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Mercruiser oil in carb


84EdH's Avatar
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10-25-10, 10:43 AM   #1  
Mercruiser oil in carb

I have a 1979 228 Mercruiser with a 305 chevy V8 and Rochester Quadrajet. I have been having a problem with idling and stalling all summer. I recently had my carb rebuilt. I tested the rebuilt carb and it ran flawlessly for two hours on the river, without the breather hoses from the valve covers connected to the flame arrestor.

I connected the breather hoses back up to the flame arrestor and took the boat out Sunday and ran it another two hours and it ran perfect. However, thedock is about 1 mile up a no wake zone area, which requires idling and as we idled up this area the engine idle started to get rough and I had to keep bumping the accelerator up in rpm to keep from stalling. Once at the dock it woudnt idle at all. It would stall out, but immediatley start right up with a couple of feeds from the accelerator pump. but would not idle. I removed the flame arrestor and it still would not idle. I noticed a thin film of clear oil all over the carb, both inside and around the edges of the carb where the flame arrestor sits.

It seems oil is being dumped into the carb from the breather hoses and gumming up the idle jets/system. Is this possible? This engine has no pcv system.....just hoses pushed into grommets on the top of both valve covers.

sorry for the long post.....any help appreciated

Ed

 
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10-25-10, 08:08 PM   #2  
Does it smoke at start up? I'm thinking valve seals are going bad.

 
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10-26-10, 03:31 AM   #3  
I dont see smoke at start up from the exhaust. I did a compression check last eve and had pressures from 145 to 135 on all but one cylinder which showed 120lbs. This low cylinder stayed the same with oil down the spark plug hole. Both vent hose sides seem to blow smoke about same running at about 3200 rpm. you dont see much smoke at idle through these vent hoses.

 
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10-26-10, 03:45 AM   #4  
Are the vent tubes loaded with dripping oil? Even so, it takes quite a bit of oil to stall my 350's when I fog them for the winter.

Since it has only four hours on it, I'd suspect a vacuum leak has developed at the new gasket, or gasket seal is interfering with the idle mix.

 
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10-27-10, 08:40 AM   #5  
yes. the tubes are pretty oily and you can see oil on the outside of the carb (that ran down from the flame arrestor and on the top of the carb around the accelerator pump etc.

I didnt really think about fogging the engine....that is a lot of oil and it seems to clear out pretty quick in spring.

I doubt a new vacuum leak. I have been too careful and it seems to run strong as soon as you pump the throttle a couple of times.

 
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10-28-10, 08:20 PM   #6  
Valve seals wouldn't show up on a compression test but the one low cyl not coming up with oil in the cyl would indicate a valve problem. Valve guides could also cause this.

 
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10-28-10, 09:47 PM   #7  
well it seems at least a valve job is in order, which is not too surprising for the age of this engine.

thanks for your help

Ed

 
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