Heat and jetting

Hey guys, got my carb tuned perfect yesterday (I thought. Went down from 68 till I stopped 4 stroking at 64.)

Today I do some runs and at WOT, top speed I hear it. The brrrr that I believe is four stroking. (If someone can sanity check me and confirm that this weird sound I’m hearing at max revs is four stroking that would rock).

I’m gonna go down to a 62 and try again. Just curious though, could the few degrees it’s changed in temp from yesterday to today have cause this? Is the the air that much thinner when it’s hot out?

Re: Heat and jetting

I should note it actually feels cooler today, so I don’t understand it. Will check for air leaks as well. Really strange, can’t figure it out.

Re: Heat and jetting

62 did it. Still a mystery as to what’s caused my sudden need for a down jet. Runs nice and strong now. Beat my dads revel in a race lol.

Re: Heat and jetting

Maybe an air leak somehow sealed itself lol

Re: Heat and jetting

It can be, about 20-30 degrees f air temp on a highly tuned bike will change the jetting one size, but usually stockish bikes won't be so touchy.

Sometimes a plug fouling will make you 4 stroke, so you will be tuned 'perfect' one day but a bit rich and then a few miles later the plug will soot up and now you're four stroking.

Re: Heat and jetting

> Graham Motzing Wrote:

> -------------------------------------------------------

> It can be, about 20-30 degrees f air temp on a highly tuned bike will

> change the jetting one size, but usually stockish bikes won't be so

> touchy.

>

> Sometimes a plug fouling will make you 4 stroke, so you will be tuned

> 'perfect' one day but a bit rich and then a few miles later the plug

> will soot up and now you're four stroking.

That is my guess. I just put a new pipe and filter on so I was starting from a high rich guess at 68, worked down. I think you’re right, the plug got mildly fouled (wasn’t too bad at all, maybe a tad rich) and I started four stroking. I’ve only got evens so I can’t try a 63 which may be better, but a 62 seems to be working fine for me. Plug seems good, chocolate but not oily, smoke isn’t too bad, and no more four stroking at WOT top speed. Hopefully my motor doesn’t explode.

Re: Heat and jetting

Oh this was you with the wrong mounted circuit pipe? Yeah the air leak you will get from the pipe being mounted wrong will fuck you up. If I were you I'd wait to ride it until you can mount it right but I was in your shoes once and back then I would have 100% sent that shit

Re: Heat and jetting

> Graham Motzing Wrote:

> -------------------------------------------------------

> Oh this was you with the wrong mounted circuit pipe? Yeah the air leak

> you will get from the pipe being mounted wrong will fuck you up. If I

> were you I'd wait to ride it until you can mount it right but I was in

> your shoes once and back then I would have 100% sent that shit

Pipe not leaking, torqued to the mating surface properly, and bailing wire seems to hold the end perfect for now at least.

There may be a bad crank seal or something, the engine could stand a full rebuild but meh. It’s just mopeds!

Re: Heat and jetting

ARGH! Started four stroking again. I hope that’s what this is at least. It kind of sounds like a popping, brr sound, sort of like if I were to let off the throttle slowly at high speed, but it only hits in at WOT top speed. I’m gonna check my plug to see if it’s fouled, this is very annoying. I’ll check for air leaks again. My float bowl gasket is mostly toast, doesn’t leak much, but do you think that that needs to be airtight? Could that be my issue? Stock 12 bing btw.

Re: Heat and jetting

FF751EF7-2669-4B1F-A985-C8709F00DC28.jpeg
29F0FE28-036D-44C4-A874-63A52C9138F8.jpeg

Not really proper plug chops, but looks just about normal. Maybe a tad rich? Not oily just sort of chocolate leaning on the darker side.

Would going down a jet once more to a 60 be ridiculous? Feels low, but it’s like everyday the bike richer and richer. Probably have a leaking crank seal, def a bad case gasket. This issue may be kind of unavoidable without a rebuild (which I’m a bit lazy for right now). Thoughts?

Edit:

I should note I’ve done nothing with my needle setting. Don’t remember what it is right now, but I’ll check at some point. Shouldn’t really matter for what I’m experiencing though, right? This is WOT. (edited)

Re: Heat and jetting

At a 60, bike makes power, doesn’t four stroke at top end WOT. Throttle up to WOT also feels better. Doesn’t lean bog either. Engines up to temp, will throw in a fresh plug and do a plug chop minus chop.

