MarkB. Posted March 7, 2014 Report Share Posted March 7, 2014 OK, gang, Here are the symptoms: Drive 510 for approximately 20 minutes at 50 mph on country road. After twenty minutes or so the car starts to slowly lose power. 2 more minutes and carbs sounds clogged and will not rev. Pull over, wait 20 minutes. Car will restart and run (back home) for 20 minutes then die as before, hopefully as I'm rolling up the drive. L20b with 1100 miles since rebuild dual DCOE 40s Matchbox dizzy/'79 coil electric fuel pump fresh gas Amb. temp 72 degrees Water temp < 200 degrees Oil pressure nom. Suggestions? Quote Link to comment
banzai510(hainz) Posted March 7, 2014 Report Share Posted March 7, 2014 soon as it dies. Tap on the carbs where the gas line goes in. maybe the needle valve is getting stuck thus you running out of gas. then start the car. or have 2 poeple one tapping as one is trying to start. loose power . Im winging this one but ck the valve lash . I just make sure the valves wiggel when the lobe is pointing up. Dont have to pull out the feeler gauges. Usually the exhaust valve gets tight and youll loose a cylinder. I assume you got a fuel reg for those carbs as most electric fuel pumps are OVER 5pounds pressure. You want like 3-3.5. maybe try soem starter fluid also. when it dies partly open carb shoot fluid iin. and start. if fires right away then you kow its a carb issue and your elelctrical is fine. alway ck for intake tightness and the spcers inbetween carbs for cracks Quote Link to comment
MarkB. Posted March 7, 2014 Author Report Share Posted March 7, 2014 Thanks hainz, I do have an adjustable pump set at 3 lbs. Upon further review of the archives, I understand this could also be the dreaded 'Vapor Lock". I do not have a return line. Its a little unclear to me how that would work. I'm reading some of those old post now. Lots of flame; not much data. Quote Link to comment
ggzilla Posted March 7, 2014 Report Share Posted March 7, 2014 Yes, the symptoms match vapor lock. Of course it could be something else. A return line is not needed to avoid vapor lock. 510s have gone millions of miles wo return lines. 1 Quote Link to comment
datzenmike Posted March 7, 2014 Report Share Posted March 7, 2014 If this were summer in El Paso, maybe. Has to be awful hot to vapor lock when driving. It mostly affects re start. Is it just above freezing and damp in El Paso this time of year? If yes it could be carb icing. Quote Link to comment
ggzilla Posted March 7, 2014 Report Share Posted March 7, 2014 All it needs to vapor lock is the fuel line run too close to the exhaust. Quote Link to comment
MarkB. Posted March 8, 2014 Author Report Share Posted March 8, 2014 No, today was 72, sunny, relative humidity below 50%. Nice day -- until the car died. DSC_0348 by mbriggs65, on Flickr This is my engine. The fuel line comes out in the usual spot and winds behind the engine. Quote Link to comment
datzenmike Posted March 8, 2014 Report Share Posted March 8, 2014 That an EI coil? Does it get too hot to touch? Quote Link to comment
MarkB. Posted March 8, 2014 Author Report Share Posted March 8, 2014 I got it at oreilly and it was supposed to be for a 79. I didn't touch it for temp. Quote Link to comment
datzenmike Posted March 8, 2014 Report Share Posted March 8, 2014 Back to basics. Fuel and spark. Next time it quits pull coil wire off and hold near ground while cranking... spark??? If yes then ignition can be assumed good. That will leave fuel. Can you hear the electric pump when it quits? Quote Link to comment
banzai510(hainz) Posted March 8, 2014 Report Share Posted March 8, 2014 Next time it quits pull coil wire off and hold near ground while cranking... spark??? forgot to mention this but tstill is usaully the first thing I do. simple 1 min ck. Quote Link to comment
MarkB. Posted March 9, 2014 Author Report Share Posted March 9, 2014 I do hear the fuel pump on after the car dies. I can't tell if it changes pitch. I will pull off the coil wire and check it. I'll go drive around tomorrow morning 'till it dies and check it. Can I assume either the coil's overheating or the fuel is? One other clue: I have Spal fan on the front of the radiator, and no fan behind so there's not a lot of air circulation under the hood. Quote Link to comment
ggzilla Posted March 9, 2014 Report Share Posted March 9, 2014 Assume nothing. Test it. 1 Quote Link to comment
datzenmike Posted March 9, 2014 Report Share Posted March 9, 2014 I assume the fan is blowing air into the rad???? Quote Link to comment
