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Suzuki EN 125 losing power


tomh65
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Hi all,

I bought this bike 10 years ago and it ran fine until recently. Now it runs ok on the flat, but loses power going uphill. I can be doing 40mph at the bottom of a brow, but going back uphill with the throttle full open, the bike slows to 20MPH. When I step down gears and the revs reach 8000RPM, the bike goes even slower.

Can anyone please help with some advice on this problem?

The carb was cleaned and serviced, but same problem is occurring.

Cheers.

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Did you enjoy Christmas too much :lol:


does it run fine except for up hills?


When was the air filter last replaced?

LOL!! It started way, way before Christmas :cheers:

It runs fine on the flat up until around 7-8K RPM, then feels like it is pulling back

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What maintenance has been done on it? Things like filters, Valve clearances, plug, oil, etc...... 8-)

Oil & filter change about 500 miles ago, also new air filter same time new plug 2 weeks ago.

Valve clearance? (not fully up on engines, sorry) How is that done?

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What maintenance has been done on it? Things like filters, Valve clearances, plug, oil, etc...... 8-)

Oil & filter change about 500 miles ago, also new air filter same time new plug 2 weeks ago.

Valve clearance? (not fully up on engines, sorry) How is that done?

You'd need a manual for the bike if you haven't already got one.....calling Spanner...... :wink: :lol:

I'm guessing on that bike it will be set with tappet adjustment. Basically it's adjusting the gap between the cam and the valve stems. If the gap is not set correctly you'll either have valves not closing fully (loss of compression) or not opening fully (not enough fuel/air mixture getting into the combustion chamber or exhaust gases not being expelled fully) ........either can cause the symptoms you are experiencing. ...... :wink:

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Thanks everyone for all the answers so far...

I saw a similar post about a GN125 (similar engine to mine). There was air intake/leak answers on there too. I will try simple attempts before trying the expensive option.

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Thanks everyone for all the answers so far...

I saw a similar post about a GN125 (similar engine to mine). There was air intake/leak answers on there too. I will try simple attempts before trying the expensive option.

You can check for inlet manifold leaks quite easily.......have the bike on tick over and spray wd40 around the inlet manifold.....If the rev's rise when doing this you know there's a leak around there...... :wink:

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This really does sound like a dirty carb... This is what used to happen on my SR. Cleaned it well and all good again.


Who cleaned it before? These old 125s don't have fuel filters so if you've gone into reserve or close to running out of fuel since last cleaned it may well have picked up some dirt and passed it to a jet.

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Thanks everyone for all the answers so far...

I saw a similar post about a GN125 (similar engine to mine). There was air intake/leak answers on there too. I will try simple attempts before trying the expensive option.

Try this :thumb:

https://www.dropbox.com/s/pjhga7bmb5fb8s1/Suzuki%20gs-gn-gz-dr125-manual-eng-copy.pdf?dl=1

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Thanks everyone for all the answers so far...

I saw a similar post about a GN125 (similar engine to mine). There was air intake/leak answers on there too. I will try simple attempts before trying the expensive option.

Try this :thumb:

https://www.dropbox.com/s/pjhga7bmb5fb8s1/Suzuki%20gs-gn-gz-dr125-manual-eng-copy.pdf?dl=1

Cheers mate, I will look at that.

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  • 2 weeks later...

Just a random question and an afterthought...

I had a new exhaust pipe fitted last year, and coincidentally, that's when the power loss began. Do manufacturers fit restrictors in exhaust pipes?

Will removing the baffles make any difference?

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The engine also cuts out even when warm after riding a few miles at high throttle (between 6-8000 RPM). I have to drop down gears just to get near 25 RPM uphill, even on a low gradient hill.

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If it's running too rich (sorry for sounding a bit green) how do I adjust it? Is it the carb screw that sets the idling?

Hi, I think your gonna have to have a look at the carb, but first check the things that don't need to much dismantling like the Air Filter, check its clean, also look at the float heights, (the mixture screw should not need changing unless someone has already moved it). What type carb do you have is it Slide or CV , the manual I sent you should give you a clue, Check Cylinder Compression, just shout up if not sure :thumb:

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Thanks for your reply Spanner. From the manual, it looks very much like the CV carb.

I have just replaced the in-line fuel filter. I only rode it from the mother in law's (about 1,5 miles) since changing. It reached 7000 rpm and this time didn't falter. But on an uphill, it was still sluggish. Valve clearance has also been mentioned, so I have just watched a couple of you-tube videos with a view to having a go at checking that when I can.

I have had the carb cleaned by 2 different dealers, but it made no difference to the power.

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Just a random question and an afterthought...

I had a new exhaust pipe fitted last year, and coincidentally, that's when the power loss began. Do manufacturers fit restrictors in exhaust pipes?

Will removing the baffles make any difference?

If you go to page 179 of the manual , there is a diagram of the cv carb, look at item 20 on that page ,that is the mixture screw, if you can and there is no blanking plate over it, screw it in all the way gently and counting how many turns it takes to go in, once it comes to a stop, be very gentle, turn it out one and a half to one and three quarter turns out, that should set up the mixture :thumb:

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