ace 100 carb tuning

[lukenessmonster]

I finally got my motor built. new top end, new bearings, bushings and seals, new gaskets, honed cylinder. I've got good spark, points clearance is at .013 When I try to start it, first kick or two it will start up and run for a couple seconds then die. then wont start. Looks like its getting way too much gas. I've dropped the needle clip from the third notch to the second notch. I've tried turning in the mixture screw from the 1 1/4 turns that the book suggests, Ive tried turning up and down the idle speed knob on top of the carb. but nothing seems to be working. I've never worked on a two stroke that doesnt have reed valves, is there something im missing? I also have dipped and thouroughly cleaned the carb. I am at 6500 feet above sea level so that will make things run rich, but I feel like it should still run. is there some timing adjustments other than the points gap? I haven't worked on a two stroke since I was a kid. Any suggestions would be greatly appreciated.

[Bullfrog]

While you have dipped and thoroughly cleaned the carb, I'm wondering if you have cleaned every air and fuel passage in the carb. Wear eye protection and confirm that spraying carb cleaner in the end of each and every passage in the carb body causes carb cleaner to come out at the other end of the passage. This is especially important for the passages relating to the pilot circuit (pilot jet passage and pilot air passage).

Note that the screw you identified as the "mixture screw" is actually the pilot air screw. Turning that screw "in" reduces the air being introduced into the pilot circuit . . . so turning that screw "in" causes the mixture to be richer. Turning that screw "out" will make the mixture "leaner".

While you have the carb apart, make sure that the floats will actually float. If they are "fuel logged", they will not control the fuel level in the float bowl properly. Also check that the float level is set properly.

Ed

[MTrat]

Also remember that dropping the needle clip raises the needle.

[Al Harpster]

I've been through the 20mm Ace mikuni more times that I can count. Many more.

If the carb is clean through and through and the standard jetting is installed it works well.

The best way to know it's clean through and through is to disassemble everything as shown in the carb's exploded diagram. The diagram is available on the strictly hodaka website where the total part breakdown for the Ace 100 is displayed. Confirm that all the jets you have are marked with the same markings as standard jets in the parts list. If you have the patience and time you can make your own replacement bowl gasket. These often come apart with multiple assembly and dis assembly.

You may want the 90 or 95 main jet for altitude. I don't know about that. Adjusting the needle position is fine tuning.

In the case where it won't stay running the specific needle position and jet size are probably not the problem.


Ignition timing is controlled by point gap. I found it difficult to adjust point gap through the flywheel with the feeler gage, but if you are careful and repeat your measurement it should be good enough for a start and run.