Topic: '80 650C Main Jet Size

[tatjunkie]

Ok so i'm trying to figure out what size main jets i have, so i have a reference for tuning the carbs. The link below has a table, and for the '80 650, it has a main jet listing of 90. For the 81-82 650C, it has a listing of 120.

http://www.motorcycleproject.com/motorcycle/text/specs.html

I have an '80 650C, so should i assume that i'm supposed to have 90's, or 120's? Also, what would those jet sizes equate to? The main jets I have now are .035" roughly, and i know that because when i was cleaning the carbs yesterday (and it started up for the first time in 5 years when i was done, so i'm stoked about that) i was pushing buildup out of the main jets with a length of .035" flux-cored welding wire and it was a perfect fit. I KNOW YOU'RE NOT SUPPOSED TO DO THAT, but the carb cleaner bath wasn't doing it and neither was the spray can.

Can anyone help me out here please?

Phil

[tatjunkie]

Oh, if it helps .035"=.889mm.

Actually I might've answered my own question? .889mm is damn near .9mm, which could be the 90? That seems a little too simple to be right, but then again it's a jap bike, not a brit bike 

[razor02097]

Its not 120... maybe 90 or 95

[tatjunkie]

Sweet deal. Well not really, but at least I know where I'm starting! Thanks razor

[cb650]

90 is stock for a 80.  the 120 jets are for the cv carbs they got in 81 up

[tatjunkie]

should i go ahead and order bigger mains for my open intake setup? they're really not even going to have filters, just screens to keep wandering insects out...not a daily rider obviously. going to modify a mac 4-1. i haven't let it idle longer than 20-30 seconds, mainly because there's no exhaust mounted right now, just kinda hanging in the exhaust mounts. but correct me if i'm wrong, i don't think the .9mm mains will give enough fuel for the setup i'm putting together. stock engine, open carbs, either a mac or my own custom pipes for an exhaust. preferably a modified mac system, as i'm not the best welder.

i know this information is in other threads, but through putting together bits and pieces from other threads, i'm still a little unsure. call me a slow learner!

[Pinhead]

The stock jets are pretty lean from the factory; you'll definitely need bigger jets if you're going to run open-intake. I'm running 102.5's on the '79 with a stock intake airbox and paper filter, less the filter cover.

[tatjunkie]

I appreciate it, Pinhead. I'll order some up and see how she runs.

[kslrr]

Just to give you some more info, I ended up using 110 mains, 47 Idles, and a 35B Jet-Needle vs. the 59A (which was in the carsb when I got the bike) on my '79 engine with stock pipes and OMG Pod filters with no filter oil.  You will need more than 105's or 110's for open intakes and 4-1 Mac's.

[tatjunkie]

So if I were to run the 90s for a week or so, could I get away with running slightly hotter plugs til I the new main jets come in? I don't want to hole a piston or anything here, I just really want to get it on the road. Ha the bike and I have been waiting for a while now!

[Pinhead]

My bike wouldn't even run with the 90's unless the air filter, filter cover, and exhaust were EXACTLY stock. Any deviation in any direction and the bike would die. IMHO if it runs and doesn't feel too terribly "flat" it shouldn't hurt anything. I'd just stay light on the throttle until you know if it's running too terribly lean or not.

[razor02097]

A lot of things would go into what jet size you should run.

Intake
Exhaust
Temp
Altitude
Humidity

All effect your A/F ratio.

[kslrr]

I wouldn't do it.  I'd wait.  Or do what I did to figure out what size I needed:  I drilled out the mains with a 0.04" bit making them ~113's and the idles with a 0.016" bit making them ~47's.  With a little math you can figure out what Inch bits equal what jet size or if you have metric bits, it's a direct correlation.

[tatjunkie]

Ok, after picking up new carb connecting hoses, exhaust collars, exhaust gaskets, and 105 main jets (which are actually 102.5 but i didn't notice until i got home, 45 minutes later) i turned in the air screws so they were all set the same, and it still runs pretty lean. as in i have to have the choke 1/4 engaged or it'll die when i blip the throttle off of idle. the jets helped a bunch, but they're probably not going to be enough. in the mean time...

a) where are you guys getting your parts from?
b) those of you that drill out your jets, how does it turn out? just curious if i can't source new idle jets.
c) is it possible on these keihins to move the needle jet down in clip position?

PS it was really depressing spending $230 dollars on less than a pound of parts today!

[Bill/BentON Racing]

CB650C  was 90 mains,exact same specs as CB650 model #PD50B for both bikes,35 pilots,float level 12.5mm

[Pinhead]

Ok, after picking up new carb connecting hoses, exhaust collars, exhaust gaskets, and 105 main jets (which are actually 102.5 but i didn't notice until i got home, 45 minutes later) i turned in the air screws so they were all set the same, and it still runs pretty lean. as in i have to have the choke 1/4 engaged or it'll die when i blip the throttle off of idle. the jets helped a bunch, but they're probably not going to be enough. in the mean time...

a) where are you guys getting your parts from?
b) those of you that drill out your jets, how does it turn out? just curious if i can't source new idle jets.
c) is it possible on these keihins to move the needle jet down in clip position?

