Topic: cb550 crazy idle issues

[rcollins09]

So I just got done rebuilding the 069a carbs on my cb550 and got everything back together. It  has all been bench synced and have the vacuum sync gauges hooked up. I started the bike last night and it was fine carbs were running good and pulling the same vacuum. I kick started it today and the rpms shot straight to redline like I had the throttle wide open. So i backed off the big idle screw to the point its not even touching, I sprayed wd40 on all the boots thinking there was a leak, even loosened up the throttle cables thinking one of them was to tight. After all that i started it again and it shot to 3500rpm for a few seconds then slowly started working its way back up till i would shut it off. I can not for the life of me think of what else would cause this….

sohc4 master minds out there HELP ME!

[OneWheelDrive]

Did you tighten the lifter arms onto the cam that lift the slides?  All I can think of is slides that are stuck open.

[rcollins09]

Yup the 13mm brass caps I tightened, and the 4 adjusters are all tight and set to where I at least think they should be by measuring the slides.

[TwoTired]

PD carbs have a choke knob at the bars.
They also have a throttle up cam tied to choke operation with it's own adjustment.
You didn't mention anything about choke or its adjustments.

If the fuel level in the carbs is too high it might be sucking extra gas droplets to advance the RPMs.

If you have vacuum leaks in the carb couplers, it can suck air and advance the RPMs, as the the idle is to be adjusted a "little" rich.

If you don't have the stock air box/filter and exhaust system, none of the carb metering jets/adjustments is correct at stock settings.  (You didn't mention anything about this either.)

After doing the carb vacuum sync, you have to put the plugs back onto the vacuum tap locations.

You also need to have the fuel tap in either ON or reserve depending on the gas level in the tank.

The fuel in the carbs needs to be clean of any debris.

The carb venting system needs to be clear.

Yup the 13mm brass caps I tightened, and the 4 adjusters are all tight and set to where I at least think they should be by measuring the slides.

PD carbs don't have brass adjusters, and there are only three carbs that can be adjusted. #2 is master.
What is it you actually have?

If you have earlier carbs rather than the PDs, 4 adjusters can be skewed so that the slides can't close, and then the engine can't idle, as the symptom is similar to holding the the throttle open.

[rcollins09]

The choke is closed when this happens, if i even move to open the choke the rpms scream to redline.

The couples for the carbs are seals i checked for leaks there.

I do have the stock air box stock filter and basically stock exhaust its a different muffler but darn close to the same back pressure.

When i rebuilt the carbs I did notice the previous owner had 100 main jets in it which i left and replaced the o rings with a 38 pilot jet.

The carbs are spotless clean now in and out.

I actually have the vacuum sync gauge still hooked up when this issue happens. due to still wanting to fine tune it.

I guess i could remeasure the float height but i was very cautious as to get them exactly at 22mm before sealing up the float bowls.

[TwoTired]

Actual PD carb float settings for the CB550K are either 12.5mm or 14.5mm depending on year model.  If you have #38 press in pilot jets, then 14.5mm is correct.

[rcollins09]

Well i guess ill start there, I know i have them at 22 I though that is what it said in the honda cb500-550 shop manual.

[TwoTired]

The PD carbs weren't offered until 1977 with the K3 model.  They are described in chapter 19 of the Honda CB500-550 Shop manual.

Are you certain you have the PD carbs?

[rcollins09]

wow im a dumbass I have the 069A Carbs I was reading an article earlier about the PD carbs and just typed if without thinking! I apologize!

[phil71]

when you say you bench synced... just out of curiousity, did you make adjustments to all 4 or just the 3?

[TwoTired]

If your main idle knob can be backed out and the engine still runs, then you have skewed all the slide adjustments to limit closure travel.

I guess you used the drill bit method to bench sync, and never insured the slides had the capability to fully close.
It's one of the reasons I think that noobs should never learn this method.

Anyway, guess what?  You have to go back and do it again.  Get a slide to fully close, assign it master status, and don't adjust that one again during bench OR vacuum sync - ever.   Adjust the others to the master.  Then the big idle knob can effect a proper and consistent idle speed.  Perhaps there are other issues, too.  But, that one is the first to fix, imo.

Cheers,

[dave500]

of course the igniton is spot on and the advance unit free to move?

[Duanob]

069A that's a F model 550 right? They are similar to the 74 - 76 K model carbs than the 77 - 78 PD carbs if memeory serves me correct.

Just a thought since I did this once but did you forget to hook up the return spring? This will definitely cause your symptoms.

[rcollins09]

Thanks for all the advice guys I did figure out i did the bench sync WAY off i misunderstood the correct way to do it. So none of the slides are closing completely…Yes noob mistake but everyone of us was there at some point. TwoTired I messaged you already today but thanks again. Ill report back when i pull them back off tonight and readjust everything once more.

Thanks Everyone.

[Duanob]

"Yes noob mistake but everyone of us was there at some point"

No problemo, that's why this board is so entertaining!  j/k.

[rcollins09]

Just got done re bench syncing them, then put them back on. Hooked up the vacuum gauges re adjusted everything to 10lbs vacuum and the bike runs beautifully! Thanks guys

[zurek]

I'm so glad I found this tread, I have the same issue with my PD carbs….I’ll try to redo bench sync tomorrow