Topic: 1977 CB550F Won't Stay Running With Choke Off

[MarrisLauter]

For starters, this bike was stored in an underground parking garage and was not run for three years. I put a new battery on it, drained and replaced the old fuel and oil, and got her to start on the first kick. However, the idle speed was all over the place. It would run at 1200RPM with the choke on, and then randomly shoot up to 4-5000RPM and stay there until I shut the bike off. The bike would still stall out as soon as the choke was taken off at this point, even if the bike had run for 15 minutes and been well warmed up.

I took the carbs off and into a shop to be inspected and cleaned. The mechanic replaced one of the main jets which he said was no good, cleaned the carbs well, and replaced many of the gaskets on it. It looks brand new in comparison to when I dropped them off as there was a considerable buildup of old gas deposits in there.

I put the carbs back on the bike and tried starting it up again. Having similar problems, except the bike does stay stable with the RPM (doesn't randomly shoot up any more). When I start it up with the choke on, the bike runs at 1100RPM, and as soon as I take the choke off the bike stalls out completely. I can run it with the choke 3/4 off, once it gets past that point it stalls. I should mention that this bike does have air pods on it from the previous owner.

My question is, should I adjust the idle speed to account for this stalling? It seems like when I do this, the bike runs at a higher RPM with the choke on and still stalls out when it's off. Should I play around with the air mixture screws on the carbs and reduce the amount of air allowed in? I noticed they were dialed out 3 turns when I checked, and I reset them to the factory 1 1/2 turns out.

Any advice would be greatly appreciated!

[uksparky]

If your carbs are PD46 ..... the idle pilot jets are plugged up..... (had same problem when i got my 550)...they press in the carb body inside float bowl...... if not that ...what cond is the rubber between the carbs and head.... vacuum leak

[Scott S]

 The F model didn't come with PD carbs, that I know of.

 Make sure you're operating the choke lever properly.  It can be a little counterintuitive if you've never had a 550 before. Remove one of the outer pods and watch the choke butterfly.  You wouldn't be the first person to use it backwards.

[TwoTired]

The choke isn't a total cure for the inefficiency of a cold engine.  It needs throttle, too.   Some chokes have a fast idle cam that bumps the throttle during application.  Your carbs don't have that.  So you have to hold the throttle open to keep the RPM at 1500 or so until it warms up.  The idle knob is set for normal warm operation idle speed.  That setting won't work for a cold engine.

During routine operation, I don't use a stationary warm up.  And proceed moderately while the engine warms.  It is not difficult to reach down and incrementally bump the choke down while riding those first few blocks.  You only need enough choke to allow for some acceleration.  Conveniently, your hand is on the throttle during riding and can keep the RPMs up.

Theere are others that like to twiddle with the idle knob for a stationary warm up, and then reset it again during the ride after warm up.

I do have an one F model (the 76) that has a "cruise control" device fitted.  It's a friction lock that will hold the throttle grip in whatever position set.  This can also be used for a stationary warm up, holding higher idle.

Cold engines don't atomize fuel as well as a warm one, and this effects idle speed, for the very same slide setting.

Modern vehicles have computers that sense temperature and adjust for optimum mixtures at whatever demand placed upon the throttle.  The SOHC4 uses a computer located about 2-3 ft above the seat.  Those sometimes need additional programming.

Cheers,

[jgger]

Lloyd you are the best! I want to quote you if it is ok.

The SOHC4 uses a computer located about 2-3 ft above the seat.  Those sometimes need additional programming.

I.love it.

[dave500]

a lot often need re booting!

[MarrisLauter]

Thanks for the replies everyone!

 Make sure you're operating the choke lever properly.  It can be a little counterintuitive if you've never had a 550 before. Remove one of the outer pods and watch the choke butterfly.  You wouldn't be the first person to use it backwards.

