Dyno - Firstimer

The mixture looks remarkably stable. Almost too good based on my dyno run experience.

I have seen a very simialar hp response when vibration caused fuel frothing at higher rpm. Expecially common when extended inlet tracts are fitted without good mountings. I recomend Mikuni fittings.

Place your hand on the carbs during a dyno run to check for harsh vibration and also look for signs of fuel frothing out the tickler.

The stable mixture does not fit this interpretation but its worth checking anyway. I guess you have checked for fuel feed rate already.

After that you will need to go for cam and ignition timing as mentioned by others. I doubt exhaust is doing this.

Hang on !

I just re read this.

exhaust is based on Norton tuning sheet, 1.5" I.D pipe 30" from head to meagaphone , 24" tapering up to 4" with a
3" dia reverse cone 1 5/16,

-- silencing is by a 3" dia absorption tube the length of the megaphone packed with
fibre glass packing --

What does this mean? Have you got a tube with glass fibre inside the megaphone ????

If this is so then throw it away - you dont have a megaphone you have a street muffler. The way to silence a megaphone is a big silencing can at the end - and I cant see that in your photo.

Seriously - I had a "megaphone" (Campbell systems??) like this on my 500 Dommie when I bought it. Looked very smart. The only issue was when I switched to a "standard megaphone" with no internal silencing hp instanly increased from 37 to 42 bhp rear wheel.

As Steve said " you are killing it with what you have inside the mega....get that out first "

Smart looking bike

If you're copying Peter Williams specs - exhaust etc. He used several different configurations. Note that he ran super long intakes - 12" from end of 32mm Amal to head. Maybe your longer ex specs are for that????

33's /

What FUEL . what Ign & Timing ?

Unless its built with a bit of clearance , Id think quite some miles required before the things freed up .

Silly TR750 on utube appears to be 90 Hp , not the 5.000.000 claimed at the time .

NORTON was a Engine Dyno - so figures are Shaft Hp . Still .

temperature stabilizeation if Fan Cooled and bedded in etc ??

Id think 240 - 270 . apparently millilitres per minute ( c.c.'s )

220 would be W H I T E if its useing any fuel .
To strong a retard Fed up the thing on long intakes , no idle below 1100 , dropped a cylinder .

What Plugs ??

Right , the clocks ticking, next week end is rapidly approaching and thanks to a dyno run I now realise I ve got a sick motorcycle!

Monday I'm going to ring NRP exhausts to get a quote! However they wont be able to sort anything this week so its down to me , with some help and guidance , please.

The internal baffle in the megaphones measures 1.1/2" dia and 13" long flared out to fit tightly in the megaphone , about 1/2 way down, at the reverse cone end the 1.1/2 " perforated tube flares out to the 3" dia reverse cone and the perforated pipe is wrapped in exhaust wrap.

The general consensus is that the exhaust is the likely culprit , so what can be done?

If I gut the megaphones of baffle tubes and wrap, re fit the reverse cone modified with a short 3/4" lip to accept a gibson end can borrowed of a 350 Honda. It will look shit but will it work?

any ideas gratefully received.

How loud is it with those reverse cone bits removed. ?

I had a street dommi with those, and the reverse cone bits killed the performance.
It was a bit loud without them though !

Would seem you need those big silencing can on the end of some EMPTY megaphones, ditch the fibreglass pads.
Watch that uncorking it may require some bigger jets...

We can't guarantee it's the exhaust, but if the cam times up properly and the ignition seems OK, it's the place to look.

johnm makes a good point about how the mixture looks too perfect. Maybe it's not to be trusted? Did it make more or less power when it was richer?

Can you simply remove the megaphone? If it's not welded on that's what I would do to see what happens on the dyno.

I remember chatting to a good tuner who took a customer's bike to the dyno and his method was to run the bike on the dyno with just the header pipes, no silencer/megaphone. He simply cut bits off the header until the power was where he wanted it and added a megaphone/silencer afterwards.

Something like this might suit the look of your bike, but never having used this particular type I can't say how well it works. I use the long megaphone Supertrapps and they work well.

Im prepared to richen mixture if I go with the empty pipes. will noise test them first before going forward.

when we did the first dyno run , the power was recorded at 51 BHP and the fuel ratio was showing 10.5 :1 rich.
changed the jets to 220, the power went up and the ratio improved approx 11.5 : 1 ,dropping to 200 ( no 210's) put the ratio at whats shown on the readout.

The Megaphone is welded on .

I can see dyno work becoming very addictive, and very expensive , a day off work, a 200mile round trip plus ther dyno time!!!!

