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

Well I acquired this Rover Mower with a Suzuki Engine a little while ago
Upon getting the mower it ran but hunted really badly at idle and full speed.
Initially I gave the carby a good clean and replaced the air filter as the filter as it was a homemade job.
Upon putting the unit back together which wasn�t easy, the unit ran a lot better�.. However once the unit warmed up it started hunting again, albeit only minor but more than enough to annoy me.
I found it strange that the engine doesn�t hunt until it warms up. To others this might not be strange however I haven�t seen this before.
So far:
I checked the top and bottom crank seals. Both are in excellent condition and so now signs of leaks. The bL88dy flywheel was difficult to get off.
I gave the carby another clean today with carby cleaner and compressed air. I double checked the gaskets against the carby and they are all good. I am thinking it might be worthwhile getting a new set as I understand they are prone to leaking.
I removed the exhaust and checked the pistons/ rings. They are in spot on condition.
Upon re-installing the carby today and firing it up the engine now doesn�t start. It fired for a second or 2 on the first pull and from then nothing. Think I need to check the carby again.
I re-checked the linkages and everything is as per the manual. The choke opens and closes as it should when you adjust the throttle
Not sure what I have done wrong with the second carby clean. It started easily and ran good however now nothing.
I�d appreciate some suggestions as I think this mower has done very little work. Some photo�s below for everyone�s reference.

Oh and I forgot to mention that I should I bit in the fuel tank that looks like its come loose from the cap�������..

I havent had a lot of experience with the rover/suzuki engines, does it fire if you put a bit of fuel down the carb? With these I have found the easiest way to get the carby off without having dramas with the linkages is to take the two nuts that hold the air filter housing on, tighten them against each other on the studs sticking out and unscrew the carb mounting studs out of the block.

Personally I would say there is a minor blockage there somewhere, it may be worth one last time pulling the carb down and blowing everything out with compressed air...

The symptoms seem fairly consistent with a floating fuel blockage upstream of the carburetor. I suggest you do Joe's test and find out if it will start and run very briefly if you put a spoonful of fuel into the carburetor intake or directly into the cylinder. If it does you've proved it is a fuel blockage. Try disconnecting the fuel line where it attaches to the carburetor, and see how long it takes to fill a cup with fuel, directly from the fuel line. If the fuel does not run full stream, clean out the tank, tap, filter if it has one, and fuel line so that you get full stream flow.

Thanks Grumpy and Joe. I'll get on the job tonight.

I should have thought of removing the studs that way just like the way I do it on a full crank victa 2 stroke engine. thanks joe. That would have saved me a lot of fiddling and obcene words flying around my shed yesterday afternoon.

Thoughts on the fuel cap photo's? Something definately looks wrong.

Hi Jaffa J

Like you, I've encounted problems with my mower.

Having removed the carby because of a starting problem,I was unable to complete the task at the time and having had to leave it for a while, am now having difficulty in remembering how to connect the linkage closest to the bottom end of the throttle cable.

Any assistance you can provide is greatly appreciated.

Regards

Steveo

I ended up following your instructions and doing one more clean of the carby. I also checked the fuel flow from the tank and it had a constant stream.

Upon re-assembling the carby and engine it fired on first pull and didn't hunt whatsoever and full speed which I thought was great. Medium throttle was also really great however at low idle it started to hunt again. Not badly but enough to annoy me.

I am sure I have the linkages and choke adjustment right as it starts first pull when cold. Throttle response is also good.

Is there something I have missed on the minkuni to clean for low speed adjustment? I have ordered fresh carby gaskets from the online store.


I was also after confirmation if my fuel cap is stuffed. Perhaps this could be contributing to the low speed issue. See photos in previous post.

Steve I'll post some photos once I get it spot on for you.

If you had the fuel cap installed when you did the fuel flow test, the cap can't be causing the problem. If you didn't have the cap installed, repeat the test. Your problems have been consistent with a fuel cap blockage - it has much the same effect as a floating blockage in the fuel line - but it should have been eliminated from consideration by the flow test.

