Topic: More carb sync questions

[mycb750k6]

I really have read everything I could find on the subject - couple of times but still have things i don't understand fully.

1. Bench syncing - any particular drill size? 1/4" or the smallest bit or wire you can find or just enough to see light through from the other side? - How much light.
2. Start with number 2to bench sync? I have a cb750 K1
3. I've noticed bench sync adjustments do indeed affect the adjustments of the other carb slides - right? So this same behavior should be expected with engine syncing?

1. Engine sync - start with 2 or the lowest reading?
2. Turning the adjustment nut clockwise (1) raises that slide, (2) lowers the pressure in that slide and the morgan tube,(3) riches that carb - Yes?

1. General questions - when the slides are all really close to being shut, the pressure should be high on the meter~20-30? How should it idle.
2. If the slides are open enough for a lower pressure, 10-12 - how should it idle?

I have two K1s. The first starts and idles cold at 950-1000. A real pleasure. The one I'm working on idles at 1100 only after warming up and even then wants to die occasionally. So I want to re-sync it again. I should say all the pre-requisite tuning has been recently performed, carbs dis-assembled and cleaned, idle screws polished and at 1 out, emulsifier tubes cleaned and polished, idle #40, main 120, clip in center, bench-sync'd and rubbers soaked in rubber re-new..

#1 K1 idles at 950 with a morgan sync value of 20
#2 K1 idles after warmup at 1100 with a morgan value of 10-12.

I'd like #2 to run like #1 if it takes all summer. an someone fill in what I'm missing.

[Gordon]

1.  Bench-synching is only to get them somewhat close just to get the engine to run so you can do a vacuum synch.  It sounds like both of yours are already running pretty well, so a bench synch would probably just make things worse.
2.  The K1 doesn't have a fixed carb, so all can be adjusted.  It doesn't really matter which one you start with because you'll be going back and forth the whole time.
3.  Yes

1.  Just pick one and go.
2.  (1)yes, (2)to a certain extent.  If you raise the slide enough on one to increase the overall idle speed then all will be pulling more vacuum. (3)no.  Adjusting the slide height has nothing to do with changing the air/fuel mixture beyond the changes that happen automatically through the throttle range.

1.  Slide height determines the engine speed.  If the slides are mostly closed then it's either idling or it's stalling from lack of air.
2.  If the slides are open, either because the throttle stop screw is turned in all the way, or you're holding the throttle grip open, or all slides have been adjusted too far up, then the engine won't be idling, it will be revving fairly fast.

I can't say this often enough when it comes to vacuum synching:  Don't worry about the actual reading on the gauges.  Many people get way to caught up in what the reading is rather than just focusing on the only important part which is getting them all the same.  If it helps, cover the numbers with some tape so you can't even see them.  You don't need them.  If you adjust the slides evenly to get a specific number reading, all you're doing is raising or lowering the idle speed.  It's the exact same thing as twisting the throttle to open the carb slides, just more complicated because you're doing them one at a time rather than all at the same time through the throttle linkage.  

Your complaint about one of your K1's only idling at around 1100 is falling on deaf ears with me.  The lowest mine will idle at this point is around 1500.    

[mycb750k6]

Well thanks Gordon for chiming in. I appreciate it. I'm going to go re-sync the carbs again today anyway. Obsessive compulsive disorder sound familiar? Anyway, what do you think the slide openings would look like at 1000 rpm idle or does that question not have any meaning. BTW, 1500 rpm would drive me bonkers. And I still don't get why one bike would be more cold blooded than the other. Why would one start up and happily idle at 950 and when warn will even idle at 800.

Anyway - So I should start with the lowest morgan reading and turn each of the other adjusting nuts clockwise until they come down to the pressure of my baseline carb? Like I said in the first post, I've noticed adjusting one on the bench does seem to affect them all so I need to allow some time for them to settle? I'm thinking an 1/8th turn at a time maybe?

