An Easy Fix To Keep Side-Draft Carbs From Losing Their Prime

A lot of cars, especially those with side-draft Webers, tend to lose their prime after sitting for a while. This problem makes these engines difficult to start without pouring a bit of fuel into the float bowls. According to Weber expert Mike Pierce, the issue is common with some older Ferraris and is maddening for owners.

We were experiencing this problem on our Weber-equipped Lotus Elan. As avid boaters, we turned to that world for a solution: What about using the same kind of priming bulb found on every outboard engine back in the day? 

Pierce, also a longtime boater, exclaimed that he’d never thought of that approach. As long as the engine received enough fuel, he said, he saw no reason why this wouldn’t do the trick.

So we went to a local boat supply store, spent about $10 on the part, and gave it a try. We located the bulb beneath the trunk mat to keep things subtle. The install took about 15 minutes and solved the problem. If our Lotus sits for a few weeks, we’ll just open the trunk and give the bulb a few squeezes, quickly sending enough fuel to the carburetors. 

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wspohn
wspohn Dork
12/4/20 10:51 a.m.

I have never had any issue with any of my Weber carb cars self priming, mind you they were all using electric fuel pumps. 

I guess if it depended on a mechanical pump it might take some priming to fill the float bowls, but I wouldn't feel too good about having one of those rubber squeeze bulbs anywhere near my car. I have seen too many aged ones where the rubber starts cracking and eventually leaks.  Having that happens on a car with electric pump would be very bad with gas spraying all over.  Not so bad on an engine that was sucking through the bulb via a mechanical pump on the engine - you'd probably get gas dribbling, but not spraying around.

Not the same issue on boats - if you are using the bulb every time you use the boat you are monitoring bulb condition. On a car where many people don't open the bonnet unless something goes wrong (like the engine seizes for lack of oil, in some cases), the monitoring isn't likely to be anywhere near as frequent.

On the whole, I would think that installing a small flow through electric pump would be a better option for priming.  I did that on my old Jensen with a big block Chrysler and sixpack. That was a lot of float bowls and once they dried out after sitting for a week or three, a lot of cranking to get the thing going and the little low pressure pump did the trick (you can plumb it in so it is a side circuit and doesn't interfere with the volume the mechanical pump wants to suck when running).

cosworth1
cosworth1 New Reader
12/5/20 3:18 p.m.

You can also install a one-way fuel check valve in the main line right before it gets to the carbs, keeping the fuel from draining back. Look for the ones that specifically state that they withstand ethanol rich fuels.

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