Suzuki GZ Y 125 marauder cannot idle without issues

[aly]

Hi guys I've tried my best to solve this problem with my motorbike, but cant seem to figure out how to fix it, im giving up and asking for help, hopefully someone out there with more experience can help me.

The bike is a 2000 model, with 12,500 miles on the clock, it was sitting for about the past 3 years before i got it running again.

The motorbike has trouble idling.. and it seems no matter what carb setting i choose i either have to deal with hanging rpms or a fouled spark plug.

The manufacturers default setting is to turn the fuel mixture screw 1 and 5/8 turns out from seated, but in my case this stalls the motorbike, while the tickover screw is set over the first hole it covers in the carb. if i screw the fuel screw out by about two more turns so almost four turns out from seated, letting more fuel in, the bike idles fine and there are no hanging rpms, but the spark plug fouls real quick. This also has the effect of stalling the bike after riding it a while, with it sometimes conking out or jerking me forward when the throttle is applied.

The tickover screw is about 4 screws in after touching the part that controls the butterfly valve or throttle. If i screw it in the rpm's do increase and i can turn in the fuel screw back to the manufacturer default setting, but the rpms hang when blipping the throttle. It seems that the more in i turn this screw the more the rpms hang which give me the impression it is too far in as it is actually idling on the next circuit rather than the idle circuit. The idle tends to increase as i keep riding the motorbike in this condition, but the result is the same, the spark plug gets fouled after some time (dry black carbon all over it) and the bike starts conking out again, all within an hours ride.

I have taken apart the carburettor, cleaned all the jets, replaced the pilot jet with the same 12.5 jet, and made sure all the passageways are clear and not blocked (confirmed with carb cleaner). I have checked the float level, if there are any holes in the float, the float valve, and gaskets/o rings have been replaced, and the valve seat has also been checked for leaks all according to the Haynes manual. The choke is not stuck, and there are no air leaks on the top, the engine side or airbox side of the carb (checked with carb cleaner method) and no fuel leaks near the bowl or drain nipple. The motorbike has had two oil changes 10w40, new oil filter, new battery, new spark plug (DR8EA) and i also tried an iridium plug (DR8EIX) which also got fouled. The air filter i did not change as it was brand new when i got it three years ago but as i did not finish work on the bike, it has not seen any use until now. I have checked resistance on the throttle position sensor and the starter coil and all checks out fine. I have also checked valve clearances and did the cam chain adjustment. The fuel tank has had the filters replaced on the petcock unit and an inline fuel filter added. I also filled it up with fresh 97 octane fuel and gave it a fuel injector treatment (silverhook 4 stroke). I have also checked that the throttle cable is working correctly and not getting caught on anything.

The bike runs and rides and i can get it up to 60 mph but i just cant trust it as it stalls in traffic due to the idling and carbon fouling issue. It tends to stall when idling and in 1st gear, sometimes there is a lack of power as i open the throttle and it just dies so i have to keep revving it high to keep it from dying. I hope someone out there can point me in the right direction, I cannot think of anything else to do

[jaffa90]

Long shot, if you have a good blue / cracking spark and providing you have enough valve clearances then i would check the exhaust for blockages .

[Teflon-Mike]

So the bike is 18 years old, and has been sat derelict for three of them; and the plug keeps fouling.

My very first reaction is resusitation failure. When a bike is laid up for long periods, the piston rings have a rendency to stick in the piston grooves and not seal, even if the bore wear isn't too bad... to start with.

15 year old leaner legal before it was laid up... I doubt that the bore wear was great to begin with, add 3 years of the iron piston rings sat in alloy piston grooves not moving, what oil there nay have been there drying or draining, and add a little corrosion between dissimilar metals... and rings stick.

At low crank RPM, cylinder presure gets past stuck rings, bike wont idle.

