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Chiefbauske

Carb problem? High RPMs?

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I’m having major issues with my hitachi carb. At first my rpms were skyrocketing (wanna day 3-4K?).  It was backfiring alot and this was after a heavy rain fall. Once I took off the air filter I looked into the carb and saw The secondary valve seems to fluttering a million times a second and I can’t seem to figure out why. I want to say it’s a vacuum leak in the diaphragm but when I took the old carb off the diaphragm seemed okay. I never thought to check for a vacuum leak before hand. I’m not experienced with carb that much unfortunately and my brand new carb just came in but won’t be able to be installed until after the carb to manifold gaskets come in. If this doesn’t work I’m just going to upgrade to a Weber. I also noticed the bootle on the choke (I think it’s the choke) it’s small about an inch tall and quarter inch wide was torn. Does anyone have any idea why this is happening? 

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The sunny was made for 40 years. Do you really mean a B-210? Maybe a later 210? Year?

 

The rubber boot you refer to is likely the top of the accelerator pump. You sure it's the secondary? It's the hole farthest from the valve cover.

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Hey mike you’re the exact person I was hoping to answer my question! And it’s actually a Nissan Datsun Sentra B11. But I was told to refer to it as a sunny when talking to Datsun fanatics. At first I thought it was a vacuum but like you said in earlier posts you’ve never seen a high idle caused by a vacuum leak. Therefore what could it be 

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The Sentra is an 84 model sedan. It has 103k miles exactly on it and has been garage kept until I bought it about three months ago. I’m a lead mechanic at a ford dealership so I’m pretty knowledgeable when it comes to edlebrock carbs and the like. It’s just these Japanese made carb are killing me ??‍♂️

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Like an '82? I think '83 and up were some sort of EFI. Man I've only seen them in wrecking yards. Never really looked at one but a carb is a carb right?

 

If this is on a cold start up a fast idle is normal. Once warmed up it should reduce to normal idle speed.

 

I had an unexplained fast idle once that turned out to be the secondary for some reason wasn't shut completely. I pushed it closed and it worked fine after that. (just sticky) The secondary is pulled open by an internal vacuum signal using a diaphragm. The throttle on the primary has a linkage that helps pull it closed. 

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Yeah high rpms unpon a cold start is normal but this is like wild my dude. Like 3k-4K rpms. When at idle the primary would be slightly open (as usual I believe) but the secondary is at full open. I’m hoping it’s not just a “stuck valve” situation and I wasted some money on a shitachi carb and it could’ve been solved with a screw driver forcing it to shut from where it was stuck. Fingers crossed

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Use a flash light. If the secondary is open you'll see it.

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Already did when it was on. It was moving back and forth but always in the on position. Like it was trying to go back to its shut position. Sounds like it was stuck. When I tore apart the carb I was easily able to get the valve in the same stick position. Stupid me. Should’ve thought about it before buying another carb. 

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 Open and close the throttle and watch the vacuum diaphragm where it connects to the secondary throttle plate. It should be closed. Usually theree is a lever on the primary throttle linkage that helps push it closed. It's also an interlock and prevents the secondary opening unless the primary is at least 2/3s open. 

 

Again this is the usual set up for an Hitachi carb.

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