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Just had my DCOE40 rebuilt and I can't get my 1969 Euro 1750 Spider to run correctly. Once warm car runs, but rough, both carbs spit back badly and it returns to idle speed VERY slowly after blipping the throttle. After trying to adjust the carbs for hours as per the manual (i.e. cycle between theidle speed, sync between the two carbs and four mixture screws) I decided it was most likely an ignition problem so installed a new electronic dizzy and coil to no effect.

Fresh plugs. Ignition and cam timing are spot on. I'm running a mechanical fuel pump with no regulator. I also considered the symptoms may be consistent with air leaks. I have not replaced the carb mounts but they're fairly new and examining the rubber portion of the mounts from inside the individual throats with a lozenge mirror and bright light reveals no cracks. I also tried double gaskets on the carb to mount with no effect and upon close visual inspection the mounting surfaces appear to be tight. When 'Quick Start' is sprayed around the back of the carbs the revs do rise momentarily but this MAY be due to atomized amounts finding it's way into the throttle shaft and the intake w/o the cold air box. Visual inspection notwithstanding, does this suggest I have air leaks? I've also replaced the bit of vacuum hose that leads to the brake booster and the small line at the other end of the intake manifold that vents back to the cam cover.

The carbs were rebuilt by one of the regular Alfa Owner advertisers so I assume they're correct and I don't want to send them back unless I eliminate other possibilities. I'm also reluctant to remove the intake manifold and replace the carb mounts if there's nothing wrong, but that is where I'll go next unless there are other suggestions.

Any help is greatly appreciated and all my best to those that help keep these wonderful machines on the road....Albert
 

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Did they perform correctly before you sent thm out? It is NEVER wise to run without a pressure regulator that will deliver too the Webers 3# pressure at idle and no more than 4# shut off.
Quick start is a bad spray for leak checks. It is too volitle and can get into the enriching mechanism as fumes and cause changes in speed. WD-40 or even Brakeclean will do the same sprayed directly into the enriching mechanism at the back of the Webers.
If it's the throttle shafts, you have a serious issue with your rebuilder. There is a plate or linkage, behind that a spring retainer, a leather oil soaked seal held in place by the spring, a ball bearing assembly that should be packed with grease. The shaft is an air tight seal in the bearing I.D. and the bearing O.D. is an airtight seal in the Weber body. Shaft leak = poor rebuild.
Slow return to idle can indicate weak butterfly return springs, but more often poor butterfly plate set-up or excessive friction in the bearings.
More common is excess ignition advence from too fast initial idle that you MAY NEED to make it run if something else is not correct. What engine? What chokes, What jetting ? Which DCOE's? Which fuel pump?
Was the engine a FI conversion? FI manifold or correct Weber manifold? Weber support rod mounted correectly from the engine mount to the Webers?
All these questions AND answers should have been addressed by your rebuilder.
I restore vintage Webers for BB members and as they will tell you, these are questions I ask each customer. Further should there be ANY problem, I'm there to answer questions or make it right. Contact your rebuilder.
 

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