Author Topic: Carby ??  (Read 1832 times)

cobbadog

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Carby ??
« on: 19 October, 2019, 10:58:23 am »
As you may know I've been having issues with getting the David Brown Cropmaster running properly. It would appear that the silly little spring on the needle and seat has been a fair amount of the problem and with this removed it no longer starves for fuel, yippee!
Next problem is air mixture. The engine runs rich and at idle sends up black smoke from the chimney. No matter where the air mixture screw is, all the way in or almost out of the carby it makes no difference to the way it runs. On full revs it runs ok but has flat spots when it revs up from idle. Not coughing just hesitating a few times then it revs fine.
I have had the carby totally apart, made new seals for the throttle shaft but the old ones I fitted a while back, "O" rings were in perfect shape but the latest thing they suggest to fit is nylon washers so I did that as well to get the best seal possible. All galleries are perfectly clear as you can clearly see through them all. Main jet tube and jet are clean as and so is the bowl.

Any clues to solving this problem please?
Cheers, John & Dee. Coopernook. NSW.

asw120

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Re: Carby ??
« Reply #1 on: 19 October, 2019, 08:33:07 pm »
Not much comes to mind, but....
Blocked breather hole,
High fuel level.
Have you tried to see if the idle comes good after turning the fuel off and letting it run out of fuel?
If it cleans up and revs like a Victa when the fuel is turned off, I would think fuel level.
I wonder if there is a drain you could put a drilled out screw in with some clear nylon hose on it to see the fuel level when running?
Mt Inter was doing this a while back. Was a tiny piece of crap in the needle and seat.
I'd live to know what you find in the end.

Jarrod.

cobbadog

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Re: Carby ??
« Reply #2 on: 19 October, 2019, 09:45:38 pm »
Cheers mate.
I always shut the fuel off when shutting it down as I dont like leaving fuel in the bowl. By doing this it made no difference to the way it runs.
With the fuel level I also thought of this so I installed another washer under the needle and seat to lower the seat down which in turn lowers the fuel level. On this carby the needle and seat fit into the top of the carby body and the only way to adjust fuel level is to add or remove washers. Fortunately there is a drain tap on the bottom of the bowl as this is a TVO engine (petrol/kero) so I can fit a clear tube onto that and face it upwards to see the level but since adding the extra washer the carby has stopped flooding but your idea is a good one and needs to be checked.
The needle n seat are crystal clear and no crap inside anywhere in the carby. Both jets and the jet tube are seating properly and are clear.
What I have found that has been contributing is a coil lead that is not quite up to scratch on the multimeter and one HT lead was not right and giving a bad reading. So I will get some new leads on Monday along with new fittings.
Next out came the plugs. Black as charcoal. Cleaned them up on the wire wheel and pushed a brush up inside the recess of the plug and tapped it on the bench and a heap dropped out. Kept doing this until all was clear. Ran the multimeter over these as well and still found one was not right so a new set of plugs on Monday if they have stock.
Last was the points. Looking at them they were in good condition with no pitting at all. I still gave them a rub with the points file and then checked the gap.
So I put the plugs in and did a start up and it sounded alright so I took it for a run down the street. Got going and wasn't too bad but a couple of minutes later it played up so chucked a u-turn and parked him up until I get the leads and plugs.
The story continues soon.
Cheers, John & Dee. Coopernook. NSW.

cobbadog

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Re: Carby ??
« Reply #3 on: 21 October, 2019, 02:38:21 pm »
Still playing with this and thought of a few things last night after receiving a link to Solex Carbies cleaning and tuning them.
First thought was, is the blanking plug opposite the bleed screw (air mixture screw) suppose to be open to allow air in. NO. It is a blanking plug and although it looks like a jet from the outside it is definitely a blanking plug.
Then were all the jets the correct size. YES.
Again are the galleries clear from blockages. YES.
Cheers, John & Dee. Coopernook. NSW.

