A65, running very, very rich.

[geraldhattrick75]

My 1965 A65 lightning (with single carb head) is running incredibly rich. (Even just on tickover).

It suggests that I need a new pilot jet for the Mikuni VM32 565 carb, however I don't know the size of jet, nor can I read it on the jet itself.

Does anyone on here, running a Mikuni VM32, know what the correct jet/s are please.

Failing that I'm inclined to buy a new carb, possibly an Amal monobloc- any ideas of the jetting please?


Any other suggestions would be greatly appreciated........ Please.

Dave.

[DAVE BRADY]

Hi,

Only running a 30mm.  You could ask Allen's for their recommendation.

Dave.

[Spaceman]

Allens list kit VM32-0170-K for the A65L and I assume the 170 refers to the main jet size. I run a VM32 on my other non-BSA single and that uses a 175 main jet. It actually came from Allens (previous owner) with a 185 main jet which was much too large and caused it to run very rich.

I doubt if the pilot jet will be causing the problem but I suggest you check that the enricher (choke) is both switched off and the plunger valve that the enricher uses is in good condition otherwise you could well end up with a very rich mixture!

[cdsdorset]

As spaceman said. Take a close look at the enrichment/choke unit. Is the seal in good condition od "dimpled: if its worn you will be permanently running on a bit of choke.

[pockets]

was it running ok before? could be float level to high or the needle jet needs lowering.

[geraldhattrick75]

Thanks for all the replies, they are very helpful...

Not sure of how the bike was running before I rebuilt it. I just used everything that came with it, including the mikuni carb...

(I did phone Alans up a while back but they (eventually) recognised  it as a VM32 565 "as supplied to BSA in the early days")


Dave/ Allen, I'll phone Alan's and see what they suggest re jets and a carb kit.

I'll take a closer look at the Enricher valve set up and confirm that the seals come with the kit.

Ill let you know how it goes...

But thanks again it's much appreciated,
Dave.

[DAVE BRADY]

Hi,

Thinking back to when I had 32mm Mk2 conc. on a Thunderbolt, I had a similar problem and it was the richening jet for the choke.  It is the same principal as the Mikinui and quite crude.  Basically a rubber bit blocking a hole. I made a replacement and it worked. 
If you are unsure if this is the problem then warm the engine a bit and then block the jet off by shoving a small rubber disc down on to the jet and see how it runs.

Dave.

[Spaceman]

On my other bike, I need the enricher turned on to start the bike but need to switch it off almost immediately afterwards because it causes the bike to run very rich and lumpy. Unfortunately, unlike a normal AMAL choke, the Mikuni device is either on or off and therefore can't be backed off as the engine warms up. Because of the way it operates, it should be fairly obvious if the enricher is operating as you turn it on or off by the way it effects the running of the engine. However, even when off, the additional fuel flow might not be fully stopped because of poor sealing and that could cause the engine to run rich.

[geraldhattrick75]

I've rather assumed that the Mikuni is a VM32, there being no real info stamped onto the carb body (other than 565.00), but upon measuring the venturi I find it's actually 29.88mm- which would make it a VM30, wouldn't it?

Not that makes any difference according to Allen's, as there are so many variants of a VM30.
And, given that this was originally raced, the jetting might not relate to anything road based.... (I'm hoping that Mark (Guitarznbikes) might be able to throw some light on the Mikuni's history, as he used to own it)

These are photos of the cold start plunger (VM18/144 I think?)

Worth replacing methinks...


I really am totally stuffed with this Mikuni carb issue so thanks again for all your help.

Dave.

[cdsdorset]

The carb I'd should I think be stamped just by thd "choke" housing.

[DAVE BRADY]

Hi,

It does look a bit worn and may also have gone hard over the years.  I believe that replacements are available.  You could try sticking a bit of soft rubber on to it just to try and eliminate it as the problem.

Dave.

[Spaceman]

The VM carbs are all very similar with just the choke size being different. The '65 A65L had a 1 1/8" choke which is 28.6 mm and so anything bigger than that would be ok. Worth checking whether this A65L had the cylinder head inlet diameter enlarged?

This starter plunger is probably ok - the plunger body closes off the air passage when fully lowered and the rubber seal closes off the fuel inlet hole which is at the bottom of the plunger cavity. Provided the plunger descends fully when the enricher is switched off, everything should be ok.

However, it would be interesting to know what the jetting currently is which will be marked on both the needle jet and the main jet. As said, I would expect the main jet to be a 170 and I have seen another A65 listing this as the size also.

[geraldhattrick75]

The carb I'd should I think be stamped just by thd "choke" housing

.
F'raid not CD, the only markings are '565.00' near the choke  and 'W5  2  1' on the head facing side

[geraldhattrick75]

However, it would be interesting to know what the jetting currently is which will be marked on both the needle jet and the main jet. As said, I would expect the main jet to be a 170 and I have seen another A65 listing this as the size also.

The main jet looks to be 190, the slide is  2.5, while I can't read the pilot jet size.

[geraldhattrick75]

The needle jet is 169   P-2 (not sure what the P-2 means mind)