Is there an idle mixture adjustment on the carburetor? If there is, richen the idle. If that fixes it, it's done. If turning the idle mixture screw toward rich doesn't have any effect, try leaning it off and see if it gets worse. Whenever an engine runs properly except that the idle mixture screw has no effect, you know you have a carburetor malfunction in the idle circuit.

Thanks for that

I did the flow test with and without the cap on and it didn�t make much of a difference. The petrol was flowing freely from the tap.
I had another look over the engine on the weekend and its worse again. It is now hunting at high and low speeds.
I have cleaned the carby as thoroughly as I know how how. Could it possibily be the needle seat? I couldn�t remove it during the cleaning process. I did however remove the top jet and float chamber. I gave it a good clean with carby cleaner and compressed air.
Grumpy, Could you please explain how the mixture screw works as I havent worked on this type of carby before. I did try adjusting it however it didn�t make much difference.
To make the process easier I have included an extract from the manual detailing the carby setup.
The mower usually starts first pull when cold and if I move it to full speed from the choke position it runs beautifully��.but as soon as I move the thottle leaver it starts to hunt and high and low speeds. I hope this makes sense.
I am determined to get this machine running again as it seems like a damm good unit.

Is this a Suzuki M120X? I have the impression that it is, but need to confirm that.

We have been blaming your problems on lean mixture, which is probably correct but needs to be verified. Try applying small amounts of choke when the hunting or rough running is happening, and see if that cures it. If it does, the problem is clearly lean mixture. If applying even large amounts of choke does not eliminate the symptom, it will probably not be due to lean mixture and the carburetor is the wrong place to look. The rest of this post only makes sense after you have proved that the engine runs perfectly with the right amount of choke applied. Conversely, if the choke makes no difference to the problem, you will need to look for a mechanical issue in the governor system.

Have you cleaned the fuel filter? Have you carried out the flow test by putting the cup under the carburetor, with the float bowl removed, so you are checking the whole system from the tank through the filter, tap, and hose?

Here is the M120X service manual:
http://golftechs.us/Manuals/Suzuki

As long as you have cleaned the carburetor's fuel intake fitting, so it can't be restricting flow, the only float bowl problems that could be causing lean mixture are low float level, or a sticky or stuck float mechanism. I think the float level is not adjustable, but a problem with a worn needle could affect the level slightly.

To answer your question about the pilot screw, the carburetor's idle system has an idle jet, which Japanese carburetor manufacturers call a pilot jet, and an idle mixture screw, which they call a pilot screw. The amount of fuel flow through the idle system is mainly limited by the pilot jet - the pilot screw is merely an idle mixture fine tuning device. I can usually only make any useful adjustment with pilot screws by attaching a tachometer and maximising the idle speed - there may be no effect on idle quality.

You are aware of the possibility that your problems are due to an air leak through a gasket or some other fitting, into the crankcase or the intake pipe. This can be a tricky fault to find, especially in the case of a leaky crankcase gasket for instance.

Grumpy, when the choke is applied the hunting ceases completely.

I need to try the test you indicated below by removing the float bowl. I only completed the test with the hose removed from the carby and that didnt identify any problems with fuel flow. I will also give the fuel filter another clean.

I have ordered some fresh carby intake gaskets however the current ones seem to be in really good condition. Bruce suggested I replace them anyhow.

I checked the float needle and it doesnt seem to have worn away of have been damaged.

Have you checked carefully all the way around the crankcase joints for leaks? Note that this engine uses sealant, not a gasket.

