Topic: Open pipe muffler questions...

[whoismattclark]

I am trying to get this spare CB550 that I recently picked up running smoother.  I have a few posts running about this bike.

One current problem is the exhaust.  It has stock headers running to an open pipe.  The bike runs rough, and I was wondering how much you guys think the open pipe is attributing to this? 

I'm looking at options like welding a contemporary can from a sportbike onto the original headers, or trading pipes with another bike (the silver one) which has what I think is a vintage kerker 4-into-1 exhaust, or just buying a $50 slipon.

Any advice, and any thoughts on the ill effects of an open pipe without an adjusted carb?


thanks,
MDC

[cntrhub]

I wouldn't go to the pipes at this time. I would first square away (full tune-up) valve adjustments, compression check next, then timing, carb sync/adj., and then see if this cleaned up the drivability?
Then if the problem is still there, do your weld repair and check again? Long and short of it, is a jetting issue... if the tune is done first.

[mutters]

Mate,I can guarantee the lack of muffler and associated lack of back pressure will cause you no end of problems on a motor used for road .Some of our sports oriented people could tune your machine for dragstrip work with no muffler, but thats about the extent of any use I know of ,for this setup.
My suggstion is to go for a slip on job (there will probably still be some tuning involved )then youv'e got asolid startingf point
After that record every change and adjustment made, that will make life sooo much easier
best of luck matey. cheers  jeff

[Jim Shea]

So, who is Matt Clark?
The engine will run OK if the carbs are tuned to suit the exhaust, be it open or with a baffle, but you will have probs if you just leave the engine untuned and take all baffles out! How do you know the carbs are currently set up correctly?

[Lumbee]

...if you want to use the current exhaust u'll need to jet up.  Stock jetting should be 110.  So with open pipes u'll want to jet up...120's maybe.  If you don't want the hassle of carb tuning I'd got back to stock pipes and start there...

[whoismattclark]

I should have said that I have given the bike a full tuneup -- adjusted the valves, checked timing, adjusted cam chain tension.  Outside of a minor timing issue (see other post), everythings good, and I will be moving on to the carb.  Before the bike was even running I pulled the carbs and gave them a good cleaning, so I know they are tuned to stock.

Before I adjust the carb though, I need to decide on my type of exhaust system.  I don't like the open pipes, btw.  It's a PO thing, and it's way too loud for my tastes.  Sounds like I'm riding a lawn mower.  I'm so impatient I think I'll just pull off the exhaust from my silver bike. 

The main reason I was considering other options is because it took me so long to get those stock headers on the bike and the exhaust are brand new.  It's the princple really.  I should at least get a few miles of use out of those $16 gaskets and all that effort.  I'll give it a few days, and if I can't find a donor or cheap replacement silencer, I'll swap the pipes.  It is necessary to replace those copper gaskets each time the exhaust is removed, correct?  I've seen multiple posts on this, and I'd hate to risk an exhaust leak, and have to pull the whole system again (once was enough for me....and i thought pulling carbs with stock airbox were bad!).

thanks all,
MDC

[scondon]

     You can get "universal" slip-ons pretty cheap(as little as $30) and I would get one just to make your diagnostics/ressurection easier. Get the bike running well and THEN start monkeying with different exhaust/jetting.

     If all you did was remove the muffler/baffle without rejetting and possibly changing the needle clip positions(and this can be just the start) then your bike will run Loud, Hot, and Crappy.

[nteek754]

Hey there scon I run a 73 750 with a kerker on it with no baffle just the cone piece in the end NOW If I take the cone piece out wow sound really mean but big time power loss hence the lack of back presure yup good to have a decent tune up but cheap checking is to put something in there damn vacum cleaner pipe just to get some back presure to see if thats your problem then if yes well invest in something for a new muffler or  beer can whatever good luck Craig  seven fifty four ever

[scondon]

Hey there scon I run a 73 750 with a kerker on it with no baffle just the cone piece in the end NOW If I take the cone piece out wow sound really mean but big time power loss hence the lack of back presure yup good to have a decent tune up but cheap checking is to put something in there damn vacum cleaner pipe just to get some back presure to see if thats your problem then if yes well invest in something for a new muffler or beer can whatever good luck Craig seven fifty four ever

    Good point. The cone piece will provide some restriction so for some exhausts removing the baffle may not have as drastic an effect as having a "straight pipe".

[Terry in Australia]

It's an interesting question, my K1 is running standard (for Oz) jetting of 105 mains and #40 pilot, slide needle on middle position etc, but I've since fitted a set of straight out drag pipes and pod filters, with no ill-effect at all. Starts great, runs smooth, and pulls like a train! Cheers, Terry.

[scondon]

It's an interesting question, my K1 is running standard (for Oz) jetting of 105 mains and #40 pilot, slide needle on middle position etc, but I've since fitted a set of straight out drag pipes and pod filters, with no ill-effect at all. Starts great, runs smooth, and pulls like a train! Cheers, Terry.

       Must be that Aussie air When I've done that the bike runs OK thru the mid range and super lean at high rpms. The ticking sound when I shut off the motor is deafening.

Aside: Shouldn't you be working or something

[whoismattclark]

    Good point. The cone piece will provide some restriction so for some exhausts removing the baffle may not have as drastic an effect as having a "straight pipe".

I don't have a cone piece, I have a header then a straight pipe...just a $5 jobber from Autozone or some such (PO did this).  It's not even flush to the header pipe since it's larger and I'm guessing meant for automotive use.  Held in place with a single bolt, PO drilled thru the header, goes in one side comes out the other.

[Caferacernoc]

You definitely need something on the end of that header or it will never run right with the stock carb jetting. Universal slip-on of some sort should work good. I had pretty open pipes on my last 550 and I needed to up the main jet to a 120 to get it to run strong and clean with no hesitation at high rpms. And it still had a midrange stumble. You need a muffler on an otherwise stock bike.

[n9viw]

Ditto the restrictive exhaust- seems like you don't care for the PO's handiwork anyway, so get you a cheap slipon and go from there. Tuning, definitely. Start with the valve gaps, then points gaps, then static and dynamic timing. A lot of problems simply go away when ordinary maintenance is taken care of first.
If your carb jetting is stock, then you need intake and exhaust that's as close to stock as possible. (BTW Lumbee, the stock jetting for a 750 are 110 and 40, or 35 for some late models; the stock jetting for a 550 are 100 and 40, or 38 for late models.) Remember that almost any change done to the intake and exhaust may need some tweaking to run properly. I'm running pod filters and 4-2 turnouts with no baffles on my '76 550; when I first started with stock jets, it was like I was running on 2 cylinders. I jetted out to 120, then back down to 115, where it ran (and plug chopped) great. Not all mods will need jetting work, but drastic ones will.