MarkB. Posted March 9, 2014 Author Report Share Posted March 9, 2014 Yes. Its a "pusher" fan and it does blow through. Coolant stays cool; < 210 most of the time. I have no issues on the engine itself overheating. And I agree; assume nothing. Test. Preferably, one thing at a time. Quote Link to comment
datzenmike Posted March 9, 2014 Report Share Posted March 9, 2014 Should have a 180 thermostat so I wouldn't expect the engine temp to be more than 185 or so. 210 is close to boiling point of water. Gas, depending on the many additives, boils between 100F and 400F. If an alcohol blend then the alcohol boils off around 180F. If your under hood temps get anywhere near 200F that may be enough to cook the gas in that 8 foot long fuel line. Quote Link to comment
H5WAGON Posted March 9, 2014 Report Share Posted March 9, 2014 Good Fuel Filter? 1 Quote Link to comment
datzenmike Posted March 9, 2014 Report Share Posted March 9, 2014 From the description it runs fine at 50 for about twenty min. before the problem starts. A part plugged filter would be plugged all the time. Quote Link to comment
smoke Posted March 9, 2014 Report Share Posted March 9, 2014 Given the dew point of your climate, this is a bit of a long shot, but I would say when it falls down, another thing to check would be how cold your carbs are to the touch. If they feel like a block of ice, you may have found your problem. Quote Link to comment
Ottoman0331 Posted March 11, 2014 Report Share Posted March 11, 2014 In my my 81 280zxt I had issues in the summer where the fuel pump would overheat and kill the engine. I would have to sit beside the road for 20min or so. Then it would start up just fine. I would have close to the same symptoms you are having except that I had efi. Quote Link to comment
Rick Rodchester Posted March 12, 2014 Report Share Posted March 12, 2014 my truck had a similar problem. this is going to sound dumb, but I ignored it for too long. Seafoam! I put 8 ounces in about 9 gals of gas, and in about 20 miles, all the idling and wanting to die problems went away. sounds like you have a slightly different problem, but it can not hurt. Quote Link to comment
MarkB. Posted February 5, 2015 Author Report Share Posted February 5, 2015 I can't believe it's been a year since I started this post. Life intruded last year and I had to walk away from my Datsun. It sat under its cover since then. I've visited the forum, but mostly to see what VTR posted in some of the other areas. In any event, I'm back at this problem. In reading fuel pump posts and related older posts, I have sorta decided to heed Datzunmike's advice about the most reliable Datsun being a stock Datsun and return to a mechanical fuel pump. But the L20b didn't have one when I bought it. So do I need a spacer? If so what depth and if anybody has a recommendation on a replacement mechanical pump, I'd love to know. Any help is appreciated. Quote Link to comment
banzai510(hainz) Posted February 5, 2015 Report Share Posted February 5, 2015 if elelctgric pump shoots gas and you got 3 pounds on the reg should be fine. a stock mexico replcement pump comes with a spacer I believe. Mine was 29.99 at O rileys. like I worte before the needle can stick and make it run out of gas. also ck the funnels inside for loosen and ck the jets if they back out. This is a 1/2 hr to 1 hr to figure out not a year. Now the gas is old in the car. but 1 yr shouldnt be bad as i le mine sit also. Quote Link to comment
MarkB. Posted February 6, 2015 Author Report Share Posted February 6, 2015 Thanks Hainz, Off to O'Riley for the pump. Actually the tank is bone dry. I thought to attack this and be as thorough as possible. I drained the tank and took it to be cleaned. It only had a couple of gallons in it anyway that I can use in the lawn mower. By removing the tank, I had access to the electric pump I put in 14 years ago. I am going to disconnect it and then hook up the "new" mechanical pump. I'll need to eliminate several feet of fuel line under the hood and turn the pipes around on the DCOEs. Trust me, the year off of Datsun fun was NOT intentional. Quote Link to comment
robrob Posted February 6, 2015 Report Share Posted February 6, 2015 Hay hope that fixes it. If you dont get that spacer you can still use the pump. My old pump never had one and when I put the new one on I guess it pumped more fuel. my carbs would flood until I mounted a regulatory. Its a cheap ORiley one so I still have to set it at 4 but it works. Quote Link to comment
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