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  #1   IP: 205.188.116.70
Old 10-17-2010, 06:05 PM
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Engine only runs at full or partial choke

I had a similar problem at the beginning of this season in my late model A4 in my 1970 Morgan which I posted and was helped thru the difficulty. The problem has appeared again. I had found a water leak into the cylinders from the head gasket, I pulled the head, cleaned the ports, cleaned the block, replaced accessable hoses, installed a new thermostat, new gaskets, retorqued the head to the proper settings, checked tightness of the exhaust manifold and carb bolts. The engine starts right up and runs smooth but only with the choke out either full or half way. I adjusted the carb idle screw and adjusted the throttle screw over and over again trying to find the right balance all to no avail. The fuel and the fuel filter were all new this season.

The engine running smoothly under full choke in her slip, is exhausting water in a normal manner. I get good spark to the plugs. I did notice that if I cut back on the choke the engine will "search alittle" but she will rev up strong if I give it throttle, I suspected an air leak but everything is tight and there are no fuel leaks. The oil looks good no appearance of water contamination.

The carb is essentially a new carb from Moyer. I welcome some experienced advice.
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  #2   IP: 24.224.206.117
Old 10-17-2010, 06:56 PM
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Leave her tied to the dock and put the power to her...does she rev up; does she sputter and rev; or does she just not have it...let me know when you get a chance.

Best
Mo
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Old 10-17-2010, 07:12 PM
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If you have to choke it she could be starved for fuel as well..fuel pump could be getting weak. If it will run with choke in try to throttle and see how it is; if you need to keep choke pulled you may have an air leak or starving for fuel. Just because you changed fuel filters this year does no mean they are not fowled; this may very well be your problem. Another thing to look at is the pump itself - mechanical or electric.. and try and determine if you are getting enough fuel; if all this fails look for a small leak in your exhaust manifold that is messing with your mixture...You sound like you have A4 knowledge and capability so doublecheck the obvious, choke connection and it's range of motion; air leaks at carb; hang with it there and more members will jump in here and help you out...some of these guys have the links to all this stuff.

Best
Mo
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  #4   IP: 173.166.26.241
Old 10-17-2010, 08:10 PM
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It sounds like insufficient fuel is getting to the main jet and discharge nozzle. The smallest piece of material in the main jet will cause your symptoms. Most members now have a second, final, so-called "polishing filter" installed just before the carb typically downstream of the fuel pump. The large scale introduction of ethanol and other pollutants into gasoline mean that we have to assume that years of accumulated impurities in fuel tanks and systems will find their way downstream to the carb unless opposed by quality filters. The MM online catalogue lists two types of filters - you need to have both. It is pointless to keep cleaning the carb unless you take steps to keep it that way. Once you have good filters in place, remove the bowl plug and drain the contents into a clean container. You may catch the culprit.
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Old 10-19-2010, 09:36 AM
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Thanks for the tips. Always good to get fresh ideas. I plan on checking the carb today for sediment and will replace the water separator filter also.

The carb is , as I said, essentially new and I had pumped out the old gas and replaced it with fresh 92 octane fuel.

I welcome any other suggestions, this forum is truly a lifesaver.
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  #6   IP: 76.7.149.31
Old 10-19-2010, 11:05 AM
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First I would set the idle mixture to the factory setting. I think it is 1 ˝ turns out. Then remove the flame arrester and visually check for proper choke operation. I would then check for flow to the carb. Disconnect the line at the carb and see if you have good flow. If yes then the pump and filters are OK. Then reattach and open bowl drain and check. If yes the the needle valve is OK. As stated above it takes only a tiny piece of crud to mess things up. How did you check for air leaks? Did you check the carb to manifold connection? Do you have a scavenge tube? Is the connection at the spacer/manifold tight? Keep us posted. Dan S/V Marian Claire
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Old 10-19-2010, 03:17 PM
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Hi guys, well I pulled off the carb and blew thru the various openings and orifices, no blockage. I removed the fuel bowl and there was some sediment particles in the bottom. I remounted the carb and again, she starts right up under full choke.

Leaving her running at full choke, very smoothly initially then after about five minutes begins to decrease rpms, then regain speed, decrease engine speed, then regain rpms again then decrease rpms until she stops, some minor backfiring, just a few "pops". I have never had a backfire situation with this engine in the thirty five years I have owned her. It is actually running worse now then a few days ago when I first experienced the full choke problem.

I had checked the carb screws and the exhaust manifold nuts for tightness earlier.

