Intro 1972 Irish Green 1.7L; help needed with jerking engine |
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Intro 1972 Irish Green 1.7L; help needed with jerking engine |
andreic |
Oct 6 2018, 09:11 PM
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#1
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Member Group: Members Posts: 172 Joined: 21-December 15 From: Madison, WI Member No.: 19,479 Region Association: Upper MidWest |
Hello,
some of you may remember me. After owning for several years a red 1975 1.8L 914, on which I reinstalled the L-Jet, got it to work well, and have sold this summer, I am now working on a 1972 1.7L D-Jet which I got this spring. Photos attached. So far I got the brakes to work well (new front calipers from PMB were installed, and all four flex lines were replaced), replaced all fuel lines and the fuel pump, replaced all vacuum lines, new spark plugs, points, cap, wires and rotor. Also adjusted all valve clearances. I did a compression check and all was well, I got around 120lbs on all cylinders. What still plagues me are two engine issues. One is that when the engine is cold, if I rev it up it will make a loud noise that sounds like a bad rattle. It is only there on hard acceleration, and it goes away almost completely as the engine gets warm, say, after 10-15 minutes. I have come up with several ideas what it could be: exhaust noise from badly sealing exhaust ports; valve noise; or something else in the exhaust (the muffler is an aftermarket one, and I am not sure if there isn't something in it rattling). Another issue I have is that the car is not riding smoothly. It is hard to explain, but even if I am driving at constant speed, not moving my foot on the gas, it will jerk ever so slightly forward every couple of seconds, as if getting some extra power. The issue again is much more visible with the engine cold, but even properly warmed up you can feel it. It is stronger when accelerating than at constant speed; on acceleration the car really stumbles some times. When the engine is cold it can be pretty bad, enough that some times I worried if I would be able to climb a hill. I first thought it was ignition related, but after going through everything electrical I doubt it is this. (Replacing the spark plug, points, cap, wires and rotor changed nothing.) The car also seems a bit underpowered compared to my other one. I am starting to wonder if the two things (the rattle and the jerking) are not related, and if it could be a valve issue. By the way, once or twice in the span of an hour's worth of driving I thought I heard a mild backfire. Any suggestions on what could be the problem? Any help will be greatly appreciated. Andrei. Attached thumbnail(s) |
andreic |
Oct 12 2018, 07:42 PM
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#2
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Member Group: Members Posts: 172 Joined: 21-December 15 From: Madison, WI Member No.: 19,479 Region Association: Upper MidWest |
OK, finally some progress. I noticed on the instructions on how to adjust the timing that someone commented that the vacuum lines should be disconnected when adjusting the timing. With them off, the timing changed quite dramatically, even at 3500 rpm. Readjusted it this way, and the car runs much better -- no more backfiring, fairly solid acceleration, very little hesitations.
I still have the "trailer towing" issue -- slight jerking at constant speed, more so on acceleration. But I think I figured that out too; I disconnected the TPS, and no more jerking! So I guess my problems were a misadjusted timing, and a bad TPS. Three questions: 1) Where do I get a good TPS board to replace my worn one? 2) Is it normal for the vacuum lines to make such a big difference even at wide open throttle? My timing was off by probably 5-10 degrees (one whole rib on the fan) with the vacuum lines on versus off. I thought the vacuum lines were there to lower the idle when the throttle is closed, and to increase the advance on acceleration from idle. I simply wonder if my canister on the distributor works properly. 3) Sometimes the car idles at 1800 rpm (the first 10-15 minutes of driving), after which it settles to a 900 rpm idle when fully warmed up. Is this normal? Thanks, Andrei. |
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