Leak diagnosis and high idle issue

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mgarcia1387
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Model: 2000
Year: High Windshield-68-70

Leak diagnosis and high idle issue

Post by mgarcia1387 »

Hello everyone long time listener first time caller,

I picked this 1600 up last summer. One of the previous owners switched out the Engine and I was told that there was an issue with a high Idle and so the car sat in a garage since 1983. My friend helped me get the car running. However, it looks like there is some coolant leaking from the thermostat gasket as well as the head gasket? (photos attached) The chokes are not attached. My friend and I replaced the thermostat, radiator, master brake cylinder, moved the battery to the trunk and replaced the rear wheel brake cylinders last summer. I have a replacement tachometer as well. The fuel filter seems to be clogged as it has been sitting for 40+ years. Lastly, there is definitely a leak in the exhaust and looks like the previous owner used a coffee can as part of the down-pipe! Does anyone know anyone in the Colorado Springs or even Denver area that could help me get this running again? Im trying to diagnose this leak and the high idle right now. Any information would be great!

Mike
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Solex68
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Re: Leak diagnosis and high idle issue

Post by Solex68 »

I'm sure their must be someone nearby. You'll find a lot of helpful people on this site and a lot that would love to drop by give you help or advice. These cars are like magnets to 311 owners. I've helped many in my nearby town getting their car diagnosed or just throwing in my 2 cents.
I once helped a guy in Fullerton pull an engine one day. I had never met him before but I was willing to help get another car on the road.
Greg a.k.a SOLEX68 - http://www.datsunvents.com/
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68 2000 U20
Always willing to help another Datsun Roadster owner
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Gregs672000
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Re: Leak diagnosis and high idle issue

Post by Gregs672000 »

Greetings and Welcome! We can help...
Not likely a head gasket leak unless you're seeing white smoke or water/coolant mixing in the oil or rad. You more likely have a bad gasket or corrosion on the housing. Make a new gasket from material that IS FOR water exposure, or get a new one from a vendor. Note that the original gaskets had a metal staple embedded into the gasket that is used to ground the sensor that must be there and not covered by sealant or the gauge won't work. You can add some bared copper wire to mimic the staple. Alternatively, you can wrap a bared wire around the sender securing nut and ground it on the nut/stud (see pic). Wire is held on with a small zip tie. Also make sure to cut the gasket so that the air bleed holes are not covered up, look closely at the housing and where the thermostat rides... There's a spot where the thermostat rides in the groove but allows air to pass (needed for the system to burp out trapped air).

We can address the high idle too, but we will need more info, and it will be important for you to understand the carb linkage and how to adjust/balance dual carbs. Look things over, do some reading on this site, and we'll be able to help you. Go ahead and buy a "snail" style carb air flow balancing tool (amazon) so you will be able to work effectively on the carbs... balance is key.

Change out the fuel filter (maybe several times... those cheap VW plastic filters work good for this until all is clean). Disconnect your fuel line off the tank (be prepared for gas dripping) and at the pump and filter and blow compressed air through all the lines... don't blow it back into the tank. Clear all the fuel lines to the carbs and clean the in-line filters at the float bowl fittings (inline screens).

You can get a replacement header from a vendor... better than trying to weld the manifold... it won't last. Get a flex pipe when you do the header as well, will save a ton of headaches.

Since you're new to U20 engines, there are some things to quickly check. 1) remove the cam/valve cover and check the timing chain guide for chain strikes on the underside where it juts away from the head. This is a common problem that can destroy an engine in seconds when this part breaks off (its called the "evil L" for a reason). Easiest option is to cut it off flush if it's bad, as replacement requires disassembly, BUT inspect and report back first. You will want to shim the chain tensioner with nylon washers to keep the chain close to tight. It is hydraulic and does not tension enough at start up, allowing the chain to cut the guide. 2) check for the 3.5" or so long oil tube being present when you do an oil filter change. It's designed to keep the oil in the filter as U20s starve for oil on start up and must fill the filter first before some other upper parts of the engine, like the tensioner.

Review the tech wiki for stuff like this and to familiarize yourself with this great engine. We are happy to help, and there are no stupid questions!
:smt006
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notoptoy
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Re: Leak diagnosis and high idle issue

Post by notoptoy »

The leak at the thermostat housing should be pretty straightforward. Remove the housing and clean up the mating surfaces, make sure the housing is flat, run it across a piece of fine sandpaper on a flat surface to clean it up and make sure it is smooth and flat. Replace the gasket and use a very thin amount of sealer. With any luck, the residue on the block is just from the thermostat housing leak. Do the easy stuff first and see if that helps.
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jrusso07
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Re: Leak diagnosis and high idle issue

Post by jrusso07 »

Can't tell from the pics but be sure the high idle speed screw is not in contact with the manifold. It is a screw in the linkage that you turn in to set the high speed (3000 rpm or so) so you can balance the carbs at running speed. Like Greg said, read the carb balancing section in the Tech Wiki
Joe

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theunz
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Re: Leak diagnosis and high idle issue

Post by theunz »

Lots of good advice already given. It’s possible that you have an air leak in your intake system contributing to your high idle. As mentioned worn throttle shafts are a known problem. You can check for air leaks by spraying carb cleaner around the shafts and the area where the carbs bolt to the manifold. If there is a leak you will hear the idle speed spike upwards. If you haven’t already done so drain the fuel tank and flush it out with a gallon or so of new clean fuel. There is a drain bolt on the bottom making it a cinch. A compression and or leak down test can help determine if your head gasket is leaking.
Mike M

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nismou20
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Re: Leak diagnosis and high idle issue

Post by nismou20 »

Just from observation too you seem to be missing the vac hose to rear carb. Check your old fuel too in the tank, may need to clean that out.
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