1973 MGB GT- A little rust 30/08

Needless to say I also like Webers on a "B".....Keep up the good work!

So new gasket set ordered and you can see the difference between the two here



But when I offered up the new gasket, it didn't exactly go to plan..



So I ended up getting out the gasket paper. Annoyingly I'd thrown out the original gaskets as I thought the set I had would cover everything





Not my finest work but accurate enough to do the job. Soon got the middle housing of the gearbox in place and bolted down.



I've used a bit of sealant on all the gaskets, not so much that it all gets into the box, but hopefully enough to stop it leaking like a sieve! Next I tried to put the overdrive unit back on but ran into a bit of trouble.. More on that in a sec. I went back and put the side cover on





Anyway the overdrive. First key thing, there is a ball bearing which has to go in the slot near the circlip, then the cam for the overdrive oil pump can go over this.





I tried to slot the overdrive on but it only got so far before getting stuck. Took it back off to see what it was getting hung up on





It's hard to see but theres two rows of splines for the gearbox shaft to mesh with, they'd become slghtly misaligned. To align them pressure has to be taken off the clutch in the overdrive by levering against the bars at the end of the unit like so



By levering there, I was able to reach into the splines with a flat head screwdriver and turn them independently. The annoying thing is that they only turn one way (I assume as part of the mechanism to stop the OD engaing in reverse) so if you turn it a bit too far you have to go round to the next spline.

Anyway, I got them all aligned, put the gasket on with some sealant and slotted it in place.





It's a bit fiddly getting all the nuts and bolts in as some of the nuts need you to lift the overdrive back up a bit to get the nut in. Next I had to get the oil pump itself into the overdrive. This was probably the most difficult part of the whole job, as I had to install it going up from underneath. Don't do it from the top as it is too easy to drop parts into the casing!! (yes I did it, but thankfully I managed to fish them out!)

I didn't really take any photos as it was one of those jobs, but basically this is the hole for the pump and you can see the cam in there





As the oil pump is sprung (I took a photo of the parts a couple pages back) its pushing back as you try to screw the plug in, but eventually I got it in place and tightened up. Once this was done I turned the gearbox over by hand and made sure I could see the oil pump plunger move as it rode on the cam. That was all good so chucked the sump back on



I changed over the reverse light switch which I bought yeaars ago back when I had the car on the road. Also put the remote housing back on the top of the box





Last job for now was to put the new roller clutch release bearing in the clutch fork, I had planned to bolt the fork in also but I hadn't noticed that the old pivot bolt had some wear so a new one is on order





Aside from that, the gearbox is all but finished So I can turn my attention back to the Weber and getting it cleaned up

Thank you very much, if my ramblings can be of some entertainment then all the better!


Tonight was spent looking over the Weber again, trying to remove the bits I hadn't already taken out and noting down the specs of all the various jets and tubes that go within.



The internal throttle return spring was here, until I managed to shoot it across the room while removing it under tension I did try to drift out the roll pin holding the lever to the throttle shaft but no luck so far.

The screws for the throttle plates were very tight but eventually came out and now the aforemetioned internal throttle lever is about the only thing holding the throttle spindle in still.

I got the float detached from the carb lid which revealed the needle valve and I also managed to wrench the fuel filter screen out using some pliers, there was a lot of sediment and gunk sticking it in place!









I've got a couple books which I've been using as references, How to Power Tune MGB Engines and Weber Carburetors Tuning Tips and Techniques, both of which have slightly different ideas on what the specs of the jets should be but they're not far off each other. The actual parts in the carb I have are quite a way off so maybe my thinking of "oh it came off an MGA engine, thats basically the same" wasn't well founded!

In any case, I knew it was going to need some new parts, and will need some rolling road tuning at some point. So I'll order a service kit, and some other bits and try and find the best stuff to get everything squeaky clean with

Thank you I try to make the photos as clear as possible as primarily they serve as a reference for me so I can put things back together somewhat correctly


I'm trying to keep the momentum up on the B since I've got back into it so a few things have happened this week. First off, I made a random ebay purchase of an old Leyland Special tuning manual as it was very cheap



Now amongst other things, it covers fitting a Weber 45DCOE carb to a B, and gives some suggested settings for the various jets and venturis



I've been doing a bit of nerding out comparing these to the other two books I have





Obviously a lot of the final spec depends on the needs of the engine you're bolting the carb to, but I find it interesting to see where the different specs align or disagree with one another. I've not bought any bits for the carb yet but I'll be ordering a rebuild kit soon and will make a best judgement at a starting spec for the jets and venturis based on my plans for the engine.

