in depth carby

Victa G4 Carburetor In Depth Guide Part II

Our continued guide to understanding and fixing a Victa G4 carburetor.


    • Flat Head Screwdriver
    • Pliers
    • Carburetor Cleaner

Step 1

Insert the cam back into place and ensure that it is moving correctly, that it does so with relative ease. Turn the cam clockwise as far as it will go and then begin to reinsert the throttle cable – thread the cable into the appropriate grooves to hold it in place and slot the gold ball at the end of the cable into the cam (having the throttle in the off position makes this easiest).

Step 2

Next re-install the ignition wires by first turning the throttle to the middle position then place the cover and plug over the wires and insert the red wire through the hole in the body of the carburetor where it is supposed to go, push the cover flush against the carburetor body. The second ignition wire will be inserted at 90 degrees to the first, you will notice there are holes in the cover for this wire to be threaded through.

Step 3

Place the poppet valve through the designed hole from the bottom of the carburetor body, the pointy end should protrude from the hole in the center of the cam. With the poppet valve in place you can now place the lifter in position – the lifter has written on it which side is intended to be place down – its three prongs slot into grooves on the inside of the carburetor body.

Step 4

Place the small spring into the grooves on the lifter then┬áplace the diaphragm over the pointy end of the poppet valve, it should clip in place – the shiny side of the diaphragm should face upwards. Also clip the metal retainer onto the end of the poppet valve – the flat side of the retainer should face down.

Step 5

Now we can move to the front of the carburetor – inspect the primer cap and ensure there aren’t any cracks or missing pieces (check the primer bulb too). Place the primer o-ring around the sides of the primer cap – as you do look out for any breaks or cracks in the o-ring. Place the small jet into the primer cap with the pointer end down then hook the float in place – when pushing the float up as much as possible the small jet should limit its movement; if this isn’t the case then the jet will need to be replaced.

Step 6

Move the primer cap and all the bits we have now attached into position in the front of the carburetor body, there is a line on the front of the primer cap which indicates the correct orientation of the primer cap – if the carburetor leaks petrol when reassembling this orientation is the first thing to check. Clean out the main jet and the screw the primer cap in place – gently tighten the main jet so as not to thread the plastic primer cap.

19 Responses to “Victa G4 Carburetor In Depth Guide Part II”

  1. Whew! what a job I’ve been having recently with my Victa, owned for the last 23 years!! with very little problem, however recently the decompressor valve went, I replaced it along with the carb diaphram and changed the kill switch to a manual.

    Now I can get the engine to run but its so erratic, can you confirm 2 things here,

    1. Is the carb needle definetely pointy end down, this seems so wrong as one would expect this to seal the fuel, but happy to be proved wrong.

    2. I have a spare brass fuel jet which has no hole on the “outside” and another which has a small hole in the slotted part of the jet, which one is correct? the holed one is original and ran fine for years but now lets fuel leak out, perhaps if the needle is the wrong way around.

    I also replaced the head gasket as a matter of course.

    Its been a brillaint piece of equipment and I think its something minor to sort but just cannot seem to get it running smoothly.

    Any help would be appreciated,
    from Scotland UK

    • lachlan Osmotherly June 13, 2015 at 7:56 am Reply

      Hi Rob

      1. The carby needle is pointy end down (Or Pointy End towards the brass seat) This is what creates the seal when the float rises.

      2. Where does the fuel leak from the primer bulb or the jet? There should be a hole in the shaft of the jet and a hole in the end that sits inside the carby.

      If it’s running very fast you may have air leaks causing a lean mix, you should cover the whole the original ignition wires resided in and check the air hose for any leaks if this is happening.

      Any further details about the behavior of the mower would help me suggest solutions.

  2. Dear Lachlan,

    Thats a real scottish name from here no doubt you will know your ancestory.

    Anyhow have managed to change the carb needle to pointy end facing the float, replaced both float and needle.

    I’ve changed the jet to a “non holed one” ( in the original outside slot, think it has just worn through from the inside) which I’ve now changed. Fuel was coming out of here but not the primer bulb.

    I used araldite on the old kill wire grommet hole on the carb body to seal following your advice about perhaps it might be air getting in. No diference

    Checked and changed the diaphram.

    Checked both carb springs look fine.

    Checked the operation of the throttle cable, it does move the cam inside the carb its OK with full movement.

    Checked the rubber ring at the inlet manifold its OK.

    The air filter is old so I removed it just incase it was clogged, no diference so placed back in.

    Changed the decompressor valve which was needed, now that bit is perfect.

    Fuel is getting through from the tank OK, checked the air inlet on the tank cap, its OK.

    So, I can get it started easily enough I keep gently pressing the priming button, if I dont keep priming it just conks out after about 20 seconds.

    The revs stay pretty much on the high side, I tried to move the inner rod to position “A” and tried the other positions too but no change.

    Tried changing the body of the carb with a second hand one — no diference.

    I’ve had many motorcycles over the years and still do all my own car maintenance so I should be able to sort this one out but cant it would appear!!!

    The air hose next to the carb could do with a wee tighten up but I have run carbs on bikes before with no air filter so I didn’t think this would be too much of an issue.

    Now at a complete loss…………Grrrr

    Any help would be appreciated

    • lachlan Osmotherly June 14, 2015 at 7:09 am Reply

      Hi Rob

      The pointy end should face the brass seat in the primer cap not the float.

