Synch vs Balanced

[cowb0y]

I am havin a low end problem and I justed finished the high rev method to tune the carbs. Seems to run better, but still slugs/serges at 2k. Most noticable in first gear. Other than that smooth. Wondering if I should just ride it and not worry or try to get it all smooth for better gas mileage??
What are your thoughts, CafeKid?

 

[TheCafeKid]

I am havin a low end problem and I justed finished the high rev method to tune the carbs. Seems to run better, but still slugs/serges at 2k. Most noticable in first gear. Other than that smooth. Wondering if I should just ride it and not worry or try to get it all smooth for better gas mileage??
What are your thoughts, CafeKid?

Again I'm not motor god. Can only tell you what has or hasn't worked for me and my semi educated guesses as to why. Without knowing other factors involved (first what bike are you talking about? Have you adjusted you valve clearances. This is part of basic maintenance and will effect running. Carbs clean? Stock jetting? Stock intake and exhaust system? Etc) stumbling or surging is usually a symptom of being lean. However what I sometimes have trouble with when the bike us running very close to right is discerning whether what I'm feeling is a result of being too rich or too lean. Plug chops taken at the throttle position that you seem to have the trouble with will be most telling.

 

[TheCafeKid]

What if your vacuum lines are off? :-k

What lines are off and why?

 

[cowb0y]

What lines are off and why?

The two vacumm lines on the carbs; between 1&2 and 3&4.

I have a dyna jet kit in with stock air box (pods tryin my patients) and harley fish fin pipes. Read with dyna kit, to leave vacumm lines off.

Bikes an '80 GS 1100L with an '83 tank. Been havin issues with petcock in "On" so been runnin it in Prime (PRI) with much success. I jus swap it to ON when I park for a while so bowls dont over flow.

Also, havent done a valve job yet and have put 3500 miles on it since I bot it. So plannin on that soon. Have been gettin 45-47 mpg, so not too worried.

Glad you are willing to share whacha know. I appreciate it.

 

[TheCafeKid]

The two vacumm lines on the carbs; between 1&2 and 3&4.

I have a dyna jet kit in with stock air box (pods tryin my patients) and harley fish fin pipes. Read with dyna kit, to leave vacumm lines off.

Bikes an '80 GS 1100L with an '83 tank. Been havin issues with petcock in "On" so been runnin it in Prime (PRI) with much success. I jus swap it to ON when I park for a while so bowls dont over flow.

Also, havent done a valve job yet and have put 3500 miles on it since I bot it. So plannin on that soon. Have been gettin 45-47 mpg, so not too worried.

Glad you are willing to share whacha know. I appreciate it.

Wow, thats quite a combo there...LOL. If youre having problems like ya say, its not really relative to RPMs, but throttle position. The carbs are broken into different circuits, which are feeding different throttle positions (some positions are a bit of a combination of circuits..) If, while just cruising along, no matter the speed, but only using about 1/8-1/4 turn of the throttle, it may be that your pilot circuit is just a bit lean. Try opening the mix screws a 1/8 turn or so till it seems better. But if its more 1/4 or so turn of the throttle thats giving you trouble (it might help to mark off the throttle positions with tape, 1/8, 1/4, 1/2, so on) it might be that you simply need to drop the needle clip on your needles a notch lower, effectively raising the needle and alowing more fuel to flow in earlier stages of the needle circuit. Like I said, plug chops are the most effective and telling as to whether you are lean or rich in any given throttle position.

Valve adjustment will slightly change the way your motor breathes, so you may find after adjusting the valves, that your problems actually go away. Id seriously suggest checking your clearances, and adjusting them if need be per the manual.

 

[Dan Ruddock]

Tolerances in volumetric efficiency from cylinder to cylinder are very small unless the engine is a piece of junk.

The carbs need to be flowing the same volume of air throat to throat for the engine to run smoothly. This is why they need to be synched. Dan

 

[Steve]

The two vacumm lines on the carbs; between 1&2 and 3&4.

