A bit OT – Vintage SOLEX carburettor jet sizes

[Steve WithnellParticipant @stevewithnell34426]

[Steve WithnellParticipant @stevewithnell34426]

I’m “assisting” in the re-furb of a SOLEX carb off a 1930 saloon car. It’s running a bit rough at idle and the carb has the wrong size pilot jet – size “70”. The handbook says it should be a “60”.

 

I thought “70” = 0.7mm and since I have access to some much smaller ones (“45” from stationary engines) obvious to drill one out! However a 0.7mm drill is too big to pass through the “70” jet so wonder what the game is here.Anyone got a clue?

 

Not quite model engineering but the forum certainly has the right audience.

 

TIA

 

Steve

 

 

[John Stevenson 1Participant @johnstevenson1]

The numbering sequence on carbs has to do with how much fuel it passes in *something* divided by seconds.

 

*something* being millilitres,ounces or ferkings

 

Somewhere have an old Amal book and it may have conversion tables in it, not sure not had to look at it for ages.

 

John S.

[Bill StarlingParticipant @billstarling10428]

Dear Steve,

 

Try a flow of 70 c.c. per minute. I have a raft of information for pre-war Bowden carburetters and they give jet sizes calibrated in c.c. per min.

 

All the best,

 

Bill.

 

PS You’ve just made my day. It’s the first time I feel I’ve made a positive contribution to this forum – even if it’s not about model engineering.

[Steve WithnellParticipant @stevewithnell34426]

So, I need to open up the diameter of a “45” to reflect a volume increase, or track down a genuine “60”!

 

Sounds like flow will be very sensitive to change.

 

Thanks

 

Steve

[Speedy Builder5Participant @speedybuilder5]

See if you can get hold of some SWISS REAMERS – these are 5 sided tapered reamers which come in sets from about 0.005″ upwards.

[adyParticipant @ady]

I’ve only worked on cars from the 1970s and they always had a couple of bits you could tweak and get a richer/leaner mixture at idle.

There was both an idle mixture and an air bleed screw, these should eliminate any flow issues through the needle when you’re idling.

 

The idle was always the easiest bit, you had a pretty big envelope where the engine was tolerant.

Advancing/retarding the TDC spark point seemed to make a big difference and a warmed up engine was like night and day compared with a cold one.

The hardest bit was trying to tune an old banger for when she was running under load because of the dynamic nature of a car engine.

 

You can do these things by ear.

There is a Glass topped see through sparkplug called colour tune which will let you view whats going on in the chamber, very handy if you’re a tweaker.

Going back 30 years now…my colour tune had an adapter which would let it be used in bigger spark plug ports, ebay might have an “old” colourtune set with this adapter.

 

What I found made the biggest difference to my old 1970s manual tweaking bangers was installing electronic ignition.

 

edit:

I wouldn’t go drilling holes in the carb unless you’re totally out of options, and especially for an idling issue, the main purpose of the carb is to do things right when the engine is doing work.

The original owner may have fitted a different needle because she was running too lean under load, which could damage the spark plugs.

There are also loads of petrol head sites around which you can ask, happy tweaking.

Edited By ady on 13/06/2011 00:37:19

[Richard ParsonsParticipant @richardparsons61721]

A bit Off topic –beer measures
A Pinnikin is 4 ½ Gallons (Imperial Gallons not your measily U.S gallons)

2 Pinnikins = 1 Ferkin
2 Ferkins = 1 Kilderkin

2 Kilderkins = 1 Barrel
1 ½ Barrels = 1 Hogshead

It is now getting a trifle sultry over here so I have an excuse to drink a Hogshead or two.

Loud belch!

Dick

[adyParticipant @ady]

Social Media Sobriety Test:

According to Webroot, who offer the Social Media Sobriety Test
to Firefox users, “Nothing good happens online after 1 am”. This test
is designed to prevent you from making that regrettable late night
Facebook post.

You can then adjust your settings for the best times to prevent embarrassing posts on Facebook, MySpace, Twitter, Flickr, and YouTube. Just select the sites for which you want to be tested before logging in, and the times you’re most likely to post something you’ll regret later. When you attempt to log on during those designated times, you’ll be required to take a sobriety test that includes following a finger around the screen with your cursor, or typing the alphabet backward. Things I’m not certain I can do at any time of day, in any condition.

