Hazard a guess? Sparky Carb

[RickB]

This is on the 78 Midget w/ the Datsun motor & Hitachi downdraft carb.

Adjusting the jet while the engine is running -
It's got this metal tube with a screw inside. Turning this while the engine is running I put my screwdriver in there and turn and sometimes I see a small spark inside and when this happens the engine stumbles.

This has an electronic distributor.

I've also had trouble with dieseling on shut down and with maintaining a steady idle.

Thoughts, ideas, WAG's???

 

[bthompson]

Static discharge igniting the mix? (This would be the WAG )

 

[Guest]

Got a pic of the tube?

What is your idle speed and timing set at?

Some of the older carbs had an electric anti- dieseling solenoid that would cut off fuel to the idle circuit when the key was turned off preventing a siphon effect on the remaining fuel causing run on.

Maybe this solenoid is shorting out intermittently and juicing the carb causing the spark. This may be part of your idle problem as well as it may short then close the (idle) circuit causing your idle to drop.

It might be sticking open on shut off causing the diesel efffect.


It's gonna look like a condenser (but a little larger) with a wire in one end and the other end screws into the carb.

Pull it out, ground the body of it and juice the hot lead and see how it moves.
(it's a simple electromagnetic needle valve, it should jump in and out.

I'll have to pull the Bug (VW) out and check mine on that one to see how to test for an internal short. Solex's used them as well. The quick "fix" was to cut the end of the needle off in order to get it to idle, but it might diesel after that. ( and you might have a really hard time finding the right noid for that carb). So don't jump up and do it. Also, the valve helped prevent from completely draining the fuel bowl on shut of from the siphoning.

Then again it might be on the dizzy side too depending. ( cause of spark and idle drop from redirecting voltage for the coil or a plug). A pic of the carb location relavent to the dizzy and other wies would be most helpful.

 

[jvandyke]

I remember from my Opel days that the Solex ones were often overtightened, for some reason they were supposed to be installed loosey goosey. My Opel had a Weber so no experience.

 

[RickB]

Here's a picture, you can see the jet adjuster there and the solonoid:

 

[Guest]

Get it to about 2500 rpm and unplug the noid. It should still run if not go up a little higher. Once you get the the idle adjusted where it'll say running w/ the noid disconnected, touch the screw again and see what happens. if it's still zappin', try the same with the choke wire. Granted, this is a WAG but the only thing that makes a little sense onther than bad plugwires. Also I would chech for a spark if you put the screwdriver elsewhere on the engine. (i.e, manifold, valve cover, elsewhere on the carb body, t stat housing, etc..) Are YOU the ground? Can you feel it?

I see some wires in the foreground, are all the wires in the bay o.k? Anything bare or suspicious?

Does this carb/engine use that stupid electric "heater" gasket under the carb? (look for two wires under the carb.)



sidenote: you might want to dump that air filter for a bigger one as you can't fit 150cc's through a knat's arse. I know space is an issue and choices are limited.

Alotta people ran those small "performance" filters back in the 70's, and all they did was choke the motor down and make them run rich. They are restrictive new and once they get a little dirt, you might as well use an old dirty sock (not recomended).

(please note that I write in a comical tone that seems misunderstood here as insulting and abrasive, so please don't be offended, it's meant as humor.) ( I'v yet to encounter a loud south Louisiana "smiley" that would correclty inflect my true tone and intent.)

 

[RickB]

I pulled the solenoid and once I got it off I found the red wire broken.
This may have caused both problems, the dieseling and the sparking.
I repaired it and can no longer see any spark no matter what I try.
Seems to shut right off now too.

Sometimes it is that simple. :wink:

Oh - the filter is a K&N and while I don't want to get into any more air filter discussions I can just say this one does let air get through. I think it blocks the small sticks & stones, but air and very small rubble can probably get through.

 

[Guest]

I think it blocks the small sticks & stones, but air and very small rubble can probably get through.

:lol:

I thought it was paper.


I didn't run one on my dirt track car for that very reason. (only thing close you can race around here)

I figured I'd rather save the engine for later then a little more power for a short time. All the other guys went to them and sure 'nuff, started smoking and losing power after a while. Still have 250# compression across the board on a 116K stock engine w/ 1000 miles of it at racing speed.



I have a K$N on the wife's Expedition that I let a buddy talk me into when gas was $4.oo a gallon.

He SWORE he got 3-4 mpg better with that and another P.O.J that I won't name on his truck and I was GUARENTEED better milage. Needless to say, I knew better but did it anyway.

I think it helped some as now my wallet is a little lighter thus dragging the truck down less.

It'll eventually pay for itself in three or four hundred years.
( minus addtional engine wear repairs)

Thanks for reminding me to take that dirt dumper off. I forgot.

 

[Guest]

accidental overpost. :blush:

 

[RickB]

I figure if it keeps mice out it's a doin' it's job!!

 

[Guest]

I pulled the solenoid and once I got it off I found the red wire broken.
This may have caused both problems, the dieseling and the sparking.
I repaired it and can no longer see any spark no matter what I try.
Seems to shut right off now too.

~Hey~, you owe me some tacos mister!

 

[RickB]

 

[Guest]

. :lol: