lostinthe202 Posted March 23, 2009 Report Share Posted March 23, 2009 '85 720 4x4 I was having a problem with a high idle. I changed the vacuum lines and capped off the vacuum advance line for the disty. It now idles more normally (though I don't know what normal is) but the idle is a bit rough, gonna check the timing. Also, when I rev the motor and let it idle down it does fine, but when I'm driving and I put in the clutch to come to stop if I'm on the brakes it will die. If I just put in the clutch, no problem, even light braking is OK, but when I get the pedal down it stalls. So does this mean I still have a vacuum leak somewhere so there isn't enough available for the booster? Or is there an idle compensation do-hicky that is not working? More suggestions please! Thanks! Will- Quote Link to comment
datzenmike Posted March 23, 2009 Report Share Posted March 23, 2009 If you are saying you now have no vacuum advance, connect it back up. While idling in the driveway. Apply brakes and see if it affects idle when in in gear clutch down or in neutral clutch up. To test the brake booster.... pump brakes with engine off to remove any residual vacuum in the system. Hold brake down and start motor.... pedal should drop slightly. Quote Link to comment
lostinthe202 Posted March 23, 2009 Author Report Share Posted March 23, 2009 Ah, OK, yes I now have no vacuum advance. I misunderstood in my other post about the broken part, I thought you said that I could cap it off and it wouldn't affect anything but perhaps you meant having it hooked up to vacuum all the time wouldn't affect anything? I'll get my hands on a thermal vacuum valve As for the booster, it is good. Quote Link to comment
datzenmike Posted March 23, 2009 Report Share Posted March 23, 2009 You should run vacuum advance. A motor will run fine with vacuum advance on all the time but it produces more emissions. There are several things in the emissions equipment that delay vacuum advance when needed to reduce emissions. Quote Link to comment
lostinthe202 Posted March 23, 2009 Author Report Share Posted March 23, 2009 Right on , thanks! Will- Quote Link to comment
ggzilla Posted March 23, 2009 Report Share Posted March 23, 2009 Dying when coming to a stop is usually caused by a vacuum leak. For testing, leave the distributor line plugged. If you plug it in and the distributor is leaking that is a problem. Inspect every hose and vacuum line. Any that are cracked or burnt, replace them. Adjust the idle to 750 RPM -- that works OK for just about any Datsun for testing purposes. Borrow a friend's RPM gauge. Or buy a $20 rpm tester from Sears. Quote Link to comment
lostinthe202 Posted March 24, 2009 Author Report Share Posted March 24, 2009 You should run vacuum advance. A motor will run fine with vacuum advance on all the time but it produces more emissions. Does producing more emissions in this case equal a drop in gas mileage? I haven't gotten it on the road yet, but just curious Dying when coming to a stop is usually caused by a vacuum leak. For testing, leave the distributor line plugged. If you plug it in and the distributor is leaking that is a problem. Can you elaborate on this? Not quite getting it, most of my carb experience is the with banks of four if you get my meaning;) and those were easier to rebuild then doing your taxes! Inspect every hose and vacuum line. Any that are cracked or burnt, replace them. Done and done, replaced every vacuum line already. Man I hate the 80's seems like their solution to the whole emissions debacle was to keep adding shit until they got the results they wanted rather then re-engineer anything. I bought 5 feet of the stuff thinking that would be plenty and I had to go back for more!! Thanks again guys! Will- Quote Link to comment
ggzilla Posted March 24, 2009 Report Share Posted March 24, 2009 Most 20 year distributors are leaking vacuum. So if you connect the hose to it, it leaks. Not sure how else to explain it. If you know yuors not leaking, connect away. But for testing, just disconnect and plug the vacuum advance hose. Some people drives theys for years like this. Yes, it use a bit more fuel and a bit more pollution but run pretty good even so. Quote Link to comment
lostinthe202 Posted March 24, 2009 Author Report Share Posted March 24, 2009 Ah I get it, sorry I misunderstood. You mean plug at the distributor not before the advance right? Quote Link to comment
datzenmike Posted March 24, 2009 Report Share Posted March 24, 2009 Pull the distributor cap off and the advance hose off the carb end and suck on it. The rotor will turn clockwise. Hold tongue over end. Rotor should hold position until you remove your tongue from the end. If this works, then the vacuum advance diaphragm is OK. Replace the hose and the cap. Quote Link to comment
ggzilla Posted March 24, 2009 Report Share Posted March 24, 2009 Yes that's one way to test it. Quote Link to comment
bucket Posted March 25, 2009 Report Share Posted March 25, 2009 my bad for but'n in on another thread but it seems like a good place to slip in my own situation. is there any thing on su's choke that can effect the idle? i changed heads last week from a u67 to an a87 and the only tricky thing was hookin back up my chokes b/c i couuldnt find the sweet spot but i left it at the only spot i got it running. now it idles about 900 though. before i get a timeing light and all that to dive in any thaughts? Quote Link to comment
Wharf Rat Posted March 25, 2009 Report Share Posted March 25, 2009 I got to get my honey to ck MY vac advance:D Sorry just a sick mind wondering, just for the hell of it disconect the brake booster and plug it at the engine. Start it and see if your idle is better, I'm thinking your booster may have a little leak inside. Quote Link to comment
lostinthe202 Posted March 26, 2009 Author Report Share Posted March 26, 2009 I got to get my honey to ck MY vac advance:D Bwaaaahhaaaaahhahahahahahahahha disconect the brake booster and plug it at the engine. Start it and see if your idle is better, I'm thinking your booster may have a little leak inside. You talking to the hijacker or me? Quote Link to comment
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