OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Rover Suzuki 2 Stroke

Thanks Grumpy. I most definitely used compressed air after each go of soaking and removing the oil build up. It appears the engine is running better after following this process.

It is a pleasant engine to start, it is idling very well. Full speed is great as long as you get the throttle adjusted at the right full speed setting.

I use the following process when using the engine and wouldn�t mind your thoughts as it is still a little touchy when adjusting the engine to full speed which makes me think the choke mechanism might be a little sticky. I could be wrong through.

1) Start on choke, wait a few seconds and then move the throttle to full speed, this hardly ever provides any issues. Full song sounds great.
2) Move the throttle down to idle , it then ides really well
3) Move the throttle back to full speed and I actually have to push the lever onto the choke for a second and then adjust it back to full speed. Following this process gives no problem������however if I push the lever from idle to full throttle it hunts. Follow the process of moving from idle to full speed by giving it a little choke then back to full speed and ����.no hunting.

Maybe I am on the wrong track but could the choke be a little sticky?

All the intake gaskets and brand new BTW.

I haven�t got a Jet drill kit so that might be a good idea to give the mrs for a Christmas present.

Getting very close now.

Hello Jaffa J,
I have been frustrated with setting these up in the past.
I must admit I just haven't been able to get some of them right.
After reading this post, can add a little bit.

1. fuel cap - the piece that is falling into the tank, the plastic they are made from shrinks to the point where it drops into the fuel.
2. there is a small hole that needs to be cleared in the exhaust port, it gets hidden because it is normally blocked with carbon, this seems to make them run better when it is cleared.(you may have done it already?)
3. I have noticed in the past with a lot of them that the governor spring gets stretched, this plays mary hell with getting them set right.
4.I have found that after a really good run the smoke clears and the power increases.

It is a fine balancing act between where the governor arm is on the shaft, the tension in the governor spring and where the mixture screw is set, also how your throttle cable is set.(I know what the manual states about the governor arm, but I have adjusted where it sits on the shaft slightly)

The only down side to these engines is how much you have to take apart each time to make minor adjustment's.
Sorry to cut in on this thread, but just trying help.
From Mark

Thanks for that, Mark. Your experience is likely to be useful here. With regard to Item 2, the function of the small hole in the exhaust port is to act as a decompressor. If it is blocked it becomes difficult to pull the starter cord, but there should be no other effect. On the other hand if the exhaust port, spark arrestor, or muffler is obstructed, any point of performance could be adversely affected: those areas should be kept reasonably clean. Jaffa, to verify that the engine has a fair chance of operating perfectly, please check that the exhaust port and muffler are clear, and that the engine shows compression pressure of at least 90 psi (that is the minimum service figure: it should be 120 psi).

Jaffa, one point to verify here is whether your engine has electronic or breaker-point ignition. The earlier units had breaker points, and they have to be set up carefully (the manual specifies use of a dial indicator, like on the old Kirby Lauson 4 strokes) to get the right ignition timing. Your slight instability problem sounds as if it could be due to an ignition timing error, so we need to know which system your engine has.

It sounds as if your engine is very sensitive to the precise adjustment of the speed control cable, and the setting of the choke linkage. You should lubricate the cable, and ensure that it slides smoothly, with no hysteresis between opening and closing. (In other words, there is no wind-up in the mechansism, resulting in the linkage being in a slightly different position depending on which direction the control is moving in.) You will recall adjusting the mechanism slightly to get the kill switch to work properly. You may now have it out of adjustment at other points in its travel. Please check the assembly against this diagram and instructions:

I have often thought about that hole in the exhaust port and the slot in some of the Victa powertorque ports aswell.
I clean them out and didn't really know why, thanks.
Here is an image of the Suzuki port, anyway.

Thanks for posting the picture, Mark. I wanted to ask for one but didn't think it would be a reasonable request when it wasn't relevant to the case.

The principle of operation is very similar to the normal 4 stroke decompressor which momentarily bumps the exhaust valve open about halfway through the compression stroke. Of course the 4 stroke ones disable themselves when the engine is running more than about 1,000 rpm, while that Suzuki one operates all the time - but is so tiny that its effect at high engine speeds would be negligible. Briggs has its Easy Spin feature on the side valve engines, which holds the inlet valve open by a few thousandths of an inch during the compression stroke. They say their experimental work showed that it had a negligible effect when the engine was running.

