Dangerously disobedient throttle on Lexmoto ZSB EFI 2019 (Video Footage)

[kaiser-swaghelm-ii]

https://www.youtube.com/watch?v=KRnKVY3Pdnw

In the video, I have tippexed the throttle so you can see that my throttle control is slight and solid.

It does this on the road too, If needs be I can upload footage of it climbing from 24mph to 35mph on a dead level road in gear 2 with 1% throttle twist.

For the whole 6 months I have had her I have a really bad problem with the throttle. So basically in all gears.... If I apply a very slight throttle, the RPM will climb on it’s own and never find a stable rpm. It’ll pop and crackle and hover around allot.

It’s really apparent when in slow traffic doing 20 mph or so.... With only the slightest possible throttle open, the bike will slowly over the space of a few seconds, climb from about 3000 to somewhere around 7000 rpm.

Which in real time terms, means that unless I let off of the throttle, pull in the clutch or apply braking pressure... with a slither of throttle open, the bike will start to try and rear end the car in front of me :L

It’s a horrible feeling.

It can go from 24 mph to 35 mph on it's own with no throttle change. NOT VERY SAFE!

I have been slowly working my way through the Chinese, Taiwanese & Korean 125cc Motorcycles (2003-2015) Haynes Manual

Haynes Part #MOL4871 Maintenance list.

I am running out of things I can blame this on at this point

It’s such an obvious and intolerable problem. But yet I am running out of tricks.

I guess that’s both a good thing and a bad thing.

Because my list of probable causes is now very slim indeed.

Here’s a current list of the solutions I have tried.

We replaced the Lambda sensor, so it's not that.

The valves are perfectly in spec 0.15 out -/- 0.10 in.

I've given the drive chain the proper tension.

The throttle cable is set correctly with about 3-5mm of free play and no snagging. (all the way through the steering range is tested)

The clutch cable is set correctly with 10-25mm free-play (I have mine at about 11mm)

The air filter is clean and the sponge filament is basted but not dripping in engine oil as per the manufacturers maintenance guide.

The wiring is clean and functioning, no warning lights. (I solved the low voltage warning, there was a lose wire that had sheered off.)

The spark plug is new, we replaced that.

The oil strainer had some plastic debris on it but is clean now.

The cam chain tension and timing is spot on.

The rocker arms and valve heads are in immaculate condition.

The cam chain looks as good as new.

The oil is clean and the right level.

The throttle returns to fully closed with no problem.

I fitted a new clutch lever and cable with grease.

The engine Idles absolutely spot on at 1.6k with no fluctuations or miss-fires.

The Bike starts first time every time

The battery holds charge and delivers the correct power with no low voltage problems.

The transmission is working smoothly and without faults. (It looks in damn good condition too when I had a peak earlier this week)

The Fuel filter is clean and the pipes and feeds are ship shape with no kinks.

The clutch pads themselves are absolutely fine, In fact they look way more pristine than I thought they would.

I cleaned both front and rear calipers, brake pistons and all thoroughly with acetone then lubed the pistons with brake fluid.

The front pads needed replacing so I got those in, the rear pads where fine .

I have bled and replaced the brake fluid in both front and rear master cylinders.

No pulsing or friction on the brakes.

I have replaced the front brake disk due to slight warping.

I have thoroughly inspected all seals and gaskets on the engine case and I see no oil leaks what so ever.

I have double checked all of the wiring as per the diagram in the Haynes manual.

All electrical systems function as they should including the Fuel gauge.

I replaced the speedo because of that casing damage that was there when I bought the bike.

The suspension is damped correctly and feels spot on.

It runs at high load and Rpm with no issue.

The fuses are all intact and working.

The ECU is functioning, thought I don’t know to what level of accuracy.

My list of things I think it could be are as follows;

A Vacuum issue with the air intake manifold, maybe a small leak in the intake system?

A faulty TPS? (I think this is the most likely, but experts might not share that opinion?)

Maybe an incorrect programming on the ECU?

The Bluetooth transmitter for the ECU?

Maybe dirty fuel tank D: I( mean I am scraping the bottom of the barrel with that one)

It’s behaving like I have the throttle open about 80% or so when in actuality,

my throttle is open so slightly, that if I even slip one mm forward the throttle cable is out of range and the throttle is completely released.

It’s just such a shame that it is still so disobedient and dangerous at low speeds and RPM,

Because when it’s not, it rides absolutely brilliantly.

[rennie]

Turn the handlebars away from hard left to the central position, does the problem go away?

If so your throttle cable is wrongly routed and by turning hard left you are pulling it too tight

[kaiser-swaghelm-ii]

Turn the handlebars away from hard left to the central position, does the problem go away?

If so your throttle cable is wrongly routed and by turning hard left you are pulling it too tight

 

See bullet points The throttle cable is set correctly with about 3-5mm of free play and no snagging. (all the way through the steering range is tested)

Yeah trust me, I have more than tested the throttle cable. It is definitely not the throttle cable... but that should be abundantly clear from the video footage.

Thanks for the reply though

[rennie]

I did read it but then I watched the vid!

Looks too tight to me and the bars are to the left throughout the whole vid

[rennie]

If that's not it then I have no idea

[kaiser-swaghelm-ii]

I did read it but then I watched the vid!

Looks too tight to me and the bars are to the left throughout the whole vid

 

Yeah i'm sorry that I didn't bother to show the full handlebar rotation, but your just going to have to trust me that it's not the cable.

