Topic: 1976 550K + 087A carbs = trouble

[gregk]

i've read pretty much all the information regarding these 087A carbs on the 76 model and there appears to be no printed information on these carbs.  There is also alot of posts regarding these bikes and carbs and a common problem with a "hovering idle" or a "hanging idle".  I have this problem on my bike and like many others have cleaned the carbs (many times), checked the tune up data and adjusted to specs, with no change to the running order of the bike.  Many have claimed that the carb data is the same as the 022A carbs used on earlier models of the 550K.  Does anybody have any info on the 087A carbs or a solution to this problem.  About the only adjustment I haven't tried is changing the float level from 22mm. 

greg

[TwoTired]

Did you do a carb vacuum sync?

There was a post that said the air bleed screws were solid tipped rather hollow and cross drilled, referencing a Honda parts list.  Would you check yours?  I can't be certain if my set was "meddled", as it has the hollow screws, and there are other signs they aren't "virgin".

You do know that these carbs will not "automatically" adapt to induction and exhaust changes, right?

[gregk]

I haven't checked the air bleed screws, will investigate tonite.  I tried to sync the carbs but get little or no reading on the gauges at idle.  The bike has 2548 miles on since new.  This has been very frustrating to me as i have three other SOHC bikes and was able to set them up to run perfectly.  There is nothing changed from stock on the bike- pipes are stock, carbs appear to be stock, all air cleaner parts are in place along with the filter. 

[TwoTired]

I tried to sync the carbs but get little or no reading on the gauges at idle. 

How can that be?  The physics of the falling piston on the intake stroke and the near closure of the carb slides demands there be a negative pressure reading in the intake tract.

You've got something wrong with your test gear or the engine mechanicals.  Carbs won't fix that!

Done a compression check?  (Either pressure gauge or leak down)?

Cheers,

[gregk]

The vaccuum gauges worked well when i used them on my other bikes, so i was supprised when i got these low readings.  With no vaccuum the motor would not run !  The compression was even across the bank, I have forgotten the exact readings, as i did this last summer,  but seemed to me that it was close to 100 psi. 

[TwoTired]

Were the slides installed with the cutaways facing the air filter or the intake valve?

[gregk]

The cutaways were installed facing the air cleaner.   Not sure if they could be installed any other way? 

[Duanob]

Everything you described sounds like a major vacuum leak somewhere. The o-rings between the intakes and head can get brittle and crack. The intake rubbers can do the same especially when someone over tightens the clamps. The 087As are easy carbs to deal with. they just need to be clean, clean, clean. make sure the jets haven't been messed with I believe they are the same as the 022A, 38/100. Make sure all the rubber carb o-rings and gaskets are good. it's not miles that ruin them, it's time. Hanging idle can also be a problem with old sticking throttle cables, even with a spring and a return cable they will still cause the idle to stick.

[TwoTired]

I tried to sync the carbs but get little or no reading on the gauges at idle.   

I feel you need to solve, explain, or understand this issue first.

The only way the carbs, themselves, can prevent a vacuum reading is if the slides are open, letting atmospheric pressure reach the sync port from the air filter.

The cutaways are supposed to face the air filter, btw.

Good luck!

[Raef]

does the reading on the sync gages change if the choke is applied, is so the slides may not be not closing, if not, you may a valve timing or seating problem.

Mark

edit

I was assuming you have checked for cracked rubbers or leaking/missing o-rings at the intake manifolds

[gregk]

I've  sprayed  the boot areas with W-D 40 and don't see any change in idle speed.  All the rubber o rings and boots appear (to the eye) to be in good shape.  i've checked the advance unit and it also seems to advance and retard properly. 
I did not try putting the choke on while I had the vaccuum gauges hooked up.  Good advice, thanks.

[Duanob]

At pennies a piece it's worth it to just replace the o-rings. It takes a few minutes. When I first got my bike it wouldn't run except with the choke fully on. After I replaced the o-rings and checked the boots (good shape) I could at least run the bike without choke. The WD-40 bit never works for me anyway. you would really need to cover the crap out of the intakes to make any difference. All you're trying to do is plug any and all vacuum leaks with the spray. Good luck with that.

The no vacuum at the gauges is the weird part. All you need for that is good compression and no vacuum leaks really. And a free flowing exhaust. One of those things is affecting your vacuum into the motor.

[Nortstudio]

I have the same set-up you do.  '76 550k with 087a carbs.  I think I may have been the one referenced earlier.  I have not had the hanging idle, but definitely have had the bogging/hesitation (at about 1/8-1/4 throttle).  Two-Tired has tried to walk me through some steps for tracing the issue. 

