Hi, I have just set the timing up on my bus and want to set up the carb now. The mixture screw is set at the manufacturers base setting the float level is set up too and the idle screw also set up to base settings. However, the mixture is still too rich I think as the plugs are new yet well sooted up. I have a standard 1600 twin port type 1 engine and just want to know what jet sizes I should have or need in the carburettor for this engine? I have read the big threads on this carb but, cannot see a definitive answer. Anybody any ideas?
@mikedjames is your man for the weber . Very helpful chappie He runs a 1641 but should be very close and will no doubt be popping in shortly ....
@mikedjames is your man for the weber . He runs a 1641 but should be very close and will no doubt be popping in shortly ....
Ba sically the primary jetting is set rich and the secondary jetting is set lean out of the box. As the stock throttle pedal linkage does not open the secondary throttle fully the average installation runs rich. The richness is to compensate for the lack of preheat with a shiny EMPI air filter sitting on top of the carburettor while the manifold freezes. Which is what you get in the kit. The trick with EMPI kits is to know which bits to leave off.. But the lean wide open throttle gives a bit of a risk on long runs of overheating. Looking through the log of changes Primary main 130 Secondary main 140 Primary idle 47 Secondary idle 80 Primary Air corrector 160 Secondary air corrector 180 This is with heat risers on the EMPI progressive manifold, hot air from a stock oil bath air cleaner with sawn off cold air inlet, a throttle linkage with 1.17:1 increase in movement over stock for full throttle (either bellcrank at carburettor , use the better quality manifold with crank, or a Buttys Bits pedal linkage that lets you adjust the movement)
What do you mean by this? "hot air from a stock oil bath air cleaner with sawn off cold air inlet" I have an oil bath I could use but, a shiny scat air filter fitted.
I use the stock oil bath with a plenum box on top of the progressive. Made it myself but you can buy them. I cut off the teapot spout bit on the cold air intake to allow more air in. According to the Manifold Air Pressure (MAP) sensor this setup loses under 1 psi of air pressure to the manifold under the secondary throttle plate at wide open throttle. Peak RPM has been recorded at over 5200 rpm or 35mph in second gear so it is not stopping the engine breathing too much. Still try to stay under 4500rpm normally...
I can definitely do that, what oil do you use in the oil bath and how much do you put in? I can now also see why I have a second hole in the rear tin next to the pulley. As a matter of interest do you have your electric choke still connected? If not how does yours start? Mine has no choke and seems to take forever to start, that said I have only this week timed it properly and don't know if that will make a difference yet.
The hot air comes through a 'stove pipe' fitting that you can still buy, but alternatively the end of the hose goes over and points at the fins on the number 2 cylinder head. The oil I use is engine oil - I usually chuck some used oil in there because before I fixed my engine, the breather from the blowby on the worn out engine was feeding it constantly with used engine oil anyway. Yes, I do have the electric choke connected, with an insulating plate on the fan housing to stop short circuits. The progressive carburettor will not work properly unless the electric choke is working or somebody has mangled it to stop the choke operating at all. With the choke permanently active it will cause extreeeeemely rich idling, but there is a vacuum circuit that pulls the choke off at high load (fast flow through part open throttle) , and then airflow through the choke holds it open at high speed and wide open throttle. So even when it is permanently active, the choke only really messes up the idle mixture. There is a second throttle end stop screw round the back , which is used to set the cold idle, pulling on the wire going down the left hand side of the carburettor as well as pulling on the choke flap mechanism against the vacuum from the venturi of the carburettor. Then when the choke clicks off (in three steps on the cam) , the cold idle screw jumps off a cam, and then the little screw on the left side of the carburettor sets the idle speed. If the choke is always on, then the mixture will be very rich and you are close to flooding the engine on warmer days or warm starts. Basically when the progressive is installed in the place of the stock carburettor, it behaves pretty well the same as the stock carburettor except that it does not restrict the engine at higher RPM in the same way as the stock. I find that it starts pretty well first time with a tap on the throttle, sometimes fires and then dies and starts the second try but generally very quickly.
