View Full Version : vacume leak somewhere

09-16-2011, 08:57 AM
So we put everything back in from the carbs to the manifold, and I've got minimal power to two cylinders, and when I cover the air intake to the carbs, the rpms go up. I'm sucking air in somewhere, right?

09-16-2011, 10:07 AM
Not sure I understand how you determined low power in 2 cylinders. Restricting the intake suggests maybe you need to adjust the jets as you are enriching the mixture. Of course a leak is possible too.

09-16-2011, 01:18 PM
The highly scientific method of pullng a plug and sticking my thumb over the plug opening...

09-16-2011, 04:09 PM
My idle just sped up considerably when I put the UniSyn on the mouth of the carb. Do I understand correctly, this means that the nut needs to be lowered to enrich the mixture for normal running? I'm having an awful time doing adjustments that everyone else seems to do easily.

09-16-2011, 07:53 PM
Nelson- Yes, down is richer and
you have a VERY unusual set of carbs so it isn't as easy as usual.

09-17-2011, 08:32 AM
I've found that adjusting the carbs on a spridget is'nt all that easy. The newer unisyn's ahve been critisized for not being sensitive. I can't hear well enough to use the ear and tube method.
I try to get the butterfly's perfectly matched to when they are picked up by the linkage by using a feeler guage then match the jet adjstment exactly to 12 flats down. I then match adjustments until the lifting pins show a close to correct mixture but always keep the carbs matched. Adjustments after that are dependant on plug reading, gas mileage, performance.
Got to have a reason to get under that hood!!


09-18-2011, 07:12 PM
Yes, the Unisyns' sensitivity is marginal for Sprites. There's a very narrow range where that adjuster is closed enough to get a reading but open enough that it doesn't affect the carb adjustment. It will work though--you might have to sync them with that little red floaty thing near the bottom of the tube. I suppose that adjusting the butterflies with a feeler gauge is close enough, but the nice thing about the Unisyn is that it measures the air flow directly.

But as for the original question--covering one carb doesn't tell you much. It just means that you're running on one carb. If the engine speed increases, it might just be that the one carb is closer to being adjusted right. Or, there might be something less obvious going on. I've noticed this phenomenon myself--even on a well tuned car, you can sometimes get a speed increase when you cover one air intake.

To find vacuum leaks, use the well established method of spraying something like carb cleaner on the places where leaks are likely. If the engine speed changes, then you have a leak.

09-19-2011, 07:49 AM
OK, had to take a time out to paint the car, now were back after the carb issue.