Too Lean?

Fitted a Trispark ignition and re tuned the engine & Carby's. After a couple of runs the engine now dies when you crack the throttle from idle.
Engine idles beautifully.
Is there a simple single explanation for this, like too lean a mixture? Carbys are pretty new amals.

need mo info. Fast throttle snap or just normal throttle to ease off from a start? Float level too low? New zinc oxide crap in the like new pilot jets? Maybe the Tri-spark idle stabilization curve resisting off idle rev up? Plugs can do this sort of thing too. Air leaks like a loose float bowl or manifold have done this to me while otherwise responded just fine rolling.

Try running in the idle pilot screw until it gets a bit lumpy at idle (rich). Reset idle stop and see if that helps. That's if no air leaks, balanced and the usual clean jets stuff.

Dave
69S

Try using a bit of choke as a test, if pick-up is then good it points to weak mixture.

Dave.

I would think that a fresh ignition, particularly a TriSpark, might require ground zero status as far as tuning is concerned. Validate everything. Valve clearance, carb jetting, timing of course! Do some plug chops. Make sure it's all good to get the most of what you have.

Thanks for the replies.
Does someone have a photograph of the correct fuel level in the float bowl as seen in a sight tube .
What I am doing is running a plastic clear tube from the float bowl drain plug up the side of the carby . This way I can see exactly the fuel level in the bowl.
I need a reference photo of this set up from a nicely running engine to compare with my levels.
It seems to me that as the carbys are at an angle my levels could be low. ( my ticklers dont seem to be effective on the new carbs.)

If your ticklers aren't working, I'd say you've got the floats too low. Happened to me. I set up my new stay up floats to the Amal spec and I got no tickling and starting. I put the float levels back to the original height and now everything is fine. I'll see if I can find the measurement.

I'm pretty sure I used 0.08" below the top of the float bowl. That's not the fuel level, that's how low below the top of the float bowl front of the float is.

While you're there you may want to check to make sure your petcocks aren't leaking and the needle valves too.



Dave
69S

Float levels must be set to the manufacturer's spec. The hardest part of carburation to get right is the jetting at three quarters throttle. Try lifting the needles one notch, and your motor should run up cleanly. When you ride the bike around a twisty road, it should be leaned off until it coughs in corners by dropping the needles, then lift the needles one notch. I use methanol in my motor, and I've made my own needle jets. I also use Mikuni 6dp needles which are pretty lean all the way down. If you are using petrol, you are pretty much obliged to use factory made needle jets, and needles. The main jet setting should be as per the Norton manual, but give the bike some hard runs on a cold morning to check your plug colours.

Here's what I mean about the sight tube allowing a visible height of the fuel in the fuel bowl.
Clear plastic tube is tempararily attached to the AMAL fuel bowl drain plug hole. Photo's show fuel level with bike on the centre stand.
Is this a correct optimum fuel level for a Norton used for everyday riding?

Go to the Old Britts website and find the link for tuning Amal carbs. It's got some pretty good information. It calls out a float height from the top of the float to be .06" to .09" I think and that would make the .08" mentioned by Dog T to be right in the middle. It also calls out the fuel level in the float bowl to be .170" (rich) to .240" (lean) and from your pictures it looks your fuel level is well outside of that range on the lean side.

Tha amount of times i have questioned this fuel hight on Norton "Leaning carbs" to get the fuel level correct in the needle jet...well its over the gasket hight at the front and 1/4 inch low at the back, the picture here shows the fuel level..BUT not in the centre..Where it should be. Plus its way out of spec!
DogT's picture shows the float bowls level on his rig...once fitted to the bike LEANING they will be way low. Trust me i have pissed about with these for months on a 650ss that wouldnt run right. In the end i made new manifolds that where "flat" so the carbs didnot lean, BUT did'nt make that much differance :?:
Setting the level to the bowl rim is fine,providing the carb is fixed flat, but when the carbs are inclined..where is the level supposed to be set?

I've just had a look at the AMAL website. As you suggest they give this information for fuel height .( set up ,I presume to be on the bench with a level float bowl). :arrow:

'The correct fuel level for all Mark 1 Concentric carburetters is 0.21” plus or minus 0.040” below the top edge of the float bowl. Thus when the needle valve is being held shut by the tangs of the float, the level of the fuel will be between 0.17” to 0.24” (4.33mm to 6.35mm) from the top of the bowl.

The fuel level can be checked by removing the float chamber and observing fuel running into it. The fuel flow should be sufficient to hold the needle valve open until closed by the action of the float. Insufficient fuel flow will cause the needle valve to seal under its own weight before the float rises far enough to press the valve shut. The level of the fuel can then be measured down from the top surface of the float chamber.'

