Topic: CB550 bogs at high throttle & sometimes stalls

[bmcdonou]

Hi all.

I have read a few threads on this and got some ideas, but didn't find my answer and so thought I'd post to get advice.

I am a recent owner of a 75 CB550 in a 73 500 frame (stock air and 4into4 pipes). I have an issue that when I try to give it a lot of throttle it bogs down and will even die (in neutral and in gear). It idles and operates at lower throttles, but when trying to accelerate rapidly, it has issues.

I mainly drive around my city and not needed to accelerate like this before. It wasn't until recently I tried to open it up to see how it performed; to see if I'd feel comfortable taking on an express way. I also have noticed in general that its power is very flat at higher RPMs; It almost feels to me to be held back by something.

Some background on the bike and context of things I've gotten into (in case they are /I am the issue):
 1) High idle (above 2k, and would creep to ~2.5k). I kept playing with the screw; did not like below 1.5k
 -->To fix this, I did static timing. It was set a bit ahead (to the right) of the F mark and so I adjusted. I also cleaned the points and checked the spacing (which were fine - surprised as thought adjusting would be needed after timing). This resolved idle which is now ~800 cold and 1200 when warm.
 2) Wire #2 had melted and was repaired by prior owner.
--> I changed the coil w/ new wires, caps for 2&3, and plugs all around (plug for #1 was very black, others were okay but I changed). #2 and #3 seem to be operating fine now. I also changed oil as it smelled like gas (perhaps bc #2 was dead)
 3) I noticed when revving down (engine braking) there would be a clanking noise (not terrible but noticeable)
-->To fix this I adjust the cam-chain tension and I no longer hear the noise.

So far, given the flat performance / bogging:
 - #4 does not get as hot as the others (exhaust pipe) - initial thinking this was the culprit (#4 intermittent), but surprised it would cause that much bogging / stall.
--> I cut back the wire, changed the cap and plug. Confirmed it has spark. I've remove the cap during idle and doesn't change performance & still not as hot at other cylinders. I assume it is not the points or coil because that would equally impact #1?
-->I checked the timing again (static only, was fine) and that there wasn't a lot of arching (see very little/none).

I want to check off that it isn't electrical before moving to carbs. I live in a high-rise and removing and rebuilding them wont be easy for me as I don't have a great place to do that. Plan was to do that in the winter. So in following least path of resistance, any recommendations?

My thoughts:
1 - Replace #1&4 coil, points, and condenser --> I am not sure this is it bc #1 seems fine, but figure I can try.
2 - Inspect the advancing mechanism --> How would I tell if this is bad or not?
3 - Get a timing light and do timing at idle and advanced --> just trying to avoid extras tools as I don't have tons of space
4 - Issues w/ fuel? Admit that I have left the petcock open a few time to find gas drained / on the garage floor.
5 - Valv spacing?
6 - Carb sync?
7 - I think that is it...other than inspect / rebuild carbs?

[ekpent]

 They do run like crap on only 3 cylinders so given that the #4 pipe is colder then the rest I would start there with either its spark plug,cap or carb. A wet rag should have a good sizzle when touched to the exhaust head pipe if all is good. Easy to compare to others.

[jonda500]

easy stuff first - check for compression in #4 - turn over with a finger in the spark plug hole
John

[bmcdonou]

Did more troubleshooting. Switched the orientation of the coils and #4 still not as hot, and still bogging and stalling. Given that, not the coil, wires, caps, plugs, or points / condenser (for #4 issues, anyway)

Out of curiosity, I took the point plate off to check the advance. Not sure if I would know if something wrong, but it looked clean, springs still attached, still movable, etc. Put back together and thus had to redo the timing. I actually got it closer to the F mark (before it was ever so slightly ahead). Checked gaps (still no adjust needed). Fired up and #4 still only warm. However......wasnt bogging. Took for ride in garage (only first gear) and couldn't get it to bog. Same in neutral. I suspect, however, it will come back and I am not that lucky.

I also tightened the carb boots just to make aure not a vacume issue and checked the airbox for impediments. I also slightly bumped the idle screw to get above 1k. If when I ride and creeps up again, I'll bump it back down.

I will take it for a ride tomorrow, if not raining, and see how it does. I will also check the compression. I think this is fine bc admit that when checking the spark on #4, the bike actually started. So when I went to hit kill switch I let go of plug, it got close to hole and shot up....scared the crap out of me. But will check again jtb sure.

[HondaMan]

Low fuel level in the #4 carb bowl can cause this: so can leaking O-ring(s) around the mainjet(s). Most rebuild kits in the last 5 years for these carbs have O-rings that are too thin for the mainjets, letting them leak vacuum and fuel past the jets in an uncontrolled way. This usually causes trouble right around 1/4-1/3 throttle, with poor power above that. Even harder: if the carbs were rebuilt using Keyster needles and jets, it will act exactly as you describe, from the beginning after the rebuild. Sadly, I see quite a few carb sets this way (all of these Fours) from those parts. Hopefully yours still has the Honda Keihin parts?

Fuel flow question: how are the fuel hoses routed to the carbs? Since it is a tight fit to get them in the correct holes and turns, the hoses are often routed below the carbs and then back up. This causes the fuel to flow very slowly into the carbs, so when speeding up on the road, they just run out of fuel.

