Topic: jetting vm30's for cb350 twin?

[mlinder]

How far out you have the air screw?

[johnspeck]

How far out you have the air screw?

i have them 2 turns out with the 45 pilots.

spoke to rick @ accu-products...he suggested going smaller in the air jets, and going back to the 25 pilots.

[johnspeck]

ok, making some progress!

i finally got some parts in the mail, and i was able to spend some time over the past couple days dialing them in.

unfortunately, i haven't been able to locate #176 needle jets any bigger than a P-6.  so i've been trying to get the carbs tuned as well as i can with those needle jets.

with 2.0 air jets, the mixture was too lean.  so i went down to a 1.0.
started with 115 mains.

when test-riding, i would get to a point in the throttle where the bike would struggle.  i'd reach down and choke the left carb.  if it ran better, i knew i was too lean.  if choking didn't improve it, it was too rich.

through many hours of trial and error, i've really got the bike close.  not perfect yet, but rideable.

i haven't been able to use the 6L1 needles, which are much richer.  even at the leanest clip settings, they bog.  going to a larger pilot didn't work either.

i finally settled on 150 mains, 6F4's in the richest clip positions, #176 P-6 needle jets, 25 pilots, 0.5 air jets, 2.5 slide cutaways.  air/fuel mixture screws are set 2 turns out.
i'm still a little lean up top, but 160 mains were too rich, 140's too lean.

at this point, i think i need to go up a size in the needle jets, but i can't find anything bigger in the #176 P's in stock anywhere.
so i'm thinking i might need to try and find a machine shop capable of enlarging my P-6's properly, without charging an arm and a leg.

today, i'll head to my friend's house to properly sync the carbs.

i'll report back once we've double-checked timing and performed the sync.

[crazypj]

Take a look at Victor Machinery exchange in New York.
 They have reamers in small sizes, not a big deal to ream out a few thou, as long as you can measure hole accurately to start with and know how far your going.
Alternatively, drill cross holes slightly bigger at base (or add a few cross holes) and enlarge holes higher up and use larger main jet (you only need #76 & #78 drill bits, pretty sure that's what I used)

PJ

[johnspeck]

cool, thanks for the tip pj.

SO, i get over to my friend's house.  we check the timing and points.  they needed a little tweaking, so we got that perfect.  then synced the slides.  the cables had come off-adjustment slightly.  once the slides were exactly synced, we vacuum synced the carbs.

my friend (who's a good bike wrench) took it for a test ride, came back, messed with the air/fuel screw.  he richened it up considerably.  he ended up at 3/4 turn out.  took it for another ride.  came back and said, "bigger pilots!"  he happened to have a pair of 35's, which he gave to me.  he also suggested going up in the mains, and bringing the needles down to the middle clip position.  we ended up with the air/fuel screw at 1 turn out.

i rode the bike home, and it was pretty good.  not perfect, but waaaay more in the ballpark.  then, in crappy stop-n-go traffic on the freeway home, i noticed my headlight wasn't reflecting off the back of the car in front of me.  turned around, noticed my tailight/brake light weren't working.  the neutral light works, horn works, starter was NOT working, no lights..hi, lo, or otherwise.  but that's another thread entirely....

AAAGHHH!  I LOVE OLD BIKES!

so, i'll mess with it a bit more, but at least i can actually ride the bike now.  at highway speeds, the bike pulls hard to about 7k rpm, then you feel it start to hestitate if you give it more gas.  if you lightly roll it on, it'll sort of 'catch', so i'm thinking still lean up high.

[crazypj]

Just saw this on Caferacer.net, couln't link so copy and paste.
 Its using different needle jet and massive main jet


Saml01
Tricycle

USA
16 Posts
   
Posted - Aug 10 2009 :  2:50:26 PM
I changed the title so if anyone ever raises the question again it will be easy to find.

I contacted Sudco and asked them about the kit that sporting for less distributes for them. This is the configuration.

4/042 #190 - Main Jet
VM22/210 #35 - Pilot Jet
#6DH7 - Jet Needle
#159 P-5 - Needle Jet

Jet Needle info can be found here:http://www.sudco.com/CatalogJPG/126.jpg
Needle Jet Info Here: http://www.sudco.com/CatalogJPG/130.jpg
Pilot info: http://www.sudco.com/CatalogJPG/135.jpg
Main Jet: http://www.sudco.com/CatalogJPG/137.jpg
Its known as the "Right" Idle Screw VM32.

And. How to Synch Mikuni carbs.

http://www.650motorcycles.com/CarbSync.html

[johnspeck]

hey pj, thanks for posting that.

i was speaking to my friend who runs #159 needle jets on his xs650.  i asked him if he ever dealt with the over-rich midrange.  his solution was to remove the air jet entirely.
any thoughts on that?



i just started a new job, and i'm riding the bike to work, a little over 40 miles round trip.
it's able to get there and back, but it's still not dialed in.  .5 air jets, 35 pilots, p-6 needle jets, 6F4 needles in the richest position, 150 mains, mix screw 1.5 turns out.  still too rich, but leaning it out has been equally hard to dial in.  dropping the needle seems to starve later throttle, and my richer needles are too much so.

my thought is trying my 30 pilots, all else similar.

