Author Topic: Can I clean my carbs without having to re sync?  (Read 13119 times)

0 Members and 1 Guest are viewing this topic.

Offline mathbishop

  • Enthusiast
  • **
  • Posts: 118
Can I clean my carbs without having to re sync?
« on: January 04, 2013, 09:33:28 AM »
I have a CB400f that has probably never had a good carb cleaning and I have been putting it off because of lack of free time and worried about screwing something up. My question is if I can remove the carbs let them sit in a simple green solution for a good long time and then pop em back on my bike without having to readjust anything?

I know it wont be thorough but I figure it would do some good. Thoughts?

Offline flybox1

  • My wife thinks I'm a
  • Really Old Timer ...
  • *******
  • Posts: 14,289
Re: Can I clean my carbs without having to re sync?
« Reply #1 on: January 04, 2013, 09:37:01 AM »
you wont screw it up. we are here to help you.
do it right. a SG bath wont do.  get in there, dude. pull the bowls and clean them as they should be cleaned.
if they've never been cleaned, you'll probably need new soft parts, like the o-rings.  all the brass parts can be cleaned up and reused.
yes, you will need a carb sync.
« Last Edit: January 04, 2013, 09:42:47 AM by flybox1 »
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline bjbuchanan

  • Master
  • *****
  • Posts: 2,274
Re: Can I clean my carbs without having to re sync?
« Reply #2 on: January 04, 2013, 09:45:28 AM »
If you don't tamper with the position of the locknuts on the slide needle you shouldn't need to sync. Tear it apartment noting idle and air screw turns or just set it to the stock settings.

A sync in either case would be good though but not necessary if it was already close.
The dirty girl-1976 cb750k, Ebay 836, Tracy bodykit
Round top carbs w/ 38 pilots, middle needle position, airscrew 7/8ths out, 122 main jet
Stock airbox w/ drop in K&N, Hooker 4-1

Don't trust me alone with a claw hammer and some pliers

Offline Really?

  • I've come to the conclusion that I AM a
  • Really Old Timer ...
  • *******
  • Posts: 5,290
Re: Can I clean my carbs without having to re sync?
« Reply #3 on: January 04, 2013, 09:45:57 AM »
After a couple times, it will be a no brainer.  Chances are, you will do it a few times this go round.

In the meantime, if it is running and you ride it, pour some seafoam in the tank.  Found at most auto parts stores and walmart.
I don't have a motorcycle, sold it ('85 Yamaha Venture Royale).  Haven't had a CB750 for over 40 years.

The Wife's Bike - 750K5
The Kid's Bike - 750K3

Offline mathbishop

  • Enthusiast
  • **
  • Posts: 118
Re: Can I clean my carbs without having to re sync?
« Reply #4 on: January 04, 2013, 10:05:08 AM »
Is a carb synchronizer kit a must have when re syncing?

Offline Deltarider

  • Really Old Timer ...
  • *******
  • Posts: 8,174
  • ... but some animals are more equal than others.
Re: Can I clean my carbs without having to re sync?
« Reply #5 on: January 04, 2013, 10:25:36 AM »
I share one with a friend and haven't used it in decades. I can benchsync within 2 cm Hg. That's well within the 3cm Hg Honda prescribes for my model. If you must have one, I'd advise you to buy it together with friends or let them buy other tools you don't need often (dwellmeter, strobe light or torque wrench). The more we share, the less (future) waste for the planet. Do a search and you can even make your own for a few bucks. A Honda dealer is supposed to sync a 4 cyl. within 45 minutes btw.

And yes, you can clean your carbs without sync no probs.
« Last Edit: January 04, 2013, 11:20:15 AM by Deltarider »
CB500K2-ED Excel black
"There is enough for everyone's need but not enough for anybody's greed."

Offline flybox1

  • My wife thinks I'm a
  • Really Old Timer ...
  • *******
  • Posts: 14,289
Re: Can I clean my carbs without having to re sync?
« Reply #6 on: January 04, 2013, 10:50:31 AM »
if you make the assumption that your carbs have never been fooked with by anyone before you got your hands on them, then yes, you wont need to sync.
you can also assume they are perfectly clean on the inside and are working properly.
so just leave them on and ride   ::)

you'd need a vacuum gauge to do a proper sync, but a bench sync can get you pretty close for now.
« Last Edit: January 04, 2013, 11:21:42 AM by flybox1 »
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline mathbishop

  • Enthusiast
  • **
  • Posts: 118
Re: Can I clean my carbs without having to re sync?
« Reply #7 on: January 04, 2013, 11:33:10 AM »
Im trying to clean them out because I know my bike isnt running as well as it could. Took it on the freeway and was maxing out at 70mph. So disappointing, the RPMs were really low and as soon as I got off the freeway the bike died. Im going to swap out my condensers and do a carb rebuild and see what happens after that.

