Re: Winter fixes
Posted: 19 Oct 2015, 12:31
Woodray
I have used colour plugs before as I had a couple of Ducati motorbikes during my twenties and they (colour plugs) are the greatest thing for tuning idle mixtures on engines, mainly because you can actually see the colour of the flame inside the cylinder. Once you know that you have the engine running on the idle mixture circuits, turn the mixture screw/s out until the flame starts to turn orange (rich) then turn them back in until the orange goes away and you are left with a nice bunsen burner blue flame, job done. Then set your idle level screw to the desired rpm and recheck idle mixture. When I had my motor bikes I had two of them and a set of vacuum gauges. Once a week I would ride the Ducati home from work and when it was in the garage, in with the colour plugs and set up the vacuum gauges, make sure that both carbs are reading the same vacuum level and in ten minutes perfect idle. However they are not designed for WOT power runs. This is best achieved with dyno tests or now that these things are available, Air/fuel ratio and EGT pyrometer gauges. I now have both and as I have previously mentioned the air/fuel ratio gauge constantly reads lean as the pipe has an air leak. My cousin (a machinist), is currently trying to design a temporary fix for this. The exhaust system is on its last legs and a new one is now on the agenda which will fix this issue completely.
Your comment about the exhaust water is valid as any sort of moisture will destroy the oxygen sensor and I take the water off that pipe when I am running the oxygen sensor. This involves taping the water hose on that side of the boat out over the deck. In my case the water in the exhaust is only a sound level aid to try and take two or three dB off the top of the noise level.
The big problem with the new (870) carb was figuring out what we had to do to ensure the carb was only running on the idle circuits, as mentioned previously the power valve in a holley can flop open if the value of the power valve doesn't sit below the vacuum level of the engine at idle. Once I sorted that out the colour plug sorted the idle mixture in a few minutes. The holley carbs have an idle mixture screw on each side of the carby and the final bit of the puzzle was to make sure that the two idle mixture screws were correctly matched.
The base level tune is now sorted, the next step is to work on the mixtures in the top end which is controlled by the primary and secondary main jets, in conjunction with the power valves. The 870 comes with 80 size main jets standard and a power valve in both metering blocks, this proved to be too rich and I have now dropped the main jets front and rear down to 75's which my mate and I feel is more realistic for this engine. As the air/fuel ratio gauge is constantly reading lean (due to the exhaust air leak) we are relying completely on the EGT pyrometer gauge (current research tells us that about 1300 degrees F is about right with good top end mixture) to tell us how we are going at the moment. The new exhaust will fix that issue, but not before Naranderah.
By the way both the air/fuel ratio gauge and the EGT pyrometer gauge both have memories which means that I don't actually have to watch them while I am driving the boat, I can come back to the bank and press the memory button on the two of them after I have pulled the engine kill switch cord and shut the engine down. A ten minute session on the water, about five laps to warm the engine up, about three laps at 3/4 throttle and about three laps at WOT and we will know what the top end EGT is and whether we need to change jetting. My mate thinks that the main jets should be 76's and I have put 75's in, he is a little more conservative than I am, but Naranderah is 568 feet above sea level, we will see.
The reason that I am writing about all this on here is in the hope that the information I am providing may help some other owner/driver with knowledge that will be of some help to them in sorting the tune in their boat.
Bob
I have used colour plugs before as I had a couple of Ducati motorbikes during my twenties and they (colour plugs) are the greatest thing for tuning idle mixtures on engines, mainly because you can actually see the colour of the flame inside the cylinder. Once you know that you have the engine running on the idle mixture circuits, turn the mixture screw/s out until the flame starts to turn orange (rich) then turn them back in until the orange goes away and you are left with a nice bunsen burner blue flame, job done. Then set your idle level screw to the desired rpm and recheck idle mixture. When I had my motor bikes I had two of them and a set of vacuum gauges. Once a week I would ride the Ducati home from work and when it was in the garage, in with the colour plugs and set up the vacuum gauges, make sure that both carbs are reading the same vacuum level and in ten minutes perfect idle. However they are not designed for WOT power runs. This is best achieved with dyno tests or now that these things are available, Air/fuel ratio and EGT pyrometer gauges. I now have both and as I have previously mentioned the air/fuel ratio gauge constantly reads lean as the pipe has an air leak. My cousin (a machinist), is currently trying to design a temporary fix for this. The exhaust system is on its last legs and a new one is now on the agenda which will fix this issue completely.
Your comment about the exhaust water is valid as any sort of moisture will destroy the oxygen sensor and I take the water off that pipe when I am running the oxygen sensor. This involves taping the water hose on that side of the boat out over the deck. In my case the water in the exhaust is only a sound level aid to try and take two or three dB off the top of the noise level.
The big problem with the new (870) carb was figuring out what we had to do to ensure the carb was only running on the idle circuits, as mentioned previously the power valve in a holley can flop open if the value of the power valve doesn't sit below the vacuum level of the engine at idle. Once I sorted that out the colour plug sorted the idle mixture in a few minutes. The holley carbs have an idle mixture screw on each side of the carby and the final bit of the puzzle was to make sure that the two idle mixture screws were correctly matched.
The base level tune is now sorted, the next step is to work on the mixtures in the top end which is controlled by the primary and secondary main jets, in conjunction with the power valves. The 870 comes with 80 size main jets standard and a power valve in both metering blocks, this proved to be too rich and I have now dropped the main jets front and rear down to 75's which my mate and I feel is more realistic for this engine. As the air/fuel ratio gauge is constantly reading lean (due to the exhaust air leak) we are relying completely on the EGT pyrometer gauge (current research tells us that about 1300 degrees F is about right with good top end mixture) to tell us how we are going at the moment. The new exhaust will fix that issue, but not before Naranderah.
By the way both the air/fuel ratio gauge and the EGT pyrometer gauge both have memories which means that I don't actually have to watch them while I am driving the boat, I can come back to the bank and press the memory button on the two of them after I have pulled the engine kill switch cord and shut the engine down. A ten minute session on the water, about five laps to warm the engine up, about three laps at 3/4 throttle and about three laps at WOT and we will know what the top end EGT is and whether we need to change jetting. My mate thinks that the main jets should be 76's and I have put 75's in, he is a little more conservative than I am, but Naranderah is 568 feet above sea level, we will see.
The reason that I am writing about all this on here is in the hope that the information I am providing may help some other owner/driver with knowledge that will be of some help to them in sorting the tune in their boat.
Bob