Topic: 75 CB550 won't start

[TheOtherOne]

Here's my story:
I bought my 75 CB550... barely ran but engine started no problem. Battery was dead so seller was starting off a car... yikes. Carbs needed cleaning.

So:
1. I rebuilt carbs.... bike sounds like it wants to start... but doesn't... thought it might just be flooded... waited but still would not start. Feels like it wants to though
2. Pulled plugs.... looked fouled... replaced
3. Engine would still not start.... again, sounds like it wants to though, and now I get some backfiring
4. Spend awhile adjusting each of the four idle screws on the carbs but no luck
5.  Also, despite a new battery, it will not power up the bike, unless I hook it up to a small generator. Since the previous owner had been using a running car to start the bike for potential buyers (battery was completely dead), I think the rectifier and regulator might be fried.
6. I also thought the ignition coil was shot, but I am definitely getting spark

So these are some of the facts.... anyone have any thoughts on why this bike is now not starting and what I can do to get this engine to turn over? I thought I rebuilt carbs correctly, there were no complications.

Much respect!

[tonycb650]

are you testing the bike with carb intakes open? i heard that 550s don't like to run without the air box and filter hooked up and sealed compleatly.

[rshelbert]

Its hard to say why it will not run now.  Start up procedures can be a pain, the previous owner may have spent allot of time getting it running or sprayed some fluids into the carbs directly who knows.  I once had a guy sell me a bike and I asked him the start up method, he told me to pull it behind a truck around the block, at least he was honest with me.

Just to a once over with the basics, if the engine is sound it will run with the below adressed.



New plugs (looks like you already did that)

Make sure all 4 plugs are firing (make sure you check the fire across the gap, a fouled plug will make spark across the body and will ground out when screwed in)

Set static timing  to ensure its firing when its suposed to.  Note the condition of the points for burning, pitting or wear. 

Make sure you are getting gas to the carbs (open the overflow to each carb to make sure)  I have put carbs together wrong and the float would never even let gas in at all.

Check compression as well  (low compression bikes are a pain to get running)   If its low check valve adjustment as they may be to tight.

Check valves anyway if compression is good

If you are getting good fire, have compression, fuel and a good battery it will run regardless of the condition of the other electronics at least as long as the battery holds up  .  Try not to let the other stuff send you on a wild goose chase as to what is wrong.  They will have to be adressed in good time but not to just make it run. 

[TheOtherOne]

Thanks for the responses... I have noticed that at least one outer carb boot seems a bit cracked, I have not checked the inner ones yet... i have to say I have never thought too much about them before, but wondering if that might be a potential cause...

... anyone know if it could be?

Thanks

[TwoTired]

You could try disconnecting the rectifier for starting.  Reversing the jumper lead polarity can destroy these and the wires going to them.  I guess you don't have a meter to measure the voltage getting to the coils?

If you clean the carbs, then you are absolutely sure that the slow jets and, in fact, the entire slow mixture delivery system is spotlessly clean and functioning, right?

Do the choke butterflies close completely and have you interpreted the markings on the choke for correct operational position?


Cheers,

[fastbroshi]

Thanks for the responses... I have noticed that at least one outer carb boot seems a bit cracked, I have not checked the inner ones yet... i have to say I have never thought too much about them before, but wondering if that might be a potential cause...

   Those boots can be a prob, with everything else being a known good.  Last time I started mine, it was the second one of those post-rebuild, see-how-it-goes-around-the-block things, and it wouldn't start.  So I tightend up the rubbers, finding they had loosened a bit from the first ride.  Fired right up.

[martino1972]

you didnt install the floats up side down.

[bender01]

Recently learning about point gap I realized i was using too thick of a guage.. Poor math skills here. It gave that same response of wanting to go but not. I read a post @ doing it beside the road in the dark and gapping them with a piece of paper. Get it ready to start and loossen one of the sets of points a little to close the gap some and see if it starts to buble to life alittle more. Start on the left side as thats 1 and 2 cyl. Just a thought.