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Engine Problem

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drbill
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Joined: Mon Oct 31, 2005 1:04 pm
Location: Redmond, WA

Engine Problem

Post by drbill » Mon Aug 03, 2009 3:28 pm

Greetings all. The MBL engine in my 1951 sportsman sedan has been virtually trouble-free since I acquired her in 1997. Every winter I shoot preservative oil into the carburetor and engine cylinders and treat a full gas tank. This system has served me and the engine well. Plus cleaning and periodically replacing the plugs.

This summer I started the engine on the hose as usual before dropping her in the lake. Starting was facilitated with a shot of starting fluid, and she seemed to run as usual; including idling as usual. On launch she was harder to get started. The priming pump ran for quite awhile. After the engine started (starter fluid again)), she ran rather rough at first but smoothed out at higher rpm, then performed as usual at top speed. I ran her for ten minutes or so at variable speeds, then went top the dock. When I throttled down the engine killed, and he fuel pump was running.

Since then she has been hard to start, the fuel pump runs forever, and when I do get her started she runs well only at higher throttle than would allow shift into forward, and kills the second I try to reduce the rpm to idle speed. I

It would seem unlikely to be a problem with spark, and it seems to me that the engine is not getting fuel. A clogged fuel filter comes to mind, although in the past my experience is that when the fuel filter is the problem it starves more as the rpm increase. Any ideas? Thanks.
Bill

Niqjh
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Post by Niqjh » Tue Aug 04, 2009 6:06 pm

Could be a vacuum leak/intake leak?

drbill
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Joined: Mon Oct 31, 2005 1:04 pm
Location: Redmond, WA

Post by drbill » Tue Aug 04, 2009 8:20 pm

It would seem unlikely, as it runs a all speeds except idle. I have about decided it is a dirty low-speed idle jet, and will try carb cleaner and removing it externally if possible. If no go will take the carb off and clean it. Been there, done that and had no parts left over. Thanks for the thought
Bill

jahearne
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Post by jahearne » Thu Aug 06, 2009 12:41 am

Check your plugs; they might give you a clue.

My guess would be a bad needle/seat causing the float level to be too high fouling out during idle, but running high rpm burns enough fuel not to foul.

Second guess perhaps the fuel pump is too weak; you can place a vacuum/pressure gauge between pump and carb in a tee to see how many pounds its pushing. No... you're running good at high rpm.

Other than that, bad fuel, weak octane or ethanol ate up some rubber components...


Good luck,
JOhn
John & Wendy

Niqjh
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Post by Niqjh » Sat Aug 08, 2009 11:04 pm

Let us know what you find out. I proposed vacuum/air leak as thats the only thing I have encountered on a vehicle that made an engine not idle, but run seemingly
fine under high throttle or load. I had a Firebird with an OHC 6 that when I had headers installed, the exhaust shop neglected to put bolts back in where the old exh manifold bolted to the intake under the carb.
So I had 4 huge holes in my intake, but you couldnt see them without removing the carb, which I did, thinking it needed serious re-jetting after the tube header install. The thing would not idle, but ran as long as you kept mashing the throttle. Seems like any ignition or fuel problems would manifest themselves in the reverse manner, ie idle ok but not run under load?

drbill
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Joined: Mon Oct 31, 2005 1:04 pm
Location: Redmond, WA

Post by drbill » Mon Aug 10, 2009 2:29 pm

Thanks to those who have responded to my plea for help. Yesterday I convinced a mechanic friend to give me a hand, as I am not quite as flexible as I used to be in close quarters. We first hooked an outboard motor fuel tank to the carburator, and I started the engine while he pumped the bulb. The engine took right off, and ran quite normally (so long as he kept pumping the bulb). Next we took off the canister-type screw-in fuel filter, which was clogged with tiny rubber bits from the deteriorated fuel line. After rsplacing all the hoses and installing the new filter the engine started right up and ran normally. We also suspected a small air leak in a hose. I am still concerned about the fuel pump. It is electric, and always primed the carbureor and stopped before I stared the engine. Now it keeps on running, though it seems to be improving and one time did stop, which is like old times. I am trying to find a replacement pump. It appears that the comment about rubber parts due to ethanol was right on. Thanks to all. Anybody got a fuel pump?
Bill

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evansjw44
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Concerned

Post by evansjw44 » Mon Aug 10, 2009 4:51 pm

I would think that you might have debris stuck in the float valve in the carb. If so, you are filling the drip bowl in the bottom of the carb air horn with fuel. One back fire and you'll have a big blaze on your hands.

I don't think electric fuel pump have any business on an old style engine that wasn't designed for it. Your insurance underwriter will agree with me.

The whole M K and W family of engines (and Chryslers and Grays etc) did just fine on their mechanical fuel pumps. People only added the electrics when there was something wrong in the fuel system they couldn't figure out. The early 283s ('59 and '60) were delivered from the CC factory with electric fuel pumps but they were retrofitted because of fire risks.


If you found fuel line debris in your filter its likley that your hoses are not suitable for the ehthanol that is in the the fuel we buy today and that's why they shreaded.
Jim Evans

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