General FZD issues

[timgarman]

Hi Folks

This might be one for Chris?

I have just fitted my FZD and I'm having some running issues that I'm hoping someone can diagnose.

Firstly, just to be clear, mine is a 32/26 (not the more usual 32/28). The problem I'm having is that it's running too rich.

This is what we know so far:

1. THE ISSUE: Fuel is being dumped through the accelerator pump plunger nozzle in the venturi WITHOUT operating the accelerator pump plunger. This is causing the carb to run way too rich.

2. The problem is not with the pump plunger non-return valve (this is operating and only working one way).

3. The accelerator pump plunger diaphragm lever has got enough clearance on it (so the diaphragm is not stuck half open).

4. Have pulled out the accelerator pump weight and pump jet ball bearing to check this is sealing ok. It appears to be working. We did note that the bush that forms the seal at the top had the groove facing the opposite way to the groove in the carb body. This seemed to be wrong so we set it to match.

Here are a couple of questions to go with this:

Are there different sized pump jets?
Are the emulsion tubes for the main circuit?

Here is a short video link of the carb running. Not sure how clear it is looking into the venturi but probably clearer at the end of this clip:

[ame="https://youtu.be/euDlndWo1Ns"]https://youtu.be/euDlndWo1Ns[/ame]

Thanks – Tim

 

[the hobbler]

Evening Tim;
The fact that you have a 26/32 FZD rather than the more common 28/32 is really irrelevant. You may find that due to the slightly smaller venturi, less air flows through which might lead you to needing slightly smaller jets. I have a 128 main and a 38 slow running (idle) fitted to my carb (a 28/32 on a tuned 652cc engine)---I would suggest that you start with a 125 main and a 35 (if available) slow running jet. With regard to the accelerator-pump, I have a 50 jet fitted, with 6mm of thread showing below the adjusting nuts. 'Eurocarb' can supply 35/40/45 jets as well as a 50. The adjustment of the operating rod controls the AMOUNT pumped and the jet controls the RATE.
The Emulsion-tube---the job of the Emulsion-tube is to emulsify the previously metered air (from the air-correction jet) with the fuel coming from the main jet. Its influence is more marked at less than full throttle and during acceleration. The emulsification of the fuel is affected and influenced by the diameter of the tube and the number and location of the holes. Often a change of Emulsion-tube will call for a change in size of the main jet and the air-correction jet. I have a 6747/3 Emulsion-tube fitted (the 6747/6 seems to be no longer available)--my engine starts well, idles smoothly, picks-up smoothly and runs well.
With regard to your accelerator-pump constantly bleeding fuel, I honestly don't have an answer. I would suggest that you drop Euro-carb an e-mail (I have always found them to be very helpful)--MBG might also be able to help as they often fit the FZD carb to 500/126 engines.

 

[timgarman]

Hi Tom

Thanks for the response and the info. I'll drop the same info into the Eurocarb and see what they suggest plus MBG. I've tried the local Fiat enthusiasts too so should come up with an answer somewhere.

Tim

 

[Bambino]

Hi Tim,

I've been away at work and only just now seen your post. Certainly is a bit dribbly, isn't it.

As far as I know, and I'm no expert here, is that there are two main types of accelerator pump - the internal piston type and the (usually) externally mounted diaphragm type (attached photo). The FZD has the latter.

When you squeeze the accelerator quickly the diaphragm is actuated by external links and pushes the fuel load contained in the small pump chamber through internal channels until it squirts out into the main venturi chamber. When the accelerator returns the diaphragm relaxes and the chamber refills from the main float chamber via a one way ball valve. These fuel channels are separate from the main fuel galleries used in the other carby circuits (starting, idle and main).

I guess the only way fuel could be continuously leaking through the accelerator circuit is if the main float chamber is too full (float level incorrect, float full of fuel, inlet needle valve stuck open etc.) or somehow pressurised though I don't know how the latter could happen.

In the first instance I'd be checking your float. Contacting the real experts is also always worthwhile

As to your other questions, Tom is onto it.

Kind regards,
Chris

 

[timgarman]

Thanks Chris, that's really helpful.

A couple of pictures attached. One of the FZD in place (need to sort out a pod filter). Second one shows the top off and the grooved bush that holds the accelerator pump weight and ball bearing in place. Groove apparently going the wrong way (?). Sorry it's a blurry pic.

Here's some answers I've had already, which are all helpful and give me a bunch of things to check (with some duplication which is also helpful):

From someone local: Check the float level setting it may not be shutting off or needle and seat might need looking at. I've run these carbs in the past and they are perfect for these motors.

From Eurocarb: If all the valves are working there’s not much else that could be wrong. I notice from the video that the engine vibrates a lot and this can cause the pump arm to be compressed - have you tried undoing the pump rod screws?
Yes, the emulsion tubes are for the main circuit.

From Middle Barton Garage: Many used or new FZD’s are fitted with a float needle valve suitable for a motorcycle. You need to be using the car valve otherwise it will run rich, badly, drip fuel etc.

