View single post by Esprit2
 Posted: 01-06-2014 09:52 pm
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 338
> Is it OK for fuel to be in the carburetor side hose?

No, that's not normal. However, it's most likely the hole in the vacuum switch's diaphragm that is the root cause problem. By allowing a full time manifold vacuum to exist in the hose, where a vacuum shouldn't normally be, it's drawing fuel out of the carb, rather than fuel forcing it's way into the hose. Fix the diaphragm hole/ vacuum leak and see if the fuel leak goes away as well.

> Second, the vacuum switch has two fittings, one larger
> than the other. Which vacuum switch fitting is toward
> the carburetors?

Sorry, I'm really not trying to make light of your question, but there are also two mating hose diameters. The large one goes on the large spigot, and the small one goes on the small spigot.

But without beating up on that any further, +1 on Brett's comments.

"IF" you don't have to pass an annual emissions inspection (and in must States, cars of this vintage don't), then just remove/ blank off all the bits in the blue/aqua Throttle Bypass circuit. Remove the vacuum switch and hoses, and plug all the ports. Remove the Throttle Bypass Valves from the carbs, hand-cut solid gaskets (no cut-outs or holes in the center), and re-install the valves. The solid gaskets effectively eliminate the valves, while re-installing the valves plugs the hole/ scar in the side of the carb and 'looks' right.

The Throttle Bypass is an emissions thing to minimize the spike in oxides of nitrogen during closed throttle over-run, and the engine will run better without it. On over-run, the resulting strong manifold vacuum causes the vacuum switch to open and admit vacuum into the blue hose circuit, causing the bypass valves to open. That provides a Air/Fuel flow path around the butterfly, keeping the idle rpm up, and weakening the manifold vacuum until the over-run period ends. That really messes with throttle response and a consistent idle. Deleting the system makes the engine more responsive and pleasant to drive. No more or less power, just more pleasant to drive.

The Thermal Compensator is supposed to make a slight mixture adjustment for cold weather operation. If it's working well, it's really not a problem. Most aren't working well any longer, and cause more small problems than they solve. Most Jensen-Healeys don't get driven in real 'Winter' conditions, so the Temp Compensator's value is further diminished. IMHO, remove the plastic cover, turn the screw to permanently, firmly seat the plunger/ needle at the end of the bi-metallic strip, and replace the cover.

If anyone living in the Northern tier is still driving their J-H in Dec-Feb, then it's easier to make a small tweak to the idle mixture twice a year... cold & warm. If yours is a fair weather car, then just tune the carb for the best idle and performance during your prime driving season, and don't sweat the storage season. If it doesn't get cold enough where you live to warrant seasonal storage, then you don't really need the Thermal Compensator... IMHO.

The green hose to the distributor is vacuum RETARD. It retards the ignition timing at closed-throttle idle, and goes away once the throttle is cracked open... it's not a factor in normal driving. Beyond emissions effects, vac retard gives a more benign idle. On the other hand, it also slows off-idle throttle response. You'll get alternate opinions on whether to leave it, or remove it and plug the ports. For daily driving, you might want to leave it. For spirited driving or motorsports (autocross), delete it and plug the ports, then adjust the ignition's idle advance to 10-12 degrees BTDC and the carb for strongest idle/ best running. Set the idle rpm to 1000 rpm.

Enjoy your car...

Last edited on 01-06-2014 09:57 pm by Esprit2