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-   -   Shaking like a big block mopar (http://www.mastercraft.com/teamtalk/showthread.php?t=72417)

Czechmate 04-10-2016 06:14 PM

Shaking like a big block mopar
 
I just picked up a 1984 Stars and Stripes and have a diagnostic question: at idle the motor shakes, not really like a worrisome shake, but more like a 454 with a big cam at a red light. The motor sounds good and runs well , I did notice it puff out a little white smoke this morning when I started it up in my driveway. What could the shaking be? Soft mounts? Or maybe a tune? Its a ford 351 with 938 hours.

JimN 04-10-2016 06:32 PM

Quote:

Originally Posted by Czechmate (Post 1231004)
I just picked up a 1984 Stars and Stripes and have a diagnostic question: at idle the motor shakes, not really like a worrisome shake, but more like a 454 with a big cam at a red light. The motor sounds good and runs well , I did notice it puff out a little white smoke this morning when I started it up in my driveway. What could the shaking be? Soft mounts? Or maybe a tune? Its a ford 351 with 938 hours.

It can't run rough AND good of it doesn't have any modifications.

Did you remove the plug wires recently? Re-check the firing order and make sure the plugs, wires, cap & rotor are in good condition. If they're all OK, check for spark on all cylinders using a spark tester, not just a timing light. If that's OK, check the compression/cylinder leakdown.

tph 04-11-2016 03:50 AM

351 idle
 
1 Attachment(s)
It should run like this:

CantRepeat 04-11-2016 07:21 AM

That puff of white smoke at start up is probably valve guide seals starting to leak.

whiskeyriver 04-11-2016 09:04 AM

Sounds like carb issues. Choke partially closed, float level, leaky power valve? I would remove the flame arrestor and make sure the choke butterfly is opening fully. Also after letting it run for a bit switch it off and look down the carb throat for dripping fuel, there should be none.

Czechmate 04-11-2016 02:52 PM

Quote:

Originally Posted by tph (Post 1231108)
It should run like this:

Ill post a video of mine running soon for comparison.

Quote:

Originally Posted by whiskeyriver (Post 1231118)
Sounds like carb issues. Choke partially closed, float level, leaky power valve? I would remove the flame arrestor and make sure the choke butterfly is opening fully. Also after letting it run for a bit switch it off and look down the carb throat for dripping fuel, there should be none.

The last owner did say that the carb floods periodically, but he has been driving this boat this way for years and said he hasn't noticed anything troublesome. I think he may have gotten comfortable with the way it runs, and thus thinks of it as normal.
Ill check the carb out and let you know what I find.

thatsmrmastercraft 04-11-2016 03:14 PM

Quote:

Originally Posted by Czechmate (Post 1231232)
Ill post a video of mine running soon for comparison.



The last owner did say that the carb floods periodically, but he has been driving this boat this way for years and said he hasn't noticed anything troublesome. I think he may have gotten comfortable with the way it runs, and thus thinks of it as normal.
Ill check the carb out and let you know what I find.

Sounds like you may have a needle & seat going. You can also have problems if fine crud id getting through your filter and getting stuck in the needle & seat. If it wants to flood when it's running, if you put it in gear and crack the throttle open for a couple seconds, this will usually wash the crud out so the needle & seat can close properly.

Have you checked for a vacuum leak at the carb and the spacer? When it's idling, spray some carb cleaner around the base of the carb and spacer. If the engine speed increases, you have found your leak.

Have you looked at your spark plugs to see the color? That may show a rich or lean condition and give you something to chase.

If you do need a car rebuild, I would be happy to do it for you. I have done a lot of carbs for members here over the last few years.

Czechmate 04-13-2016 10:34 PM

Quote:

Originally Posted by thatsmrmastercraft (Post 1231245)
Sounds like you may have a needle & seat going. You can also have problems if fine crud id getting through your filter and getting stuck in the needle & seat. If it wants to flood when it's running, if you put it in gear and crack the throttle open for a couple seconds, this will usually wash the crud out so the needle & seat can close properly.

Have you checked for a vacuum leak at the carb and the spacer? When it's idling, spray some carb cleaner around the base of the carb and spacer. If the engine speed increases, you have found your leak.

Have you looked at your spark plugs to see the color? That may show a rich or lean condition and give you something to chase.

If you do need a car rebuild, I would be happy to do it for you. I have done a lot of carbs for members here over the last few years.

So I did a quick run through and everything looked fine. The guy had the rotor and cap, wires, and plugs changed three years ago, and the boat has had minimal use since. I found a local shop who is going to do a more detailed diagnostic, so ill be waiting for those results!

Ive got another question: After reading through the original manual that came with the boat, it states "Unleaded fuel should not be used". So I'm assuming unleaded fuel has been used in this boat for quite some time. I know with older motors the lead helps reduce cam wear correct? Is it really necessary to now add the lead additive available in stores? Or is it fine to keep adding in 93 octane unleaded?

paco_06 04-13-2016 10:43 PM

Quote:

Originally Posted by Czechmate (Post 1232263)
So I did a quick run through and everything looked fine. The guy had the rotor and cap, wires, and plugs changed three years ago, and the boat has had minimal use since. I found a local shop who is going to do a more detailed diagnostic, so ill be waiting for those results!

Ive got another question: After reading through the original manual that came with the boat, it states "Unleaded fuel should not be used". So I'm assuming unleaded fuel has been used in this boat for quite some time. I know with older motors the lead helps reduce cam wear correct? Is it really necessary to now add the lead additive available in stores? Or is it fine to keep adding in 93 octane unleaded?

Yeah, supposedly unleaded will prematurely wear valve seats. Personally I think you're alright. I find it much more important to protect from ethanol. Use an additive to combat it if non ethanol fuel is not readily available.

thatsmrmastercraft 04-13-2016 10:48 PM

Valvoline VR1 20W/50 has the needed additive package containing Zinc to provide the lubricant for the Ford's cam and lifter needs. There are some other oils as well, but this is my oil of choice.


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