Airbox looks pretty good.

Any other things I should look at?

Offline flybox1

  • My wife thinks I'm a
  • Really Old Timer ...
  • *******
  • Posts: 14,289
Re: Can I clean my carbs without having to re sync?
« Reply #8 on: January 04, 2013, 11:38:53 AM »
why swap your condensers? how do you know they are bad?

Matt, complete EVERYTHING in the recommended 3000mi tuneup....
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline mathbishop

  • Enthusiast
  • **
  • Posts: 118
Re: Can I clean my carbs without having to re sync?
« Reply #9 on: January 04, 2013, 11:42:35 AM »
They are all sticky and nasty, I was told that will help the top end as well as stop the bike from dying after cruising for a while. Cheap and easy fix.

Offline Really?

  • I've come to the conclusion that I AM a
  • Really Old Timer ...
  • *******
  • Posts: 5,290
Re: Can I clean my carbs without having to re sync?
« Reply #10 on: January 04, 2013, 11:46:55 AM »
The 3k tune-up is well worth the effort.
I don't have a motorcycle, sold it ('85 Yamaha Venture Royale).  Haven't had a CB750 for over 40 years.

The Wife's Bike - 750K5
The Kid's Bike - 750K3

Offline flybox1

  • My wife thinks I'm a
  • Really Old Timer ...
  • *******
  • Posts: 14,289
Re: Can I clean my carbs without having to re sync?
« Reply #11 on: January 04, 2013, 12:00:05 PM »
just a rinse out isnt good enough.
pull out the main and pilot jets, as well as the emulsion tube under the main jet.
clean them, and poke a wire through all the small holes in them to clear them out.
spray carb cleaner and compressed air in every passage to ensure nothing blocks the flow of clean gas.

dont forget to check your tank for debris.  drain, rinse, empty, repeat.
anything left settling in your tank will be suspended when you fill up, and be flushed down into your carbs to cause more mayhem....unless you've got some sort of inline filter attached.
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline Geeto67

  • A grumpy
  • Old Timer
  • ******
  • Posts: 2,822
Re: Can I clean my carbs without having to re sync?
« Reply #12 on: January 04, 2013, 12:09:23 PM »
for the kind of problem you are describing I would check and lube the ignition advance mechanisim before blaming the carbs. What do your spark plugs tell you?
Maintenance Matters Most

Offline mathbishop

  • Enthusiast
  • **
  • Posts: 118
Re: Can I clean my carbs without having to re sync?
« Reply #13 on: January 04, 2013, 12:39:02 PM »
Not really sure what the spark plugs are telling me, I pulled them out the other day just to have a look see when the bike was cold. One was a lot cleaner than the other. I ran the bike to let it get warm pulled them both again and they looked a lot similar to each other.

Offline flybox1

  • My wife thinks I'm a
  • Really Old Timer ...
  • *******
  • Posts: 14,289
Re: Can I clean my carbs without having to re sync?
« Reply #14 on: January 04, 2013, 12:49:07 PM »
the deposits will tell you how good the fuel burn is.
they all should be tan/brown.
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline Geeto67

  • A grumpy
  • Old Timer
  • ******
  • Posts: 2,822
Re: Can I clean my carbs without having to re sync?
« Reply #15 on: January 04, 2013, 01:23:11 PM »
Not really sure what the spark plugs are telling me, I pulled them out the other day just to have a look see when the bike was cold. One was a lot cleaner than the other. I ran the bike to let it get warm pulled them both again and they looked a lot similar to each other.

They are telling you that you need to learn how to read spark plugs. The "best" one isn't rust but just a slighly powdery toasted brown, like a roasted marshmallow.



your plugs are the most direct link to reading the health of the engine. This includes carb problems, timing problems, internal problems....you name it.
Maintenance Matters Most

Offline mathbishop

  • Enthusiast
  • **
  • Posts: 118
Re: Can I clean my carbs without having to re sync?
« Reply #16 on: January 04, 2013, 02:35:32 PM »
Very confident that my mixture is oil fouled. Looks like I could use some new gaskets on this puppy as well.


Offline flybox1

  • My wife thinks I'm a
  • Really Old Timer ...
  • *******
  • Posts: 14,289
Re: Can I clean my carbs without having to re sync?
« Reply #17 on: January 04, 2013, 02:46:13 PM »
love that plug reading picture.
what do the caarb internals look like?
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline mathbishop

  • Enthusiast
  • **
  • Posts: 118
Re: Can I clean my carbs without having to re sync?
« Reply #18 on: January 04, 2013, 03:00:01 PM »
So far I have just looked at the 2nd one from the left in that picture. I always hear people saying how gunked up thyre carbs are. But for a carb that has probably never been rebuilt mine dont look too gunked up...or do they???

