Enrichment circuit on Lance 250 carb By billg (Read 2,108 times)

[billg]

I just replaced a head gasket on my Lance Duke Touring 250. When I got it back together it works like new except that it needs throttle at a cold start up. I checked the electric enrichment device and it works and is withing spec resistance wise. I put my pinkie in the enrichment outlet at cold start up and got no change in idle. The float is set to manual spec. I put a small hose into the enrichment outlet and drew gas fumes, so it appears to be delivering gaseous fuel. Does anyone have any suggestions?

I am thinking the carb might not be in the correct position.  On the Duke 250, the notch on the carb output side will not fit into the corresponding notch shape built into the rubber intake joint (as it probably does on the Honda Helix) and still allow the air intake box to fit.  Maybe I have the carb tilted too much?

Read more: scooterdoc.proboards.com/conversation/49581#ixzz3GrOyoHxF

[Alleyoop]

I think you carbs fuel mixture needs to be tweaked. For cold starts the carbs need to be pretty well set otherwise it may be getting to much fuel or not enough fuel and they need a little throttle.
Alleyoop

[Bashan]

That damn carb will not fit into the notch on my 250 either. Just eyeball it to make its even while on the center stand. Did you watch the enricher work while hooked up to the bike's electric supply or hooked to a battery?

[billg]

Yep! I hooked it up to the battery and watched it extend (about 1.5 min.) and retract (10 min. or more). I then was particularly careful to make sure that it aligned properly when attaching to the carb. It does heat up properly after everything is assembled. It still takes 1.5 min. before it will idle from a cold start on its own.

Read more: scooterdoc.proboards.com/thread/11019/enrichment-circuit-lance-250-carb?page=1&scrollTo=96771#ixzz3GumZzRkG
billg,Alleyoop,Bashan

[billg]

Alleyoop,

I was hoping that wasn't it.  The Duke Touring 250 has one glaring design flaw.  The carb sits about 1.5" off the frame.  I bought a special motorcycle carb adjusting screwdriver with a 90 degree bend at the end hoping to be able to adjust the idle mixture while running the engine.  No luck!  Even that won't reach it because of the interference with the frame.  I am looking into shortening the bent end.  There has to be a setting that works because this machine did work right at one time.

[Alleyoop]

Since it will not idle without help until the extra fuel is cut off then it is to rich, Give the Fuel ratio mixture 1/4 to 1/2 turn clockwise turn and notice next time you cold start it if it gets better.
Alleyoop

[Bashan]

Just for my own curiousity, have you checked the voltage from the bike to the enricher circuit?

[Guitarman]

That was my thought Rich. Sounds like there is a short or something between the power source and the auto/choke.

[Alleyoop]

He connected the Enricher to the battery which provides more juice so it will extend rather quickly. So I do not believe there is anything wrong with his ENRICHER.

Now if the tool does not work for you Just loosen the clamps holding the carb in place and just rotate it enough to get at the fuel mixture screw. Better and faster than taking it off and what not then just rotate it back straight and tighten the clamps again and try it.
Alleyoop

[billg]

Alleyoop,

Yes, my thought exactly.  The idle adjustment screw is on the output side of the carb and adjusts bleed air, not fuel, so it must be turned counter-clockwise (admitting more air) to lean the mixture.

[billg]

Bashan,

The enricher is working properly because idle is normal after about 1.5 min., meaning that the enricher has extended and cut off extra fuel.

[Alleyoop]

Oct 23, 2014 14:55:58 GMT -6 billg said:

Alleyoop,

Yes, my thought exactly.  The idle adjustment screw is on the output side of the carb and adjusts bleed air, not fuel, so it must be turned counter-clockwise (admitting more air) to lean the mixture.

I think your confused, There are TWO adjustments to a carb actually 3 but we will leave the third out since that is usually not a problem.
#1. Fuel Ratio Mixture Screw: controls the amount of fuel from the pilot jet- This screw is on the INTAKE MANIFOLD side of the carb(Turning this screw COUNTER CLOCKWISE De-Restricts the Fuel passage more and ALLOWS MORE FUEL to pass through the passage and out to the motor, Turning this screw CLOCKWISE Restricts the Fuel Passage more and ALLOWS LESS FUEL to pass through the passage and out to the motor).

#2. Idle Speed Screw: Controls the amount that the BUTTERFLY is open or closed- This screw has a Spring under it and turning it clockwise raises the IDLE and turning it counter clockwise lowers the idle. It does this by pushing on the Throttle control wheel more to raise the idle and less to lower the idle. Actually it is doing the same thing as if you twist the throttle grip but in finer adjustments. It does exactly the same thing the throttle control cable does when you twist the throttle grip.
Hope this helps explain it. If not I can put up pictures of the carbs and the parts labeled.
Alleyoop

[billg]

Yep! You're right! Even though the idle mixture screw is on the engine side of the carb, it does admit fuel. I knew it when I noticed the plug to a drilled hole passing through the idle mixture screw channel (at 90 deg. to it) and going right to the float bowl. I then carefully turned the screw to full closed and opened it one turn. Perfect, even though the manual says 2 to 2.5 turns.

I was working from an article about small engine carbs that said (not a direct quote) that usually, if the idle mixture screw is on the engine side of the carb, it regulates bleed air and if it is located on the input side of the carb, it regulates fuel.

Goes to show you can't assume anything. Trust those crafty Japanese to make an exception. My guess is that this arrangement makes it easier to adjust for (and spot)leaks developing leaks in the manifold between the carb and the engine.

I really do appreciate the expert help. Color me impressed.

[Bashan]

Oct 23, 2014 14:59:32 GMT -6 billg said:

Bashan,

The enricher is working properly because idle is normal after about 1.5 min., meaning that the enricher has extended and cut off extra fuel.

Understood, the other scenario is that there is no voltage to the enricher and it is not moving. The engine is set too lean and when it finally warms up the extra gas makes for an adequate mixture to run half way decent. It has happened several times on the forum. Further, 1.5 minutes is an abnormally brief time for an enricher to start working, that could point elsewhere. It never hurts to explore all possibilities.

[billg]

Thanks! Now I know what you mean. I'll check the voltage to the enricher.