WTB - Muffler for 600cc GB500

[sammcj]

Just bored out my GB500 to 600cc.

Current muffler is holding her back, won't pull at all over 5k.
I'm look for an affordable muffler that looks OK to put on her.

Between the $100 - $250~ mark

[avgas]

Correct me if you want - but if you want to increase hp/torque or "pull" as you have put it......er a big bore muffler wont do it (infact the standard pipe is your best bet).
Have you considered a slightly more mild cam or bigger carb? Pipes have always given me better low down pull in the rev range. Always some mid range increase - but virtually no top end pull (well between 5-6.5K).
A slightly mild cam seems to do wonders in this area.

[xwhatsit]

slightly mild cam seems to do wonders in this area.

By that do you mean... a little hotter cam? As in, more overlap and lift? I hear people talk about `mild cams' and that suggests to me the opposite.

You can buy a new EMGO short reverse-cone megaphone for not much more than $100. Then just gut it. One of their megaphone range comes with bugger-all baffling to begin with but I don't know which. Sometimes known as WFO instead of EMGO, all bike shops carry their stuff.

Funny that putting an open pipe onto my little single has given the same results as Avgas describes -- good midrange boost, but doesn't want to scream to redline any more. Short shifting is the way to move quickly now.

[AllanB]

Shorty Megaphone is 430 mm long - a fiber packed straight through, but there is an internal diffuser - these are loud! A anti social pipe!

'Dunstall' replicas - the wide mouth one is a long version of the above 660 mm - removable baffle so you can repack or 'adjust' to suit. I've run these and they were loud as well but the packing they come with is crap and a repack with a decent fiber wool (muffler specific) quiets them down. A rowdy unit that can be tamed.

The one with the greater reverse cone is the same length as the long one above but it has fixed internal steel baffles. A quieter pipe that is close to a early 1980's stock sound level. A nice pipe. unlikely to require any carb adjustments.


All 3 are available on order from bike shops or on Trademe - $100 - $110 each. They are all made in Taiwan but of pretty good quality - good weight metals, clean welds and the chrome proved robust.
They have a adjustable slider on the back for fitting.

OR

For a bit over $400 (I think) Cycleworks in Welly make a nice full system for the GB.

[sammcj]

Thanks for the help guys.

Keven from KG motorcycles here in CHCH has told me the current carb will be sufficient for this engine, he's told me the current exhaust seems to have quite a baffle going on inside it, he drilled it out to 16mm but can't get all the way through.

When it was a 500 it would REALLY rip into life around 5-7k now, it has nothing over 4.5 what-so-ever.

He has assured me this is the pipe - but after all the BS I went through with this rebuild (taken him weeks to try and fix the loss of power and the pop-and-stop on idle problem which is still not resolved) I'm starting to have my doubts, the problem is that I know very little about engines and everyone I know in the bike scene here in chch raves about KG - bar perhaps his lack of time-management.

[AllanB]

Budget Motorcycles in Wilsons Rd has the mufflers I mentioned on display in their shop.

[mark247]

By that do you mean... a little hotter cam? As in, more overlap and lift? I hear people talk about `mild cams' and that suggests to me the opposite.

From what i understand a mild cam is going the same way as a lumpy cam or hot cam or whatever, but not that "extreme." For example, my mate has a lumpy cam in his escort and the thing barely idles at all, goes like a cut cat, but it doesn't idle well. Where as if you have a slightly milder cam than that, you can get more top end power, but still idle fine. Someone correct me if I'm wrong. I'm sure my terminology is all wrong

[vifferman]

If I were you, I'd save some more coin and go to Motorcycle Exhaust Specialists (or whatever they call themselves now). They did a great job of my twin s/steel megaphones on my VF500 in '96 or whenever it was.

[AllanB]

He has assured me this is the pipe

He'll be able to order one of the $100 pipes mentioned, either Forbes & Davies or Darby stock them. It sounds like you have spent some coin with him so ask if he'll do it at cost, slap it on and let see if it revs - they should be a easy fit on the stock header as they come with reducers if desired (I'm vaguely sure the stock muffler is removable????).

If you do this go for one of the free flowing ones for your hot rod.

If this works, it confirms fairly cheaply that the stock pipe is just too restrictive for the engine mods and you can save for a custom pipe built if desired. You'll be able to sell the slip on on trademe later if you go custom build.

Actually if the stock muffler just unbolts - I'd remove it and go for a hoon - it will be illegally loud but if she revs then the engine is being choked .......... - just tie up the outlet end of the headers to a footpeg or similar with wire if it is only supported at the head to avoid any risk of breaking a exhaust stud.

BTW bloody nice looking bike.

[Bonez]

I can certainly vouch for the quality of the WFO mufflers shown. Had one on the CB550 and my mate has had a pair on his 500 Pantah for years. Give the insides a good spray fish oil before you fit them.

You've got an after market system by the looks. Should be easy enough to cut the muffler off and weld some tubing to fit the above mufflers. On a standard system you can make an adapter that steps down to take the WFO items using the from clamp and front part of the muffler that mounts on to the collector (something I'll do to Gerble) or cut the out edge of the collecter outlet, weld around the inner pipe to seal it and mount the muffler directly to the inner pipe. You may have to make a fitting for back muffler mount.

[sammcj]

Great! I've just emailed Forbes and Davies for a price.
I'm not sure they'll sell to me directly but it's worth a shot.
Getting a quote for the 17'' short cone.
Can't wait to get this bike going like she could be.

[sammcj]

OK just got a Dunstall replica!

http://www.trademe.co.nz/Browse/List...x?id=212134063