Attention happy weber 34dat owners

[Boneyt25]

Having trouble getting the auto choke to engage, but managed to set mix and idle not too bad.

Also upgraded throttle link bodge.

[Boneyt25]

Right,

So a friend lent me a gunson gastester, so I set it all up with revs and mixture. And it's been running spot on..auto choke engaging. Plenty of extra power.... until!

We were almost home from a 20mile run so 15 miles in, had to brake a bit hard. Someone else's fault. Not sure if the braking is related.

But

Since then ... it started bogging down real bad. No power at low throttle , wanting to stall. Kangaroo at low throttle. But flat out throttle still had power. This was the case for all speeds.

It was like it would only run on the second choke/flap.

So , initially I thought it was flooding... and second flap allowed more air , so would run?

But I'm also wondering if maybe jet issue, I'm not sure exactly how the fuel is distributed via main and secondary jets.

Now the above happened the first time I ram it after installation. I thought it was a throttle cable linkage issue. But I recall , gunning it in the test run in a panick trying to get it back to the driveway,

And after that was better, so I'm not sure if I'm getting blockages . Or if it's overfuelling.

Advice, on the symptoms above , would be most appreciated!

Before I strip it ....and probably make it worse!

[ash1293]

Does sound like a blocked jet.

If it idles probably not the idle jet but more likely the primary.

Very easy to pop out and clean.

Remember when setting up with Gunson etc you are really only setting the idle mixture.

Anything much above that is done by changing primary & secondary jets & air correctors.

[Boneyt25]

So ,
Carb apart again here.

Fault ....
Dove 60 miles , all fine.
Drove back 50 miles, then ...
Stalling at roundabouts etc. Eg when idling. And only able to drive on secondary. Otherwise kangaroo..
Feels like overfuelling. But I might be wrong.

Guess at problem.
Thinking overfuelling. So maybe needle valve , or pump pressure too high.. original mechanical pump still fitted and working.

Stripped carb, with service kit at hand.

Found the following.
No fuel filter installed inside carb.... now installed.

Removed float needle and seat....2 pieces of hard rubber sitting under seat. Most likely bits of old hose..
Fitted new float needle and seat.....think new float is everso slightly larger, but came with specific kit.

One jet was found to be partially blocked....blockage cleared.

Checked and set float level....

Re assembled.

Started, went to high idle, all seemed OK.

However .....
I have some questions.

No1.
What is the blocked off pipe at the front ( nearest front of vehicle) of the carb. Mine has a short piece of hose with a bolt in it to cap it off. I cant find specifics about it anywhere, but possibly vapour catcher missing?
What should be there?

No2.
The carb has a return fuel line. This is connected to the return to the tank.
As such, does this rule out pump pressure (being too high) as a problem. And thus making a regulator pointless.?

No3.
On the left hand side (near side) of the carb. There is 3 screws on a plate, behind the plate is a spring and diaphragm attached to what I assume is the "main" jet.

This unit has a bb in it for the diaphragm to action against. It has a slot for a flat screwdriver. It is very tight but I managed 3 full turns and it didn't seem to be unscrewing at all..
What is it?
Can it be removed? If so how?
Or is it pressed in ?

No 4.
If I have my window open whilst driving , I get the smell of exhaust fumes . But don't ANY other time. Any ideas hoe this is possible. Other than back engine hatch seal. However, this looks new and only seems to happen with window open at speed.

Thanks in advance.
Think that's everything. ... for now!

Cheers

Steve

[hubcap61]

Answer to question 1, as far as I know it's a breather pipe, I have a length of hose over the top of gearbox. I fitted my Weber 10 years go without issue.

[Boneyt25]

Thanks, I'm going to do this, and see If it makes any odds at all. I'll report back if there's any noticeable effects.

[ash1293]

[ash1293]

Right, just been out and taken a few shots of my 34Dat.

1) pipe I think you are referring to on mine is connected by a vacuum pipe to the elbow on top of the air filter housing.


