Jump to content


Photo
- - - - -

L24 running extremely rich


  • Please log in to reply
46 replies to this topic

#1 CGraves

CGraves

    Advanced Member

  • Members
  • PipPipPip
  • 116 posts
  • Location:Wilmington, NC
  • Cars:'72 240z, '74 RB25 260z

Posted 14 September 2016 - 06:26 PM

So my car is running ridiculously rich at the moment. Black smoke, gas smell, fouled plugs, bad MPG etc. I'll toss a pic of the plugs at the end so you can see what I'm dealing with here.

 

So far I've put new plugs in and after 20 minutes of driving they are even blacker than the old ones. I've also adjusted the carb I think? I turned the adjusters all the way in which should be lean and then backed them out 1.5 turns and it's still rich. That leads me to my question.

 

Is it possible some trash from the gas tank got sucked into the lines and clogged the return line which forces all the gas into the Carbs because it can't get back into the tank? I'm gonna try and blow through the lines this weekend and take the carbs off and see if I can find anything else, but just in-case is there something I might be forgetting that I should try first?

 

m8VXdDE.jpg



#2 Roadster-ka

Roadster-ka

    Advanced Member

  • Members
  • PipPipPip
  • 95 posts
  • Location:Vallejo
  • Cars:71 510 wagon

Posted 14 September 2016 - 06:40 PM

Stuck chokes?

#3 CGraves

CGraves

    Advanced Member

  • Members
  • PipPipPip
  • 116 posts
  • Location:Wilmington, NC
  • Cars:'72 240z, '74 RB25 260z

Posted 14 September 2016 - 06:49 PM

The choke lever on the console works and the engine idles higher and lower when you pull it so they aren't the issue I think.



#4 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 69,360 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 14 September 2016 - 06:53 PM

The maximum fuel pressure is set be the relief valve in the pump. With ot without the return working it can onlt build to what it's designed to do. The return line has nothing (zero) to do with fuel line pressure. It's job is to allow cool fuel from the tank to circulate pad the carb and prevent the stagnant fuel from boiling in the heat. that's all it's for.

 

 

SUs???

 

Are the chokes connected and shut off???

 

With the air filters off reach in and with fingernail lift the slide fully and let drop. It should move with slight resistance but no tight spots or sticking and should seat with a 'click'.

 

One or both float chambers are flooding. The float chambers are outside the body of the carbs so easy enough to get at.


Posted Image

#5 Roadster-ka

Roadster-ka

    Advanced Member

  • Members
  • PipPipPip
  • 95 posts
  • Location:Vallejo
  • Cars:71 510 wagon

Posted 14 September 2016 - 07:01 PM

The choke lever pulls down the nozzles. They can and will stick down even with the lever in the closed position. Like Mike said, remove the air filter and see if you can push up on the nozzles. They hang down below the center of the carb body.

#6 CGraves

CGraves

    Advanced Member

  • Members
  • PipPipPip
  • 116 posts
  • Location:Wilmington, NC
  • Cars:'72 240z, '74 RB25 260z

Posted 15 September 2016 - 07:50 AM

I disconnected the choke cables and the rear carb is stuck fully choked. I suppose I'm just gonna have to take it apart. :/



#7 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 69,360 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 15 September 2016 - 02:59 PM

The choke simply raises the needle. It's tapered and will let more gas in to run it richer. You should be able to fix/adjust without tearing it apart.

 

Does the piston slide up and drop down smoothly on the rear one???


Posted Image

#8 CGraves

CGraves

    Advanced Member

  • Members
  • PipPipPip
  • 116 posts
  • Location:Wilmington, NC
  • Cars:'72 240z, '74 RB25 260z

Posted 15 September 2016 - 04:20 PM

The pistons both slide smooth and they move when I apply the throttle.

 

The little gold circle in the middle of the carb with the needle in it doesn't move at all no matter what I do. I tried turning the mixture screw until it was as far up as I could turn with no visible change in the height of the gold circle.



#9 Doctor510

Doctor510

    Senior Member

  • Senior Member
  • PipPipPipPip
  • 646 posts
  • Location:Mesa, AZ
  • Cars:Many 510's

Posted 15 September 2016 - 06:03 PM

The choke simply raises the needle. It's tapered and will let more gas in to run it richer. You should be able to fix/adjust without tearing it apart.

 

Does the piston slide up and drop down smoothly on the rear one???

The fuel nozzle the the part that moves up and down acting as the "choke".  His "nozzle" on the rear carb is stuck.



#10 Doctor510

Doctor510

    Senior Member

  • Senior Member
  • PipPipPipPip
  • 646 posts
  • Location:Mesa, AZ
  • Cars:Many 510's

Posted 15 September 2016 - 06:04 PM

The pistons both slide smooth and they move when I apply the throttle.

