Topic: 1978 CB550 will not start

[man-bot]

For the life of me I cannot get my CB550k to start!  It's driving me nuts - here is a bit of background:

-bought the bike last year and it was a pain in the butt to start, might burble then had to sit for 10 mins and the would burble some more but eventually would fire up and run just fine

- decided I should tune it up before this season began as it was getting warm so I did a tappet adjustment, filed and set the gap on my points and checked timing.

- I had cleaned and rebuilt the carbs last year but removed them again to double check there wasn't an issue.  Jets were clean, all is good as far as I can tell.  90 main jet, 42 slow jet (should be 38 according to the shop manual).  Air mixture screw is 2 turns open.

- have good spark on all plugs.  Bike came with champion RA6HC - I know These aren't correct but the bike will run with them (at least last year it did)

- after it wouldn't go today after removing the carbs, checked they were clean and adjusting float height to 14mm per the shop manual I check the plugs and they weren't wet.

So what the heck is going on?  I am at my wits end here...  All help is appreciated.



- I get nothing at all - no burbles... Will fire with starting fluid but then cut out

[rklystron]

Personally I would suggest starting at ground zero. Question 1 is what is the overall condition of the engine? You can determine this with a compression tester for a basic indication. The compression should be depending on model you have between say 150 to 170 psi. All cylinders should read +- 10%. If that looks good and you have good spark, fuel and timing are the next items I would look at. Also take some time and adjust valve lash to make sure they are set properly. .002 intake and .003 exhaust. This would also be a good time to set the cam chain adjuster. The biggest problem I have found on these bikes is the pilot jet is clogged. Make sure they are open and not restricted. Take them out of the carb and look at them closely. You may find your problem there. Best of luck.

[man-bot]

Thanks - I haven't checked compression but it has fired on all cylinders without issue and had no power problems when running last year.  Valves were just adjusted to the manual specs so I'm good there.  Pilot jets are clean - checked and diubl checked today....

[Duanob]

Are you getting gas to the carbs? Pull the fuel lines from the fuel tap and start there. Gunk and crap can clog your intank filter. Next check the float bowls by loosening the drain screws to see if you're getting fuel. If you get fuel to that point you will probably have to pull the carbs and do yet another cleaning. 

[man-bot]

Definitely have gas flowing, float bowls all can be drained...

Hate pulling those flipping carbs!

[SanDogDewey]

+1 on re-cleaning the carbs. If its starting on the "juice" and dying, its not gettting gas. Are the plugs wet?

[TwoTired]

I don't like champion plugs for the Honda.  Even so, the correct heat range for the 550 is RA8 which is a hotter plug,  Colder plug don't work as well when the engine is cold.  These resistor plugs are also non standard and may be contributing to the problem, particularly if the battery is weak or the electrical wiring is dropping a lot of volts getting to the coils.
Take the plugs out, at least, and see if the white insulator is now black.  The black stuff siphons off spark.

Do yourself a favor and get some NGK D7EA.

Also, you should verify that the choke plates are fully closing.  It's usually a knob/cable adjustment.

You didn't say if you have stock induction and exhaust, which matters.

I'd also check the battery voltage.  And you should state, if you are using electric start or kick start for the attempts.

Cheers,

[rklystron]

+1 on checking the battery voltage.

[man-bot]

The white insulators are indeed black - I have a set of DR7EA but the resistors won't help there as well!  Oddly when I popped them in last year the enigne had a knocking sound so I removed them- no sign of physical damage to the plug and they measure the same as the champion lengthwise so I don't know what the problem was there.

I'll double check the battery voltage but all checked out a week ago. 

As far as the set up I have the stock airbox and a 4-1 exhaust on (don't like it but my 1 of my originals is rotted out...)

I have tried both electric start and kick start - starter works just fine... other than the bike actually firing up.

I'll get some D7EAs pop them in and check the choke plates although they were moving freely when I just removed the carbs.

[TwoTired]

I'll get some D7EAs pop them in and check the choke plates although they were moving freely when I just removed the carbs.

Moving freely and closing completely are two different functions. 
Just saying.

Cheers,

[man-bot]

Okay - I put D7EA plugs in and I checked the choke cable and it theoretically should be closing the plates all the way (I did not remove air box).

If I hit it with a shot of starting fluid it will start up with the kick or starter button - but I can only keep it running if I open the throttle and keep it at around 5000 rpm (with choke all the way on). Below that it dies...

Thoughts?

I did check and the plugs are wet and smell of gas.

[TwoTired]

If I hit it with a shot of starting fluid it will start up with the kick or starter button - but I can only keep it running if I open the throttle and keep it at around 5000 rpm (with choke all the way on). Below that it dies...

Thoughts?

I did check and the plugs are wet and smell of gas.

Still follows the symptoms of pilot circuit blockage.  The application of choke forces fuel from the mains and throttle valve fuel circuit.  So, choke is probably working.

Do all 4 plugs show wet?

You sure you didn't put the floats in upside down?  This can make the fuel level too low for the pilot jet to pick up fuel.

When you checked the carb's pilot circuit, did you "prove" all four exits ?  Forcing fluid into any one of hem should get flo to all the others.
1 - Pilot Jet
2 - Pilot air jet.
3 - IMS hole
4 - and finally the exit hole into the carb throats.