From someone else local: Excess fuel pressure! Put a manual pressure reduction valve in the feed line just before the carb. Dial it down. Go for a spin, if you feel hesitation at revs stop, dial it up a notch and go again. The standard pump produces too much pressure for that carb forcing the float down

You're pretty timely Chris, will be stuck into it again tomorrow. Hoping to launch at Christmas.

Tim

 

[the hobbler]

Hi Tim;
I am running my FZD with the standard (mechanical) fuel-pump. I also have a fuel return system on my carb (it came off a mini variant). This allows any surplus fuel to just get cycled around. On the advice of Eurocarb, I have the lighter of the 2 floats (5.5 grams). I also have one of the 'Pod' filters that people put on these carbs---do you want it? I run my carb with just an inlet trumpet on it, so it is surplus to requirements (still in its box).

 

[timgarman]

Hi Tom

Thanks for the pod offer, can I come back to you on that. Still trying to problem solve.

 

[timgarman]

Folks – we've gone through a heap of tests on this FZD 32/26.

Any further help would be greatly appreciated.

Here's a link to another YouTube clip, a view into the venturi.
[ame="https://youtu.be/6_jWZZGLDao"]https://youtu.be/6_jWZZGLDao[/ame]

The same problem persists. The mixture is way too rich and fuel is being dumped into the venturi even after accelerating – so without accelerator being used. Also, it's spitting in rather than a nice strong fine jet. Hopefully the new video shows this.

Here's what we now know after following up on some of your helpful comments on the forum and from others:

It's not being caused by excessive fuel pump pressure (we've tested this by gravity feeding fuel to the carb).

It's not the needle and seat.

It's not the float level. Currently the float fitted is the larger 7.5g.

It's not the pump non-return valve. (We haven't replaced the O-ring seal on the non-return valve, although we have replaced the valve itself. Could the O-ring be faulty? Seems unlikely.)

It's not the pump diaphragm.

It's not the pump weight or pump ball bearing (however we're wondering if there is a heavier weight available? If not we might consider making one.) The reason for this is with the smaller venturi on the 32/26, more air would be sucked through creating a greater vacuum and so sucking more fuel, perhaps requiring a heavier weight?

The idle jet is currently size 38. We could try a 35 as Tom suggests?

Note the attached photo of the pump jet we found fitted. Way shorter than the correct one and not long enough to protrude into the venturi as the correct one does. We've now fitted the correct size 50 pump jet and it has improved the behaviour slightly. Should this go any smaller? (The fact that this FZD has been messed with makes me wonder if one of the tiny holes into the venturi has been drilled larger?)

Here's an interesting point. The length of our pump rod measuring from the angle to the end of the longest part is around 45mm. We suspect this is wrong and too short. Can anyone measure theirs, from the angle on the longest side. Tom suggests there should be 6mm clearance where the locking nuts go, but if we include both locking nuts we get no clearance. This was a new part sourced for the FZD, but I suspect the wrong part?

We've tried disconnecting the accelerator pump diaphragm and there is still fuel pouring through the accelerator pump nozzle when running. It actually runs better this way though.

Can anyone tell me if the progressive circuit is operated through the accelerator nozzle?

Sorry this is a long question but we're head scratching currently.:bang:

 

[Bambino]

The fact that this FZD has been messed with ...

Oh-oh

In general carbies are purely passive devices that react to pressure differentials to permit fuel flow. If you have continuous flow maybe your jets have been butchered - drilled out etc. The fact that they don't spray but rather drip is also not right. To a certain extent the accelerator pump jet will squirt, but the others should have a nice spray effect.

Also as far as I know, the progression circuit usually takes the form of a number of extra holes drilled to enrich the mixture as you open the butterfly. They are drilled way down near where the butterfly touches the barrel and are usually part of the idle circuit. The attached photo is of the progression holes in a DCOE carby body.

My FZD spare parts are stored remote from my home and I won't be down there until later in the week, but will certainly take photos for you when I go there Friday.

If the carby has been abused, it may be that the jets have been drilled out. It's a common 'modification' performed by knuckleheads wanting a cheap easy 'go fast' conversion. It never works, wastes fuel and ruins good jets.

Hope it all gets better soon,
Chris

 

[the hobbler]

Tim;
The accelerator-pump operating rod should be 57mm long (measured from the inside of the angle), with a measurement of 13mm from the angle down to the spring stop. Yours is definitely too short! I have looked carefully through the 'Eurocarb' parts page for the FZD, but they do not list the accelerator-pump rod as a spare part. They list a 'Rod' p/no 7167, but with no description. The part that you need is No 38 on the diagram, Dellorto part number:-6402-24. With the correct rod in place, and the lever held DOWN by the spring, this may cure your problem.

 

[Bambino]

Dug around in the garage and found an incomplete FZD.

The accelerator pump rod is about 63mm long from angle to the end of the long threaded part.

