Topic: How often do your carb sync?

[super pasty white guy]

So, I finally finished the spring tune-up with a carb sync and holy cow, I hadn't realized that I needed one so badly.  Thing is, I did it last year too.  I'd have thought that the sync was a pretty long lasting job.  This year, I used fingernail polish on the adjusters to see if that makes it last longer (pearlescent seafoam green-  if you want to know).

How often you you sync yours?  And why?

Dave

[Gordon]

About once a year or when I've had them off the bike for whatever reason.  On my 750 at least, they tend to stay in synch as long as I haven't had to mess with them. 

[Master Ted]

How about a "not yet option"?

I've got to get the tool... It's on my basic needs list.

[Black Hercules]

Hey! Dave just read your post on carb sync, I have a 78 cb750k, newbie here , how do I go about syncing carbs, I got my bike last september
and so far I gave bike fresh oil,new air filter, going to change spark plus, sorry  to ask on this question on your post, but very good topic, but I think that my bike
is runnig rich.. Thanks Raul from Long Island , N.Y.C

[Bikebuff]

Yeah, that's on my list of things to do this Spring.  Bike is almost ready to roll-finally, and that's one of the things yet to do.  I suppose I need to buy/rent a sync tool too to get the job done right. 

Git 'er done!

[Soos]

Every time i open mine up I carb synch them, but I plan on only once a season if i can leave the carbs alone long enough.

l8r

[Kevin D]

It's been checked once, about 35 years ago.

[super pasty white guy]

Hercules,

Here's the info on syncing (at least for k1-k6).

It's really not that difficult, attach gauges using the sync ports.  Keep twiddling the adjusters till you get the gauges to match. 
Then tighten the locknut and curse when it knocks everything out of whack.  Repeat. 

Drop the sync port screw, spend 10 minutes finding it resting in the grease of the swingarm.

Ride

I'm a neophyte, so it still takes me awhile to do damn near everything.

[Mountainman]

Hercules,

 
Then tighten the locknut and curse when it knocks everything out of whack.  Repeat. 

LOL... That is the damn truth!

[TwoTired]

The gauges go on every tuneup; 6 mos. 3000 miles.  It's in the maintenance section of the owners manual. 

Carburetors - Check and adjust if necessary.

[brandon]

I'm going to be buying the gauges in a week or two from Z1. Curious though, when syncing the carbs is it best to adjust to the high or low end of the OEM specification?
My bike has pods and the OEM 4-1 exhaust, stock jetting. CB400F.

As of now, I've used Two Tired's light method with what sounds like pretty good results btw.

[medic09]

Hercules,

 
Then tighten the locknut and curse when it knocks everything out of whack.  Repeat. 

LOL... That is the damn truth!

Yup!   

Dunno how often.  Last time I had them in the sink, the wife came home before I finished.  She wasn't too happy... 
(honestly, with my commuting, I should do them every six weeks or so!)

[Black Hercules]

Thanks super pasty white , I will perform carb sync, after I pull my carbs out for cleaning

Hercules,

Here's the info on syncing (at least for k1-k6).

It's really not that difficult, attach gauges using the sync ports.  Keep twiddling the adjusters till you get the gauges to match. 
Then tighten the locknut and curse when it knocks everything out of whack.  Repeat. 

Drop the sync port screw, spend 10 minutes finding it resting in the grease of the swingarm.

Ride

I'm a neophyte, so it still takes me awhile to do damn near everything.

[BobbyR]

I'm going to be buying the gauges in a week or two from Z1. Curious though, when syncing the carbs is it best to adjust to the high or low end of the OEM specification?
My bike has pods and the OEM 4-1 exhaust, stock jetting. CB400F.

As of now, I've used Two Tired's light method with what sounds like pretty good results btw.

If you are talking about the carb synch there is no OEM Spec. What you are doing is adjusting the slides until each cylinder is pulling the same vacum. Now on the cb750 and probably on yours one carb is not adjustable. This carb is your reference and all other carbs should read the same as the reference carb. This is a bit different than when you use a guage to tune a car carb.

[super pasty white guy]

I think that he's referring to item 4 on page 1.
  Start the engine, loosen the adjuster screw lock nut and turn the adjuster screws
  so that the vacuum gauges connected to the carburators are all indicating
  uniformly (within 3.0cmHg) between 16 to 24cmHg. (Fig. 20-15)

I'd like to know what the effect of being high or low on this range is as well.