I had a carb that varnished hole 4.  And was able to clear it by removing the IMS and squirting aerosol cleaner into that hole to flush it into the carb throat.  It only happened on one carb for me.  But with today's gas blends, I don't see why it couldn't occur on all of them.

Cheers,

[man-bot]

I only checked plugs 1 and 4 and they were wet.  The floats are in the correct way as I initially installed them upside down last year.  I'll double check my float level - it was much less than 14mm when I adjusted it... Maybe I set it too high.

I am mildy embarrassed in that I didnt check all 4 sections of the pilot circuit... I didn't know there was 4 to check!  I had been looking for a pictorial of some sort to show the path I should check but couldn't find one.  I sprayed carb cleaner through the jet and it came out of the tube on the air box side (for all 4).  Where is the IMS hole? I didn't see where it exits in to the carb throat - is it behind the cylinder that throttle moves up and down?

Thanks for the help... I really think this May be the problem - even though my hands dread taking the carbs off again!!

[TwoTired]

In front of the Carb bowl on the PD carbs is an Idle Mixture Screw (IMS)  Remove the screw and there is a hole for the screw (beware the spring, flat washer, and tiny o ring, they yield to the force of gravity at random intervals, particularly if you don't pay attention).  The tip of the screw extends to the exit hole in the carb throat.  If one bottoms the screw (gently) it will shut off all flow into the the carb throats.  If varnish or gum has built up at the exit hole or screw needle tip, it also shuts off fuel flow to the carb throat.
I have cleaned just this portion with carbs still on the bike.  Ain't exactly fun, but it was faster than removing carbs from the bike.  But, it's tough to tell if you've succeed until the bike runs and all the head pipes heat at idle.  With the IMS removed, you could shove a guitar string into the hole and all the way into the carb throat.  You may need to do this if the gum/varnish is too hardened.  I had to once.

Simple, eh? 

Cheers,

[Popwood]

Pay attention to TT, he knows of what he speaks.

With the carbs on and off, are you sure you have the carb boots on tight? No leaks? What about your air filter? How old? The paper filters ought to be replaced every couple years, otherwise air flow is restricted.

[Popwood]

Never mind this one, was a dupe of the previous. Argh, don't understand why I get these "time-out messages" when it's only a minute or two to write and hit the Post button.

[man-bot]

Ah! IMS - I didn't get the abbreviation.  I took a look at the spare set of carbs I have and can see where the exit in the carb throat is... Looks like tomorrow I'll be removing the IMS and seeing if I can feed a git string through each carb.

Thanks a ton for all your help - Fingers crossed i can get her to run tomorrow! 

[Grabcon]

It looks like the last post mentioned this, but the air filter typically over looked. My sons 78 550 would not start after similar things to what you explained. Changed the air filter and lo and behold it started and ran fine.

I also agree with the usage of Champion plugs. Don't use them.

[man-bot]

That is a good idea on the air filter... I'll call the local Honda shop and bring one in.

Here's hoping I can report back that it's running

[man-bot]

D'oh!  Can't get the filter through Honda anymore... What are you guys using these days - the uni filter?

[TwoTired]

D'oh!  Can't get the filter through Honda anymore... What are you guys using these days - the uni filter?

WHAT?  Really?  That's really bad news for the lean burn 78 on ethanol blended fuel.  The UNI NU-4055 will drop in, but it will make the carbs run the engine leaner/hotter.  If done along with an exhaust system change, I think a carb rejet, readjust is going to be needed.

Oh fun.

[man-bot]

I think there is an aftermarket one that is like the OEM filter you can get from David Silver Spares, and one from a company called MIW - but I can't seem to find anything local here in the Toronto area.

Took all of the IMS out and spayed carb cleaner in, then compressed air and stck a git string in... But no luck.  She won't even fire with starting fluid now (with air filter in and out, and choke in and out).  Needless to say I'm depressed... Looking like I'll have to pay someone to fix it.

[Lavis500]

If it's not starting with starting fluid, I'd imagine you have an even bigger problem.  I got curious with my 500 one day while I was in the middle of a carb rebuild.  I had never tried to start it, and the first thing I did when I got home (bought the bike online while I was out of country) was tear the carbs off and start cleaning because I knew it had been sitting with gas in the carbs for 5+ years.  I wanted to get SOME kind of baseline, so with the carb rack OFF the engine, I just sprayed some starting fluid into the open intake tracks and pushed the start button.  It fired, revved up and fell.  It was enough to tell me a handful of things:  1) All of my exhaust pipes warmed up.  2) I have spark to all cylinders.  3) All of my cylinders have some compression.  4) Timing is OK.  5) points are OK.  In retrospect, I'm not sure if it was the smartest idea, but it told me everything was OK.

Point of the story is that if you have compression and spark you should be getting ignition of starter fluid.

[man-bot]

Finished my pity party and decided to do this right rather than hand it off to someone else...

Pulled the carbs off yesterday (and actually managed to not completely tear up my hands... going on may be a different story!).  I'm going to:

• Pull the jets and make sure they are clean
• Spray carb cleaner - then compressed air through the 4 passages that TT told me about
• Pass a git string through each passage as far as possible as well
• Double check and reset float height if required
• Reinstall and cross my fingers...

Any words of advice or tips here - hoping 3rd time is a charm...

(FYI - carbs were off and apart, individually soaked in simple green last year... hoping all is still good there).

[rklystron]

Hope this works for you.. My fingers are crossed as well. Good luck!