Grumpy & Mark
Thanks for your comments, I really appreciate it. I have tried to the best of my ability to address your questions.
1) The fuel cap and breather cap underneath the cap have been replaced with a brand new unit. Mark I had no idea how the original piece fell into the tank but now I know.
2) The small decompressor hole in the exhaust port is free from carbon. I gave it another clean to be sure about its condition.
3) I am fairly confident the governor spring has not been stretched it has good shape without any strange bends. I am also confident the governor arm is positioned correctly on the shaft as grumpy and I discussed this process earlier.
I do agree with your comments about how difficult the engines are to work on. Any fine adjustment requires time to dismantle everything. Its bl**dy frustrating.
I checked the compression and it is 110 psi so that is within the high end. I don�t think that is the problem.
I re-checked the exhaust post and it is free from carbon. I also check the exhaust and ran compressed air through it. It doesn�t appear to be blocked however if you have a better method of testing it I am open to suggestions. The exhaust did appear to be heavier than I expected but not blocked.
Grumpy unless I am mistaken the engine has electronic ignition. There was no breaker points under the flywheel unless the points for the engine are set up differently?
I did some investigating with the cable and you were exactly right with regard to the linkage being in a slightly different position depending on how the cable is adjusted. Can you please advise how I should lubricate the cable and the linkages if you think necessary?
I have also rechecked the linkages and they are as per the manual. Well they looked to be good with me checking!
I think I have addressed all the questions. We are getting close I think����..

Hello Jaffa J,
Have you noticed on the governor arm there are 3 holes, your governor spring can be placed in the top hole or the bottom hole, it is normally in the middle. You can raise and lower the rpm by plus or minus 150rpm.
It might be something to try, I have done it in the past and the machine ran better at a lower or higher rpm. The manual tells you.

With the muffler you can tap it all around with a rubber mallet, it may free some carbon up.
There are other methods people use, like heat the muffler, I have never done it.

I have never seen one with points.

With setting up the cable, I normally have the clap loose then I set the throttle to neally full choke. Then I push the cable at the clamp and watch the choke plate close, then tighten the clamp. This ensures the choke is closed when starting.

When starting I always look through the gap between the cowl and the air cleaner and watch the carby for the choke lever to move across.
They wont start without the choke closed.

My method for lubricating Bowden cables is to move the mechanism so all the cable inner is sticking out at one end - that is, either full choke, or switched off. Then hold the engine so the cable runs vertically down from the end with the exposed cable inner. Put a drop of oil on the inner cable where it sticks out, and operate the cable full stroke a few times. Then put on another drop and do it gain. Proceed that way until the cable inner is wet at the far end as well, due to oil running the whole length of the cable.

Well I investigated the throttle linkage problem a little more closely and I didn�t like what I found.
1) When you move the throttle from idle to full speed the engine hunts badly and doesn�t run well at all. I checked the position of the butterfly and when adjusted using this method it is fully open with no choke.
2) When you start the engine and move it from the choke position to full throttle (The position I thought it was running correctly at) the throttle butterfly is slightly closed and running proportionally on choke. I should have noticed this problem earlier as the full throttle running sound was slightly strange but not bad.



These findings again led me back to the carburettor to retrace my cleaning steps as there is obviously still some sort of restriction. I stand to be correctly if you think otherwise.
I did some more reading and went back to this carburettor picture where item 15 (nozzle) removable however I couldn�t get it out. Could that be the problem?
So it appears when it was running ok it was running proportionally on choke. I should have noticed this earlier.

Item 15 appears to be the emulsifier. If it won't come out that is usually because of hard-set gum holding it in. It happens quite often. I suspect that your soaking softened the gum temporarily but did not remove it, and it just set again afterwards. It seems to me that your cleaning work has not been fully effective.

Best next step is to go back to the cleaning, get all the removable parts out, and blast them with carb cleaner under pressure, then blow them dry with compressed air. From your symptoms it is probably getting lean mixture from the main discharge system all the time, but sometimes this is being overcome by the choke not opening properly. The primary culprits are probably the main jet (Item 8) and the emulsifier (Item 15), since the problem is associated with the main system, not the idle system.

Here are some images of the tube taken out, to support Grumpy's words.


Use the right size blade to get it out, they are easily ruined.

Now that is a clean carburetor Mark, thanks for showing what one looks like.

Jaffa, remember what carburetor cleaner is: it comes in a spray can and has "Throttle Body & Carby Cleaner" or some similar message on it.

Here is an example of what it looks like, but your speedshop will have half a dozen brands. Don't bother trying anything else, you'll just waste your time and probably damage parts when you try to get them out when they are stuck in by petrol gum. Nothing else I've seen or tried dissolves petrol gum in any sensible period of time.

I have most definately been using the carby cleaner. It is the Nulon Brand. I need to work on getting the emulifier out and giving it a good clean. I will also have another look at the main jet however I am confident it is clean already.
Hopefully I get the emulifier out without damaging it.
Im away for a few days now however when I get back I'll update you on how I go.

Lets hope this solves the problem.

Cheers guys.

