Topic: 76-550 all is not well in garage find ville!

[gregk]

Don R

Patience is a virtue i have been told.  I'll figure it out, it's just a matter of time (and patience)
i have read virtually all the materials that comes up on various searches and it seems that these 550's will have this problem but no apparent easy fix with the exception of routine tune-up procedures.  I will go back to the basics this weekend and redo all the tune-up.

ColinMc

There are no diaphrams in these carbs, i understand that the later carbs did have diaphrams. 

greg

[westondc]

exact same issues with my cb500 including "lowering the rpm by putting slight pressure on the slide lifting arms on carbs #1 and # 2." tried everything exept pulling carbs for a another cleaning. i'm working on it this weekend. will post if i come up with anything.

[TwoTired]

took the slides out and polished the bores and slides - arms seem to operate freely.

It's ok if you want to side step the question.
But, there are several connections between carb slide and the common linking actuation shaft that have springs and shoes on ball studs designed to hold the slides in the same relative position.  If there is play in the slide actuation linkage, the slides are not held in stable position.
So, I am asking if you put it back together with all the parts in the right orientation and with lubrication.

Good luck!

[gregk]

took the slides out and polished the bores and slides - arms seem to operate freely.

It's ok if you want to side step the question.
But, there are several connections between carb slide and the common linking actuation shaft that have springs and shoes on ball studs designed to hold the slides in the same relative position.  If there is play in the slide actuation linkage, the slides are not held in stable position.
So, I am asking if you put it back together with all the parts in the right orientation and with lubrication.

Good luck!

No I didn't take the entire actuating arms apart.  I did take the cap and springs out and squirt a little 3 in1 down the hole. 

greg

[TwoTired]

ok, a little more prodding....
see:
http://images.cmsnl.com/img/partslists/carburetor-cb550k2-four-usa_bighu0038e4007_c5b6.gif
I'm talking about the parts within 29 and 13.
How certain are you that they are currently assembled correctly?

[gregk]

TT

parts in group 29 are in the correct order.  Group 13 was also all in place when i took the slides out.  It does seem that the bike has a better vaccuum when it is cold and i don't get the hanging rpm until it warms up.  The vaccuum then drops off.
 
Someone said that if it is worth doing, it's worth doing twice.

greg

[Spanner 1]

Greg, one more idea from me........ early this year while working on another member's 750, trying to sync. etc., we were having a simular problem and found one carb was over-filling ( Possible causes = float height wrong, stuck valve, gas-in-float ) and gas was welling in the carb throat and getting sucked in to the motor and causing the RPM's to increase dramatically without touching the throttle, the increased vacuum tending to lift the slides all by itself, ( honest! )...........might be your problem ?? In other words, I'd re-check fuel levels in the bowls.....

[TwoTired]

The only bike I had issues with creeping, inconsistent idle was my 78 550K.  It has PD carbs,  But, the problem was corrected with a proper vacuum sync.
I suspect someone tried to sync them by ear, as they were all over the place, and the head pipes did not heat evenly during idle.
I have never worried about the raw numbers on the gauge, only that they were the same all the way across them at idle speed, and would return to the same number after blipping the throttle.
FWIW

[gregk]

I've got to think that the hanging throttle and low vaccuum are somehow connected.  At an idle, the gauges will barely register, at 2500 rpm they all pull 5.5 inches of Hg.  (well below the specs)
I'm going to go through the whole process again this weekend and hope to find a leak or high float. 
I can get the throttle to return to the stop without hanging at 2500 rpm but it will not idle, motor quits when it gets below 1000 rpm.  Its either the normal idle with the hanging throttle or no hanging throttle and no idle??
judging by the weather, I'll have all winter to figure this out.

greg

[fastbroshi]

Did you take apart the slides and arm actuation linkage?

+1, I couldn't get my carbs to sync until I made sure the carbs' "arms" were loosened on the rack's shaft; apparently mine had seized preventing proper adjustment.  Since the arm was seized to the shaft, adjustments to a particular carb's adjusting screw moved the whole shaft.  Don't know if that's by-th-book correct, but it fixed my sync problem. 
   
    You said when you push down on 1 and 2, the idle goes down.  Does that mean that 3 and 4 don't move when you do this?  If so, it's wrong.  They should all move in conjunction.  Maybe this shaft wasn't tightened down after your cleaning.

