I purchased a boat late last summer with twin Volvo Penta 320's and SX single prop drives. The boat has a stalling issue when returning the throttles to idle, if not done slowly. After haulout for the season, I noticed the exhaust bellows are not connected to the outdrives, leaving a gap of a couple inches. Could this be the source of my stalling issues?
Exhaust bellows
- Thread starter woodshoes
- Start date
Let me make a remark from a MerC Alpha owner's perspective: MerC usually has an Exhaust BELLOWS, and it connects from the Transom Assembly to the Outdrive. When the Drive is in Trailer position, both ends are connected. But MerC also offers an Exhaust TUBE, which connects only at the Transom end. In Trailer, a GAP will show.
So... does Volvo Penta do the same thing? If you're seeing the gap with the drives RAISED, could be it has Tubes and not Bellows.
That said, I don't think exhaust bellows or tubes are behind your stalling problem. The MerC Alpha has a cutout switch to help get the drive out of gear going to Neutral. If you had those drives, I'd say look for a sticky Lower Shift Cable. The one from the engine down to the inner transom assembly, but to my knowledge no VP uses the Switch.
It's not a good idea to back any I/O down hard. Risks forcing water up the exhaust to the engine. VP and MerC both had "Shutters" in the top of the Y-Pipe to offer some protection against that. Same idea as the rubber flaps you see over some inboard exhausts at the transom. VP came out recommending removing the Shutters. MerC still wants them in place and I always replace them. I towed a disabled bowrider with a VP that seemed to be waterlogged. They had anchored from both ends with the stern toward a light chop and a lot of boat traffic. My thought is that water was forced in through the exhaust. Leave Shutters out if you want, but please don't back hard or anchor stern to the weather.
So... does Volvo Penta do the same thing? If you're seeing the gap with the drives RAISED, could be it has Tubes and not Bellows.
That said, I don't think exhaust bellows or tubes are behind your stalling problem. The MerC Alpha has a cutout switch to help get the drive out of gear going to Neutral. If you had those drives, I'd say look for a sticky Lower Shift Cable. The one from the engine down to the inner transom assembly, but to my knowledge no VP uses the Switch.
It's not a good idea to back any I/O down hard. Risks forcing water up the exhaust to the engine. VP and MerC both had "Shutters" in the top of the Y-Pipe to offer some protection against that. Same idea as the rubber flaps you see over some inboard exhausts at the transom. VP came out recommending removing the Shutters. MerC still wants them in place and I always replace them. I towed a disabled bowrider with a VP that seemed to be waterlogged. They had anchored from both ends with the stern toward a light chop and a lot of boat traffic. My thought is that water was forced in through the exhaust. Leave Shutters out if you want, but please don't back hard or anchor stern to the weather.
Thanks for the input. When the drives are down completely, there remains a two inch gap from the end of the rubber tube to the outdrive. The stalling can be coming off plane to an idle or even say from 1000 RPM's to idle. I just thought it is coincidental not to have bellows connecting to the drive and stalling. The engines start hard when warm and sometimes opening the throttles are necessary to get them started. The flame arrestors were very dirty and I replaced the plugs but has not cured it.
Is there rubber "bellows" material on the drive, probably with a clamp, as well as on the transom assembly? If so I'd be certain it was failed exhaust bellows. Of course somebody could have removed a stub from one end and left the rest on the other. Surf around and see if you can find a parts diagram. That'll tell you. Are these carbureted engines or some form of electronic fuel injection?
There is nothing on the outdrive, nothing pleated like bellows, just a short stub on the transom fixture. The engines are throttle body FI. I may have to call in the dealer in the spring, almost had a collision with another boat in a congested river when they stalled.
Sounds like you have Exhaust Tubes. Please post your model designation and somebody here can take a look.
If it's EFI, it might be TBI/Throttle Body Injection (two injectors in a fixture that looks like a carburetor, right below the flame arrestor), or MPI/Multi Port Injection (four, six or eight individual injectors, one per cylinder). In either event, it'll have an IAC/Idle Air Control Valve. On our boat, GM 5.7L TBI, the IAC looks like this
The cavity on the left is for the electrical connector. The mounting flange is two screws, and all to the right of the flange is all in the throttle body. On EFI engines, the throttle body plates close completely at idle. The ECM tells the IAC to run its pintle (the plunger on the right in the pic) in and out to provide the right amount of air to keep the engine running at the idle speed programmed into the ECM. You can see where IAC problems would disturb your idle. The IAC passage into the TB can get restricted or plugged. Throttle Body Cleaner with a spray wand can clear that. Some mechanics clean the IAC itself. Many more clean the passage but replace the IAC. First IAC I bought for our MerC carried a Sierra number and cost $60. I just bought another one that cross-referenced to Standard Motor Parts for $20.
If it's EFI, it might be TBI/Throttle Body Injection (two injectors in a fixture that looks like a carburetor, right below the flame arrestor), or MPI/Multi Port Injection (four, six or eight individual injectors, one per cylinder). In either event, it'll have an IAC/Idle Air Control Valve. On our boat, GM 5.7L TBI, the IAC looks like this
The cavity on the left is for the electrical connector. The mounting flange is two screws, and all to the right of the flange is all in the throttle body. On EFI engines, the throttle body plates close completely at idle. The ECM tells the IAC to run its pintle (the plunger on the right in the pic) in and out to provide the right amount of air to keep the engine running at the idle speed programmed into the ECM. You can see where IAC problems would disturb your idle. The IAC passage into the TB can get restricted or plugged. Throttle Body Cleaner with a spray wand can clear that. Some mechanics clean the IAC itself. Many more clean the passage but replace the IAC. First IAC I bought for our MerC carried a Sierra number and cost $60. I just bought another one that cross-referenced to Standard Motor Parts for $20.
Heh! It just tickles me what they charge for a 'marine' component and what some people insist on paying.
The IAC (Idle air control) and the TPS (Throttle Position Sensor) would be things that, if not working right, would cause your problems.
The IAC (Idle air control) and the TPS (Throttle Position Sensor) would be things that, if not working right, would cause your problems.