Managed to finally get the electric choke fitted. The jets renewed and the carb refurbished and fitted. I have set the idle mixture at 2 turns but, now I am stuck can you explain where I go from there and how to set the choke and then adjustments etc, it would help me greatly.
I haven`t a clue with the Weber ... BUT There`s a man that can , or should that be men , they used to specialise in Webers . As you`re presumably in Yorkshire it`d be worth getting the van over there if at all possible . They push the fabrication side of things but set up a mates 32/36 on his Beetle and turned it from wheezing asthmatic crawler into a smooth drive-able peach It was about 8 or 9 years ago but worth giving them a call and seeing if they still do it ..
Setting up a progressive carburettor. You really do need an accurate rev counter to make sure your idle speed is actually 800-900 rpm. The setup is all a lot easier with a CO2 or wideband AFR meter, as rather than listening for best idle you can simply adjust for 14.7 AFR on a wideband meter. Start by pressing the throttle firmly with everything cold. This sets the carburettor up with the auto choke active, and the cold starting throttle setting screw sitting on a stepped cam under the electric choke capsule. The choke capsule should be set up with the loop in the end of the bimetallic element hooked over the pin sticking out through the slot in the plastic dust cover over the choke mechanism. The end of the bimetallic element moves to the left as it heats up looking from the front of the car. So what you do is move the element clockwise until the flaps at the top of the two barrels of the carburettor are in the closed position. In this mode when you start the engine, additional fuel is fed through the main jet, thanks to the vacuum caused by the choke flaps and the throttle is set by the screw at the back. Set the screw at the back that sits on the cam just above the distributor vacuum pickup pipe for a reasonable idle - 800-900 rpm when totally cold. The idle screw does nothing. In this mode the engine RPM will generallly rise to about 1500-1600 as the engine warms up, if you do not touch anything. If you open the throttle and the engine develops vacuum two things happen - one is the choke flaps are sucked down by the vacuum of the manifold so the enrichment reduces, and also the vacuum caused by air speed in the primary barrel at wide open throttle operates a diaphragm which pulls on a bar which pushes against the bimetallic strip in the choke capsule. So in this mode, which is what you have when you do not have the choke connected, hot idle is fast and rich, but normal running is OK as the engine pulls the choke off when needed. Let the engine warm up with power on the choke capsule - or wait until when you blip the throttle, the screw on the stepped cam drops off the end of the stepped cam and the throttle shuts and the choke flaps drop open. In this state, the wire on the left side coming from the choke mechanism to the main throttle spindle should be loose. When you know where to look, you can see an L shaped bit of metal pop up out of sight on the left of the carburettor in between some pillars. The throttle opening is controlled now by the screw that is on the left side of the carburettor looking from the rear of the engine through the hatch. A tiny adjustment here will open the throttle a lot, and render the idle mixture screw completely useless, with high idle speed. What you need to do is to adjust the screw on the left maybe 1/8 of a turn at a time until the idle speed is well under 1000 rpm - if you are above 1000 rpm the distributor will feed in timing advance and mess with your mind (you set it all up then suddenly the idle speed collapses so the centrifugal advance vanishes and the engine barely runs) . At this point you can do a lean best idle adjustment - of tweaking the idle mixture screw for the fastest idle, then repeat shutting the throttle with the adjustment screw until idle drops into 800-900 rpm range, then repeat the lean best idle adjustment and so on. It is not done in one go but in stages. Then try blipping the throttle, and the idle speed should return to the same as before the throttle blip. If it runs faster or slower there are two possibilities : The RPM was well above 1000 when you set the timing and the idle mixture, so you need to slow the engine down with the throttle stop screw and re-do the timing then re-do the idle mixture and throttle setting. The other very likely possibility is that the EMPI return spring is basically not providing enough return force on the throttle cable. Ideally it needs to be stretched some more, and arranged to directly pull against the throttle cable to push the mechanism shut when you let your foot off the pedal. Because the throttle plate opening on a progressive is extremely sensitive, it only needs a slight variation in pressure on the end stop screw even when it is touching the casting of the carburettor , to move the idle speed up and down a few hundred RPM... Do not do what I did and set up the spring on the opposite side of the throttle spindle to the cable- you end up producing a high side force on the spindle which jams as it has both the force of the cable and the force of the spring pulling in the same direction. If the spring lines up with the throttle cable its effect is improved as it does not put a side force on the spindle. With insufficient spring tension , I would see idle speeds from 850 to about 1400 rpm which could be changed by blipping the throttle so the throttle plate settled down differently. An air leak in the manifold may also produce this kind of effect if a small crack opens and closes as the carburettor moves around.