As revs pick up, the compression wont leak away so fast, and theres likely less pressure there anyway, as cylinder filling is most complete at opeak torque revs, probably hald max power revs; so all condusive to the symptoms so far.

Black sooty plug... could be over fueling.... but winding mixture screw out shouldn't cause that much residue.... burning oil though will....

I would stop tinkering with the carb, before I made more problems than I solved; get a good screw type compression tester on there, and see what compresion readings I got with the throttle wide open, before I went any further.

And after 3 years of derelict, I would expect gummed rings, and on an 18 year old bike, I would expect it to be due a rebore or re-barrel...

A-N-D working on bikes this old or older, I plan a rebore/rebarell as course, in resusitation to avoid these sort of niggles and base line the engine.

In the process, taking head off and rebuilding with new stam seals, re-grinding or at the very least lapping valve seats, that on laid up motor are want to rust and pit and not seal too well; to dodge silly questions there; as well as detail cam timing set and valve adjustment set, not just tickling a manual or stuck cam-chain tensioner in vein hope.

IE I would expect to have to look at the scary bits inside the engine, and eliminate them from investigations before I started messing with the bits on the outside like carbs or exhausts or ignition wires..

On which score I would never put an iridium car plug in a car, let alone a motorbike! And even less one of the fancy petal electrode ones, that mask the spark!

The engines are designed to run on a simple standard plug; if they dont, a harder irriduim wont do bog all, but cost you extra money, and notion that it will last for ever, likely hinder you doing any other proper maintenence! NOT a great 'mod' in my book...

But your bike, your call...

Get a compression tester on it, and work from there.
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[aly]

Thank you guys for the replies, they are much appreciated, I have checked both of your suggestions and have found the following:

The exhaust is not blocked but there is a really small exhaust leak right in the middle of the pipe near the rear brake where i'm assuming the two pieces were welded together.

The compression test results are as follows:

Haynes manual nominal values are : 142 - 213 psi
Haynes manual service limit : 114 psi
Cold start compression test with wide open throttle result : 185 psi
Hot engine compression test with wide open throttle result : 177 psi
Hot engine compression test with wide open throttle and a teaspoon of engine oil put through the spark plug hole : 200 psi

The compression seems to be in spec but i dont understand why it has reduced slightly when the engine is hot, i thought it would increase, and also as the oil has increased it to 200psi am i correct in saying that it means the piston ring is slightly worn but still in good nick?

[aly]

Also one last thing, i took out the spark plug after a ride with the default carb settings on the idle mixture and tickover screw and the spark plug is showing the correct tan colour, but it still dies when idling.

[Teflon-Mike]

Hmmm... compression readings on little engines tend to be rather vague at the best of times; especially if using push fit type plug hole union, because volume of spark-plug hole, and potion not filled by plug is much more significant proportion of swept cylinder volume.. and push fits tend not to seal so well, when they have to be held in place whilst cranking.

Those look pretty good though... screw-fit tester? Anyhow; readings are all in book spec... but lower end of nominal, and are lower on hot engine, which is a bit counter intuitive. but still.

They 'look' healthy enough, but we still have to apply some skepticism to them.

Oil through plug hole 'ugh'... old trick to get tired engine started, or get readings up. Oil takes up space, raises compression, so you can get some very high readings by doing it if you use a lot, as in more than a cc or so, and dont purge it by spinning over for a while before using guage. More usually done to help free up gummed or coked in rings.... that idea may give some notions.... bore wear may not be too bad, but rings still sticking, and or, readings could be high because combustion chamber full of soot from previousely burned oil.... maybe...

Oh-Kay.... park that for now.... back to last message; its looking at the oily bits; Have you critically checked the tappet clearances?

Tight tappets will open valves early and shut them late; like a hotter cam, it wont be so want to idle. Loose tappet clerances will open valves late and shut them early, like a soft cam, still be loath to idle propely.

