really random tickover on Aircooled CT

[dugcati]

Right where do I start!... I am gutted as I have paid for Brighton breeze and me van aint running!

I have a 1776 CT with weber 34 twin carbs (yes yes I know CT's are sh1te before you all jump down my neck - I don't have the money to splash out on a 2.0L lump!)

It's been built with new barrels/pistons, was never run and then stood for a few years then I bought it.

When I came to check/set up the engine I found a really odd idling issue in that cylinders 1 and 3 (the two nearest the front of the van) are not really doing much at tickover.

The effect of this is that I cant get the engine to time up properly as it dies when I get to around 5* BTDC, the book states timing should be 4-6* ATDC


Things I have done to prove what and where the issue is.....

Using new fuel
checked carb jets and even rebuilt the carbs
gone back to standard solex single carb (checked that for jet sizes too)
changed coil over for several others
changed plugs
changed plug leads
Tried with/without idle stabiliser unit
switched over to traditional points dizzy from the electronic one which has no vacuum on it ruling out bad vacuum
swapped out condenser
even went to the stage of rotating the dizzy through 90* and then re-leading it to try and move the problem to cylinders 2 and 4 with no joy
I have an old Gunsons see though spark plug kit thing which allows you to see the colour of the igniting fuel inside the cylinder/s and it looks good in all cylinders so unless it's running really lean (on twin webers?.. not likely!)
Valve clearances have been checked and reset
Compression test shows in the green on the scale (cant remember the actual reading!)


Given what we have done to date I can confidently say the issue ain't electrical or carb as they have both been totally replaced in the fault finding exercise

Were at a loss as to why it ticks over so poorly on these two cylinders yet it will rev up and appears to run on all four cylinders - removing plug leads on 1&3 does nothing to tick over regardless of what we do.


The only last thing I can thing of is that the engine has shorter con-rods on those cylinders?



I am currently standing next to the van with a lit match near an open petrol cap!! - can anyone enlighten me as to where the issue could be/where to look next and stop me from dropping the match into the tank!

[VWCamperfan]

Ahh... I have a similiar set up on my van. I think I may know what this is. Your mixture is ok, as you have checked it with the Gunson colourtune thingy, compression is ok, valves ok, in fact everything is ok... Apart from the volume of mixture getting into cylinders 2 & 3.
You have a twist along the carbs throttle valve shaft. What this means is that the 2 front carbs are a little more open than the rear two.
A vaccuum guage that sits on top of the carbs and meacures the amount of air going in should confirm this.
The cheapest solution to this is to open the carb, place a softish object into the rear carb and force the throttle shaft closed a little which will twist the shaft back into position. Eg. it will leave the throttle plate of cylinder 1 or 3, whichever one you do first, open a little more.
Don't use too much force as this could bend the throttle plate or twist the shaft too far. Just try a little at a time, remove soft object and check running.
If you can get a feeler guage or a very small drill bit between the throttle body and throttle plate, this should give you a better idea of what is happening. Dont drop the drill bit into the carb though!
Ps. your engine has been altered from the standard CT engine and it probably wont run at the specified timing. Trial and error there then!

[dugcati]

That's a great theory VWCamperfan and thanks for taking the time to reply - but I have just realised I gave the impression to people that I am running twin dual carbs which I am not - I am running dual singles so back to the drawing board

[VWCamperfan]

Ahh well, kept me busy for a while!

Thats a bit of a strange one then! I can only guess at a small airleak on the inlet manifolds for those cylinders.
My van has vaccuum assisted braking as it was a larger engine originally and I had to drill and tap into the manifold to get the vaccuum for the braking but you probably wont have this if this was the engine that came with the van and so I will rule out a leak there.
Just as a suggestion, try enriching the mixture and check running of cylinders 1 & 3 again. If they seem to have power then, it may just be an air leak somewhere.
Check exhaust temperature from each cylinder as well, as any that arent firing properly will be cooler than those that are.
Other than that I'm at a bit of a loss as to why they're not giving any power!

[CovKid]

Agree, as I've mentioned elsewhere, they hate air leaks and it can be anything from wear in throttle flap shafts (common) to leaky gaskets on the inlet pipes. Any ingress of air and it won't idle properly. Other indications can be conking out when you come to a stop at junctions. Shafts can be rebushed. I always take em to Roger Ball in Clacton (Totlands Drive) as he fits phosphor bronze bushes and makes sure it fits to tight tolerances. If anyone needs his number let me know. Also a guy here in Coventry that can do them too.

[dugcati]

it turned out to be that the engine has (now had) an engle110 cam in and it was out by a tooth!

I took the Engle cam out as I was a little suspicious of the emissions side of things - probably be OK for a year or so but I though I'd go back to a standard cam

Now just to get those pesky weber 34ict's sorted out!