Scott -  I did take one of the filters off to confirm that I was using the choke correctly because as you stated, it is a bit counter-intuitive

If your carbs are PD46 ..... the idle pilot jets are plugged up..... (had same problem when i got my 550)...they press in the carb body inside float bowl...... if not that ...what cond is the rubber between the carbs and head.... vacuum leak

uksparky - I'm really hoping the idle pilot jets aren't plugged, as the carbs were supposed to be thoroughly cleaned recently. The rubber between the carbs and head seem to be in good shape, all clamps have been tightened nice and snug. I did spray a bit of starter fluid around these boots with the engine running and didn't notice any increase in rpms - not sure if this is a fool-proof method of checking for vacuum leaks but it seems to be an indicator that there isn't a large leak here.

During routine operation, I don't use a stationary warm up.  And proceed moderately while the engine warms.  It is not difficult to reach down and incrementally bump the choke down while riding those first few blocks.  You only need enough choke to allow for some acceleration.  Conveniently, your hand is on the throttle during riding and can keep the RPMs up.

Theere are others that like to twiddle with the idle knob for a stationary warm up, and then reset it again during the ride after warm up.

TwoTired -  How bad would it be if I was to leave the choke at 3/4 open for a decent time while first riding? If the smoke from the exhaust doesn't look too rich, is this really hurting anything?

I feel like I may need to lube up the throttle cables a bit too as I have noticed the engine has stuck at some higher rpms when twisting the throttle, but can be dropped when pushing the throttle forward (doesn't snap back on it's own everytime, and is almost always a slow descent back down to idle).

Another thing I've noticed is that the previous owner had his spark plug gaps set to 0.55mm. I've replaced 1 and 4 with new NGK plugs with the factory 0.6mm gap, but I'm having issues reaching plugs 2 and 3. My 18mm deep socket is too fat to fit in the recessed area for these plugs -  is there a better socket for removing these?

Also TwoTired, my computer lags more than this bike so far, so obviously my program isn't helping with this problem solving too much 

Thanks again everyone

[Bankerdanny]

My experience with my 550F is that it only needed choke for a mile or two and you could completely open it within 10 minutes on a cold day and 5 on a warm one.

[Mooshie]

Once Dash is started (CB550F) I have to immedietly turn off the choke.  He only needs it for the literal start.  I would check the carb jets and rubber then check where the idle is set (it may be too high or low)

[TwoTired]

Lloyd you are the best! I want to quote you if it is ok.

The SOHC4 uses a computer located about 2-3 ft above the seat.  Those sometimes need additional programming.

I.love it.

Go for it!

[TwoTired]

TwoTired -  How bad would it be if I was to leave the choke at 3/4 open for a decent time while first riding? If the smoke from the exhaust doesn't look too rich, is this really hurting anything?

The risks of running too rich is washing the lube off the cylinder walls which accelerates wear.  And/ or building carbon on the spark plug insulators which can lead to misfires and dead cylinders.

If you are asking whether it hurts the engine to ride a mile or two with partial choke,  well it hasn't hurt mine noticeably in the 40 years I've been riding it that way.

Perhaps in another 40 years it will be different?    (...Like I'll live to 110! HA!)

Cheers,

[RustyF]

Moosie, When I got my 550K it had been siting for a while and had similar starting/running issues - would only run on choke above 4500 rpm and would not idle.  I cleaned the tank, installed new petcock, pulled the carbs and had to soak the pilot jets in chem clean over night as they were plugged solid.  Once all the jets were clean and I could see light thru them I cleaned the carb bodies. Reassembled and used card spray to verify the air passages were all clear...there are 2 air passages on the airbox side for each carb that you can spray thru (1 is pilot circut & the other main jet).  Once you verify (with the jets installed) that you get steady stream of carb spray thru all 8 passages you can check the float level settings and then reinstall the carbs - start with pilots at 2 turns out. I am trusting that you are using the stock airbox & filter.  My bike has fast idle cam on full choke and fires off & runs @3500 on full choke.  Once you get it to run and idle your next step is to vacume sync the carbs and your fuel issues should be solved.This is what it took to get my bike running. I then found 2 bad spark plug boots and the points needed to be cleaned and reset.

I have about 3,000 miles on the bike once I did all the above.  Hope this helps, Rusty