RESULT! CU running lean, what could it be?

[81AirCooled]

My old CU has been giving me headaches ever since I bought in August last year, in fact it`s been impossible to use. It`s been cutting out, misfiring, backfiring and generally running like a 2 legged dog.

I've just got off the phone to the garage /VW van/T3 specialist and tuning workshop) where it's now been a couple of weeks and the problem is the engine is running too lean, even though the carbs seem to be getting enough fuel?

Here`s what I changed before I took it to the garage;

Fuel filter
Air filter
Sparks
HT leads
Dizzy cap
Vacuum hoses

There was an airleak at the carbs and the previous owner had messed with the mixture so I took it to the garage. They`ve
fixed the airleak at the carbs with new gaskets but the emmision test tells them it's still running very lean i.e. drive=engine death and haven't been able to trace the fault.

The guy also told me that these carbs don't have/didn´t have the conical shaped fuel filter at the fuel intake so that´s another thing ruled out.

At the moment I´ve got to trust in the garage and I do but has anyone here have an inkling at what the issue could be assuming the carbs are getting enough fuel?

Thanks

[BOXY]

There's a metal pipe that runs across the bulkhead and joins to the manifolds below each carburettor. On the right hand side it fits to the manifold with a rubber elbow, and on the left there's a rubber tee piece because the brake servo hose in connected to it. If the rubber joints are split or letting air in you'll get a weak mixture.
The right hand elbow "popped" off on my van and it would start & run if I tickled the throttle, but cut out at normal idle and misfire on acceleration. If those joints look ok check the servo pipe itself, are your brakes ok, or is the pedal stiff? The last place I'd look would be the carburettor mounting flanges themselves and fit new gaskets with a smear of Hylomar just to be sure.

[81AirCooled]

Thanks Boxy, forgot to mention that I´d already changed the rubber bits before taking it to the garage. Could be the flanges like you say. I hope the garage can trace the issue over the weekend. What I´d really worried about is that it´s an engine problem that can´t be "fixed" without a rebuild. But normally this issue should stop at the carbs right?

[BOXY]

But normally this issue should stop at the carbs right?

Well the inlet manifolds under the carbs could be letting air in if their joints aren't sealed, or if they are cracked?
Have you checked that all the adjustment screws and blanks on the carbs are in place and the fuel solenoids are all tight? The air box could be letting in too much air if its damaged, not sealed around the lid or missing an air filter. If the fuel pump is delivering the right amount of fuel and there are no air leaks then all that's left are the carbs themselves. Maybe the throttle spindles are leaking air, or the main or idle jets are blocked? Did the previous owner re-jet or adjust the float height when it had a problem before?
At least the garage should be able to swap bits about to try to pin down where the problem is.

[Taipan]

Assuming its got twin solex carbs, its probably the butterfly spindle bushes that are worn and letting in air.

[sarran1955]

Hello,

I agree with 'Boxy'.

Check for air leaks with a few squirts of WD 40 in the potential trouble spots.

Also worth checking is that your ignition timing is spot on.


I hope this may help.

Cordialement,

[81AirCooled]

I hope the guy phones me tomorrow telling me he`s found something easy and cheap to fix I get the nasty feeling the carbs are just simply worn out though. Anyone know where you can get spares for the normal twin carbs? Apparantly the parts are hard to come by in Germany and I don`t want to pay a premium if I can avoid it.

[jason k]

bin them and fit a pair of dellorto drla 36 or 40mm carbs

[81AirCooled]

Ok so it´s Monday and it goes from bad to worse I just got off the phone with the garage and despite spending all day Saturday on it they were unable to find the problem. Basically it's like this -

Air leak at the carbs is sorted, it's idles fine and doesn`t cut out anymore. The carbs were cleaned out and they`ve also checked the gasket at the inlet manifolds to cylinder head and everything is ok.

The issue remains that there`s a lack of power and a very lean mixture. The garage has had it on the rolling road and apparantly the engine is running at something like 40 bhp and the emissions are all wrong. I asked if they´d done a compression test and apparantly that's all fine. The checked the ignition and the timings good and the ignition amplifier shouldn`t cause this problem accoring to the garage.

The fuel filter is new, the garage has changed the fuel to rule out contamination and the mechanical fuel pump is ok.

Only thing U can think of now is the rotor which is the limited kind. Would that cause an issue like this?

thanks for your advice, I`m at my wits end

[81AirCooled]

Forgot to add the garage tried other working carbs off another vehicle with the same results

[kevtherev]

have you got the emmissions read out?
the O2 reading will tell you if there's a big leak

which my money is on

cracked inlet manifold?
cracked head
burnt exhaust valves

what were the compression test readings?

[81AirCooled]

He hasn`t said exactly but he did say there was "no CO" - I`ll check with him tonight when I give him another ring. The wife is going to kill me, we were due to go away over easter and I can`t see that working out now.

[81AirCooled]

I can't afford to have the engine reconned but I see there's a 2nd hand CU on ebay that I might have to go with if my engine is past it. How long would it take for a garage to change the engine in terms of hours?

[ermie571]

ermmm unless you find out that it is deffo the engine,,,,then swapping another cu in won't make the blindest.

Get those compression readings and the emissions up on here then the air cooled lads will have a better idea.

Em
xx

[kevtherev]

I can't afford to have the engine reconned but I see there's a 2nd hand CU on ebay that I might have to go with if my engine is past it. How long would it take for a garage to change the engine in terms of hours?

That's it... .... buy someone else's trouble
you could change it in a day