I'm pretty sure you will be aware of this, but the jets (main and idle) and the emulsion tube are prone to collecting hard gum, which will not disappear just with a quick spray with carb cleaner. I cleaned a Honda carburetor last week that had its main jet, its idle jet, and 14 small holes in its emulsion tube, clogged completely, and unable to pass carb cleaner. I had to put jet drills through all of them, then follow up with carb cleaner. I had another (same model) Honda a few months ago that ran just slightly lean (not bad enough to cause hunting) and I found its main jet was down from 0.55 mm to 0.45 mm due to gum. I was unable to shift the gum with oxy torch tip cleaners, but after a good going over with the tip cleaners, a blast of carb cleaner fixed it completely.

I tend to remember the jet and emulsion tube hole sizes now, and am not satisfied until I get a jet drill of exactly that diameter through each hole.

Well I completed the flow test with the carby bowl removed last night and I am now confident I need a new petrol cap, unless of course you think otherwise.
So the result went like this:
1) I opened the fuel tap and the stream out of the carby bowl was steady, then after about 5-6 seconds it started to splutter, however when I took the cap off the fuel flow returned back to a steady stream.
2) When I tightened the cap back up after 5-6 seconds the fuel flow started to splutter again
So from this test I gathered the part of my petrol cap from earlier photos definitely has a purpose. I do apologise for not conducting this test properly in the first place. With the carby bowl removed the results were much more obvious.
Secondly I noticed a feature in the manual about setting the throttle linkage correctly. It specifically referred to the governor arm mount being would clockwise before installation with the throttle butterfly in the open position. I might need to repeat this process if you think worthwhile.

Thanks for that very clear report, Jaffa.

First, it seems certain that your lean mixture problem stems from a fuel cap malfunction. I suspect that by screwing the cap right down without that spacer piece that had fallen out, the fuel cap vent did not operate. You may find that you can re-attach the loose bit and get it working again. Of course a new cap would work even better.

Second, those in-the-crankcase centrifugal governors mostly work in much the same way. It is important to set the angular relationship between the governor paddle in the crankcase (which bears on the plunger that is pushed out by the centrifugal weights) and the governor arm on the outside of the engine, because the plunger has a very limited operating range. So, you rotate the paddle's shaft to bring the paddle into contact with the plunger with the engine stopped and the plunger fully retracted. Then you pull the top of the governor arm to the full throttle position, and lock the arm to the paddle's shaft. This means that no plunger movement is wasted. The plunger's role is to push the throttle toward closed, with an amount of force proportional to the engine's speed. The governor spring's role is to pull the throttle toward open, with an amount of force proportional to the speed control setting. So, if you set the speed control to maximum, with the engine stopped, the governor spring will be fully stretched and will pull the throttle firmly into the wide open position. When you start the engine, the centrifugal mechanism will push on the plunger, trying to rotate the paddle's shaft and move the governor arm toward the closed throttle position. The governor spring will keep trying to open the throttle and the paddle to close it, and they will fight each other to a standstill at some engine speed that the manufacturer decided should be the maximum. The speed is usually about 3,000 rpm for mowers, so the blades won't throw stones dangerously hard.

I suggest that you fix or replace the fuel cap, set the governor linkage as directed in the workshop manual, and then give it another run.

Righto I think things are looking up!
Last night I did the following:
1) Replaced the two carby gaskets and the air filter gasket.
2) Replaced the carby bowl washer as it was dodgy with a proper fuel proof washer
3) Re-installed the throttle linkage making sure the paddle shaft shaft was turned clockwise and joined to the throttle control when at full throttle.
4) Re-installed the choke rod to ensure and ensure the choke was fully closed when in the choke position.
5) Installed my new fuel cap and spacer. This spacer didn�t fall into the tank so that was a plus!
Result:
Mower started very easily and ran at full speed really well with no hunting at all. It kept running after stopping and starting several time with no hunting at full speed. You have to get used to the full speed position setting.
The mower idled reasonably well, however at idle it sort of hunts ever so slightly. You can see the governor arm moving slighting however I want to understand if this is normal feature at idle speed. The idle is quite smooth and never stalls with no coughing or spluttering from the engine.
Would adjusting the carby screw we spoke about earlier enable the finishing touches to be put on this mower?
When I first adjusted the screw it was in tight. What adjustment do you suggest if applicable?
The funny thing is the guy that gave me this mower said the local shop tried to fix it but couldn�t. I do like a challenge.

