engine stumbles/hesitates during onset of acceleration

I don't think the vacuum advance not working would make an astoundingly noticeable difference and as Steve says I don't think it's your problem. I run my Xs with the stock electronic ignition without vacuum advance and just set the timing at 10 degrees at idle and have no issues. In fact the car pulls very nicely from idle.

Using a distributor from another later Fiat makes it hard for any of us in the US to help you. Any chance you can borrow a stock ignition system?
 
carl said:
I don't think the vacuum advance not working would make an astoundingly noticeable difference and as Steve says I don't think it's your problem. I run my Xs with the stock electronic ignition without vacuum advance and just set the timing at 10 degrees at idle and have no issues. In fact the car pulls very nicely from idle.

Using a distributor from another later Fiat makes it hard for any of us in the US to help you. Any chance you can borrow a stock ignition system?
Click to expand...

Yes, I didnt know it wasnt a stock unit until now. I had a 1300 X before and just thought it was an upgrade that came with the 1500 engine. I understand it will be difficult to help me out for anybody in the US, but I think its a similar model as was discussed in this thread on xweb I found:

EI Distributors - too good to be true?

I've seen a certain So. Cal. eBay seller listing various electronic ignition distributors for Fiat Uno/Panda/Tipo, looks to be offering both the block-mounted type & the cam-end-mounted type distributors...
xwebforums.com
 
fiatfactory said:
that's simple, both workshop manuals are not for the model / market that your car was supplied for.

USA spec cars have vacuum advance modules ... European spec cars do not ... well X19's don't anyway. You have a distributor from an Uno /ritmo fitted, thats why you have a vacuum module on your distributor... but the car wasn't "born" with one.

You could check the function of the vacuum advance module. with the engine off, remove the distributor cap. By mouth, apply suction to the hose that runs to the vacuum module on the distributor, you should see the rotor move and then return when you cease suction... that will confirm the unit functions... if the unit is hooked up properly is another test... but as your carburettor did not come from the factory with the correctly positioned vacuum port, that's why I kinda doubt it's been hooked up correctly.


SteveC
Click to expand...

Thanks Steve, that clarifies a lot. I simply didnt know it wasnt a stock distributor. If the ignition system is not likely to be the culprit (plugs clearance OK, new wires), do you have any ideas what to look for next?
 
If you found the cam timing to be out before - 8 degrees at the crank more or less is 1 tooth off at the cam - so it sounds like your cam was retarded before you replaced the cam belt.

That would have led to a situation of low manifold vacuum at idle...my guess is the previous owner futzed with the carburettor in an attempt to "rectify" the issues he was having.

You have altered the cam timing back to where it should be... ignition tming sounds like it's where it should be... I would be thinking the PO has swapped the idle jets primary/secondary or futzed with the settings.... stumble at 2500/2800 sounds like a transition (carburettor) issue to me if the ignition and cam timimg are verified, and simply swapping the prim/sec idles can cause this, or a lean primary main.

SteveC
 
fiatfactory said:
If you found the cam timing to be out before - 8 degrees at the crank more or less is 1 tooth off at the cam - so it sounds like your cam was retarded before you replaced the cam belt.

That would have led to a situation of low manifold vacuum at idle...my guess is the previous owner futzed with the carburettor in an attempt to "rectify" the issues he was having.

You have altered the cam timing back to where it should be... ignition tming sounds like it's where it should be... I would be thinking the PO has swapped the idle jets primary/secondary or futzed with the settings.... stumble at 2500/2800 sounds like a transition (carburettor) issue to me if the ignition and cam timimg are verified, and simply swapping the prim/sec idles can cause this, or a lean primary main.

SteveC
Click to expand...

Yeah, I think you're right. The settings on the carb were a mess when I got the car, and after some adjustments the settings now seem to work decently. Your comments made me realize something else too and I now know why I have no vaccuum advance on the distributor: When I got the car, it had one of these metal sport filters on them, which I replaced with the original filter housing: The line from the vacuum unit on the distributor was connected to the carb via a T-piece of which the other end leads to the airfilter (I believe that's called the intake hose, the line going from the carb to the crankcase ventilation hose). I think the line was plugged when I got it, and I thought this was done because those sportfilters have no place to connect that vaccuum line to. Without thinking, I unplugged it and connected it to the right spot on the filter housing, not realizing that this would mess up the vaccuum to the distributor... All vacuum is lost through the intake hose.

Anyhow, I just took the line off the filter housing, plugged it and took the X for a test drive: I need to take it out tomorrow again just to be sure, but most of the hesitation/stuttering upon acceleration is gone! I still stutters a tiny bit of it when I press down the accelerator too fast but holy moly, this makes a huge difference. Apparently, the loss of vaccuum advance on the distributor was the cause of the worst of my problems..

Now I need to do something about the idle speed because its a little high, but this has made a big difference already. Thanks everybody!
 
It's fixed! turned out to be a loss of vacuum to the (non-stock) Electric Ignition distributor that was causing the problem (see previous post). Car runs like a dream... at least for now ;)

Thanks Steve and everybody else for your great help!
 
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