Topic: Exhaust Pressures Feel Different

[DaveBarbier]

Hi guys, I'm starting to ride around my '78 CB550K since the weather is getting nicer up in CT. This is the first time I've really ridden it around since I bought the bike back in October. I noticed that the puffs of exhaust out the tail pipes are not even in pressure. I have a 4-4 stock chrome exhaust system on it. Two of them are weaker than the others. I'm guessing something is wrong. What could it be?

[fendersrule]

Not an expert, but carb syncing would be your #1 thing to look at. Even timing could probably change the pressure.

other than that? Probably not much.

[Deltarider]

Start with the timing, then check the timing and once you're at it check the timing just to be sure.
You'll be amazed how many motors can made run perfectly without doing a sync. Serious.

[DaveBarbier]

Start with the timing, then check the timing and once you're at it check the timing just to be sure.
You'll be amazed how many motors can made run perfectly without doing a sync. Serious.

Haha, timing, got it. Before I started it up I adjusted tappet clearance, cam chain adjuster screw, point gap and timing. I did the timing statically with a test light. I didn't use a strobe light. I'll double and triple check the timing but is the strobe light much more accurate than the static timing with a test light or is the static method just fine?

Thanks

[fendersrule]

People can argue about static vs strobe timing for a CB750 for pages.

Personally, I feel the CB750 responds best to strobe. Even with using a strobe there's a couple methods to do....either strobe it at Idle, or strobe it at advance.

A dwell meter is a great idea regardless on the CB750.

[DaveBarbier]

People can argue about static vs strobe timing for a CB750 for pages.

Personally, I feel the CB750 responds best to strobe. Even with using a strobe there's a couple methods to do....either strobe it at Idle, or strobe it at advance.

A dwell meter is a great idea regardless on the CB750.

I have a CB550, is that specific to the 750, or can that be applied to the 550 as well?


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1978 Honda CB550K

[DaveBarbier]

Now, there are also some other things going on too. After riding it for about 20 minutes the other day the header pipes on the 4-4 are turning a gold color...evenly on all of them. I just pulled the spark plugs and this is what I see. In descending order left to right (cylinders 4-3-2-1). Any way this can be related? I put the plugs back in and noticed that the weak ones were 3 and 4. 1 and 2 had good pressure.




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1978 Honda CB550K

[ekpent]

2nd one looks prettyy good, third one looks lean and the outer two rich. Are the carbs nice and clean ? How long has the bike sat since you bought it and started its new life. May take some miles to get good even compression back in all cylinders if it has sat for a long time if the ringare not permanently stuck.

[DaveBarbier]

2nd one looks prettyy good, third one looks lean and the outer two rich. Are the carbs nice and clean ? How long has the bike sat since you bought it and started its new life. May take some miles to get good even compression back in all cylinders if it has sat for a long time if the ringare not permanently stuck.

I'm not really sure how long it sat. Based on what the PO told me I'd guess about a year or so. I didn't even think about the rings and that after riding and heating up it might seal better.

I don't know what state the carbs are in. The bike itself is pretty dang clean (even the gas tank), but I did find out that he was riding it without an air filter.

Do you think it would be best to rebuild the carbs first before trying to sync them? It seems a little daunting at the moment.


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1978 Honda CB550K

[ekpent]

Do not let it get too daunting. I like that word it sounds nice. The good thing is that it is running. You have not givin' a lot of background info on the machine or what you have done to it yet. I am just looking at your plugs but there are some very informative people on your model that will chime in I am sure if you keep it alive with more information and pictures which are worth a thousand words    

[Dave Voss]

Do you think it would be best to rebuild the carbs first before trying to sync them? It seems a little daunting at the moment.

Given that you've only had this motorcycle a short time, and that it sat for a while, I would recommend taking the carbs off and at minimum give them a thorough cleaning, renewing seals, jets, etc. as necessary.  Most of what you'll want to clean is accessible after removing he float bowls, many times the slides are not very dirty and can be left in place.  At worst, you'll spend some time to ensure that they are alright, but at best you may find and fix issues along the way.  Pay special attention to making sure that the internal passages and jets are clear so that fuel flow to each cylinder is not different due to the internal condition of the carbs.

But before that, I would ensure that the valve clearances and ignition timing are correct.  Then clean the carbs and put some miles on it, followed by a carb synch.  Sometimes running it a bit helps restore compression, intake flow, etc. all of which will affect the carb synch enough that you'll want to repeat it later on.  If you find that the carbs are holding their synch for periods of time, then you'll know that the engine's running condition has stabilized.

[DaveBarbier]

Thanks for the replies guys. On my to do list is to verify the tappet gap and timing...with a timing light this time. I just ordered new points and condensers off eBay for piece of mind. I want to be sure I'm getting a proper spark before diving into the carbs. Then I will definitely take them off and clean them up. Can I spray carb cleaner in there or do I have to watch out for rubber parts?

Ekpent - I haven't done too much yet. I've just been replacing parts that need it, such as tires, brake lines pads/shoes. As well as cafe modifications. Eventually I'll put together a build thread where I can pose questions more efficiently.