I have a dyna jet kit in with stock air box (pods tryin my patients) and harley fish fin pipes. Read with dyna kit, to leave vacumm lines off.

Those are not exactly "vacuum" lines, they are "vent" lines. Generally recommended to leave them off if you are running pods. If using stock airbox, the lines should go back over the airbox and rest in quiet airspace. The determination is not the Dynajet kit, it's the type of air filter and where the dead air space is.

Also, havent done a valve job yet and have put 3500 miles on it since I bot it. So plannin on that soon. Have been gettin 45-47 mpg, so not too worried.

You don't need a "valve job", you need a "valve adjustment". BIG difference. :-\\\

YOU have put on 3500 miles, how long before you got the bike were they adjusted? If you have no idea, it's WAY past due. Gas mileage is no indication of whether the valves need to be adjusted.

.

 

[cowb0y]

Guess I'll see into puttin the vent lines back on. Glad to get this kinda stuff cleared up.

The symptoms lead me to believe the pilot jet circuit issues. What are the stock and other incremental pilot jet sizes.

I have adjusted the mixture screws (ones most forward and top outward flat head screw available with carbs mounted and bike running) to the highest idle, one carbs at a time, with the engine cooling in between. Which smoothed out my 3-4k bogging down.

Now just a surge/slug at 2k, so probably 1/8 throttle. Maybe I need to go up in pilot jet since the main jet is larger than stock, and then readjust the air mixture screws individually again.

Whacha guys think?

 

[Guest]

Tolerances in volumetric efficiency from cylinder to cylinder are very small unless the engine is a piece of junk.

The carbs need to be flowing the same volume of air throat to throat for the engine to run smoothly. This is why they need to be synched. Dan

Not understanding the reason for the confusion...the term (carb sync/balance) seems pretty self-explanatory.....balancing the function (metering) of the carbs to each other, for uniform performance. Balancing engine components (cranks etc) or compensating for discrepancies in manufacturing are not being addressed here.

 

[TheCafeKid]

Not understanding the reason for the confusion...the term (carb sync/balance) seems pretty self-explanatory.....balancing the function (metering) of the carbs to each other, for uniform performance. Balancing engine components (cranks etc) or compensating for discrepancies in manufacturing are not being addressed here.

Yeah, im not getting it either. A motor is nothing more than a big air pump.. You're balancing the amount of A/F that is drawn by each cylinder. Each one isnt going to draw the same for WHATEVER reason. It is the vacuum created by the motor that draws air thru the carb which draws air across the jets/venturi what have you that delivers and or mixes fuel. Each cylinder may or may not create more or less vacuum than the adjacent one. If the carbs are all set the same, this would cause an un even pulse. One cylinder loading up on AFM and the others less...

WHY each cylinder may not pull the same as the next is DUE to manufacture discrepancies, un-even wear pattern from one to the next, etc etc etc. The SAME reason compression rates are NOT the same from one cylinder to the next.

The same can be said for the carbs themselves..

I am not arguing about balancing actual motor parts, etc. Im talking about balancing the amount of AFM each cylinder is allowed to draw... that is all.

 

[Guest]

First off, please understand I'm not trying to be argumentative . But for that rationale to work, there would not be a 'master' un-adjustable reference carb to which the others are matched.....it would suck (no pun intended) if that particular cylinder had a vacuum discrepancy due to poor manufacturing ....ALL of the carbs would be freely adjustable to better match/compensate their respective cylinders. When we adjust 3 carbs to a fixed reference carb, we are seeking uniformity in metering, taking volumetric efficiency of the cylinders as a given.

