Quirks of Mikuni/Solex's and Webers

[sillycar chick]

Billzilla,
A question about these loose venturis....
Had never heard of this until i found this thread. How do you tell if they are loose? And how do you retighten them? From what I have seen, they are held in by the nuts on the outside of the barrels, and there is a slotted screw inside the nut (like you would use a screwdriver on).... which one do you tighten? soooo confused....
Thanks,
Dana

[Billzilla]

Billzilla,
A question about these loose venturis....
Had never heard of this until i found this thread. How do you tell if they are loose? And how do you retighten them? From what I have seen, they are held in by the nuts on the outside of the barrels, and there is a slotted screw inside the nut (like you would use a screwdriver on).... which one do you tighten? soooo confused....
Thanks,
Dana

Take the air cleaners off, and stick your middle (longest) finger down the carby throat. In the centre should be a firmly-held auxiliary venturi.
I've come across a number of them (pretty much every one I have seen in person) and heard of a large proportion here and in other forums where the auxiliary venturi is loose. This can happen no matter how carefully or tightly you do up the little locating screw & nut that holds them in place. They'll do with an untouched carby from the factory as well and this is most often how they are found.
There's the other thread on Mikuni's and it shows them in pieces in a diagram, you can see the screws/nuts there. (I think, I haven't really looked I must admit)

Okay, I got off my arse and looked, here it is ->



They're the screw/washer/nut combination that comes in at about a 45deg angle from the sides. You can't realyl see them from the top of the engine, you have to either get underneath or reach down and feel for them.
The auxiliary venturi is the middle of the three little tubular-like things that go down the throat of the carby in that diagram.

I'm really not sure of a way ot totally curing the problem - other than to go to Webers or EFI. Rodger may well know more though.

[Rodger]

Hi Dana and Billzilla,

Yep I agree most times I see this problem and mostly in the S5 Solex (commonly 2T-G). As they become loose the first time they start to rattle which only makes things worse. There are locating posts, one rectangular and one round, on the top of the Venturi which wear down.

Please do not simply tighten the screw as all that happens is it damages the bottom of the Venturi.

Best solution is to take all of them out and check for wear around the posts. If they are ok then a drop of silicone on the round post helps. If the round post is worn too much there is a method of repairing them. New Venturis for this model are extremly rare.

A quirk of the age of the carbies.

I just can not wait for all these fangdangled EFI things to become 20 or more years old and then we will see lots of cursing from the EFI brigade. In fact, sorry Dana, how is your twenty year old or so, 3T-GTE going?

Carbies may be old technology now, but hey they are not like computers (read EFI), always changing.

Regards

Rodger

[mrshin]

Well, it's pretty hard for something that is no longer used to be updated/improved...

Also, many of those fandangled EFI things from 20 years ago are still running better than their non-fandangled cousins

[Billzilla]

I just can not wait for all these fangdangled EFI things to become 20 or more years old and then we will see lots of cursing from the EFI brigade.

You mean like the 1983-odd 4AGE's?
That's 24 years ago mate.
True enough they have the odd problem, but they're a vastly better thing than any carby.

FWIW my Mikuni's started to fall apart all by themselves at age 12 years.

[river]

Hi,

Fixed for you.....

You mean like the 1983-odd 4AGE's?
That's 24 years ago mate.
True enough they have the odd problem, but they're a vastly better thing than any poorly tuned carby.

FWIW my Mikuni's started to fall apart all by themselves at age 12 years.

Carbs need to be tuned often and require maintenance. There are some amongst us who enjoy the task of tuning and working on their carbs. I guess that's why mine are 34 years young and still going strong.

seeyuzz
river

[oldcorollas]

fwiw, i've had the venturis on downdraught webers and Aisan carbs also come loose and rattle around... nothing a bit of fuel resistant epoxy can't fix

[RT104GT]

Hi,

Fixed for you.....



Carbs need to be tuned often and require maintenance. There are some amongst us who enjoy the task of tuning and working on their carbs. I guess that's why mine are 34 years young and still going strong.

seeyuzz
river

Mine too. 35 yars really hard life and one rebuild costing $400 for 240,000 km.

Pretty robust.

Clue to loose venturi is not to overtighten in first place.

[Starfire]

Can you still get rebuild kits for the 2TG carbs?

[joey]

Is one of solexs quirks popping? When i drive they make a popping sound and the power cuts out for that split second it pops (this only happens very occasionly)... i only ask this becasue i was discussing it with someone who also has solex carbs and his does the same

[Starfire]

That sounds like a backfire...

[Turdinator]

Is one of solexs quirks popping? When i drive they make a popping sound and the power cuts out for that split second it pops (this only happens very occasionly)... i only ask this becasue i was discussing it with someone who also has solex carbs and his does the same

I've been told that when a weber pops its because its running lean. But my setup is quite rich and i still get the occasional pop. Mostly when i've been cruisin for awhile, then put my foot down, and the plugs are a bit dirty. But sometime it'll do it comming out of a sharp corner. I wonder if thats to do with the fuel moving around in the bowls?

[Rodger]

Starfire,

Yes you can get rebuild kits still for the Solexes typically found on 2T-G, that is the S5 type but the Mikuni kits are getting rare.

Check the Sponsors page for my web site RMCarburetors.

Joey, does it pop as though it misfires whilst cruising at 80-100km? This is a sign of a lean mixture. Pilot jet maybe one step too small or could go up one step on Main Jet.

It could also be that they are not quiet balanced.

Turdinator, try a Pilot/intermediate jet one size bigger in your Webers. The Main system maybe rich but at anything under 20% throttle and most of the fuel is being drawn through the Pilot system.

Regards

Rodger

[sillycar chick]

Mine pops ALOT but only when you use the gears and compression brake using the engine
I think mine are due for a balance and richen up with jetting.... will wait till the ported head goes on though, so the carbs suit the head.

[joey]

Joey, does it pop as though it misfires whilst cruising at 80-100km? This is a sign of a lean mixture. Pilot jet maybe one step too small or could go up one step on Main Jet.

It's not so much happens at high speed, more mid to high rpm before changing gears. The country hick that i had taken my carbs to get rebuilt ect did say he leaned them out because i argued the fact that i thought they were running rich (turned out to be a drilled out pilot jet so replaced with a normal sized one... maybe he use a smaller than normal pilot, will check that today actually) so he changed the pilots and leaned it out aswell....
Lesson learnt: Never trust a guy that looks like Quagmire and says he's worked with solexs before.

Is changing the mixture done by turning one of the screws on the solexs? If so where abouts is it located and which way (clockwise/anti-clockwise) increases the amount of fuel. Might just increase it a tad to see if it makes a difference.

Cheers, Joey