Gas smell 30-60 min after engines secured

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bigralph
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Gas smell 30-60 min after engines secured

Post by bigralph »

I posted a little about this in my moving thread(Need a little personal advice). My 1990 F32 Twin Crusader 350 has an odor about 30-60 minutes after turning the engines off. It is getting better with everything I do, but it isn't gone yet. So far, I discovered the fuel/water separator filters were missing gaskets and replaced them. Next, I noticed the Port Engine fuel filter can was leaking about a drop every 10-20 seconds (after shutdown). Last night, I finally replaced the filters in both enigines. The starboard can was dented badly from a PO using a wrench to tighten the can, but the can was full of gas. The port engine, the one I saw leaking previously, was empty of gas and the gasket was hard and compressed. Someone mentioned an antisiphon valve. I can't find that in my OEM manual and I haven't found a link to show me where that valve should be. Also, I don't think this is the fuel lines as I only smell it after the engines are off. By the way, it was much more than an hour last night before I smelled the gas this time. In fact, this morning, I still wasn't sure that I was smelling gas as much as residual exhaust smells that backed up into my salon, I'm just expecting a gas smell.

Advice? Links?

Thank you.
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BobCT
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Re: Gas smell 30-60 min after engines secured

Post by BobCT »

There's an unwritten rule... if you smell gas, there's a leak. In other words it's not just an exhaust smell after shutdown if it smells like gas. I've tried to talk myself into that a few times and every time there was a leak once I kept looking.

I would say the anti-siphon valve would be low on the list but it is right below the fitting on top of the tank. The copper line if you have the original setup. As I've posted before, it just looks like a fitting until you remove it. Check the filter to fuel pump connection on each end, that's a steel hard line if original.

Bob
1988 10m mid cabin
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Big D
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Re: Gas smell 30-60 min after engines secured

Post by Big D »

Do you have a clear tube going from the fuel pump to the carb? If so, check that line. They can get brittle over time, and if the fuel pump diaphram has failed, it will leak into this tube that may continue to drip after the engine has been shut off. If you don't see this tube, it may be missing. Check to see if there is a port or nipple on the pump where a tube should be hooked up to.
She was a 1969 36 ft wooden beauty with big blue 440s that we'll miss forever.
And thanks to the gang, 2012 Trojan Boater Of The Year
bigralph
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Location: Memphis, TN

Re: Gas smell 30-60 min after engines secured

Post by bigralph »

This is a Crusader 350 CID 270 HP 78279 SN.

I am extraordinarily unhappy, but thankful be alive. I believe I have a crack in my intake manifold port engine, 2 inches below the carburetor, dead center of the manifold. When I was testing my alternator, I just happened to see this seconds after turning the engine off. You can kinda see bubbles in the close picture below; when I first arrived, gas was visible on the outside of the crack and puddled on top of the manifold for a few seconds until it evaporated.

Here is the top view of the manifold, look slightly lower than the flame arrestor and to the right
20140323_130820_resized.jpg
20140323_130820_resized.jpg (184.07 KiB) Viewed 6814 times
Here is a close in view
20140323_130809_resized.jpg
20140323_130809_resized.jpg (195.34 KiB) Viewed 6814 times
I realize this looks really obvious now, but look at the condition of my paint. I didn't see the crack because I've been looking at so many other problems and the paint flakes everywhere, I just didn't notice the 3" crack in the damn manifold. I'm very discouraged.

Anyone have any ideas? Websites show $350-1400, for a new manifold and I've never done anything like this before. I have some mechanical skills, but I've never rebuilt an engine. This just seems daunting. I also saw some stuff today at autozone for filling engine cracks - that sounds like a bad idea, but $21 vice $1400, hell, I have to at least think about it.

Please share thoughts and any advice.
mikeandanne
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Re: Gas smell 30-60 min after engines secured

Post by mikeandanne »

Changing out an intake on a 350 chev is easy,and it is hard to believe that a used intake for that engine could be more than 50 bucks------that being said you have to make sure that is really a crack and not the fuel running down from the carb gasket----clean up that area and watch closely-----one more thing, talk to a local engine machine shop as they may be able to stitch the crack for you---never seen an intake crack like that though-----good luck with it---Mike
Dreamweaver
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Re: Gas smell 30-60 min after engines secured

Post by Dreamweaver »

The choke pull off is a thermal one and has a passage coming up to provide heat,there is really no gas runners there to provide the fuel to the crack to bubble,the spot gets very hot so any spilled fuel would boil and appear to bubble.

