Dr. Blair on Dyno Hill- Place your bets!

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Reggie said:
It was when I had the Amal Concentric Mk2s fitted (which I never really got on with).

Dr. Blair on Dyno Hill- Place your bets!
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Beautiful bike
What was the issue with the MK2 carbs?
 
I had a Dunstall 2-1-2 system back in the day.. myrecollection is of an improved mid range but little or no difference on top end. Had massive issues with its build quality . Pea shooters do not seem to work with it. Threw the whole thing in the dustbin in the end ..
 
baz said:
Beautiful bike
What was the issue with the MK2 carbs?
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They seemed to be inconsistent with the choke. One day the engine would be chugging when cold and in traffic queues near my house, so I would turn the choke off and then it was spitting back until it warmed up, then another day it behaved much better. The final straw was when I was in The Netherlands and the newish needle clip dropped off dropping the needle into the needle jet.
Maybe it says more about me, but I found the Mk1s much better and now have FCRs which I really like. Apart from a wear issue earlier this year, I never need to touch them.
 
Brooking 850 said:
Reggie, what size are those Mk 2's, 32 mm or 34 mm?
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They were 34mm and fitted with a Steve Maney curved billet manifolds to my S. Maney stage 2 cylinder head.

I had to get a friend who was an engineer to trim the stub end of the manifolds slightly off square to very slightly splay the carbs and I also recall having to trim a bit off the carb castings.

Sorry to derail this thread a bit.
 
Reggie said:
They seemed to be inconsistent with the choke. One day the engine would be chugging when cold and in traffic queues near my house, so I would turn the choke off and then it was spitting back until it warmed up, then another day it behaved much better. The final straw was when I was in The Netherlands and the newish needle clip dropped off dropping the needle into the needle jet.
Maybe it says more about me, but I found the Mk1s much better and now have FCRs which I really like. Apart from a wear issue earlier this year, I never need to touch them.
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Did you have the choke cable conversion? Or the on off lever's?
I remember on my t140e it was choke on to start which meant revving to over 3000revs or nothing
You couldn't pull away with the choke off until the engine was fully warmed up (my neighbor's loved me)
When I converted to cable it transformed it
The only other issue I can remember was the slides galling up and getting really tight
 
I had a 2-1-2 system with Dunstall muffs. back in the 70's on a stock Mk 1 850.
A bit softer on the low end, smoothed out in the middle, pulled much harder on the top.
Bumped the mains to 270's.
The stock silencers killed the top end, needed the Dunstalls.
I predict 3-5 mph more.

The Dunstall muffs also pulled harder than the 850 Pea shooters with the stock crossover pipes.


Edited: What kind of muffs are you going to run?
 
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worntorn said:
I spent the afternoon getting the headers out of the collector pipe. One took maybe 30 minutes of struggling to come free, the other was still welded in with rust after 2 hours.
I finally cut the pipe on the bandsaw, peeled out the rusty inner part from the collector, then tig welded the cut off collector bit back on. The side which came out ok was only in the collector by about 3/4". The side that had to be cut was in a full 2" and rusted right in, so cutting was the only way.

When first applying pressure to the end of the header up at the exhaust port end, when trying to get things apart, the welded straight stub and flange came right off!
This was strange as the welds all look ok.
Turns out the weld was almost entirely situated on the curved header pipe. It was just laying there beside the stub with only a tiny bits of weld here and there connecting to the stub and even those bit were only fused a few thou in.
On looking at the stub after it came off, there was virtually no weld pentration into that piece. If this is way Dunstall welded, no wonder the welds broke.

Does not inspire confidence!

Glen
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The poor welds on the Blair exhaust I tried in ‘83 is the reason I went back to stock peashooter exhaust. My opinion of Dunstall equipment was permanently ruined from this experience.
 
illf8ed said:
The poor welds on the Blair exhaust I tried in ‘83 is the reason I went back to stock peashooter exhaust. My opinion of Dunstall equipment was permanently ruined from this experience.
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I agree
My system rotted out on the Y piece very quickly
The down pipes weren't too bad I actually still have them somewhere!
And strangely the dunstall silencers didn't rust
But from Y section backwards it just rusted out, I'm surprised there are any systems still about
 
I probably would have quit fooling around with it when the pipe welds gave out.

My bet is I doubt you'll get anything significant out of it up top without extensive experimentation.
 
MichaelB said:
I had a 2-1-2 system with Dunstall muffs. back in the 70's on a stock Mk 1 850.
A bit softer on the low end, smoothed out in the middle, pulled much harder on the top.
Bumped the mains to 270's.
The stock silencers killed the top end, needed the Dunstalls.
I predict 3-5 mph more.

