BS34 Jetting Question

[nikiforova]

So I've gotten my '83sk up and running nicely again. Was able to take it out for a solid 25 minutes uninterrupted around town a few times this week. I have noticed a massive flat spot around 1900-2400 rpms. It almost seems like its starving for gas! Ive been sifting through the Carb guide instead of paying attention in class and I have a few questions. I am thinking of installing the Jet Kit from Mikes XS that comes with #7F6 slide needles, #45 Pilot Jets and the 135 and 145 Main jets. I am also planning on chopping my exhaust to just around the rear break pedal and running the non tapered pods for intakes.

I see that the bs34s have a fixed slide needle, and mikes says to drill out the slide lift hole with a provided 3.0mm bit.... but how? That seems risky. I feel like, at the very least, I should try running the 45 pilots and the 145 mains and hopefully that increase in richness will carry the slides circuit before drilling it out.

The guide seems to say that upping the mains on the bs34s will help even if entirely stock, so with any mods to move up at least two sizes. Is a 145 with 45s and the #7F6 needle putting me in the too rich territory?

 

[Jim]

When it comes to carbs, you best bet is gonna be sticking with factory parts.... Mikuni in this case. That Mikes kit uses Chinese repops, not Mikuni. Look for Niche Cycle for OEM Mikuni parts.

Is the plug over the mix screw removed? You'll need to be able to adjust them to fine tune it. Give us some pics of the top front of the carbs if you're not sure.

My 34's had the same flat spot off idle. Going up a size or two on the pilots helps.... what fixed mine was a small (3mm?) washer under the needle clip to raise the needle slightly. I you can't find info on that, let me know and I'll see what I can find on mine.

 

[jpdevol]

The Dyno Tune kit you are referring to (phase III with 145 main) may be too rich with stock headers. If you've only got a flat spot at 1900-2400 rpm, try a couple of 3mm washers between the plastic ring and the clip to raise the needle.

The 7F6 needle isn't really that - but does work on higher mods.

Edit: and everything Jim said.

 

[nikiforova]

When it comes to carbs, you best bet is gonna be sticking with factory parts.... Mikuni in this case. That Mikes kit uses Chinese repops, not Mikuni. Look for Niche Cycle for OEM Mikuni parts.

Is the plug over the mix screw removed? You'll need to be able to adjust them to fine tune it. Give us some pics of the top front of the carbs if you're not sure.

My 34's had the same flat spot off idle. Going up a size or two on the pilots helps.... what fixed mine was a small (3mm?) washer under the needle clip to raise the needle slightly. I you can't find info on that, let me know and I'll see what I can find on mine.

Ive got the plug over the mix screw removed and theyre running about 3 1/4 turns out.
I see that 5twins says here that increasing the pilots and mains can have the same effect of shimming because the richness bleeds over. I found some information on the shim at mikes xs. It looks like i should just be able to pickup a washer from the hardware store, no?

 

[nikiforova]

The Dyno Tune kit you are referring to (phase III with 145 main) may be too rich with stock headers. If you've only got a flat spot at 1900-2400 rpm, try a couple of 3mm washers between the plastic ring and the clip to raise the needle.

The 7F6 needle isn't really that - but does work on higher mods.

Edit: and everything Jim said.

I also seem to be redlining right around 5k rpms which seems low. enlarge my mains?

 

[jpdevol]

Should be able to find 3mm washers locally. Do you have a tach? Should be revving up to 7500 cleanly. Not enough info. to answer

 

[2XSive]

......one other option. I have found this needle from Mikes to be the one good carb part from them. Original BS34 needle installed on Canadian bikes, eh. Fully adjustable and helped smooth out my acceleration. BUT I would try the washer shim first as stated.

Edit: wrong link. Stated its for the 38s, but search Mikes. They should have them for 34s
Edit again: was the correct link if you read the description.

 

[650Skull]

Do not drill out the hole in the slide. That idea for the kit they sell is for a bike that has been upgraded to a 750 with the 2 into 1 exhaust system.

If you buy the adjustable needles make sure you buy the needle jets to go with them

 

[5twins]

Just a plain old M3 washer is what you're after to shim your needles .....

..... and it goes like so, between the clip and plastic spacer .....

 

[nikiforova]

Alright, so my current setup is a 45 pilot with 135 main and two washers on the needle as a shim. Wish I could give results right now, but my battery is on the charger Dont know why it would be at 12.01 volts after not running for five days......

 

[gggGary]

Only ONE washer on a needle. I found out the hard way two wshers make the needle bind bad juju.

 

[jpdevol]

Only ONE washer on a needle. I found out the hard way two wshers make the needle bind bad juju.

For shiming; In between the plastic ring and the clip?

 

[gggGary]

Yup top of the needle will hit the cap in the slide. At least thats what happened to me. Could mod that cap i guess.

