Author Topic: 75 CB550F Dies on Gas and Carb Weirdness  (Read 714 times)

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Offline BaconMafia

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75 CB550F Dies on Gas and Carb Weirdness
« on: September 22, 2019, 11:47:31 AM »
Hi everyone. This is my first post on this forum so if I messed anything up or something like this has been posted in the past, I apologize in advance. I promise I did some searching ;D.

Time for a long story.

I recently purchased a 1975 CB550F with 6000 miles on it with the intention of it being my first street bike. It is in great condition and looks like it was stored inside all its life. However, the previous owner stopped riding it and let it sit for a while. When I brought it home, I drained all the gas, put new ngk plugs in, changed the oil and got one cylinder firing. After that, I realized that I was being lazy and should have just taken the carbs off from the start so I did. When I opened the carbs up, I found the mains, which are size 100, were clogged so I unclogged them. The pilot jets seemed fine, size 38, but one of them was broken so I had to fish that out. Just for kicks, I installed the carbs back on the bike and cranked it over to see if anything would happen and it started right up on every cylinder but the one with the broken jet which is the left most cylinder. It would idle fine but once given gas, it would die. After that, I ordered 2 #38 pilot jets, 4 new #100 main jets since the old ones had o rings that were crumbling and looked on the forums for possible reasons to why it would die giving it throttle which yielded the carbs need cleaning again.

Once the package came, I cleaned the carbs with cleaner down every passage way and they look clean now. I installed the new jets only to find out that the PO had drilled out the pilot jets big enough to stick a .65mm drill bit straight though it. So, I bought 2 more #38 jets, put everything together, started it and fired right up with all headers getting warm although the left most cylinder was still a but colder than the others but not by much. I vacuum synced them all and had it idling smoothly at about 1200-1300 rpm. However, once I gave it more than I'd say a 1/4 to 1/3 turn, it would bog and sometimes just die. Today, I checked if the needle clips were in the right position on the outer two cylinders. I found them in the second notch from the top. The carbs are stamped 069a but, I found out today that the #2 cylinder's carb is marked 022a which cannot be right.

For more information, I am using the stock airbox (read that it is the best system unless you are seriously racing), had the cam chain adjusted, the COLD compression is 120 psi on all 4 cylinders and when you look down the spark plug holes, you see nothing but factory crosshatching, mixture screws 1-1/2 turns out and the valves are adjusted to 0.003 intake and 0.004 exhaust. The spark plugs on it are black but the only action it has seen is idling and blips up to about 4k.

Do any of you have any advice on why it is bogging down on throttle? I know these do not have an accelerator pump (is that what they are called?) so it will not immediately pick up on throttle but it should not just die. One thing I have not done yet is check the ignition timing but it does rev nicely when giving it light throttle inputs. I have also not checked the needle position in the inner two cylinders, which includes the 022a carb, as it is hard to reach with the carbs still on the bike but having one 022a carb still cannot be right but it should still rev right? Or is all of this normal and I am expecting too much out of this thing? Any advice would be awesome.

Sorry for the long post but I wanted to give as many details as possible. Also, this is not not street legal yet as the title is in the mail so no plug chopping yet.

Offline evinrude7

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Re: 75 CB550F Dies on Gas and Carb Weirdness
« Reply #1 on: September 22, 2019, 05:28:49 PM »
so you've ridden the bike and it will shift through the gears if you go super light on the throttle? 
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Offline seanbarney41

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Re: 75 CB550F Dies on Gas and Carb Weirdness
« Reply #2 on: September 22, 2019, 05:36:48 PM »
You need to get a service manual and do ALL the maintenance and tune-up, not just the carb stuff.  Done in the correct order, carb stuff is last.

Pretty sure 022a and 069a are the same carb body, just with slight jetting changes.  If one pipe is cool enough to not vaporize water instantly, that cylinder is not running right. 

Carb boots have to seal perfectly or you have problems.  Uncommon for this to be the case on a bike that sat for long.  Also there is an o-ring between the cylinder head and intake manifold that is often problematic.
If it works good, it looks good...

Offline BaconMafia

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Re: 75 CB550F Dies on Gas and Carb Weirdness
« Reply #3 on: September 22, 2019, 06:33:05 PM »
Thanks guys for the replies.

Currently, I have not ridden the bike on the street as I do not have plates for it yet so the only action it has seen is with it in neutral. That will change shortly however but it still shouldn't bog and die when applying more than 1/4 throttle in neutral right?

As for the carb boots, they are still soft and seem to seal well and I replaced those o-rings that seal the manifold as they were flattened. The bike also idled smoothly so hopefully there is no vacuum leak. I will look into the stuff listed in the service manual and see if it changes anything.

I also took a look at the 022a carb needle and saw that it was in its 4th position from top and it appears the needle is slightly different from the 069a carb. Is it problematic to run 022a and 069a carbs at the same time?

Thanks again for the responses.

Offline maxheadflow

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Re: 75 CB550F Dies on Gas and Carb Weirdness
« Reply #4 on: September 22, 2019, 08:40:13 PM »
Did you pull and clean the emulsion tubes?

Offline scottly

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Re: 75 CB550F Dies on Gas and Carb Weirdness
« Reply #5 on: September 22, 2019, 10:55:31 PM »
Either burn the black off the existing spark plugs with a propane torch or replace them with new plugs. If they were carbon fouled from before your recent work, they won't work properly, even if you have fixed the original problem.
Don't fix it if it ain't broke!
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Offline 1976cb750f836

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Re: 75 CB550F Dies on Gas and Carb Weirdness
« Reply #6 on: September 23, 2019, 08:31:04 AM »
Richer those needles 1 clip position down.
Is it better with choke on?
Restrict the aiebox flow some and c if that helps.
Sounds lean.

Offline BaconMafia

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Re: 75 CB550F Dies on Gas and Carb Weirdness
« Reply #7 on: September 23, 2019, 10:20:34 AM »
Thanks for the tips.

I went ahead and punched out the emulsion tubes and cleaned them. The holes were not clogged but there was some grit and crud at the base of them. I also burned the carbon off the plugs as well.

Have not started it yet but will post an update when I do. If that doesn't fix it, I will see about raising the needles.

Thanks again.

Offline BaconMafia

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Re: 75 CB550F Dies on Gas and Carb Weirdness
« Reply #8 on: September 24, 2019, 02:08:53 PM »
Alright...

So I got it running finally. I had to sort out some ignition problem with 1 and 4 not getting any spark with the fault being points not making contact anymore. They look old and worn too so that will go onto the shopping list.

Anyways, it was put onto the road and it seemed to pull strong so the little crud in the emulsion tubes was the issue it seemed. Now it seems to not like idling when it gets warm now so that is the next thing to tackle.

Thanks again for the info everyone.

Offline RAFster122s

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Re: 75 CB550F Dies on Gas and Carb Weirdness
« Reply #9 on: September 25, 2019, 01:43:08 AM »
TEC points, avoid Daichi Chinese points as they are nothing but trouble if you can get them adjusted...  Definitely do not even consider and Daichi condensers, numerous cases of dead out of the box or failing shortly after installation.
Entire points plate with points and condensers from Honda is good way to get the TEC brand.

David
David- back in the desert SW!