What's Wrong With My Carb?

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mds
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What's Wrong With My Carb?

Hi Everyone,

I've just rescued a Qualcast Suffolk Punch 35S. The previous owner - a neighbour - left it out for the scrap man when he couldn't get it started. I took it home and soon realised he'd had the carb apart and put the float back in upside down! 

Beyond that, he'd taken a pair of snips to both the throttle and the drive cable. I tinkered with it, and managed to get it running - albeit with a pair of mole grips holding the carb open! It ran perfectly and is in very good order so I've splashed out on some replacement cables and fitted them both.

Now, I'm stuck! The throttle cable is connected correctly as far as I can tell, but something's not right with the linkage. Hopefully you can see the video below:

https://1drv.ms/v/s!ArItlfZQfRNimxh3rw4biu4Tnw-X

.....and showing the linkage:

https://1drv.ms/v/s!ArItlfZQfRNimxl7PIq-a3a1f0Ag

As you can see, the butterfly is not being opened despite the throttle cable being pulled fully. Can anyone advise where it's going wrong please?

Many Thanks!

 

 

 

 

wristpin
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Cant really see what's going

Cant really see what's going on from in your vid but perhaps a recap of the throttle control and governor action will help.

The engine speed is the product of the control cable trying to open the throttle and the governor trying to close it. This achieved by the cable being connected to the throttle butterfly via a link tensioned by a spring, the cable and spring try to hold the throttle open (by stretching the spring)while the governor arm tries to close it.

With the engine not running the cable should move the throttle butterfly shaft to full speed but as soon as it is fired up you should see the reaction of the governor arm trying to close it.

Applying this to what you have in front of you may suggest that something is not hooked up correctly.

This may be of assistance

https://www.dropbox.com/s/vsy8xt2syoyfxky/Suffolk%20Dellorto%20linkage00...

Chris G
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Yes it is hard to see what is

Yes it is hard to see what is going on there. Have a look at the download Wristpin has provided, its probably something simple.

That lever should move with the mildest of pulls, its not stuck on that pivot circled is it?

Also do you have that return spring circled properly fitted?

mds
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Thanks both!

Thanks both!

I was hoping the videos would show that, although the throttle cable is being contracted, and the linkage is moving unhindered, the movement isn't sufficient to open the valve. In the first video, you can see the governor spring is being tightened, but that's the extent of movement. The bell crank is not being moved by the vertical link - which I expect it should be (?) to open the butterfly valve?

Chris G - thanks for your photo, it's very helpful. I don't believe there's anything stuck or being fowled, but I'll have a look at the schematic - thank you Wristpin! - and see if I can work out what's amiss.

Cheers !

wristpin
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The upward action of the

The upward action of the Governor arm is trying to close the throttle against the downward pull of the Governor spring so if this is not opening the throttle butterfly could it be that the horizontal link is hooked into the wrong hole in the throttle spindle plate?

mds
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Yes - I think the link to the

Yes - I think the link to the valve

is wrong. How does it come off? I can’t seem to wiggle it free..

mds
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Edit: Swapped the linkage

Edit: Swapped the linkage around and it now seems to function more like a carb! 

Just need to get a fuel hose for it tomorrow and hopefully be good to go! Thanks very much for your guidance! I’ll revert once I’ve got it going...

Chris G
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Good result! I was going to

Good result! I was going to say to remove the carb from the manifold then its easy but you have sussed it :-)

PetrolHead
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Hello, all new joiner and

Hello, all new joiner and first-time post. I have the same mower lurking in the garage that I took apart to clean up and change a few gaskets a long time ago. I managed as assemble it but had exactly the same issue described above with the carb not functioning properly - with exactly the same solution - so wanted to thank all for helping on this post.

I set the engine by first getting it idle as slow as possible then adjusting the mix half way between lean and rich. then resetting the idle. Blades are blunt but I still got a fairly decent mow from it.

PetrolHead
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I'm stuck. I thought had this

I'm stuck. I thought had this running but when I took it out it started at first but that was it. I have checked the spark and it is good. I haven't stripped the carb side yet, but this was previously cleaned and there is fuel in the bowl (if I press the release valve it leaks out).

I think it may not be set up right. The relationship between the governor and carb, and the mixture and idle setting.

Can anyone suggest a procedure to get it (1) started then (2) set up correctly? 

wristpin
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This sort of issue is easier

This sort of issue is easier solved “ in the metal”, but assuming  that it was running ok whenever you last played with it I would - 

Drain all the fuel from both the tank and carb and refill with a bit of pump fresh fuel.

Screw in the idle stop screw fully to hold the throttle open regardless of the Governor linkage.

Squirt a bit of fresh fuel or carb cleaner straight into the air cleaner.

If it then fires up, gradually reduce the idle stop screw down to the stage where you can achieve a satisfactory setting balancing it and the idle mixture screw.  

Your original images are not the most informative but it looks like it may be a Dellorto carb . In that case there is no adjustable main jet, just an idle mixture adjustment, so if it won’t run with the throttle held open it suggests a blockage of the main jet/emulsion tube.

 

PetrolHead
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Thanks so much, I did this as

Thanks so much, I did this as well as carb off and clean. It started first pull (yes it has a delleroto carb).

It ran for a few mins, I had it idling OK. Seemed good, then failed again and would not start. So I left it.

I am wondering if the machine is worth the effort? How does a Punch 35S rank in terms of quality gear - it does NOT have the QX cassette.

Also, when it runs I feel that it smells a bit more than my other machine - maybe it is sucking a bit of oil up not sure. Do these engines have any common failures areas?

 

wristpin
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Difficult by remote control

Difficult by remote control but return to basics. Tank vent, fuel flow to the carb . Thorough clean of carb with all jets etc removed using the thin tube on an aerosol of cleaner to blow through all orifices etc.

Unlikely , but it could be an ignition issue. The simplest is that your idle setting on the throttle control is moving the tag too close to the kill wire and it’s making contact due to vibration. If your engine has electronic ignition it could be a dodgy coil. If the joint between the coil case and the potting material around the windings and electronics separates , the damp can get in and cause issues before total failure. Take the plug out and in subdued light see if there is a consistent spark when pulling the rope.

Other than the coil issue those engines are pretty reliable.

wristpin
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Difficult by remote control

Sorry the save button on the iPad appeared not to register but then did a double post.

PetrolHead
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I removed the brass pin with

I removed the brass pin with holes in it and gave it a decent clean with compressed air. And the mixture screw was cleaned. Where is the tank vent? I've installed a new stop valve and pipe.

wristpin
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Where is the tank vent?

Where is the tank vent?

Hole in the tank cap.

You need to clean all the passages and orifices in the carb .

hillsider
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While on the subject of

While on the subject of checking and clearing jets and passages have you checked the Cap nut that holds the float bowl in place and screws into the main jet passage? If that is partially blocked strange things will happen.