The Dunstall muffs also pulled harder than the 850 Pea shooters with the stock crossover pipes.


Edited: What kind of muffs are you going to run?
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I'll start with the Dunstall look alikes that came with it. These are supposed to be louder and less restrictive than Dunstalls.

Glen
 
Schwany said:
I probably would have quit fooling around with it when the pipe welds gave out.

My bet is I doubt you'll get anything significant out of it up top without extensive experimentation.
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After reading about the performance benefits of this type of exhaust for years it's worth a bit of effort to do a Mythbusters on it.
If it performs well, I can clone it in 304ss with strong welds.

Glen
 
worntorn said:
I'll start with the Dunstall look alikes that came with it. These are supposed to be louder and less restrictive than Dunstalls.

Glen
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I've got them on a Trident and was very surprised at how well the bike pulls with them, they also seem to be well made , another first for Wassell.
 
trident sam said:
I've got them on a Trident and was very surprised at how well the bike pulls with them, they also seem to be well made , another first for Wassell.
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Really?
I have a set of these copies
I had them in storage for quite some time and when I went to use them they had a film of surface rust
I'll give them a try sometime
Cheers
 
worntorn said:
After reading about the performance benefits of this type of exhaust for years it's worth a bit of effort to do a Mythbusters on it.
If it performs well, I can clone it in 304ss with strong welds.

Glen
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Glad you are doing a test where you actually measure something (time or distance to accelerate to a speed) as opposed to the Butt dyno which, in my experience, is wrong more than it is right. I did a lot of track and dyno testing back in my engine building days and it was interesting to find how often a change where someone said, "You can feel the increased power," turned out to be reduced power!

"How can that be?

A couple of reasons: the first is the classic "louder is faster." Inevitably, any time a louder exhaust (or intake) system is installed, virtually EVERYBODY will comment how much more power is available. We once measured a 13HP REDUCTION in power with a "high performance" exhaust system compared to the OEM exhaust system yet the driver reported that the aftermarket "clearly had more power..." ;) The dyno (and the dragstrip) showed the opposite.

Another reason is another classic: the "hole" in the power curve caused by adding a larger carb or modified camshaft, or a modified exhaust without considering the rest of the system. There is now a flat spot in the power curve that wasn't there before and the engine seems to "come on the cam" at some RPM - usually upper mid-range. That "surge" in power is felt as a power increase but in reality, the engine is coming out of that hole in the power curve. When compared with the pre-modified performance, it is found that although top end power MAY be OK, low and midrange power has been reduced, resulting in poorer acceleration overall.
 
baz said:
Really?
I have a set of these copies
I had them in storage for quite some time and when I went to use them they had a film of surface rust
I'll give them a try sometime
Cheers
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Baz,
My OCD prevents me allowing rust (on the outside anyway) :)
 
MexicoMike said:
Glad you are doing a test where you actually measure something (time or distance to accelerate to a speed) as opposed to the Butt dyno which, in my experience, is wrong more than it is right. I did a lot of track and dyno testing back in my engine building days and it was interesting to find how often a change where someone said, "You can feel the increased power," turned out to be reduced power!

"How can that be?

A couple of reasons: the first is the classic "louder is faster." Inevitably, any time a louder exhaust (or intake) system is installed, virtually EVERYBODY will comment how much more power is available. We once measured a 13HP REDUCTION in power with a "high performance" exhaust system compared to the OEM exhaust system yet the driver reported that the aftermarket "clearly had more power..." ;) The dyno (and the dragstrip) showed the opposite.

Another reason is another classic: the "hole" in the power curve caused by adding a larger carb or modified camshaft, or a modified exhaust without considering the rest of the system. There is now a flat spot in the power curve that wasn't there before and the engine seems to "come on the cam" at some RPM - usually upper mid-range. That "surge" in power is felt as a power increase but in reality, the engine is coming out of that hole in the power curve. When compared with the pre-modified performance, it is found that although top end power MAY be OK, low and midrange power has been reduced, resulting in poorer acceleration overall.
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Both very good points.
More experienced people, wise to the noise aspect, can hopefully factor that out of the equation.
But I think the second point is far more difficult to detect on the arse Dyno, even if you’re aware of it and actively looking for it, it can still trick yer !
 
Schwany said:
Could you elaborate on the FCR wear issue just a little?
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The rods on the link arm with the little wheels (that lift the slide) came loose on the left hand carb. That part was £80, so not cheap.
 
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