 

The little gold circle in the middle of the carb with the needle in it doesn't move at all no matter what I do. I tried turning the mixture screw until it was as far up as I could turn with no visible change in the height of the gold circle.

Get it loosened so it can move up and down freely.  Often you my have to remove the carb to do this.  Go for it!



#11 CGraves

CGraves

    Advanced Member

  • Members
  • PipPipPip
  • 116 posts
  • Location:Wilmington, NC
  • Cars:'72 240z, '74 RB25 260z

Posted 15 September 2016 - 08:18 PM

I'm assuming this is the piston? This piece moves up and down smoothly on both carbs, but if you push it all the way up it falls back down to the neutral position, is that how they should work?

hE2iTgy.png

 

This piece however, is what I think is stuck.(Not my pic I got it off google and drew a circle on it.) That inner gold circle doesn't move up or down no matter what I do. 

 a4Uje6P.png



#12 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 69,360 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 16 September 2016 - 09:06 AM

I think it should move down when choke is on and up when off.

 

tech_su_03b.jpg

 

7 is the choke pull knob

9 the choke lever that pulls down on the needle seat. As the needle is tapered, more gas gets in as the seat is lowered.

 

This picture is not an exact one of the SU but the principle is the same.


Posted Image

#13 CGraves

CGraves

    Advanced Member

  • Members
  • PipPipPip
  • 116 posts
  • Location:Wilmington, NC
  • Cars:'72 240z, '74 RB25 260z

Posted 16 September 2016 - 11:07 AM

Well I figured out what the problem was. http://i.imgur.com/uh2LZ41.jpg

That needle was way longer than any other needle I have for SUs so I assume someone bent it like that so it would fit properly.

Also sorry for not embedding the image but I'm on mobile so that's not an option.

#14 Dolomite

Dolomite

    Senior Member

  • Senior Member
  • PipPipPipPip
  • 1,047 posts
  • Location:The Ville, Cali
  • Cars:1971 2dr 510, 1990 Supra turbo, 1970 MGB mutt job turbo

Posted 16 September 2016 - 11:25 AM

In my experience, bent needles are usually from back fire. That one is way too fucked for that though. You need new needles. Use a straight edge when installing so shoulder is flush with the bottom of the piston, they will synch and tune better this way. When you lift the pistons and let go, they should drop down and make a metallic click at the bottom. If not, they're not centered and will be hard to synch correctly. Last, they need to have the same amount of oil in the dash pots. Get this all correct and then it's set and forget for the most part.
Chrome door handles are under rated.

#15 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 69,360 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 16 September 2016 - 01:28 PM

uh2LZ41.jpg

How the hell would that slide up and down through the jet?????


Posted Image

#16 CGraves

CGraves

    Advanced Member

  • Members
  • PipPipPip
  • 116 posts
  • Location:Wilmington, NC
  • Cars:'72 240z, '74 RB25 260z

Posted 16 September 2016 - 01:48 PM

I have ABSOLUTELY no idea how this worked as long as it did. I'm astonished to be completely honest. Also I have a couple bottles of carb oil. How much should I put in each one.

#17 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 69,360 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 16 September 2016 - 01:58 PM

From Club 1200....

 

 

Fill between these two lines.

 

20162.jpg

 

You may want to experiment with the viscosities of the oil. Thicker slows the opening of the slide and forces an enrichment of the fuel air mixture. This is somewhat the equivalent of the accelerator pump on a regular carb. If the SU's open too quickly they will run lean and the engine will 'fall o it's face'. Likewise too rich will give poor mileage so thinner will help. I've heard that ATF is widely used 


Posted Image

#18 CGraves

CGraves

    Advanced Member

  • Members
  • PipPipPip
  • 116 posts
  • Location:Wilmington, NC
  • Cars:'72 240z, '74 RB25 260z

Posted 16 September 2016 - 02:00 PM

Ok thanks mike. I've actually got 2 bottles of the original oil these carbs came with. I'm not sure what the viscosity on it is though.

#19 CGraves

CGraves

    Advanced Member

  • Members
  • PipPipPip
  • 116 posts
  • Location:Wilmington, NC
  • Cars:'72 240z, '74 RB25 260z

Posted 16 September 2016 - 04:20 PM

Alright so small update. I rebuilt those 2 carbs but it seems like most of the stuff I had in the kit didn't really fit my SU's but I put new needles in at least and cleaned them up. Now they run worse than before. I think someone has done some custom work to these carbs. 

LUCKILY however I have another set of SU's laying around so I'm gonna take them apart see what I can do and put them on my car. If those don't work then I'm just gonna burn the car to the ground.



#20 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 69,360 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 16 September 2016 - 04:39 PM

These needles are connected to the bottom of the slides. You said both slides moved up and down fine. I wondering how that's possible with the needle bent like this.


Posted Image