Thanks for all your posts

As I remember, I followed the NEW Amal site recommendations and I'm pretty sure I got results like you are showing in your pictures. Way too low, and I couldn't even tickle the carbs. Then I went back and set it up like the old carb instructions, by measuring the top of the float from the top of the bowl at .08" and then everything came together and has been working fine since.

Looking at the fuel level in your pics, I'd say you'd be lucky if you can get any tickle action and it looks way to low to me. But I actually don't know where the fuel level is supposed to be. If I were you, I'd try the .08" float to bowl top and see what happens if you're not having any luck with the current instructions.

Dave
69S

Did this a few weeks ago when I put in the new stay-up floats. I scribed a line on the inside of the float bowl .21" down from the top edge and used something simiar to the DogT method. The top of the floats ended up about even with the top of the float bowl when the gas was at the right height.

It seems to work fine. Now I get instant squirting when tickling. Before I had to wait maybe 15 seconds. This is on the Amal carbs

I have read most AMAL tuning tip's, Setting the fuel hight with plastic floats to the "Correct" hight is just impossible! How do we bend the plastic needle fork on the float?
Plus when the fuel level is measured FLAT it drops a mile when the carb is tilted! I found a differance of a 1/4 inch vairation when the carb is fitted.
All this Bull SH#t regarding fuel hight on a Norton engine is a total waste of time :!: deleving into setting for norton ,the web site i was reading just said "Norton requires a differant approach" but did not say what...If you have a tilted carb ...FORGET TRYING THE GET A MANUFACTURES FUEL HIGHT...its impossible...

..FORGET TRYING THE GET A MANUFACTURES FUEL HIGHT...its impossible...john robert bould

Click to expand...

Amend to the seasoned wisdom expressed. Thankgoodness Norton Amals are not very sensitive to the float canted fuel level once sufficient to start and run - the pilot screw can compensate almost perfectly. But I've had a decade stored 850 that would barely start, bogged to stall with throttle and then not settle down idle nor respond to pilot screws till I nail bopped the needle seat level into range the pilot screw did become effective then did it again a couple more times going by best idle pilot screwing direction till about 1.5 turns out and the '74 become normal operator for its city life again. Also been able to fudge float level to mostly compensate for clapped out slide/bores lean-ness too. Age old dilemma - do ya follow instructions to the Tee for just good enough or get down and dirty by pure feel and ear - then measure to have numbers to type? Some times the optimal float level bumps into ticklers so add them to correct or lower fuel level and pilot turns out to compensate. Then if still not quite right suspect the plugs have fouling issues after the period of poor mixture combustion,... ugh. thank goodness for amercian V8 economy packs.

Then there's the tidbit of information at the bottom of JBA's float page.

"ADDENDA: May 2010 - The Norton ATLAS/DOMI engine with the carbs tilted forward, require a different setting. From what I have found is original spec noted as 3/32" ABOVE the float bowl (~94 thou). However in measuring several carbs, there is not enough clearence for 94 thou, it measures closer to 75 thou. In any case you can measure the recess in your carb and thickness of gasket and calculate a theoretical maximum float height - leaving at least 10 thou clearance."

http://www.jba.bc.ca/Bushmans%20Carb%20 ... tml#5FLOAT

I haven't tried that, but since things are running fine, I doubt that I will.

Dave
69S

I dont think Amal made any alterations to the carb fuel hight for the Commando "tilting carb engine" ..Reason being when new carbs are ordered from Allens ,well they dont send out special's ,or ask ..nor is the carb box marked "COMMANDO ONLY"
Or if floats or bowl's are ordered ..they are all the same. which is wrong?
I can only conclude the fuel level needs to be within a range for the engine to suck it past the needle...1/8 either way as very little effect. Thinking back the 650ss had a fuel hight 3/8 below the bowl rim when tilted the correct amount at the centre possition.

DogT said:

Then there's the tidbit of information at the bottom of JBA's float page.

"ADDENDA: May 2010 - The Norton ATLAS/DOMI engine with the carbs tilted forward, require a different setting. From what I have found is original spec noted as 3/32" ABOVE the float bowl (~94 thou). However in measuring several carbs, there is not enough clearence for 94 thou, it measures closer to 75 thou. In any case you can measure the recess in your carb and thickness of gasket and calculate a theoretical maximum float height - leaving at least 10 thou clearance."

http://www.jba.bc.ca/Bushmans%20Carb%20 ... tml#5FLOAT

I haven't tried that, but since things are running fine, I doubt that I will.

Dave
69S

Click to expand...

john robert bould said:

1/8 either way as very little effect.

Click to expand...

That's what I'm thinking.

Dave
69S