Topic: 74 CB550 muffler too restrictive? / which OHMS coils to install

[orange550]

I just bought a 74 CB550. Got it running decent. The previous owner installed a new muffler; pretty sure it's from a Harley sportster. He only put 200 miles on it with the new muffler. air filter is clean, fuel flow is fine, but the bike feels a bit sucky at higher speeds; like it needs more air flow. Wonder if the muffler could be too restrictive.

Also. The plug wires are a bit hinkey. I'm going to install new coils and wires. (I also plan to install electronic ignition in the near future)  Was looking at the "Real Deal Dyna Ignition" at Dime City. I wonder if I should install the 5.0 ohms or 3.0 ohms. Just pleasure riding. I hear the 3.0 might be too hard on the charging system. Oh, and I assume I should use the graphite plug wires if I'm installing the electronic ignition.

[dtmmil]

3.0 on the coils, and you can usually find complete dyna kits that come with the coils, wires, the dyna plate and all.

[Bodi]

I think you should use the 5 ohm coils. The "extra" spark from the 3 ohm coils is minimal, and the added electrical draw is considerable. The 550 alternator will manage the load (barely) but why add the extra load? With the brush rotor, I would still want to reduce electrical load to extend brush and rotor life.

[orange550]

Thanks for the responses.

Any thoughts on whether the muffler could be too restrictive?

Also, Bodi, I see you're in Toronto. Do you know of a great shop that sells parts for the old Honda's?

Thanks!

[Rgconner]

Check out HondaMan's ignition. I just put it on and it is a sweet setup!

He also sells resistor packs to let you use 3 ohm safely.

[TwoTired]

5 ohm coils if you do much city driving.  If all you do is highway driving or keep the engine above 3000 all the time, then the 3 ohm is tolerable.
But, know that idling WILL deplete the battery and the more load you place on it the faster it depletes.
Stock coils are 4.7 to 5 ohm, and they worked pretty well since 74, no?
Stock plug wires are metal core. The core last longer than most humans and are unlikely to be "hinky".  The jacket insulation, not so much.  If not cracked, they still wok fine.  There should be resistance in the ignition path.  Spark plug caps/boots had that resistance from the factory.  Graphite wires have built in resistance, break down with time and must be replaced frequently (compared to metal core.)  You'll have to decide where you want to put the resistance, in the wires, in the plug boots, or in the plugs.  Choose only one place.

Your muffler is probably too restrictive, particularly if it is quiet.  But, read the spark plug deposits for better info about how it has effected mixture.

A new air filter is required replacement every year if it is paper type.  I don't care how it looks.  The paper collapses in on itself, and it can never be cleaned thoroughly.
 
You could try a test without the filter element just to see what effect it has.

Anyway, addressing all performance issues begins with thoroughly completing the entire routine 3000 mile tune up checklist.

Cheers,

[Danno]

I agree with two tired on this he recently helped me realize that my condenser problem with my ignition was too little resistance in my ignition circuit leading to it eating condensers like candy and i agree the minor payback for a new coil pack versus the low charging of the 550 made me decide that the ability to replace my plug wires every year was not worth it and as long as your plug leads are not cracked and are still long enough to do the job why spend 200 dollars when you don't have too

[dave500]

I think you should use the 5 ohm coils. The "extra" spark from the 3 ohm coils is minimal, and the added electrical draw is considerable. The 550 alternator will manage the load (barely) but why add the extra load? With the brush rotor, I would still want to reduce electrical load to extend brush and rotor life.

these dont have brushes in the alternator.

[zackblack]

If your coils are still good and your wires are "mushy" on the inside (happens to the 'soft' insulation between the wire core and the outer shell) then just replace the wires (there are several posts here on how to do it) for about $4.00 (7mm metal core wire available from NAPA for about .50 a foot).

[orange550]

Thanks for the continued responses. I might try to splice the plug wires and save a myself a few bucks for now. I think the coils are fine.

On the exhaust, I wonder if there might be a back pressure measurement or is that making too fine a  point of it. I want to replace the muffler, but it would be nice to have a sense of what would be appropriate. I know I can put one on, and see how it's running, rich / lean...

I was thinking about the full 4 - 1 MAC exhaust for it, but I've read mixed results here. Some say it's way too loud. I don't might louder then stock, but I don't want it ridiculous. Further opinions on the MAC?

Thanks!

