weird engine noise (recorded)

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anvilsteel

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Hi folks,

Lately my xs is making a weird noise. I don't know what it is.
It sounds mechanical and the engines seems to, sort of cough and falls back in revs:eek:

I have a 750cc big bore kit, a new pamco ignition which timing is o.k.
Carbs are synchronised and the mixture seems to be allright (according to the nice blue flames as seen through the colortune plug). Cam chain tension is what it should be and the valves are set according to the specifications.

The engine makes this noise after a cold start. When it's warmed up the noise dissapears eventually.
Should I worry about this (a piston thingy)?

I've recorded it with my Phone.
You can hear the mechanical clicking in the entire video, but best between 50 and 60 seconds.

Any feedback will be highly appreciated.

 
I think I hear a lean-fire, skip-fire, spit-back.

Check the plugs, or better, replace them.

Try this:
Remove one plug, leave it connected and grounded to protect the coil.
Start engine, adjust idle so it'll idle on one cylinder.
As it's idling, see if the syndrome persists.
Then, repeat for other cylinder.

Report back whut happens...
 
O.K. Twomany,...thanks for your tip!

I tried your suggestion. The iridium plug on the left side was coffee brown, the one on the right was black and a little wet. I suppose this means the right cilinder was running too rich.
I changed the right plug for another. The weird sound was still there.
After this I adjusted the Mix screw (BS 34 carbs) using the dead-cilinder method.
This puzzles me. I expected to find the point where tempering with the mix-screw would result in higher revs. Both cilinders didn't rev up,...The engine just stopped with the screw all the way in and all the way out. So I decided to screw them both 2,5 turns out.
What could this be an indication for? Am I doing something wrong?
Perhaps it is wise to take of the carbs apart and clean them. Maybe one of the diaphragms is leaking?

Nevertheless the noise is less frequent now. Perhaps because of the other sparkplug or another setting of the mix-screw (it used to be 3 turns out instead of 2,5).
 
If it didn't do that spit-back thing during the dead cylinder method, might want to recheck the ignition timing.

Too much fuel? Recheck the carbs.
 
Pamco ignition timing is good (rechecked it today).

I guess a complete cleaning and inspection of the carbs will be my next step.
 
anvilsteel said:
Pamco ignition timing is good (rechecked it today).

I guess a complete cleaning and inspection of the carbs will be my next step.
Click to expand...

Hi anvilsteel,
IMHO that should have been your FIRST step, not your next one.
And that's a COMPLETE teardown to the very last little jet, needle, orifice and internal passageway.
Except don't mess with the butterfly shafts unless you are ABSOLUTELY SURE that the shaft seals are hooped,
they are a bear to work on.
 
The teardown will, of course be complete. I own an ultrasonic-cleaner which will come in very handy.
I don't agree cleaning the carbs should have been the first step. I swapped the PAMCO ignition with the upgraded model. After that the noises started. So it seems logical to me that the first place to look at would be the ignition.
But, on the other hand you could not have known that because this info wasn't in my thread...
 
anvilsteel said:
The teardown will, of course be complete. I own an ultrasonic-cleaner which will come in very handy.
I don't agree cleaning the carbs should have been the first step. I swapped the PAMCO ignition with the upgraded model. After that the noises started. So it seems logical to me that the first place to look at would be the ignition.
But, on the other hand you could not have known that because this info wasn't in my thread...
Click to expand...

Hi anvilsteel,
yes, but shit happens especially it happens inside elderly motorcycle fuel systems.
It's entirely possible that the carbs crudded up at about the same time as the ignition upgrade.
 
Anvilsteel---After listening to your engine run it makes a sputter at 29 sec. and guess what .... mine does the same thing occasionally. I also feel it is ignition, mine is Pamco with E-advancer. I'm keen to see what you come up with. tim
 
Hi Timbeck,

I doubt the problem is the Pamco with E-advancer. Mine gives a good spark and the timing is set with a timing light. So that works as it should..
My guess is that with my new PAMCO and the ultimate black coil (before I had the 'old 'Pamco with the green coil and which I upgraded with the E-advancer) the sparks will be hotter/better. Perhaps this means re-adjusting the carb settings.

This weekend I'll clean the carbs and work further from there.
I'll post my findings here.
 
Ok, I cleaned the carbs.
No difference in sound and the the right carb started leaking fuel through the air filter (xs performance pod).

Took them off and opened the carbs again: O-ring floatneedle-seat was leaking! Because it was years ago since I last took apart the carbs I've ordered new jets, needles etc. at Heiden Tuning. So I will rebuild the carbs with new components.
I'm waiting for the stuff to be delivered, shouldn't take too long as he is in the Netherlands too.

Then a question: I took out the advance rod for cleaning and greasing in the process of re-installing the PAMCO. Can it be put back in in only one way? Or is it possible that I mistakingly turned it 180 degrees, and what could be the result of that?
 
Few days later;

I completely rebuild the carbs.
They had a lot of flaws. When examining every part closely I saw that there were two different needles in the carb. I replaced them for new 5HX11 needles with new needle jets. I put in 2 new floatvalves and seats.
I rejetted the carbs with new genuine Mikuni jets: pilot 45, main 145 and air 135. (750cc with pods)
I also switched an old Carb Slide & Diaphragm Assembly for a new one.

I adjusted the floats according to specs.

The noise, however, persists. :doh::doh::doh::doh:
But now only on the left side. Carbs are in sync. Timing is ok.
When it's idling the revs are lowering once in a while and then the left carb is coughing out some mist. After that the revs go back to normal after which everything repeats itself.

I'm guessing now that the valves are the problem. Maybe on the left side they don't close fully on the intake side? Carbon build-up?
 
Last edited:
checked, rechecked and triplechecked it (with Gunson timing light).
The Pamco works fine, there is a steady consistent spark.
I have brand new Iridium plug, new caps and wires.
this really puzzles me...
 
Last edited:
I dont know anything about the E-Advance. Have you messaged Pete? Did the problem start when you installed the coil/advancer set up?
If the problem is only in one cylinder, what about swapping the cylinder your ignition leads feed too? See if the problem moves from the left to right side. If it moves then you know its something in that system? Maybe the coil is somehow bad for example. If it makes no difference, then its something else. Just eliminate possibilities beginning with the simplest to test.
 
Hi Wherearewe,

I already tried that option.
It makes no difference.
Because the carbs have exactly the same set-up and the Pamco is ok I am now suspecting the valves.
Altough I'm not a complete noob it's some sort of uneducated guess, I guess,...

Before taking the engine out and opening the top end (which will be my maiden voyage) I'd like to rule other possibilities out
 

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