Vibration in 1979 Chrysler140 HP Lower End

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radarmilo

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I have a newly purchased 1979 140 HP Model #1409B9B Serial #2038 and at low RPM (700-1800) there is a noticeable vibration that comes through the hull of the boat. It stops once I've powered up beyond 1800 rpm. The gear oil is freshly replaced and has remained clean. The prop has a couple noticeable nicks on each of the blades and I'm wondering if the vibration can be caused by that. It seems odd that the vibration would stop as I increased my rpm though.

Any help would certainly be appreciated. I have really learned a significant amount about my OB since finding this forum.
 
Frank Acampora

Frank Acampora

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Jan 19, 2007
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Re: Vibration in 1979 Chrysler140 HP Lower End

EDIT: Uhhh! Did you clean or replace the sparkplugs? Fouled plugs may give poor performance at low speeds yet fire quite well at higher RPM.

Normally I do not recommend messing with carbs because this is a fast way to destroy an engine.

However, your problems occur from idle to about 1800 RPM. This is the point (Roughly speaking) where the high speed venturi and jet start functioning. Thus: It is a reasonable assumption that the low speed circuits in your carbs are not functioning correctly.

SO: Remove the carbs, disassemble, and clean them. Reassemble and install, setting the float level correctly and setting the low speed needle as outlined in the sticky at the top of the forum--synchronizing timing and carbs.

No guarantee that this will solve the problem, most Chrysler and Force big engines do have a range of RPM (usually at the transition point between low and high speed) where they simply run rough.
 
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radarmilo

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Re: Vibration in 1979 Chrysler140 HP Lower End

Thanks for the replies

First thing I did after I bought the boat was replace the spark plugs, impeller and ran a couple of tanks of seafoam through the system. Start up and idle improved dramatically after that. I thought I'd keep the carb and lower end rebuild for my winter project. My prop has a nick in all three blades about half the size of a dime right where the blade meets the shaft. I had heard prop damage can cause vibration but I never thought it would be bad at low rpm and go away as you increased your speed. Actually thought it would be the opposite. Unfortunately a pic of the prop won't be available until this weekend when I get back out to the cottage.

I'm thinking as an interim measure I should simply grab a replacement prop now as it's becoming obvious to me that I'm going to need one anyway. I can throw it on this weekend and will update the thread early next week.

Thanks again
 
R

radarmilo

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Re: Vibration in 1979 Chrysler140 HP Lower End

Looks like it was as simple as 2 loose screws on the anode.

Thanks to all
 
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