You guys rock.


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1978 Honda CB550K

[ekpent]

You are doing well. The carbs of course are very important in the running of your engine. If it is pretty much a stocker do not spend the dollars on new brass pieces/rebuild kits when and if you go to clean them. Stock Honda stuff is better I believe unless tuning is needed. There are places to buy just some certain gaskets for the float bowl etc if you need them. Good luck on it.
   Do not do too much at one time though while you are tuning. Do the carbs first, see how it works. Then do the points etc after but if you do it all at once you may by stymied if a problem arises 

[DaveBarbier]

Do not do too much at one time though while you are tuning. Do the carbs first, see how it works. Then do the points etc after but if you do it all at once you may by stymied if a problem arises 

Ah, right. Limit variables. Smart.


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1978 Honda CB550K

[Duanob]

Looks like your number 2 (3rd one over from the right) isn't firing at all. The easiest way to check for spark is pull the plug, put it back in the plug boot and hold it against the engine with a pair of pliers or something so you don't get shocked. Crank the engine with the kill switch on and in bike neutral. If you don't see a spark or have a weak spark, try clipping a 1/4" off the end of the wire. Careful not to go too much ar you may have problems reaching the plug. The boots should unscrew from the wire. Numbers 1 and 4 or pretty rich.

[DaveBarbier]

Looks like your number 2 (3rd one over from the right) isn't firing at all. The easiest way to check for spark is pull the plug, put it back in the plug boot and hold it against the engine with a pair of pliers or something so you don't get shocked. Crank the engine with the kill switch on and in bike neutral. If you don't see a spark or have a weak spark, try clipping a 1/4" off the end of the wire. Careful not to go too much ar you may have problems reaching the plug. The boots should unscrew from the wire. Numbers 1 and 4 or pretty rich.

When I started the bike for the first time I checked each header to see if it was hot. I burned my index finger then my middle finger then my ring finger and finally my thumb. All four were hot was my conclusion, haha. So it is apparently firing, unless it's getting heated through the other cylinders firing, but it all felt the same to my fingers.

Thanks for the insight though. I hear it might be good to cut off a smidge of the wires anyway to make sure it's a good hot spark. What do you think?


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1978 Honda CB550K

[Duanob]

Looks like your number 2 (3rd one over from the right) isn't firing at all. The easiest way to check for spark is pull the plug, put it back in the plug boot and hold it against the engine with a pair of pliers or something so you don't get shocked. Crank the engine with the kill switch on and in bike neutral. If you don't see a spark or have a weak spark, try clipping a 1/4" off the end of the wire. Careful not to go too much ar you may have problems reaching the plug. The boots should unscrew from the wire. Numbers 1 and 4 or pretty rich.

Thanks for the insight though. I hear it might be good to cut off a smidge of the wires anyway to make sure it's a good hot spark. What do you think?


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1978 Honda CB550K

The plugs don't lie you have a different story for each cylinder. Cutting the wires ends a bit never hurts.

[DaveBarbier]

Looks like your number 2 (3rd one over from the right) isn't firing at all. The easiest way to check for spark is pull the plug, put it back in the plug boot and hold it against the engine with a pair of pliers or something so you don't get shocked. Crank the engine with the kill switch on and in bike neutral. If you don't see a spark or have a weak spark, try clipping a 1/4" off the end of the wire. Careful not to go too much ar you may have problems reaching the plug. The boots should unscrew from the wire. Numbers 1 and 4 or pretty rich.

Thanks for the insight though. I hear it might be good to cut off a smidge of the wires anyway to make sure it's a good hot spark. What do you think?


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1978 Honda CB550K

The plugs don't lie you have a different story for each cylinder. Cutting the wires ends a bit never hurts.

I cut the wires about 1/4". I haven't checked the plugs since then though. I'll do that soon. I also verified that the cam chain adjuster screw was adjusted properly and the valve tappets were also. I actually had to adjust 5 or so of the tappets because they were off. Not sure if I just didn't do them right the first time or they loosened up... The ones that were off all had a larger gap, not smaller.

The muffler back pressure is still not even but I have new points and condensers coming tomorrow that I'll put in and time with a timing light. We'll see what happens after that. There has been a loud ticking noise coming from the top of the motor also. I'm starting to think, since my adjustments are good now, that it's a small exhaust leak. I'm using old (probably original) exhaust gaskets. And I have new ones coming in a few days. That also might account for the uneven pressures at the muffler.


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1978 Honda CB550K

[calj737]

Dave - next time you want to test header temps, a little spit or water dripped works wonders... Saves on the Band-Aids too.

[DaveBarbier]

Dave - next time you want to test header temps, a little spit or water dripped works wonders... Saves on the Band-Aids too.

Haha, thanks. I was trying to make a gauge. First degree burn=running rich, third degree burn=running lean, second degree burn=perfect!


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1978 Honda CB550K

[calj737]

If that's true, then use your feet, the skins tougher there and you'll get more accurate measurements. Or test earlier before they get scalding hot.

Hopefully you didn't get too badly scorched- having a bit of fun at your expense, forgive the levity!