[Danno]

if you are going for lower back pressure a 4 into 2 system will be less restrictive than 4 into 1
and a 4 into 4 like stock can be even less restrictive but the stock silencers were actually quite restrictive
most 4 into 1 are less than stock but less than 4 into 2
the least restrictive but best sounding would be a 4 into 4 with custom silencers to be less restrictive
I run my own custom made 4 into 2 pipes that I can raise or lower the back pressure as I want they are pretty loose right now but a year ago they were set up restrictive the intake was restricted and the jets were stock to get 45 mpg
now it gets 38 highway 34 city but still better than the original 32

[dtmmil]

I have a 4-1 muffler here, do you know what brand your 4-1 is now? Do you have the OD of your collector, I could measure this one I have and see if it would fit, if you would be interested in going that route. PM me if your interested, I will try to look back at this post to though.

[orange550]

Hey dtmmil, I'd be interested. Will PM you.

On the coil wires: I ordered some NGK splice kits. I also found some generic 4 cylinder automotive plug wire kits. They have the plug cap mouled into the wire. I was thinking of using these... and adding the spark plug screw top since these auto plug caps are for the larger "posts". I would assume that these moulded in plug caps are resistance caps?

Thanks!

[zackblack]

I would assume that these moulded in plug caps are resistance caps?

Assume nothing! 

Your best bet, if you are going to use aftermarket wires, is to just buy bulk solid core wire.  Napa sells bulk 7mm solid core wire for under $0.50 a foot (I bought eight feet and left myself a bunch of room on each wire).

The molded plug caps on automotive wires are not resistance caps.  If you want to do it like you describe then you need resistance somewhere - you don't have it in the caps and/or wires so you'll have to buy resistance plugs.

[orange550]

I didn't realize that the moulded auto caps are not resistance... glad you mentioned that. I've already purchased a generic set, but they are plenty long. Guess I'll cut off the caps.

Thanks!

[zackblack]

You will find that if your wires are "squishy" that they will be all the way up the wire.

I would cancel the NKG  kit order (If you can) and buy some heat shrink tubing (large diameter to fit over the wires) and just cut the existing wires off leaving about 2", strip off about 1" of the existing wire, solder the new wire on then cover with a little electrical tap then - as a final layer - the heat shrink tubing.

Save yourself some coin.

The other alternative (which is a more permanent fix IMO) is to follow the advice in this thread:

http://forums.sohc4.net/index.php?topic=10429.msg98088#msg98088

I did it to my coils - it does work.

[orange550]

I was just thinking about soldering. Would be better. Maybe I'll dig into the link on the more permanent fix as well.

On the wires I picked up: They are copper core, but the box describes them as "Carbon impregnated core to suppress radio static". Would this mean the wires have some resistance? Enough that it might be ok to use the moulded ends? Or should I just use the hard plastic screw ons from the bike?

Thanks.

[TwoTired]

On the wires I picked up: They are copper core, but the box describes them as "Carbon impregnated core to suppress radio static".

Copper core does not equal solid or stranded core wire.  What you have is resistance wire rated in some number of ohms per foot of length.  Good quality wire will be labeled with it's rating.  Anyway, to attain the proper resistance, you have to have some minimum length.  Since autos have bigger engines that length is usually longer.  For a bike, that usually means less resistance.  The wires you have naturally break down and deteriorate with time and use.  Expect to replace them every 5 years while the bike gradually runs more poorly. 

Would this mean the wires have some resistance? Enough that it might be ok to use the moulded ends? Or should I just use the hard plastic screw ons from the bike?

Resistance core wires are NOT compatible with the screw in spikes of the stock plug boots.  If you have committed to use resistance wire, you are committed to the non resistive boots.  Oh, and forget about soldering resistance core wires, unless you enjoy exercises in frustration.

If your stock coil wire needs replacing or extension, use the NGK 8083 (J1) lead splicers, and 7mm stranded wire core leads with the stock hard boots.
http://www.oxygensensor.net/ngk_wires/8083.php

Yes you can put the peanut butter lid on the mayonnaise jar and vice versa.  It won't kill you.  But personally, I don't like mixing those contents.

Cheers,

[orange550]

Thanks for the info. I'd rather use the correct wire. Sorry to be a noob, but I've attached 2 pics from the wire that I purchased... I wonder if you can tell if it is actually the proper 7mm stranded wire core?

Thanks

[TwoTired]

Thanks for the info. I'd rather use the correct wire. Sorry to be a noob, but I've attached 2 pics from the wire that I purchased... I wonder if you can tell if it is actually the proper 7mm stranded wire core?

Thanks

Kinda looks like the right stuff.  You can use the splicers and stock plug boot with that, I think. 
However, is that white stuff inside really soft foam?  If so, maybe that won't work well with the splicers and stock plug boots.

[orange550]

Kinda looks like the right stuff.  You can use the splicers and stock plug boot with that, I think. 
However, is that white stuff inside really soft foam?  If so, maybe that won't work well with the splicers and stock plug boots.

The white stuff is rubber, so hopefully it'll all work out.

Thanks.

[zackblack]

Looks exactly like the wire I bought.