PS it was really depressing spending $230 dollars on less than a pound of parts today!

Even with the correct jets the engine will run like that until ilt's good and hot. Take the bike for a ride and after a few minutes I'm willing to bet you'll be able to run it without choke.

[kslrr]

I got my jets here: http://www.z1enterprises.com/catalog.aspx?pid=HPCF2

I used Kester rebuilt kits at first because I wanted the adjustable Jet-Needle.  After 6 months, the needles had groves and pits in them.  Kester's bras is soft.  What I found then was that the needle from a PD-50A carburetor had a lower clip position (richer) than the PD-50B carbs which were on the bike to begin with.  So, I mixed parts from the 2 different carb models to get what I needed.  go find yourself a motorcycle salvage yard.  It can't hurt to have spare carb parts on hand.  I've got 4 sets of carbs, and 2 engines, for my CB650C.

I drilled out a set of the 90's and idles just as a way of figuring out what I needed before I ordered.  Drilling is not the most accurate because you can't be sure each jet ended up the same, you might leave bits of loose brass behind and someone said the holes don't end up round.

[tatjunkie]

Ok, so how hot is the motor at operating temp? I took it around my neighborhood yesterday (funny looks from the rest of suburbia) and off-idle didn't get better but the block and head were putting off some real heat! I think some of the symptoms I was experiencing yesterday were due to lack of back-pressure, cause right now my exhaust dumps right under the crank case.

Kslrr,
The closest motorcycle salvage yard to yakima,wa is in lynnwood,wa 2 1/2 hours away, I can only take the time to get over there once every couple weeks if that. I really miss our local yard!

I'll look into that z1 enterprises, but there's a honda dealer in a close town that carries a large variation of parts, for a price.
Did you say you drilled out your pilot jets, or your idles? And I'm not sure we're on the same page so I'm gonna go newbie...by idles are you guys referring to the slow jets?

Also, do you need to get to the needle jets from the top cover? As in taking out the slide assembly and all that?

[kslrr]

Hey Tat, yea when I say idle I guess I mean the slow/pilot jets, though I thought pilot jets were only in CV carbs.  My old brain forgets.  Jet-Needles, yes they are accessed by pulling out the slides which requires pulling out the throttle shaft and all linkage which requires pulling the carbs off the bike.  These 650 carbs are a PITA!  I sould know.  I had the 650 carbs apart at least 6 times for cleaning, mixture adjustment, bowl overflows and leak fixing.  My 350F carbs are so much nicer to work on.

[Pinhead]

Get that exhaust worked out before you do anything else to the carbs. If nothing else, just get a set of 2-inch straight pipes and attached to your current pipes to give your exhaust a length of "collector."

[tatjunkie]

I appreciate the info guys! Yeah I'll come up with somethin' on the exhaust and then tinker with the carbs.

Kslrr, there's no "pilot jet" per say, but the air screws on the engine side of the float bowls are technically pilot screws, but that's a little confusing which is why everyone calls them air screws I believe.

And how do you get the slow jets out?! And if somebody says "electrical tape and pliers" I'm gonna laugh myself into a seizure!

[kslrr]

Don't laugh. To get the slow jets out, you do just that.  Though I didn't use tape, I just got a good hold on them with a small pair of Vis-Grips (needle nose type) and gently rocked them from side to side while pulling.  They came out fairly easily with not much damage.  To firmly hold the carbs, while still mounted to the rack, I strapped the carb rack onto a 1x4 and clamped that into my bench vise.

[tatjunkie]

Kslrr,
I threw the electrical tape in there to keep the pliers from chewing up the jets...I really can't believe my redneck way was actually the right way! Haha!

Razor,
I'm pretty much at the back-pressure I'm going to have, so I decided to go at it. I finally got tired of screwing around so I picked up a tach to put on for the carb-tuning process. Once I realized that what I thought was a really high, loud idle was actually an incorrectly adjusted throttle cable (causing it to "idle" around 3k) I adjusted that back and now it's all set.

There are really no big problems until about 42-4300 RPM, at which point it gets fuel starved. So I'm going to get bigger main jets (again) and maybe I'll catch a break and they'll have jet-needles also. The latter one's kind of a long shot, but we'll see.

On a side note, I got back from a 15-20 minute ride and took an external temp reading of the case...is 300 degrees usual for these bikes? It seems way too hot to me, but I'm new to street bikes. Again, that temp is an external reading, not oil temp.

[kslrr]

As far as what goes for "normal" temp, you'll see quite a range depending on where you look.  300-400/500 at the headers; 200-300 maybe on certain parts of the head; maybe 250-300 on the valve covers since they don't have fins.  As long as your oil temp is between 180 and 220, your ok.

Now don't take my word as gospel.  These are educated guesses based on some readings on my CB350F and CB650C.  Others like TwoTired probably have more accurate readings.

[razor02097]

most consistant temp you will get is from the oil.  That still only tells you the core temp of the engine and not nessesarily the temp of certain parts of the motor.