Colt Update and Strange Carb

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Simon
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Colt Update and Strange Carb

Hi guys,

Time online has been very limited but I've been beavering away on my Suffolk Colt. I've learnt a lot and after a lot of perseverance I'm up and running - mainly! I'll include a picture of it at the bottom of this thread.

The mower has a strange carb which I haven't seen before - with just 1 jet on top, and where the other jet would be there isn't anything other than a blanking screw. I've been inside the carb and everything is clear, unblocked, new gasket etc. But whatever I do I cannot get it to run with no choke, it has to be in the position shown in the photo below. Can someone advise please? I can't find any information on the internet either as all the diagrams have two jets. Here is a picture of it, you can see the jet at the very top and the blanks where the other jet would usually be......

 

This is the mower, not exact paint colours but I'm happy enough with it, just have to do the grass box next........

Many thanks,

Simon

hortimech
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You appear to have a carb off

You appear to have a carb off an A98 Alloy engine, so the carb (which has a fixed main jet instead an adjustable one) is probably jetted for the A98 engine. If, after cleaning the carb again and ensuring everything is spotless, it still doesn't run off choke, I think you will have find another carb, or a new lower half for yours that does have an adjustable main jet.

 

Simon
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Thanks for your reply. I went

Thanks for your reply. I went through the carb and cleaned everything, unblocked everything and so on. I actually have a spare bottom of a carb from another colt - just the bit with the float and a jet in, is that what you mean? That will give me the second jet and make tuning easier?

hortimech
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Well, yes, by fitting a lower

Well, yes, by fitting a lower half of the carb with an adjustable main jet, this must make tuning easier ;-)

Simon
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Thanks I'll have a go and see

Thanks I'll have a go and see what its like. Is the carb that's currently on it not used very much?

merryman
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I seem to recall that there

I seem to recall that there is a brass fixed jet behind that blanking plug. Once I removed and cleaned it, the engine I was working on, ran a lot better. I believe the change to fixed jets was a nod to emission control, ridiculous when you consider something like a 90s V8 Range Rover would put out more pollution in a mile than a Qualcast Punch produced, all season. I noticed that the list of production modifications for the Qualcast Mowers that recently appeared on here, listed a change to an adjustable main jet for the DelOrto, that carb really did have problems in fixed jet form.

Simon
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Bit of positive news! Put a

Bit of positive news! Put a new bottom half on which gave me the second jet and I managed to get it running lovely. So thanks for the advice of doing that.

I ran it a bit later in the day and it ran until the fuel in the carb bowl was used up then stopped. Primed again and it ran again then stopped once used. Fuel is going out of the tap and down the pipe into the carb but not filling the bowl without pressing the primer.

I've just had a look and I think I can see a little fuel seeping out of gasket between the top and bottom of the carb - it's dark so I'll have to double check tomorrow. Would that mean air is coming in through that gasket and stopping the bowl filling? I have some hymalar I put round it.

wristpin
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Sounds a bit strange ,

Sounds a bit strange , shouldn't need jointing compound. Pull the fuel pipe from the tap and hold a jar under the tap and check the fuel flow for 30 seconds. If it diminishes try releasing the tank cap. If it then picks up check the venting in the cap. Also check the gauze / nylon mesh filter above the tap.  If that's alright drop the float bowl and do the same . If the flow is weak there may be some obstruction above the needle seat. Unscrew the seat and check again. If there is a good strong flow out of the needle seat have a look at the tip of the float needle and check that it's not slightly hooked and hanging up when it should drop to admit more fuel. The float needle is usually fixed in the float but I suppose that it could have been pushed upwards through the float and be cutting off the fuel too early.

Simon
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Hi wristpin, thanks for the

Hi wristpin, thanks for the troubleshooting method - it worked! It was a mixture of some gooey gunk around the neadle seat allowing only a dribble of fuel to pass through and the point on the top of the float was straight but a bit jagged at the top (it looked like someone had been using it to clean jets or holes in the carb). Anyway, replaced it with an old one and it runs nice.

I had a bit of a disaster putting the carb back together though. I was screwing the left hand bolt in which attaches the top to the bottom of the carb and I thought it felt like it was just spinning rather than tightening. The next minute it snapped off with the end left inside (I wasn't applying hardly any pressure). So I only have one bolt holding the carb together. I think its snapped bridging the join but it didn't really feel tight before it snapped.

Is it OK to run it and see how it goes? Alternativley will it be a case of drilling it out, re-threading and get a new bolt? One problem fixed and another caused :-(

wristpin
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It will probably run ok with

It will probably run ok with just one screw but be gentle pushing the air filter on .  With the tension off the screw you may be able to tease it round with a fine pointed scriber or pick or if you have an old pin punch , a bit smaller than the diameter of the sheared screw, sharpen it to a fine chisel edge and tap it onto the top of the screw and see if there's enough grip to turn it. Warming the bowl up in boiling water or with a heat gun may expand it enough to release its grip on the screw.

If it comes to drilling , make very sure that you get the pilot hole centred. It's too easy for it to wander off into the soft alloy. I've got a small selection of left hand spiral twist drills for such emergencies , some times they will spin a sheared screw out on their own.

Simon
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Thanks again, I'll see how it

Thanks again, I'll see how it goes and follow what you've said should anything happen. The air filter is empty at the moment, whats the best materal to put in it? I have some coarse sponge which goes in fish tank filters, but what is the best thing to use?

wristpin
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The correct foam filters are

The correct foam filters are quite fine and still available but any open cell foam is better than nothing.

hillsider
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Do be aware though that some

Do be aware though that some foams dissolve in fuel as I found out after carefully making a replacement filter.