Topic: Bike Runs! Finally! Huzzah! ...And Over Revs!

[Paul E.]

I dropped in a new set of TEC points and everything ran beautifully.  For the first time!  Ever! 

Well, there was one minor hiccup.  While idling I would rev the engine and it would stick at 2k RPM.  If I flicked the throttle a bit it would settle back to 1200 RPM.  So I went ahead and took it out for a short ride.  While riding the RPM would hang around 3000 after I had let off the throttle.  If I flicked it it would still hang at around 3000, but if I started to adjust the idle knob it would drop down to 1000 RPM.  So I decreased the throttle idle by backing the knob off in hopes that it would fix the over rev issue but that didn't fix it.  It just made it so that I had to hold the throttle open a little when idling.  What's going on here? 

Can't wait to ride it more!

Specs:
1974 CB550
Stock Air Filter  ---> Uni Foam Filter in the mail
Carbs 022A
Air mixture screw set to 1.5 turns out
750 Mac Exhaust
Stock Jets 100's and 38's
22 mm float height
New D7EA plugs
New NGK Caps
New TEC Points

[fastbroshi]

Have you tried checking for leaks around the carb boots (both sides) with spray can starter fluid yet?  I think carb cleaner would work too.  Any leaks would manifest themselves in a blip in the revs when you spray an area of the boots that is leaking. 

You didn't mention it but I know you replaced the intake manifold o-rings so we can rule that out.

[dave500]

check the advancer isnt sticking and recheck the timing,you might try a quarter turn in on the air screws,have yours got a hole in them like this?

[killersoundz]

check the advancer isnt sticking and recheck the timing,you might try a quarter turn in on the air screws,have yours got a hole in them like this?

I don't mean to hijack the thread but the air screws I replaced from a rebuild kit on mine had holes in them like that. WHAT IS UP WITH THAT? What are you supposed to do with those? It seems like it would completely screw everything up if one ended up with the hole passing through and the others blocking or whatever variation.

[dave500]

what happens with the hole type is even if you bottom out the screw itll only go so rich,(in that photo check where its been seated in the carb,you can see a wear ring mark around the tip before the hole)itll stay some what lean,you can solder them up as shown or find the early solid type,its akin to the idle limiters on smog equipped carbs on cars back in the day,you could only enrichen the idle so far,,it dosent really matter what direction the hole ends up at with these type.
the air does a 90 degree turn where this screw is,it dosent flow through so to speak.
air enters the sideways hole and exits the pointy end hole,even with a solid one air passes around the needle and exits near the pointy end,you have more idle/off idle control with the solid type,it seems not many people know this,the pod fans might have a slight improvement using solid ones?i dont want to encourage them though!

[Paul E.]

check the advancer isnt sticking and recheck the timing,you might try a quarter turn in on the air screws,have yours got a hole in them like this?

My air screws definitely have holes in them!

How would you check whether the advancer is sticking?  I've never done that before.

Have you tried checking for leaks around the carb boots (both sides) with spray can starter fluid yet?  I think carb cleaner would work too.  Any leaks would manifest themselves in a blip in the revs when you spray an area of the boots that is leaking. 

You didn't mention it but I know you replaced the intake manifold o-rings so we can rule that out.

I'll grab a can and see if I can detect any leaks on the carb boots once I get my battery back in.  The PO put in a walmart battery that has a tendency to slowly die so I picked up a AGM battery from a local auto parts store only to find it's a touch to wide for the stock battery box.  Hopefully going to fabricate something to hold it in place tonight.  Especially since it's too rainy to ride!

[Spanner 1]

A vacuum synchronization will cure your problem, very common on a bike who's carbs have been apart and off and on the bike ....

[Paul E.]

I looked for leaks in the carb boots and couldn't see any.

 I didn't see anything like this:

  
I sprayed some lubricant on them in order to detect some smaller fissures but wasn't able to see any bubbling.  The airbox side boots did seem to have worked themselves a little loose where they join the plastic air box.  So I went ahead and nudged them back in to the holes.

So I took it out for a short ride and the idle problem persisted.  Now however it seems to have returned to its old ways.  On Friday when I rode it everything seemed great, but today when I go over 3000 RPM instead of getting acceleration it sputters and acts sluggish with some light popping.  On Friday when I would do that it would almost slide me off the seat!  I'm not sure what has changed between Friday night and today to merit such a difference. 

Tentatively, I think I might order a set of vacuum gauges, jets (one size up and one size down), and pull the carburetor back off the bike so I can really examine both sides of the carb boots. 

Was a consensus ever reached on repairing carb boots with liquid electrical tape?  I read through this post and it seemed to resist the gasoline pretty well: http://forums.sohc4.net/index.php?topic=34863.0

[lucky]

Before the carbs can be tuned all other issues must be fixed.
You can easily tell if the advance unit is working by connecting a timing light.
If it is running and the timing is on the F and you rev it up and the timing shows the advance marks lining up then your advance unit is working.

FACTS:
Specs:
1974 CB550
Stock Air Filter Box
4 into 1 MAC exhaust.
Carbs 022A
Air mixture screw set to 1.5 turns out
Stock Jets 100's and 38's
22 mm float height
Needle clip on the 4th groove down from the top? (stock position)

[Mercutiojb]

Having very similar problems on my 77. Will chime in if I discover the issue.