Mine were set to 22-23 cmhg, but that's just cause I was lucky to get them even, much less at a certain value.

dave

[Tom Stark]

Hey! Dave just read your post on carb sync, I have a 78 cb750k, newbie here , how do I go about syncing carbs, I got my bike last september
and so far I gave bike fresh oil,new air filter, going to change spark plus, sorry  to ask on this question on your post, but very good topic, but I think that my bike
is runnig rich.. Thanks Raul from Long Island , N.Y.C

Running rich has nothing to do with carb sync.  You need to have your carbs sync'd for best efficiency.  If they are out of sync, it will not make the bike run bad, it will hurt the gas mileage to some extent, and cut down on the efficiency.  I have a Corvair, (dual carbs), and guys are alway saying things like "If they are not in sync it will be hard to start, run rough, etc."  All BS.  I could put one carb at 50% throttle and the other at idle, the car would run fine.  Would not idle, would have to give more throttle for the same speed than if they were right, because one bank would be pulling the other down, but it would still purr right down the freeway, buring 30% or so more gas than it needed to!
Tom

[brandon]

I think that he's referring to item 4 on page 1.
  Start the engine, loosen the adjuster screw lock nut and turn the adjuster screws
  so that the vacuum gauges connected to the carburators are all indicating
  uniformly (within 3.0cmHg) between 16 to 24cmHg. (Fig. 20-15)

I'd like to know what the effect of being high or low on this range is as well.

Mine were set to 22-23 cmhg, but that's just cause I was lucky to get them even, much less at a certain value.

dave

This is what I'm referring too. I'm curious to know which side of the scale is best. Also on my 400F all four carbs are adjustable for synchronization. Obviously since there is a difference in adjustable numbers, it must have some corralation to throttle response, idle and petrol consumption.

[seaweb11]

My k8 carbs were done when I did the resto..........2  1/2 years ago.  Still running strong

[techy5025]

Adjusting carbs is like aligning the old color tv sets. After diddling with 40 or so adjustments and a list of maybe as many instructions, the last one said "go back and adjust any control as necessary to achieve overall best picture". 

Jim

[Gordon]

I think that he's referring to item 4 on page 1.
  Start the engine, loosen the adjuster screw lock nut and turn the adjuster screws
  so that the vacuum gauges connected to the carburators are all indicating
  uniformly (within 3.0cmHg) between 16 to 24cmHg. (Fig. 20-15)

I'd like to know what the effect of being high or low on this range is as well.

Mine were set to 22-23 cmhg, but that's just cause I was lucky to get them even, much less at a certain value.

dave

This is what I'm referring too. I'm curious to know which side of the scale is best. Also on my 400F all four carbs are adjustable for synchronization. Obviously since there is a difference in adjustable numbers, it must have some corralation to throttle response, idle and petrol consumption.

It's a difficult concept to grasp until you've actually synchronized your own carbs, but the reading on the guages is of absolutely no concern.  If it helps, take a strip of tape and cover up the numbers so you don't get distracted by them.  All that matters is that they are all at the same level.  Once they are at the same level, raising or lowering that uniform level reading will only serve to raise or lower the idle speed, which would be the exact same thing as turning the idle stop screw in or out. 

[crazypj]

I've got gauges but only do carbs when I think about them ( not very often )
PJ

[TwoTired]

Running rich has nothing to do with carb sync. 

I disagree.  It can if the richness is associated with specific cylinders, rather than all the cylinders in general.

You need to have your carbs sync'd for best efficiency.  If they are out of sync, it will not make the bike run bad,

What?  Out of sync carbs will most certainly make the SOHC4 idle poorly.

I have a Corvair, (dual carbs), and guys are alway saying things like "If they are not in sync it will be hard to start, run rough, etc."  All BS.  I could put one carb at 50% throttle and the other at idle, the car would run fine.  Would not idle, would have to give more throttle for the same speed than if they were right, because one bank would be pulling the other down, but it would still purr right down the freeway, buring 30% or so more gas than it needed to!
Tom

Tom, the SOHC4 has one carb per cylinder.  The corvair feeds multiple cylinders with a carb.  So, this comparison is apples and oranges.  And, there is a lot of behavior that is different between the engines.

With the SOHC4, a badly out of sync condition can cause a cylinder to not fire at all during idle, and you can have cold head pipes.  Further, any out of sync condition will make some cylinders fire stronger than others. A rough idle would be expected.

Cheers,

[techy5025]

One of the former Honda mechanics that attends our weekly bike ride gave me a piece of advice regards setting the idle adjuster during carb setup. I was saying that it was hard to set them as the adjustment range vs. effect was so broad.  He said to deliberately misadjust the carbs so that only one was delivering power and then adjust it's idle screw.....repeat for the other three. Having done that...then match the vacuums for all four. Sorta like optimizing the adjustment effect...sounds reasonable.

Jim

[Gordon]

He said to deliberately misadjust the carbs so that only one was delivering power and then adjust it's idle screw.....repeat for the other three. Having done that...then match the vacuums for all four. Sorta like optimizing the adjustment effect...sounds reasonable.

I don't tend to associate the idle mix adjustment with synching the carbs.  For me, those procedures are completely separate.  Unless you're talking about the idle speed stop screw, but then there's only one which controlls all four carbs.

[Ibsen]

At every tune up. But synching the carbs is the final step in a full tune up. Everything else has to be adjusted first. 

And is they wrote in a magazine:

"20 minutes with a Morgan Carbtune works wonders, restoring an even tickover and giving the bike a creamy off the throttle engine response."