Motorcycle Tuning Part III
Using the Dyno and reading the information
Let’s take a closer look at last week’s problems and see how they are solved.
The Ducati 999 was interesting because as we noted last week there was more than one possible cause contributing to the problem. An obvious cause of a misfire is spark plugs which had already been replaced. The bike was here for re mapping anyway so we went straight ahead and mapped both cylinders which were very rich. At the end of that it was running a lot better as you can see from the graph – however the misfire was still there.
So we know it’s not a fueling issue. This bike has the ignition coil in what would once have been a plug cap and they can be tricky to test under load. Standard bench test proved inconclusive so in this case we just replaced them and as you can see from the final graph it was the correct choice.
What does this say about motorcycle tuning on the dyno? Well, there isn’t a pop up a screen that says “hey this is what’s wrong, do this or replace that”. There are many occasions where testing and measuring doesn’t give us all the answers or pin point the problem straight away. You have to remember that for any issue there’s always a number of possible faults, sometimes two issue’s or more causing one problem.
The dyno provides information that is otherwise not available to a mechanic, it’s quicker and safer. The trick is in knowing the mechanic’s understanding of what each components job is and how it ties in with the finished product. Then you can use that information, following a course of action, measuring the results which then leads to the answer and reward.
GSXR750 fuel starvation
This next one is interesting because it’s clear the bike is not getting enough fuel as the revs build up. It’s often mistaken for needing a remap to correct a modification, such as exhaust and air filter.
However from our experience we know the change required is never that dramatic so something else must be causing the problem. Because we have the bike on the dyno we were able to connect a fuel pressure tester and watch the gauge while riding the bike in a safe environment.
What we discovered was that as the revs rise, fuel pressure at the injectors was dropping off, starving them of fuel and the bike of power above 6000 rpm. The cause could be fuel lines leaking and if they run inside the tank to the pump you won’t see it, or maybe a pressure regulator problem, or the pump is worn out. This problem was solved by fitting a new fuel pump.
Early model Yamaha R1 missing horse power
Remember the old model Yamaha R1 from last week with 160,000km on the clock. It should produce about 125 hp. The fuel mixtures suggested it was running rich, however lots of bikes have rich mixtures like this one and they aren’t missing 25 hp. A cylinder leakage test revealed there was nothing to support the notion this engine was tired. The cam timing was correct as per factory specs, and there was no funny business going on with the intake system. That leaves the exhaust..?
The exhaust system on this bike was completely stock, and this model has an exhaust valve opening and closing depending on the rpm. The higher the rpm – the further the valve opens. It’s driven via cables by a servo motor regulated by the ECU. If it doesn’t open the valve far enough at the correct rpm it creates a restriction in the exhaust and a loss of power. Again there’s more than one thing that can go wrong here to cause this problem. Poor wiring or connections, broken or seized push/pull cables. Cables fitted back to front so the valve is open when it’s meant to be closed. Sounds silly, but you’d be amazed how often this happens. As it turns out all these things were correct but the servo motor driving it was past its use-by date and was not opening the valve fully. A replacement resorted this classic to its former glory.
Enough head scratching and analyzing, tune in next week when we’ll make a great bike even better by installing a power commander and tuning it on the dyno for more power acceleration and improved economy.