cobbadog

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Re: Carby ??
« Reply #4 on: 21 October, 2019, 02:47:49 pm »
Next was again making sure everything else was where it was suppose to be and work out where does the air come from and go to. SO I have put up pics of the top and bottom side by side and then marked with an arrow where the air comes from and goes to. Although it is tricky to see, you should try taking a pic of it, there are no blockages but at least I now know roughly where the air bleed screw should be to start metering the air flow. The link posted has been a great help and I have confirmed the jet sizes with the chart and only the main jet is slightly different being a little bit larger than middle of the road on the charts. But this should not effect the running rich at idle and the idle jet (g) on the chart I think is the right size as I cannot read it properly.
Cheers, John & Dee. Coopernook. NSW.

cobbadog

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Re: Carby ??
« Reply #5 on: 21 October, 2019, 04:49:12 pm »
Something I have just now noticed is what I thought was the blanking plug marked as "W" is not and it is the screw to hold the choke tube in place. In the picture of the Solex FV carby there is no sign of the air bleed screw or the plug, yet it is there on the carby and is mentioned in the section on 'slow running pages 14 -16 on how to adjust it.
Cheers, John & Dee. Coopernook. NSW.

cobbadog

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Re: Carby ??
« Reply #6 on: 22 October, 2019, 09:04:35 pm »
Picked up some new plugs today while in town and called into Rustic Spares for the new plug leads to make up myself along with all the new connections. Then John suggested a new needle and seat and so I took a couple home to try. Had every intention to fit the needle n seat, make the new plug leads and fit the new plugs and then the phone rang with work so all this has to wait until tomorrow afternoon.
Cheers, John & Dee. Coopernook. NSW.

asw120

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Re: Carby ??
« Reply #7 on: 22 October, 2019, 10:34:21 pm »
As you say it runs just the same until it stops after you turn the fuel off, I am thinking a high fuel level is not the problem.

I am wondering now, how did it run before the rebuild? I missed that bit.

For the record; I have had oversized mains affect the idle adjustment on a car, twice now - both times with aftermarket Holleys (a 350 - two barrel and a 600 - four barrel) They would idle with the screws bedded until I put smaller mains in. Having said that, they are very different to what you are working on.
I have also had a perforated power valve give a very rich idle, but I highly doubt you have one of those.

Wisely, you are not neglecting the electrics. Be interesting if something there fixes it.

Finally, I forget now, do you have even compression? (no leaky intake valves blowing back through the carby and picking up fuel twice for that cylinder)

Your updates are much appreciated; we have all had these sort of troubles and I usually learn something from threads like this one.

Don't despair - you will get it!

Jarrod.

cobbadog

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Re: Carby ??
« Reply #8 on: 23 October, 2019, 07:49:37 am »
G'day Jarrod,
Yeah before the paint work and being off the road for about 12 months as I did brakes and oil seals inthe back end, changed the front axle over from another tractor but the engine was done a few years back and used to run fairly well and nothing like this mess. No compression tester to do that but that is another option to look at if the electrics dont help resolve the issue.
Not pissed off about the troubles just annoyed.
Cheers, John & Dee. Coopernook. NSW.

cobbadog

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Re: Carby ??
« Reply #9 on: 23 October, 2019, 03:53:16 pm »
Latest update !
Well I made all new HT leads and one for the coil. All tested perfect once made then again fitted into the cap. All new plugs fitted and the needle and seats that I bought home do not fit so they can be returned to John, thanks John for the loan.

So now I know exactly what it is NOT. Non of the above or I am confident it's not the carby.

From start up today I got a whole new set of issues and the main one is backfiring. So next attempt is to check the timing and fix that if required, then try a new coil and see where that takes me.

 :o
Cheers, John & Dee. Coopernook. NSW.

cobbadog

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Re: Carby ??
« Reply #10 on: 24 October, 2019, 02:46:05 pm »
Well guess who swapped #1 n #2 plugs leads over causing the back firing?   ME  !!!!!!
That sorted that issue and then I did the start up and it jumped straight to life but still running rich. So back to the bleed screw (air mixture screw for us Aussies). I slowly a bit at a time wound it out a 1/4 of a turn at a time and not making any difference until I actually pulled the screw all the way out. The immediate result was the engine sounded smoother like it use to sound, so this points me back to the carby yet again.
Ever feel like you are going around in circles?
Anyway, in the pic below that I posted before it shows you both top and bottom of the carby and where the screw goes through. So the screw makes no difference until it is removed in total so that points me to the last of the 3 openings, the one closest to the head of the screw is somehow different to the one on the opposite side but they look identical when you poke around in there and shine a torch. It actually waits until the screw is all the way out, not just at the point where the taper would be above the 3 hole.

