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Lexmoto Michigan EFI 125CC Has A Problem

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Twpsin
L Plate Warrior



Joined: 19 Oct 2021
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PostPosted: 21:40 - 19 Oct 2021    Post subject: Lexmoto Michigan EFI 125CC Has A Problem Reply with quote

Hi there!

So, I’ve been having some issues with my bike (Lexmoto Michigan EFI 125cc) for some time now, and I need some advice from people who have more experience than I do!

It’s having some engine trouble which is causing it to no longer idle, and when you touch the throttle it completely dies; before you say it is the Carb, it is an electric fuel injection, and I shall explain the tribulations I have gone through with that aspect of the bike below. This has been something I have been working on for a few weeks now and I am completely stuck.

So, backstory!

I’ve had this bike for just over a year and it’s been great, however for parts of this year it has been sat in the garage whilst I was finishing off University. Since coming back home, I have been attempting to get her started again, with minor victories and setbacks.

The electric fuel pump was faulty and did not fire, so it has since been replaced and works great, and it has had a new fuel injector. This improved things massively as it started well, but new problems have presented themselves in the bike struggling to idle for longer than 10 seconds; it starts well, but then dies off, and if you touch the throttle, it kills the bike off, unless you rapidly twist from max rpm to
minimum, which seems to force some air into her.

Firstly I thought this was an air intake issue, and so disassembled the throttle body to check it over and give a small clean, so all is good. Next I thought it could be a fuel issue, however have double checked all of this and it is working well, and the spark plug has also been checked and is working well.

So, I am very stuck. It seems to be an air related issue, however I have no idea where to move on from here: I cannot tel if it is getting too much or too little air, and I have tried running the bike with the air filter in and out of the air box with no detectable difference occurring. I have even bought a new battery to see if it was an issue with power, but this has changed nothing. Now it has begun to lead me to whether compression is an issue, however this bike can be made to run if you rev hard and let it go, and occasionally gets into a rhythm and idles very well.

I am really stuck and have no clue which way to proceed, so some guidance around what to check would be a lifesaver, as I really want to get back on the road!

If you require anymore information please do not hesitate to ask, and thank you for reading through this fairly long, very erratic post.
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WD Forte
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PostPosted: 23:11 - 19 Oct 2021    Post subject: Reply with quote

What year? mileage?
does it have an eml? any codes flashing up?

First thing I'd do is check the colour of the plug
if its black/sooty I'd suspect it may be overfuelling because
you say its starts easy but cuts out soon after and wont tick over.
If the plug is sooty check the temp sensor in the head

Clearing and a reading of subsequent dtc's could give useful clues
but as its Lexmoto, a lack of info on these would not surprise me.
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Twpsin
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PostPosted: 23:22 - 19 Oct 2021    Post subject: Reply with quote

It’s a 2018 I believe, and it’s done around 10,400 miles (most before my time).

It has the orange engine light, which doesn’t surprise me.

The plug was very sooty, so you could be right; how would you stop overfueling?

I can find next to no information on this bike, an owners manual/manufacturer’s guide has been nigh impossible to find, so I wouldn’t even be able to guess how to read the dtcs.
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WD Forte
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PostPosted: 23:46 - 19 Oct 2021    Post subject: Reply with quote

You can probably get an owners manual but as its chinese you'll be lucky to get a dedicated service/workshop manual and even then
useful info on efi system an can be hard to pin down even on a
Japanese big 4.
I would presume they'd prefer you take it to a lexshitto shop where they can take money off you.

Lexmoto dont make bikes, they buy them from a Chinese factory and rebadge them.
the Michigan is also known as a Sinnis hoodlum,
(Sinnis do the same buy/badge thing)

You may find a code reader for it on Ebay but I've no idea if it will be useful or not.
If its cheap it may be worth a punt

temp sensors usually have a negative temperature response in that as they get hot the resistance drops, so some tests with a meter may shed light on things.
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WD Forte
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PostPosted: 23:49 - 19 Oct 2021    Post subject: Reply with quote

Typical engine light behaviour is for the eml to light at ignition on
for a few seconds then go out
It it stays on or lights when the bike is in use, this usually indicates a fault
has been detected.

Not sure but think it has a Delphi efi system so try turning the
ignition
On-off, On-off, ON in quick succession and leaving it ON count the flashes from the eml

117 or 118 indicate temp sensor faults
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Twpsin
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PostPosted: 07:13 - 20 Oct 2021    Post subject: Reply with quote

The engine light does turn off when I fire the engine, however I don’t remember what happens after because I now rarely look; I’ll have another look later today.

When replacing the fuel injector a week or two ago, I did notice there was a slight difference in the new and old injector as the previous obviously came with the bike, and the new one was from a Sunnis OEM parts place. On the side of the previous injector it says ‘S50’, whereas the new ones says ‘S60’; could this be the issue? Does this mean it is a more powerful injector?

The rest of the ID numbers are the same on them, just those two, and after doing a bit of research it did say that it would be fine for the Michigan.
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Mysteriass
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PostPosted: 09:45 - 22 Oct 2021    Post subject: Reply with quote

Could be a bust sensor, probably one of the engine temperature sensors.

