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Old 04-14-2010, 07:24 PM   #1
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skipping when hot datsun pickup


I have a 78 datsun 620 pickup. 2.0. The truck runs great when you first start it and drive for about 30 minutes or so, after that is loses all power, it will still idle but it does not have enough power to pull itself. I have installed a new points style disrtibuter and coil, new fuel filter, new fuel pump, and have been through the carb twice. with no changes. Does anyone have any advise? i'm stuck

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Old 04-15-2010, 06:28 AM   #2
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skipping when hot datsun pickup


Check for excessive exhaust back pressure with a vacuum gauge.

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Old 04-19-2010, 07:15 AM   #3
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skipping when hot datsun pickup


do you have a catalytic converter? the age of your truck?? you might. but in the event that you don't,
you can look into: checking that you are not over heating, 30 min is more than enough time to over heat. do a compression test, pull one plug at a time. check your timing when it's cold and then the same check after its hot, if it has changed, then id think about a new timing chain. you have alot of age on that little engine so it could be alot of things, in many cases it is deeper than just maintinence issues.
by not having enough power, does that mean it sputters and backfires? if it doesn't run bad when hot, and you have checked everything else, then i say it's not the engine.
is it a manual tranny? it could be your clutch not engaging properly/or at all when hot. if it's an auto, then it could be your tourque converter. pm for additional info
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Old 04-27-2010, 09:18 PM   #4
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skipping when hot datsun pickup


cylinder compression is the same hot and cold (180 on all 4), no cat, when i got the truck it had this problem, i thought it may be a back pressure issue with no muffler so i installed a muffler with no changes. i pulled the intake and exhaust manifolds the valves and ports are clean, valve springs are tight, timing chain is tight, timing chain guides look new, one thing i noticed is the intake manifold has coolant ports that lead to the head, but the head has no coolant passage to match, i am not sure if it is the correct head or if this would even cause a problem. the exhaust manifold heat shield is also gone. the motor itself is solid, it is fuel or heat related. Is it possible that with no heat shield and no coolant port that i am having a premature ignition in the intake manifold (vapor lock)?
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Old 04-27-2010, 10:37 PM   #5
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skipping when hot datsun pickup


I had an 81 with the Z20 engine that did that EXACT same thing. I know you said you went through the carb twice, but a rebuild kit was the only thing that saved mine. This was a while after a headgasket replacement, and the timing chain was fine. Maybe you got a bad pump that overheats - had one of those too, brand new.

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Old 04-28-2010, 12:42 PM   #6
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skipping when hot datsun pickup


Quote:
Originally Posted by pulse_tuning200 View Post
cylinder compression is the same hot and cold (180 on all 4), no cat, when i got the truck it had this problem, i thought it may be a back pressure issue with no muffler so i installed a muffler with no changes. i pulled the intake and exhaust manifolds the valves and ports are clean, valve springs are tight, timing chain is tight, timing chain guides look new, one thing i noticed is the intake manifold has coolant ports that lead to the head, but the head has no coolant passage to match, i am not sure if it is the correct head or if this would even cause a problem. the exhaust manifold heat shield is also gone. the motor itself is solid, it is fuel or heat related. Is it possible that with no heat shield and no coolant port that i am having a premature ignition in the intake manifold (vapor lock)?

did you check to see if you have coolant flow? a miss match in parts would likely mean you have no coolant flow. if the head isn't getting coolant, then it would be a big factor. u might not have the right intake manifold either. you'll have to run the numbers on both parts. call a few yards, they would be the most able to identify your given parts. the heat shield would be in place to contain heat and keep everything else from getting burned up. if you have anything close to the exaust manifold, check to make sure you didn't melt anything like wires.
so the basics of what your problem is, is that you are infact overheating, then your carb sprays a set amount of fuel down the throat wich in turn, over-atomizes, and that creates a lean situation.

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