Topic: '75 CB550 - HELP NEEDED

[sniper1]

I have been chasing gremlins on '75 550. Here is the problem:

I recently rebuilt this bike, just finished (or so I thought...) two weeks ago. Bike ran good for about a week or so. Last weekend it started having issues.

It seems to run fine when cold. When it warms up a bit (after about 5-10 minutes of riding) it suddenly starts to bog down. It feels like its starving for fuel. It won't go over 4000 rpm or 40 mph. The tone of muffler is really low and "bassy." Sometimes it will surge forward like its getting gas again, but quickly bogs down again. Today, I checked valve clearance again (.05 intake, .08 exhaust) all good. Made sure cam chain adjustment done, good. rechecked timing and breaker point gap, all good. I only checked 1 and 4 spark plugs, they were a little black, nothing major, so a little rich, maybe. I didn't pull 2 or 3.

I did recently rebuild the carbs with all new inards: 100 mains, 38 slow, air mixture screw out 1 turn. Bench Synched them and then vaccum synched. It ran good for about a week after doing this. Now all this.

Bike has 12k miles on it. 4-1 MAC exhaust, stock airbox w/new filter, everything else stock.

WHAT COULD POSSIBLY BE THE PROBLEM??

Fuel?
Electrical?
Spark?
Air?

Soichiro's curse???

WTF??

[Mo]

hmm. Could be out of sync carbs. The fact that you have new jets installed hints at that. Have you tried to re-sync them?

[luap]

.05 an .08 isnt stock but I think hondaman recommend that. .02 an .03 is stock from book
Fuel? wheres your needle clip?"It feels like its starving for fuel" you set the floats correct 22mm
Electrical?have you tested battery?
Spark? pull the plugs an rest them on the head
Air?so a little rich", maybe- not enough air. you turn your air screw out more

[Frostyboy]

You could try releasing the cap on the gas tank, if it's not venting properly it will hold the fuel back due to low pressure in the tank. I say low pressure because vacuum seems too strong a word.
Of course don't forget that the nylon sock on the petcock might be gunked up after all these years with such low mileage as well.
Turn the petcock off, place a container below the outlet, turn the fuel on & see what sort of flow is there perhaps.

[mronegear]

sounds like a fuel problem to me.
How is the inside of your tank? clogged petcock or breating vent?
Do you run the bike with inline filters?
Does the bike rev over the 4000 when its not boggin down? If no its set up way to rich,
turn the air-mixture screws out more (max. 2 turns) Where is your neddle cliip position at?
nedds to be at 2nd grove from top at the f model and 4th groove from top at the k model.
Does it run on all 4 cylinders? check temp of the headers.
good luck!

[sniper1]

OK, I got around to pulling the plugs. Here are some pics. Its 1,2,3,4 from right to left in both pics.

One thing I did notice was that I only had the air mixture screw out on the carbs 3/4 turn. I was playing around with it and thought it seemed to run better like that than 1 1/2 turns out. Maybe I was wrong.

Could that have caused the rich mixture and bogging/surging issues?

Can I still use these plugs? or should I replace?

[luap]

Could clean those plugs ride it see where you at an when your good put new plugs in

[luap]

MRRON
nedds to be at 2nd grove from top at the f model and 4th groove from top at the k model
where did you get that info from?

[DJ_AX]

...
One thing I did notice was that I only had the air mixture screw out on the carbs 3/4 turn. I was playing around with it and thought it seemed to run better like that than 1 1/2 turns out. Maybe I was wrong.

Could that have caused the rich mixture and bogging/surging issues?
...

yes .... could have

[Killer Canary]

Did you determine which cylinder(s) isn't functioning? that would tell us a lot.

[LesterPiglet]

My plugs are like that after idling if not sootier. Clean them and reuse. I don't understand people throwing away perfectly usable plugs. I shouldn't think your engine will run properly with the air screws turned in that much. 1.5 turns give or take should be close.

[sniper1]

Did you determine which cylinder(s) isn't functioning? that would tell us a lot.

I haven't yet. I will clean these plugs, back out the air mixture screw again and see what happens.
I really don't want to have to pull the carbs and take them apart again if I don't have to.

[sniper1]

My plugs are like that after idling if not sootier. Clean them and reuse. I don't understand people throwing away perfectly usable plugs. I shouldn't think your engine will run properly with the air screws turned in that much. 1.5 turns give or take should be close.

Ok, thanks. I'll give it a shot.

[seanbarney41]

that pic with the plugs in your hand?...are they displayed in order l to r  cylinders 1, 2, 3, 4?,...if so, 1 and 4 look alright, 2 and 3 look bad...I'd be lookin' at your ignition system...

[sniper1]

that pic with the plugs in your hand?...are they displayed in order l to r  cylinders 1, 2, 3, 4?,...if so, 1 and 4 look alright, 2 and 3 look bad...I'd be lookin' at your ignition system...

Anything in particular? I did check timing and made sure it was correct. Points were gapped correctly and timing was right.

[seanbarney41]

Are you sure that all four cylinders are even firing?  I've seen when sparkplugs get that sooted up, the spark don't jump at the electrode, it will go somewhere else...so even if you got spark, it won't fire the cylinder.  I'd start by checking for 12 volts at the coil, maybe a dirty black/w white stripe connector for the 2/3 coil?  Check coil primary and secondary resistance, spark plug cap resistance?  Two Tired has excellent instructions for this in the FAQ.

[LesterPiglet]

If they weren't sparking they would be wet not sooty tho looking again I do see a bit of a shine off them.

[sniper1]

The plugs arent wet. They are just sooty.

[LesterPiglet]

In that case my four plugs are like your 2 and 3.

[mronegear]

MRRON
nedds to be at 2nd grove from top at the f model and 4th groove from top at the k model
where did you get that info from?

2nd from Top is stock for the Supersport and 4th from Top is stock for the k Models. My manual tells
me that and i'm pretty sure that is correct.

[sniper1]

OK, I installed new spark plugs and fired it up. It does not appear to be firing on cylinders #2 and #3. When it started it was running very rough, had a very low tone, and when I felt the header pipes, #1 and #4 were hot, but #2 and #3 were cold.

Any thoughts on where to start checking. I am now thinking electrical. The points are gapped correctly, and I used a static method to set/check ignition timing. That went good for both 1 & 4, and 2 & 3. Plugs are new and gapped correctly. Tappet valves good.

What else could it be??
- ignition coil?
- plug wires?
- condensor?
- points?
- anything else?

This phenomenon came on relatively slowly but now seems permanant. What would cause this?

ANY HELP IS GREATLY APPRECIATED!!

[luap]

pull 2 plug out an lay it on the head kick it over look for spark
check the blk/wht wire off coils make sure getting a soilid connection from power

[windwalker]

methanol is playing havoc with our motorcycles. if you have fuel filters remove them. the alcohol is dissolving the glues that hold them together or fuel tank liner gelling? good luck

[sniper1]

methanol is playing havoc with our motorcycles. if you have fuel filters remove them. the alcohol is dissolving the glues that hold them together or fuel tank liner gelling? good luck

The only fuel filter is the sleeve on the petcock. I agree, stupid ethanol. Politicians are not only screwing up the whole country,,,,,they're screwing up our bikes!!!!

[sniper1]

Is there any way of testing by putting #1 and #4 wires on #2 & #3 to see if they go. I think the timing would be off, but would it work just to see if they fire?