Suzuki 2 Strokes

So I'm stumped again!

After dial gauge timing the 380 ('72), new rings new clutch and carb sync, I figured I was all set! Don't get me wrong, the bike is running "better" than before (more consistent characteristics), but now I am noticing what I suspect is detonation almost exactly at 5500 RPM or if the motor is under substantial load ie; 4-6th gear between 4k-redline. 1st and second doesn't hickup much.

What I am hearing is a shudder, rattle of sorts relatively in sync with the revs of the motor.

My question is; has anyone else experience this same type of issue after timing their 380? I am not 100% sure of the sound of detonation so I'm not sure if I'm chasing a ghost or what. I even swapped needles in the carbs to ensure they weren't worn and causing the bike to go rich between circuits. Plugs show a nice light brown on the ring so im truly flummoxed.

EDIT: In addition to the other inquiries, has anyone had pre-ignition or detonation because of carbon build-up on domes of pistons? This is a common cause for knocks in cars, perhaps also in these old 2 strokes?

Can anyone hook me up with proper timing numbers for a 380J so as to compare with my info? The last thing I want to do is blow this baby to kingdom come!

In the sticky at the top of this section, look in the general specs and info post. You will find all the specs for the GT380K. The best I can tell, the J was exactly the same
Depending on the thickness of the carbon build up on the pistons, the dial indicator is no longer accurate. You would be better off timing to the marks on the case and see if that 'coming apart' sound goes away.

Great point about the carbon! And thanks, completely forgot there was 380 details up there. Looks like I may have found it... Appears I somehow got ahold of timing specs for the A model (2.09 l/r and 2.05 c). The J model is 2.99mm l/r and 2.93mm c. Suppose this could very well be the issue.

Sorry you had to answer the obvious but thanks as always! Will report back.

My 10 cents worth is this: I've found the factory timing spec for my 380M (2.25mm BTDC) to be too advanced for my bike, even with shiny clean piston crowns and cylinder heads.

Like you, I got mild pinging in the mid-range (4,000rpm upward). I knocked the timing back to 2mm BTDC and no more pinging at all. There's no detectable difference in performance either.

I have a theory that Suzi recommended quite aggressive ignition timing to make the bikes feel a little sharper in mid-range running. However the stock motors are so mildly tuned that a couple of degrees retarded will make no difference to power, but WILL stop you holing a piston ...

Thanks Craig, my thoughts too.

I'm going to reset it to the proper timing for the year. If that's still too hot I'll use the pinwheel marks and see what I get!

I don't know. Remember when these strokers were built there was real gasoline! Even today if you find a station that sells 'real' gas, it's still crap compared to what was available in the day. I think all our bikes are starving for LEAD They say lead is deadly but when you think about it, so is life. I absorbed enough leaded gas as a kid I should have been dead years ago. Buy hey, big brother is protecting me. I feel safe now. Those little emoticons on the left is missing a good 'moon' shot

Haha! Yeah that too! I've read over and over that these things absolutely hate the watered down bean juice were forced to feed them. Anyone know a legitimate 'octane booster' to run? Just for the hell of it at this point!

I use Lucas octane booster in my Harley and it works great. Not sure how it will work with 2 Stroke engines though

After returning my T350 back to the road in 2000 I was plagued with pinging and blamed it on unleaded petrol despite using 98 octane unleaded and octane boosters.

Years of playing with carburettors was useless in reducing pinging until replacing crank seals could no longer be ignored whereupon all pinging stopped even with our 91 octane. It was all caused by lean mixture and I happily use 3mm advance not the standard 2.77mm without pinging.

Pinging experiences

Me never timing: I mean changing a few degrees never helped. Nor does higher octane (87 -93) ever really fixes on streat engine (intended to run 87) or the root problems listed below

Carbon build. yes pinging, only once engine is hot/fully warm and hard pulling or small throttle high revving/pull

Small end bearing (worn, rust pits) sounds similar to pinging, but should also hear when light load where piston inbetween coasting and powering ahead. (or some other mechanical issue can sound like pinging, ring rattle, large piston clearnance, some hunk of tin rattling).

Seal/air leak: only small throttle openings, here the air leak becomes significant with respect to carb opening, and only here once rpms are higher. can mask by over riching pilot, needle position but that causes other problems ... normal running too rich.

Plug gap too wide and heat range way off (too hot). this is a stupid mistake which of course i never did

I think people have other experiences like sharp edges... interested to here

Thanks for all the feedback guys.

I retimed the bike to the CORRECT J model spec, raised needle clip one position and bam. Smooth power all the way up to redline. I think the timing was just so far advanced that it was causing that chatter. Amazing that these bikes will run so far out of spec.