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seattle##gs

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I have been working on a 71 trying to get the carbs running right at idle. everything is in excellent condition.

New top end.
JC did the full package to the head.
New premiers
Dual throttle cables
Digi-synch vacuum gauge
I know lots of tricks to get things running right. However, it has been fighting me for a long time in the idle dept. Anything off idle is very good. The problem is a constant rising and falling of the idle, rough running, and NOTHING solves the problem. Today I noticed the brown-blue wire had fallen off the zener diode so I made up a new one. This SEEMS...PERHAPS...MAYBE...to have solved the problem. however, I can't make the connection between poor idling and no voltage regulation. The battery is an AGM and reads about 13.40 volts, high for these batteries but maybe reasonable considering unregulated voltage. So perhaps the Boyer was driven too hard? As the idle was rising and falling I could almost count the seconds between the highs and lows. Any ideas on this? Explanation please
 
Check your cable runs are good.

You do have to carefully clean the premier's from new and check all the Jets needles etc are the same and at the same setting. You should have a 19 idle Jet. My premier's came with different mainjet sizes and needle clip heights
 
Last edited:
Mine was running very badly with all new parts like you, it was down to the wrong pilot jets supplied with the premier carbs.it is an 850 and as above should have had 19 size pilot jets, with 3 rings on the jet.
 
I just got same, ordered for 19 got 17. You have to check for the three rings on the end of the removable idle jet.
Blow out all passages check with the tiny drill 78. Passages in the body as well. Two tiny ones on the engine side of the
slide.
Might as well check the slide as well.
As for the voltage thing I will tell you I see as high as 15.3 and that is using the replacement rectifier regulator Goffy supplies. But then I see similar with the stock system. Worrying so I always run with the lamp on. If you have a LED headlamp that wont help much!
 
What ignition are you using, if it has idle stabilisation you will struggle to tune using the pilot mixture screws as when the revs drop the curve will reraise the revs giving confusing signals. That is why I have reverted to colortune for pilot mixture setting, once the mixture is set then you can use the throttle stops and vacuum gauge to balance the slides and set the idle speed. I then go back and redo the colortune but its rarely out.
 
A couple of notes from my side:

  • I would definitely be going for the #19 pilot jets - it made a huge difference over the #17s that they shipped with.

  • You should strip them down and blow everything through with the airline - I have found swarf in brand new Premiers.

  • Set it up by ear first - with the balance tube connected between the inlet manifolds - this seems to make it idle smoother.

  • Check the fuel height inside the bowls with everything installed, not the float height with the float bowl off the bike.
    The stay-up floats are more buoyant and sit higher than the old style floats.
    With the float bowl assembled, I have sometimes found the top of the float to be sat against the carb body, but the float needle not seated fully.
    Andover has a cute little tool to aid fuel height measurement: https://andover-norton.co.uk/en/shop-details/20569/fuel-level-checking-kit-amal-mk1

  • Have you left the choke slides in place or removed them? If removed, did you block the redundant hole up in the mixing chamber top?

  • Do you get the same issue with the petrol tank lid open? Just make sure it's not being caused by lack of fuel flow due to vacuum in the tank.

There are a couple of things that spring to mind.
 
It has the standard Boyer that everyone has.
I installed the #19 pilots to begin with
I am using the white floats and brass needles. The aluminum needles have caused problems in the past.
I have adjusted the fuel height using the andover fuel checking kit
I have removed the chokes and plugged the hole in the carb top
The other night I carefully sanded both sides of the manifolds and the carb to insure flatness. I used a sandwich of gasket-phenolic-gasket with Yamabond between the motor and manifold. Then used a paper gasket between the manifold and the carb, omitting the o-ring. Everything is air tight and no leaks.
I did not blow out the carbs so that is the next thing to do.

The right side exhaust consistently feels weaker than the left no matter what I do. One thing I can do is remove the Amals and install my own single Mikuni that I know is running well. That way I can say if it is carb or something else. You wouldn't believe the amount of time I have in solving this problem.
 
