FH641V-AS21...been fighting a misfire since last season

Discussion in 'Mechanic and Repair' started by mynewride, Mar 23, 2014.

  1. mynewride

    mynewride LawnSite Member
    Posts: 11

    I have a gravely pm148z. It has the kaw FH641V-AS21 engine on it. Last year it started missing after it had been running for a little while. Come to find out Gravely used the wrong fuel lines in the tanks. They melted and somehow made it past the fuel filter into my carb clogging it. I replaced the tank pick up lines and pickups as well as cleaned the tanks thoroughly. I disassembled the carb and cleaned it thoroughly as well. The mower had never run better. It ran like good for a few weeks, then all of a sudden it started missing again. It would miss under load, but sounded much worse with the deck disengaged. I cleaned the carb good and it seemed to help. I cleaned the carb several times at the end of last season. It seemed to be less effective as I ended the season. I even replaced one of the coils that I thought was missing once once the engine was hot.

    Now this season I roll it out and clean the carb, change the oil, fuel filter, and checked the air filter. This thing misfires like crazy on high idle. sounds like my hayabusa when I slam into the rev limiter. I did a little research on here and found the pilot air screws covered by a little cap. From the factory the right cylinder was turned all the way in. The left cylinder was turned out 1/2 turn. These seem way off to me. Next I found that one of the main jets is not labeled. the other is marked like 114. The pilot jets are labeled 44 and 46.

    According to Kaw service manual the pilot jets are correct. However it says that the pilot air screws should be turned out like 1.5 turns and 2.5 turns. Next It says that the mains should be a 122 on the left and a 128 on the right. If I look it up on the online microfiche it shows that they should be both 114. I think the microfiche also shows the pilot jets different. What jets should I be using? Also when I turn the pilot airscrews out to the factory specs the mower will backfire bigtime when I start it.

    Something interesting is that when I engage the deck to put a load on it the engine seems to quit missing. I have no grass to test it on as of yet.

    I would pay someone to tell me what is wrong. Im sorry for the book, but I just wanted to give as much info as possible. I have talked to several local shops and the mechanics have no idea. How can i pay somebody 75 per hour if they have no idea where to start?

    It is so frustrating. Engine has 2000 hrs on it.

    Please please please help.
    Im desperate. Hell I will send money via paypal to the person who helps me figure out my gremlin.
     
  2. mynewride

    mynewride LawnSite Member
    Posts: 11


    Anybody have an idea?
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  3. jeannewyatt

    jeannewyatt LawnSite Member
    Posts: 85

    Try checking the valves or maybe a bent pushrod.
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  4. larryinalabama

    larryinalabama LawnSite Fanatic
    Posts: 16,253

    All my FH Kawasaki engines have had chronic coil failures, all of them interminate.
     
  5. herler

    herler LawnSite Fanatic
    Posts: 5,145

    You're just going to have to eliminate some of these possible causes right out, and by that I mean drop in a brand new carburetor, don't forget to replace the gaskets as well which... You say you cleaned the old one, by this I assume you removed it, see here we go again... Did you replace the gaskets?

    I have learned over the years, most ANYTIME a carburetor comes off it is usually best to replace the gaskets and the fuel lines along with it. Granted, on some machines the fuel lines don't require carburetor removal so then it's not such a big deal with that part.

    By gasket set I mean the gasket(s) that go between the carburetor and the engine's intake port, sometimes there's more than one (such as if there's a spacer or a manifold of some sort), on that note I dare say the intake manifold's likely all right, assuming it's the bolt down kind.

    If these gaskets are not replaced, there's a fair to good chance re-using the old gaskets results in an air leak.

    If I had time to play around with it I'd likely order up TWO gasket sets for the carburetor, when they come in replace the old set with one of the new... Then if that doesn't fix the problem, order up a new carburetor and replace that (and I have a spare set of gaskets if needed thou in this case it would probably be all right to re-use the replaced ones).

    If I don't have the time, I would order up a carburetor and the gasket set, replace the whole kit and kaboodle.
    Which, that might be the way to go anyway, replace the whole thing, carburetor and gasket(s).
    That way we have eliminated this as one of the possible causes, assuming the fuel lines are still less than one year old.
     
    Last edited: Mar 27, 2014
  6. mynewride

    mynewride LawnSite Member
    Posts: 11

    Thank you. I will check them
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  7. mynewride

    mynewride LawnSite Member
    Posts: 11

    I can replace the other one.
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  8. mynewride

    mynewride LawnSite Member
    Posts: 11

    Gaskets have about 10 hours on them.
    Something else to note is that I get a lot of blow by out of the breather. I have pulled it out of the carb and have it vented to free air as the oil was plugging the lower air jets. No idea why the oil is coming out of the breather. Could the furl pump cause this?

    Fuel lines are all new. There is little in the carb to wear out. A new carb is 300. I can replace the entire engine for a grand or so.

    So I guess I will replace the other coil and check the push rods. I will also replace the gaskets and owing in carb.
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  9. mynewride

    mynewride LawnSite Member
    Posts: 11

    So is the carb supposed to have 4 bolts or 2?

    What are the main jets and pilot jets supposed to be? They list different ones in the service manual and on the microfiche. That's not counting the ones for different elevations. Also the ones in my carb do not match up to either the manual or the microfiche. The pilot jets are the correct size. 44 right and 46 left. I think the mains were both 114. The service manual calls for a 122 left and 128 right.
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  10. mynewride

    mynewride LawnSite Member
    Posts: 11

    So far I have replaced both coils, plugs, all fuel lines, in tank pick ups, carb has been removed, disassembled, cleaned and replaced with NEW gaskets. The engine runs great for about 15 min then it starts to misfire on high idle. It does not seem to care now whether or not it is under load. it sounds absolutely horrible on high idle with no load. The heads are free and clear of debris.


    Does anybody know of a good replacement for a FH641V-AS21?
     

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