Thanks @mikedjames I will have a go Friday, I don't have a wideband afr meter so will have to make do with ears. So I have my choke set up so that with nothing on and everything cold and no throttle the flaps are closed, is this correct?
The idle setup info from Mikedjames is correct, but you need to make sure your fuel pressure is correct first. Aim for 2.5-3.0 psi and you should be fine. Stock jetting on a UK supplied genuine Weber is as follows MAIN JET 137 140 AIR CORR 165 160 E/TUBE F66 F50 IDLE JET 60 50 PUMP JET 55 and we have seen very good results on a stock 1600 with this. What do you have in your carb at the moment?
@Martin Eva at Webcon I have the jet sizes @mikedjames has said at the top but, don't know what the E/tube is I didn't check that, I also have an electric fuel pump and filter king with pressure set to 3 psi as seen on a pressure gauge on a tee piece from the regulator to the carb.
@yorkieman I wouldnt worry about the emulsion tube for now and If the pressure is set to 3psi that should be fine. Have you set up best lean idle as @mikedjames mentioned? You mention the mixture screw and idle speed screw are set at manufacturers base settings, but Weber make no base setting recommendations. I know some US sites state you have to have the mixture screw at 2 turns out, but ignore that, its rubbish. The mixture screw is there to fine tune the mixture flow through the primary idle jet and the setting is what your engine needs. You want to try and get a setting between 1 and 2.5 turns out, any further in and the idle jet needs to be reduced and any further out and the idle jet needs to be increased.
Martin, thanks for the input - I moved away from the stock supplied European Weber jetting because I have a decent hot air feed, and I had an AFR meter as an alternative to rolling road visits. So the primary idle jet was too big (this compensates for fuel not making it to the valves as vapour or suspended in the air) , and the big hole in the transition as the secondary throttle cuts in and the air flow rate halves suddenly was somewhat filled in by making the secondary idle jet larger - as it is not an idle jet in the secondary barrel but provides fuel before the secondary main jet cuts in .. One trick I did with the idle mixture setting screw was to solder a 10mm brass nut on the end of it so I can reach it with a stubby ring spanner.. or finger tips in rubber gloves .. and adjust it more easily. The friction with the spring and the original screw was too small to make it easy to turn .
Comparing jets MAIN JET 137 140 ( 137 170 ) AIR CORR 165 160 (170 180 ) E/TUBE F66 F50 same IDLE JET 60 50 ( 45 80 ) PUMP JET 55 same Leaner at idle, richer at WOT, partly because a bus driven at 4500 rpm or less limits the air being sucked through the carburettor to a lot less than it can actually deliver (e.g. imagine a Ford Capri GT 2.0 or Ford Granada 2.0 according to the Weber book) .
Thanks for that, I have not set anything up yet in terms of best lean idle, all I have done is actually try and get the engine to start by replacing the choke back on the carb and as stated changing the jets etc as recommended by @mikedjames. Your right though I adjusted the idle speed screw and the mixture screw as per aircooled.net in the states. So I have to go through the process of setting it up hopefully Friday, I have a wideband afr setup arriving this week so hopefully that will make life a bit easier. As a matter of interest I have replaced the original mixture screw with the webcon one in the refurb kit I bought, strangely it is quite different and is a little longer than the original and the spring is a lot less compressed on the new one at two turns, so not sure if its the right one.