I would second the carburetor leak if you pull it off and clean the base you can lay it on a piece of glass to make sure it is not warped,sometimes the heat of a hot engine will cause the fuel to boil or peculate in the carburetor that has no spacer under it ,it may be doing that.The pictures may be playing tricks but where the back carb mounting bolt is looks cracked,to me anyways.

Like already posted the intakes are cheap there are tons of chev 350 ones laying around,that one looks like a very early 70s or late 60s as they switched to electrical choke pull off mid to late 70s,the difference would be if you do remove the intake,between automotive and marine would be or could be brass inserts on the water jackets,if not the early vintage intakes are beefy,you should be able to convert to the updated choke pull off and use a block off plate for the thermal one if it is giving problems.
Richard
1978 F28 Flybridge twin 351s.
bigralph
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Location: Memphis, TN

Re: Gas smell 30-60 min after engines secured

Post by bigralph »

I'm not a gear head. Can somebody please elaborate on the choke pull-off?

The immediate PO that I bought the boat from had the carbs rebuilt for me to buy it. What y'all are saying is that the carb base plate is warped or there is a missing tube - correct? Let's assume the carbs, really the engine, but stick with the carbs for now intimidate me more than most things. When I first looked at the bubbles last Saturday, I thought I saw gas drip splash and bubble on the crack I'm showing in the picture, but then I really studied the cracks and the gas stopped very fast. So, I assumed it was coming from the manifold out, but what I think you're saying is that gas doesn't go in that part of the manifold, so it would have to be dripping out of the carb. Correct?

Ok, next piece of the puzzle, when I started this thread, I was looking for the canister for the fuel filter. I found that and replaced both during this past weekend. The STBD canister, the one that was crushed, was full of gas, just like last time when I found the filter. The PORT canister was empty. So, if I"m adding things up right, the gas is siphoning from the fuel filter canister, that's immediately in front of the fuel pump and in line with the block to the carb and dripping out, I've tightened the rest of the leaks out and not ruling out the antisiphone valves I never found, my problem preventing me from going on the water may be the expensive carb job done last year immediately prior to me buying the boat - 1000 miles away where I have no recourse except to redo something again. Is this correct?

I greatly appreciate everyone's help.
Dreamweaver
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Re: Gas smell 30-60 min after engines secured

Post by Dreamweaver »

In your first picture attached to the manifold,center of carburetor is the blue painted round thing or thermal choke pull off.

How it works is there is a coiled spring that when the engine is cold expands pushing the small blue rod up closing the flap in the carburetor,also called a butterfly,when that flap is closed it forces the engine to draw more fuel then air which is needed on a cold start.I may have the whole expansion contraction thing backwards but you can get the jist of the concept.

As the engine heats up the heat causes the spring to contract,while it does it pulls the rod down slowly to open the flap and allows more air to enter the engine,if it does not open you will see black smoke coming out of the exhaust,known as a sticking choke.

There is a runner or passage inside the intake manifold that carries exhaust and gets very hot,your engine gets to its hottest temp when you first shut it off because all cooling actions have stopped,oil and water circulation.If you have an internal leak in the carb when you first shut down it will suck raw gas in and sit on the top of the inside intake manifold and boil and vaporize or even boil out of around the gasket.You will smell it strong.

Also in the picture the runners that have the 2 4 6 8 firing order feed the fuel air mixture to the valves,the only way you can have fuel boiling out of the crack is if the carburetor is dumping massive amounts of fuel down the exhaust ports.If it was a crack you would hear it as an exhaust leak on start up then it would seal as it warmed up,expansion and contraction.

When the engine is running and hot you would be able to boil water on that spot where the choke pull off is.

What causes the carb to overflow? Inside are floats that control a needle where the fuel lines come in.Take the back off of a household toilet,flush it and watch it fill up,same concept,as the level of gas in the bowl is consumed the floats drop and open the needle allowing more fuel to enter,when the bowl is full the floats rise pushing the needle up shutting off the fuel.

