaking and allowing burnt gases through. There's a definite ring of black crustiness that will stop that valve sealing and can only get worse over time. You could try some of the fuel additives that purport to clean valve seats and the like - it might work...

Another option is to get hold of a remote inspection camera, as Dale says and have a good look around inside. Aldi and Lidl have been known to offer them on occasions. A compression test may confirm your suspicions, as well. But I suspect that a strip of the head in question may be necessary.

Firestarter · #5 Post by **Firestarter** » Wed Jun 24, 2015 7:33 pm

Dalemac wrote:What do you mean by a mix reset?

CO pots set, as it was set a few weeks back but for some reason was now running very lean according to Griff. That has made a significant difference, but not fixed it

Dalemac wrote:Have you done a compression test? Should at the very least indicate you have a leak somewhere. What about smoke? Do you have any blue smoke? If so, does it only happen on startup and go away with riding or does it happen constantly?

Nope, no compression test as I haven't got a tester. No smoke at any point, and I was following Alad on it at the weekend and couldn't see anything

Dalemac wrote:Have you removes a spark plug and looked at the condition of the barrel and piston? If you know anyone with an inspection camera it will be particularly useful here. Otherwise the only real way to tell is going to be vale cover off, cams off and head off.

New plugs in a couple of weeks ago as part of the ongoing diagnosis. Old plugs looked nice and tan brown

Dalemac wrote:There is a lot to consider when removing cylinder heads (finding TDC, cam position/removal, valve removal (if valve seats need replacing), etc). Have you done any it before?

Nope, but there's a first time for everything. I've done enough similar bits and pieces on cars. But I'm hoping it's not necessary... (see next post)

Dalemac wrote:What mileage is on the motor, out of interest?

28,000 miles, so still a young 'un

Firestarter · #6 Post by **Firestarter** » Wed Jun 24, 2015 7:40 pm

Right, as I had everything in bits last night, that's where the photos came from. Discussions at the weekend reminded me I had a problem with the airbox, where I'd cracked a piece off adjacent to the throttle body mounting meaning there was a bypass route into the TB around the velocity stack - dunno if that is significant as it's all from the airbox, but thought it's worth a look. The bit had come loose, and there was a gap between the airbox and the throttle body, not going via the velocity stacks. Re-epoxied, refitted, and everything seems much, much smoother. Might be the placebo effect of "finding" a problem and sorting it, but it does seem a lot smoother on my commute.

So a few more days are in order to see how things are working out, but hopefully a step in the right direction. Definitely nowhere near as rough as before the weekend.

As for the valve coking, will try some cleaner and check it in a few weeks. Hopefully as Mango suggests that will shift it, otherwise some direct cleaning is likely required. However it doesn't look oily on further inspection, so hopefully not a stem seal leak, just a bit of build-up