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.
Hi,
Only running a 30mm. You could ask Allen's for their recommendation.
Dave.
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!
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.
was it running ok before? could be float level to high or the needle jet needs lowering.
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.
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.
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.
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.
The carb I'd should I think be stamped just by thd "choke" housing.
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.
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.
QuoteThe 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
QuoteHowever, 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.
The needle jet is 169 P-2 (not sure what the P-2 means mind)
Just going back to the start of the thread, you said that your A65 was running rich. It would be worth doing a check on the plug colour after running the bike at half throttle for a few hundred yards and then stopping the engine quickly. If sooty then it would show it is running rich.
If this is the case, it would be worth buying a 170 and 180 main jet (only a few pounds each) and then trying each in turn to see which produces the best result. You should see a very noticeable difference in the way the engine runs as you change the main jet size and it will help you determine which size is optimum.
Size P2 is in the middle of the 169 range of needle jets. The other A65 I came across with a Mikuni used a P6 which has a slightly bigger hole. This A65 also used a 6DP1 needle and it might be worth reading off what needle you have although there is a lot of them to choose from.
For the time being, it is probably better to start off with checking whether the main jet is correct. Once that is sorted, one way or the other, you can then normally you turn your attention to the needle and needle jet which, hopefully, will be ok.
Thanks spaceman, plenty for me to get on with over the weekend.
I've rebuilt the carb and glued a nice rubber pad to the choke plungery thing, just in case it was, as suggested, causing problems.
I'll see if that makes any difference then turn my attention to ordering a 170 and 180 main jet.
Quote
Just going back to the start of the thread, you said that your A65 was running rich. It would be worth doing a check on the plug colour after running the bike at half throttle for a few hundred yards and then stopping the engine quickly. If sooty then it would show it is running rich.
It was the really sooty state of the plugs after the engine had been idling for 5/ 10 minutes that kept causing the engine to stall.
I also did do a couple of one mile local circuits (circular route so as to arrive back on my drive as the engine cut out, again from the sooty plug).
I will do everything that you and everybody else has suggested....... Everything...
Thanks again....
Bummer, I glued a nice rubber circle on to the 'cold start plunger thingie' and after doing 1/2 a mile (-ish) the plugs had sooted up badly again. (Incidentally, I had lifted the choke lever before setting off on my huge journey...)
So strike that one....
I've ordered a variety of 'Pilot' and 'Main' jets..... We'll see what happens with them.....
Thanks again for all your suggestions ....
Dave
It might be worth checking the float level while you are waiting for the new jets. According to Allens it should be 24 mm. I might try the measurement on the Spare Mikuni I've got later but, as far as I understand it, you need to measure the distance from the bottom of the float to the float bowl gasket flange with the float needle just about to close the fuel valve. To change the float level, it's a question of carefully bending the tab on the float arm.
From my own experience of tuning the Mikuni on one of the bikes I ride, even a main jet size 10 too big, resulted in sooty plugs and lumpy running. I can't image what the engine would have run like with a +20 main jet.
However, I don't know whether a 170 main jet is optimum for this bike - it would have been interesting to know from Allens what size they recommended although it would probably would have to be for an A65T rather than an A65L. If the main jet is too large then trying a smaller size will quickly show whether this is the cause of your problems.
Just measured the float level on my spare Mikuni which appears to be 24 mm but it is not a straightforward measurement. Rather than taking the measurement at the point where the float needle valve closes, you have to take it at the point where the float lever tab just contacts the valve needle. Worth checking the level just to rule this out as the problem.
Thanks Spaceman, I have already had a go at sorting the float level with the neat little metal rule that Alan's suggested......
Alan's couldn't find any info on float level, or anything else for this carb as being a '565' variant (for BSA). They just said "best guess would be to make sure it lies parallel to the gasket base.....
The lack of model specific info is the curse of this thing.....
As an alternative, I jhave been looking at an old Amal monobloc 389/ 95 that I have in the garage. I should be able to convert it to a 389/ 202 (as used on the Thunderbolt) by changing the appropriate jets/ slide and etc..... (I've found full details on t'web.....)
Only a thought at the moment, but it might well be a cheaper option, and at least it would be standardised... at last.
Thanks for your help and patience...
Dave.
Hi Dave,
Thinking back to earlier posts re this carb. I think that it had run with the Mikuni so assuming that you have not changed anything then it should run now. You have cleaned everything and set it as best you can but the richness is now the problem.
As suggested it could be the 'choke' not cutting off the fuel when the lever is raised. This is the first thing I would check as it is the only thing that would have deteriorated/hardened over time.
Is the carb a 30mm? I had 30mm on a 650 Thunderbolt and had it set up by Allen's. At the time I think they said that it would be close to ideal but gave me a couple of spare main and pilot jets just in case.
I think that this is what they gave me:- Slide 3.0, main 190, needle jet 159, needle 6DH2, air jet 1.0, pilot 20.25. I think the needle is in the middle notch.
Even if yours is not quite the same then if it is close and everything is clean then the engine should run well enough to not need the choke and for a test ride to determine if anything is needed for fine tuning.
Incidentally, I have now fitted the carb on a long stroke 750 BSA and it runs well without any alterations.
Dave.
I would personally stick with the VM30 a little longer at least until you have tried the smaller main jets. As said, the carb setups from Allens need to be regarded as a starting point and tuning the main jet size is very simple especially compared with the other carb settings. The advantage of the Mikuni carb is that they are very good for performance especially compared with an AMAL although that can be at the expense of fuel consumption!
In terms of float level, I noted that the float pins that contact the float arm are 10 mm from the bottom of the floats and therefore simply measured the distance of the float arms to the gasket flange when the float arm tab just touched the needle valve. This gave 14 mm giving a total float level of 24 mm which is the same figure quoted by Allens for the VM30?
Yes, I will take your advice and stick with the Mikuni- once I've received the jets (7th to 14th of July), but I'll look at cobbling together the Amal 389/ 101 conversion, as a back up...... just in case.
(I reckon that once the VM30 spots the Amal, wot I is building,.... it'll start playing ball...)
thanks once more for all your valuable suggestions.
Dave.