[Salmonser]

Having similar problem with my '72 500. Funny thing is. It's got a 555 Big bore, no air box, the olde mac 4into1, and the problem started only after the first 100 miles after the rebuild. Haven't delved too far yet, but the shop is slow. Will tell you if i figure out what's happening to mine.

[gregk]

Got into the carbs again this weekend and went through the whole clean again.  This time I pulled the needles as i was curious about the height.  They were set in the second notch from the top.   Some data indicates the needles are to be set in the 3rd notch and some indicate the 4th notch.  Not sure which is correct as these carbs  ( 087A) were only used on the 76 models.  Anybody have any other experience with these carbs?  i have read most of the search material and they are apparently the same as the other numbered body carbs with the exception of the larger screws that hold the float bowls and the jets are 100 and 38. 
I have ordered new gasket sets for the carbs in the hope that some of the rubbers on the jets/needle and seat are not sealing.

greg

[anparkinson]

My 550K3 was exactly the same. It had sat for 14 years in a damp garage. I took the carbs apart, soaked all jets etc in carb cleaner, blew air through everything and no change - still massively flat at around 3000RPM.

Stripped them again and found the problem - the idle jets (push fit on the K3) were about half blocked. From memory they should be 0.42mm so I got a .4mm model drill and reamed them out. Loads of white powder came out.

Put them back together and the bike ran beautifully.

I balanced them with a feeler gauge on the butterflies on assembly with No2 as the ref. About a year later I borrowed a mate's vacuum balance kit and they were all perfect - no adjustment needed.

[gregk]

anparkinson

Luckily the jets in these 087A carbs are removable and i was able to clean them out with carb cleaner and air.  Plugged jets are not the problem. The bike will idle. When I try to balance the carbs, I run out of room on the idle set screw.  That and the fact that all the vaccuum readings are well below the specs.  I am going to replace all the gaskets and o-rings and see what happens. 

greg
 

[TwoTired]

When I try to balance the carbs, I run out of room on the idle set screw. 

If you are running out of room on the idle set knob, then you have skewed all the individual slide adjusters so that the slides can't fully close.
This would explain the low vacuum at "idle".

With the idle knob backed out, you MUST be able to completely shut the slides in each carb.  This is why I choose the
"light method" to bench sync the carbs.  Shut off the light = shut off the air.  Then when you vacuum sync the carbs, you pick one carb that you never adjust, and adjust all the rest to equal the vacuum on the non-adjust carb.
The slide cutaway must face the air filter, btw.

The engine won't run with all the slides fully closed, and you will have poor vacuum if the all the slides are open too far.  But, you then set the idle knob to make the slide open just enough to idle (when fully warmed up), and you should then have normal vacuum.

I've not found any meaningful difference between the 086A carbs and 022A carbs.  The slide needle should be set to the 4th groove from the top.  (Assuming you are still using the stock needles; 272304, and have the stock air filter and exhaust)

[gregk]

I now have gone through the carbs again and rechecked the float height and set the slides.  Also replaced the o rings and gaskets.
Replaced the carb rack on the bike and it will now rev and return to an idle without hanging up.
The vaccuum at an idle is still minimal but is even across all the carbs.  If i raise the rpm to 3000, they all pull at 5 cm Hg. 
I am unable to road test the bike now due to the snow/cold but am now satisfied that it will run better (not perfect) but better. 
I don't have an explanation as to what the "fix" was regarding the hanging idle but its gone!
I'm going to revisit this in the spring when it warms up.

greg

[westondc]

ok, a little more prodding....
see:
http://images.cmsnl.com/img/partslists/carburetor-cb550k2-four-usa_bighu0038e4007_c5b6.gif
I'm talking about the parts within 29 and 13.
How certain are you that they are currently assembled correctly?

Fixed the same problem, idle would hang at 3000rpm after warm up. dismantled parts 29 & 13. sprayed them with carb cleaner, blew them with air and followed with WD40. opened the carbs, held the idle jets to the light and noticed one was still clogged. cleaned it and reassembled. started the bike, warmed it up and adjusted the idle screw. synced the carbs and the problem was gone. runs like a champ