A65, running very, very rich.

[Spaceman]

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.

[Spaceman]

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.

[geraldhattrick75]

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.

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....

[geraldhattrick75]

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

[Spaceman]

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.

[Spaceman]

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.

[geraldhattrick75]

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.

[DAVE BRADY]

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.

[Spaceman]

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?

[geraldhattrick75]

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.