Chris

 

[timgarman]

Thanks Tom. This is definitely something to tick of the 'might be' list.

Thanks Chris for the comments and the photos. Very comprehensive, as ever. And all the comments from Forum folks are certainly helping to speed this project along (after 4 years I use the word 'speed' loosely).

I'm concerned that one of those holes may have been drilled, especially since the pump jet found in place was way shorter than the correct one. Can anything be done if it has?

 

[the hobbler]

Morning Tim;
The world just gets curiouser and curiouser---I managed to measure the accelerator-pump operating rod on the carb on my car last night, and just like Chris's, it measured-----63mm! Due to the fact I have had a real stinker of a cold, I measured the 'easy to get at' carb yesterday---my apologies. Why there should be any difference in pump-rod length between an original carb (albeit to fit a different car, in this case a mini variant) and a brand new carb (the one that has given me hassle) beats me. My suggestion is 2-fold; (a) ignore all the jets that the carb came with and replace them with pukka new ones, so that you know exactly what is in the carb and, (b) make yourself a new, correct length, pump-rod. Get a length of the appropriate size bar, put the required right-angle bend in it, thread the other end, crimp or braze a spring stop onto it and get a new spring from Eurocarb (part number:- 6403). If you want all the exact dimensions off the 63mm rod, just let me know. From what you have described, it sounds as if a complete plonker (or, in 'Chris parlance', knucklehead--this is a family friendly Forum) has played silly-buggers with it and made a complete b---x of it! Set up properly, these FZD carbs are very '500 friendly'.

 

[timgarman]

Hi Tom

Thanks for this. It's certainly part of the plan to fabricate something.

But Chris and Tom – what do you think if the body has been drilled? Am I looking for a new body then?

 

[Bambino]

Hi Tim,

I've attached a photo of the three progression holes in my spare carby. The other hole is for the idle mixture. You can see where the butterfly would normally sit.

This carby body is not in great shape - a couple of the bolt threads that hold the cover are completely stripped and the throttle shaft holes are more elliptical than circular, but otherwise all of orifices seem in the right place and the right size.
I reckon if the po did anything it would have been to drill out the jets.

Keep us informed as to your progress.

Chris

 

[the hobbler]

I tend to agree with Chris. As you can see from his pictures, drilling out the
progression holes in the venture/choke area of the carb would, due to VERY limited access, prove to be almost impossible. So it is more likely that the previous owner of the carb has buggered around with the jets, hence my suggestion that (unless you have a proper set of jet needles/drills) you totally ignore what is on the jets and get yourself a new set and start setting up the carb with known jets. I have done some more research and discovered that Dellorto did in fact fit different length Accelerator-pump rods on different FZD models (24/30--26/32--28/32). They varied between 57mm to 67mm, but NOT as short as 45mm. Setting the carbs up to run well definitely seems to change as to where people live---air density? The settings are also affected by how much the engine is tuned. My engine had the head very carefully ported, (including the elbow manifolds) with bigger inlet valves and a sports exhaust, so a lot of
air goes through it, which of course means it needs more fuel to run
smoothly. Although my engine isn't the most economical, the plugs are a reasonable colour, and it goes like stink!

 

[timgarman]

Sorry to be pedantic guys – just trying to understand the consequences of drilling through the carb body.

Are you saying that even though the body 'may' have been drilled, it's still useable with adjusted jets?

 

[timgarman]

I think I was mis-understanding the way a carb would be modified. More likely the jets would be drilled I believe?

Just replaced the main jet with a smaller 125 size. Also the O-ring on the pump non-return valve which was a bit thicker than the old one.

Each replacement improves the performance of the FZD slightly but hasn't completely cured how much fuel is pouring into the venturi. It's not a nice squirt / jet.

There's not much left to tamper with, but the finger of suspicion is pointing at the pump weight or the pump jet ball bearing. The theory being that with a smaller venturi (32/26), air is being sucked through a smaller area creating a stronger suction. So maybe the weight needs to be a bit heavier? Either that or the ball bearing is faulty and is not closing the gap effectively.

Next step, weigh the weight and make something a bit heavier.

 

[Bambino]

Hi Tim,

I dug around in my spare parts box and came up with a photo of all of the tuning parts used in the FZD.

From left to right they are -

Idle jet
Emulsion tube
Main jet holder and main jet
Air corrector
Accelerator pump jet holder and jet
Needle valve and seat

... and yes, your accelerator pump jet is way too short and likely not an FZD part.

I would think that it'd be highly unlikely that anyone has altered the carby body as the exchangeable parts are all that are required to match the carby to your engine. Hopefully the thread on your unique pump jet is the same as the real article.

Chris

 

[timgarman]

Thanks Chris.

More work on this tomorrow. I'll let you know how it goes, but our gut feeling is that the issues are solvable and it's getting better by stages.

We'll need to make a new accelerator lever.

What have others done for this? The FZD shape means the existing lever from the Weber carb doesn't reach or even go in the right direction, so I'm assuming you FZD users out there have made a new lever?