 

[TheCafeKid]

First off, please understand I'm not trying to be argumentative . But for that rationale to work, there would not be a 'master' un-adjustable reference carb to which the others are matched.....it would suck (no pun intended) if that particular cylinder had a vacuum discrepancy due to poor manufacturing ....ALL of the carbs would be freely adjustable to better match/compensate their respective cylinders. When we adjust 3 carbs to a fixed reference carb, we are seeking uniformity in metering, taking volumetric efficiency of the cylinders as a given.

And I'm not disputing that. I'm not saying that balancing the carbs is an effort or attempt to make up for a deficiency in one or more cylinders or any such truck. I'm saying that the reason you sync them is to assure that the flow and pull of each cylinder is relatively the same across the board. You have to stop thinking of the carbs as one unit or all the cylinders as one unit. Cylinder 4 doesn't give a rats ass what carb three is feeding cylinder three. But since three is the unadjustale carb you need to more or less meter why cylinder four is allowed to pull so that it matches cylinder three. Yes the volumetric efficiancy is an assumed constant but no two cylinders Are going to pull the same volume of air in the same constraint of time when you take into consideration the fact that one worn valve seat can, albeit minutely, speed up the time in which the cylinder takes in a specific volume of air vs another with a not worn seat. The adjustment you are making not only effects the carburetor but also the cylinder. I am not trying to insinuate anything about making up for any type of defect or slop or anything I'm simply saying that if you were to set the butterflies at exactly the same opening, and then check vaccum levels you'd see that they are in fact not the same. Maybe I'm making it sound more complex than it really needs to be.

 

[sscott]

Hey TCK,
I didn't want to hijack this thread. I understand what you are explaining in the thread but still confused about the butterflies. In the CV carb rebuild tutorial (page 35 of 53 the carb is totally apart and labeled. I don't see a butterfly anywhere. ( I did just get home from work, 24 hour shift, so perhaps my eyes are messing with my brain LOL) I do see however the rails for the choke for example. Is that the butterly you are referencing? :-k

Thanks for the help!

 

[koolaid_kid]

Look on page 5. The tutorial calls it a throttle plate, but it is really a butterfly valve. The top pic shows it closed, the bottom pic shows it open.

 

[sscott]

AAAAAAAAAAAAHhhhhhhhhhhhhhhhhhh

Now that makes much goodlier sense to me!

Thanks! :clap:

 

[cowb0y]

Here's a great explaination of carb theory and it helped me to understand adjustments more clearly.
Have a look. . . http://www.iwt.com.au/mikunicarb.htm

 

[TheCafeKid]

Here's a great explaination of carb theory and it helped me to understand adjustments more clearly.
Have a look. . . http://www.iwt.com.au/mikunicarb.htm

That also explains plug chops pretty well. That, IMHO is the single most effective test in seeing which way you need to go in any specific carb circuit.
Well.. short of maybe having an AFM meter in your set up, but thats somewhat complicated...

 

[Guest]

And I'm not disputing that. I'm not saying that balancing the carbs is an effort or attempt to make up for a deficiency in one or more cylinders or any such truck..

Okay, that is the impression I got from the earlier post. Let's move on.

 

[koolaid_kid]

That also explains plug chops pretty well. That, IMHO is the single most effective test in seeing which way you need to go in any specific carb circuit.
Well.. short of maybe having an AFM meter in your set up, but thats somewhat complicated...

Actually, that's an AFR (Air to Fuel Ratio) meter, a.k.a. Wideband. At around $300 initial outlay, it is more expensive than it is complicated...but also a lot more accurate.

 

[TheCafeKid]

Actually, that's an AFR (Air to Fuel Ratio) meter, a.k.a. Wideband. At around $300 initial outlay, it is more expensive than it is complicated...but also a lot more accurate.

Rght you are. I was refering to it as air fuel mixture (afm) meter but you have the proper terminology there. By complicated I simply meant to
measure it acurately per cylinder you'd have to either have a long sniffer you could get up each header from the back or have a bung installed in each header. Otherwise you're only getting AFR readings of the over all exhaust right?