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#1
IP: 152.163.100.136
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Runs only on full choke
I have an early model A4 with a Zenith 61 carburetor. The engine wasn't started for over a year, but it now starts and runs good when the throttle is set about 1/4 open and at full choke. When I release the choke, though, the engine thottles down and dies. It remains running only if I keep it at full choke. It restarts easily when choked, but still needs full choke to keep running.
The idle mixture is set at one turn off of its seat, and the main jet adjust is set at two turns off of its seat. Can anyone help me? |
#2
IP: 38.118.55.154
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Whenever an engine requires full or partial choke to continue running, it's virtually always the case that there is a restriction somewhere within the carburetor, in most cases within the main jet itself.
Don |
#3
IP: 64.12.116.134
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Runs only on full choke
Don Moyer:
While working on my Zenith 61 carburetor, I stripped the screwdriver slot in the main jet in which the main jet adjustment needle seats, and cannot remove the main jet to do a thorough cleaning of the main jet passage. I have been able to remove and clean, with a wire, the main discharge nozzle. I can insert a wire through the main jet and blow through it, but can you recommend a drill bit size to dress up the main jet orifice, which might help the needle to seat better? Last edited by BBH; 08-27-2005 at 04:03 PM. |
#4
IP: 38.118.55.154
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BBH,
The diameter of the orifice of the fixed part of the adjustable main jet is .0449". Don |
#5
IP: 152.163.100.134
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Trouble starting
Don Moyer.
As a followup to my previous email on my Zenith 61 carburetor, I am still having difficulty starting my early model Atomic 4. I recently installed a new main jet assembly, but that didn't help. Now the engine won't even start with a full choke. I am now reworking all passages, chambers, and orifices on the carburetor for blockages. I have a few questions. 1. How critical is the built-in fuel scavenge feature of the Zenith 61 for starting (and running) the engine? (It appears that the fuel scavenge feature consists of an immovable small-bore tube that extends down into the deep well in the lower housing, and a mating passage in the upper housing that extends approximately 1-1/2 inches up into the opening through which the throttle shaft extends.) 2. Does the venturi tube in the Zenith 61 require a specific orientation when installed? On page 4-4 of your Service and Overhaul manual, in step 2 of "Reassemble the upper housing as follows," you refer to Fig 7 "for proper relationship between gasket and tube," but I am not sure what the proper relationship is, other than that passgeways should not be covered by the gasket or the venturi should not be installed upside down. Also, in reassembly instructions accompanying exploded views that I have of the Zenith 61, it is stated to position the venturi so that its machined flat is towards the fuel bowl, but my venturi has four machined flats at 90 degrees to each other. I am assuming that any one of the four flats can face towards the fuel bowl, but I can't see how the positioning of the venturi affects the operation of the carburetor. 3. In desparation, can I ship the carburetor to Moyer Marine and have MMI determine if the carburetor is in working order, and can MMI actually test the carburetor on an early-model engine? Last edited by BBH; 10-12-2005 at 01:57 PM. |
#6
IP: 38.118.52.41
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BBH,
The scavenge tube is critical mostly in the sense that it's required by the Coast Guard. I don't believe that the scavenge tube is playing any part in your current difficulties. I agree with your assessment of the orientation of the venturi tube. I have never heard of any requirement to have the flat spots facing any particular direction, and the tube is idiot-proof in terms of which side faces upward. It will only go into the lower housing in one way. All of this, of course, leaves unanswered the question of why your engine will not start. Before sending us your carburetor, I have a couple questions: 1) When you're trying to start (with the choke fully closed), do you see raw fuel puddled in the bottom of the intake throat? 2) When you remove the 7/16" hex-headed pipe plug from the bottom of the float chamber, does fuel run out? Don |
#7
IP: 165.1.210.208
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Full Choke Required to Run After Exhaust Replacement
My A4 in our 1981 C&C 32 will run only with full choke after replacing the exhaust. I’ve read many similar posts and have taken a number of steps. It ran well prior, and I’m cautious to pull things too far apart without a logical path from original issues so I thought I would seek wisdom from the group. Here is the situation. The engine was running well early in the season. In July the exhaust rusted through at the top of the exhaust loop, above where water is injected in. I rebuilt and installed exhaust. It would not start. I had spark so I was suspicious it was water in the cylinders (must have got in when pressure dropped when exhaust split and water was still being injected into exhaust). I removed the plugs, added a bit of engine oil to the cylinders (to avoid rust), and let it dry out. I replaced the sparkplugs with new. It would then run smooth but only with full choke. I realized I had not gapped the sparkplugs, so i gapped them to .35. It then ran very rough, (perhaps some oil left in cylinders). I cleaned the plugs, reinstalled, and it’s now back to running smooth but with full choke only. I’ve cleaned the flame arrestor. Checked that the choke lever opens and closes choke. I’ve adjusted idle adjustment screw opening it up by half a turn - no change. I closed it entirely and tried at 1.5 and 2 turns out. No change. My next step, I suppose, is to clean the carburetor and check the fuel filter (electric fuel pump). My dilemma is that it worked fine, till the exhaust failed. Working backwards from that, everything like water in the cylinders and fouled plugs makes sense. But not the carburetor.
I welcome this groups collective wisdom. |
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