BS 38'S QUESTION

Hello,OLJO here again.Upon inspecting my carbs again,I found the needle spring on the wrong side of the Diaphram.Looks like some one has tampered with it before .My question is,should my needle's be adjustable?The ones I found in the carbs are not.1980 750 G Twin. Thanks,,OLJO

In the USA the needles were not typically adjustable by 1980. Some early bikes may have had adjustable needles, and in countries other than the US where emissions were more relaxed.

Thanks for the info,right now my bike cranks good and I can dial in a smooth idle after it warms up a bit,but when i'm at that setting I cant excellerate without it missing pretty bad.I put shorty clamp on mufflers on it when I first bought it 7 years ago and it ran fine.It probably hasn't had 500 miles put on them but they make me wonder if they have changed and changed my mixture.I was thinking of upping my main jets to see if it was a higher rpm problem.It has 125's in it now and I ordered 130's.I've got a lot of valve research to do but I was waiting on winter to tacle it.I'll do that on another post in engines later.

Another Question .When I first went through the carbs one of the brass floats was beyond repair from sitting on it's side in the gas muck.I found a plastic one at local salvage yard that would fit and put two plastic ones in,Thats the way it's running now.I'd like to get the brass ones back in just for peace of mind.I found one on ebay that looks similar that will fit lots of Yamaha 650's with BS 38's and some Kaw 750's but doesn't list my twin .Do you you think I might take a chance on this fitting?They sell for about 17 bucks including shipping.

Any time you modify things like the float you are opening up yourself for possible issues.

To test the system you should perform the "clear tube" test. That will measure the fuel level in the float bowl and that's what's critical to the function of the system.

These bikes were lean from the factory, by installing the shorty mufflers you have leaned the mixture further. What pilot jet are you running? I believe the G came with a 40 while earlier models came with a 45, but a few members here have reported that a 50 if perfect. Are you running the airbox or pods? the rebuild kits for these carbs comes with a needle that has slots to adjust the clip height. If you have changed the intake and exhaust significantly it might be worth it to change to the later model BS34 carbs as there are more parts available to tune with.

Thanks for the information.The pilots are 45 and mains are 125. should know something in about a week.So,,, the 34's will fit ? I have wondered what will ,just in case I have to carry it a step futher.I'm gonna get the brass floats back in it,do the clear tube , go ahead and change to 130 on mains cause that's what I ordered and see if theyr'es any difference better or worse .The butterflies seem to be right on. My next move will probably be pilots.I will for sure post the outcome of all my trials.I read so many post's that never give an end result! I have some more post here I will follow up on too.

Sorry,Docto,I'm still running the stock air box.

I will be watching your results. I have a 750 twin project that will be running the airbox with a K&N filter and a custom exhaust. I'm going to start with a 50 for the pilot and 130 for the main and go from there.

I cannot confirm the BS34 carbs will fit but i think they probably would. The part number for the later model engine heads is different because they introduced the smog system, but i think otherwise the head was unchanged.
BTW if you're having trouble finding main jets search "N100.606-SIZE" to find jets. They are listed as pilot jets for jetskis, but i bought some and they indeed are what you are looking for.

I ran my old 79 KZ750 Twin with a 2:1 header and stock air box with K&N filter.
I found that up here in Colorado, (less air at 5,280 ft to 14,000ft), it ran pretty darn good in the flat land prairie and started to get very slightly flubby above 10,000 ft.
That was with CORRECT float bowl fuel level, the needles up only one click, one size up in the main jet.
And up here, I always run the "all in" ignition timing a tiny bit retarded from standard sea level timing.
However, I never really had any of these other issues you are experiencing.

Well that's not true... i just remembered that I had a leaky diaphragm when I first started refurbing the bike and had to replace it.
That was a little more difficult over a weekend to figure out. They looked perfect but one was not.

I gave that bike to my son, who drove it like this for about 4000-4500 miles that summer and then sold it to his buddy, who put another 2000-2500 miles on it before he asked me to help do a tune up!!
Then he let it sit outside all Fall-Winter and Spring without doing any winter weatherization.... nothing, not even covered.
LOL Lazy ass kids.
I told him he didn't deserve to own it and to sell it... I checked out.

Update. the float came in ,got it in and fitting fine.The jets came in too big.still no change in running.Gonna return the jets and I found some more and ordered them .Should have my pilots tomorrow.i set up and did the clear tube test and got them at about an 1/8 inch below the gasckets..I'm gonna talk to My local bike guy about doing the valves pretty soon.I wanted to try a little rejetting first. And I know what you mean about kids Mission :dry: .I have two,one does great the other doesn't want to get started.

Update.Got the 50 pilots in.No change.Waiting on mains anyday now.Also ordered a valve cover gasket,... Still thinking about them valves.Made some washer baffles and tried adjusting for different back pressures,no difference.For anyone listening here's what I got now.Bike cranks right up,sometimes need a little choke .Both cylyders heat up evenly.The smoothest sound of idle is with the air fuel mix about 1/2 to 1 turn out.with ocassional popping.Still idling unevenly,up and down.cannot rev much without stumbling.If I back the air fuel mix out about 3 turns I can ride if I take it easy,any quick rev it stumbles like it loses everything until I back off.Anytime I pull the plugs they are powdery sooty,Not wet,and will wipe off easily.This bike ran great until it set for a bout 6 years,I have new points and condenser,new coil,new plugs,orignal air box,cleaned and adjusted carbs a dozen times.But I haven't soak cleaned them.New battery.Checked most of the wiring.Dont know if a rectifier could cause these syptoms or not.the timing advancer seem to be working rightand I'll have the mechanic time it while he's checking my valves.It just throws me that the plugs look rich ,but trying to run the bike sounds like lean.Reving causing stumbling and popping.gonna keep at it though,a good brain bender for me.More later,,,OLJO