Topic: Got it running -What's next? CB550K1

[quidger]

Got the 1975 CB550 barn dweller running. Removed and cleaned the carburetors, new spark plugs, new points & condensers. I statically timed it & bench synced the carbs. It fired up and ran fair.
Some back firing but only from #4. Pulled the plugs to check them and they had a fair amount of black carbon after only 10 to 15 minutes running.
Should I next attempt check the valve clearance (never done this before and I'm a little apprehensive as I read one thread on the forum that said "DON'T TRY THIS WITHOUT SOMEONE EXPERIENCED TO HOLD YOUR HAND BECAUSE IF YOU'VE NEVER DONE IT BEFORE YOU COULD REALLY SCREW UP YOUR ENGINE") or sync the carburetors or check the compression.
I know all of these things need to be done, but I need to know in what order should I proceed.
Amazing how much I've learned in 6 weeks on the forum. I still have a long way to go but it's fun learning. Thanks for all the advice and input. Please keep it coming.
Here is a pic of the old CB. Should have taken a pic the day I hauled it home. Believe it or not it looks great compared to what it did 6 weeks ago. 5 years in a barn is hell.

[Aaron Richard]

If you have a service manual, you should be all set. Just read everything carefully before you proceed on the particular project, take your time, Double check your work and you will be fine.

[TwoTired]

Got the 1975 CB550 barn dweller running. Removed and cleaned the carburetors, new spark plugs, new points & condensers. I statically timed it & bench synced the carbs. It fired up and ran fair.
Some back firing but only from #4. Pulled the plugs to check them and they had a fair amount of black carbon after only 10 to 15 minutes running.

Better look into carb #4 again.  Probably something to do with float levels or bad orings.  You do have all the spring clips that retain the main jets with good orings in place, right?

Should I next attempt check the valve clearance (never done this before and I'm a little apprehensive as I read one thread on the forum that said "DON'T TRY THIS WITHOUT SOMEONE EXPERIENCED TO HOLD YOUR HAND BECAUSE IF YOU'VE NEVER DONE IT BEFORE YOU COULD REALLY SCREW UP YOUR ENGINE") or sync the carburetors or check the compression.

I don't think you are done with the carbs yet.  But, a preliminary compression check won't hurt, just to know the cylinders are relatively equal and he valves are closing.  Until you run it a hundred miles or so, the compression check is just advisory, anyway.  The rings will have to re-seat and any rust on the cylinder walls could effect the compression test.

Usually the valves are adjusted before a compression check is recorded for posterity.  They certainly have to be adjusted before a Carb sync, unless you don't mind doing the carb sync twice.

5 years in a barn is hell.

Was it some functional malady that caused it to find neglect in a barn?  Might have to address that, if you haven't already.

Cheers,

[quidger]

I think TT may be right with the float on #4 having an issue. When I put the carburetors back on the bike after I cleaned them, the float bowl on #4 started running gas out of the overflow. I tapped the bowl with the end of a screwdriver and it quit.
I'll take the carbs off again tomorrow and re-work them a bit.
I bought two bikes from the rancher out of his barn. Both were CB550's. One was the 1975 with 35,000 miles on it that hadn't been started for 5 years. The other was a 1978  with 9000 miles that was his daily (as daily as you can get in Nebraska) rider. The '75 had not been ridden for years because it did not have a title and he bought the '78 that was titled and let the '75 sit. He told me that the'75 actually ran better that he '78 but after he bought the newer bike he forgot about the '75. He basically threw in the '75 as a parts bike when I bought the '78. I did some detective work and found out that the owner of the bike had committed suicide 17 years ago. I tracked down his next of kin through obituary records and contacted him. He had the title changed into his name and sold the title to me for $100. So if I kinda got a twofer. When we were walking through the barn I saw what looked to be a '60ish S90 Honda without a tank on it. I had just restored a 1968 S90 the winter before and I said to the guy,"Is that a Super 90?"I wanted it as a parts bike, so he threw that in as part of the deal also. So it was actually a three-fer.
Long story, but no, the seller did not indicate to me that here were any major issues or problems with the bike. That's why I'm on the forum - so you guys with experience can help me through the mechanical issues.....and so far everyone has been way helpful.
I'll post after carbs come off of the 1975 again tomorrow and see how she runs then.
,

