Carburetor mysteries

[george garside]

[quote="AlanBartlett"]I'm currently using the early carburettor on my engine and am wondering what does the tool look like to get the jets out of the bottom of the carburettor, am having fueling problems or so it seems, so would like to check out all posibilities of the carb.[/quote

undo hex nuts with suitable sapnner and then you need a sort of little box spanner with a sqare end of the appropriate size to unscrew the jets - it is not unlike some bleed keys for central heating radiators to look at but of a different size ? a bit of sqare tube of right size with a hole for a T bar could be made.

george

[AlanBartlett]

I have tonight had another go at this, and have narrowed it down to lack of fuel. The pump is pumping adequate amount of fuel through the line, but I have found the problem lies in the carb bowl and the fuel stop plunger. If I over fill the bowl, the car will start and run, but soon die, so i think it has something to do with the float level inside the bowl, that its not quite getting enough fuel in the bowl. because the float is shutting off at the valve, i remember hearing something about putting perhaps a washer behind the valve to effect the float level/ fuel level but not sure on this one, though i have tried this and this has made no difference.

[Forumadmin]

Putting a washer behind the valve will lower level which is not what you want. Is it possible the float is the wrong one or upside down?
Or perhaps the valve is the wrong length.
Can I confirm this is brand new petrol in the system....if it is old, the engine may start; but die quickly.
It could be a metering oriface is blocked. Overfilling would flood the carb but, when running, the idle metering oriface is not drawing any fuel into system.

[Tony Fearn]

Hi Alan.
You don't say what type of petrol pump is on the engine, but if it's the original one, with the glass filter bowl, check the valves under the two brass nuts on the pump body, and make sure the fibre washers are replaced under the nuts and then check the cork gasket that sits on top of the glass filter bowl. The screw below the bowl needs to be tight to effect a good airtight seal. You might need to make a new gasket.

Apparently some modern petrols spoil this cork, and if you're getting air into the pump system, then of course it won't have enough vacuum to deliver the fuel to the carb. as it should. The same goes for the later pump type that has a steel cap held down with a bolt. There's a cork washer under the cap which may need renewing if it has gone hard, and the cap needs to be tightened down so there's no air ingress. But care with the tightening of the bolt on this type of pump, (which perhaps, and you need to verify this, is a metric thread??? if it needs renewing) as it's easy to strip the thread in the casting.

Tony.

[AlanBartlett]

Forumadmin,

The petrol is new from a can i went and bought last night, also the float as far as im away can only go one way up because it has a recess at the top for the needle valve to locate and sit in, valve length I am unsure on, could there be variable lengths? Also all pipes and body is clean and an inline fuel filter put in, but every time i pump fuel in no blockage is apparent.

Tony

I've been using the later type pump, which the cap now that you mention it, does have the cork ring present, and isn't perished or broken. which im fairly happy with, as have had the pump apart a few times in the last 6 months just to check for stuck valves or bits of muck in there, but it all seems to be ok, when ever you bring fuel up from the tank it seems to shoot a large squirt of fuel from it both when you prime the pump by hand or cranking over the engine.

When I've had the bowl off of the carb, you can also tilt it slightly to see petrol flow out through the beak as it were, which means there is no blockage in the block, you can also blow through the beak and have air come through the jets at the bottom, so im happy that is also all clear. I've also had a feeler guage down through all the gasket seals connecting the carb to the manifold and this has shown no gaps in between the carb and the gasket and the gasket and manifold, so this all tightened down sufficently, though I don't think this is the problem as its more to do with the carb itself.

[george garside]

the following may be worth trying;
check that the flow from the pump into the carb is completely clear - I think there is a gauze filter in the inlet from the pump.

try a different needle valve if you have one - also check that the seat for the needle valve is clear as it may just be possible that it is seating on compressed 'crud' which would have the effect of it closing early i.e. before the float has fully floated!

try a different float if you have one

try a different carb which if engine runs will at least prove that the fault is within existing carb

A long shot ( or should it be longer shot) is to carefully check the slow running tube for cleanliness & adjustment as it may just be possible that when you fill the float chaamber from a container you are filling it to 'flooding' level so the engine is starting and running on 'flooded' fuel rather than stuff going through proper passages in the same way as an engine can be primed & started by pouring a small amount of neat petrol down the venturi.( or by squirting 'easy start' down the venturi.

do these one at a time , otherwise you wont know which did the trick ( not that any of them is guaranteed to work!)

george

[AlanBartlett]

Hi George,

Ive had the engine running previously quite well on the early type bronze carb, this seems to be working fine, i also made up a tool out of an old socket and an allen key to the jets you mentioned earlier. I'm just trying to establish why the carb would suddely stop working for no aparent reason. As for your suggestions im going to start by flushing through the valve again and see what happens, as for your post about the running on flooded fuel, I think this is the case as ive over filled it its in effect leaking into the throttle chamber and getting down to the plugs there for iginiting and running, but its also creating a substatial amount of drip from the bottom of the carb and not the bowl end either. Have also checked several times that the float is actually floating.

