Suzuki EN125 won't rev above 5000rpm

ireson75 · L Plate Warrior Joined: 19 Nov 2012 Karma :

Hi all,

The problem I am having is that my bike is not revving above 5000rpm under load (fine at idle), unless you get a bit of speed up and really give it the beans (very noisey and doesn't want to!), however above this and it pulls quite well.

I understand the main jet is the fuelling part of the bike when it is under load?

It has a very noisy exhaust, which is a cut and shut job that ideally I would change, however I don't really have the money to buy a new one. Also, both the old and new (fitted 10 miles ago) spark plugs are quite badly coked up... I have taken the carb apart and all seems fine, however it is running a 120 main jet which seems a bit large- probably causing it to run rich. I have ordered a 110 and will give that a try however I am unsure.

There is no manual for this bike as far as I am aware, and the only manual that is vaguely similar is the GS125 which has a different carb so I have nothing really to go off... Doh!

What would you recommend doing? New exhaust time? Is an exhaust going to have that much of an impact?

Sorry for the essay- if you need better clarity please ask!!!!

Thanks very much,

Tom

humanbeing · Nova Slayer Joined: 20 Mar 2011 Karma :

Nope. · World Chat Champion Joined: 16 Feb 2011 Karma :

Ok,

According to the manual posted above the main jet should be a 110. Make sure you buy a Mikuni 110 as another manufacturers 110 will most likely be a different size. Jet sizes and other carb specs are on page 89 of the manual.

From another thread on here, valve clearances are as follows:

ADM (IN) 0.04 0.07 mm
ESC (EX) 0.13 0.18 mm

They're also worth a check.

If I were you, I'd start by draining the tank and float bowl and filling them with fresh petrol. Failing that, I'd re-install the correct main jet and give the carb a good clean with carb cleaner and compressed air. Making sure to clean the emulsion tube (jet carrier).

If that doesn't help then I'd check the valve clearances (the process for which is described in the above manual and is pretty clear even if you can't read spanish).

If those things don't work then come back and we'll give you some more ideas.

EDIT: What do you mean by the exhaust is a "cut and shut job"? If its blowing it's not brilliant, it shouldn't affect the engine that much I wouldn't have thought but it's always a possibility. Does the exhaust look coked up? Might be worth de-coking it and see if it helps.
____________________
Former: Derbi GP1 50, Sachs XTC 125, Suzuki GSXR 400 GK73A, Kawasaki ZX7R, Suzuki DR250, Yamaha RD350
Current: 2011 Yamaha XT660Z Ténéré, 2003 Yamaha YZR-R1 5PW (In Build), 2009 Kawasaki ZZR1400

Lord Percy · World Chat Champion Joined: 03 Aug 2012 Karma :

My bike is a GN125 and had a very similar problem in that it literally could not do anything above 7000 revs, but only when under load. It could rev to the maximum if the engine wasn't in gear.

For me it was one of the jets (sorry can't remember the various names for them) being the wrong size so fuel provision was not as it should be.

If the main jet is the biggest, thick, long one with many holes in the barrel, then yep that's the one I had wrong in mine. Problem seems almost ok now, but my new carb is obviously an imitation and not genuine Mikuni so it still doesn't quite act right, but good enough.

Also, I'm pretty sure the EN125 is included in the GN125 Haynes? Or at least they will very likely share the same carb.

Nope. · World Chat Champion Joined: 16 Feb 2011 Karma :

ireson75 · L Plate Warrior Joined: 19 Nov 2012 Karma :

I have to say thank you so much for all your help!

It is reallly appreciated!

The exhaust has the end can from a different bike, causing it to be pretty noisey, however I don't think it should have any significant affects....

My new 110 jet still hasn't come in the post, but when it comes I will give it a try and report back Very Happy

When I took the carb apart initially to see the general condition, the emulsion tube looked fine, however now I have a manual I will check that out!

Thanks again Wink

Nope. · World Chat Champion Joined: 16 Feb 2011 Karma :

ireson75 · L Plate Warrior Joined: 19 Nov 2012 Karma :

Well, took the machine out for a ride today and thought I should feed back.

The changing the main jet has totally changed the bike, it now rev's cleanly all the way through the rev range! Not perfect but pretty good- the top speed still isn't right so might try a 105 main jet... and then sell it!

Cheers for all your help,

Tom