Help analyze engine sound.

[tsimi]

I need help analyzing my engine sound.
Before sme background info;

I had a MJ #94 in my carb and when driving with WOT I could hear a light *ziiiiiing* sound.
I read somewhere here in the forum that that means it runs lean so I thought since the temperatures anyway are dropping recently I'll go up to MJ #96.
Now I don't have that *ziiiiiing* sound anymore but what happens is following;

When I cruise around I can hear some sort of "brabrabrabrabrabrabrabrabrabra" you know the engine sound like the piston is going forth and back.
Now when I crank it full to WOT for 10-15 seconds and release the throttle this "brabrabrabra" sound is gone and I hear.......nothing...or maybe
some sort of *vvvvvvvvvvvvvvvvvv* like it is driving in an empty/neutral gear. then i quickly apply throttle and release it again and the "brabrabrabrabrabra" is back.
Is this normal? Or is this some sort of a sign that I need to take serious? If so what could be the cause of this?

I hope what I just explained makes sense. Kinda hard to explain in words.

[drandon]

Is that BMF exhaust an expansion pipe" Mine made the same sound evolution when I upgraded my exhaust pipe to a Stage6 Pro Replica. Nothing to worry about IMO.

[adlyman]

Sounds are always so hard to analyze cause they vary so much from bike to bike.
Going by your background info and the fact you went up 2 jet sizes it sounds like the brabrabra sound is probably 4 stroking from being to rich. Maybe try a 95 MJ and see if the problem gets better.
Always pays to get back into the WOT plug chop game when you have changed jets or when the seasons change or in your case when you hear a suspect noise. Unless you have tuning aids installed like EGT or lambda gauges then plug chops are your best option.

I've always found that when my 2 stroke minarelli's always run best when they get a more hollow 2 stroke braaap but unfortunitly that's usually when they are at their leanest which is dangerous.

[katastroff]

Oct 2, 2015 6:40:40 GMT -5 tsimi said:

I need help analyzing my engine sound.
Before sme background info;

I had a MJ #94 in my carb and when driving with WOT I could hear a light *ziiiiiing* sound.
I read somewhere here in the forum that that means it runs lean so I thought since the temperatures anyway are dropping recently I'll go up to MJ #96.
Now I don't have that *ziiiiiing* sound anymore but what happens is following;

When I cruise around I can hear some sort of "brabrabrabrabrabrabrabrabrabra" you know the engine sound like the piston is going forth and back.
Now when I crank it full to WOT for 10-15 seconds and release the throttle this "brabrabrabra" sound is gone and I hear.......nothing...or maybe
some sort of *vvvvvvvvvvvvvvvvvv* like it is driving in an empty/neutral gear. then i quickly apply throttle and release it again and the "brabrabrabrabrabra" is back.
Is this normal? Or is this some sort of a sign that I need to take serious? If so what could be the cause of this?

I hope what I just explained makes sense. Kinda hard to explain in words.

A recording of the sound you make when you imitate your scooter would be very usefull for the diagnostic.

[tsimi]

katastroff said:

A recording of the sound you make when you imitate your scooter would be very usefull for the diagnostic.

[tsimi]

Thanks for the help guys.

drandon

It looks very very similar to this exhaust just in flat black.

49ccscoot.proboards.com/post/81609/thread

adlyman

Yeah I know what you mean. Mine runs also best when driving towards the lean side that is why I was worried about the *ziiing* sound at WOT with the MJ #94.
I still haven't tried a #95 yet since I don't have one but I hope that I can get one soon.
I would love to take a video but I got no GoPro and I also doubt that I can record that sound in good quality since it happens only at high speeds and the wind sound would probably mute it out.
I don't know if you guys have that sometimes but when you go downhill the engine sounds like it shuts off and gains and gains speed and then when you release the throttle and crank it again it gives you some sort of a kick and the *brabbrabbrab* sound is back again.
That is how I hear/feel it.
My CHT shows no overheating all is in normal levels. When cruising I get 150-170F If I do a couple of WOT sessions I can see 190-200F and when I turn off the engine and the cooling shroud stops the CHT goes up till around 220F.
Thus far I haven't seen anything higher then 223F. But then again I am still in break in phase and therefore don't drive like I stole it style, yet.

[Deleted]

If you drove it like you stole it, your scoot would be painted flat black, ha ha.

Bill