[george garside]

Alan, jus another 'long shot'. Try starting & running it with the throttle stop screwed well down , at leasst halfwayh, possibly more. If it will start & run with throttle stop well open it would indicate a blockage somewhere in the idling parts of the carb.

george

[Forumadmin]

Alan,
I had a similar problem on the Dellorto. The jet had actually come out! It was flooding the carb. Engine started OK but then died. You could tell mind as black smoke came out of exhaust.

So I suspect flooding. Does float float?
leakage passed main jet? Fibre washer?

[AlanBartlett]

Sp i have had it running, roughly on, and really bad starting, but the only way i was able to get it to start was as george said was to wind the throttle screw quite far down and eventually it fired up, but ran really rough. But on ebay I managed to find a carb with the same part number 30 vefh, so tonight i swapped all the jets over into my bowl and it fired up straight away, have yet to get it to idle properly how id like it as its still quite fast, ive taken a picture of my internals now this "new" one seems to be off an newer car, circa 1946, as a few differences to mine, but the overall jets fit in the same holes but are numbered differently. from the picture what would be the best configuration out of the two carbs internals.

[Keith Andrews]

have yet to get it to idle properly how id like it as its still quite fast

,
What are the butterfly bushes like? any slop?
The butterflies lined up in the bore properly?
Does it look like the butterflies have been screwed with in the past? ie the ends of the screws that hold the butterflies in.

Going from comparing the jets old and new, new being bigger, assuming none of them have been drilled sometime in the past..Having bigger jets and worn butterfly bushes 'patches' the mixture back to some sort of resemblence of 14.2 afr.

Check the butterfly bushes...generally the most common headache in old re used carbs.

[george garside]

Alan - I assume your ebay carb is not off a jowett. Also your existing carb looks to have different jetting to standard. The original jets should be
main80
comp80.
slow r 50

the 'new' jet sizes could well becausing the poor running.

The choke tube should be 25 and it may be that the' ebay 'choke tube is a adifferent diameter.

george

[AlanBartlett]

Hi george,

according to the listing it came off of a jowett 1945, possibly a bradford, the carb looks the same overall but has a few differences between mine like another jet located in the bowl, leading to an outside copper pipe, also what seems to be another hole in the throttle tube. but apart from that the newer carb has much better throttle bushes than mine. will get some more pictures up when i get home for possible idetification. one of my main concerns was the slow ruinning screw and the differences between mine and that, perhaps mine lost its point as it appears to blunt compared to the other one.

[Keith Andrews]

my main concerns was the slow ruinning screw and the differences between mine and that, perhaps mine lost its point as it appears to blunt compared to the other one.

That is a worry..that taper is quite critical....as are the butterfly bushes...and its not just a matter of re sharpen. That taper is a prescsion machined parts and so is the other end inside the carb...If it has been rounded , bent, worn a groove it also indicated that the inside seat has been damaged.
This usually happens on old carbs when the person cant get good idles/mixtures and the cause is , after stripping and cleaning not working, vaccuum leaks thru the butterfly bushes.
Keep in mind theseold engines are very tollerant of having wrong jets....
EG we drop in factory jets in a good carb, and it runs quite well, yet those jets are calibrated for the old British Pool fuels of 1936 to 1954, octane about 65 and none of the volitile hydrocarbins in todays modern fuels, and a very different Spefic gravity.

[AlanBartlett]

Tonight tried the ebay carb as standard to see if anything would happen, and pretty much it started straight away though i havent cleaned it yet, all ive done is clean the jets, now it wouldn't idle as slow again as id like it but having a look through a part zenith manual its because it has a copper tube below the throttle chamber which one end is linked to an unknown third jet in the bowl, and the other was open to air, this was causing the high idling speed, now what fills this hole appeard to be a nut according to the diagrams in my manual. On a better note, the butterfly bushes are seemingly in alot better in condition than my carb, this was also present in the very responsive acceleration, much more instant than both of my other carbs. possibly the best ive ever known it. even though the idle was high. So I think the thing to do now is to clean up both carbs and see if i can get one to run properly. this is all new terrortory to me but would like to know more about this subject.