Flat spot/hesitancy/surging at 4500/5500 rpm

[Jimmyuk]

Hello all,first of all i would like to introduce myself as a new DT300 owner from the UK,my names Jim.
I bought the DT from a member on here...Frankie1949 i believe.
After the purchase i was aware of a few faults with the bike,namely the wandering steering and a terrible flat spot/surging at about 4500rpm that co-incided with 35mph,these problems were a right royal pain in the butt.
However the steering problem was quickly fixed,this was not the tyres or pressures,it was the head bearings themselves,they were notching in the central position.
A strip down and cleaning and re greasing has elimated the wandering ,imprecise steering and now tracks good even with 70% worn rear.
The hesitancy/surging problem was really killing my enthusiasm for the machine and was making it impossible to ride the bike smoothly at low throttle openings.
After doing some google searches it became apparent that there was quite a few DT owners with this problem,but nothing in the way of a fix.
So i set about having a good strip down to check for anything untoward in the fuel injection system.
Plug is a iridium and fine,oil is fresh,once past the hiccuping at 5500 it takes off like a banshee,so fuel pressure must be ok.
Disconnected all the sensors and the injector itself,ended up with the dash displaying 3 different sensor failures  eek...panic stations...how the bloody hell do i get rid of these then....managed to do it eventually....phew.. .
Anyway after checking all connections and the injector etc....it became apparent that one of these sensors....the MAP sensor(the one with the locking tab on it) had a direct effect on the running of the bike depending on its position.It can be rotated through 180% more or less.I reset this position to the maximum engine speed obtainable (ticking over).
Put the bike back together and tried it out.......Well i cannot believe the transformation it has now got a beautifully linear throttle response all the way to 6k were theres a tiny bit of a flat spot and then continues as it should.
Absolutely NO trace of the hesitancy/surging at the 4500/5500 range and has restored my faith in the machine.

Obviously this may not work for everyone but it certainly worked for me.

[MotoRandy123]

Hmm. I read about this on a Singapore site and they seam to think it was the Variator.
It was surmised that there are 2 different ones and one was made for speed and the
other for economy. Some have change the variator and even the ECU to fix this.

 I'm not visualizing how to adjust the MAP sensor. Do you have a picture? The MAP
on other bikes is fixed and looks like this;


It's just a temp and pressure sensor so just hangs in the airstream...

[Cortez]

Nice exhaust.
Time for Dr Pulley sliders!

[Cortez]

Hmm. I read about this on a Singapore site and they seam to think it was the Variator.
It was surmised that there are 2 different ones and one was made for speed and the
other for economy. Some have change the variator and even the ECU to fix this.

There's no doubt there's 2 different variators out there, but from about June/July 2011, there
should be only one (the LGE5, like in People 300).

The older version kept the revs lower and made the bike rather slow under 60mph (just barely
faster then other 22-23hp 250-300cc bikes, which is easy to fix with 14gr Dr Pulley sliders).

[Jimmyuk]

I'm not visualizing how to adjust the MAP sensor. Do you have a picture? The MAP
on other bikes is fixed and looks like this;

It's just a temp and pressure sensor so just hangs in the airstream...

I think the sensor in your pic is the TPS isnt it? Throttle position sensor.

This is the MAP sensor...


The symptoms (for me anyway) are absolutely nothing to do with variator.
This is a direct result of a lean running engine,probably to get through the tough Euro 3 emissions and noise regulations.
Its a trait shared by many injected bikes and why power commanders are doing a roaring trade.

My knowledge doesn`t go as far as knowing what the MAP sensor does,but all i can post is how it worked for me,unless i managed to inadvertently fix something else ?
My bike FWW is the newer variator model.

Jim

[wheels]

Previous bikes the TPS (throttle position sensor) is factory setup to "pass/lean" emission tests at various rpm ranges.  On previous bikes I had the TPS re-adjusted (rotate sensor) from factory specs to smooth out acceleration issues.  In any case if you self adjust don't forget to do the TPS/ISC reset procedure.

The DT300 service manual is a bit fuzzy to see clearly.  On one picture the MAP seems to be on the muffler side (all by itself) shown mounted in the scooter, in another picture of just the throttle body it seems to be on the opposite side.

Too lazy right now to remove the tub for confirmation.   I have an occasional starting/dying/idle issue which I will look at in the future.

Appreciate your sharing of info.

[MotoRandy123]

Well I found this in a PCX150 tech doc. It seams the throttle position sensor is
in with the temp and pressure sensors on some bikes, so you probabily adjusted
that to fix it.

[Cvitalo]

MAP sensor rules. Wow, I also had this problem. I advice everyone to do this. I have never done anything complicated on any scooter, and I'm not a mechanic. But this is very easy to fix. It is a trial and error method. I also find that about 11.00 o'clock instead of 13.00 o'clock position (looking from the left side of the scoot) makes the best of it. I didn't move it too many times. It seems that now it consumes a little bit more fuel than before, so maybe I will just play with it a little bit more. As I say, as many trials you make, more the chance for the best results.

