Higgspeed chambers

[Glyn.G]

Hi all,
I've just fitted my new Higgspeed chambers to my 1977 GT380 and I'm over the moon with the way the bike runs and sounds, It will now pull uphill in 6th with ease and red lines no problem. The only problem I have is I seem to have lost the fine adjustment of the idle speed. It will tick over at 1000rpm, which is a bit low as it sometimes stalls at lights, but when I try to lift it to bit to say 1200-1500rpm using the adjusting screw it shoots up to 2000rpm or above with only the slightest touch. It was fine on the stock exhausts and I'm still using the stock air box and filters. I think I've read somewhere on the forum that I may need to screw the air mixture screws in a 1/4 turn.
Anyone got any ideas

[caidenw11]

Especially in 2 strokes, your fuel settings affect motor speed too. What you described to me sounds alot like your running too lean. With your new pipes, there is a greater amount of airflow. More airflow means more fuel is needed. Unscrew your needle valve/fuel screw on your carburetor a bit, then mess with your idle. You should always re adjust when changing to a better pipe, as 2 strokes oil themselves with their fuel. Not having enough will burn up your piston! Hope this helps

[Craig380]

Weather is colder now so air is denser, try screwing the pilots IN by a quarter turn and see what it does ...

[titan performance]

Take care until you have made the adjustments, running lean can melt pistons.

[Vintageman]

It sounds to me like you may have a pilot(s) jet/circuit compromised: regardless if you feel the only change you made is the exhaust. This circuit plugs easy and can do so over a period of time

My experience is 1/4 turn on a screw will not correct the issue if I properly interpret what you wrote.

If you have not done so in a while I suggest you remove and fully clean carbs and see if you find issue with pilot circuit: pilot jet condition/size, air passage from air horn to pilot air screw adjust to pilot jet. Pilot air screw tip condition and the two small holes in the body of the carb are clear.

Also many times I have found going up one step on the pilot jet size is a good idea when running chambers, maximizing low throttle performance over wider RPM range if you want that. You can open the air screw up to better than 2 turns if you feel too rich.

If pilot circuit is too lean/plugged and you coast in gear with throttle at small opening you can hole pistons in short time.

Chambers are amazing!

[Glyn.G]

Cheers for all the advice, I can say with quiet confidence that the carbs are ok as I have cleaned them very recently and all was ok up to the point I changed the pipes. I was running with the air/fuel screws set at 1 1/8 turns out on the standard pipes just to be on the safe side after a top end rebuild so as to run a little on the rich side. I don't quite get one of the replies to my question which is to unscrew the air/fuel screw more because the bike may be running lean, surely that would make it leaner. I think I'll try Craig380's advice and screw them in another 1/8th of a turn and see what happens.
Cheers again for all your help, it was back in the 70's when I last had a 2 stroke and I just rode em! never had to rebuild one.

[Vintageman]

I hope i wasn't miss interpreted, To be clear I said you can go out on air screw if you choose to install a "larger" pilot jet for reasons I stated previously. And, only then, if you find it was a choice that made it too rich you can lean it out a tadd by turning out air screw.

Again, I have never seen a case where the you can't hold idle unless you move the slides up so much you go beyond the intend of the pilot circuit and encroach into the jet needle and needle jet... if that is what you did

Did i missinterpetted you?

Also, look for vacuum leak.

I have never seen this much change converting from stock exhaust to chambers for low speed circuit.

Please reply back with air screw 1/8 in tweak affect or what else you find...

We all can still learn from each other's experiences.

Fun stuff

[Glyn.G]

Hi again,
Set air/fuel screws to 1 full turn out as suggested ( screwed them in another 1/8th turn ) which should mean it's running on the rich side. Went for a good 50 mile run. Idle speed has improved a little but still erratic, when pulling up to a stop the idle speed is steady at 1100 revs for about 20 seconds then it climbs to around 1700 revs. If I leave it without blipping the throttle it will suddenly drop back to original 1100 revs. No amount of fiddling with the adjusting screw makes any difference except to drop the slides so it won't idle at all or raise them too much so its idling over 2000 revs.
Maybe I'll just have to settle for the 600revs fluctuation ?
Cheers Again.

[yeadon_m]

At a quick guess, I'd say you have an air leak somewhere!
It really should not do that.
Mike

[Glyn.G]

Think you are right about the air leak. I've ordered a decent set of clamps for the new carb intake rubbers I have recently put on. The ones that were supplied with them were rubbish ( cruzinimage ).
I just hope the main seals aren't on their way out !

[Vintageman]

"look for vacuum leak

How about the hose from carb to petcock leaking?

How about carb to carb shared fuel enriching/starter hose line... it if has... I think it does?

I have heard some cruzinimage stuff like rubber boots no good as well. Are they cracking?

[2strokelove]

Ordered Higgspeed for my GT550. Still waiting and its been over 2 months now!! They do sound nice on the 380's though!!

[Glyn.G]

Will check for vacuum leaks when new clamps arrive as I'll give the carbs another thorough going over. I think it will be a case of eliminating things 1 at a time.
Don't worry 2strokelove, my pipes took 3 months to arrive as Dave at Higgspeed is swamped with orders. It's worth the wait.

[Tripleking]

My bike was equipped with old Bassani chambers when I got her. I still have them on. She pulls great mid-range, but fades fast right after 7,000. I already had to repair one pipe. When these go, I am considering Higgspeed chambers. Also considering for my T250.

[tz375]

Just out of idle curiosity, what is it about Dave Higgs chambers that suggests they will peak at higher RPMs. The only set I have seen in the US in the metal were on a Kawasaki H2 and that peaked at relatively low revs.

The lowest peak after 3 into 1 that I have seen are stock and J&R followed not long after by Jemco and Bassani.

None of them peak very high on a 750 at least. I cannot comment on the 380 or 550, but it makes me wonder what you have seen or read that suggests a higher peak.