Not sure where to continue ////Problem solved!!!

[Sweden]

Hi,

Anyone who has any idea of any typical faults of a bad idling 1256 with Zenith 301Z carburettor.

First let me give you a background.
The engine is rebuilt with new carb, petrul pump, everything that sparks etc. The car has been driving beutiful since September until 3-4 day ago when I took it for a long drive and it started to go more and more bad. Just before I got home it sounded like the car was running on 3 cylinders only)

As I just had changed to a new carb I figured that that was the problem. My first assumption was that air was coming in somewhere on the foot of the carb so I opened and changed to new gaskets, but before I started the engine I opened the dizzy and found the the points didn't have enough gap so I adjusted them. After that the engine was going good with one exception. Going idle the rpm:s whent up and down and up and down.

My next step was to change the sparks and the ignition leads as at least the leads where NOS and I was anyway going to replace them. Still the same issue...

Now to be sure that the carb wasn't leaking any air I used starting gas around the foot and the cables but that didn't affect the RPM, but spraying into the airfilter made the RPM go up. So to me that was the proof that that wasnt the issue. (But still the engine didn't stop when tightening the air screw.)

Now my attention whent to the vacuum unit on the dizzy and I changed it to another one (used) but still the same issue. (Pulling off the small hose between the vacuum unit and the carb made the vacuum unit react and the engine stopped so it seems to be working though)

Just before writing this mail I have turned the dizzy in different directions to make sure that it didn't have anything about ithe gnition setting, but the rpm has gone up and down when turning it in any direction.

Now I need the forums knowledge of what that could be the next step.. I have some ideas myself that I havent tried.

1. Change to new points (They look fine though) My issue with this is that it might be hard to find in Sweden, but I will check tomorrow (I think the the dizzy is the same as on the Triumph spitfire mark 3 and 4)

2. Take of the airfilter and put my hand on top of the carb to make the petrol flow which might take away some dirt that might have gone in as there are no filter between the petrol pump and the carb. If that doesn't help take the apart and clean.

3. Adjust the valves (During the assemby of the engine I adjusted them but the motor was cold so they might need some small adjustments) This is hardly the issue but I'm starting loose options...

Any ideas?

/Christer

[hbpeter]

If the engine revs are going up and down at idle it sounds like the engine is 'hunting', i.e. the mixture is too weak. Try the throttle stop screw.
Peter

[Sweden]

Thank's,

But that doesn't help. Allready tried.. Taking it down will only make the engine stop at the low rpm:s.

/Christer

[lisbon_road]

Engine speed going up and down is probably an air leak. The points issue I suggest was a separate thing, personally in the long term I would get electronic ignition as points on Vivas are (in my opinion) always a problem. The engine speed going up and down will not be caused by points or by valve gaps. You will hear if the valve gaps are out from a tapping noise - it can happen very fast, but doesn't really cause much problem apart from the noise.

For the air leak, I would disconnect all the breathing stuff and plug it. You can do that with a cork, or even your fingers. It might be an air leak between the carb and the manifold or the manifold and the head, if you are lucky, you might hear them as a sucking noise.

Keep us informed and we will try and help. This is a typical sort of problem that when you have fixed it, whatever it is, it will be very easy and you will be really pleased. Just a matter of finding it!

Your pictures on the other post are fantastic, really looks like fun.

Jon

[Sweden]

Jon,

Air-leaks have been my first assumption, but as described I have not found any so far. There has been no sign of leaks using starter gas, but I will try to disconnect all the breading stuff and plug it as you say. I may have missed the exact spot where the leak is using starter gas even if I think I have tried to spray from any angle to any possibel leaks.

Thank's
Christer

[xwv2300]

Try checking for air leaks on the manifold to head joint, i had this once and took ages to find.

[AUTOMAN]

easey way to do this is to spray wd-40 arround the manefold arround the edges. this will create a tempary seal and the engine will run smoother for a few seconds. If this solves the problem, then change the manafold gasket.

Ian.
AUTOMAN.

[Sweden]

Thought I had it just a couple of hours ago. Plugget the hole that goes to the breather hose (The strange hose between the carb, engine and airfilter) The engine started to go better idle. When I took the hose away it fell apart in to two pieces... After cleaning/gluing and securing everything with some nice tejp, pretty sure ther where no more leaks I started, but no

Well... I will give it a new shot in the weekend.

/C

[Sweden]

The issue has been that the screw for the air-mix was broken. After searching and searching for air-leaks i started to take the carb into pieces. Guess if I was confused when I un-screwed the air-mix screw but on the inside of the carb I still had the top part from the screw sitting visible from the inside of the carb. I have no idea of the reason for this but my only guess is that it is a NOS carb and the screw may have got stuck as it probably been lying around for 35-40 years, and when I adjustet the carb it just cracked which I couldn't see from the outside... Anyway, now the Viva is im perfect shape again after a new carb adjustment and a stroboscope adjustment of the dizzy to 9 degrees.

Doesn't it feel good to have solved a problem after so many hours in the garage and so many additional hours just trying to understand what the root-cause is. Now I will give my self a Lagavulin or two to increase the mood I'm in.

Thank's for all the responses though.

Rgrds
Christer

[lisbon_road]

Well done, feels good. Enjoy the Lagavulvin.............