[crazypj]

I was going to try that, at present I'm making new air jets.
 Had to buy tap and die and some small drills (0.5mm~1.15mm)

PJ

[johnspeck]

i think (hope) i have my problem figured out.  correct me if i'm wrong.

i've come to the conclusion that i really need a larger needle jet.  every other thing i've tried has given me problems.

riding it home yesterday, it wouldn't pull under load over 7 grand in 5th gear.  i can rev it up in 4th and lower, but it still feels wrong.  won't pull very well up hills in 4th either, but it's revving higher so i have a little more speed.
i had to limp it home on the freeway with the choke on the left carb (couldn't reach the right one while riding).  it would actually get going and i could ride at speed.

i've got the 6F4 needles on the richest settings, but my 6L1's are too rich, even at the leanest clip setting.  a bigger main doesn't work, but it's definitely starved up top.
it's a little lean feeling off idle, even with 35 pilots, and tweaking the air/fuel mix away from 1.5 turns out makes it either lean or feeling sluggish and smelling way rich from the exhaust.

i think i've got a sort-of 'bottleneck' with the needle jets (P-6 bleeds).  i've had to put the teeny .5 air jets in to balance the mix in the jet.  anything bigger is so lean i can't ride the bike.

rick merhar told me the P-5 primary is flow equivalent to a P-8 or P-9 in the bleeds.  with my P-5's, i had great pull, just fouling plugs when cruising at mid-throttle.

since i can't seem to find #176 P-8's or 9's in stock anywhere...

i've finally given up, i'll be switching back to the #159's.  i should see my replacement today in the mail.  i slightly dinged one of them getting it out of the carb.
i'll try removing the air jets entirely.
i HAVE to get the bike right so i can get to and from work everyday.

i also received some settings from another guy with vm30's on a cb350, but he hasn't run the bike yet.  he bought them set up for our exact config (filters/mufflers) from a reputable racer.  i'll mess around, see what i come up with.
they're pretty similar to the info you just posted pj.  big mains, 159 NJ's, 35 pilots, etc..

[johnspeck]

ALRIGHT!

got the replacement 159 P-5 needle jet in the mail today.

replaced the bleed-type needle jets with the primary two-stroke type.  messed with some settings, took some test rides.  took the air jets out, 150 mains, 6F4 needles in the 4th clip position (1 from the top), mix screws 1 2/3rds turns out, 25 pilots (tried 35's too rich, don't have two 30's).
the bike has great pull, great idle, and i'm finally able to use the needles with these NJ's in something other than leanest clip settings.
i'll mess with some 30 pilots when i can, but at least it's running close to right!

[pampadori]

better then me, i can't even get this CB350 i have with VM30's to start so that i can begin tuning. 
140 mains and 40 pilots is what i have as my starting point.
it fires a couple times but no go yet.
guess i'll get some new plugs and see what i can figure out.

[johnspeck]

better then me, i can't even get this CB350 i have with VM30's to start so that i can begin tuning. 
140 mains and 40 pilots is what i have as my starting point.
it fires a couple times but no go yet.
guess i'll get some new plugs and see what i can figure out.

try smaller pilots to begin with.  i'm getting best idle and off-idle throttle from 25's.  i'd guess you're way too rich down low.  see if backing out the air/fuel mix screws to 2.5 turns out makes it seem any easier to start.  (don't go out further than that)

[johnspeck]

still feels just a touch lean near the top when you wind it out in lower gears, a touch rich in mid-throttle, haven't had a chance to try WOT.
even with air jets removed, i still have a rich midrange messing up my plugs.  next try is the needles in the the leanest clip position, maybe swap in the 140's.

at least i can ride it throughout the throttle range.  even gave a co-worker a ride yesterday.

[pampadori]

Do you think 2.0 air jet is too big? where is a good place to pick up some air jets for these?

[johnspeck]

Do you think 2.0 air jet is too big? where is a good place to pick up some air jets for these?

what kind of needle jets do you have?  if you have the primary #159 type, the 2.0's are a good place to start, because the mids are way too over-rich.  i actually have my air jets removed to run with p-5's.

with the bleed #176 type, with 2.0 air jets i found i was way too lean (with p-6 needle jets).  i eventually went down to 0.5's, but even then, the bike didn't run right.
i need to either have the p-6's enlarged (since i can't seem to find the #176's in anything larger in stock anywhere), or just run with the #159's i'm currently running, and clean my plugs daily.

don't have the loot to get the #176's to a machine shop right now, so...

[crazypj]

Are you talking throttle slide cut away or air corrector jet screwed into intake side of carb 'bellmouth'?

PJ

[johnspeck]

Are you talking throttle slide cut away or air corrector jet screwed into intake side of carb 'bellmouth'?

PJ

pj,
i removed the air corrector jets screwed into the intake bellmouth.

[Saml01]

HA HA. Im glad my information has become of use to someone.

I took my CB360 out for the first time since I got it and almost didnt make it home; plugs were black.