When a sensor busts, it can send crazy bullshit back to the ECU. The ECU assumes the crazy bullshit is real and takes its vaccine...I mean it responds to the crazy bullshit by altering the fuel flow. It's like the ECU doesn't watch Alex Jones or David Icke - it just believes what it's told by minions of the fat controller.

So let's say, for example, that the engine temperature sensor is bost. The sensor reports to the ECU that the engine is 100c and the ECU craps itself and tries to provide an appropriate fuel delivery for a 100c engine right off the bat. Obviously a cold engine won't find much joy in trying to run on that.

I'd find out what engine your chinese version is based on. Then get the haynes manual for it. That'll give you the sensor test ranges and how to do them. Hopefully your chinese copy will be near as dammit enough to work.

The other thing you might be able to do is get a wireless bluetooth ECU test kit and mobile app. Then you can see if a sensor is giving a mal-reading and either manually adjust it on the fly or reset it.

Take a look : https://youtube.com/watch?v=VZJF09Z7MMo

I haven't got much love for EFI but if you can get over being pissed off about it, do a bit of reading and watch some videos about it, then things start to make sense and you'll be able to diagnose EFI problems yourself.
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steve the grease
Crazy Courier



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PostPosted: 19:31 - 22 Oct 2021    Post subject: Reply with quote

Has it still got the Pre uni petrol in it. RThat could be a cause , or have you drained the old fuel out?
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Nobby the Bastard
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PostPosted: 21:06 - 22 Oct 2021    Post subject: Reply with quote

Does it have a lambda sensor? When they fail the system will assume loads of oxygen in the exhaust so too lean and will richen up the mixture.
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Easy-X
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PostPosted: 22:20 - 22 Oct 2021    Post subject: Reply with quote

Nobby the Bastard wrote:
Does it have a lambda sensor? When they fail the system will assume loads of oxygen in the exhaust so too lean and will richen up the mixture.


That's a good shout. The lambda sensor's an integral part of the closed-loop system and a quick Google search throws it up as an idling problem on all sorts of engines.
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Twpsin
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PostPosted: 22:26 - 25 Oct 2021    Post subject: Reply with quote

So, an update on the trials and tribulations of the last few days.

I bought a Bluetooth OBDII reader, which has been really useful, as it has allowed me to look more into the ECU. I have drained out the old fuel, clean out the lines, and inspected the inside of the fuel tank properly, as well as bought new fuel and ran it through a little to see if it has made a change. It did not, but it’s good to do.

I bought some new engine oil and spark plug, and did an oil change, which has improved the running of the bike a little, and did also need to be done, so a nice bit of maintenance which I can tick off.

Whilst perusing the sensors tab of the app my OBDII unit uses, I saw the intake manifold absolute pressure was very strange. It’s base reading was 12.75 psi, and when the bike turned over and hit around 6 psi it fired, but I could not get it to stay at this level for long because of the idling issues.

This has now lead me to whether compression could be a bigger issue than I first realised, and could mean the MAP sensor could need replacing, or whether the compression of the bike isn’t up to scratch.

The lambda sensor could be a culprit, so I shall look into that as well.

Any thoughts of where I could go from here? I went to a bike shop today and had a chat with the receptionist, whom mentioned valve clearings could be a possible culprit, but since the bike does turn over and I can get it to run, that would make that void, right?

My knowledge on how pistons and compressions works with engines is a bit of a gray area, so some enlightenment and education would be greatly appreciated!
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Easy-X
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PostPosted: 22:55 - 25 Oct 2021    Post subject: Reply with quote

I had a Keeway that started running a little rough when the weather turned cold - it was fine once the engine had warmed up. Getting the valve clearances on spec cheered it up quite a bit.

You can get a cheap compression tester from Amazon, FleaBay, etc. if you have a penchant for filling out your tool collection.
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Mysteriass
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PostPosted: 23:40 - 25 Oct 2021    Post subject: Reply with quote

Bit of a cop out, but you could replace the entire throttle body (EFI's equivalent of a carb). Sensor and all.

Something like:

https://www.ebay.co.uk/itm/363590511720

Great thing about many 125's is that you can buy a bulk of bike bits off ebay for the cost of one consultation with a mechanic. Even if you don't know what the problem is just keep replacing parts until it works. It'll still end up being cheaper than taking it to a garage and you get a pile of spare parts to hoard, click your claws over and barter in the coming Mad Max world.

Those Chinese 125's ... all the rage in the wastelands.

Even while I'm fiddling with something trying to fix it ...always nice to know there's some fresh bits on their way for when I inevitably break the very thing I'm trying to fix. Only to find that there's something else entirelly wrong with the "working" part I ordered therefore needing more bodges and yet more parts and even more harsh language.
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WD Forte
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PostPosted: 02:07 - 26 Oct 2021    Post subject: Reply with quote

So its compression now is it?
Probly needs new piston rings then
Is the chain slack too?
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Twpsin
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PostPosted: 18:43 - 01 Nov 2021    Post subject: Reply with quote

[quote="WD Forte"]So its compression now is it?
Probly needs new piston rings then
Is the chain slack too?[/quote]

So, another update for you all!

