Carb vacuum balancing question.

[bushyb]

Originally Posted by bmwrench

Check the valve clearances.

Thanks Done

[bushyb]

Originally Posted by cycleman2

Sometimes people get the atomizer in backwards after a carb rebuild. The bike will run but not well as its not getting enough fuel. Also check that both cylinders exhaust is generating heat.

Thanks, not quite sure of the comment above but you might be onto something. I removed the left carb and on removing the main jet and nut the needle jet just fell out but the atomizer remained in place. Now I am not sure that this would cause the problem that I have as the main jet when screwed in would hold the needle jet in place. Any ideas on how to remedy this? Thanks

[boxerboy81]

If the needle fell out then it can't be held in correctly. Maybe the holding clip needs replacing?

[disston]

He said the "needle jet" fell out. The "jet needle" is held in place by a clip. Notice in the former it is a "jet" the modifier being needle so it's not confused with the main jet. And in the later it is a needle the modifier being jet so it is not confused with the "float needle" or something else.

The atomizer and the needle jet are held in place by the venturi. Sometimes the atomizer will fall out and sometimes it is stuck because it is bent. They are very thin.

Notice the venturi in some parts micro-fiche pictures does not seem to have an O-ring;



In the above picture there is no O-ring shown on the venturi. But there is an O-ring shown on the idle mixture screw and in the blub for these parts (not shown at all in my reproduction) there are two part numbers for #13. One is the idle mix O-ring. The other is the venturi O-ring.

I had weird symptoms until I figured this out because my favorite parts guy told me there was no O-ring on the venturi. There is an O-ring on the venturi and now he knows also.

[motog]

Originally Posted by bushyb

Thanks, I have had another look. It seems the problem could be the left carb, with everything disconnected and engine warm adjusting the mixture on that carb makes no effect to the idling. I can close the mixture screw all the way and there is no change. So I am assuming the must be a leak on that left carb. Would that be correct?

Most probably. Tear the carb down, rebuild it with all new parts. Have had the same problem on several carbs over the years. New o rings, jets, gaskets etc has always fixed it. The parts aren't expensive but it is a half day job and I've always done both carbs at the same time.

Jim

[boxerboy81]

Originally Posted by disston

He said the "needle jet" fell out. The "jet needle" is held in place by a clip. Notice in the former it is a "jet" the modifier being needle so it's not confused with the main jet. And in the later it is a needle the modifier being jet so it is not confused with the "float needle" or something else.

The atomizer and the needle jet are held in place by the venturi. Sometimes the atomizer will fall out and sometimes it is stuck because it is bent. They are very thin.

Ahh, well spotted. I musta read it too quick
The needle jet and the atomiser falling out isn't a problem to be concerned about, and if the atomiser didn't fall out but the nj did, it still wouldn't matter. Gravity rules, but the atomiser might get "stuck" in it's hole but easily dislodged regardless. Here's how they line up, mit o-ring, in my BINGS 11/1981 RS.

[_cy_]

Originally Posted by motog

I've always done both carbs at the same time.

unless you've done so many carbs you've lost count (500+ for me) .... do ONE carb at a time. take lots of digital pic's to help during reassembly.

before taking any adjustable part out. make note of original position. lightly bottom any mixture screw taking note number of turns. this will allow returning carb back to original settings and help in trouble shooting.

a spray can of Berryman Chemtool with a long nozzle is your friend. carbs have all sorts of tiny openings, orifices, internal passages, etc. goal is to make dead certain each and everyone of them are open and clear. even if you've got access to some nasty carb dip and soaked parts. with glasses on, spray each and every opening to test. if spray comes out other side, you've got proof positive sign orifice/passage is clear. use real carb cleaner to do this with. carb cleaner is formulated specifically to desolve carb gunk.

[bushyb]

Originally Posted by boxerboy81

Ahh, well spotted. I musta read it too quick
The needle jet and the atomiser falling out isn't a problem to be concerned about, and if the atomiser didn't fall out but the nj did, it still wouldn't matter. Gravity rules, but the atomiser might get "stuck" in it's hole but easily dislodged regardless. Here's how they line up, mit o-ring, in my BINGS 11/1981 RS.

Thanks that is just what it looks like, It is the second part from the left that dropped out the needle jet. I also have just read in the Hanes book that they also talk about it dropping out. All O rings are in good condition. I am in any case going to order a new kit that most properly will that about two weeks to get here in this part of the world.



I need to satisfy myself that it's this carb giving problems. I thing I will clean it again and re-fit the carb get it warm, close down the idle on the right carb and raise the idling on the left and try the mixture adjustment again. Thanks

[supershaft]

I am real familiar with these carbs. Idle problem? After a couple of carb checks, I get a leak down tester and listen for a leaking valve. It's very often a huge time saver. They won'tr idle right with even the tiniest valve leak, let alone a bigger one.

[supershaft]

I forgot to add an important part of my advise: HEARING the leak takes some experience. On the intake side at least and it is usually the intake side that is leaking in my experience, if you are not sure if you are hearing a valve whistle, squirt so brake cleaner in the port. You will hear the bubbling for sure! If you have a leaking intake valve that is! Good luck!

[baloneyskin daddy]

Take both carbs off after the motor is warm and do a compression check.

[bushyb]

Originally Posted by supershaft

I am real familiar with these carbs. Idle problem? After a couple of carb checks, I get a leak down tester and listen for a leaking valve. It's very often a huge time saver. They won'tr idle right with even the tiniest valve leak, let alone a bigger one.

Originally Posted by supershaft

I forgot to add an important part of my advise: HEARING the leak takes some experience. On the intake side at least and it is usually the intake side that is leaking in my experience, if you are not sure if you are hearing a valve whistle, squirt so brake cleaner in the port. You will hear the bubbling for sure! If you have a leaking intake valve that is! Good luck!

Thanks, you not the first one to mention this. I am not familiar with just how to do it. Anyway I went and bought new O rings again and have fitted them and reset mixture screw back to recommendations of 1 -1/4 turns out. This causes a miss on both exhausts. I the adjusted them by ear out to the highest idle on each carb. This was done without the throttle and choke cables connected and the idle screw adjusted way out....



The bike idles nice and constant but a tad too high about 1100 rpm??? The left carb is better but you can just about close the mixture screw all the way in before it faulters to die.

I then use a single dial vacuum gauge to check and compare the reading from the left and right carbs. I got them petty close to the same and then stuffed it up a bit and stopped because I was concerned of overheating. On returning I connected the home made manometer. Which was once again had the oil sucked out of it on one side as soon as I started it. Right now I think I must blamed the home made manometer, which is 1/4 inch in diameter (too big I think) and about 8 m long with a short piece of 5/32 ID tubing fitted in the pipe which fits perfectly over the pickup. Maybe the larger diameter and then the smaller diameter make it too sensitive to use especially if there is the slightest of imbalance.

Yes I have done a compression test a time back and it was pretty good.

[bushyb]

Originally Posted by baloneyskin daddy

Take both carbs off after the motor is warm and do a compression check.

Right I did a quick compression check with WOT.



Left 140 and right 135



The bike has only got 51000km on it.

[_cy_]

got all sorts of manometers, but my favorite balancing tool is a Unisyn. don't let the low cost ($25) fool you. it does an excellent job at low flow and high.



here's a digital dwyer


magnehelic


here's an unusual one... Wallace & Tiernan Precision Pneumatic Calibrator
with Series FA-145 Dial Manometer

[disston]

Wow!

Those tools are worth more than my motorcycle.