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Me again,

I am at my wits end with this problem.
(I have even consulted every Italian mechanic over 60 years old in Montreal )

Whenever I am running hot, (coming off the expressway after a 30 minute drive as an example) my spider starts to lose engine power when I start to slow down. I have to play with the choke to keep the Rpm's high enough to make it to the next curb.

The car will not die right away, but if I push on the accelerator it begins to buck. Back-off on the gas and it will idle rough but not die.

The problem is frustrating because by the time I bring the car to the shop it runs fine, and it is almost impossible to reproduce the problem.

Can anyone help???? I don't know what to do anymore.

To get the specifics, my Spider is a 1974 2000cc, with Dell'Orto Carbs. My compression is excellent, plugs and wires are new.
When on the highway, my Temp gauge is always stable.
 

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Sounds like a lean mixture...again! What is this? A lean mixture plague or something?
The symptoms sound like there's not enough fuel at the carbs. Could also be mild vaporlock that a weak fuel pump can't overcome. I'd check/change the main fuel filter that's in the glass bowl/pressure regulator assembly in the engine bay. And any other fuel filters that may have been added to the system. If the filter(s) are OK, I'd then test the fuel pressure. It should be approx. 3.5 PSI.
Cracked fuel hoses upstream of the pump can let air into the system lowering both pressure and volume. US models have a fuel tank vapor recovery system that, if not working, can cause a vacuum in the fuel tank as the fuel is being used that the pump eventually can't overcome.
 

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Maybe misadjusted float level? In decel fuel sloshes forward? Just a guess on my part since I have no experience with Dellortos.
 

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Hey 74Spider:

I am going with Papa on this one. I had a similar problem with loss in power almost like a fouled plug. End up on the side of the road still running. Then after idling for a bit it would run fine. Turned out to be a dead primer pump in the tank. I removed the primer pump off the end of my fuel gauge sender. Added additional hose to make up for the lack of the pump so the gas off the bottom of the tank could be drawn. And added a filter/strainer to the end of the line to keep from drawing debris. I then replaced the stock three outlet fuel pump with a 6-9lb pressure new two outlet electric from autozone. Capped the return line that went to the pump which made the third outlet. I ditched the additional inline fuel pressure regulator. Did this as I was getting only 3-5lbs at the carbs. Works like a charm. I am running dual 45 webers.

Best Regards,
John M
 
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