 

[5twins]

This binding needle thing doesn't make a whole lot of sense to me. I mean, there's a hole in the center of the needle retaining plate for the top of the needle to stick through if need be, right? It also doesn't sit up tight to the plate to begin with because of the little spring on top of it. Theoretically, there should be at least 2mm of space available. I base this on an aftermarket needle, or the Canadian needle, being set in it's middle slot (#3), then changed to it's lowest (#5) slot. That would raise it 2mm since needle clip slots are 1mm apart. Here's the generic needles from the Cruzinimage kit compared to the stock BS34 5HX12 and some others .....

The generic Y265 has it's middle (#3) clip slot aligned with the fixed clip on the 5HX12 .....

 

[gggGary]

This binding needle thing doesn't make a whole lot of sense to me. I mean, there's a hole in the center of the needle retaining plate for the top of the needle to stick through if need be, right? It also doesn't sit up tight to the plate to begin with because of the little spring on top of it. Theoretically, there should be at least 2mm of space available. I base this on an aftermarket needle, or the Canadian needle, being set in it's middle slot (#3), then changed to it's lowest (#5) slot. That would raise it 2mm since needle clip slots are 1mm apart. Here's the generic needles from the Cruzinimage kit compared to the stock BS34 5HX12 and some others .....

View attachment 224628

The generic Y265 has it's middle (#3) clip slot aligned with the fixed clip on the 5HX12 .....

View attachment 224629

OK slept on it, this was a while ago. The issue is the little needle spring coil binds. Moving the clip wouldn't change the spring length but shimming the clip does. You might be able to shorten the spring to avoid binding.

 

[jpdevol]

I was puzzled a bit, at first, on the comment, then you explained that it wasn't the washers themselves binding; just not enough room at the top. I reckon if one needed to raise a stock needle to get right, it would be easy enough to "relieve" the top of the needle - maybe spring too if it coil-binds. I think the needle needs some free movement. I had one bound up once, but don't remember the cause now

Anyway, if Niki shows back up with some more info, it may indicate a larger main is needed: only one step up ATM.

 

[5twins]

OK, I get it now, the spring is the culprit. So far, shimming a stock, fixed BS34 needle is something I haven't needed to do. That may be because I change mains, pilots, and air jets. Making all that richer bleeds over into needle territory (midrange) and makes it richer too.

 

[nikiforova]

Oooh thanks for the heads up on that one. I’m currently running two washers, but I’ll take one out today. The 135mains and 45 pilots and two shims seems to be doing well. Bike was dying because of plugs and worn o rings on my float needle. Got it out for 45 minutes and didn’t have any issues… except for running out of gas early on lol. I’ll take one of them shims out and that should help it even more.

Running some uni pod filters now too instead of the k&ns. Diaphragm are holding a vacuum which is nice. Just needed to clean the seat and use some grease to seal it. Hell it’s even revving up past 7k for the first time since I bought it.

It seemed to want to stumble and falter a bit just off idle while it was warming up, but that didn’t seem much of an issue when warm. Didn’t hesitate at wot either. Revved all the way up smoothly. I decided not to go with the straight pipe as it seemed to be more work than it’s worth. The muffler is already quite loud and I don’t wanna know what it’ll sound like straight piped lol.

TLDR: my setup is 45 pilots, 135 mains, stock airs, needle shimmed twice. After reading Gary’s experience I’m going to drop one washer. Seems to be running better than at any point in the past. Stock exhaust and uni pods

 

[5twins]

Yes, I've started to grease my diaphragms as well. I use red rubber grease, a special grease made just for rubber. And not only do I apply it to the seal groove in the carb top, I rub it all over the entire diaphragm. So far, the results have been great. It seals very well and appears to make the diaphragm soft and supple .....

The stock exhaust is usually very quiet. If yours is loud then maybe the P.O. drilled the baffles out? If that has been done then it would be freer flowing and combined with your UNI pods that could require another size up on the mains (to 137.5).

 

[nikiforova]

Yes, I've started to grease my diaphragms as well. I use red rubber grease, a special grease made just for rubber. And not only do I apply it to the seal groove in the carb top, I rub it all over the entire diaphragm. So far, the results have been great. It seals very well and appears to make the diaphragm soft and supple .....

View attachment 224754

View attachment 224755

View attachment 224756

View attachment 224757

The stock exhaust is usually very quiet. If yours is loud then maybe the P.O. drilled the baffles out? If that has been done then it would be freer flowing and combined with your UNI pods that could require another size up on the mains (to 137.5).

Yeah that very well might be it. The P.O. def did some work to it. It came w/k&ns and the needle already shimmed so it wouldn’t surprise me if he also drilled out the baffles. If the stock exhaust is pretty quiet this one’s either been tampered or replaced, but it looks stock for the single exhaust model. I’ll go ahead and order a few different size mains and air jets when my next order of parts is due. Going to have to get a center stand and I want some smaller gauges since I’m going cafe bike. That’ll have to wait cause out of pocket tuition is kicking my ass rn lol