Motad too restrictive

[florence]

After riding my 500/4 for fifteen years with a motad I have fitted a different exhaust.  This move was prompted by the shocking price that Motads seem to be now and the lack of availability of down-tubes.  (Motad now only supply the whole system).

Anyway, I was shocked and stunned to discover that the machine has suddenly more low-down and mid-range power.  Overall the bike responds better.  I can only conclude that the Motad was suffocating the poor thing.  The 'new' system is an old Laser 4-1 which I think is from the early eighties and has been lying dormant in someones garage, the sort of thing we always used to fit and now I can remember why.

[matthewmosse]

The laser system is good on power but boy is it loud I've had louder but I found the noise from mine started to annoy me eventually so I welded up the motad. Best set up I had was a k&n filter that used the standard mixing chamber on the inlet side so it looked stock until you lifted the seat and a bsm exhaust (what silvers sell) The previous owner had found the silencer had rotted really quickly and had cut and shut a bsa rockett 3 raygun silencer on. Massively more power, fruity exhasust but loud. Could spin up the rear wheel on my outfit easily with that set up.

[florence]

That's cool, the laser isn't horribly loud but I thought if it gets too much I could chop off the end part and weld on a universal silencer, but I love the idea of the raygun silencer.  If I can find one I will add it to my pile of bits.

[Bryanj]

Motad was always built to be as quiet as standard so yes it is more restrictive than a Laser, but with VOSA getting all uppity with the MOT men you are supposed to be as quiet as standard now

[Spitfire]

Had the same problem with my F1, the downpipes were NOS but the silencer was a BSM one from DSS, far more restrictive than the standard one, and the effect on the plugs was bad.
The plugs sooted up all the time, running from 1 to 4 they went from nearly the right colour to black, a change of plug type helped but was not a 100% cure, 4 holes drilled in the silencer backplate was the answer. My MOT tester is happy with the sound and I am happy with how it goes.

Cheers

Den

[andy_c101]

I've got the opposite problem!
I've got four-into-four universal silencers (dunstall look-alikes) & she's running lean, & feels breatheless at 60mph.
I was thinking of trying to raise the jet needles in the Keihin carbs to richen the mix.
Anyone tried that? or is it case of neeing larger jets (currently size 90 main jets).

[SteveD CB500K0]

It depends on what throttle opening the lean running is exhibited.

3/4 to full throttle = mains

1/4 to 3/4 = needle

Easier to start with the needles as you don't have to buy any parts!


Note the above is a simplification (Two Tired would shoot me!) - more details here

[florence]

If running very lean, make sure you don't have any leaks between the carb and the engine.  I have had them suck air past the rubbers before and this make them run very lean.  I've got bigger main jets in mine, can't remeber what number but greater than 90.  For some reason 110 comes to mind but that could be erroneous.  Anyway, whatever it is, it was sluggish with the motad; now it pulls like a train.  I had considered changing the front sprocket down a tooth to lower the gearing.  Now no longer necessary.