Topic: 78 CB550 still not running as good as it should

[5youngs]

I have posted a few questions and gotten quick and very helpful information on the questions and I had another question.

I have just replaced the rectifier with a new one from Oregon Cycle parts and have a voltage regular coming in from the same company.

Anyways, the bike does not pull like it should and it idles up and down. The #2 cyclinder does not get as hot as #1, #3, and #4. I can see that because when we (my son) polished the head pipes the were all back to their chrome luster and after running them for a bit #1, #3, and #4 all turned the straw color from the heat, but #2 stayed pretty much the chrome color.

The #2 cylinder is running, just not as good and the other 3 and I was wondering if anyone has any ideas. I have pulled the plug and it has good spark.

Did I not clean the carbs enough? As said before on a previous post I thought the carbs we all cleaned the same and both the main and low/pilot jets appear to be clear through the different information I had gotten from the site and subsequently the tests I performed seem to indicate everyting  was good on the carbs.

Any ideas?

Thanks, Mark

[mbrooks]

I don't have an answers for you however I have similar problem with a CB650.  Number 2 has spark, fuel in the bowl and all else seems normal.  The problem arose after I disassembled the carbs due to a leak in the small hose connecting two of the bodies. Interested in any answers you get or your input. (Spark appears normal, synchronizer is in line, fuel is in bowl and jet appears clean, needle is straight...scratching my head!)

[TwoTired]

okay ideas.

Have you sychronized the carbs with manometers?

All other carbs must be adjusted to match the slide opening and cylinder demand of that on #2.

The slow jets (pressed in) have tubes attached (buried in the carb cavity).  These have cross drilled holes in them to premix air and fuel before it is metered and delivered to the carb bore.  Did you pull the slow jets to clean these attached emulsion tubes?

The main jets have emulsion tubes, too.  Were these verified clear?

It would also be helpfull to know the color of the deposits on the spark plug center insulator.  You can compare yours to the pictures at:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

Has a compression check verified all cylinders are mechanically sound?

Have you verified your spark advancer?

Let us know what you find.

[5youngs]

TwoTired,

I have not sychronizied the carbs yet, hope to have someone look at it this Saturday with a manometer. When I did re-assemble the carbs I was quite sure they all were set the same and pulled the same.

I was able to pull the slow jets out on all 4 carbs and make sure they were cleaned and the cross holes were cleaned as well.

The main jets were cleaned and the cross holes were cleaned also.

I did not check the plugs yet.

Have not checked the compression yet.

Am not sure about the spark advancer. It looks like it just needs to be checked to make sure it is clean and tight. There does not appear to be any adjustment according to the manual. Perhaps I am wrong on this.

I did put a new voltage regular on it from Oregon Cycle Parts last night and it did make the charging more consistent at least by looking at the headlight while it revved up.

I also am thinking that the floats are not all set the same. If they were not close to each other on their tolerances would that be a problem?

Thanks, Mark

[MikeDeB]

It sounds as if you should go through a complete tune up to make sure everything is adjusted properly.

First, make sure all valve clearances are spot on and the cam chain tension is adjusted properly.

Next, set the points gap to .012".  I know, the book says .012 to .016 but the closer you get to .012 the easier it will be to statically time the engine.  Because it can be a little difficult to find the high spot for the opening of the points I pull the advancer mechanisim and after checking to make sure the weights aren't binding on their posts I measure the high spot of the points cam (with a digital caliper) and place a small cheater mark there with a permanent marker thus insuring consistancy in the points gap.  Also, make sure the points are in good condition; no peaks.  After the points gap is set then perform a static timing of the engine.

Make sure all plugs are in good condition and gapped properly and that all plug boots and HT leads are in good condition.

Now it's time to synch the carbs.  Check and verify that the floats are adjusted to the proper height.  This will affect the idle and overall running of the engine if they are not.  Make sure all clamps are snugged down to prevent any air leaks.  You can do a bench synch to get them close by using a small drill bit to set the slide height.  Adjust each one so the drill bit will just pass under the slide of each carb.  Once mounted on the bike, use a manometer to complete the synchronization.

Hope this helps.

[TwoTired]

Perhaps, this will help.  With a carb for each cylinder, you've got 4 engines interconnected with a common crankshaft.  It's going to run the best and smoothest when each of those engines behaves just like the others.

I have not sychronizied the carbs yet, hope to have someone look at it this Saturday with a manometer. When I did re-assemble the carbs I was quite sure they all were set the same and pulled the same.

Mechanical alignment of the carbs is a great starting point.  However, you do you know that each cylinder is drawing the volume of air?   This is why a compression test is helpful.  Also, very small differences in slide openings are very significant during very low settings of throttle.

I did not check the plugs yet.

This is your window on what is happening  during the combustion process.  And, combustion residue can tell you if you are getting too much or too little fuel for the task.

Have not checked the compression yet.

You can never get carb adjustments to solve a mechanical cylinder deficiency.

Am not sure about the spark advancer. It looks like it just needs to be checked to make sure it is clean and tight. There does not appear to be any adjustment according to the manual. Perhaps I am wrong on this.

You simply need to check for operation with a stroboscopic timing light, to verify advance with increased RPM.  Also, helps to verify that the static timing was done correctly.

I also am thinking that the floats are not all set the same. If they were not close to each other on their tolerances would that be a problem?

Theoreticaly yes.  But, I wouldn't think it would be as severe as your trouble description reads.  But, if they were off far enough...

Is it possible that the drilled passagways in the carb bodies may still have flow restrictions?  These route both fuel and air.  Just a thought.

Also, how confident are you that your freshly cleaned jets didn't get plugged with new contaminants?  The slows are only about .016 inch in diameter.  Chunky fuel won't fit through that.