Re: Heat and jetting

Looks fine to me. A fresh rebuild is like $50 and 2 hours of time for a beginner.

Re: Heat and jetting

Dirty30 Dillon /

> * wormdirt * Wrote:

> -------------------------------------------------------

> Looks fine to me. A fresh rebuild is like $50 and 2 hours of time for a

> beginner.

It's a ZA50, so nope.

It looks fine to me, but I've seen a source of random 4-stroking be inhaling trans oil. Keep an eye on it, if it randomly 4-strokes again, check the trans level.

Re: Heat and jetting

> Dirty30 Dillon Wrote:

> -------------------------------------------------------

> > * wormdirt * Wrote:

>

> > -------------------------------------------------------

>

> > Looks fine to me. A fresh rebuild is like $50 and 2 hours of time for

> a

>

> > beginner.

>

> It's a ZA50, so nope.

>

> It looks fine to me, but I've seen a source of random 4-stroking be

> inhaling trans oil. Keep an eye on it, if it randomly 4-strokes again,

> check the trans level.

Will do. There's a very minor oil leak between the crank cases, and (maybe) at the trans cover. I recently checked the fluid and seemed to not have lost any so I'll keep an eye on it. If it four strokes at a 60 I'm not going down anymore lol, too scared.

Re: Heat and jetting

Looks a good colour. Now it is down to fine tuning of the needle first, rather than a jet change.

Re: Heat and jetting

Its possible your float is letting in too much gas and not shutting off at high rpms with all the shaking.

Re: Heat and jetting

Well, after my first ever moped seizure, and like 15 bucks worth of piston rings, some carb cleaner, and way more work than I want to do for a long long time, it’s running again. Stuck a 64 on there for safety. Discovered (or created) an air leak at the top of my carb. Could very likely be the issue. I’ll see if I start four stroking at 64 but won’t down jet. I’ll replace that thin gasket at some point and see if that helps. Either way runs well, and most importantly isn’t stuck.

Re: Heat and jetting

roots to wings /

What jet is supposed to be in there for your stock setup? You can easily look this up on Myron's Mopeds.

Re: Heat and jetting

If your running a really over size carb for the bike just 10 degrees will make a difference.

Like the guy early said it really don’t mess with stock bikes ..

I had a 72cc bike that stock had a 16mm carb ..after stage 5 porting and a spanny etc I got to a 30mm carb that ran great in Florida on the normal hot sticky mid day 85 to 95 and 80% humidity with 105 main ,,and a dark brown plug .., but if I rode out at 8am and it’s 72degrees … ish the plug would turn light light tan to gray in the middle .. the 110 main would fix it ,,,, then 60 degree morning 115 main or it would lock up ..

I REALLY don’t no your term 4 stroking ?

As in what the bikes doing ??

If you are running a to bigger jet for the air temperature the plug will be really dark brown and at the end of each gear if you hold it out to get maximum REVS it will feel like it’s pulling back and sound bad ,, same if your a no gear bike but at max speed .. if this is what you mean … as it 4 strokes as you say … roll the throttle back just like .1/16 to 1/4 and if it clears even picks up a little speed … your to fat ..on the main by a little bit .FOR that day that air temp ..

Yep 2 cycles …. Like a women …. A hot one that knows it ..

hard to get it just right … but when you do

( oh yer baby ) !!!!!

Re: Heat and jetting

Dirty30 Dillon /

4-stroking is a fairly standard 2-stroke motor term, has been for a number of years.

What is a "stage 5 port," lol

Re: Heat and jetting

EH 📣FCC of the QCB /

> Dirty30 Dillon wrote:

> -------------------------------------------------------

> 4-stroking is a fairly standard 2-stroke motor term, has been for a

> number of years.

>

> What is a "stage 5 port," lol

Yes, I two would like to know about this stage 5 porting 🤔.

Re: Heat and jetting

It’s 4 and then some personal extra mods that would not be a mod that you could just do on any two stroke ,,, something just to the application for the goal of that bike and what it is needing to do … a trade secret to that port shop ,, or port master ..

Or you could say something this person believes works ,, and others feel ,,, or maybe would feel … if they had such knowledge…… is not a justified mod .

Still can you explain this American term

4 stroking

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