If the little rubber tip on the needle is bad,or the floats are bad or out of adjustment it will allow the pressure or even suck up the fuel in the lines after shut down.If the floats are bad they will adsorb fuel and become to heavy to float and stop the flow of fuel.

So,easy way to check is to bring the engine up to temp,remove the breather after shut down and with a flashlight look down inside the carburetor and see if it is dumping fuel,if you see any at all then you now know why and the fix.They may have rebuilt the carb but not replaced the floats or they are sticking.

To check if the carb is warped or has a bad gasket,while the engine is running spray carburetor cleaner with the supplied little tube placed close to the base,spray around the entire base in little spurts and listen to the engine speed,if it increases then you either have a bad gasket or warped carburetor.

This may or may not be the problem but just another diagnostic step to find it,it does not matter if the manifold is cracked at this point you need to find out the gas aspect first which could also be your smell problem among what others have posted.
Richard
1978 F28 Flybridge twin 351s.
bigralph
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Location: Memphis, TN

Re: Gas smell 30-60 min after engines secured

Post by bigralph »

Here is my weekend update.

I didn't actually do anything, except start it and observe. As you all said, the gas is dripping out of the carb, not coming from inside the block. I can't say much more than that it is dripping down the side of the portion of the carb that the choke pull off is attached too (I'm guessing that would be the choke). The time I saw gas, I ran the engine hard for about 10 minutes (2000 RPM). I turned engine off and the area around the choke pull off was steaming gas. I then started the engine back up and had a friend gun the engine a little, but never actually saw gas form anywhere. The other weird thing is when my friend was gunning the engine, the area around the choke pull-off would steam a wisp occasionally, but I never saw what was putting fluid on the block to steam away.

Going to probably ask a mechanic from the marina to look at this. The carb seems a bit beyond my grasp. I could've handled replacing the intake manifold, I think, but think I'll have a guy that knows a little of what he's doing work on the carb.
Dreamweaver
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Re: Gas smell 30-60 min after engines secured

Post by Dreamweaver »

It sounds like it is dripping gas from the stem that the lower butterflies and choke rod attach to.Not much one can do there unless it is dumping gas as it is a precision fit with no gasket or seals.

If that is the case you may be better upgrading to a newer manifold and carburetor with electric auto choke,lots of the marine ones around on bad engines that are not that expensive.The choke pull off springs are getting hard to find.

For what it is worth you have a very desirable vintage 60s 4 bbl intake on a 87 up truck motor.That intake and carb is worth some nice dollars to an automotive restorer.Do not let anybody tell you it is junk for the scrap if it boils down to that.

You would still need to look at all the other things in the fuel system that others have posted as this could still be a result of,after the engines have been run and you open the fuel tank gas cap,if it has pressure then maybe a plugged vent line even.
Richard
1978 F28 Flybridge twin 351s.
bigralph
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Location: Memphis, TN

Re: Gas smell 30-60 min after engines secured

Post by bigralph »

Update: yesterday, I could not replicate the leak. I tried running for a long time. I tried manipulating the choke and throttle while sitting on the engine and nothing. Wouldn't leak. Called the marina guy that talks me off a cliff occasionally and he suggest I tighten the 4 bolts on carb for the hell of it. I managed to get one full turn on the forward, stbd bolt, which would be closest to the leak. This wasn't a muscle bulging torque the bolt down turn, it was an easy turn with a wrench. In all, I got a whole thread with little resistance. Then I managed to get about a 1/2 to 1/4 turn on all the other 7 bolts (other engine too), but the catch is the engine was a temp at this point, metal would've fully expanded and maybe that expansion somehow made it easier to turn the bolts.

Regardless, i dorked with the engine for about an hour before and after tightening the bolts and could get it to leak. So, i took the boat out and, as posted on my depressing story, managed to get her on a plane 5 or 6 times, each time with more power from the stbd egnine, consistent power from the port engine, the one with the leak.

Maybe I fixed the problem or maybe the problem only surfaces at cold temps outside. Regardless, I didnt' smell too much gas, as in I smelled exhaust and the pipes from the head to the flame arrestor smoked a lot and I could get a gas smell from it, but certainly not a raw gas smell like I had in the past.

I will update this tread with any new info.
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