Changing the tuning on Weber 32/36

[ajp]

Update - quick spin around the block showed a little hesitation still at low revs, but better than before and no obvious flat spot...progress 

Going to order a smaller primary idle jet and see what that does.

Cheers all

[Merscury]

Should think you're probably looking at a 45 for the primary Idle jet. The reason I suggested cleaning the transition port is that at low throttle ie pulling off or gentle acceleration that's where a lot of your fuel is coming from and it can get partially clogged. No need to dismantle the carb, if you look down the primary barrel its just a drilling in the aluminium just above the throttle plate.

[ajp]

Thanks.

Am I right on the float height settings?

I've been going around in circles on the interweb!

[Merscury]

Webers instructions say for the DFEV which is the one I have, the height is 36.5mm in the closed position.   

Weber recommends setting the height of a plastic float from the bottom of the float to the bottom of the carb top plate, with the plate held vertically and the float hanging downwards, making light contact with the needle valve.       

print screen windows 7

[Merscury]

I've also come up with this diagram which probably shows better what I was trying to explain about the throttle plate position at Idle.     

[ajp]

Excellent info, thanks 

[snoopy]

You are learning a lot Andy, a straight twin choke Weber with synchronised venturi would be easier to tune but you do not get the economy of running on the single choke and having the second for performance when you want it.

Paul's picture B with the speed screw in to far will give you the stumble as the enrichment is already open before you accelerate and before the pump jet squirt goes in.

[ajp]

Hey Keith, you're right , but it's a very enjoyable learning curve and I very much appreciate all the help, ta.

I've been reading a great deal about buggy parts and I know twin carbs make a lot of sense, but there's a stubbon streak in me that likes the idea of making the single carb work well...once I get my old Land Rover sorted & sold I'll be shopping for a new engine and my bloody mindedness fancies sticking with the single carb still - I ought to know it well by then!

Having said that, I do have a weird pair of Solex 36/40 pdsi carbs off an old industrial type 4 engine that once lived in my '74 Bay bus...hmmm...

[ajp]

Quick update - still have a flat spot at low revs with gentle acceleration. Press through a bit quicker and it's cleaner revving. When cold and choke in operation there is no discernible flat spot.

Currently - primary idle 45, 130 main, secondary idle 60, 135 main

Manifold below the carb body getting pretty cold after a trip...I'm planning to play around with heat into the intake next. I want to drive the buggy through the winter and everything I've read about these carbs says heat is essential for good running.

Currently perfectly usable, just having fun trying to get things as good as possible

Cheers
Andy

[snoopy]

Have a look on Peters manxmaniac site he uses a weber and hot air pick up pipe assy and is an all year round driver.

[Merscury]

Hi Andy, The webers do suffer from icing more than most and for cold weather use, a hot air intake together with heat risers is a must. Like Keith says there are plenty of examples on Peters site, I've put some photo's of mine below because there aren't any on his site. I take the heat from the cylinder head but I think the surface of the exhaust is a better option as it heats up quicker. When the weather turns colder I also block off a section of the air filter on the opposite side to try and promote the intake of hot air. You'll notice on mine there is a knob at the bottom of the orange silicon pipe as I made a valve (like a choke flap) so I could turn off the hot air in the summer if required. Another thing I did was to convert to a manual choke, which in winter enables me keep the choke half on a little bit longer (ie choke flap open but still on the last notch of the extra fast idle). Take a look at Peters site as there are lots of different ideas there.

[ajp]

Thanks guys, will do my research.

Nice set up Merscury - very tidy & colour co-ordinated

[Doon L004]

Andy

As much heat as possible is the answer to getting this carb to work properly in all seasons, I tend to drive my Doon more in the autumn, winter and spring due to work commitments

The link below should give you some idea's to think about:

http://www.chris-jordan.org.uk/making-the-weber-3236-dfev-work-on-a-buggy.html

Chris

[ajp]

I've enjoyed playing around with my carb. I've read all I could find on the web and taken it apart more than once, played with multiple jet combinations, put in a new diaphragm and cleaned it many times, but never managed to fully tune out the low rev stumble off idle.

I think that I may that I got to then bottom if the issue today though. I read somewhere about throttle shaft play and checked mine after a great, but cold, 60 mile run out this morning and sure enough there it is. When the cable first pulls the throttle linkage against the return spring there is a noticeable change in revs before the throttle spindle turns. Pushing the spindle nut with my thumb does the same thing.

Presumably this play leads to a momentary vacuum leak that would cause a lean spot and therefore the stumble?

Not sure whether DFEV carbs can be modified to take out the play - anyone ever fixed this?

Off to do more reading...or look for another Weber

All good fun,
Andy

[snoopy]

Good to see you are still enjoying the buggy. Advancing the ignitiona degree or two may help also have a look at the vacum advance to see how it cuts in.