[Gordon]

At any low idle speed the carb slides will appear to be fully closed.  As far as the difference between the two, they're two different bikes that have had different pasts and have each worn in they're own way.  It's not surprising at all that there would be a difference of a couple hundred rpm in the idle speed each can attain.  It could also just be a discrepancy between the two tachometers.  The stock tachs can be pretty far off, especially at idle speeds.  Have you checked the idle speeds with a separate electronic tach?  

If you're going to pick one carb to synch the others to, it's probably best to pick one that's in the middle rather than the lowest or highest.  Since your carbs don't have one that's fixed in place, it's possible to over-adjust all of them so that the idle speed won't come down to a reasonable level and the throttle stop screw has no effect.  

1/8th turn might be good, but you'll probably end up turning them even less each time.  You'll see when you start that very small adjustments can make a big difference.  I find that blipping the throttle between adjustments helps to settle them all back down to their "at rest" positions.  

Don't forget to run a fan on the motor to keep it from overheating, and get your auxiliary fuel tank set up. 

[HondaMan]

The K1 came with 2 types of carbs: the 657A carbs on "old factory" bikes and the 657B carbs from the "new factory". The idle air passages are slightly different between them, as are the idle air screws: the "B" carbs have screws with holes in their pointy little ends. These holes provide better atomization of the fuel at throttle-crack levels, smoothing the launching in 1st gear, but the ones without the holes (and which have larger body passages) idle lower and smoother. It's possible you have one of eachm hence the difference.

Another thought: if you have just one leaky intake valve on the non-idling one, that's the culprit. First, make sure the valve lash is set properly (they idle better at 0.003" intake lash). Then, take a compression check: if one cylinder is lower than the others by more than about 5 PSI, thats the one. 

[mycb750k6]

Thanks Gordon and H-man. I was wondering what tools I should buy now since I have with this big wad of cash in my pocket. I assume I can buy something to run a compression check with the motor in the engine? Plugs 2 and 3 are a bear to get at. Also an electronic tach seems like a worthwhile investment too. So H-man, maybe it's time for that head job sooner than later. I was always under the impression that low compression meant worn cylinders and rings rather than valve leakage but they probably both contribute?

One thing I'll say about these "low mileage" bikes - don't trust the odometer, especially if the bike's look doesn't match the speedo mileage. So who knows what the valves and rings really look like. I set the valve lash while the cover was off the motor because it's a lot easier that way so that part is good. I've got 200 miles on this bike since it's transformation but still have quirks are annoying. Wish I had you guys experience.

[justind511]

is syching th carbs just turn the air screws? this seems so cunfusing! i have 022a's i dont see anything to adjust on each carb except the airscrew thing

[Gordon]

is syching th carbs just turn the air screws?

No.  Do you have a manual?  If not they are available for free download at the top of the SOHC4 Tech forum. 

[mycb750k6]

OK this is what i have. It's still set up if I should do more!!!!

[mycb750k6]

I don't know why there are three copies.

[Gordon]

I don't know why there are three copies.

All you have to do is post the URL in the message body.  If you click the "YouTube" button it will post extras.

[mycb750k6]

OK thanks Gordon, I fixed it. So now it does start and idle better cold and I can coax it to 1000rpm at stop lights when warmed up. But it does seem to run smoother on hard acceleration as well. Thanks guys. I don't know what else I can do.

[Gordon]

I don't know what else I can do.

Just ride it and enjoy it!

[faux fiddy]

Going through an old three fifty and have the same questions.

Oh, aquired dead and not running.

1)  I was told 1/8" drill bit for starters on a ballpark adjustment so it is what they all are measured to.

2)  "Fixed"  carb, as in 2 I believe was suggeted here. What is that?

The sync screws  and yokes holding them I have come from different bikes.Several of the adjustment nuts were frozen on the threads.  One had a large glob of what  looked like yellow/orange paint  that prevented the nut on the adjustment from turning. Was this "fixed,"   and was this done at the factory or in a shop?

