Pilot jets

Thanks, Peter.

I've no engineering background at all beyond what little I've picked up from DIY and trial and error and reading of the various magazine technical articles though I do enjoy tinkering with mechanical things. Not always to their best performance! Your information is helpful. I did recently buy a set of very small twist drills and one of them is just about the right size. Whether I can manage to use it without breaking it remains to be seen since it seems so fragile. In any event now I've put the Monoblocs back on the bike I don't need to investigate the Concentric issue for the time being so that can go on the back burner.

Just to change the topic, in my earlier thread about my rebore Anna asked about my petrol consumption now I'm back to twin carbs. I've filled up three times since fitting the Monoblocs and my consumption has worked out at 55.3mpg for the first tankful, which improved to 61.8 followed by 60.4 subsequently. Compared to some of the figures quoted in the earlier "Manxman" thread I'm pretty happy with that. My previous consumption with the single Concentric over around 3,000 miles was just 60mpg so I'm also happy compared to that too. Not very happy with the weather over the last few weeks though. It's been very wet, and frequently very windy so this has curtailed my continuing running in somewhat. Roll on next spring!

The 25 pilot jet is 17 thou, to clean it out you use a 16 thou drill which cleans it out but does not resize it, so using an 18 thou drill on a 17 thou hole may get you close to the 19 thou hole. I get metric small drills for cleaning out Koni 76 series shocks 0.5, 0.8 and 0.85mm oil transfer ports off ebay, which is also where I got my set of 16 thou drills.

Thanks, Peter.

I've no engineering background at all beyond what little I've picked up from DIY and trial and error and reading of the various magazine technical articles though I do enjoy tinkering with mechanical things. Not always to their best performance! Your information is helpful. I did recently buy a set of very small twist drills and one of them is just about the right size. Whether I can manage to use it without breaking it remains to be seen since it seems so fragile. In any event now I've put the Monoblocs back on the bike I don't need to investigate the Concentric issue for the time being so that can go on the back burner.

Just to change the topic, in my earlier thread about my rebore Anna asked about my petrol consumption now I'm back to twin carbs. I've filled up three times since fitting the Monoblocs and my consumption has worked out at 55.3mpg for the first tankful, which improved to 61.8 followed by 60.4 subsequently. Compared to some of the figures quoted in the earlier "Manxman" thread I'm pretty happy with that. My previous consumption with the single Concentric over around 3,000 miles was just 60mpg so I'm also happy compared to that too. Not very happy with the weather over the last few weeks though. It's been very wet, and frequently very windy so this has curtailed my continuing running in somewhat. Roll on next spring!

Previously john_holmes wrote:

â?I get metric small drills for cleaning out Koni 76 series shocks 0.5, 0.8 and 0.85mm oil transfer ports off ebay, which is also where I got my set of 16 thou drills.

How did you search for it on Ebay?

Fritz

Here are some ......http://www.ebay.co.uk/itm/Am-Tech-20Pc-MICRO-HSS-TWIST-DRILL-SET-0-3-1-6mm-Small-Precision-Miniture-F930-/151844527902?hash=item235aa39f1e:g:4UAAAOSwI-BWGSNg

Cheapies, but adequate for a one-off drilling in brass. I used a set for drilling MZ jets when I was racing.

Previously ian_cordes wrote:

Here are some ......http://www.ebay.co.uk/itm/Am-Tech-20Pc-MICRO-HSS-TWIST-DRILL-SET-0-3-1-6mm-Small-Precision-Miniture-F930-/151844527902?hash=item235aa39f1e:g:4UAAAOSwI-BWGSNgâ?

Thank you Ian.

Unfortunately delivery UK only. But this link gave me an idea what to search.

Fritz

They might be handy for Lance though.

How about these Fritz...........http://www.ebay.co.uk/itm/20-PIECE-MICRO-HSS-DRILL-BIT-SET-METRIC-IN-CASE-TITANIUM-COATED-STORAGE-CASE-13B-/370775730235?hash=item5653f4a83b:gG4AAOSwDk5T-gL5#shpCntId ?

Those are the ones I use on the series 76 Koni ports that get bunged up with the dissolving bump stop washer, you will also need a holder

http://www.ebay.co.uk/itm/Copper-0-2-8mm-Mini-Micro-Drill-Bits-Keyless-Hand-Chuck-Holder-UK-Seller-/331676159619?hash=item4d39708e83:g:xjYAAOSwPcVVzY3y

For the 16 thou drill bits they came from the US and I got them by searching for #78 drills, a box of 10 was $10 or so a few years ago.

Thanks, John.

I was wondering how I would go about using such fine drill bits with my usual hand drill and you've provided the answer. I've already made the purchase in readiness for when I get round to dealing with this matter.

The link Ian provided to the drill bit set shows a set which looks exactly like the one I bought a few weeks ago by chance, though my set has a blue box. I suspect this won't affect the drills' performance!

Thanks for your various comments. I continue to learn.

Previously fritz_wettstein wrote:

Previously john_holmes wrote:

â?I get metric small drills for cleaning out Koni 76 series shocks 0.5, 0.8 and 0.85mm oil transfer ports off ebay, which is also where I got my set of 16 thou drills.

How did you search for it on Ebay?

Fritz

Here is a UK company that sells direct. They also have an Ebay store

http://www.proopsbrothers.com/index.asp?function=search

Just search for "drill bit".

Also you can hold those drill bits in a Dremel with an extra small collet and use it freehand.

A tale of mystery indeed!

Hello Lance,

I've just read your article in RH336 and can relate to your carb problem.

I fitted a newpairof genuine amal concentric carb bodies to my 74' Commando and had similar problems as you.

Stuttering and missingon one cylinder.

I tried most of the stuff that you did and then gave up in the end and refitted the original carbs and all was well again.

However, recently I came across the new carb bodies whilst tidying my workshop and decided to take a closer look at the offending carb body.

By holding my fingers over the pilot jet circuit outlet holes and spraying carb cleaner into the pilot jet adjusting screw hole I discovered a very small air leak at the mixture chamber blanking plug (on the underside of the carb body next tojet holder).

The blanking plug just seems to be pressed into the carb body, I gave it a tap with a socket and a small hammer and retested for leaks, all ok, new carb bodies now refitted and motor running sweetly!

Perhaps this helps may solve your mystery as well.

Thanks for your comments, Gordon.

As mentioned before I'm currently back on the original Monoblocs and trying to run in the engine following its rebore, and am presently very hampered by the long spell of wet weather and now the cold weather, being rather a wimp and a fair weather rider! However I've noted your experience and will at some stage check out my Concentric to see if this might be the problem.

Yet another learning experience!