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1970 roadster 1600 carb questions


fryanbacon

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So working on our old roadster I've gotten to a standstill where I got the engine to run but various lines and parts on the carb seem to be disconnected and I can't find where they go. I wasn't very successful in finding anything about my situation online so I was hoping some of you may be of help to me

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I believe the two hoses are for use in the event a float sticks and the bowl overflows. Naturally you do NOT want gas spraying all over the hot exhaust manifold so extend and run them down below the side of the engine.

 

 

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I would imagine this and the one on the other carb. is for holding the choke cable which you don't seem to have. Looks like this.. single pull with dual cables...

 

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Thanks so much! ill have to look where those cables go and another question for you,

The line that goes to the distributor was disconnected and when i hooked it back up it would spark when it touched the firewall. When it rested against the firewall it cranked at a normal speed but when it wasn't touching i would crank very fast. The line seemed to have fuel running through it and i was wondering what i should do with it?

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If it goes to the distributor it won't be fuel but probably a vacuum advance from the  front carburetor?

 

 

This is a negative ground correct? There should be a ground cable from the battery to the block. It should also have a ground to the body sheet metal also.

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It is the distributor vacuum advance line.  My RL411 engine connects this line to the rear carb which is set to open slightly before the front carb.  This promotes better idle and faster acceleration [a trick used by the Datsun USA race team in competition].

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The bowl overflow lines on SU's are made of copper and are bent to release the overflow down at the frame level.  My Jaguar has the same setup.

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yes it is a negative ground, and i'm very confused as to why it sparks occasionally, and looking through parts we have i found a choke cable for the carbs.

 

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Sparks because the body may not be grounded. Make a jumper out of 8 Gauge wire with crimped and soldered lugs on the end. I jumpered from the engine bracket bolt to the emgine mount bolt on the body about 4" apart. The body is isolated from the engine transmission and rear axle by rubber mounts. Even the shock absorbents.

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Where does the battery ground cable go? It should go to and bolt to the block. If it is, make sure it's clean and tight. If it's bolted to the body move it to the block or head.

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You want to be sure there are good sized grounds connecting 1)battery to body or engine, 2) body to frame and 3) engine to body.

 

Each piece can be isolated by bushings so you have add grounds.  It very much sounds like your car is grounding through that cable.

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Grounds are important on the Roadster, that is why all are talking about it, there should be a wire mesh ground cable going from the starter mount bolt to the frame, the negative battery cable should go to the side of the block and mine has another wire going from the negative post to the body sheet metal using one of the regulator mount screws, if you do not have this cable your engine/body ground will be the accelerator cable which will melt the plastic cover and ruin it, mine melted at half throttle the time I forgot that body ground.

That vacuum advance sparking when you touch the body worries me, is the ignition on when it sparks?

Edited by wayno
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40 minutes ago, fryanbacon said:

It goes directly to the side of the engine bay below the battery tray. I thought it was factory but maybe it was something somebody else did

 

For the battery to ground it has to get back to the body. This is not good as it should have a direct connection to the negative side. It will try to gtound through the throttle linlage or cable, or anything that connects the block to the body metal that can conduct. I had no ground to the body on my 521 and the battery fell over and the positive touched the body .... it grounded through the throttle cable to the engine and melted it.

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You know i did notice that the throttle cable did get a bit warm so i will definitely fix that. Thanks for lending your knowledge and experience so i didn'thave to make the same mistake 🙂

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11 hours ago, wayno said:

Grounds are important on the Roadster, that is why all are talking about it, there should be a wire mesh ground cable going from the starter mount bolt to the frame, the negative battery cable should go to the side of the block and mine has another wire going from the negative post to the body sheet metal using one of the regulator mount screws, if you do not have this cable your engine/body ground will be the accelerator cable which will melt the plastic cover and ruin it, mine melted at half throttle the time I forgot that body ground.

That vacuum advance sparking when you touch the body worries me, is the ignition on when it sparks?

it only sparks when i'm cranking on it

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So it only sparks when the ignition is on and the engine is moving/vibrating from cranking it over trying to start it.