Of the carb itself, I had a bit of a fight getting the throttle plates and shaft out, there was a roll pin which needed drifting out of the shaft and lever for the internal return spring which was tricky.



These are the bits inside the ends of the throttle shaft, theres a small leather (I think) seal on each end. When I come to rebuild it, I'll use sealed bearings so should be able to omit this part





The carb is almost totally stripped down now, the only thing causing an issue at the moment is the spill jet at the bottom of the fuel bowl. I think previously I mentioned the head was a bit ruined by the screwdriver slipping, well I had a small victory in that I could make the flat head in it again by using a chisel. It started working in that the head started turning ever so slightly, then it sheared...





Great. I have managed to get a screw extractor into the end of it, just waiting for a long reach handle to turn it.

In other news, got some of the last bits for the gearbox, namely the pivot bolt and a pushrod for the clutch fork assembly.





Then while cleaning some of the loose B bits out of the shell, I decided to take a bit of a closer look at the interior, I did know there was a hole in the rear of the passenger side floor so knew at some point I was going to have to take it back to bare metal.







Got the chisel and hammer out and started at the bitumen type sound deadening to see what happened







Can see a fair bit of garage floor through there.. Also had a go at the drivers side, noted there is a plate at the front right seat mount. I should have remembered seeing this before as I have changed the seats in the car previously





Didn't get all the sound deadening up but got a good start on it, found a couple more holes on the passenger side near the poppers for the carpet mats







Bit of a scattered update but plenty to keep me going with

Your floor looks exactly the same as what mine did. I redid mine end of last summer. The rear triangular bits, and where the floor press stud things where. Is there a more enjoyable way to spend an afternoon than on rebuilding carburettors?

I do like a carb rebuild - And I do like a DCOE/DHLA(twin) or 2 or 3 or 4 but not 6 that's just daft flyingphil

Only consider the 36 or 38 in a 45

Unless trying to drag out every last bit of air from a given carb body the maximum advised choke size is body size -7mm so for a 40mm DCOE its 33mm and for a 45 - 38mm and for a 48 - 41mm - This is to provide a good signal to the jets throughout the operational range of the carb. The outlet of the aux venturi that the main jet is connected to is positioned at the narrowest point in the choke. The air speed at the choke point is a large factor in the atomisation of the fuel and the higher the signal at the aux venturi the better the main fuel jet, air jet and emulsion tube can work. The best practice is to use the smallest choke size possible for the power required. That provides the best all round drivability and economy - headline numbers from a 40mm choke may well be higher than for a 38mm choke on an all out racer spending all its time at Max RPM, but for a fast road car a good torque spread is more favourable and the smaller the choke size generally the better the torque.

The old Weber manual I have suggests 36mm chokes as a conversion on an MGB and generally this is for performance based conversions - For example the Ford Capri 2000 suggestion is 2 x DCOE 45 with 34mm chokes and those will feed 160BHP.

The DCOE 45 - 13 is the correct version for the MGA - with 34mm chokes and 3.5 aux - The MGB suggestion is the DCOE 45 - 9 - with a 4.5 aux I don't have what the spec differences are between the 9 and the 13 but could be associated with progression hole drilling.

Sizing will ultimately depend on the engine state of tune cam duration and max RPM.

Sorry for rambling on.

This page from a book in the above posts lists the 13 -





Out of interest with the MGB book what is Stage 5 that they list the 40 as the option for. Also the note that a richer 175 be used for endurance racing - Pretty sure that would be weaker than a 185.

If just going fast road specification the 36mm choke would be favourite until more extreme porting and big valve head work is incorporated. 12:1 and cast iron - The days of full fat all the lead 5 Star. Interesting advice on different plugs in the cylinder pairs. Thanks for posting that.