Correct jet size with racing pipes?

[sportston]

Doe anyone know what the correct jet size is for running a stock GT380M 1975 engine with racing pipes?

[Vintageman]

I have a 74 GT380L with Jemco 3 into 3. All stock otherwise.

Did not have to change any jetting. Not always the case, but this one runs perfect

Only just recently did I step up my pilot one size (was bucking a little... means your close though), but really did not make much of a difference

Fine tip plugs like Iridium’s helps me get pulling power up to and pasted 9000 RPMs which is not over rev.

I use stock timing as well for I mostly just cruise around and play music with those 3 lovely wind instruments

[Craig380]

If you're still using the stock airbox and filters, and the engine is otherwise standard, the standard jetting should be fine. Just ride it with a little caution for a while until you're sure the spark plugs are showing the mixture is OK.

In fact, my own 380M with J&R pipes (everything else standard, apart from removing the airbox intake rubber snorkel) is probably a little bit rich through the range. It will hold wide-open throttle and illegal speeds way longer than my neck muscles, or other traffic, will allow. It runs cleanly with no flat spots through the rev range so I've left it well alone apart from tweaking the pilot screws.

Also, another vote for Iridium plugs, gapped at 0.6mm / 24 thou. You can them for around £6 each online, they're WELL worth it, they simply never foul or need checking.

If you're using non-standard filters, then you'll have to take it very carefully, checking and re-checking the plug readings and mixture.

[sportston]

Thanks for the info. The engine is standard as far as I know. I know it is really bad to use the conical air filters, especially on a 2-stroke, because you lose the inlet expansion chamber, which smooths things out. So I will be sticking with standard air box even if I eventually hot the engine up. I would be interested to know how to hot the engine up though if anyone has any tips.

[zk0ot]

my 380 with spannies and UNi foam filters is running 105's i believe. also upped the pilot a size or 2

[sportston]

my 380 with spannies and UNi foam filters is running 105's i believe. also upped the pilot a size or 2

Hmm. Can you translate please? Are "spannies" a type of exhaust? and what are "unifoam" filters? Are they like pipercross sock filters or do they fit inside the standard airbox?

[Craig380]

Spannies = expansion chambers = race-type aftermarket exhaust for two stroke engines.

Uni filters are foam 'socks' similar to the Pipercross style, you remove the airbox and fit them over the carb mouth.

If your bike has a decent airbox and the filters are in good condition, I'd strongly recommend sticking with those until you're happy with the bike's running. The filters should be washed in petrol, dried and then dampened with clean oil (2 stroke or 4-stroke oil). Not dripping wet, work the oil in with your hands so that the filter will just leave a light trace on the back of your hand if you dab it.

You can remove the rubber inlet snorkel at the back of the airbox as it is restrictive, gives you a bit more induction roar

[sportston]

Ah right. I've not heard them called spannies before. I am keeping the standard airbox on mine, I don't want to trade off top end for midrange. But I have made my own foam air filters for inside it using proper air filter foam. Saved me a fortune. Couldn't believe the price of the genuine suzuki ones! I may well try removing the snorkel as you suggest. My bike does have a set of racing pipes with expansion chambers, but I have yet to refurb them and fit them. I've never had a decent 2-stroke with standard pipes on as I know they make a big difference to the performance and sound. I just hope the little racing pipes I have won't deafen me too much. The tailpipes are very tiny and I doubt they muffle the sound by very much. I remember as a kid riding on the back of my Dad's KH250 with a set of microns on and that was so loud you're ears would be ringing for a while after riding it. Sounded great from afar though.

[Craig380]

What make of pipes are they, do you know? Do they have an end-can or removable baffle-tube? If so, you can pack that with silencer wool (most bike shops sell it for about a fiver, wrap a few layers tight around the tube and secure with wire), that helps reduce the decibels by quite a bit.

Might be worth checking if the air filter foam is intended to be used dry, or if it should be lightly oiled. Perhaps leave the snorkel in place until you're confident the jetting is on the rich side. The filter foam may be less restrictive that the standard Suzuki foam, although that will be balanced by using the standard airbox.

Good luck with it, keep us posted on progress!

[sportston]

I have no idea what brand they are. They don't have removable tail pieces like a set of 2-stroke Microns, instead they have removable baffles. Well, I say "removable" I've managed to get two of them out, the third is very stubbornly refusing to budge, so I've left it to soak for a few days in diesel and will try again soon. They are pretty ancient, haven't been used for quite a while, covered in a dings and rust, one of them has a stress fracture and they all need some refurbishment. I haven't noticed any writing on them or logos. In an ideal world I'd get them re-chromed but am doubtful that I can do that very cheaply. So instead, my plan is to weld up the stress fracture, paint the expansion chambers satin black, cover the tailpipes with home-made stainless slip-ons and shiny up the chrome downpipes with a good bit of flatting and polishing. It might take me a few days but should be a lot cheaper than a new set of Allspeeds. I probably will repack the baffles too, but after I have given them a good decoke.
Oh and the home-made air filter foam doesn't need to be soaked in oil as far as I know. It appears to be quite thick, thicker than a normal suzy part so will be fine.

[Craig380]

Do they look like these? These are J&R power pipes on my 380. They were originally the slip-on type, a previous owner welded on some headers.

[sportston]

Do they look like these? These are J&R power pipes on my 380. They were originally the slip-on type, a previous owner welded on some headers.

Yes they are very similar. Mine look like they were slip-on type but someone welded them also. But mine have shorter tail pipes and dont have the nice sticky-outy bit at the end like yours. Nice bike by the way. Love that shade of blue.