Turning the pilot screw anticlockwise should richen the idle mixture slightly. Because it is a 2 stroke, I suggest you adjust the pilot screw for the best idle quality you can get, ensuring it is running at idle speed when you make the adjustment. (As the speed rises, the main jet begins to contribute to fuel supply as well, so the slower you can run it when making this adjustment the better.)

Remember, this is a 2 stroke. They don't idle well, but some are a lot better than others. If you are able to find a pilot screw position that gives the best idle quality, and it deteriorates when you turn the screw either way, all is well. Don't expect it to make a big difference, though: it isn't like a whipper snipper or chainsaw carburetor where each of the screws (H and L) tunes up sharply like a short-wave radio. The pilot screw has a very small effect because it is in series with a small jet and a small air bleed orifice.

I took your advice and was actually pleasantly surprised on how much better the idle is after adjustment of the mixture screw. It took quite a few adjustments to get the idle to improve. There is barely any movement in the governor arm at the idle position which made me a lot happier.
I also made some minor adjustments to the choke rod which assisted greatly in the opening and closing of the choke butterfly. I have noticed that without the butterfly completely closed the engine will not start when cold. It is usually a first or second pull starter when cold now.
This weekend I will take the blade plate off and clean the string collected up around the shaft. I�ll also put on 4 new blades.
The pull cord is already in really good condition so I see no need to replace it.
I�ll also take it out for a run in the long grass down the back of my suburb and let you know how it performs to finalise the thread.
If you anyone has any other suggestions for these engines I�d appreciate your thoughts because I would like to ensure the engine is reliable as possible
Thanks again grumpy

Just a simple word of caution, Jaffa. I recommend that you follow the engine manufacturer's instructions on how much oil to put in the fuel, not the oil manufacturer's. Any recommendation of higher ratios than 25 to 1 petrol to oil is good for the environment and extends the life of the spark plug, but it is not good for the piston or rings, and perhaps the bearings. Personally I would think carefully before using less oil than 25 to 1, but of course your neighbours' air quality expectations are not a trivial matter. In the end I personally follow the engine manufacturer's instructions, especially if they say 25 to 1.

Remember, keep the air cleaner clean. Otherwise you'll find you waste your time tuning mixture, because you will then have to start again each time you service the air cleaner.

I'll look forward to your report when you have given it a workout.

You raise an interesting point on the fuel ratio.
The manufacturer�s recommendation is 50:1. This recommendation is also clearly labelled on the new fuel cap I received which has 50:1 clearly labelled on it.
I have however been running the engine on 25:1 as the majority of other machines recommend this ratio. I figured it couldn�t hurt the engine with the exception of fouling a plug and being a little smokey on start-up. I plan on continuing to run the engine of 25:1 unless you think otherwise?
I didn�t get a chance to seriously test the engine on the weekend in long grass however I mowed my lawn without any issues.
I get back to you about the machines performance in the long grass.

The lower petrol-to-oil ratio will make the engine run a bit leaner than normal. This is partly because oil is more viscous than petrol and therefore restricts the fuel flow through the main jet, and partly because there is a bit less petrol in the fuel, and the oil doesn't really burn properly.

I take it you are running the correct spark plug, so you can probably check that it isn't overly lean by inspecting the plug after you have run it under load continuously for perhaps half an hour or so. If it comes up very pale brown, or whitish, it is too lean and you'll have to reduce the oil or you'll damage it. Of course there is no issue at idle, since you have already tuned the idle mixture.

I've already given my opinion on petrol to oil ratios: I like to protect the piston and rings by providing them with enough oil. However with a fixed main jet, to me the risk of cooking the piston through lean mixture isn't worth taking.