Jetting Q about chambers & stock airboxes

Craig380 · Post by **Craig380** » Fri Mar 20, 2009 8:22 am

Calling all exhaust / chamber gurus ...

I've got the chance of a set of street chambers (with repackable baffles) for my 380.

I would plan to run them with stock airbox & filters, stock carbs. Engine is bone stock too.

Would you recommend jetting up on the mains in any case?

Or, because the induction system and motor is standard, just keeping a close eye on the plug colour etc and jetting up if it looks like it's a little lean?

Thanks in advance for your advice.

cheers, Craig

tz375 · Post by **tz375** » Fri Mar 20, 2009 9:35 am

I would start with mains 2 sizes larger and work down, and raise the needles 1 step.

Get idle right and the off idle response, then set the main jet - flat out long run and check plug color. Then get the midrange right.

Order 3 sets of mains, stock, 1 up and 2 up and go for it - or get over to stinkwheels/Gibsons and set it up on their dyno

EZ · Post by EZ » Fri Mar 20, 2009 10:47 am

Buffalo-guy · Post by **Buffalo-guy** » Sat Mar 21, 2009 4:21 pm

Craig. I set up a friends 73 380 that had Bosanni pipes, and all other things stock. It worked out well with stock jetting, but no sustained high speed runs were made, so TZ is right to upsize on the side of caution, and go larger on the mains because the pipes definitely make the engine breath better. My wife, on the other hand, aquired a 74 380 that has the same Bosanni pipes, and we decided to experiment a bit. I read somewhere that 380's could do well at the top end with a switch to 550 carbs, with their stock jetting. As the carb bodies are the same castings as the 380, they bolt right up to the 380 yoke, and look absolutely stock, even to the trained eye. On start-up, it was gratifying to have instant improvement in response, and a real snappy bark from the pipes. No street tests yet with this set-up, but spring is coming, all too slowly here in cowtown, to quote Rick. Good luck with it, and I look forward to hearing of your results. Cheers. Fred

frappy · Post by **frappy** » Sun Mar 22, 2009 12:26 am

My street Elsinore needed rejetting and needle clip adjustment when I installed a Torque Engineering expansion chamber. The combination of chamber and rejetting really increased the bike's power band over the stock pipe. Plus, it sounds frapping fabulous.

Craig380 · Post by **Craig380** » Sun Mar 22, 2009 8:56 am

thanks all, if I get the pipes (which I hope to do Monday), will report.

Craig380 · Post by **Craig380** » Fri Oct 02, 2009 2:09 am

Update, chambers arriving at the weekend

A set of 70s Allspeeds, will let you know how I get on.

Good job too, the internal baffle 'donuts' on two of the stock exhausts have collapsed

rngdng · Post by **rngdng** » Fri Oct 02, 2009 5:32 am

Only seven months for shipping!?!?!?!?!?!?!?!?

How did you have them shipped; United Snail Service? FREDEX?

Lane

Craig380 · Post by **Craig380** » Fri Oct 02, 2009 8:13 am

luckily no, I got outbid on those chambers earlier this year.

This is a new set, in better condition. Just need to repack the end cans and they are good to go.

The makers of Allspeeds always claimed no need for jetting changes if the intake side & motor was otherwise standard.

That also means no major increase in power, but I'm not bothered about that ... it's more that my existing set of factory pipes are now badly deranged internally, the Allspeeds are a lot lighter than the stock pipes and sound great too.

Post by **oldjapanesebikes** » Fri Oct 02, 2009 9:05 am

Craig380 wrote: ... the Allspeeds are a lot lighter than the stock pipes and sound great too.

I have Gibson pipes on my custom GT and agree completely

I think I did end up one size bigger on the main jet, and the clip is in centre position using the BS40 CV carbs.

Craig380 · Post by **Craig380** » Fri Oct 02, 2009 10:20 am

I'll keep an eye on the plug / piston crown colours and see how it runs.

It's already on the rich side (stock airbox, filters & carbs) so it's not exactly near the knuckle right now ... maybe an airscrew or needle clip adjustment will be enough ....

Craig380 · Post by **Craig380** » Sat Oct 17, 2009 11:24 am

Well, chambers fitted this weekend, and boy do they look good.

A 40+ mile shakedown ride showed they also work pretty well -- maybe need a twiddle on the pilot screws to get the low-rev / below quarter throttle response fully sorted, but it pulls well from 3,500rpm (almost as good as stock).

A slight fluffy / flat bit around 5,000 but at 5,250 the exhaust note hardens to a BWAAAHHH and she just takes off. The result is it pulls 6th gear much better.

Haven't done a plug chop or full-throttle run yet but I'm pretty pleased with things so far.

Buffalo-guy · Post by **Buffalo-guy** » Sat Oct 17, 2009 4:49 pm

Fiddling with air screws won't fix what you're discribing. Sounds like you need to raise the needle a notch, to richen the mid range. Go from the middle groove (3rd) to the fourth, and if it still needs further improvement, go to the 5th. It is definitely more labour intensive, but the air screw only effects your idle mixture. There will most likely be other trains of thought to come, so be patient, and definitely do the plug check. Cheers.
Fred

Craig380 · Post by **Craig380** » Sun Oct 18, 2009 4:50 am

Cheers Fred -- I will keep a careful eye on things over the coming miles.

But so far, it seems to be in the ballpark for street riding, it's certainly no harder to ride in city traffic, and the added punch at 5K upward is something else

Craig380 · Post by **Craig380** » Sat Oct 31, 2009 2:36 pm

Interestingly, a couple of rides further on and it seems like it's richer in the midrange (3,500 - 6,000) with the chambers. Plug colours are darker brown than before, and leaning off the pilot airscrews a quarter-turn has improved part-throttle behaviour.

Still no sustained high-rpm / wide open throttle runs but it seems safe and is running great so far ...