5.0 Mercruiser stubmles @ low RMP

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djkj6

Recruit
Joined
Jul 18, 2010
Messages
4
Hello all,

We recently purchased an 03 Tahoe 202 with a 5.0 liter Mercruiser MCM engine and the boats runs great except for slow speed. Once you crowd the throttle a bit it acts like it is stumbling and does this for about 4-5 seconds then all of a sudden it cathes up, surges forward and is fine and. It only seems to do this when I am in gear, either direction and runs fine once you get past this point in the throttle. I have been searching this site for two days trying to find some pictures to allow me to understand what everything is called so I can properly communicate but it appears that mercury marine has sucked all of the literature off of the web, "this will affect my next purchase", so forgive me if I am unable to communicate effectivley. At first I thought it was possibly the primerpump/pickup pump on the carb but now that I have looked at the carb a bit I feel like it is more of a spark advance issue, however since I do not have a manual I can't easily determine what parts are what with the electrical system. If you have any recommendations or material to help educate me I would be much abliged. I have found some stuff about the Thunderbolt V ignition system and am digesting that tonight.

Thanks
 
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patrick1010

Cadet
Joined
Jul 13, 2010
Messages
7
Re: 5.0 Mercruiser stubmles @ low RMP

If it has a primer pump it should be on the front of the carb and you could pump it by hand and look down the barrels to see if it is pumping. sounds almost like timing. I would start by putting a timing light on it and checking out distributor. might be a mechanical advanced and it could be gummed up. How many hours on the boat?
 
D

djkj6

Recruit
Joined
Jul 18, 2010
Messages
4
Re: 5.0 Mercruiser stubmles @ low RMP

The only thing in the distributor is a sensor so I was figuring it is electronic advance, as for the primer pumpt I have not unhooked the throttle cable and worked it to see what goes on. I have no idea about the hours on the boat either. I did notice on the sensor in the distributor that there was some rust on the screws that hold the circuit board in place. If I can learn enough about my ignition system I plan to check timing one night this week. I have never run this boat with muffs so I need to learn a little more about all that so I feel comfortable testing.
 
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John_S

Rear Admiral
Joined
Jun 21, 2004
Messages
4,269
Re: 5.0 Mercruiser stubmles @ low RMP

If it hasn't had a tune-up, start there:

Plugs, rotor, dist cap, clean flame arrester, choke operation?, idle mixture, idle speed, timing.

If it still an issue, I'd look more toward a fuel / carb issue.

Get the manuals, read, ask questions, decide if you can do it, buy tools, read, ask questions, preceed.
 
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