I've usually found it hard to get a consistent idle with a newly rebuilt engine. My theroy is they run hotter especially if let to set and idle after good ride (like in adjusting the idle) or restarting after say a fuel stop. I'd say be a bit patient with it until you have about a thousand miles or so on it.
 
gtiller said:
A couple of notes from my side:



  • Check the fuel height inside the bowls with everything installed, not the float height with the float bowl off the bike.
    The stay-up floats are more buoyant and sit higher than the old style floats.
    With the float bowl assembled, I have sometimes found the top of the float to be sat against the carb body, but the float needle not seated fully.
    Andover has a cute little tool to aid fuel height measurement: https://andover-norton.co.uk/en/shop-details/20569/fuel-level-checking-kit-amal-mk1
Click to expand...
I have those permanently connected to my Amals. I pull the pipes over the back of the carbs, and then put a connector in. There are 4 benefits,
1) Check the float levels any time.
2) Visible debris sump
3) Drain the carbs VERY easily
4) When tickling you can see the fuel level rising and let go before you get smelly fingers etc.

As with most fuel pipe they harden so it's best to replace them annually.

Cheers,

cliffa.
 
Years ago when I first built my 850 I fitted a Boyer. The bike would not idle reliably what ever I did & I tried everything over the next few years apart from the ignition. Then someone on this forum mentioned that he had experienced the same problem & cured it by fitting a Trispark. I fitted one & it was like owning a new bike. This may or may not be your problem but it's worth trying another make of ignition or refitting the points.

Martyn.
 
cliffa said:
I have those permanently connected to my Amals. I pull the pipes over the back of the carbs, and then put a connector in. There are 4 benefits,
1) Check the float levels any time.
2) Visible debris sump
3) Drain the carbs VERY easily
4) When tickling you can see the fuel level rising and let go before you get smelly fingers etc.

As with most fuel pipe they harden so it's best to replace them annually.

Cheers,

cliffa.
Click to expand...
I put a crossover tube between them for a permanent installation, my main thought was that fuel levels would be matched. I disconnected it because I thought it might be causing the problem for some reason. Not so. It was a long shot.
I like the 1000 mile idea.
 
So I pulled off the premiers and installed a 34 single Mikuni. Most of the problems disappeared. It needs a lot of running at this point and more fine tuning.
 
Keep the Mik on whilst you get everything else sorted and the break-in done.

FWIW, I’m with Matchless, the Boyer would be a serious suspect in my book.

Whilst you’re running the Mik, give the Amal’s another strip, inspect, clean.

You might trying putting them in a large pan of water, bringing to the boil, and leaving to simmer for 5-10 minutes with a splash of washing up liquid in it. I’m not joking, in the absence of an ultra sonic cleaner, it’s a good way of agitating and removing trapped debris from inaccessible places.
 
I did that on my caliper, surprising what floated to the top.

I would remove the air screw and pilot jet and then tap the carb bodies on a clean piece of wood and see what drops out. I suspect that the swarf collects in the centre pilot mixing chamber. The piece in mine was cylindrical, so I could have been looking straight though it to the other side.

Let us compare notes...


Cheers,

cliffa.
 
I will give the premier a good cleanout.....it is new and unlike earlier models there is actually a chance of cleaning it out.
I will not rule out the Boyer as a potential problem though my experience is that the work or don't work. They are tough little units and last years.
 
Matchless said:
Years ago when I first built my 850 I fitted a Boyer. The bike would not idle reliably what ever I did & I tried everything over the next few years apart from the ignition. Then someone on this forum mentioned that he had experienced the same problem & cured it by fitting a Trispark. I fitted one & it was like owning a new bike. This may or may not be your problem but it's worth trying another make of ignition or refitting the points.

Martyn.
Click to expand...

This is also my experience with the old analog Boyer, but I am sure If I had fitted a later Boyer (Digital or Mk4) it would be also fine.

Regards Marcel
 
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