Truthfully, I am at wits end on this one.
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  #8   IP: 206.230.48.34
Old 10-19-2010, 03:54 PM
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Backfiring -- are you sure it's really backfiring? not just dying loudly? -- makes me think:
  • Misconnected wires (triple check 1-2-4-3, NOT 1-2-3-4!!)
  • Sticking valves
  • Profoundly mistimed
Varying engine speed makes me think:
  • Dying fuel pump
  • Air leak in fuel system
  • Bad condenser
  • A return of your water problem
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  #9   IP: 76.7.149.31
Old 10-19-2010, 04:41 PM
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Sorry if I am repeating but did you check for good fuel flow to the carb? What kind of fuel pump do you have? Did you use WD-40 to check for air leaks? Do you have a primer bulb? Dan S/V Marian Claire
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Old 10-19-2010, 04:58 PM
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One more test before giving up for the day, I retorgued the head after the engine was warm and ran a compression check. 90 pounds across the board for all four cylinders.
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  #11   IP: 205.188.117.69
Old 10-19-2010, 05:18 PM
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Sorry, forgot to mention I had good fuel delivery to the carb from the mechanical pump which was rebuilt within the past few years. I had checked the spark to the plugs on the first day I had a problem.

Hand cranking the engine when the head was off, after cleaning the block
( also cleaning the head of carbon build up ) each valve opened and closed smoothly.

When just running the compression check, the plugs looked good were new
the beginning of this season.

I did not get to spray anything around the exhaust manifold to look for air leaks, I plan to do this tomorrow morning. Needless to say I already have burns working around the hot manifold in the confined space, something you can appreciate.

Thanks guys for taking the time to help me with this, it's becoming like a soao opera.
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Old 10-19-2010, 10:44 PM
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gary...since you have a mechanical pump, you have TWO bowls to check....the fuel PUMP bowl, and the bowl in the carb. There is a drain plug on the bottom of the carb bowl (to confuse you even more, some have two!!), the one on the side of the bowl gives you access to the main jet...this is often a trouble spot...you need to spray some carb cleaner directly in that jet to ensure it is free & clear...sometimes you can successfully flush out a piece of crud by opening that access port (be careful not to lose the fiber washer) and pumping some fuel thru the carb bowl with the mech fuel pump lever....but if it was me, while I had that plug out, I'd spray the heck out of the jet itself. If THAT doesn't do it, then you'll need to crack the carb open and get all the other jets.

I think that was what Dan was alluding to...did you get some carb cleaner in the main jet in the bottom of the carb bowl??

If you do a little digging around the forum, there are lots of diagrams of the carb and pictures of them apart, etc... I had this problem last fall, and it turned out to be a piece of teflon i used in sealing threads upstream in the fuel system.

Ok - where is Jerry with a picture of the carb with the jet showing?

check this - http://www.moyermarine.com/forums/showthread.php?t=3697
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  #13   IP: 205.188.117.69
Old 10-19-2010, 11:35 PM
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Hi, Yes there are two fuel bowls. I did remove the pump bowl and clean it and I removed the plug on the bottom of the carb housing and fuel flowed out into a cup. I then removed the carb completely from the engine to check orifices, excess fuel flowed out of the openings however I did not disassemble the carb.

I plan to attack the problem tomorrow using WD40 looking for air leaks and spray carb cleaner as you suggest.

I appreciate the guidance.
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Old 10-20-2010, 07:26 AM
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Good deal. The carb is not that hard to work on. Getting the halves apart without tearing the gasket takes the most finesse. I assume that your main jet has not been modified into an adjustable. Make sure you clean out the two small holes in the throat. A small piece of SS wire and cleaner works well. As you remove the parts sometimes the gasket/O ring will stay in the body and then come flying out when you blast it with cleaner so have a nice clean area to work on and wear safety glasses. I check, look thru each piece, as I take it off before I clean it. I usually can see the offending crude. Each jet/part should have a nice round opening when held up to a light. Good luck. Dan S/V Marian Claire
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Old 10-20-2010, 08:30 AM
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Quote:
Originally Posted by Marian Claire View Post
Sorry if I am repeating but did you check for good fuel flow to the carb? What kind of fuel pump do you have? Did you use WD-40 to check for air leaks? Do you have a primer bulb? Dan S/V Marian Claire
How do you use WD 40 to check for air leaks? Are you spraying in on
fuel hose connections?