However. Mine idles great, has great off idle throttle response, mid range is non existent, going wot gets it past the stumble in the middle.

My first step is to bring the needles down to the lowest setting in hopes it clears up the mid range, if not then im looking for new needles and possibly new mains.

Where have you been buying yours and whats the current state of your bike?

[johnspeck]

HA HA. Im glad my information has become of use to someone.

I took my CB360 out for the first time since I got it and almost didnt make it home; plugs were black.

However. Mine idles great, has great off idle throttle response, mid range is non existent, going wot gets it past the stumble in the middle.

My first step is to bring the needles down to the lowest setting in hopes it clears up the mid range, if not then im looking for new needles and possibly new mains.

Where have you been buying yours and whats the current state of your bike?

i have bought my mains at two local shops, as well as online.
try carb parts warehouse in ohio.

currently, my bike runs good except for the over-rich mids.  i need to get the #176 needle jets i have enlarged, going from a P-6 to a P-8.
ideally, i wouldn't have to pull my plugs and clean them every time i want to go for a ride.

what's been changed on your bike from stock?  those mains are a little big if you're only running different air filters and mufflers.  i like a 150.

[Saml01]

Nothing has been changed on my bike except the air filters and mufflers. I'm thinking the 190's mains are too big as well, but ill only know after I try tweaking the needles. Also keep in mind my engine is slightly larger then yours.

I was just thinking this morning, to make this whole trial and error processes simpler, im going to have two bungs welded into my exhaust and just pickup an AEM UEGO, I run one in my car, so why not run one on my bike. It will remove all the guess work in running rich or lean in a given throttle opening.


Where online did you buy the jets?

Im confused, you want to enlarge your needle jets yet you have a rich mid range? Isnt that counter productive?

Whats the current setup you got going thats producing a rideable bike?

[crazypj]

Even on a 360 (356cc) 190 main is way too big.
 Hex jets have different numbering system to round head jets so flow rate is totally different
 I made emulsion tubes to use round heads so my jet numbers are way smaller. ( which has led to a bunch of confusion  )
 The correct amount of fuel for 360 is about 105~110cc/min at max rpm which translates to a 110 round head  precision high flow main jet. (depends on intake length and exhaust system, proper tuned length needs bigger jets)
 I know I need 112.5 but I can't find any and can't find a drill to make some (being trained as precision machinist does have some advantages  )

PJ

[johnspeck]

Nothing has been changed on my bike except the air filters and mufflers. I'm thinking the 190's mains are too big as well, but ill only know after I try tweaking the needles. Also keep in mind my engine is slightly larger then yours.

I was just thinking this morning, to make this whole trial and error processes simpler, im going to have two bungs welded into my exhaust and just pickup an AEM UEGO, I run one in my car, so why not run one on my bike. It will remove all the guess work in running rich or lean in a given throttle opening.


Where online did you buy the jets?

Im confused, you want to enlarge your needle jets yet you have a rich mid range? Isnt that counter productive?

Whats the current setup you got going thats producing a rideable bike?

look at http://www.carbparts.com/ for online stuff.

why do i want to enlarge the needle jets?  well, the carbs came with #159 primary-type needle jets, which are suited for two-strokes, although it seems a lot of guys use them in four-stroke applications.  they are very rich in the mids.  i have P-5 #159 needle jets.
i went to a #176 bleed-type, which is 'proper' for a four-stroke, P-6 size.  with all my other carb settings the same, the bike went from pulling hard and overall totally rideable, although fouling plugs with the mids (with the #159's), to not being able to pull under load above 5500 rpm, they were so lean with the #176's.
the additional air premixed in the bleed-type needle jets just leaned things out so bad i couldn't ride the bike.
i ended up reducing the air correction jets to richen up the mixture, but once things looked right in terms of plugs, the bike was under-fueled.  it would start to crap out under load, and choking the carb would help, so i know it's lean.
rick merhar at accu-products (who i also bought some jets from) stated the flow equivalent to a P-5 #159 would be around a P-8 or 9 in a #176.  i can swap air correction jets to dial in the #176's if they're a little rich.
i just want to get the plugs reading right, and my #159 P-5's are too rich yet in the mids/upper mids.

my settings that are producing a rideable bike, albeit fouling plugs:

150 mains
2.5 throttle slide cutaway
6F4 needles, leanest clip settings
#159 P-5 needle jets
25 pilots
air correction jets removed (the biggest i have is a 2.0, and this is in effect putting in a 'bigger' jet, to lean out those mids)
air/fuel mixture screws 1.5 turns out

[Saml01]

Have you thought about trying leaner 159 series needle jets to get rid of the rich middle?

[johnspeck]

Have you thought about trying leaner 159 series needle jets to get rid of the rich middle?

that's another option, i just don't have the money right now to do anything.  i'm hoping i'll meet a local gearhead who knows a sympathetic machinist.

[Saml01]

Yea man, these needle jets aren't cheap. 15 bucks a pop from sudco.

What do you think is a safe needle jet to try going leaner from p-5 without having to buy 5 of them?

I wish there was a way to tell the approx effect from going down one step.