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L24 running extremely rich


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#21 CGraves

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Posted 16 September 2016 - 07:14 PM

I honestly have no idea how they were working prior to this. The only thing I know is that I made them worse so that leads me to believe custom work has been done here.

#22 CGraves

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Posted 17 September 2016 - 07:35 AM

Alright well I swapped the other 2 carbs and now it doesn't even run. Anyone got any ideas?

#23 datzenmike

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Posted 17 September 2016 - 07:37 AM

Float chambers got gas in them?


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#24 CGraves

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Posted 17 September 2016 - 07:55 AM

Yes, it will fire and run if you hold the chokes all the way up but the second you give it any gas it falls on its face and dies.

#25 datzenmike

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Posted 17 September 2016 - 08:06 AM

Are the dampers full of oil?

 

What are these other SUs off of???


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#26 CGraves

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Posted 17 September 2016 - 08:14 AM

They are both filled to the correct amount of oil and they came off a 240z I'm not sure what year though.

#27 CGraves

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Posted 17 September 2016 - 08:39 AM

I figured it out. I'd like to start this out by saying either I'm retarded or zcardepot is retarded. The carb rebuild kids they sell don't fit any of my SU carbs needles and seats are either too big or too small. I'm about to rebuild 2 of them with the best parts from each other so hopefully I'll have 2 working carbs in a couple minutes.

#28 CGraves

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Posted 17 September 2016 - 10:04 AM

Okay new carbs went on and when you apply slow steady throttle it will rev up and work fine but if you give it a lot of throttle in one go it backfires through the carbs.

#29 datzenmike

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Posted 17 September 2016 - 10:19 AM

Lean backfire. Not getting enough fuel for the air going in.

 

 

Look in the open SU and watch the slides. Do they both lift at about the same rate? If one jumps ahead of the other maybe the damper isn't working.

 

Needles too large or seats too small or both. Basically the jetting mixture is wrong. Now this could be on just on one of the carbs causing this.


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#30 CGraves

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Posted 17 September 2016 - 11:58 AM

Okay mike first of all I'd like to say thank you for dealing with me and if there's anyway I can pay it back please let me know.

Anyway id like to update the post. IM RETARDED. I reversed the #3 and #4 plug when I changed the plugs. Everything runs like a top now.

#31 datzenmike

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Posted 17 September 2016 - 12:05 PM

Ha ha, hey.... it was a cheap easy fix.


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#32 CGraves

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Posted 21 September 2016 - 05:43 AM

Okay so another problem I'm experiencing a loss of power randomly. I've only had it happen in the middle of third and fourth gear but it will be fine then randomly a huge backfire will happen and then no matter how far I press the pedal I get nothing.

Is it just some water in the tank/bad gas or is there another problem I should look into?

#33 datzenmike

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Posted 21 September 2016 - 05:59 AM

Happen under prolonged load, like climbing a hill? passing? that may be a clogged fuel filter. The engine is using fuel faster that it can be sucked through a part clogged filter. The filter may be new but the tank dirty so it's just doing it's job. They are cheap and easy to replace to find out.


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#34 CGraves

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Posted 21 September 2016 - 06:01 AM

Nope I live at the beach so it's literally driving on perfectly straight roads cruising at like 40 MPH.

That's why I think it might be bad gas. Also I live in NC and there's currently a gas shortage so that leads me to believe there's something wrong here.

Also if it's a fuel filter is there one at the tank and one in the bay or is it a single filter?

#35 dgi

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Posted 22 September 2016 - 04:27 PM

72 240z has a filter in the engine compartment.

 

74 260z likely has one between the tank and the electric fuel pump (if so equipped) and one in the engine compartment too.

 

Assume you are talking about the 240z.

 

Hey now, Thomasville is definitely not at the beach... you down a school at UNC-W or something?

 

dgi



#36 CGraves

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Posted 25 September 2016 - 05:40 PM

Okay so I've been cycling the bad gas out and I also replaced the fuel filter while I was at it. Prolly gonna change the plugs tomorrow too. It's running a lot better now!

 

@dgi yeah I'm going to UNCW for computer science right now. I just moved down at the beginning of the summer. It's been pretty fun so far. Found a good car scene down here too!



#37 CGraves

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Posted 27 September 2016 - 11:42 AM

Okay so I replaced the filter in the engine bay and I don't think it's the water in the tank because I can rev the engine in neutral just fine but as soon as I try it in gear it bogs and won't go anywhere. I did some research and is it possible it's a distributor/ignition problem?

#38 datzenmike

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Posted 27 September 2016 - 06:39 PM

Revving the engine in neutral requires spinning about 50 pounds of crank and rods and very little fuel is needed. When in gear under load moving a 2,800 pound car things are vastly different. If the carb or carbs can't provide it the engine goes lean and falls on it's face, often accompanied with a backfire out the carb. 

 

The ignition either works or it doesn't and certainly can't tell when you are revving in neutral or driving.


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#39 dgi

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Posted 27 September 2016 - 07:30 PM

If it bogs when you open the throttle to take off under load and then picks RPM back up and pulls, perhaps even repeats that in 2nd gear or upon sudden acceleration under load in any gear and is often accompanied by backfilre, you have described a classic SU tuning issue.  

 

The suction piston is rising too rapidly which leans the mixture out.   Normally this is prevented by the oil damper.   If the oil is too light, this lean out condition occurs.  Also, if the suction spring is too light or missing, this lean condition can occur.

 

I suggest you read about the venturi control system for the SU carbs at this link

 

I personally find 20wt oil a little too light, so I mix 20wt and 30wt 50/50 trying to reach about 25wt.  That seems to be about right for me in warm weather.  I usually run 20wt in the winter time.. 

 

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#40 CGraves

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Posted 28 September 2016 - 06:08 AM

It isn't lean backfiring so does that change anything? Is it possible that the carbs being unevenly filled would cause this? I just kinda poured some oil in them without making sure they were perfect.


But what exactly happens is first and second gear will pull fine. But as soon as you hit about 50 MPH in third or fourth it will bog and you can press the peddle down as far as you want but it won't accelerate but it will keep that speed. If you push the clutch in you can rev it as high as you like.