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Discussion Starter #1
Hello everyone,

I'm trying to familiarize myself with my 1970 Trophy by setting up the carb. I have some instructions, one paragraph of which says:

"When starting from scratch, the following adjustments may be of help: 1 1/2 turns out (counter-clockwise) from bottom on the idle air screw (the one that screws into the carb horizontally), and 1 1/2 to 2 turns in (clockwise) on the idle stop screw (the one that screw in at an angle) from the point at which the slide or 'throttle valve' starts to move up from the bottom of the chamber."

I've identified those two screws. My question is, how do I determine when the "slide or throttle valve starts to move up?"

The instructions then go on to say:

"In some cases, it may be necessary to adjust the pilot air mixture to help achieve a steady idle. This will be evident when the engine fails to idle smoothly, regardless of the idle stop screw adjustment. Turning the mixture screw in or out a 1/2 turn or so should bring the engine (or that cylinder, when two carbs are used) up to a regular rhythm at which point the idle speed can be adjusted as previously described. Finally, you are at a starting point. Using 1/4-turn increments, adjust the air mixture screw out (counter-clockwise), waiting a few seconds between adjustments for the engine speed to stabilize. Depending on the machine and the carburetors, the idle speed should increase with the first few mixture adjustments. As the idle speed increases, it should be adjusted back down to the original setting by use of the idle stop screw. At some point, the mixture adjustments will cease to alter the idle speed. This will indicate closure on the correct
mixture adjustment. Within the next few adjustment, the engine or cylinder on which the carb mixture screw back in (clockwise), usually 1/4 to 1/2 turn will restore the regular idle and will give the correct idle mixture adjustment."

My question here is, where is the pilot air mixture screw? I can't seem to find it on the carb diagram in the Haynes. Am I missing something obvious? That last paragraph is confusing.

My bike starts first kick and runs very well on the road, but the idle is high and it seems to be missing or stuttering at idle.

Thank you . . .
 

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OJ,

Don't worry about when the slide starts up. Make sure the bike is warm, if it won't idle blip the throttle and adjust the idle screw until you have some idle. Back that screw off untill you have the lowest idle that your bike will run at. Adjust the air screw until you get the smoothest idle you can get. Re-adjust the idle screw to your preferred idle speed.

You need to start with a clean idle circuit for best results.

Do a google search for Amal Carb Tuning and there is some real good stuff in there. Also use the search feature in this forum as this topic has been discussed to death.

HTH,

TD
 

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What stu said is right about when the slide starts to move. I haven't thought about this for 25 years or so but I remember having to have the air filter off of it. Then you can see the slide when it moves. You can probably feel it with you finger as it just begins to move while you are turning the screw.
But maybe tigerdale's right too... just adjusting it for a good speed. You are going to do that anyway right? But maybe your 1.5 to 2 turns is a good starting point.

Good luck
 

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Discussion Starter #8
Thank you all for the advice. That should solve my problem. I'd looked at several posts (and websites!) on Amal tuning before posting, but couldn't figure out the different terms in the instructions I had; nor could I find how to determine when the slide moves!

Now I know. Thanks again.
 
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