myoldboat2
Petty Officer 1st Class
- Joined
- Jun 3, 2007
- Messages
- 303
1974 Mercruiser 140 s/n 388xxxx
Mercruiser "Late Model I" Stern Drive s/n 390xxxx
Rochester 2-barrel carb with choke with heat tube from rocker cover
Summary: Choke works right until engine fully warm, then choke plate ends up tightly closed with a lot of tension on the choke coil.
Details:
Had my engine out and back in to replace coupler. Used carb cleaner to clean up the linkages but otherwise didn't touch the carb. Changed starter and plugs while engine was out. Back together and tested fine on muffs.
As usual started great cold with three pumps and cracking the throttle. Warm it up and go--ran great. After about an hour, when I would shut down the motor (kids waterskiing) it became hard to start. I had to give it more and more throttle while starting to get it to fire. Also, when it would finally fire, it wouldn't start right up like it normally does--it would sort of slowly build up the rpms, running kind of rough, then smooth out once up to rpm (in neutral). Then it ran great at idle, acceleration and at WOT. Engine gauge temp all day was around 135 to 140 degF.
Eventually it bogged down at idle and slowly died. Then it wouldn't start. Pulled the flame arrestor to find the choke plate CLOSED with the engine fully warm. Pushed on the choke plate--very high tension on the coil spring. Disassembled the choke, found the choke plate a little sticky in the closed position, lubed up the linkages well and put the choke back together with a lean setting. Ran the rest of the day but hard to start.
The next morning, pulled the plugs--they were still wet with gas from the flooded condition the day before. With engine cold, set choke per the manual. The coil spring hook to the right of the lever tab, then rotated CCW to lightly close. Started but again slowly went up to rpm; unusual. Watched the choke plate open up in a minute or two as the engine warmed. Ran better that day but still hard to start when fully warm, after an hour or more. Pulled the flame arrestor and AGAIN the choke plate was tightly CLOSED with a warm engine. Loosened the three screws holding the choke cover and it SPUN clockwise to relieve the tension.
1. Is this a choke problem? I noticed something in a manual that if the carb isn't set up correctly, the idle mixture screws can be ineffective (mine don't seem as effective as they should be), and the choke may not work right. My idle speed screw is turned almost all the way in to get the book idle of 650-700 rpm. Max RPM at WOT is 4600, top of the spec. I had the carb rebuilt 2 years ago and set the idle mixture screws and then the idle speed, but I didn't go through the whole carb set up procedure in the manual, so I wonder if something is set wrong. The engine ran GREAT for those 2 years.
2. If the choke is closed when cold, then opens correctly, why would it end up closed tightly with lots of coil spring tension when the engine got fully warmed? That has me stumped.
If the choke coil is suspected, the choke cover/coil is Mercruiser p/n 1397-2648 and is listed as no longer available--where would I get one if that's the right thing to try?
Thanks in advance.
Mercruiser "Late Model I" Stern Drive s/n 390xxxx
Rochester 2-barrel carb with choke with heat tube from rocker cover
Summary: Choke works right until engine fully warm, then choke plate ends up tightly closed with a lot of tension on the choke coil.
Details:
Had my engine out and back in to replace coupler. Used carb cleaner to clean up the linkages but otherwise didn't touch the carb. Changed starter and plugs while engine was out. Back together and tested fine on muffs.
As usual started great cold with three pumps and cracking the throttle. Warm it up and go--ran great. After about an hour, when I would shut down the motor (kids waterskiing) it became hard to start. I had to give it more and more throttle while starting to get it to fire. Also, when it would finally fire, it wouldn't start right up like it normally does--it would sort of slowly build up the rpms, running kind of rough, then smooth out once up to rpm (in neutral). Then it ran great at idle, acceleration and at WOT. Engine gauge temp all day was around 135 to 140 degF.
Eventually it bogged down at idle and slowly died. Then it wouldn't start. Pulled the flame arrestor to find the choke plate CLOSED with the engine fully warm. Pushed on the choke plate--very high tension on the coil spring. Disassembled the choke, found the choke plate a little sticky in the closed position, lubed up the linkages well and put the choke back together with a lean setting. Ran the rest of the day but hard to start.
The next morning, pulled the plugs--they were still wet with gas from the flooded condition the day before. With engine cold, set choke per the manual. The coil spring hook to the right of the lever tab, then rotated CCW to lightly close. Started but again slowly went up to rpm; unusual. Watched the choke plate open up in a minute or two as the engine warmed. Ran better that day but still hard to start when fully warm, after an hour or more. Pulled the flame arrestor and AGAIN the choke plate was tightly CLOSED with a warm engine. Loosened the three screws holding the choke cover and it SPUN clockwise to relieve the tension.
1. Is this a choke problem? I noticed something in a manual that if the carb isn't set up correctly, the idle mixture screws can be ineffective (mine don't seem as effective as they should be), and the choke may not work right. My idle speed screw is turned almost all the way in to get the book idle of 650-700 rpm. Max RPM at WOT is 4600, top of the spec. I had the carb rebuilt 2 years ago and set the idle mixture screws and then the idle speed, but I didn't go through the whole carb set up procedure in the manual, so I wonder if something is set wrong. The engine ran GREAT for those 2 years.
2. If the choke is closed when cold, then opens correctly, why would it end up closed tightly with lots of coil spring tension when the engine got fully warmed? That has me stumped.
If the choke coil is suspected, the choke cover/coil is Mercruiser p/n 1397-2648 and is listed as no longer available--where would I get one if that's the right thing to try?
Thanks in advance.
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