out of ideas 76 124 spider 1800

[hayesbd]

I have never done a leak down test and wondered how it worked since there was never any discussion of leak down times. I did a little digging to see how the test works and found that it's important to keep in mind that just applying pressure and watching it decay to zero in a certain period of time is not the same test as a proper leak down test. Wikipedia (http://en.wikipedia.org/wiki/Leak-down_tester) has a good explanation of what this test does - it's essentially comparing your cylinder's leakage to that of a .040" hole at a standard pressure. When diagnosing a problem with one cylinder obviously underperforming, differences between cylinders are more important than the actual percentage each cylinder shows.

At my company, we perform some functional tests on components to determine leakage rates and these use time rate of decay, which is volume dependent and not as good a method as a proper leak down tester, in my opinion. (I'm going to make some suggestions for changing our tests now.)

Brian

[RAD]

this weekend I could not find my leak down detector so I made another one basically a blowgun with a pressure gauge on the end connected to a broken compression gage less the gauge using the hose and connector, this didn't help much air pressure stayed 2-3 seconds and was gone, when air was supplied no air was heard through the carburetor or the radiator hoses but a very slight sound from the exhaust pipe and valve covers. the car was not warmed up it was still torn down to the timing belt when I was messing with it. so I made another leak down detector using 2 gaugesand at 3/32 hole between the two so the flow would be slow between them 1 gauge was 5 pounds less then the other, I tested all four cylinders there was never more than 10 pounds difference on all of them. I would set the first gauge 100 pounds the second gate showed 90 pounds. Going by this I don't have a problem or it doesn't explain what my problem is so I'll go ahead and get a leak down detector and do it again.

[RAD]

I have figured it out. everything I've done tells me the motor is fine, and it set for a week or so torn down to remove the timing belt, I decided to go ahead put it back together this past weekend and check out the new carburetor the previous owners installed its a Weber look alike 32/36 and install an actual Weber 32/36 that I have, well this didn't work the Weber at everything backwards choke was on the wrong side throttle was on the wrong side so I reinstalled the Weber look alike it only had one vacuum hose to it it was wrong, before I was putting things back from where they came from, now questioning why they went there, the one vacuum hose at the base of the carburetor they had a hose going to what I found out was the fuel tank,. I thought possibly it was a return line on the original carburetor because it bubbles when air is applied to it and they (the previous owners) thought it was the same thing. there is another line that does not bubble so I think it's high in the tank and the actual vent. so I was thinking of connecting those 2 hoses together one is high in the tank and one is low in the tank to prevent contaminants from entering, I saw there is a vent in the trunk so all should be good.

[So Cal Mark]

as I recall you wrote that you have 0 compression in a cylinder. It would take a hole in the piston or a broken valve head to get 0 as a result. The leakdown test will show where the leak is, the amount of time pressure is held is not important it's the percentage of leakage. Anything above 15% indicates an area that isn't sealing. Could be head gasket, rings or valves

[RAD]

all four pistons had 150 psi compression the first leak down test I did with my homemade tester was a blow gun with a pressure gauge the pressure I put in only stayed for 2-3 and didn't seem right so I made another leak down tester using two gauges which showed 10 pounds difference or 10 percent difference between all cylinders so all is well, turned out the new weber look alike carburer the previous owner or two had A hose was incorrectly hooked up and it runs great now.

[MrJD]

so it was the carb all the time?

LOL. excellent.