idles too fast

Edwardjohnsr
Edwardjohnsr Expert Adviser
edited November -1 in HUDSON
I finally got to try my Uni-syn on my twin H Hornet. Turns out the back carb reads a very high flow and the front reads very low. I can't get the back carb to back off enough to even it out. When I open up the front carb with the idle screw to even out the two carbs, the idle speed goes thru the roof. It seems like the back carb does not idle and is drawing a lot of air even when the idle screw is backed off.



Any suggestions on how to reduce the idle flow on this carb. I have the carb off and have set the float level to 1/2 inch. Also looked it over and didn't see any obvious problems.



Thanks

Ed

Comments

  • Park_W
    Park_W Senior Contributor
    Did you have the throttle rods to the carbs disconnected when you did the airflow check? If not, the linkage could easily have been keeping the rear carb throttle plate from closing down all the way. While the carb is off the engine, if you back out the idle speed screw a bit can the throttle plate be closed easily without any sticking?
  • Edwardjohnsr
    Edwardjohnsr Expert Adviser
    Park,

    Thanks for the reply. I think the linkage was OK but I'm not positive. I'll replace the carburetor and check it. On the second point, yes, the throttle can be closed all the way, although the carb is the original one and it does have some looseness in the shaft. I'll report back after I put the carb back on.

    Ed
  • [Deleted User]
    [Deleted User]
    Edwardjohnsr wrote:
    I finally got to try my Uni-syn on my twin H Hornet. Turns out the back carb reads a very high flow and the front reads very low. I can't get the back carb to back off enough to even it out. When I open up the front carb with the idle screw to even out the two carbs, the idle speed goes thru the roof. It seems like the back carb does not idle and is drawing a lot of air even when the idle screw is backed off.



    Any suggestions on how to reduce the idle flow on this carb. I have the carb off and have set the float level to 1/2 inch. Also looked it over and didn't see any obvious problems.



    Thanks

    Ed
    Walt here. If it's standard, you must disconnect the rear throttle rod from the cross shaft. if automatic, both rods must be disconnected. You can not just set them up with out doing the complete job.
  • Edwardjohnsr
    Edwardjohnsr Expert Adviser
    Thanks guys. Here's the latest. I disconnected the rear carb linkage (after warming up the engine). Both chokes were open, idle speed screw backed out completely on the rear carb. It is definitely better but in order to slow it down to where I want it I had to manually push down on the throttle lever on the rear carb. For some reason it just doesn't want to close that last little bit. I think I will try a stronger throttle return spring and hopefully that will do it. If it doesn't get it down enough, I'll just let it idle fast and will try to balance the carbs at a higher rev, maybe 1200 rpm. Eventually, I may have to replace the carb.



    Its always good to get the voice of experience and it is appreciated.



    Ed
  • dougson
    dougson Senior Contributor
    What idle are you trying to achieve? The fact that the throttle plate does not close all the way suggests that the carb linkage (to the power valve) may need adjustment. Or, the throttle shaft is bent or binding somewhere. Also, check for vacuum leaks around each carb. The best way to do this is to attach a rubber hose to a propane bottle. At the other end of the hose attach a bicycle pump needle. Crack the valve on the bottle and trace the needle around each carb. If the engine speed goes up a bit, you've pinpointed a leak.
  • [Deleted User]
    [Deleted User]
    Edwardjohnsr wrote:
    I finally got to try my Uni-syn on my twin H Hornet. Turns out the back carb reads a very high flow and the front reads very low. I can't get the back carb to back off enough to even it out. When I open up the front carb with the idle screw to even out the two carbs, the idle speed goes thru the roof. It seems like the back carb does not idle and is drawing a lot of air even when the idle screw is backed off.



    Any suggestions on how to reduce the idle flow on this carb. I have the carb off and have set the float level to 1/2 inch. Also looked it over and didn't see any obvious problems.



    Thanks

    Ed
    Your fast idle from the choke housing is not releasing all the way, if all else checks out. They need to be rebuilt and you can't do this job without the correct tools. Don't let any one tell you they can do it with no tools. Walt.
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