90cc two stroke scrambler carb issue - Polaris ATV Forum
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post #1 of 11 (permalink) Old 06-19-2019, 09:59 AM Thread Starter
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90cc two stroke scrambler carb issue

I have cleaned the carb.( not to say wont do it again). Bogs out when given gas unless I cover the two inlet holes at the mouth of the carb.. it has an automatic choke. I did not replace the gasket and the float bowl level seems to be good. Any ideas would be appreciated before I take it apart again. Thanks John
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post #2 of 11 (permalink) Old 06-19-2019, 11:09 AM
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It bogs out when you give it air. Covering those two holes prevents air from getting to the idle circuit and main jet emulsion tube decreasing air thus enriching the air fuel ratio.

It will not run right without the air filter box in place with a properly oiled filter - the restriction of the air box enriches the mixture.

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post #3 of 11 (permalink) Old 06-19-2019, 01:52 PM Thread Starter
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Does it have an air mixture screw?..
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post #4 of 11 (permalink) Old 06-19-2019, 01:53 PM Thread Starter
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I had the filter on but did not clean or oil it...never had one before that required it..more street rider. I will do that though..thanks
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post #5 of 11 (permalink) Old 06-20-2019, 06:12 AM
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It has an idle air/fuel mixture screw -it's on the LH side of the carb at about a 45 degree angle to the venturi located near the intake side of the carb - it intersects the hole on the left in your pic - it adjusts the amount of air let into the idle circuit - setting is simple - on a two stroke, 1 1/2 turns out from lightly seated is usually adequate unless someone has drilled out or changed the pilot jet to allow more fuel in (more fuel is more power, right? WRONG! - more air is more power - that's why turbo and super chargers were devised)

The hole in the middle at the bottom is the air passage to the emulsion tube to allow air to mix with raw fuel atomizing it before it enters the venturi - the hole on the right (deeper inside the mouth of the carb) is the air passage to the enrichener (electric choke) - the operation of the enrichener is this: it is open (allows fuel and air to bypass the slide allowing fuel rich air into the intake for easier starting) whenever the engine is not running - the enrichener is connected to one leg of the alternator so when the engine starts, AC current passes through the coil of the enrichener unit - this causes the coil to heat (the heat causes a gas in a small cylinder to expand or a bi-metal spring to move) pushing the enrichener plunger down closing the port and the fuel jet. This takes about 30 seconds to a little over a minute (depends on the design of the unit). To test the operation of the unit, remove it, connect it to a 12 volt DC source and watch the plunger slowly extend downward out of the unit (moves about 1/4 inch - 1/2 inch at the most) thus closing the choke - remove the voltage and it will slowly retract (opening the choke) - if it does this, it is working correctly.

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post #6 of 11 (permalink) Old 06-20-2019, 11:59 AM Thread Starter
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I have adjusted the idle screw ..it is idling fine...I have not taken carb off again yet..was just asking encase I missed the second screw and need to adjust it( didnt think I saw one) I will be getting filter cleaner and oil tonight and will let you know...had taken the whole thing apart as starter was not working when I bought it and the brake safety switch was not operating...I have bypassed it for now and am ordering a new one. Starts very easy.
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post #7 of 11 (permalink) Old 06-20-2019, 12:02 PM Thread Starter
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Cold start
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post #8 of 11 (permalink) Old 06-20-2019, 12:11 PM Thread Starter
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Cant figure out how to post video
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post #9 of 11 (permalink) Old 07-01-2019, 09:40 AM Thread Starter
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So I clean the filter and oiled it...seemed to fix the issue but only for a fun up the back lane..then issue of bogging out returned. Removed filter spray oiled again same result...if I cover the one hole of the carb....left looking at it runs fine..right hole doesn't not give same result......new filter? Filter box gasket?
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post #10 of 11 (permalink) Old 07-01-2019, 01:44 PM
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The left hole is the air passage for the idle mixture - turn the screw in that obstructs that hole - normally the screw is 1 1/2 turns out from lightly seated - hole on the right is the air passage for the enrichener - it is is closed off by the enrichener when the 'choke' is off - the choke is always on until the engine has run 30 seconds or more - closing that hole off effectively cuts the 'choke' off so the engine is never choked. If the electric choke has malfunctioned, it may be stuck off - you can look in the hole with a flashlight or similar light and if the choke is on, the hole will be open all the way to the back with perhaps a brass rod in the center of the hole - if the choke is off, the hole will be blocked off with a brass plunger and all you should see is brass where the brass rod was.

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