It sounds like you don't have a ground going from the battery to the body, find another heavy gauge cable and put it from where the negative battery cable bolts onto the block to the body inner fender somewhere like the regulator mount screw, or do it the way I did it in the photo below, see the black wire going to the regulator mount screw.

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ok so now im at the point where it will be cranking and starts to run then dies, and i noticed the oil dipstick smells like old gas, so would the next thing be to drain the oil? i have a ground going to the block and it doesnt spark anymore, but now it seems like its flooded or still not getting spark

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You said it starts to run, then say still not getting spark. So which is it?

 

23 hours ago, fryanbacon said:

So working on our old roadster I've gotten to a standstill where I got the engine to run but various lines and parts on the carb seem to be disconnected and I can't find where they go. I wasn't very successful in finding anything about my situation online so I was hoping some of you may be of help to me

 

 

 

 

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If it fires at all, back fires or sputters then it has spark.

 

Did you get choke cables for it???? Start up cold should have the choke on. It's not really a choke on an SU.... more of an enrichment device. When the choke cables are pulled the tapered needle is raised slightly. Or the jet the needle is in is lowered... I forget but the narrower portion of the tapered needle lets in more fuel and it runs richer.

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When the choke is pulled on the seat moves down away from the needle making a richer mixture, same as the piston in the dome raising making the mixture richer, sometimes they will not start and run without a choke.

In this photo you posted below your are holding that arm up with your finger, hold both arms up on both carbs and see if it will start and run better.

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Also how old is the gas in it, if it has that crap pump gas in it with ethanol and it is old it may have spoiled and separated and the engine will not run on that crap, I run non ethanol gas in everything I own except my work truck which I drive all the time so it always has fresh gas in it, I used to have a second tank but it got ruined because that crap gas sat in it too long and ruined it, it rusted on the inside.

 

 

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Ok so I completely cleaned the fuel system, dropped the tank and drained it, ran a new fuel line and I cleaned the pump, but I have a rebuild kit on the way, but I did notice the oil dipstick smelled like fouled fuel and wondered if the old gas got in the oil which would foil more fuel? I was thinking of just doing an at home oil change and seeing if that would fix it. Also I did have a couple sets of choke cables and I have them hooked up but it almost seems like it's getting flooded or something is fouling the plugs as I took them out and cleaned them and after 30 minutes of cranking they got black again. 

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Are the plugs wet or are they just black?

How long has this car/engine sat without running properly?

When you look down the carb you can see the piston for lack of a better word, will that piston raise and lower by itself with your finger?

Do not stick your finger inside and touch the needle, just make sure it raises and then drops by itself.022.JPG.e796bbabd87e1a1bdaf31399469b9c14.JPG

 

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Does it have drag when you lift it or is it easy to lift?

I had a R16 for a decade at least and had issues with my carbs because they sat too long and were wore out, but it did run and drive but it backfired a lot, I took it to a Datsun shop and that guy cleaned and rebuilt them and it was alright, not perfect but alright.

Does it even backfire now when you try to start it?

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On 10/10/2020 at 7:16 PM, wayno said:

Are the plugs wet or are they just black?

How long has this car/engine sat without running properly?

When you look down the carb you can see the piston for lack of a better word, will that piston raise and lower by itself with your finger?

Do not stick your finger inside and touch the needle, just make sure it raises and then drops by itself.022.JPG.e796bbabd87e1a1bdaf31399469b9c14.JPG

 

023.JPG.585eb122690511277333d6d4d58788aa.JPG

 

Does it have drag when you lift it or is it easy to lift?

I had a R16 for a decade at least and had issues with my carbs because they sat too long and were wore out, but it did run and drive but it backfired a lot, I took it to a Datsun shop and that guy cleaned and rebuilt them and it was alright, not perfect but alright.

Does it even backfire now when you try to start it?

It does raise smoothly and i had completely cleaned them of old fuel but when i lift them when starting it sputters and tries and when i let it go nothing happens. Would this mean that something in the carb raises it up when you hit the gas?

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