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  1. #1

    Need choke wide open after carb rebuild - 1200 SUV

    I just rebuilt my Mikuni 38 carbs with an SBT kit. I also put on a new Solas impeller. I went out today and it won't run without the choke open. It doesn't require it to be full open but obviously RPM's increase with it wide open.

    Ive triple checked the fuel line connections and pulse hoses. I have gas getting into the return line hose from the carbs. I have the air fuel mix started at 1 out and have gone through adjustments past 3 out.

    Even though it runs on choke, it runs really ****ty. I did have a run where it literally felt like it kicked and went wide open and was humming at 41, 5,800 RPM.

    Where should I start?

  2. #2
    Anyone have a picture of the throttle return springs (and choke) on the linkage? I want to make sure I have those installed correctly. I've searched and searched and this is like the holy grail of simple info.

  3. #3
    I've pulled the carbs and here are the new gaskets only in use during yesterday's short time getting it fired up and a short run of a few minutes. Is this significant enough to require the compensation of the choke?

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  4. #4
    So I went back through the carbs, cleaned and blew out with air. Took it out to the ramp to test on the trailer. Essentially the same situation. I could keep it running with about 20-30% of the choke plate open. I had the mixture rich at 2 1/2 and 3 and the need for the partial choke was still necessary.

    Rather than risk damage, I called it a failed effort and ready for the next investigation. Before I left I took a compression test. It wasn't fully hot but I'd call it a warm engine.

    #1 - 75
    #2 - 80
    #3 - 75

    How much does the warm engine affect compression?

  5. #5
    I'm no expert but those compression numbers seem low.. My suv is 120 on all three cold.

  6. #6
    mudslanger's Avatar
    Join Date
    Jul 2010
    Huntsville Al
    You need to borrow another compression gauge to recheck the compression. It it is still that low and consistent on all cylinders you have other problems. It could be reeds or bad gasket or seals. If the head was removed check that gasket. If the reeds were removed check that gasket also.

  7. #7
    Thanks, my plan is to find an auto shop that would check it for about $20. That's an easy $20...

  8. #8
    redneck71's Avatar
    Join Date
    Sep 2011
    middletown DE
    Is the altitude your at making your compression numbers low?

  9. #9
    hammer5312's Avatar
    Join Date
    Aug 2013
    Wichita, Kansas
    Quote Originally Posted by redneck71 View Post
    Is the altitude your at making your compression numbers low?
    Not unless there is a lake on Pikes Peak!!

    Sounds like bad compression. I'm surprised it really ran all with compression that low.
    Make sure the oil lines are attached properly, unless you're running pre-mix.
    Pull the cylinder head and check for cylinder scoring.
    My guess is, you are going to need a top end rebuild. While that is going on, I would pull your carbs and make sure they are set to original factory settings that are called out in the manual.

  10. #10
    redneck71's Avatar
    Join Date
    Sep 2011
    middletown DE
    Over at Pwctoday he stated he's at 12,000ft in CO.

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