Amal MK1 spray tube replacement

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p400

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What is the well known procedure for replacing a 900 series Amal spray tube?
Special tools? heat?



928SprayTube1.jpg
 
I am wanting to match two Amal .
Spray tube might need two drifts, one to remove and a second to install.
And the install might require more finesse than the pound out.
 
The sides are serrated, a flat topped one is not an issue as regardless of the serration orientation it will still be flat topped, the stepped ones will want to follow the serration grooves left by the previous spray tube can be slightly twisted off centre unless guided. I put a small smear of sealant on the serrated OD.
 
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As I understand it, the stepped spray tubes were developed as a fix for a batch of 850s that shipped with muted silencers. With straight thru exhaust they offer no advantage. I've used both on my 850 and noticed no differences.
 
As I understand it, the stepped spray tubes were developed as a fix for a batch of 850s that shipped with muted silencers.

Not exactly. All standard 850 carbs had the 928/107 stepped spray tubes and 928/104 needles, not "a batch".

Mutes were supplied with the bikes so they could be fitted in order to comply with local noise regulations if necessary.
 
I thought I saw a post here that said the development of the stepped tube was attributed to a California acceleration test with muted mufflers. Perhaps I'm mistaken. Maybe it was the crossover exhaust?

All I can say is that I've had the flat top 4 stroke type on my Amals for 40 years with no issues at all.
 
I thought I saw a post here that said the development of the stepped tube was attributed to a California acceleration test with muted mufflers.

Yes, but that's mufflers when fitted with mutes which were supplied separately as previously stated.
Item 18
 
Then what made the 850 unique such that it needed the stepped tubes?
 
Then what made the 850 unique such that it needed the stepped tubes?

If you read what is being said, it isn't the bike that changed as much as it is the testing requirements that changed! The bike was tweeked to pass tests earlier bikes were not subjected to!

Around this time it was not just noise testing that changed!
 
BTW, the 850 Norton spray tube is just like the ones in my Mikunis!
 
Tapped the old spray tube out, it was a 850 notched.
Tapped a new 622/074 back in with a special shaped end drift.

Noticing the spray tube 622/074 has changed from a square upper end (as shown in the large photo above) to a slightly beveled end .
Maybe to improve performance?


928SprayTube074.jpg
 
Then what made the 850 unique such that it needed the stepped tubes?
stepped jet/tube AND needle
Did you ever hear of a /any factory 850 withOUT balance pipes? Mutes probably pushed the lean tune over the edge...
Did you ever see a stock norton factory 750 WITH balance pipes?
Richer 750 jetting will always run OK.
IIRC No emission or noise test was performed on 750, only 1/4 mile times... :cool:
 
Get your 850 up to about 50MPH, then whack open the throttle.

With standard tubes, it will tend to bog or hesitate.

With stepped tubes, it will accelerate smartly.

"Or so the story goes"

ALL of the 850s I have owned, restored, and/or built, had the stepped tubes.
NONE of them stumbled or hesitated.
 
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