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Vent hose after replacing stock petcock

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Hi all- been a looong time since posting. Life changes kept me off the bike for the last couple of years. Basics- drz 400s, fcr mx carb, 3x3 mod, stock pipe.  First issue- stock petcock leaked so I replaced with the TT store Yamaha gravity petcock. Since I am running a Fcr/mx carb  I  thought I needed to cap the vent hole on the bike side, but the bike would not start with it capped. Removed the cap and it idled fine at full choke. Is that normal or do I have other issues? Let me rephrase that- I do have idle issues but I assume my cleaning of the pilot circuit was not sufficient. I'll pull the carb and have another go at that problem tomorrow. Any help greatly appreciated- Rod

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Not sure what is meant by "cap the vent hole". The stock petcock needs a vacuum signal to let fuel flow. Where the vacuum signal was coming from needs to capped off if it isn't being used on the new petcock.

Edited by npm

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Here is a pic of the vent tube. If it is capped, The bike won't start.

IMG_0753.JPG

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Cap the vent tube and readjust idle.  Otherwise, avoid deep streams or creeks

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Ok -thanks for confirming that. It dawned on me late last night that the main air jet could be clogged. (I totally forgot about this jet as it is covered by the air box adapter) I actually stumbled on the pic on some random site and the pic was mine from 10 years ago from a TT thread! 

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As a follow up, I pulled the carb to check the main air jet and it was fine. I went through the entire carb again. I had already replaced the pilot jet, main jet, needle jet and needle valve seat and o ring. I blew compressed air and sprayed carb cleaner through any hole I could find and stuck a very thin needle into the bottom of the pilot jet hole in the carb. I capped off the vacuum port and to my amazement the bike started. I need to fine tune the idle now and change the oil but hopefully I am done. 

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Correct - that is a vacuum port not a vent.  The nipple screws into a 8mm 1.25 thread in the head.  Just remove it and put a short 8mm bolt in the hole.

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