Regards,

Art
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Old 10-20-2010, 08:43 AM
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Art, yes, like that, or also around the flange where the carb & manifold meet, etc.. Especially those of us with the Indigo or Moyer PCV kit, we have double the spots for air to leak in. If there is an air leak, when you spray the WD-40 or similar (carb cleaner works too..any petroleum based spray really) the petroleum temporarily blocks the air leak, ritchens the mixture and the engine surges, helping to pinpoint the air leak.

I personally wouldn't use WD-40 since it is kind of oily & messy..I'd use a carb cleaner that would evaporate quicker with less mess.
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Old 10-20-2010, 08:56 AM
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Quote:
Originally Posted by sastanley View Post
Art, yes, like that, or also around the flange where the carb & manifold meet, etc.. Especially those of us with the Indigo or Moyer PCV kit, we have double the spots for air to leak in. If there is an air leak, when you spray the WD-40 or similar (carb cleaner works too..any petroleum based spray really) the petroleum temporarily blocks the air leak, ritchens the mixture and the engine surges, helping to pinpoint the air leak.

I personally wouldn't use WD-40 since it is kind of oily & messy..I'd use a carb cleaner that would evaporate quicker with less mess.
So it wouldn't bubble like gas grille leak checks do with soapy water?
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Old 10-20-2010, 09:05 AM
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Arrow

Art, I think it's the other way around...gas grill leaks bubble because the LPG is pressurizing the system...once you get passed the carb, the manifold is in vacuum, pulling air & fuel into the cylinders. This is caused by the intake valve being open and the piston moving down in the cylinder creating vacuum. Except for the brief moment when the pistons are at TDC, or BDC (i.e. changing direction) there should always be one cylinder drawing in air at any given time.

This is all my theory & personal understanding, so don't take it for fact.
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Old 10-20-2010, 09:44 AM
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Lightbulb A differant tak!

Gary, it does sound like a possible fuel problem however the poping doesn't seem consistant with the fuel problem. You are getting clean fuel to the carb and the pump is working. You have cleaned the carb and the problem persists. Just for the sate of argument pull the dist cap and give it a good look inside for a carbon trail and or moisture, or just put on the spare if you have one. The ignition sounds ok as you have spark however moisture and or a carbon trail can cause the spark to wander to a lug that the rotor is not pointing at~~~~pop.
As for the surging have you plugged the PCV if you have one?

Dave Neptune
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Old 10-20-2010, 10:03 AM
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Quote:
Originally Posted by sastanley View Post
Art, I think it's the other way around...gas grill leaks bubble because the LPG is pressurizing the system...once you get passed the carb, the manifold is in vacuum, pulling air & fuel into the cylinders. This is caused by the intake valve being open and the piston moving down in the cylinder creating vacuum. Except for the brief moment when the pistons are at TDC, or BDC (i.e. changing direction) there should always be one cylinder drawing in air at any given time.

This is all my theory & personal understanding, so don't take it for fact.
I was thinking of the input side fuel pump etc.
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Old 10-20-2010, 10:24 AM
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Posting this for clarity not to be argumentative:
I thought he said he had not opened the carb to clean it just removed it and shot in some cleaner.
Shawn: I also use carb cleaner. But there has been debate about safety so I suggested the WD-40. My theory is that the spray, which ever one you use, basically gets drawn in and replaces the air. My engine actually bogged down when I was searching for my air leak.
Art: I have only used the spray to check the carb to manifold connection, throttle shaft and the joint between the carb body halves. Dan S/V Marian Claire
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Old 10-20-2010, 11:30 AM
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Dan was correct " the smallest piece of crud can mess things up ". The problem is solved and the engine is running perfectly under normal conditions.

This morning, first I checked for air leaks, there were none so even though I had removed the two year old carb the other day, had clean fuel draining from it and blew air through the orifices I decided to remove it again and disassemble it. I found the problem right away...the very small brass vent fitting was blocked, I removed it and cleaned it with a paper clip. Reassembled the carb, refitted it to the engine and started her up.

The engine is running like new.

Initially, should I have just taken the carb off right away and disassembled it? Well I'm from the school of check the easy things first advancing step by step. However, since I went to the trouble to remove the carb the other day and seeing clean fuel being delivered I suspected an air leak "somewhere", I didn't take that next step and just take the carb apart. My big fear was an internal air leak at the exhaust manifold gasket, which would have involved partial disassembly of the exhaust system just to get the manifold off.
A project I wasn't looking forward to.

I only offer this lengthy explanation because maybe it will help the next person. I want to thank you all for your input.
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