Any clues please?
Cheers, John & Dee. Coopernook. NSW.

cobbadog

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Re: Carby ??
« Reply #11 on: 26 October, 2019, 02:50:31 pm »
Episode 1,234, way too many.
Once again a night of ideas on what to do to resolve this mess. Fuel level in the bowl was measured by connecting a clear plastic tube to the drain cock on the bowl and holding the tube agaist the bowl. Level was about 3/4 full. I have an aluminium washer under the needle n seat and this raises the level too high, to the top of the bowl and floods so went back to having a fibre washer with the aluminium one and back to being 3/4 full. At the moment it does not starve on full throttle standing still but might when on the road, will find this out tomorrow on a quick run up to the forrest and back.
Next was to once again strip the czrby down to being completely apart and double checking cleanliness and re-assembly ensuring that the 3 parts of the main jet are assembled correctly and fitted firmly in place.
Then with yet another read of the Solex carby link something hit me hard in the face, bloody air cleaner. This runs an oil bath cleaner and when I dropped the bowl it was not only over full but the centre ring where the air breaths in was also full of oil. So I lowered the oil level and removed the oil from the middle. Hopefully this was the right thing to do.
Still with the oil bowl off I started the tractor and ran it for a while so it was warm. Then I dropped the idle screw right back so it was not touching the stop and all the time changing the mixture although it did not seem to do much. So I kept winding the mixture screw out until it was in my hand. You can hear the air rushing in through the hole and when you put your finger over the hole the engine revs drop and runs a bit rough. Threw the oil bowl back on and nothing changed there so that is done. There is a remote chance that there is still oil inside the air cleaner where the steel wool looking stuf is and may still be choking the engine. Maybe after the run tomorrow this too will improve.
With a couple of runs up and down the back driveway it certainly pulls well with no hesitation at all where in the past it did. SO if nothing else this has improved.
All I can do now is take it for a run up hill and down dale and along the road and give it a good gallop and re access it from there.
Cheers, John & Dee. Coopernook. NSW.

cobbadog

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Re: Carby ??
« Reply #12 on: 27 October, 2019, 04:48:13 pm »
Thought I may have had this beat but no unfortunately. The further we drove the worse it got but at least we got there and back for a picture shoot so here are a couple of him in the local State Forrest just a few kilometers from home.
Since getting home I have removed the plugs and cleaned them again as they are black as can be, checked the HT leads with the multimeter, removed the coil and condensor and hooked them up to my testing machine which rates the condensor, checks it for leakage and then tests it. The coil then is connected and a voltage is sent through it and you adjust the gap in the round window to produce a good constant spark over the widest gap on the lowest voltage. Once this is set you then select 'heat' and this heats the coil as if it is on the engine and running at temp. After minutes of heating then switch to test again. I got the same result after the heating which shows it is in good working order. I then removed the points and dressed them up and also found there was a small amount of oil on the base plate so I cleaned this all up with carby cleaner and a soft rag. Put it all back together and still the same. Back on the other side the oil bath bowl is off again to check that oil has not got back into the centre section again but it is clear now.
Cheers, John & Dee. Coopernook. NSW.

cobbadog

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Re: Carby ??
« Reply #13 on: 29 October, 2019, 04:26:54 pm »
While waiting for the new needle and seat to arrive I bought a compression tester today and tried it out. I did the test on a cold engine, not sure if that is the right thing to do and got the following readings;
1 - 75 psi
2 - 75 psi
3 - 72 psi
4 - 75 psi
Each held the pressure for a short time before I released the pressure.

So the question now is, what should the pressure be and should I have done it hot? I looked in my workshop manual and it gives you all the specs like bore diameter x stroke, cu in, bhp and a compression ration of 4.7:1 but no numbers on what compression it should have.
Cheers, John & Dee. Coopernook. NSW.

asw120

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Re: Carby ??
« Reply #14 on: 29 October, 2019, 04:59:44 pm »
Sounds like good numbers to me. I figure you would hear if it was blowing out the intake.

Jarrod.