You only need 2 things:

1. To remove the seat and the seat shell with this key (same size for all screws):

http://az58332.vo.msecnd.net/e88dd2e9fff747f090c792316c22131c/Images/Products34347-1200x1200-276261.jpg

2. Picture from the manual of the MAP sensor position witch I'm putting in the attachment, so I hope you will see it here.

----------------------------------------------------

Two things you have to be careful:

1. After untightening the metal plate that holds the Map sensor firm and after rotating the sensor at any position, DON'T FORGET to TIGHT the METAL PLATE again before a test drive.

2. Not to lose that gummy ring (don't know the right name for it) below the MAP sensor. It falls down really easy. The sensor itself is not precise, it is very floppy to handle.

-------------------------

So again the whole procedure:

1. Remove the seat and shell
2. Untight Metal plate of the sensor
3. Rotate the sensor in a position of your choice
4. Tight the Metal plate over the MAP sensor again
5. Put back the shell and the seat - No need for putting the screws
6. Make a test drive
7. Repeat the same procedure again if needed...

There is one other newer topic referring to this one, but cannot find it right now. If anyone finds it, put the link in this topic.

[TANWare]

I experienced this for the first time today. It was right after a fill up of fuel. I pulled out of the station and accelerated. All was fine to about 3,500 RPM then acceleration slowed down and you could almost hear the engine loading up. Until about 4500 RPM then it freed up again. After stopping there were no subsequent occurrences.

[DiscoPotato]

I have the same issues with my DT 300i, loose steering/wandering, and the on and off surging at around 4500 rpm. These issues make me a lot less enthusiastic to ride. I will try rotating the MAP sensor, that looks easy enough...how did you fix the steering issue though? I have no idea how to service a head bearing aside from watching a youtube video on how to do it on a motorcycle

[AMAC1680]

What year is the scoot?
I've got a 2013 with over 10k miles and have not had these issues. Is it specific to certain years?

AMAC

[Cvitalo]

I have the same issues with my DT 300i, loose steering/wandering, and the on and off surging at around 4500 rpm. These issues make me a lot less enthusiastic to ride. I will try rotating the MAP sensor, that looks easy enough...how did you fix the steering issue though? I have no idea how to service a head bearing aside from watching a youtube video on how to do it on a motorcycle

I don't really understend what you mean with this steering/wandering. Are you speaking about the front wheel?

IMPORTANT:  It seems that, whatever you do with the map sensor, after couple of days or more the CPU tries to solve this on it's own. So it tries to get the same specs and hesitancy like it was before. But now with the map sensor on the other position, the hesitancy starts on some other rpm than before. For me it starts right when I start to accelerate. With Dr. Pulley sliders it ends very soon so I can live wtih this. It will probably be much different situation for every specific downtown, depending of the map sensor position and earlier exact  rpm hesitancy spot

[Cvitalo]

What year is the scoot?
I've got a 2013 with over 10k miles and have not had these issues. Is it specific to certain years?

AMAC

I was told by the dealer that this was the problem with the first 2009./2010. models only. They were very suprised because mine is 2013. also.

[DiscoPotato]

I don't really understend what you mean with this steering/wandering. Are you speaking about the front wheel?

IMPORTANT:  It seems that, whatever you do with the map sensor, after couple of days or more the CPU tries to solve this on it's own. So it tries to get the same specs and hesitancy like it was before. But now with the map sensor on the other position, the hesitancy starts on some other rpm than before. For me it starts right when I start to accelerate. With Dr. Pulley sliders it ends very soon so I can live wtih this. It will probably be much different situation for every specific downtown, depending of the map sensor position and earlier exact  rpm hesitancy spot

Sorry, I was referring to the steering/wandering issue that the OP had from his first post.

I was able to rotate the MAP sensor today, it looks like my bike prefers the sensor to be in the 10 o clock position when looking at the sensor from the left side of the bike. I performed the TPS reset every time after making an adjustment to the MAP sensor. It seems slightly better at low rpms now but seems to hesitate at highway speeds? If the CPU compensates for the map sensor adjustment every few days, I might just keep it at the factory settings and try to get used to it lol. Honestly, my biggest gripe is the steering issue, any imperfection in the road will upset the steering of the bike, and it really sucks when I'm filtering and the bike pulls towards the car next to me because of a crack or small bump in the road. I seem to be constantly fighting the steering and it gets tiring after a while.

[de dee]

I have the same issues with my DT 300i, loose steering/wandering, and the on and off surging at around 4500 rpm. These issues make me a lot less enthusiastic to ride. I will try rotating the MAP sensor, that looks easy enough...how did you fix the steering issue though? I have no idea how to service a head bearing aside from watching a youtube video on how to do it on a motorcycle

steering bearings ,.  very easy to do just takes time, buy your bearing first,  I listed them a few weeks ago ,. with the size,.  or if you want just rotate the outer races and grease them well, and re install,.  they wear in one spot,.