[Deltarider]

CB500/550s are sensitive to the right size fuellines. The correct dimensions are: for the CB500 and CB550Ks with oldstyle carbs: 18 and 30 cm length for the models with the bowltype petcock and 17 and 28 cm for models (including CB550F and CB550F1) that have the newer style petcock. Do not be tempted to have them even one cm longer. For the tube that supplies carbs 3+4, use the soft metal clamp in the middle front side as shown in the pic (horizontal is good enough). Ideal inside ⌀ is 5,5 mm. Outside ⌀ will be 9-11mm. Have this and the lines CAN'T even kink ever. Abstain from extra inline filters. Some have been lucky with them, but they can cause hazardous situations, sometimes even weeks later, seemingly out of the blue, when you have forgotten about them! Anything that passes the stock fuelcock filter, does not impede carburation, provided you drain the float bowls once a trimester.

[bmcdonou]

I took it for a ride and while it was better, I still had bogging with extreme throttle and flat power at higher rpms. If I throttle slowly it wouldnt bog at that throttle, but still flat. #4 was hotter with the longer ride, but not as hot as the others, and so I think is firing intermittently.

I thumb-checked the compression on #1 and #4 and they felt the same. Not exactly sure what to be looking for. But the suck and pop feel was the same. I did this with the ignition off and just turning it over, so let me know if
my procedure was wrong.

The fuel line for #3&4 comes up and around the back of #3 carb, then crosses to the front between #2 and the throttle cable, then in front of #2&1 and up into petcock. The fuel line for #1&2 goes behind and around #1 carb and then into petcock.

Also, given this bike had an engine swap before me, I dont know what version of carbs I have. They look different than the pic you provided.

[HondaMan]

With that fuel-line arrangement, #3-#4 will run lower float bowls than #1-#2. That could help explain the imbalance. It's much like Delta described above: the lines need to be as short as possible in this bike (and the Baby Fours) because the distance (hydrostatic head pressure) between the petcock and carb bowls is quite small. Also: are the little vent hoses that come from the bowl vent elbows in place, and exiting above and behind the intake plenum? These need to end in a high-pressure zone, like behind the air plenum or up under the seat where the air isn't moving around much at speed.

[bmcdonou]

Is the #3&4 fuel line supposed to run behind #123 carb and then around #1 into the petcock, vs the "s" snaking it does currently? I assumed the fuel lines work on gravity; didnt realize it had a vaccume aspect to it.

Btw, given all the talk on fuel lines, I guess I should say they were very hard to get off the first time i had to remove the tank. Kind of glued onto the petcock. Now come off much easier. They dont have any clamps incase that matters (air in the lines, less vaccume).

If I am correct in what you are referencing, the drain lines from the bowls are in place and they run back under the airbox and terminate in front of the real wheel. They are old, starting to crack, and need to be replaced. I didn't put much priority on them as I see people riding without them so just assumed they were to run any fuel away from the top casing and not performance related.

[bmcdonou]

Replying here to bring back to top of thread.

#4 still cold. Will look to reroute the fuel lines, but am I wrong to assume that this is likely not the issue given #3 seems to be working fine? Thought is if the fuel line was the issue, it would impact both #3 and #4.

Other than that, i think I've eliminated it being electrical. So i think next step is the carbs. Should I just pull them off and do a clean/rebuild? Is there a check I can do on #4 while attached to bike to see if I can avoid pulling off?

In terms of rebuild kits, given the feedback here about perhaps the issue being poor aftermarket jets, is there a specific brand I should buy / avoid? Was looking at the kits at common motor collective.

https://www.common-motor.com/Honda-CB500-CB550F-CB550K-Carburetor-Rebuild-Kit

[Erny]

Do you have photos of plugs?

You can relatively easy access carb 4 bowl (you just need short screwdriver) from right side w/o taking full rack off. Then you have access to main and slow jets, float and valve

[bmcdonou]

Do you have photos of plugs?

You can relatively easy access carb 4 bowl (you just need short screwdriver) from right side w/o taking full rack off. Then you have access to main and slow jets, float and valve

I dont. They were all replaced recently and #4, while it looked okay, didnt see evidence of it being too rich or lean, was replaced just to see if it was the issue.

[Scott S]

 Since mine happen to be off the bike right now, I can snap a pic. I find some long, hooked needle nose pliers are helpful for getting the hose on the nipple between the carbs. The fuel line runs under the balance tube and then through the holes in the main carb bank bracket.

[bmcdonou]

Since mine happen to be off the bike right now, I can snap a pic. I find some long, hooked needle nose pliers are helpful for getting the hose on the nipple between the carbs. The fuel line runs under the balance tube and then through the holes in the main carb bank bracket.

Extremely helpful. I also found that the manual on this site has a picture as well (whereas my hard copy does not). This makes sense now. I pulled my tank to see if I could reroute while on the bike, but no luck. So I think at this point I need to pull the carbs to reroute the lines, and while off I assume I should clean and rebuild as well.

Given the feedback on this thread and on others about shotty rebuild kits, any brands I should be buying / avoiding? I found a site, common motor collective, that operate in states (I am in Chicago) that sells a kit and claims that all their parts are tested by them before carrying. The are $25 per carb kit (so $100 for all 4).

Also, while I was at it last night, I did the value clearance, but have a question. Per the manual, I set the shaft to T14, and set the spacing for those that were loose then rotated 360 degrees and did the others (the X's and O's per the manual). However, I also watched some videos before doing it and noticed some were only doing cyl 1&4 for the T14 mark (e.g. cyl 1 then 360 degrees then 4, or vice versa), then doing the same for 2&3 but on the T23 mark. I decided to follow the manual...was this correct?

Thanks all for the help.

[Maraakate]

In regards to the valve spacing, either way is fine.  The X and O method is a "flat rate" way of doing it so you don't have to rotate the crank around 4 times.