[quidger]

Took the carbs off again today, blew carb cleaner through all orifices, polished the little brass rods that hold the floats, and put 'em back on the bike.
Did not notice anything that looked to be a problem.
Started easy but still occasional backfire from #4. At higher revs (4000-5000 rpm's) sounded good but backfired a few times when throttle released.
Could it be that the backfire is a timing issue or is backfiring always related to fuel system?
I don't having a timing light so I' ll buy one within the next week or so to try to get it running smoother.
The bike is also missing the mufflers on #1 and #4. Could that have a relationship to the backfiring and could that also affect the timing?
Thanks.

[TwoTired]

The bike is also missing the mufflers on #1 and #4. Could that have a relationship to the backfiring and could that also affect the timing?

Yes.  And No.

[quidger]

Why could the 2 missing mufflers possibly cause the backfire?

Is backfiring always related to the fuel system or can the timing be off enough to cause the backfires? I have only statically timed the engine so there is probably much room for error, I'm sure.

#1 still seems to be the culprit as far as backfiring , but when the engine gets hot and i rev to 4000 - 5000 rpm there seems to be more of a rough running in general.

Should the o-rings on the main jets be very snug and require some twisting and effort to remove. The jets came out fiarly easily without much resistance and the o-rings looked okay to my eye but I am wondering if they could be worn enough that they could be an issue and the cause of the back firing.

Any thoughs would be helpful. Thanks.

[fmctm1sw]

The bike is also missing the mufflers on #1 and #4. Could that have a relationship to the backfiring and could that also affect the timing?
Thanks.

What I would say is that without mufflers, you are changing the breathing characteristics of the engine (for those two cylinders).  Guys that go with pods and open exhaust normally go up in jet sizes to compensate.  In my experience, I get a popping sound from my bike when the mixture is too lean.  I've also gotten backfiring because of timing issues (and nearly a broken ankle when I kicked it over)...

[TwoTired]

Mufflers have backpressure to gas flow.  If you want all the cylinders to work in concert, they must be presented with the same gas flow conditions.  Back pressure effects how the cylinder scavenges during the exhaust stroke, and thus, the mixture present for the subsequent firing stroke, and how much of it is burned and how hot the exhaust gasses are.  (assumes your backfire is in the exhaust).

If you have a 4 horse team and two of them are lame, would you expect the team to travel smoothly?

Anyway, you haven't said where the backfire is occurring, the intake or the exhaust?

O rings for the main jet should fit tightly.  I usually have to use grease or silicone lube to wedge them into the recess in the towers.

Try to dig your thumbnail into the rubber, it should be soft.  If it isn't, they aren't any good.

[quidger]

I guess that I'm not sure how to tell if the backfire is occurring on the intake or exhaust stroke.
Please let me know what I should look for to determine which is which.
What is the significance of a backfire on the intake versus the exhaust?
I did not feel the o-rings when I had the carburetors disassembled yesterday. Wish I had done that. If I would have known what exactly to look for I guess I wouldn't be on the forum.
Thanks for the advice. Determined to get the old bike running correctly.

[TwoTired]

I guess that I'm not sure how to tell if the backfire is occurring on the intake or exhaust stroke.

How do you know it is backfiring at all?
Backfire in exhaust is an explosion in the exhaust system.
Backfire in the intake tract is an explosion in the induction system.
At this point, I think we need a better description from you as to what you think a backfire is and how you can tell your bike is doing so?

There is just no way to diagnose/speculate a "backfire" cause without knowing where it is.  There are quite a lot of possible causes for each.  Are you asking for a treatise on them all?