Don't push hard on the tip of the emulsifier (in the carburetor venturi) with any metal object. The tip is recessed and shaped to emit the right amount of fuel under venturi vacuum, and the emulsifier is only brass, not steel. Blast carb cleaner up the tube the emulsifier is stuck in, then push it downward from the venturi with the side of a wood or metal cylinder. If it won't move, use more carb cleaner, or soak it again in carb cleaner. That will soften the gum - just don't get impatient and use a metal object to push it. And don't ask me how I know not to use a metal object to push it:

Grumpy & Mark, I appreciate your effort with helping me.

Well after soaking the carby again I got the emulsifier out without damaging it. I actually had to buy another screwdriver as my set would not fit correctly. After removal I gave the carby another thorough clean however upon re-assembly I slighting broke the spring that goes through the connecting rod which joins the governer arm and throttle butterfly. I managed to re-shape the end of the spring however I will have to end up getting a new one I think as it is now stretched in the current position.

I did put it back together with the slightly shortened spring and guess what - pretty much no improvement at all. The main get was already clear and suprising the emulsifier was also relatively clean.

The engine idles well however with the choke completely open (as it should be) the engine still hunts pretty badly at full throttle. Could the spring be causing my issue. I have it in my shopping cart ready to order along with a couple of other goodies for other mowers.

The purpose of the spring that sits on the outside of the link from the governor arm to the throttle butterfly, strangely enough, is to prevent what Honda calls surging and I call oscillating, but is much the same as hunting.

Unless the spring is in pretty bad shape I doubt it is causing your problem, but to me it doesn't make sense to ignore a fault in the anti-oscillation system when your governor is oscillating.

At this point I don't know whether your spring was in good condition before you broke it, so I suppose it is plausible that it could be at the root of your problem. Hence I think you need to replace the spring.

For reference, the anti-oscillation spring on the small OHV Honda engines pulls the throttle butterfly open slightly when the engine is stopped and the speed control is in the stop position. I'd say it holds the throttle at something like 10-20% open.

The spring was in what I would call just about perfect condition before I broke a couple of mm off the end where it clips into the throttle butterfly. I just slightly re-shaped the end of the spring so it clipped into where the rod goes in. The spring is not bent or out of shape in any way which made me think it might not be the cause of the continued hunting.

This one is still beating me! I am frustrated with it but no enough to give up yet.

It doesn't sound as if that spring is causing the problem. Do you have a set of jet drill bits? Here is the specification of the M120X jets, as shown in the workshop manual:


As you can see, the correct main jet for England is 0.85mm, and for South Africa is 0.90mm. According to the Toro manual, the correct main jet for the US was 0.80 mm, and the lean jet for high alititude in the US was 0.775 mm. This wide range of jet sizes suggests that in at least some countries, Suzuki was pushing hard for the leanest possible mixture, perhaps for emissions control reasons. It would be useful to know what size main jet your engine actually has. This is typically measured by pushing jet drill bits through it, preferably holding-end first rather than drilling end first, so you can't accidentally make it bigger.

The float height also needs to be checked. It should be 17.5 mm, according to the Toro manual.

I do not have a set of Jet Drill bits sorry. Where would I purchase such an item given its specialist nature? Do you have a recomended brand for use by a hobbiest?

Secondly I am not sure what you mean by checking the float height. Would you be able to clarify and then I will do the necessary checks.

I am confident every removable part in the carby has been removed and thoughouly cleaned including the main jet, pilot jet and emulisfier. I will have another go at it on the weekend. The mower starts on the first pull when cold so I know the choke setting is right.

Ill await your thoughts.

This is the set of jet drill bits I use:
http://www.ebay.com.au/itm/Metric-I...AU_HardwareParts&hash=item58aa3672a9

Several people have had mysterious leanness of that carburetor, so finally finding out what size jet was fitted to the version sold in Australia would be a good thing I believe.

The M120X manual does not specify float height, or how to adjust it. The Toro manual specifies the height but does not say how to adjust it. However the Toro uses the M122X, which has detail differences from the M120X, including in the carburetor. If your float is black plastic and has a plastic pivot arm, it is not adjustable. If it has a metal pivot arm attached to the black plastic float, it is adjustable but we'd have to work out what is the reference point for measurement. If you can report which type of float you have, that will be a start anyway.

The bottom line is that we can easily make your engine richer at high speed, without changing the low speed much, by enlarging the main jet. However that would only be a sensible thing to do if the jet is wrong in the first place, which is unlikely unless your engine has been interfered with. That is why I think we should see what size jet it has, as a first step.

Ok thanks for the recommendation. I purchased the set as I thought it seemed pretty good value for money. It will also come in handy for future projects. Once I get the set I will take the measurements and let you know how it goes.
The type of float I have is exactly the same as Mark's photo example above which I believe is non adjustable however I stand to be corrected if you think otherwise.
I have re-read the thread again and the only thing I haven�t tried is adjusted the rev's as Mark said this has sometimes had an impact on engine performance. I was actually thinking about lowering the governed speed by moving the spring to the bottom slot on the governor arm.
I would love to have a carby that came off a perfectly functioning engine.