Do the tappets, double check the clearances. A-N-D whilst you have rocker cover off, have a prod and a poke, see how the timing marks line up, cam-chain stretch is like to retard the cam, even if CCT has taken up the slack.

Exhaust holes wont help matters any. If down-stream of the header, it probably isn't that bad, but... if its started to go at the union / join with the silencer, probably the low-point of system where water made by burning fuel will collect, whats the rest of it like? Are baffles hanging loose in the silencer? Are there dings in the header from kurbing? Is there rust on the long bend of header where metal most stretched thin when bent that shape?

Plug and Tan at book settings... would suggest thats where the mixture screw should be, so go with it; assume that poor idle is caused else-where.

Marauder {Sorry, WHO in their crazed mind, decided that a 125 4T single, cruiserified commuter, would 'maraud' like Gengis Khan on campaign Marketing men!} OTMH I cant remember, but I think it has a CV carb?

As such, the idle adjustment wont set the base height for the carb slide, just the 'rest' position for the butterfly.... vacuum lifts the slide 'on demand' to manifold vacuum....

A-N-D first thing folk dive in to mess with, whether engine run well or not, and the cult of 'cleaning carbs' is a PITA...... as warned more like to do more harm than good.... Soooooo

How many times has the thing been yanked off, and taken to bits?

Was it ever put back on with good new or even good home made gaskets? If the thing hasn't got a good seal to the manifold then the slide wont go up and down like it should.

Has, in strip and clean, the diaphragm been mis-seated or torn? Again, if diaphragm dont seal, it wont rise and fall like it should.

These are likely problems 'made' by ilconsidered mechanics, and if you have discounted other possibles, then they are worth investigating.

As said, mixture screw adjusts mixture; idle screw adjusts idle; so you dont try and set one with the other... and ISTR that one, and I think it is the mixture screw, on the maruder carb, has a plastic cap to detur ameteur fiddling... so have you been adjusting the mixture as you think? If not capped, has some-one else been fiddling after removing plug... and if they have removed plug, have they done any more serious damage to carb?

Meanwhile, identify butterfly stop on linkage; check screw to see how chewed up it is, and try setting the idle revs on that or if missing/chewed, on the throttle cable (As temprary test)

And from memory, bike doesn't have a rev-counter, so you are guesing idle revs when setting, and easy to set a 'low' idle on coolish engine, that drops as engine warms.

So... if all else IS ticked off the list.... you can come back to the carb... but first port should be to make sure you have identified the adjust screws the right way round, and are twiddling the right one.... and set an idle on idle adjust, when engine up to temp, and not 'too' low it drops out at traffic lights; a high idle is no big deal, drop out and restart is slightly more awkward.

See how that goes..... but do the tappets and check cam-shaft timing first.... 'yes' does look like the bore/rings maybe 'OK'... with some reservation... so onto next most likely suspects.
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[aly]

Teflon-Mike, really liking all the feedback, thanks for the extensive reply its more than i ever thought i would recieve.

I can confirm that I did use a screw fit compression tester, this one to be exact, one of the adapters did fit the spark plug theads:

https://www.amazon.co.uk/VETOMILE-Cylinder-Pressure-Diagnostic-Compression/dp/B0777F82QB/ref=sr_1_1_sspa?ie=UTF8&qid=1529697351&sr=8-1-spons&keywords=compression+tester&psc=1

With regards to the tappets, my thoughts exactly, yesterday i actually did just that and checked the clearances again.

