Hard cold start - hopefully finally fixed

[Dawgme85]

I had experienced hard cold starting for a few years, which I had, for some reason, attributed to the starter, which would crank slowly, when cold, until it would finally speed up, but still require a lot of cranking to finally get going. Once the engine was warm it started fine. I recently replaced the starter, which solved the slow cranking issue. The engine is a relatively stock 1756, but with Pertronix electronic ignition. I had also noted loose inlet hose barbs in the top plate, which I would periodically tap back into the carb, but they would eventually loosen up again.
One day I noticed bubbles forming in the fuel filter after returning from a drive, with the engine turned off. It occurred to me that the fuel was leaking back into the tank as the car sat, which indicated to me an air leak, probably at the loose barbs.
I had another 32ADFA available that had "tight" barbs, so I made the swap to this apparently good top plate, which solved the cold start problem. After a couple of weeks, however, I noticed that the fuel was once again draining out of the filter, although not as badly/quickly, and the barbs had loosened up such that I could once again wiggle them with my fingers. In the time since the original swap the barbs in the "old" top plate now felt tight again.
So, I have replaced the top plate, once again, this time with one which has been modified to use threaded hose barbs. Hopefully, this will solve the problem once and for all. While discussing this with Ray and Lori Mortensen at Performance Apex, Ray informed me that the SCCA had mandated this modification on their race cars and Lori added that when there was a news flash in the '70's about a burning car on the freeway, it was often a Fiat where the barb had come out of the carb. I actually had that happen to me once, but was fortunate enough not to have a fire. Something to keep in mind, and it's easy to check by reaching under the air cleaner to wiggle the barb. If it moves, it's loose, and if you experience cold starting issues, check the barbs. All the best!


Original top plate


Modified top plate

[aj81spider]

Thanks for the suggestion!

Where did you get the threaded barbs? Did you just tap the existing hole with a regular tap?

[Dawgme85]

Ray did the modification by removing the original barbs, then drilling and tapping the top plate to accept a standard 1/8 pipe barb on the inlet (bottom) side and a custom barb that he turned on a lathe for the return (top) line, as they are different sizes.
The surprising thing, to me, is how much the barbs/top plate shrink and swell. I thought they were just a press fit. The difference in the thermal coefficients between brass and zinc is about 65%, but the temperature stays pretty close to ambient (by touch), so I'm not sure why that clearance would open up. I'm guessing about. 002"-.003" or more?
Edit - After thinking about it, perhaps the top plate gets heated up enough, while the fuel flows at close to ambient temp to create enough of a difference to open this up? Just a thought.

[Dawgme85]

Sorry, duplicate post