 

 

[David Clark 13Participant @davidclark13]

Hi There

Does it stop me posting the alphabet upside down?

regards David

 

ǝʇǝןdɯoɔ sı ǝɟıן ʎɯ

[Gordon WParticipant @gordonw]

Explanations of jet sizes have already been given, also the firkin etc.,all very useful because this is just what we were talking about in the pub yesterday, will have to go tonight to show of my knowledge. Back to carb. jets, as said don’t start drilling anything unless you have to. Quite normal to have non spec. jets in old motors, and won’t make much difference anyway. I would first make sure the jets are all clear, common for corrosion type growths to build up, even in jets that look clear, and reduce the effective bore. Can be difficult to shift, I use a set of gas torch reamers, shock horror.

[EddieParticipant @eddie]

Hi Steve

A quick search on Google Solex Carburetor Jets revealed some intresting information.

Eddie

[Steve WithnellParticipant @stevewithnell34426]

Thanks guys, probably worth pointing out that the carb has been completely stripped cleaned, and re-assembled. JS and Bill Starling pointed out that the number on the jet was a measure of flow rate and not diameter. Although some authentic looking docs on the web say diameter, the fact is that a 0.7mm drill is much too big to pass through the clean “70” jet, so flow-rate is now the working assumption.

 

I’m pretty sure that the “70” jet is wrongly used in this carb to compensate for air leaks arising out of significant wear on the butterfly shaft. The original owner of this vehicle was well known to us and he had used solder to fill hollows in the badly worn shaft, to give you a clue as to some of the “ingenuity” that’s been unpicked in the re-build…

 

Final piece of context is that I have to hand a couple of “45” jets for this carb so didn’t see much risk in opening one up to see if the slow running improved. As it turns out, I now know that a 0.5mm is a tad under a fit in a “60” jet, so if it drills a bit oversize, as small drills are prone to do, then we can should get pretty close to a “60” size jet and see what difference it makes. The owners manual states a “60” which is what kicked off this experiment.

 

 

[Gordon WParticipant @gordonw]

Glad you’re getting it sorted. Will just point out that thorough cleaning does not always restore the hole to the proper size. An aside- I have tinned butterfly spindles etc, does not last long, some types can be restored good as new with “O” rings ,on the shaft or in the hole.

[Steve WithnellParticipant @stevewithnell34426]

I made two new shafts, one fitted with “o” rings (great minds!) and the other to “spec”. The problem is that the bushes in the carb body are a) worn and b) cast in, so need to be bored out for replacements to be pressed in and whilst this can been done by mounting on the face plate, I’ve yet to work out how to get the bore aligned well enough to the lathe axis as it’s not obvious to me what to use as a datum for the positioning across the carb throat. up/down there is latitude to be a bit out, but if left/right position isn’t right the butterfly will jam and if the rotation around the throat isn’t right the shaft will jam. The bushes are about 2/3 the depth of the hole for the shaft – so if I bore right through then I disturb the inner wall of the carb throat.

 

The “O” ring solution makes for an easy life

 

 

[Steve WithnellParticipant @stevewithnell34426]

I made two new shafts, one fitted with “o” rings (great minds!) and the other to “spec”. The problem is that the bushes in the carb body are a) worn and b) cast in, so need to be bored out for replacements to be pressed in and whilst this can been done by mounting on the face plate, I’ve yet to work out how to get the bore aligned well enough to the lathe axis as it’s not obvious to me what to use as a datum for the positioning across the carb throat. up/down there is latitude to be a bit out, but if left/right position isn’t right the butterfly will jam and if the rotation around the throat isn’t right the shaft will jam. The bushes are about 2/3 the depth of the hole for the shaft – so if I bore right through then I disturb the inner wall of the carb throat.

 

The “O” ring solution makes for an easy life

 

 

[Steve WithnellParticipant @stevewithnell34426]

I can report that the “45” jet has been drilled out to 0.6mm and the engine idling is much improved. So it looks like the “45” was a diameter after all. I need to measure up the drills and see if there was some wrong sizes…Also the shaft with the “o” ring mod works well. Just need to get it on the road and see how it runs properly warmed up

[Author]

Posts