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  1. #1

    Default honda cb750k high idle

    Hey guys i bought this 750 and it already had pod filters and a four to one drag racing exauhst. It always ran kind of weird but know when it warms up it has a high idle at 3000 rpm. Im prety sure i need to rejet but i want to know if that would take care of the problem before i start buying a bunch of parts that i may not need. Any would be very helpful thanks.

  2. #2
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    Is the bike running points with a mechanical advancer? If so you can pull the points plate (after marking it's position) and pull the advance to check that it is not sticking. It's worth lubing it anyways if you are pulling the points to check.

    Also check the air boots for cracks or splits where the carburetors meet the head. Before you start messing with jetting it may make sense to check the carbs themselves to make sure float levels are set correctly and that they're clean.
    Last edited by CarloFreeze; 02-09-2017 at 9:25 PM.

  3. #3

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    I really dont know about points, mechanical advancer. All i have noticed is the coils going directly to the spark plugs. Do you have a picture of points and mechanical advancer. Do you think the floats might have filled with gass and are stuck down?

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    Coils going directly to the spark plugs is normal. The coils are sent their "firing order" from the points. The "points" or ignition is located on the lower right front side of the engine (from the rider's perspective) There's two screws to take the cover off. Under there you'll see the points plate. Behind it is a mechanical advance unit with has weighted arms that "throw out" to advance the ignition timing. If these were stuck open then you would have a high idle.

    If it was me and I was diagnosing your issues, I would go through your carbs first. Check for air leaks in the boots by using a propane torch with just the gas turned on and the bike running. Any changes in idle at a given cylinder could indicate a leaking carb manifold which isn't uncommon. If that passes the test, I'd move on removing the carbs to checking my float bowls for debris and to check the float levels. If your floats were stuck open the gas would overflow from the tubes at the bottom of the carbs.

    There are PDF versions of the factory service manual online for free. Download it if you haven't already.

    Click image for larger version. 

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    Last edited by CarloFreeze; 02-11-2017 at 11:07 PM.

  5. #5

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    It will be worth your time to just clean the carbs first and then go about troubleshooting the rest. With it idling the way that it is I would bet that there may be gunk in them. If you don't know when the last time they were cleaned, that's the route I would go. I chased down an air leak with carb spray on my 750. With pods and the 4 to 1, you can probably bet on the rejet also, and oil the pod filters as well. If your still having the issue, what year is the bike, after 78 they started using the new kind of carbs. Good luck

  6. #6

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    Quote Originally Posted by OhhNoo82 View Post
    It will be worth your time to just clean the carbs first and then go about troubleshooting the rest. With it idling the way that it is I would bet that there may be gunk in them. If you don't know when the last time they were cleaned, that's the route I would go. I chased down an air leak with carb spray on my 750. With pods and the 4 to 1, you can probably bet on the rejet also, and oil the pod filters as well. If your still having the issue, what year is the bike, after 78 they started using the new kind of carbs. Good luck
    Its a 81. Thanks for all the info i think im headed in the right direction know

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    Sorry I didn't realize it was a DOHC motor. The factory jetting is quite lean on those so you know. I think it also is electronic ignition so that'd eliminate that variable. Still check the carb boots for leaks.

  8. #8

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    Im rebuilding the carbs know. Its gona take a long time. Im too picky so im cleaning and polising stuff hopefully it works as good as it will look

  9. #9

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    The carbs are really easy to get apart, make sure you get all the passages ( I used compressed air for the most part) but letting them sit in solvent was probably the best thing for them. Don't be shy with the carb cleaner or pipe cleaners! My shop table was a mess from all the cleaning. You may want to consider converting the vacuum petcock to just straight fuel to the carbs while your at it, (take the vacuum port between carb #2 and #3 and run a hose to your pods to help with the breathing. With you running pods, I would consider getting some 120 Jets to help you on the upper rpm for more power and less popping that these things do when we use pods. Just suggestions, you will be very happy with the performance I think!

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    these Keihen's are picky with pods and like airboxes.some get em to run right,others don't. a lot of guys run other carbs.check out some of the cb forums

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