      You have checked most of the important pieces, The symptom of the high rev’s tends to happen in a lot of aging Victa’s, When all parts look and seem to function fine the best technique to slow them down is to use 1 or 2 of the brass poppet valve spacers we sell.

      The air hose being loose probably won’t make much difference, I experienced a mower with very similar issues about a month ago, I replaced the carby body to solve its issue.

      If it keeps running while priming there is two more things I would suggest checking, Get a small needle or wire and poke it through the hole in the carby body that starts where the main jet screws in and exits into the main body of the carby, this hole can sometimes get blocked.

      The other sugguestion would be to check the seal under the pull start and the sealed bearing at the bottom of the crankcase, Because if the carby is working and not blocked the only reason fuel would not make it to the combustion chamber is a lack of crankcase vacuum due to busted seals.

  3. Ok thanks again for your help Lachlan,

    I’ll give your suggestions another go and see how I get on.

    1. Given that I’d changed the carb bodies previously it may not be a blocked hole , but I have carbon depleting EGR valve spray I used on my car I might also give that the once over while in there with the fine needle.

    2. I had the pointy end in the right place to begin with will now change that back following the advice.

    3. I’ll get back to you once I’ve carried out the checkes on the seals, are these available to buy from you guys these days?

    Your help and guidance is very much appreciated.

    Kind regards

  4. Hi there

    I cleaned my carb and the mower would not start. Then I loosened the carb and it started. Then I noticed that if I just kept to carb close to the manifold it would run,but as soon as I would fit the carb. Then the motor would smudder and stop.
    Any idea what could be causing this?
    Thanks Nuno

    • lachlan Osmotherly November 13, 2015 at 2:52 am Reply


      it sounds like your mower is being choked by lack of air flow, I would inspect your air filter and make sure there is not blockages in the hose connecting the filter to the carburetor.

  5. Great advice. You didn’t mention if there are two float valves (yellow and black0 I had an old black one in and got sold a yellow one – still won’t start. Got spark but a problem with fuel getting in. All new cover, needle and float. Could it be the screw that holds it all together?

  6. Hi lachlan Osmotherly,

    Mine is a very old MKll as far as I know. (South Africa). I have had it at least 34 years and bought it second hand.

    Just replaced the carby as I was having problems, it would start easily, but not run longer than 10 secs.

    Now it starts fairly easily and runs, but I’m having trouble with fluctuating rev’s like the governer is not working properly. The air hose for the governer up to the fan casing and into the casing, is open, but haven’t checked it down into the carb. Would this be the problem or would it be the diaphram leaking air?

    • lachlan Osmotherly June 29, 2016 at 2:25 am Reply

      Hi Peter it is more likely to be the Diaphragm leaking air, Air leaks are quite common on older victa mowers, It can also be caused by damaged crankcase seals or cracked intake hoses letting in air

  7. G’day,
    Great work with the website.
    I’ve stripped the carby and degreased it. I noticed what appeared to be grease on the internal moving parts, mostly between the cam and body.
    Did these come greased from the factory and do I need to re-grease it on reassembly?
    Cheers, Adam.

    • Hi Adam

      Either some 2 stroke oil or a small amount of grease can be used between the cam and the body, This will help ensure the throttle cable is not sticky when the carburetor is reassembled.

  8. Hi. Dr. Victa,

    My VC 300 has had all of the above easy bits serviced but still refuses to fire up.
    I have now checked the large O ring under the pullstart wheel–seems OK, but won’t start.

    Strange thing, when I remove the new sparkplug & pull the Cord the cord yields smoothly & steadily all the way to the 1m.+ of its length.
    But replace sparkplug & the Cord stops halfway out, the engine kicks back so fiercely it tugs the black plastic Cord Grip clean out of my hand & slams itself hard against the plastic cover. And after all the dramatics, no sign of a start–up. Any ideas ???

    Also a Victa apprentice I know suggested I remove the exhaust box & inspect the piston for scratches.M y Victa has had v. little use, been well housed, how in the world could the piston have been scratched ???

    Would apprec. your diagnosis & suggested treatm’t.



    • lachlan Osmotherly February 22, 2017 at 9:59 am Reply

      Hi Tony

      The most common cause of the symptoms you describe is not having the blades and blade carrier installed or having them installed incorrectly. The blades must be firmly & correctly installed in order for the mower to start correctly, if they are not the timing of the engine is disturbed and it tries to start in reverse yanking the pull cord out of your hand.

      If you Victa has had little use there should be little scratching present, Scratches are caused by a number of factors, Dirt passing through the air filter into the engine, Incorrect Fuel mix & Excessive carbon buildup inside the engine.


  9. Hi,what is a poppet valve spacer,and where do they go? I have an ageing victa and it tends to run very high revs,where on your site can I purchase them? Thank you kindly

  10. Thanks Lachlan ,I have a victa master cut 460,had purchased a diaphragm and new springs,put the carby back correctly,but it will not accelerate or decelerate,just idles ,the poppet valve looks rather past its day,as does the cam ,when I purchased mower not long ago you could only push the accelerator down half way,maybe I would need to purchase a new carby body? Cam and poppet valve,do you sell the G4 body,your help would me much appreciated,love your site and your online shop,you have been a great help,all the very best,Andrew PS is the poppet valve supposed to click into place? As mine just spins around,thanks again

Leave a Reply