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  1. #1
    Newbie
    My Bike(s)
    1980 Kz250
    Posts
    7

    1980 Kz250 won't rev over 4000 rpm

    1980 KZ 250 with a Keihin CV32 carb. Bike won´t rev past 4000 rpm. It gets there and just dies. I have cleaned the carb, adjusted the timing and valves. Everything is clean. The bike idles great but when I throttle it up to 4000 rpm it just dies. The main jet is clean and the bike used to run great. I let it sit for two years, but have since cleaned everything. Is there some passage in the carb I am missing when I cleaned it?

    I just did a test on the carb by putting a vacuum to the engine side and opened the butterfly valve. The piston behaved as expected, it was raising and lowering as I opened and closed the butterfly, and gas was shooting out of the main jet in a fine mist. I have adjusted the float level to the factory reccomendation and there is a new plug. I am completely stumped? Any help is appreciated

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  3. #2
    M-J Lifetime Achievement Award
    My Bike(s)
    '10 Kaw Vulcan 900 Custom
    Location
    Ocala, FL
    Posts
    8,530
    Quote Originally Posted by ryeshelman View Post
    The bike idles great but when I throttle it up to 4000 rpm it just dies.
    If you sneak up on 4K, does it really die or just "flat spot" and won't go any faster ??

    Does it act differently if you do that with a little choke applied ??

    Are you doing this test with a stock air filter in place ??

    Since you have already given the fuel system some attention, I'd now suspect an electrical problem.
    Hows the battery and charging system ?
    Does this model have electronic ignition .......or mechanical points and advance ??
    Don't believe everything that you think.

  4. #3
    Newbie
    My Bike(s)
    1980 Kz250
    Posts
    7
    Whether I sneak up on 4k or go right to it it does the same thing. This is when it is on the center stand and in neutral. It will rev past 4k with the choke, but not consistently and then it stalls. I have the air filter off when I am checking this. I am also using an external battery to jump the bike since keeping the installed battery charged is difficult because I can't ride the bike as is. I checked the charging once it is started by removing the jumper cables and reving the engine and the voltage increases with the rev. I have mechanical points and advance and I have adjusted the timing on them. I adjusted the valves and I noticed there is a bit of oil leaking from the valve cover. Could this possibly cause the problem? Thanks for the help.

  5. #4
    M-J Lifetime Achievement Award
    My Bike(s)
    '10 Kaw Vulcan 900 Custom
    Location
    Ocala, FL
    Posts
    8,530
    Quote Originally Posted by ryeshelman View Post
    It will rev past 4k with the choke, but not consistently and then it stalls. I have the air filter off when I am checking this.

    I am also using an external battery to jump the bike since keeping the installed battery charged is difficult because I can't ride the bike as is. I checked the charging once it is started by removing the jumper cables and reving the engine and the voltage increases with the rev.

    I have mechanical points and advance and I have adjusted the timing on them.
    So many things..........

    First, put the air filter back ON and be sure there are no leaks around the inlets.
    Then let it warm up good before you go rev'ing it.

    Then you need to have a good battery connected ALL THE TIME that it is running.
    The faster it goes, the more electrical energy that the ignition needs. Without a battery, there might not be enough.
    Also running it without a battery can damage the charging system.

    Some of your symptoms sound like fuel starvation.....but others sound like electrical......or timing advance.
    Be sure the mechanical timing advance goes throught the full range of motion without any sticking or "hitches".
    Don't believe everything that you think.

  6. #5
    Newbie
    My Bike(s)
    1980 Kz250
    Posts
    7
    OK, so after some time I have now done most of the things on your list, Easy-Rider. I have the air filter on,, no leaks around the inlets (checked with brake cleaner and no rev), Brand new fully charged battery I checked the timing with a timing light and everything is good. Not sure what you meant by "Be sure the mechanical timing advance goes through the full range of motion without any sticking or "hitches"". The pistons turn smooth and the points open and close smooth if that is what you mean. I talked with a local mechanic who said he had a similar problem and never figured it out himself, he had to send it to a Kawasaki pro. He said there was some part of the carb he was forgetting when he cleaned it. Is there some other "secret passage" in the carb besides the choke/idle path?

  7. #6
    M-J Lifetime Achievement Award
    My Bike(s)
    '10 Kaw Vulcan 900 Custom
    Location
    Ocala, FL
    Posts
    8,530
    Quote Originally Posted by ryeshelman View Post
    I checked the timing with a timing light and everything is good.

    the points open and close smooth if that is what you mean.
    So included in "everything", does the timing advance as the engine speed increases. It should, you know.

    If it has points, there likely is a centrifical, mechanical mechanism under the points mounting plate that causes the plate to turn and advance the timing as the speed increases.

    You should be able to see that timing advance with a timing light.
    It is much greater than the initial BTDC initial setting.

    Sometimes stumbling at high rev's is simply a matter of the float being set wrong and it's starving for fuel.

    Sometimes it HAS to go to the shop.....to find what you may have overlooked and that we can't see.
    Don't believe everything that you think.

