Hi Everyone,
It is a long weekend up here in Ontario CAN, so no help around the marina and we are planning to start a trip early tomorrow in our fairly new to us Bayliner Avanti 2955, she twin OMC GM 305 Cobras.
I have worked around engines for almost 50 yrs but I don't have much hair left to pull out, both engines are sick, way down on power, only pulling just over 3000rpm now and now find that the quadrajet secondary air valves are not opening.
I should probably start from the beginning, but it may be a long story.
There have been many posts with similar problems, think I have read them all.. so sorry to be repeating.
We no some history of the boat, there had been a problem with motors stalling and both carbs had been cleaned and rebuilt, but not many hours put on in last 5yrs..
Initial trials, mainly for me to learn how to handle a power boat showed that we still had a stalling problem, with the port motor stalling at idle in gear, usually only when docking!! When it was being restarted the voltage drop, presumably, killed the stbd motor..
Both port and stbd shared the same starting battery and there was only one power line to the ignition switches, I have now completely isolated the motors, added anothe feed to the stbd ignition switch, a second battery and Blue Sea ACRs between them and the house batt., whicvh has eliminated that issue.
The stalling of the port engine was found to be because the idle mixture was way to lean, restricting the air flow to the primary throats caused the idle speed to increase, adjusting the idle mixture screws out worked and the idle was faily steady at 600rpm with no more stalling..
We have not made any long runs yet, but a couple of weeks ago both motors would run fine at around 3500rpm, at that point I was not at the wheel and we never checked for WOT performance..
I had a little dwell / tach meter, used it to adjust the idle speed and found the dwell high on both, gap small. Started on the port motor, went to check/adust, they did not look good so replaced points, condenser, rotor and cap, set timing for between 8 & 10 degrees before tdc.
Started and idled fine..
The stbd cap looked newer so it was not replaced, got into major problems because the 2nd Sierra kit had a rotor 180 degs different than the original!! Once exchanged started and idled fine.
When test run the port would only pull 3100rpm, the stbd sounded much stronger and pulled around 4000rpm.
Anti syphon valve was clean as a whistle and no resistance without it when blowing air back into the tank. Fuel / water seperator looked new, but was replaced
Dismantled and cleaned, but it was already v clean, the port carb, no difference when tested, still on just over 3000rpm on port side.
This morning I switched the carbs over and did not get the result I would have liked, the port still only went upto just over 3000 and the stbd did not sound as powerfull and only went up to 3300 or so.
Opened the hatch and took off the flame arrestors to see what was happening, the air valves were not opening on either motor, the vacuum had released and when I "helped" them to open the not changed but the motors did not pick up any rpm, hopefully for just a few seconds the lean condition did not hurt anything..
So what have I done????
Apologies for such a long winded post, but felt it important to try and share as much as possible
Still with some hope...
Regards, Trevor T in Owen Sound, ON
It is a long weekend up here in Ontario CAN, so no help around the marina and we are planning to start a trip early tomorrow in our fairly new to us Bayliner Avanti 2955, she twin OMC GM 305 Cobras.
I have worked around engines for almost 50 yrs but I don't have much hair left to pull out, both engines are sick, way down on power, only pulling just over 3000rpm now and now find that the quadrajet secondary air valves are not opening.
I should probably start from the beginning, but it may be a long story.
There have been many posts with similar problems, think I have read them all.. so sorry to be repeating.
We no some history of the boat, there had been a problem with motors stalling and both carbs had been cleaned and rebuilt, but not many hours put on in last 5yrs..
Initial trials, mainly for me to learn how to handle a power boat showed that we still had a stalling problem, with the port motor stalling at idle in gear, usually only when docking!! When it was being restarted the voltage drop, presumably, killed the stbd motor..
Both port and stbd shared the same starting battery and there was only one power line to the ignition switches, I have now completely isolated the motors, added anothe feed to the stbd ignition switch, a second battery and Blue Sea ACRs between them and the house batt., whicvh has eliminated that issue.
The stalling of the port engine was found to be because the idle mixture was way to lean, restricting the air flow to the primary throats caused the idle speed to increase, adjusting the idle mixture screws out worked and the idle was faily steady at 600rpm with no more stalling..
We have not made any long runs yet, but a couple of weeks ago both motors would run fine at around 3500rpm, at that point I was not at the wheel and we never checked for WOT performance..
I had a little dwell / tach meter, used it to adjust the idle speed and found the dwell high on both, gap small. Started on the port motor, went to check/adust, they did not look good so replaced points, condenser, rotor and cap, set timing for between 8 & 10 degrees before tdc.
Started and idled fine..
The stbd cap looked newer so it was not replaced, got into major problems because the 2nd Sierra kit had a rotor 180 degs different than the original!! Once exchanged started and idled fine.
When test run the port would only pull 3100rpm, the stbd sounded much stronger and pulled around 4000rpm.
Anti syphon valve was clean as a whistle and no resistance without it when blowing air back into the tank. Fuel / water seperator looked new, but was replaced
Dismantled and cleaned, but it was already v clean, the port carb, no difference when tested, still on just over 3000rpm on port side.
This morning I switched the carbs over and did not get the result I would have liked, the port still only went upto just over 3000 and the stbd did not sound as powerfull and only went up to 3300 or so.
Opened the hatch and took off the flame arrestors to see what was happening, the air valves were not opening on either motor, the vacuum had released and when I "helped" them to open the not changed but the motors did not pick up any rpm, hopefully for just a few seconds the lean condition did not hurt anything..
So what have I done????
Apologies for such a long winded post, but felt it important to try and share as much as possible
Still with some hope...
Regards, Trevor T in Owen Sound, ON
