Datonedatsun

Fouling spark plugs su carbs

    Recommended Posts

    So I've been fouling spark plugs, my oil smells like gas and I cant figure out the issue... I noticed cylinder 4 5 6 run way richer than 1 2 3 and I turn the fuel down a bit (both run rich) fouling all 6 after about 20 mins of idle I sand blast the plugs and repeat 2 more times and decide to change the oil and no good. I know the carbs are a bit old so I was on my other su carbs that are I'm a lot better shape and now its flipped cylinder 1 2 3 are running super rich and 4 5 6 super lean so I turn down the fuel on the one carb and repeat multiple times but no matter what within minutes they foul it's like the fuel isn't going down at all when I use the fuel adjuster nut... any ideas? 

    Share this post


    Link to post
    Share on other sites

    I bought a motor that had half fuel half oil too. The head was nice and shiney under the valve cover. LOL

    Had to rebuild the carbs. Did your's just start doing this? Something is out of adjustment. If not consider rebuilding.

    Just thought about something to check. Make sure your nozzles are moving up and down with the choke lever. They could be stuck in the down position. Your choke wires could be loose or out of whack. The flat linkage bar could be bent. The small hoses could be wrong and hardened preventing them from movement. A lot of "could be" on those SUs. 

    Edited by siteunseen
    • Like 1

    Share this post


    Link to post
    Share on other sites

    Disconnect choke cables and push Nozzle (7) in figure below, up from the bottom. They are probably stuck down.

    The outside of the brass nozzle's tube usually gets gummy and dirty over time and binds in the Nozzle Sleeve(1)

    adjusterexp.gif

     

    You can remove the Nozzle and clean with carb cleaner and a scotchbrite pad but watch out for the screw and washers holding it to the lift arm (shown below):

    idlexplode.jpgw

     

    Edited by 240260280
    • Like 2

    Share this post


    Link to post
    Share on other sites

    I agree with Site and Blue. You can reach under the carbs and push up on the nozzle. You’ll feel it snap back.  If it is hanging up, it’ll cause very erratic idle and will blacken your plugs on those three cylinders. You’ll have to do this every time you choke the engine. Those nozzles are famous for binding when linkages aren’t aligned perfectly.

     

    • Like 1

    Share this post


    Link to post
    Share on other sites
    5 hours ago, siteunseen said:

    I bought a motor that had half fuel half oil too. The head was nice and shiney under the valve cover. LOL

    Had to rebuild the carbs. Did your's just start doing this? Something is out of adjustment. If not consider rebuilding.

    Just thought about something to check. Make sure your nozzles are moving up and down with the choke lever. They could be stuck in the down position. Your choke wires could be loose or out of whack. The flat linkage bar could be bent. The small hoses could be wrong and hardened preventing them from movement. A lot of "could be" on those SUs. 

     

    2 hours ago, 240260280 said:

    Disconnect choke cables and push Nozzle (7) in figure below, up from the bottom. They are probably stuck down.

    The outside of the brass nozzle's tube usually gets gummy and dirty over time and binds in the Nozzle Sleeve(1)

    adjusterexp.gif

     

    You can remove the Nozzle and clean with carb cleaner and a scotchbrite pad but watch out for the screw and washers holding it to the lift arm (not shown below):

    idlexplode.jpgw

     

     

    1 hour ago, Diseazd said:

    I agree with Site and Blue. You can reach under the carbs and push up on the nozzle. You’ll feel it snap back.  If it is hanging up, it’ll cause very erratic idle and will blacken your plugs on those three cylinders. You’ll have to do this every time you choke the engine. Those nozzles are famous for binding when linkages aren’t aligned perfectly.

     

    Alright I'll try 240260 suggestions first and if that doesnt work I'll probably just look into a rebuild kit, I just recently picked up this 240 but it didnt happen until after I took it for a drive, after that all hell broke loose lol! After work I'll get on it, thanks guys!