  8. #7
    Banned
    My Bike(s)
    Ilene
    Location
    the land of the setting sun
    Posts
    880
    Quote Originally Posted by ryeshelman View Post
    OK, so after some time I have now done most of the things on your list, Easy-Rider. I have the air filter on,, no leaks around the inlets (checked with brake cleaner and no rev), Brand new fully charged battery I checked the timing with a timing light and everything is good. Not sure what you meant by "Be sure the mechanical timing advance goes through the full range of motion without any sticking or "hitches"". The pistons turn smooth and the points open and close smooth if that is what you mean. I talked with a local mechanic who said he had a similar problem and never figured it out himself, he had to send it to a Kawasaki pro. He said there was some part of the carb he was forgetting when he cleaned it. Is there some other "secret passage" in the carb besides the choke/idle path?
    brake cleaner is probably where you went wrong, I recommend a cylinder leakdown and compression test. also make sure your float bowl drain is not plugged.

  9. #8
    Newbie
    My Bike(s)
    1980 Kz250
    Posts
    7
    Ok, I will check the timing advance, I had no idea about that. That could be the issue. The float bowl drain is perfectly clear and works, the compression is fine. After this step and one more carb clean it is off to the shop...do you guys recommend any particular carb clean dip? I have only used compressed air and spray carb cleaner. I am worried that there is some passage that I missed. I have also heard about boiling the carb in vinegar and water. This seems a little sketchy. Any thoughts? Thanks.

  10. #9
    M-J Lifetime Achievement Award
    My Bike(s)
    '10 Kaw Vulcan 900 Custom
    Location
    Ocala, FL
    Posts
    8,530
    Quote Originally Posted by ryeshelman View Post
    After this step and one more carb clean it is off to the shop...do you guys recommend any particular carb clean dip?
    A double dose of a good carb cleaner in the gas tank.
    Gumout and Berrymans B12 are my favorites; in case of a current problem, twice the recommended amount.
    Then it will, of course, take some time running to get things circulating good.

    Fuel delivery problems at high speed often are NOT caused by simple "dirt" or gunk but by some mechanical problem.......like float levels or vacuum slider diaphram trouble, if the carb has that.

    PM sent about other issues.
    Don't believe everything that you think.

  11. #10
    Banned
    My Bike(s)
    Ilene
    Location
    the land of the setting sun
    Posts
    880
    yes, make sure the slide moves also.

  12. #11
    Banned
    My Bike(s)
    Ilene
    Location
    the land of the setting sun
    Posts
    880
    also see if there is a decent muffler bearing in the end of the exhaust, you don't want that to be plugged or missing.

  13. #12
    M-J Lifetime Achievement Award
    My Bike(s)
    '10 Kaw Vulcan 900 Custom
    Location
    Ocala, FL
    Posts
    8,530
    Quote Originally Posted by limitedbyfourkawiby2 View Post
    also see if there is a decent muffler bearing in the end of the exhaust,
    "Muffler bearing" ??????

    You do come up with some good ones.
    Don't believe everything that you think.

  14. #13
    Newbie
    My Bike(s)
    1980 Kz250
    Posts
    7
    Alright, so I went through the carb with a fine tooth comb, and alas I found the smallest pinhole on the diaphragm right where it meets the slide, very hard to see. I had put it up to a real powerful halogen light and it showed up. So, I patched that with plasti dip and it worked great! Drove it around for about an hour last night. There is one little issue still. When I rev it up from idle it boggs down at a range between 3.5 and 4k RPMs. This happens when I am driving it and I shift gears too. I didn't have much time to mess with it last night since it got dark and extremely cold. Any thoughts. It is only in the 3.5-4k RPM range. Everywhere else it runs VERY smooth. It idles great and starts right up. Any thoughts?

    Thanks.

  15. #14
    M-J Lifetime Achievement Award
    My Bike(s)
    '10 Kaw Vulcan 900 Custom
    Location
    Ocala, FL
    Posts
    8,530
    Quote Originally Posted by ryeshelman View Post
    So, I patched that with plasti dip and it worked great! It is only in the 3.5-4k RPM range.
    My guess is that you still have slider trouble; now it is working but not quite right.
    And if it developed one hole, another is probably not far behind.
    If your repair made it too stiff, it won't work right either.
    I think you need new diaphrams/needles.
    Does that needle have multiple grooves at the top ? If so, it is adjustable, somewhat.
    And is the engine fully warm (hot) when you notice this flat spot ??
    Don't believe everything that you think.

  16. #15
    Newbie
    My Bike(s)
    1980 Kz250
    Posts
    7
    The needle does not have multiple grooves, and it doesn't seem like there is any way to adjust it. The flat spot occurs when it is hot and cold. I am trying to avoid buying a new diaphragm and slide because of the price, but if that is what I have to do then so be it. I applied a VERY thin coat of plasti dip, so hopefully it didn't make things too thick but it does seem like that might be the culprit. Is 3-4k RPM around the engine speed when the carb will switch from the idle jet to the main jets, triggering the diaphragm?


 

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