PJ those bolt on silencers look ok , what make are they?

Moto55UK said:

PJ those bolt on silencers look ok , what make are they?

Click to expand...

Supertrapp.http://supertrapp.com/product_sections/cat.asp?CatID=35

The website say " The muffler does not include a core. The core must be purchased separately"

I've seen those used on things like Ducati singles at the races. Being Supertrapp they won't be cheap .

Where are you in the UK and which dyno do you use?

The guy who built my Norton is in Kent and would probably sort it out quite quickly.

Up the hill to the left , way up past the edge was the start . The r.h. kinks nothing , theres a 90 left ( mph ) further on .
uninhabited when the townies went home .ALWAYS slow down at the Villages though . UNLIKE the Townies . :x :roll: :x
HRD ( Halliday Racing Developments ) is at the top now . Their dyno tuned RS 3100 new motor lunched itself LEAN .
Explained the ' test strip ' , - Rover Tuning Proceedure ( check rich or lean on SU's with choke . As PER BOOK .
" No No , we do it on a Dyno These Days . "
:shock: :? :x :mrgreen: And the test strips at the door . 2am should do it . or 2 to 4 . With a observer and R/t .

ANYWAY : May be easiest to do SANS MEGAS for the moment . Straight Pipes . As the scavenge affect would be less predominant .
If they ( mega's ) worked / were ' in tune ' , and lengthed for circuit / RPMs .

Once shes loosed up and running free , and youve established the parameters - your set to try ' experiments ' .
L O N G circuits easiest to piddle about and crack throttle for comparative impressions . Though ENDURANCE
trim will make it legit for ' Road Testing ' . 8) :mrgreen:

jseng1 said:

If you're copying Peter Williams specs - exhaust etc. He used several different configurations. Note that he ran super long intakes - 12" from end of 32mm Amal to head. Maybe your longer ex specs are for that????

Click to expand...

When I spoke to Williams in '78 I had 28" headers, with inlets 10.5" from head on 36mm MkIIs, on an 850 with short stroke head, he said that was about right for the internal config I described to him.....

We are using different things today.

Concentrate on the mega first...but to race it you will need an add on silencer....

But so far we have not heard if the bike is a good ride, only what happens on the dyno...

pommie john said:

Where are you in the UK and which dyno do you use?

The guy who built my Norton is in Kent and would probably sort it out quite quickly.

Click to expand...

yes it would be interestng to know where the OP is, I am guessing North!

I am in Sussex and looking for a dyno for later this year...Kent would be OK for me....info please...

SteveA said:

pommie john said:

Where are you in the UK and which dyno do you use?

The guy who built my Norton is in Kent and would probably sort it out quite quickly.

Click to expand...

yes it would be interestng to know where the OP is, I am guessing North!

I am in Sussex and looking for a dyno for later this year...Kent would be OK for me....info please...

Click to expand...

Jim Cray in Faversham built my Norton. He doesn't have a dyno but uses a local guy ( I can't remember who).
Jim's a BMW specialist these days but had loads of experience with British bikes.

SteveA said:

pommie john said:

Where are you in the UK and which dyno do you use?

The guy who built my Norton is in Kent and would probably sort it out quite quickly.

Click to expand...

yes it would be interestng to know where the OP is, I am guessing North!

I am in Sussex and looking for a dyno for later this year...Kent would be OK for me....info please...

Click to expand...

More like North west ( 12 miles from Oulton Park).

Ripped the baffle tube and exhaust wrap out of the megaphones and fired it up , 114.5 db at 1m , boy it sounded good!
revved pretty freely as well /
looks like Ive got some fancy fabrication work to do to make the Gibson cans fit ! But the question is , will they knock 10 db off?

SteveA asked how the bike rides, not bad is all I can say , the bike is still in development and progress is steady
problems encounted so far :- Gearboxes (2), Belt drive (1), exhaust ring / fractured exhaust (1),

when it does keep going ,it feels like it has potential , but it felt like something wasnt right , thats why the Dyno session.

Rohan said:

Remind us again - what engine, what head and compression ratio, what carbs, what ignition, what exhaust and what exhaust length and baffling,
what gearbox and what gearing.

You may need to just raise the gearing a tad, so that the torque peak happens at a slightly taller geared top speed.
Depending on track, of course.

Lovely looking cycle, you win just on looks alone. !

Click to expand...