2) pressure regulator would only be needed if using an electric pump supplying more than standard mechanical.

3) not sure. Jets/emulsion tubes/air correctors are accessed from above. Worth checking what is currently fitted and a look at earlier posts for standard supplied with kit and possible upgrades to eliminate flat spot.

Idle mixture is on side of carb base, don’t forget to remove and clean this pathway.

4) petrol smell is usually tank breathers and associated pipe work if it hasn’t been checked/replaced in recent history.

Unless smell is associated only with engine bay in which case check check all pipe work, pump spindle or sticking carb float

[Boneyt25]

That's the third variation of the 34 dat I've seen on a t25 now!

Mine doesn't have the superfeed jet. But I might make one for it!

[Boneyt25]

I've just re-jetted as per carrera s settings. As I've been fed up with certain issues .

Did seem smoother transition to secondary, and flat spot evened out I feel. Though I feel that this might be at the expense of some of the low end it did have before the flatspot.

Will drive for a while and report back. But overall smoother.

[ash1293]

That’s close to the stock kit set values, tbh I found that had a horrible flat spot on mine.

When I upped to the below it was far better.

I’ve tweaked a little further but would have to double check what I’m running now as it has been quite a while.

[Boneyt25]

Yes, I'm not sure if I've lost more than I've gained with this current set up.

I feel like I've lost a bit too much of the torque at low revs , for what I've gained in third.
That being said , I've had some other teething issues.
Chunks of debris in the float needle valve chamber. More in the float bowl. And I've adjusted the float level further as I'm sure I was getting overfuelling.

So, now I think it's settled on the other aspects, I'm going to revert back to stock again shortly and see if that makes any odds.

Also...

I havent re set my timing since changing the carb. Not sure if it makes any odds.

But I'm going to check it soon.

[Boneyt25]

Hi all,
Can anyone tell me what this electronic jobby is under my mates cut off solenoid ...........

Also, Ash I'd be interested to know what you're running now, I'm currently back to stock as had other issues and stripped carb again.

[ash1293]

Possibly a pre heater plate?

Could be wired up instead of the ‘hedgehog’ one in manifold?

Idle jets 50 & 65 - tbh I reckon a 60 on secondary would suffice.


Primary is a 125, with F30 emulsion tube & 175 air corrector.

Secondary is a 170, with F25 emulsion tube & 180 air corrector.


Could maybe lean off the primary slightly by upping air corrector to 180 to improve mid throttle mpg but without rolling road this is as far as I’ve gone.

Currently drives well for a hightop and returns on average 22-23mpg mixed driving.

[Boneyt25]

Just a little update.

So it would appear ....
Most of my weber 34 dat issues were the float. Pretty sure the needle was getting stuck open.

Also suffering blocked idle jet....

So after adjusting float several times , tried measuring etc. In the end , when I was in a bit of a hurry, I just gave it a quick tweak guesstimate. And since then it's been OK.

Now what I will say. Is that when it was getting stuck and flooding to hell. I could see fuel dripping down the chokes. And then when I got it running again it went like a fat ferrari ! With the inlet manifold saturated with fuel etc!

But since I've "cured" it..... I've got a much more stable and reliable running engine. All be it a bit tamer....

The one thing left to play with is the transition between single and twin choke operation. Very jerky if you push the pedal a bit hard, a bit quick....

To note,
I also managed to get a 2nd hand throttle linkage and a new accelerator cable fitted. Which hasn't made any performance changes, but will likely prolong the linkage bushes on the carb. I've replaced the little ones but the big spindle with the spring looked a little complicated fir me ATM.

Pretty sure I'm back to standard jetting ATM so I will prob have another little play with those.

Oh yes , put a new idle shut off valve on it. Discovered the old one had been modded to always open..... prob a waste of money. Most seem to say its only an anti run on device. 50 ruddy notes that was!

Also ..... I'm a little bit tempted by a set of weber 34ict twins. Anyone done this? Any performance gains? One major plus is it gets rid of alot of furniture on the engine..... lol