Do you ride a bike with TPI?
Thinking of buying one?
We spoke with Dave from Two Stroke Performance who knows these bikes back to front.
Here are his answers to the most commonly asked questions.
How does TPI compare to the carb models?
The TPI bikes typically have a softer bottom end power delivery, but similar top end.
The main reason is a softer ignition curve, but the location of the injectors also contributed.
This is due to a reduced opportunity for fuel/air to mix properly at low revs.
Some models have spluttered at low revs.
But the carb models can have problems too.
Since 2017 the jetting has caused spluttery power and poor fuel economy.
The finicky Mikuni carb is extremely difficult to get running consistently.
Both carby and TPI motorbikes respond very well to basic mods.
And once set up correctly both have very similar power delivery.
Do TPI bikes need rebuilds more often?
We suggest top end rebuilds every 80 to 100 hours maximum for a 250 or 300.
The TPIs are especially sensitive to top end wear.
Blow-by past the piston rings will begin to alter the crank pressure readings sent to
the ECU.
This causes the ECU to alter fueling, ignition and oiling and as a result performance will
drop.
Bottom ends are very reliable, as they are on the carb bikes.
How reliable is a TPI bike?
Generally they are reliable.
But there have been issues with some of the 17 ECU maps released by the factory.
Some maps caused problems.
Other maps have been much better.
Some give softer power and others give stronger power.
That’s why there are so many strong but differing views on the TPI on the internet.
We find the TPIs are reliable once a few basic mods are done.
The most important mods?
Use the latest 'extreme mapping' from the factory, which uses more oil.
Fit an 'idle bolt', which allows separate tuning of the air and idle settings on the
throttle body.
Lets look at specific issues.
Has a lack of oil caused problems?
On some models, yes.
A lack of oil can cause significant wear up the back wall of the cylinder, usually centered
over the rear boost port.
You can check by removing your exhaust and looking at the back wall of the cylinder for
vertical black or grey marks.
The 2018 and 2019 models used a reasonable amount of oil, although some used less than
others.
The oil tank did not have a screen in it so it was important to clean the tank and test
the output of the oil pump.
2020 models had a screen fitted to the tank but unfortunately the mapping used less oil,
causing a high number of failures on low hour motorbikes.
The factory has now released new ;extreme maps;.
These bring the oil level back to roughly the same level as the 2019 motorbikes.
Fouling plugs at startup.
This emerged with 2020 and 2021 models.
A simple solution was to pull out the cold start knob on the side of the throttle body
when starting the bike cold...
and let it idle for a few minutes before touching the throttle.
A more permanent fix is to update the ECU with more appropriate fuel maps.
The ECU 'reflash' that we offer addresses this issue.
It virtually eliminates spark plug fouling.
If you consistently foul spark plugs, you can use the cheaper NGK BPR7ES or BPR8ES spark
plugs.
These still perform very well but at a fraction of the cost.
Remember if your bike suddenly starts fouling spark plugs it might be a worn top end or
a faulty crank pressure sensor.
Spluttery power at lower revs?
Some 2018 and 2019 models had spluttering and unpredictable power delivery at part throttle
and lower revs, due to issues with the standard mapping.
The only complete solution is to reflash the stock ECU with improved maps.
But it pays to check other possible causes first:
a faulty crankcase pressure sensor,
an incorrect air screw setting, low fuel pressure,
or a worn top end.
Faulty Crankcase Pressure Sensors (CCP).
The ECU uses the data from these sensors to determine the fuel, ignition and oil needs
of the engine.
It is quite common for these to become faulty or blocked, causing spluttering and weak/unpredictable
power delivery at part throttle and lower revs.
But it will usually be fine at higher revs.
The easiest test is to swap the crankcase pressure sensor with the ambient pressure
sensor as they are identical.
If the motorbike suddenly runs better, then the crankcase pressure sensor needs replacement
or cleaning.
Be careful with aftermarket sensors.
They may appear identical to the factory sensors.
But they can give incorrect readings to the ECU.
Low fuel pressure.
This usually results in spluttery, jerky power delivery, the engine cutting out when throttle
is applied, a general lack of torque.
And overheating and a hanging idle due to running lean.
It's most commonly caused by either a faulty fuel pump, or a split or blocked in-tank fuel
filter.
The small in-line fuel filter that’s found inside the fuel hose very rarely gives any
issues.
The easiest check is to test fuel pressure with a gauge.
52 psi is the normal reading.
Incorrect air screw setting.
This is used to adjust the idle speed, but it has effects on midrange revs too.
Remove the stock grub screw and fit a longer bolt that can be adjusted by hand while the
engine is running.
Incorrect settings result in a weak or 'hanging idle', spluttery power delivery, and poor
throttle response.
Corrosion of electrical connectors or relays.
Check for this in the main relays under the seat.
Typical problems include no spark,
the fuel pump won't prime,
the dash doesn't light up,
handlebar switches don't work,
and the engine runs but splutters and won't rev out.
Do I need to replace the oil pump regularly?
Generally the oil pumps are very reliable unless they get dirt or grit inside them.
As mentioned, the 18 and 19 models had no oil screen and were susceptible.
The 2020 models and on had a screen fitted.
If you have doubts, there's a video on our TSP website showing how to test output.
Can the injectors be moved?
Moving the injectors to the front of the reed cage can increase power to some extent due
to improved mixing of the fuel and air.
But we don't recommend this without custom remapping to suit.
In any case, our development work shows the best power gains are through an improved combustion
chamber design instead.
Can you add oil to fuel?
Many riders have formed strong views based on very limited information.
Yes you can.
But usually very little of this added oil will reach the bottom end of the engine.
Overall the benefit is very small, but it is there.
When the 2020 models were released, engines were seizing at low hours and we did recommend
between a 150:1 to 200:1 oil mix in the fuel tank.
But the best solution by far is to run the new 'extreme map', or have custom mapping
done.
See the TSP website for a more detailed answer.
What are the key tips for TPI reliability?
For 2020 models and on, update to the latest extreme map.
Even better, get a custom remap.
Regularly clean the oil tank on 2018 and 2019 models.
Fit an idle bolt/spring and experiment.
Regularly check the oil pump output (see our video).
Regularly check the top end condition.
Use a good quality TPI-specific oil.
Use good quality 95-98 octane RON fuel.
Regularly clean your air filter and apply grease to the sealing surface.
Regularly clean your crankcase pressure sensor.
Improve the stock head design with a TSP Billet Head.
Thanks David for all that information.
I did get to ride a TPI bike for a week in Romania which had all the mods done and found
it ran pretty much like a carb model with the added benefit of being smoother on the
road.