Carburettor, rebuild or injection conversion?

[dt_ 7]

Hi, I've got a carbed 1.6 auto and am considering a couple of options with an intention of improving fuel economy and general ease of use.  As it stands, anything over 25mpg is a bonus, and it can be difficult to start when hot, not to mention running on after shutdown etc.

 

It has currently got a larger carb than normal (twin choke solex from an xs or similar) and I was thinking whether it may be worth attempting to convert it to spi if possible.  I know i'd need new cables, ECU, in tank pump etc among others.  Same hassle to convert to MPI?

 

Failing that, I could send off the current carb to be rebuilt, or try to source an original carb (with auto choke I believe) and fit that.  I know the car will never set the world on fire with its efficiency, but I would like to reliably see at least high 20s, maybe 30.  Car must stay as an auto.

 

What do you think?  Injection, stick with carb or refit original carb? Just wondering at this stage, could be an interesting project to get into

[Tom Fenton 1,524]

Older auto boxes are massively inefficient, I think that is likely the reason for poor mpg and you are unlikely to improve it much no matter what you do to the engine.

[Ozymandis 96]

I remeber, You have a non standard twin choke off some other PSA vehicle.

Thats why You have crap carburretion.

Find an original set up , re-condition it then fit that, it will be better than what You have now.

 

[dt_ 7]

Cool cheers for the advice.  After a bit of research the correct carb for the car is a Weber 36 tlc, which I'm assuming is a 36mm throttle body, as opposed to the 32 and 34mm on offer currently.  A few calculations state that changing to the original carb would cut the potential throttle area by about 45%, which may help with economy!  I will get looking...

[dt_ 7]

After much searching I managed to track down an original carb, manifold and inlet cowl for a fair price.  On stripping to clean and rebuild, I've noticed that the top and bottom of the main jet have been subjected to a ham fisted attempt at removal at some point.  I made my own attempt, but there's not enough brass to hold a screwdriver. 

 

 

And the base of the jet

 

 

Is this likely to give running issues in its current state?  It's obviously well secure, and air can he blown through it.  Everything else seems to be otherwise in good order

[Ozymandis 96]

From what little I can see in the piccies, that carb looks a corroded  mess that some optimist with  basic handtools has a had a go at before, I`d not have bought that.

I suggest getting Your money back if You can and finding another in half decent nick to re-con.

 

As to the jet, if it was a good working carb with no dirt etc in it, the butchery in the screwdriver slots wouldnt affect anything other than the ability to take the jet out.

 

However, I suspect thats not a good working carb.

 

[dt_ 7]

Cheers for the reply, good to know about the jet.  Car was running immediately prior to carb removal, so am hoping for the best.  After a bit of a cleaning sesh, aside from general age related marks on the body, it doesn't seem so bad, choke flap looks a bit rough but is free, and the idle adjustment hand screw is seized, but the holes all look clear.  The float is sloshing though so must have let fuel into it at some point, will need to track down one of those.  Here it is after cleaning:

Edited November 4, 2019 by dt_

[dt_ 7]

Hey, so against your advice Jay (sorry), I've gone ahead and built up the carb with new gaskets, diaphragms and even a new float as the existing one had fuel ingress.  Fitted to the car and plumbed up all fine, the car starts and runs, can be driven and has far better low end power than the solex that was on it, but the car will not run with the choke off, and on looking down the barrel, there seems to be quite a lot of  fuel coming from the main jet at idle.  There also seems to be more vacuum hose connections than the previous carb.

 

This is the carb when the car is up to temp.  It's idling quite erratically, and if you open the choke valve manually even a slight amount the car dies.  I understand that the carb needs adjusting- the cam attached to the plunger on the bottom right needs moving left so it disengages the choke as it heats (the plunger pushes outward when warm) but if that happens then the car would just cut out?

 

So is the fuel flow through the carb on idle normal, and what could cause the car to cut out like that when the choke is opened?  Also, what is the ufo shaped area to the left of the plunger for?  On googling for the last few days there are 205s fitted with this carb that don't even have that part.  Just scratching my head a bit here!

[dt_ 7]

So I've worked out that the area to the left of the choke cam is used for increasing idle when air conditioning is activated, so I've removed that to improve access to the idle mixture screw.  Still struggling with this, the carb is now filling up with fuel and chucking it all over the place.  The needle valve and float are new, could it be that there's no fuel return, and the fuel pressure is too high and forcing the needle valve open?