I bought a compression tester, and after this test my compression came up as 80 psi, which of course is not good. So, I have taken the cylinder apart, changed the piston rings and replaced the base and head gasket.

In putting the cylinder back together, I now have no compression: 0 PSI. Today I double checked and adjusted the engine timing (and am pretty sure I have it correct after watching some YouTube videos on a 4 stroke engine, if anyone has anymore information on this it would be great!)

Tomorrow I shall be checking the valve clearances after ordering a feeler gauge, so hopefully that should make some change, however if nothing comes of this, I am very worried that I have fucked up the compression more so than I already was, after taking a lot of time to put the cylinder head back together just as I had found it.

If the valve clearances does not sort the lack of compression, I feel I will have to send it off to a mechanic, which I really don’t wish to do.

Help!
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Nobby the Bastard
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PostPosted: 18:47 - 01 Nov 2021    Post subject: Reply with quote

It's hard to achieve 0 psi compression. You would get a bit even without rings.


It's feeler gauges btw. Multiple leaves of metal with different thicknesses.
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Twpsin
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PostPosted: 18:51 - 01 Nov 2021    Post subject: Reply with quote

[quote="Nobby the Bastard"]It's hard to achieve 0 psi compression. You would get a bit even without rings.


It's feeler gauges btw. Multiple leaves of metal with different thicknesses.[/quote]

Well, in screwing in the compression tester into the spark hole, turning over the engine and doing exactly the same as before, the needle did not move at all; therefore the stated 0 psi compression. That’s the facts pal.
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Nobby the Bastard
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PostPosted: 19:14 - 01 Nov 2021    Post subject: Reply with quote

Oooooo!
*lifts handbag*
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slowasyoulike
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PostPosted: 19:24 - 01 Nov 2021    Post subject: Reply with quote

Twpsin wrote:
Well, in screwing in the compression tester into the spark hole, turning over the engine and doing exactly the same as before, the needle did not move at all; therefore the stated 0 psi compression. That’s the facts pal.


Twpsin wrote:
My knowledge on how pistons and compressions works with engines is a bit of a gray area


What is a fact is that he's right - even if you shoved a baked potato on the end of the rod you should get more than 0psi. You've timed it up wrongly, and if you've got it that far out then it's time to show it to someone who actually has a clue what they're doing.
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A100man
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PostPosted: 20:49 - 01 Nov 2021    Post subject: Reply with quote

unfortunately equipped only with enthusiasm you ripped into the motor without completing all the basic service checks such as valve clearances..

.. take the rocker cover off and observe the position of the valves with piston at the top of the (compression) stroke which happens once every two revolutions - both valves should be closed. If not you've truly beggared the valve timing - start again assuming you've not already bent and valve stems.
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Easy-X
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PostPosted: 20:58 - 01 Nov 2021    Post subject: Reply with quote

Zero compression?! Step 1 would be just stick your thumb over the spark plug hole and see if you feel any push back just the verify the gauge hasn't spontaneously busted. Even with a valve stuck open a little bit you should feel something.

Once you've figured that out (I'm sure it'll be something simple) you have to be careful when refitting the timing chain on any 4-stroke. Depending on the specific engine there'll be a system of timing marks that need to line up.

For an example scroll half way down the page where I did a barrel change on an old 50cc scooter:

https://www.bikechatforums.com/viewtopic.php?t=327425&postdays=0&postorder=asc&start=25
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slowasyoulike
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PostPosted: 22:17 - 01 Nov 2021    Post subject: Reply with quote

A100man wrote:
...you've truly beggared the valve timing - start again assuming you've not already bent and valve stems.


This. Fortunately he's only done it to something that was designed to be thrown away on or before its first birthday anyway, so nothing to worry about Thumbs Up
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Nobby the Bastard
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PostPosted: 23:38 - 01 Nov 2021    Post subject: Reply with quote

Even with the timing hideously wrong zero compression is hard to understand.

Back off all the valve clearances (big gaps) and try again.
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Robby
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PostPosted: 10:28 - 02 Nov 2021    Post subject: Reply with quote

Just to be clear, you rebuilt the top end when the problem is likely to be a failed or dirty sensor.
On the initial compression test, was the throttle open or closed? Compression tests must be done with a wide open throttle. 80psi would be about right for a closed throttle.

Anyway, right now it's timed wrong, or you fitted a new piston without any piston rings. Either way, it all needs to come apart again and the job done right. Haynes do a manual for Chinese 125s, which will show you how to do it. Make sure all the gasket surfaces are totally clean (new gaskets required again), and you should also remove the valves to see if you bent them by getting the timing wrong.
Remember, timing can be out by 180 degrees and still look OK. Or it could be out by 90 degrees and smash all the valves.

You've turned a small problem into a big problem. Everything needs to come apart, be cleaned, checked and reassembled properly. Worth replacing all the sensors while you're at it, the time for a cheap fix is a long way behind you.
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stevo123
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PostPosted: 20:55 - 12 Nov 2021    Post subject: Reply with quote

I wonder if this guy opened the throttle when he tried the compression test?
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