Is / was there "fixed" carb on  the 350f?  Which?

As far as I'm concerned, the adjustment nuts are all  spinning free now, and adjstable and lubricated and cleaned. Have I  "fixed"  them?

[Gordon]

Going through an old three fifty and have the same questions.

Oh, aquired dead and not running.

1)  I was told 1/8" drill bit for starters on a ballpark adjustment so it is what they all are measured to.

2)  "Fixed"  carb, as in 2 I believe was suggeted here. What is that?

The sync screws  and yokes holding them I have come from different bikes.Several of the adjustment nuts were frozen on th thrads.  One had a large glob of what  looked like yellow/orange paint  that prevented the nut on the adjustment from turning. Was this "fixed,"   and was this done at the factory or in a shop?

Is / was there "fixed" carb on  the 350f?  Which?

As far as I'm concerned, the adjustment nuts are all  spinning free now, and adjstable and lubricated and cleaned. Have I  "fixed"  them?

"Fixed" means it is not adjustable and was never intended to be.  Yellow paint marks are just factory markings.  The 350F does not have a fixed carb slide, they are all adjustable, IIRC. 

You may have "fixed" them, but that doesn't mean they are "fixed".

[Lars]

I think your engine runs pretty nice and the reading on the Morgan is good. When I synch the carbs, I also pay attention with my ears, you can actually hear when the engine settles down and runs nice, and sometimes I go for that rather than fighting for a 100% reading which you never get anyway. All of my bikes idles at about 1100 rpm, perform well only when warm. If you adjust the idle screw when it runs cold, you will have to adjust it back when warm, so I leave it after adjusting warm. To me, it is not normal that your #1 bike is idling at 800rpm.

Bench synching has had a lot of attention on the list, but as Gordons says; it is only a start. I have bench synch quite a few carbs - I always do when I rebuild them - but they are NEVER great when I hook up the Morgan Carbtune tool.

[mycb750k6]

Ears,
OK I think I'm happy with it now and it's running great. And I do think I've finally started to "hear" them come together as they start to run at the same pressure and stop fighting with each other. I've done a bunch of bench syncing lately because I've been using different linkage parts from different carbs but want everything to remain K1, including the brass floats. So I've seen quite  a variation in slide heights when I start. I've used the tiniest of wires and also checked the amount of light coming through from the back side. This has been a huge help though, thanks. Next I think I'll replace that two-ton spring with a rubber band before I get a stroke from cranking the throttle;

[69modelj]

Ears,
OK I think I'm happy with it now and it's running great. And I do think I've finally started to "hear" them come together as they start to run at the same pressure and stop fighting with each other. I've done a bunch of bench syncing lately because I've been using different linkage parts from different carbs but want everything to remain K1, including the brass floats. So I've seen quite  a variation in slide heights when I start. I've used the tiniest of wires and also checked the amount of light coming through from the back side. This has been a huge help though, thanks. Next I think I'll replace that two-ton spring with a rubber band before I get a stroke from cranking the throttle;

Now take it out on the Ortega

[mycb750k6]

Ortega? You know I can actually hear the ambulances on their way to scrape up another rice rocket two-three times a week from where I live. That road has become too slow, too many dump trucks, too many crazies to make it any fun anymore it seems. Although having said that, there still are a couple of ton-up spots if you can find the road open. I've been frequenting Antonio Pkwy off Ortega up through Cooks corner and on through Santiago canyon. You know that route?

[69modelj]

.....Not a local there, my fiancee' lived in San Clemente, and she took me over to Elsinore.
I was there again in "09, and some guy on a big MV augusta (I think) passed us on the way back down the mountain from the lookout. At about 70 mph, downhill, just bedfore a 90 degree turn, and with a forestry service truck ahead of us no less. He passed us both, made the curve and was gone. I'll never forget it. The guy was good, but man he had bigger ones than me. Guess  I can see what you mean. Be careful out there bro. Sorry ffor the hijack