[opticaltrigger 52]

Hi Dan, just a quick thought.

Is the needle valve / float all sat at the rite height. This can catch you out a bit sometimes with rebuild kits. There should be a measurement for it somewhere....

 

All the best,

O.T.

 

[dt_ 7]

Hey, cheers for the response, I've checked the float height and it is spot on, I have also run it today with the new needle valve and needle assembly and the original valve and assembly and the same happens.

 

Fuel is spilling out of the areas circled, and flooding basically every blue arrowed area, and cutting off air supply to the jets, cutting the engine off, resulting in a fountain of fuel covering the engine.  

 

So as you've just mentioned, it can only be the float and needle valve surely.  I checked them when I built it first time, and checked them again today and both times it was ok.  Can only be too much fuel pressure, or maybe the float getting wedged down somehow, possibly by an overlapping gasket?  It's really hard to see the float operation with the carb in one piece, but when it was on the bench the float was moving smoothly

[opticaltrigger 52]

Carbs,,,,,

Well as you've got the height right that narrows it right down really.

From memory, (some of the other guy's might correct me here) but I think a fuel pressure of about 4 or 5 psi is the order of the day for most carbs.

I'm sure it's fine but just out of interest, what fuel pump do you have?  If you have access to one, a pressure gauge will sort that out. Or you could go completely nasty and rig up a bottle of fuel to gravity feed it with, hang it under the bonnet somewhere (just above the carb). If your problem goes away...... Excess pressure. 

 

Failing that, well I suppose it is a mechanical device, so I guess it can only be a mechanical issue with the carb at that point, so a further look at the carb will be required.

Try literally blowing down the fuel inlet and closing the float and valve with your fingers, just to be sure of a positive closure.

 

All the best,

O.T.

 

 

 

Edited November 25, 2019 by opticaltrigger

[dt_ 7]

Cheers for the advice, the fuel pump is an in tank electric item, either the same or similar to that of a GTi.  I've had the car running today using a large paperclip bent in such a way that I can slip it under the float through the vent hole in the top and modulate the fuel flow myself by lifting and lowering the float, however once the float level gets too high the entire carb gets filled and the car starts smoking pretty heavily and cuts out.  So its pretty much nailed as a float or needle valve issue.

 

Had carb apart today, offered brand new float up against old item and they are the same size.  I've blown down the fuel inlet and manually operated the float, needle valve seals fine.  It will seal fine under the weight of the float if I invert the carb top and blow through the inlet again, so it can't be a sealing issue.  The only problem I can see it being is that the middle gasket sent with the rebuild pack is very slightly wider in some areas and may be causing the float to foul on it and stick in position.  Another option to 100% rule out the fuel pump could be to install an in line manual fuel pressure regulator.  Are these any good?  Failing all this, does anyone know of any good carb specialists?

Edited November 29, 2019 by dt_

[Tom Fenton 1,524]

Fuel pressure too high overcoming the needle sealing.

 

You can probably only blow 1 or 2 psi. A low pressure electric pump can make c.15psi easily. An injection pump c.45psi.

 

[dt_ 7]

That would explain it, but this fuel pump is standard fit, and the Weber 36 tlc that I'm attempting to fit is the standard carb, is there some kind of standard regulator missing somewhere?

[jackherer 543]

I think every XU carb engine I've ever seen used a mechanical fuel pump driven by the camshaft directly and mounted on the front of the cylinder head.

 

E.G. https://www.ptzfuelpump.com/en/fuel-pumps/mechanical/cars/pn-4562

[dt_ 7]

Nope, it's definitely an in tank one.  What's weird is that the previous carb (non standard) was ok with this kind of pressure, however the car has had a fair bit of customisation in the past.  I can't honestly be 100% sure that the fuel pump is original but I can't see why it would need uprating for a carb fed 1600 auto.  I will order an in line fpr and see if this sorts it, unless there should be some kind of fuel return (which there isn't), or if it could be a problem with the fuel pump itself

[Ozymandis 96]

Put Your VIN into service box it will tell you which fuel pump was originaly fitted?

Im with Kieran on this, all carbed ones I ever dealt with had mechanical pumps.