Unfortunately, I have not been able to find another rack of 087a so may be swapping to 022a and whatever changes that may bring.

I'm posting so I can follow your process and progress, but will certainly chime in if I solve any issues that may shed light on your bike. 

One thing I did notice is that the hesitation decreased with the installation of better condition 4-2 exhaust (small holes in the old 4-1). That tells me that these carbs are at least subject to [subtle?] changes with the things we do to the rest of the bike.  If only I could track down that specific problem.....

Good luck to you!

[gregk]

Did you do a carb vacuum sync?

There was a post that said the air bleed screws were solid tipped rather hollow and cross drilled, referencing a Honda parts list.  Would you check yours?  I can't be certain if my set was "meddled", as it has the hollow screws, and there are other signs they aren't "virgin".

You do know that these carbs will not "automatically" adapt to induction and exhaust changes, right?

The air bleed screws are hollow tip and cross drilled. 

[gregk]

 

The no vacuum at the gauges is the weird part. All you need for that is good compression and no vacuum leaks really. And a free flowing exhaust. One of those things is affecting your vacuum into the motor.
[/quote]

The compression on all cylinders is good, the exhaust is stock and in good shape, so must be a vaccuum leak! 
I assume when you refer to replacing the " o rings" that these are the  ones in the intake manifold?  I can rule out a sticking cable(s) because the idle climbs even without the cables hooked up. 

[bryanj]

100 psi on compression is too low and i would suspect stuck rings or leaking valve seats

[TwoTired]

Can you post a picture of your compression tester apparatus?


I must say it seems rather odd that all four intake runners leak copiously and exactly the same amount from identical failures.

[gregk]

100 psi on compression is too low and i would suspect stuck rings or leaking valve seats

i found my notes from the compression test - 120 psi on all four. 

I'll take a picture of the tester tonite. 

[Duanob]

The intake to head O-rings are the same ones used for your valve tappet covers. If you have 4 new ones laying around I would start there. And check the boots while you're in there. Check them from the insides as well.

This is going to be a process of elimination as all diagonostics are. Start with the cheap and easy ones first. If that's not it then check the airflow into the carbs. If nothing blocking or not connected ( I doubt that would have a huge effect on runability) then you're probably going to be tearing into your carbs. Just do a good thorough routine cleaning and try again. I've had to do this three times with my carbs and everytime the carbs looked perfectly clean with no obvious blockages. And everytime the bike ran better afterwards.

[gregk]

Ok simple solutions first.  I'm going home armed with a small propane bottle and a bit of hose.  Should be able to find a vaccuum leak with that!  If i don't find any leaks, I'll see what happens to the vaccuum gauages when I close the choke.  After that, It's into the carbs again.  And this will be the third time I've had the carbs out.  And i didn't see that they were dirty in the first go around.  i have definitely got to figure out this bike now or I'll get discouraged like last year. 

[gregk]

Last nite i got the bike running again after sitting in the garage all winter.  It starts right up with a little choke and seems to run better when it's cold.  Checked all the inlet area with the propane bottle and no evidence of any vaccuum leaks.  As the bike warmed up, the rpm kept dropping and I kept adjusting the big idle screw until it was maxxed out!

The compression tester that I have is an automotive type with a flexible hose.  i understand that there is some error in the gauge reading with this type of gauge, but it's the only tester i have. 

I did check the compression on my 400F last year with the same gauge, just to see if the readings were relative.  Again got in the order of 120 psi and the bike is a solid runner and the compression specs for the 400 are similiar to those of the 550. 

Not sure where I'm going with this now, but most likely back into the carbs. 

[Nortstudio]

I thought the "running better when it's cold" was a sign of running rich. Can't recall if you mentioned the condition of your plugs. How do they look?

[gregk]

if I run out of adjustment on the idle screw, then the carbs are skewed and cannot return to a closed position, as someone had pointed out.  It should then be possible to adjust the slides to a position where the vaccuum at an idle is increased ?  The air bleed screw is on the intake side ( air cleaner side) of the carb.  Which way to make it leaner? 

[TwoTired]

The air bleed screw modulates the air coming from the air jet feeding the emulsion tube.
Moving the screw away from it's seat allows more air to flow in that pathway.

If you don't wish to know how it works.  Then turn it out (CC) to lean, and inward (Clockwise) to enrich the pilot mixture.

Hollow tipped air screws have a limit to their effectiveness/range of adjustment.  The limits are determined by the cross drilled hole in it's tip and the pilot air jet orifice size.

Cheers,

[Nortstudio]

From the FAQ section on carbs.

What happens when I turn the airscrew out - richer or leaner?
If your airscrew is on airbox side of carb, turning out will lean mixture; opposite if airscrew is on engine side of carb.