8 replies to this topic

[tarnofsky]

Hi all,

 

After my Moke has reached it's running temperature - which is pretty fast with the front rad compared to my other Minis with the side rad - it generally runs well.

All has been set up recently after being replaced by new parts: points replaced by electronic wizardry, distributor cap and finger, NGK spark plugs (of course set to proper gap) and silicone leads, water pump renewed, thermostat renewed, belt renewed. Valves set, engine timing set, C02 set up.

Within the carb I have exchanged the float (for an unsinkable one) and needle seat plus needle (for a Viton tipped one).

I have thoroughly cleaned the float chamber and carb bowl from the inside without using anything abrasive.

Carb has been topped up with SU damper oil to about 1/2 inch above the edge inside. Fuel filter added and clean, all rubber fuel pipes under the bonnet replaced.

So far so good and the car runs generally well.

 

What annoys me a bit is that once it has reached operating temperature, it hesitates slightly when you try to just lightly accelerate. Let's say, you go 50 mls and need to go up a slightly uphill and you just lower your big toe on the accelerator, if you know what I mean - just slightly. It's then like it wouldn't want to take that tiny bit more juice. If you press down further, it accelerates and drives sweetly.

 

The car has stood for quite some time before I bought it and I thought I should maybe replace the carb completely just to make sure everything's perfect.

Problem is: I can't find any documentation on what's supposed to be on a June/July production Cagiva Moke 998 (engine prefix 99 HB83) as standard.

The closest to a Workshop Manual I was able to find is a Owner's Manual off a 89 Austin Portugal Moke.

This states the carb is a SU HS4 (ovbiously) with an ADE needle and red spring. Nothing on the jet being waxstat or fixed.

 

Can anybody help and say what would be the standard setup for my Cagiva Moke?

 

Any other ideas what I might try?

 

 

[Shaun78]

Hi try the mini moke club forum and see if a member can help,have you checked burlen.co.uk who do the su parts,there is another member on this forum I think his name is Acdodd I believe he is a tuning man I'm sure a member can point you in his direction.

[Spider]

This is the factory Tune Up Data for your engine, while this is actually for a Mini, your Moke has the same spec engine;-

 

 

It does appear you have the correct Needle and Spring fitted.

 

In regards to the flat spot you have, it could well be from a worn Throttle Spindle. The Spindle can be replaced easy enough, however the wear usually isn't confined to just the Spindle and you'll likely find the Body of the Carb needs to have bushes fitted too. You can check for this by seeing / feeling how much play is in the Spindle, you may want to disconnect the Spring though to be sure you are checking it.

 

Another cause of this hesitation is if the Hot Spot on the Inlet Manifold has been removed, though generally, that only shows at low speeds.

 

Another thing you could try is a heavier weight Oil in the Damper. The 'stock' SU Oil is a 20 weight, try engine oil or even gearbox oil, though it shouldn't want anything that heavy.

[Steam]

You have not stated what ignition you have. In my experience the ignition plays as much a role in flat spots as the carburation particularly if the engine is not absolutely bog standard.

[tarnofsky]

Thanks for all the advice so far. Seems to confirm my thoughts it might be a worn carb.
It got better after topping Up with SU dashpot oil but still is there.
The Moke stood for a considerable ime before I bought it, so might be because of that, too.
Carb tanken apart and cleaned rhough.
Ignition is standard dizzy with new vacuum hose and connecting rubbers converted to electronic points.

[Steam]

Su dashpot oil is too thin and can cause flat spots and hesitation. If you ask 10 people what oil you will likely get 11 answers.
I use air comptessor tool oil as it suits me. Try 20W or 10W or as the factory said 30w or just emgine oil.

[tarnofsky]

Little update:
I fitted the new carb the other day and checked the old one afterwards.
Guess what... feelable play in the butterfly spindle.
Also put in 20w-50 engine oil and it ran very well. No issues at tickover anymore.
Until .. well, until I reconnected the vacuum line.
I had set up the carb as per the factory manual and it was fine and a pleasure to drive with the vacuum line blanked off.
Then I connected the vacuum line and it ran like sh@@ very rough idle and after setting the idle speed again, it still felt rubbish on part throttle and at tickover.
Vac disconnected, idle back to previous setting - smooth runner again.
I noticed that the new carb has the vac takeoff further towards the engine, so probably manifold side with mich stronger vac.
I checked a spare engine that still has the old carb on it: same position. Original carb has it further back,the hole being behind the butterfly.
Analysis: both variants were used on 99H engines.
I will now try a new Minispares vacuum box on the distributor. If that won't make a difference, do you think I should drill the takeoff hole in the carb body to come out in the behind butterfly position?
Or just leave the vacuum line blanked off?

Edited by tarnofsky, 09 July 2023 - 05:44 AM.

[Spider]

I'd suggest either of these;-

 

 do you think I should drill the takeoff hole in the carb body to come out in the behind butterfly position?
Or just leave the vacuum line blanked off?

 

The correct location is rather critical.

When at idle, the port for the vacuum advance should be 'blanked off' (as viewed from the engine side) by the butterfly.

[tarnofsky]

Issue solved.
I read an article by engine guru Keith Calver after Spider's last contribution.
Keith explained in detail why there shouldn't be any vacuum advance at idle and why the takeoff needs to be on the carburetter side of the spindle.
So, what could I do?
I pulled a vacuum connection pipe carefully out of an old carb.
I measured how deep it sat in the carb - easy to be seen as shiny and new where it was in the carb and dull anywhere above. Roughly 3-4 mm.
Drilled a 3mm pilot hole 3.5mm deep. Drilled through the case from the pilot hole's bottom with a 1.5mm drill. Finally enlarged the pilot hole to the correct 3.2mm diameter with ,et another drill.
Tapped the takeoff pipe in place with a very soft mallet and some wood between pipe and mallet. It's a press fit and needs to sit tightly to be airtight.
Next I blanked off the old pipe with a vacuum cap.
I then fitted the vacuum line to carb and distributor and fired up the Moke.
Runs nice and sweet as candy now.
Due to lots of rain I couldn't do a full test drive yet and might have to fine tune to get emissions correct for our requirements here but all issues are gone now. No problems at tickover no rough idle.
Using 20w50 in the dashpot, too.
Much cheaper than SU carb damper oil and improves tickover on all my other Carb-Minis, too.
Good advice, thanks lads!

I hope the thread helps anyone with similar challenges...

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