Offline crazypj

  • I'm brill, me
  • Old Timer
  • ******
  • Posts: 4,466
  • first 100,000 miles. 1977 CB550F
Re: Can I clean my carbs without having to re sync?
« Reply #19 on: January 04, 2013, 03:01:33 PM »
The more we share, the less (future) waste for the planet.
I wish the people who change oil every 500 or thousand miles though like this.
DIY sync gauges isn't expensive to make, I wouldn't even consider doing a carb clean without re-sync
I fake being smart pretty good
'you can take my word for it or argue until you find out I'm right'

Offline Geeto67

  • A grumpy
  • Old Timer
  • ******
  • Posts: 2,822
Re: Can I clean my carbs without having to re sync?
« Reply #20 on: January 04, 2013, 03:31:01 PM »
carbs look pretty clean to me....but then again you didn't post a pic of any of the openings in the jets.

Oh, and someone has def been in those carbs.....someone who was less than saavy with tools judging by the gouging made by a flat head screw driver on the slow jet. Also at least two of your float bowl screws is stripped out - another sign someone with hams for fists was in those carbs (upper left corner of the pic and lower right corner of the pic). Judging by how clean the bowl is inside, I would say recently too.

Next thing you are going to do - take your plugs and post a pic of all four of them (label them with a sharpie so you don't mix up what cylinder they came out of).  Post them here. Wet and oil black is oil soaked. Sooty, dry, and black is overly rich. If you have oil soaked then your problem ain't carbs. Smell them too - shouldn't have a strong odor of gas.

The next four things I would do if I were you is put the bike back together and check the static and dynamic timing (just to rule out any iggy problems). Make sure to check that the advance unit is free mooving and snaps back into place (it is spring loaded). Once you all know that works, do a compression test and a leak down test (while warm). Also look for signs of a popped head gasket. I don't think the rings would cause you to be limited to 70mph and stall (I think a sticking advance mechanisim would def do that, as well as cause you to back fire). Last thing I would check is the coil, put a spark tester on it and look at the strength of the spark cold and then hot. If the light gets weaker the hotter the bike gets - your coil is bad or going bad.
Maintenance Matters Most

Offline mathbishop

  • Enthusiast
  • **
  • Posts: 118
Re: Can I clean my carbs without having to re sync?
« Reply #21 on: January 04, 2013, 04:10:22 PM »
My bike has been cold for probably around 2 hours now. Does that matter when removing the plugs to show whats going on?

Offline mathbishop

  • Enthusiast
  • **
  • Posts: 118
Re: Can I clean my carbs without having to re sync?
« Reply #22 on: January 04, 2013, 04:27:07 PM »
Here are my plugs, the dots represent the cylinder

Offline Geeto67

  • A grumpy
  • Old Timer
  • ******
  • Posts: 2,822
Re: Can I clean my carbs without having to re sync?
« Reply #23 on: January 04, 2013, 04:44:22 PM »
Doesn't matter if they are hot or cold.

Plugs look sooty to me, not oil wet, and they aren't carbon fouled but they aren't far off,  so probably rich. When was your air filter changed last?

What size are your jets? should be 75 main, 40 low speed for the 400f accoring to old posts on this forum. Somewhere on the jet there should be a stamped number.

Let's try this: put the carbs back on, make sure there are no air leaks. Clean the plugs with some carb cleaner. Leave the airbox off, and go for a rip on the highway and see if you are getting the same problem. I have a feeling someone jetted your carbs for pods at one point and may have left them in when they couldn't get the pods to work. Or they could have accidently made the jets larger when cleaning them by using incorrect tools (this is actually quite common) to remove blockages (solvents and air are the only things you should use, those little carb cleaning files can open your jets right up if you don't know how to use them).

I am still hedging my bets that this is an ignition problem, a weak spark can cause an incomplete burn and/or the plugs to load up, as can mistiming from a stuck advance unit. But just to be on the safe side, check the jet sizes anyway. Do you have any other mods to the bike? exhaust?

« Last Edit: January 04, 2013, 04:46:45 PM by Geeto67 »
Maintenance Matters Most

Offline Geeto67

  • A grumpy
  • Old Timer
  • ******
  • Posts: 2,822
Re: Can I clean my carbs without having to re sync?
« Reply #24 on: January 04, 2013, 04:48:01 PM »
oh and a set of fresh plugs wouldn't kill ya. did you check the timing?
Maintenance Matters Most