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Chyvv

Nikki carburettors

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I currently have the standard Nikki 2-barrel thing on my 180B, I don’t care much for it, as rebuild kits are impossible to get and nobody seems to know anything about it.

I’m trying to tune the car to a roadworthy spec right now, but can’t get the thing to run right. 

 

The timing is set correctly, the car has new points, plugs and leads, but the engine runs somewhat rough, it stumbled under throttle and stalled coming to a stop yesterday (it’s an auto, but I will be manual swapping it after it’s registered).

 

I put new fuel in it (highest octane available) today but have been hesitant to drive it, as just sitting, if I apply throttle to hold a certain rpm, the engine will make a fair few quiet popping noises and run like crap. The primary nozzle appears not to spray consistently either.

 

What can I adjust that might mitigate this at least for a short time?

I feel like it will be more worth my while to change carburettors but I don’t know what the most plug-and-play answer is to that in terms of hooking up the linkages, manual choke, bolting on to the manifold, etc.

 

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1/ Check the valve lash first. I assume this is an L18? Warm engine thoroughly. Set intakes to 0.010" and exhausts to 0.012". Tight valves don't close properly and can leak compression. If the cylinder is not tightly sealed it can backfire into the intake or out the exhaust. Exhaust valves only cool themselves when they are closed and transferring heat to their seats. It's important to have some clearance with the cam so they close.

 

2/ Check the mounting bolts are tight on the carburetor. A vacuum leak kills idle, specially an automatic that is in gear and has a load on it when stopped at a light. 

 

3/ Find the idle mixture screw and on a warmed up engine in neutral turn it in or out slowly giving it a second or to to react. If the idle worsens turn it the other way till it also worsens and return to a spot roughly in the middle where it idle the strongest. Presumably the idle speed increased slightly so turn the idle speed screw down to normal. Repeat this in and out idle mixture adjustment seeking out the strongest smoothest idle and turning the idle speed down if needed. When you can't improve the idle quality any more and the idle speed is 700-800 RPM you're done. If you have a vacuum gauge adjust the idle mix for the highest vacuum reading at idle RPM.

 

Unless you have a high compression engine higher octane is a waste of money. Higher octane makes the fuel less sensitive to ignition, it doesn't make more power or do anything else..

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Took your advice, warmed up the engine and adjusted the valve lash, it ran rough for a minute or two but came good. 

The thermostat was jammed shut, which would have affected the water temperature switch and there was some excess fuel to burn off from turning the engine over to get to the positions I needed to in order to set the clearances, but in the end, it came good and ran smoothly.

I've since replaced the thermostat too.

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