Here is Mark's picture of the float. I have circled in green, the tab that is usually used to adjust float height - I'd need to look at the carburetor to be sure, but I think that Mikuni adjusts the usual way, by bending that tab up or down:





Here are two videos, one long and one short, that show you how to measure and adjust the float height:





The first one is a bit too short and the second one very, very long - it is a good-quality video of an actual trade school training session on setting small engine float heights. If you watch them both and come back with any questions, hopefully we'll get this clear.

Hello,
Things I have tried, to stop the engine hunting. please see image below.


Things I have tried to stop hunting:-
#Red arrows: try changing the engine speed by 150 rpm, try the top and bottom holes. with care you can do this without pulling much apart, I use offset point nose pliers with the governor spring relaxed.

#Green arrow: Move the governor arm one spline on its shaft closer to the carby. To get the governor arm off, undo nut then spread slot with a flat tip driver(yellow arrow) then pry it off with a large flat tip from behind. To make it easier remove the governor plate (blue arrow) 2 x 10mm bolts from memory.

I bought a mower off an ex mowing contractor of 20 years, he used Suzuki's, he used to drill the jet out, I don't know the fine details.

Here are some other images for this thread.




For those who haven't been in side one of these.



Here are my 3, all mounted up on 21 inch Big Bob bases.

Thanks Mark, from your experiences and one or two others in the archive, it seems they are a bit sensitive. I'm hoping we will learn something from the float height or main jet size.

It is interesting to see the wide range of main jet sizes listed in the manual. It is especially interesting that it looks as if the less emissions-regulated the market, the bigger the main jet. I also remember one of Suzuki's popular cars which, in Australian emissions format, was prone to surging (the equivalent of a governed engine hunting) rather objectionably at some intermediate speeds. There could be a pattern forming here.

Hello Mark and Grumpy,
Thanks for the ideas about further fault diagnosis.
To start with I checked the float height and didn�t end up making any adjustments to it as it lined up in evenly on the 35degree angle the guy noted in the first video.
I did a bit more reading about this engine and decided to give the idea of lowering the engine revs by 150 and putting the governor spring into the bottom slot (as suggested by Mark).
I re-checked everything to ensure the choke and throttle linkages were operating as they should before I re-assembled the engine.
I didn�t have high hopes that changing the revs would fix the mower but I took it down the end of my suburb for a run in the long grass. The mower performed perfectly. It started easily, it idled fantastically and full speed with nice and smooth, no hunting what so ever!
Mid-range was smooth; any adjustment to the throttle didn�t result in hunting. I re-checked the full speed setting and the choke was completely open and not partially closed like before and it was running absolutely spot on.
The engine didn�t miss a beat after mowing for at least 30 mins in the long grass. The engine was stopped and started on several occasions and I couldn�t fault it.
I had to make some repairs to the catcher as it is slightly different to the normal rover catcher. It has no cracks so it should not be a problem.
This would have to be the most challenging mower so far for me. Here as some photos of the finished product after a good work out. I will clean it up with the compressor and whack it up on my new shelves I put together before Christmas. It helps keep my shed neat and tidy. I don�t have a lot of room so I need to be tidy.
Again guys I really appreciate your help. I hope this thread can be of use to others.

That certainly lines up with Mark's experience, and gives us a good outcome for the archives. However I'd appreciate you letting us know how this mower runs after you've used it a few more times, over a period. My history of the reliability of that kind of fix over time, is not totally encouraging. Changing the engine speed cannot change the existence of a lean spot in the carburetion, all it can do is keep you from encountering it as often as previously.

Great thread guys I've just had one of these dropped off to me. It's difficult to start but seemed to run fine for the 2 minutes I tried it. This will be a great thread to come back to, should it give me some dramas. Many thanks

Michael

Michael, this thread will be kept open for a while, so feel free to add your experiences to it. The M120X has been one of our mystery areas for a long time, so the more we can do to clear this up and have a decent archive on it, the better.

Hey Guys,

I took the suzuki down to the back of my suburb again yesterday and it performed fantastically. It is one powerful unit, By far one of the gutsiest mowers I have ever used. It starts first pull just about everytime from cold and is easy to use.

I think it might be ready for a new home!

Michael,
If you need any photos I am happy to post them up to assist. I am sure Mark (Electric) will as well. I am just happy to see this mower back running properly again.

Thank you gentlemen and good to hear you got yours all sorted, Jaffa J

I'm seriously tempted to buy an ultrasonic cleaner to use for troublesome carbs (and other jobs), does anyone have any experience with them? Seems like they would be an asset in this situation.