I think You have the wrong collection of bits in Your fuel system and adding yet another non-standard bit seems like a poor idea?

 

 

[jackherer 543]

As well as checking servicebox post photos of the top of your fuel pump and the front right of your cylinder head.

 

What age is your 205?

 

I'm pretty sure that inline FPRs that regulate an injection pump down to carb pressures are only supplied by the aftermarket, they were never fitted by any car manufacturer from new. I'm also pretty sure they all require a return line to relieve the excess pressure.

[dt_ 7]

Yeah the main reason I'm going down this route with the carb is to go back to standard, adding extra mods is definitely not ideal.  Here's a pic of the engine bay showing the area where a mechanical fuel pump would be fitted

 

 

It's not the clearest but it looks like there's never been one fitted there.  It's a bit dark to get a pic of the pump, but the Haynes manual states that there was an electric unit fitted after 1986, and servicebox lists both types

[dt_ 7]

Ok here is a picture of the top of the pump, complete with about 3 decades of seat fluff

 

 

Car is a 1992 J plate.  The last carb did not suffer with any fuel pressure issues, unless maybe the float level was set so high that the needle was very tightly seated (is this a possibility), I'd love to take the solex carb to bits to see how it's set up but I know for sure that it will at least run with that carb for the time being 

[dt_ 7]

Well, I pulled the carb off the car for another look, float and height looked ok, blasted 600psi through the fuel inlet, and the needle valve resisted it with very light finger pressure to the point that it blew the line off the gun and scared the s*it out of me.  Looking at the main gasket, the one supplied was a coarse paper item, and could possibly be swelling when absorbing fuel, I snipped a bit off it where it runs round the float chamber (it was a lot wider in places than the original) and the floats are now free, and the fuelling overflow has stopped (for now).  Time to get it set up, and tackle that water fed automatic choke....

[dt_ 7]

Just remembered about this topic, not sure if anyone's interested but I'll update it anyway. 

 

No amount of work to that carb managed to get it to stop overfilling it's float bowl.   Initially the float was pinned down by a slightly larger gasket, but after modification to the gasket the float was fine.  Autochoke was knackered but that wasn't a problem as such as I was going to go back to manual choke.   Last ditch effort (I'd written it off at this point) was just to fill areas with sealant to see what effect it had, but no joy. 

 

Looked on ebay, and managed to find a nos weber 34 tlp, as opposed to the standard 36 tlc, which would mean a slight reduction in tb diameter but not significantly so.  The carb was a reasonable price (£140) so I took a risk on it, and after swapping some parts of the throttle linkage over to accommodate the kickdown cable and a few small tweaks to the idle mixture and she was running well, no leaks or anything. 

 

Following fitment of the carburettor, economy increased from about 25 to about 29-30, which was good, but I noticed the car was incredibly short of power under mid to heavy throttle, especially up hill.  So much so that steeper hills with a passenger or some load I would have to pull the choke half out to actually climb the hill.  I initially thought this could be down to the jetting and reduction in throttle diameter, but did some quick maths and worked out that it was a reduction in diameter of about 5 per cent, and this was something like at least a 50 per cent reduction in power under heavy load/throttle.  Light throttle on flat surfaces was fine. 

 

So I thought I'd have a go with the timing.  Marked the distributor body and turned it what looked like a good 10 degrees or so towards the car, no pinking.  Had to do it by trial and error as there does not seem to be any timing marks on the flywheel anywhere, or at least any that my timing light can register.  So I took it for a test blast and it really woke the engine up.  Had to back it off slightly due to some heavy load pinking at this point, but currently running really well, providing about 32 or so round town, and over 40 on a steady long journey, which i think is really solid for and old tech carb fed auto with about 110k on the clock. 

 

The old carb wasn't a complete waste though as when I bought it I got all the necessary pipework and inlet.  Once again, thanks everyone for your help previously! 

[youcalmdown 0]

Hey i have the same 36tlc carbi but have no idea where the vacuum lines go to.. any pics you had to confirm.? Thanks. Its running as well as your one did. Haha

[dt_ 7]

Damn, it's a shame you didn't send this message yesterday as I was with the car for the first time in months, with the ideal opportunity to take close ups.  What sort of problems are you having?  If it's the overflowing issue, I never solved it btw, bought a new carb...