73johnson135 crank vacuum test

J

jim dozier

Lieutenant Commander
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Jan 8, 2003
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1,970
Re: 73johnson135 crank vacuum test

As a diagnostic aid, disconnect entirely the linkages to the choke butterfiles, and manually hold all of the butterflies completely closed (I don't know how many carbs you have, you may need a hand) while someone else turns the key. See if there is any improvement. If there is you know the way to go, if not you can say nah, nah I told you so and I'll go home.
 
S

SCO

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Aug 19, 2001
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1,463
Re: 73johnson135 crank vacuum test

Jim, I know that it will work better to force those flappers completely closed(unless the force required to keep the flapper closed during crank would bend a flap as the air under suction may not be denied). I even think I probably dont have enough closing force which might be the entire cause of this poor start problem. I just want to know if it is normal for those flappers to open slightly when cranking. If that is the case, then something else is wrong if I have normal choke flapper closing force and the engine doesn't start right. If Joe Reeves says "no, those flappers should be shut tight even during the crank" then I will know the opening flappers during crank to be the problem that I have. Considering the amount of air sucked in during crank, and the small fuel idle ports, I am not sure that the flaps are meant to be 100% closed during crank. A 3-1/2 inch piston will pull a lot of air.
 
S

SCO

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Re: 73johnson135 crank vacuum test

What do I think?? the same as you Jim and Spark. I am just trying to settle the question.
 
S

SCO

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Re: 73johnson135 crank vacuum test

Dhadley says it should be fully closed during crank. I shall now find out how to make that happen. Problem probably solved. You can see how this can happen can't you, you set up statically, but when you start dynamically, things change. Thank you all. I will dutifully report the result.
 
S

SCO

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Messages
1,463
Re: 73johnson135 crank vacuum test

I taped the choke closed and cranked. Didn't start right away(7+ sec) but I think that was because I did this with the throttle closed. Soon fuel was pouring out of both carbs. When it started, goop was sprayed out the exhaust. I apparently loaded it up. I get one of these tests per day. I am going to try again today with choke taped shut and neutral throttle pulled up to 1/2.
 
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