I agree with Rohan about the gearing. With the commando engine I found it to be very deceptive. My feeling is that within limits, it doesn't matter what gearing you are pulling, the motor revs up at the same rate due to the very heavy crankshaft. I don't believe it matters much what exhaust or inlet lengths you are using. The inlet port diameter is critical - too large can destroy the torque characteristic. However for everything else, the set-up will probably be right - somewhere in the rev range. It is probably simply a matter of changing the gearing to get the best application of power for the circuit you are riding on. With my bike, I dropped a tooth off the rear sprocket, and the bike accelerated faster and I've gone on from there. The problem then comes when first gear is too high for clutch starts.
I'm assuming that you've got the timing and mixture correct, to the recommended specification

acotrel said:

I agree with Rohan about the gearing. With the commando engine I found it to be very deceptive. My feeling is that within limits, it doesn't matter what gearing you are pulling, the motor revs up at the same rate due to the very heavy crankshaft.

Click to expand...

I don't entirely agree with this statement though !!
Its the TORQUE from the fire in the cylinder that makes it 'rev up', the flywheel weight is merely an intermediary...
The bike+riders weight+aero has some influence here too, of course. !

I would agree about the gearing again though - with a strong torque curve, and plenty of ponies on the dyno chart,
it does look like it could pull taller gearing readily enough - provided the circuit for this weeks race is long enough to be of some benefit.

Playing with mufflers, megaphones and exhaust lengths probably needs to be on the dyno,
not cutting and shutting before a race without knowing what it will do...

"Ripped the baffle tube and exhaust wrap out of the megaphones and fired it up , 114.5 db at 1m , boy it sounded good!
revved pretty freely as well /
looks like Ive got some fancy fabrication work to do to make the Gibson cans fit ! But the question is , will they knock 10 db off?"


I dont know the answer. Our rules are 95 db at 20 (or 30 m?) or basically what the local council inspector decided that day !!!!

I did knock off about 8 or 9 dB with the big silencing cans I put on the end of my megaphones with no lose of hp at all measured on the dyno. The secret is to have the exhaust exit into a big chamber.

Rohan, I've found with my motor it is possible to short shift without losing much in acceleration. On most up changes with the close box, there is virtually no lag. It is very deceptive. I would expect a lower overall gearing to give greater acceleration, that is what I've always found with other bikes. With the commando engine the effect is nowhere near as noticeable. As I've said, with the close box the revs seem to rise at much the same rate regardless of the overall gearing. What has previously stopped me running higher overall gearing, has been the ratio of the first gear - it was almost impossible to get a good clutch start in races. Might have been different in the old days when we push-started. I still haven't tried the 6 speed box, however I suspect I will still have to buy a lower first gear for it. Winton Raceway is only 3 Km around and gearing is a problem. I don't know how the bike could cope with Phillip Island or somewhere like Daytona. The latter might be a bit easier - there doesn't appear to be much low gear stuff.
There seems to be a silly choice - go top end and use sensible gearing. Or build on the strength of the motor and have the gearing problems.

Moto55UK said:

SteveA said:

pommie john said:

Where are you in the UK and which dyno do you use?

The guy who built my Norton is in Kent and would probably sort it out quite quickly.

Click to expand...

yes it would be interestng to know where the OP is, I am guessing North!

I am in Sussex and looking for a dyno for later this year...Kent would be OK for me....info please...

Click to expand...

More like North west ( 12 miles from Oulton Park).

Ripped the baffle tube and exhaust wrap out of the megaphones and fired it up , 114.5 db at 1m , boy it sounded good!
revved pretty freely as well /
looks like Ive got some fancy fabrication work to do to make the Gibson cans fit ! But the question is , will they knock 10 db off?

SteveA asked how the bike rides, not bad is all I can say , the bike is still in development and progress is steady
problems encounted so far :- Gearboxes (2), Belt drive (1), exhaust ring / fractured exhaust (1),

when it does keep going ,it feels like it has potential , but it felt like something wasnt right , thats why the Dyno session.

Click to expand...

Way back when noise regs started in the UK I silenced my bike and killed it a bit.....then went back to near the original set up with just a baffle...made about 112 or so, but rules were bizzarely '110 + or - 5' so 115.....

Most I ever saw recorded by a Norton was Lloyd Dickinson's long megas at 117.....same as Reads 500MV at the same track.....

Fractured exhaust suggests not enough rubber down the line...

Depends on your budget but NRP at Bilsthorpe Nottingham, will do you a custom stainless complete system to meet noise regs and power needs for £500. He has done work on the dyno with Dave Watson's Nortons. Probably increase your power output above the open system. Of course it won't look like a works space frame exhaust.

Nigel is a nice guy to deal with and a current racer himself. If you are happy with your downpipes he might make silencers only.