After 10,000 miles of it doing this to me and servicing the throttle cable as per the manual no less than 5 times in the last month hoping it would solve the issue, I can categorically state that it has nothing to do with the cable.... This issue will replicate itself no matter how tight or loose the cable is, no matter if it is on the road doing 20 or off the road doing 0, whether the handle bars are at full left or full right or somewhere in between.

do you think it could be the TPS?

[rennie]

Could be!

[kaiser-swaghelm-ii]

Could be!

 

Yeah it's weird isn't it . I'm glad you share the same amount of scepticism as me.

What are your thoughts on it being the ECU programing?

[kaiser-swaghelm-ii]

Could be!

 

I guess as a last ditch effort of desperation I could install a cruise control unit on it XD that would solve it

[rennie]

you've lost me! I don't know.

apparently my bike has a fly by wire throttle

[exportmanuk]

Faulty Carb?

[kaiser-swaghelm-ii]

you've lost me! I don't know.

apparently my bike has a fly by wire throttle

 

I remember the day back in March when I first realised that I had a Fuel injected bike.

I had been scouring the web for videos on how to clean carbs as she was running a bit rough back then.

It wasn't until I took it in to get it serviced and the mechanic told me I had a faulty Lambda sensor,

to which I responded "What's that? Is that part of the carburettor?"

Yeah I have learned allot about my bike since then

I still have yet to solve the rough throttle issue.

It's a real shame because if I could get that ironed out the rest of the bike is absolutely lovely.

I will have the nicest running 2019 Lexmoto in Britain once that's solved xD

Fly by wire ey? I think I might jump on that band wagon once I pass my test next month.

Edited August 31, 2020 by kaiser-swaghelm-ii

[kaiser-swaghelm-ii]

Faulty Carb?

 

I assume that's a joke

[WD-40]

Looks like a throttle cable problem to me. When you release the throttle does it snap back to it's original position or does it move slowly? In your video the cable has quite a severe kink just after the adjuster. You may have routed it incorrectly or the outer sheat could be damaged. It shouldn't have any kinks. Kinks can cause binding. I would replace it. Even if it doesn't fix the problem at least you can rule it out and a throttle cable is cheap.

[kaiser-swaghelm-ii]

Looks like a throttle cable problem to me. When you release the throttle does it snap back to it's original position or does it move slowly? In your video the cable has quite a severe kink just after the adjuster. You may have routed it incorrectly or the outer sheat could be damaged. It shouldn't have any kinks. Kinks can cause binding. I would replace it. Even if it doesn't fix the problem at least you can rule it out and a throttle cable is cheap.

 

It functions perfectly well, very snappy and closes fully. I have adjusted it according to the manual.

I'm afraid the cable is not the issue.

Thanks for trying though.

I will give it a thorough inspection tomorrow and if I notice any kinks I will replace it even if it isn't the problem, as you say... it will cross it off the list.

[Mississippi Bullfrog]

Have tried removing the screen? It looks possible that the screen is fouling the throttle cable which might seem to working as it should but anything aftermarket that makes contact with a cable can affect it.

Set it at idle and spray some WD40 around the intake. If there’s a leak you’ll hear the idle increase as the WD40 is drawn into the intake. Just be aware that WD40 is highly flammable so avoid spraying near sources of ignition.

[kaiser-swaghelm-ii]

Have tried removing the screen? It looks possible that the screen is fouling the throttle cable which might seem to working as it should but anything aftermarket that makes contact with a cable can affect it.

Set it at idle and spray some WD40 around the intake. If there’s a leak you’ll hear the idle increase as the WD40 is drawn into the intake. Just be aware that WD40 is highly flammable so avoid spraying near sources of ignition.

 

The screen is actually not interfering with the default routing of the cable, but nice idea. I have reduced the snag at the end of the adjuster but that hasn't changed aything.

The WD-40 on the intake is a brilliant idea. I'll give that a go tomorrow morning. Thank you very much for the help

[fastbob]

Faulty Carb?

 

EFI ( Electronic Fuel Injection )

[fastbob]

If all else fails it probably wouldn't be too difficult to retrofit a carburettor to it .

[kaiser-swaghelm-ii]

If all else fails it probably wouldn't be too difficult to retrofit a carburettor to it .

 

That's actually a fantastic idea. thanks dude

[fastbob]

If all else fails it probably wouldn't be too difficult to retrofit a carburettor to it .

 

That's actually a fantastic idea. thanks dude

 

I would be very surprised if Lexmoto had bothered to redesign the cylinder head for EFI so I'll bet one of these bolts straight on . https://www.ebay.co.uk/itm/172946341431

[kaiser-swaghelm-ii]

See now that's clever. I agree I recon I can just throw that straight on there.

In fact, that's what I'm gonna do.

Thank you so much for your ingenious advice.

[dynax]

Have a look on CMPO you might find a carb from an earlier model

https://www.chinesemotorcyclepartsonline.co.uk/

[dynax]

https://www.chinesemotorcyclepartsonline.co.uk/search.php?manufacturer=Lexmoto&model=SK125-8&name=ZSB%20125&year=All%20Years&pageno=1&pagesize=15&category=30413

[kaiser-swaghelm-ii]

Have a look on CMPO you might find a carb from an earlier model

https://www.chinesemotorcyclepartsonline.co.uk/

 

https://www.chinesemotorcyclepartsonline.co.uk/partno_CRB062

Smart move...