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Old     (spencer3840)      Join Date: May 2005       06-03-2005, 10:49 PM Reply   
I went to change my oil today on my 89 MC prostar. I noticed the smell of gas. I just had my carb overhauled and had a issue with the needles getting stuck wide open and dumping way too much gas in. Anyways they fixed the problem and the boat works great now. Why would there be gas in my oil though?
Old    powaman            06-04-2005, 6:38 AM Reply   
Your rings could be in less then the best shape and the gas is leaking by them. Same principle as when you get "Blowby" except the other way around.
Old     (sam8)      Join Date: Dec 2004       06-04-2005, 8:16 AM Reply   

Have you changed the oil since the carb problems were solved? If not, it may be a leftover issue from the needles hanging up. Change the oil now. Fuel rapidly deteriorates oil, hopefully you have not damaged the rings. If you have the carb right and have changed the oil and are still getting fuel contamination, I think I would do a leakdown test..
With Holleys,the most common ways for fuel to get in the oil are through the carb, via leaking improperly set accelerator pumps nozzles,and via the vent tubes in floats improperly adjusted. Since somebody just tweaked the carb, I'd check the float adjustment again.
All you guys out there running Holley Carbs on boats, just info, Holley does offer a spring-loaded needle/seat assembly for most of their carbs. It is commonly called the "off-road" needle and seat, and if you get to a shop that knows Holleys, and give them your Holley List#, they can match you up with the right set up.
This needle and seat assembly and properly set float heights will really improve the performance of the carb in rough/high angle conditions. We ran them for years in multi-carb set-ups on tunnel-ram manifolds in the sand..
Old     (spencer3840)      Join Date: May 2005       06-04-2005, 8:42 AM Reply   
thanks guys, yea I just changed the oil yesterday, I only ran the boat for about 5 minutes before to adjust the new carb. and to get the oil warm enough to change.
what should I look for when looking at my oil to make sure gas still isnt getting in there? Last thing I want to do is damage my engine. I let the oil drain for several hours last night before I put the fresh in. You think I got all the gas out? Should I flush it again. I just want to make sure I don't have any remaining fuel left in the pan.
Old     (sam8)      Join Date: Dec 2004       06-04-2005, 2:09 PM Reply   
You probably did. If there is gas in the oil in any serious amount, you will be able to smell it.
Run the boat on the water, for awhile, watch the oil pressure and stop and take a whiff of the dipstick every now and then. If the carb is right and you are not getting any distinct odor, O.P. is normal, then you should be okay.

There are a number of Oil Analysis Labs out there for the seriously anal among us, like me.
I use Blackstone for regular analysis of the oil in my truck, and you could send them a sample if you are that interested. They have a website..
Old    ag4ever            06-04-2005, 4:41 PM Reply   
I sent a sample in from one of my oil changes. I change mine every year even though I only put like 25 hours on the oil last year. Mine came back with a small trace of gas, and they said it is normal for marine enignes since they run cooler, and don't get the oil hot enough to burn the gas out of it.

Don't know if that is true, but sounds good to me.

That was from Blackstone.

Also I never could smell gas in my oil, but it came back as saying there was some in it.
Old    jdk            06-04-2005, 5:49 PM Reply   
My bet is ......Fuel pump..... when the diaphram leaks, the fuel runs directly into the crank case. Change it, they're cheap too.
Old     (spencer3840)      Join Date: May 2005       06-04-2005, 11:29 PM Reply   
Stupid question but where is the diaphram?
Old    jdk            06-05-2005, 6:04 PM Reply   
Wooops, a little more expensive than I thought they were, for a marine version anyway (an automotive mechanical pump for a 350 GM is about $25). The diaphram is the circular rubber disk between the aluminium top and bottom half's in the picture.

mechanical fuel pump
Old    jdk            06-05-2005, 6:23 PM Reply   
Here's where the pump is on a GM engine. When the diaphram leaks, the fuel flows up and past the plunger finger (black tab on right side of pic.) directly into the oil pan.
Fuel pump installed

(Message edited by jdk on June 05, 2005)

(Message edited by jdk on June 05, 2005)
Old     (spencer3840)      Join Date: May 2005       06-05-2005, 8:11 PM Reply   
so how can I test to be sure its not leaking? In that picture, I have a Ford, looks to be where my water fuel seperator is located, any relation?
Old     (spencer3840)      Join Date: May 2005       06-05-2005, 8:11 PM Reply   
so how can I test to be sure its not leaking? In that picture, I have a Ford, looks to be where my water fuel seperator is located, any relation?
Old    jdk            06-05-2005, 10:01 PM Reply   
Some come apart some don't.
If yours does, go for it. If not just replace it (it's easy to do).
There will be no relation between this problem and the water separator (it has no connection to the crank case).
Old     (spencer3840)      Join Date: May 2005       06-06-2005, 9:31 AM Reply   
I thought all the fuel was routed through the carb?
Old     (sam8)      Join Date: Dec 2004       06-06-2005, 10:48 AM Reply   
In most carbed applications fuel is pulled from the tank up to the engine via a mechanical fuel pump that is driven off of the engine. On chevys, there is a eccentric on the camshaft that drives the pump.

On the 289/302 Fords, the fuel pump is bolted to the left hand side of the engine as viewed when standing in front of it. It is attached to the aluminum cover that covers the timing chain, etc, just forward of where the oil filter screws to the engine. It is held on by two bolts.

The diaphragm in the pump creates a vacuum when the pump works, drawing fuel from the tank, the unit then creates pressure which pumps the fuel to the carb. Most basic mechanical fuel pumps are pre-set to deliver 5-7 PSI to the carbs. High-perf/high volume pumps usually require a seperate pressure regulator to keep the fuel pressure from blowing the needles off the seats in the carb.

Since the pump is driven by the rotation of the engine itself, a portion of it is lubricated by engine oil, and if the diaphragm fails, it can cause fuel to be released into the oiling system. If this happens, since the fuel isn't going to the carb, the engine probably isn't going to run for long or very well without proper fuel supply.
If you are looking at a stock type pump on the Ford it will not be rebuildable; they are pressed together, not bolted together as is the aftermarket one on John K.'s small-block.
If you suspect the fuel pump is leaking, you can either simply replace it, or check it first with a fuel pressure gauge to place in the fuel line just prior to the carb and check the pump's output. If you do that,anything less than 5 PSI and I would be suspecting a problem. Perhaps the pump, or a bad filter or a clogged pickup in the tank.

If you are still getting major fuel contamination after confirming there are no problems with the carb, then start looking at the pump. It is the only other realistic suspect on a carbed engine with a mechanical pump.
Old     (spencer3840)      Join Date: May 2005       06-07-2005, 8:08 PM Reply   
thanks for all the help guys, I ran boat for little bit to make sure I wasnt getting contaminated gas in my oil. After realizing 5 quarts was too much and taking a half quart out it was fine. Boat runs great since we overhauled the carb.


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