Haynes Manual recommendation inlet valve (cold): 0.08mm - 0.13mm
Haynes Manual recommendation exhaust valve (cold):0.13mm - 0.18mm

Although I thought it was going to be tight, the inlet valve clearance was actually a little loose! i could fit a 0.15mm feeler gauge in there, i checked the feeler gauge with a digital vernier caliper to make sure it was ok and it was.. The exhaust valve clearance was okay. I used a 0.10mm feeler gauge to assess the inlet valve clearance, checking with the caliper it showed 0.11mm and for the exhaust i didnt change it as i could not fit a 0.20mm feeler in and the 0.15mm went in fine. So now my valve clearances are as follows:

Intake valve clearance : 0.11mm
Exhaust valve clearance : 0.15mm

I also have to apologise for this but i pulled the carb to see if the pilot jet had plugged up again, and while i did find a little rust in the bowl (so much for the petcock and inline filter, will have to find a better inline filter and de-rust the tank) the pilot jet was not blocked, so the carb is fine.

The carb has been taken out over 10 times, I promise you its cleaner than when it was new. I even used metal polish and a q-tip on a drill to polish the valve seat. The gaskets and o rings are all brand new, and the diaphragm is seated correctly as marked, has no tears, although the shape looked abit streched on one side, it seated well. The jet needle is also set at the correct grove as specified in the manual.

I took the bike for a quick spin today, with the now re-adjusted clearances (carb settings still at default) and the bike started to tug me when opening the throttle wide open. The power was not consistent and it was jerking me around. So i pulled out the spark plug, and this time there was a tiny drop of oil on the ground electrode and around the threads. It was not soaked by any means but it was 100% oil. I do not know if this could be down to me threading the plug too far in, and im talking maybe less than a 1/4 turn, as i am sure the gasket around the plug is slightly more crushed each time i pull the plug out to check it, and i can also tell from the orientation of the plug once its completely seated.

With regards to the exhaust, it is in good nick, it has the odd scratch here and there, but there is no extensive rust anywhere, the pipe is clean all the way, but the tiny leak is at the union. there were some tiny rust spots that i removed with autosol, which have left tiny black pits, but you can hardly see them. I also did change the exhaust gasket for a new one. As for the silencer there is no way i can access inside it. When im riding and letting the engine brake at high rpm it does make a "slight" gurgling sound but it does not backfire, i think this is normal.

Regarding all the marauding business, I've actually owned the bike for years and only realised a few months ago what I was advertising on the sides of my motorbike!! It gets even funnier when you consider its got the loser plates on it. Hopefully this time round i will pursue the DAS course, the training aint cheap but im not getting any younger..

I guess this leaves the timing that i need to check, i will investigate, thank you again Teflon-Mike

[aly]

Here is a link to the carb schematic if this helps any, im starting to think valve oil seal leak..

https://www.bike-parts-suz.com/suzuki-motorcycle/125-MOTO/MARAUDER/2000/GZ125Y-W-X-Y-/ENGINE-TRANSMISSION/CARBURETOR-MODEL-Y-/16/2556169/M/1792

[aly]

Just an update, the bike seems to be running better now, turns out the timing was fine, and the bike was fouling plugs because my float height was too high.. although it was set to the haynes manual spec. i had to reduce it for the bike to stop bogging out on acceleration, lowering the float height did the trick, now the bike does not bog out when i open the throttle or foul the plug. It still does die occasionally at stops, but i have managed to tune it so that it doesn't do it as often.

There is also some slight horizontal play on the shaft that holds the carb butterfly, and when i push it in the revs go up or when i pull it out they go down, but i dont see anyway of removing that play without replacing the entire carb.

I have noticed when i put the bike in neutral i hear a clattering sound, but as soon as its back in gear it disappears, and i do occasionally have trouble finding neutral or the bike slips from neutral into first on its own, my clutch free play adjustment is to the manual spec, I used a fully synthetic 10w40 oil, don't know if this would have an effect? Anyways the bike runs real nice now thanks for all the help and happy biking

[jaffa90]

"""There is also some slight horizontal play on the shaft that holds the carb butterfly, and when i push it in the revs go up or when i pull it out they go down, but i dont see anyway of removing that play without replacing the entire carb. """"

I sometimes get worn carbs and linkages on lawnmowers, i just use a denser air filter.
Also a fast idle / tick over can make finding neutral a pain.