    Share this post


    Link to post
    Share on other sites

    BTW....You don’t have to disconnect the choke cables to pop up the nozzle......literally a 3 minute fix if that’s the problem and it sounds like it is. Just stick your hand under each carb and push up the nozzle....you’ll feel it pop up if that’s the problem.

    • Like 1

    Share this post


    Link to post
    Share on other sites

    4 hours ago, Diseazd said:

    BTW....You don’t have to disconnect the choke cables to pop up the nozzle......literally a 3 minute fix if that’s the problem and it sounds like it is. Just stick your hand under each carb and push up the nozzle....you’ll feel it pop up if that’s the problem.

     Perfect I'll get back to you guys in awhile letting you know what's up! (Like 6 hours from now) thanks again everyone!

    Share this post


    Link to post
    Share on other sites
    9 hours ago, Diseazd said:

    BTW....You don’t have to disconnect the choke cables to pop up the nozzle......literally a 3 minute fix if that’s the problem and it sounds like it is. Just stick your hand under each carb and push up the nozzle....you’ll feel it pop up if that’s the problem.

    The front carb has a pop to it and the rear carb doesnt, but the front 3 cylinders are the ones running super lean? I pulled the nozzles and will post a pic of them, I noticed the rear carb needle sits a but lower than the front needle?

    Share this post


    Link to post
    Share on other sites

    6 minutes ago, 240260280 said:

    to set both nozzle heights, turn Idle Adjusting Nut all the way up then turn it down 3 full turns.

    Not sure 3 turns was enough looks pretty short here's some photos, these nozzles seen a bit different than my other ones 

    20190826_174822.jpg

    20190826_174834.jpg

    Share this post


    Link to post
    Share on other sites

    Great photos!

    Now it looks the same for front and rear. (needle tip showing amount is same)

    Try it. If the plugs need more colour, lower the nozzles 1/2 turn (3.5).  If it runs too rich, raise the nozzles 1/2 turn (2.5).

    Share this post


    Link to post
    Share on other sites

    4 minutes ago, 240260280 said:

    Great photos!

    Now it looks the same for front and rear. (needle tip showing amount is same)

    Try it. If the plugs need more colour, lower the nozzles 1/2 turn (3.5).  If it runs too rich, raise the nozzles 1/2 turn (2.5).

    Awesome I'll give it a shot still gonna run a quick sand on the nozzles and carb cleaner plus I need to change the oil, still have a ton of fuel in it! Appreciate the help I'll get back to you tonight or sometime tomorrow 👌

    Share this post


    Link to post
    Share on other sites
    3 hours ago, 240260280 said:

    Great photos!

    Now it looks the same for front and rear. (needle tip showing amount is same)

    Try it. If the plugs need more colour, lower the nozzles 1/2 turn (3.5).  If it runs too rich, raise the nozzles 1/2 turn (2.5).

    Alright so I drained the fuel cleaned the spark plugs and started it, got a horrible back fire and dies when given throttle, I tried turning up the fuel and it didnt seem to help? Out of curiosity when the needle goes lower that is more fuel correct?

    Share this post


    Link to post
    Share on other sites
    7 hours ago, 240260280 said:

    Lowering the nozzle adds more fuel.

    The next thing to check is fuel level in  the bowls and correct needle valve functioning.

    Alright I'll get on that when I get back again haha

    • Like 1

    Share this post


    Link to post
    Share on other sites

     I hope the "quick sand on the nozzles" means you'll be using something akin to 0000 steel wool, not sandpaper. A thin coat of lithium grease will keep them sliding. Keep in mind that the fuel level in the float bowls is the PRIMARY mixture adjustment. Ztherapy has an excellent DVD "Just SUs". You'll be an SU expert after watching it.

    Share this post


    Link to post
    Share on other sites

    Create an account or sign in to comment

    You need to be a member in order to leave a comment

    Create an account

    Sign up for a new account in our community. It's easy!

    Register a new account

    Sign in

    Already have an account? Sign in here.

    Sign In Now