Carb Mixture Screw

[nicko]

I am currently trying to adjust the carbs on a 1980 350 Strada as it has an annoying tenancy to stall at idle. The carbs are VHBZ 25s. I have squirted some carb cleaner down the idle circuit which seems to have helped a bit. My question is what is the standard number of turns out on the mixture screw? If there is a standard.

Cheers
Nick

[MickeyMoto]

Out to enrichen, in to weaken, I believe. Take what you have now and back off half a turn and see what happens. Once reliably ticking over check tappets, ignition timing then adjust the carbs... Nowt in Blue Book, but details of how to adjust.

As a non mechanical engineer (I have other skills I use day to day), but a competent mechanic that is what I would do to start with. Check the inlet rubbers for tightness and cracks too!

I am sure somebody will be along shortly to tell you how to turn up a new crankshaft using your vice, a bastard file and your missus' best lingerie... It won't help you, but hey ho!

[nicko]

Cheers Mike, regarding the missus' best lingerie it's quite good for using to wipe over greasy hands/tools......

[mbmm350s]

Hi Nick
Everything you need to know is in the dellorto tuning manual. You can probably find the Dell Orto manual on line. Also you can buy from Eurocarb. If Stuck pm me and I can mail you a pdf
Importantly it show's how to correctly set the float height
If using wife's lingerie stick to plain cotton at lower cost silk isn't absorbant enough.
Mark

[Ming]

I am sure somebody will be along shortly...

Now Mr Moto - a few weeks ago you told me off for making a political joke on your Morini forum - now I object to you posting a poorly veiled insult towards another member.

[EVguru]

How low is your idle speed? Especially if you have worn slides, you might have to set it quite high.

There is also a tendancy to run rich on modern fuel, which causes the off idle 'stumble' and can lead to stalling. For a range of idle jet sizes, you can use the mixture screws to achieve a satisfactory mixture, but just off idle you have the progression circuit. Mixture here is controlled by the idle jet and the vacuum under the slide (slide cut-away). A leaner idle jet will often improve things (I'm running 43s), but sometime a larger slide cut-away is needed (it was on my 125H).

[72degrees]

In answer to the original question, if setting up carbs from scratch the conventional wisdom used to be to start with the mixture screws about 1 1/2 turns out and then adjust in and out as appropriate to get highest idle speed. Adjust the throttle stops to get a suitable idle rpm (1500-1750), then tweak the mixture screws again. Should be done in combination with a carb balance really and in my experience the effect of temperature means that I tend to opt for a slightly high idle when really hot or it can be inclined to stall when just warm IYSWIM. That's with 28mm carbs though.

[nicko]

Thanks for the suugestions/tips etc. I had been told that the carbs had been sonically cleaned before I purchased the bike and I haven't messed around with them too much.

The mixture screws were set approx 1 turn out and the engine revs drop to 1050 - 1100 and then stalls. This is with no throttle input so isn't the off idle stumble EVguru refers to.

I shall set the screws to 1 1/2 turns out and see what happens, I'll report back.

Cheers
Nick

[Daddy Dom]

Thanks for the suugestions/tips etc. I had been told that the carbs had been sonically cleaned before I purchased the bike and I haven't messed around with them too much.

In that case, I would strip each carb individually and check everything is where it should be. When mine were sonically cleaned, some small parts were lost by the person doing the job. Paul has done a video on fitting the Dell 'Orto gasket kit, I would start there.
DD

[nicko]

OK a bit more time fettling reveals that there are no o-rings on the mixture screws, adjusting from 1.5 turns out to 2 turns out doesn't seem to make any difference and there is a split in the elbow from the air box to the carb. It's been taped over but it's by the jubilee clip on the carb side.

[EVguru]

Try raising the idle speed.

[mad muller]

had issues like this myself, as mentioned increase the idle speed i have mine ticking over about 1500 rpm any slower when it gets hot it will weaken and cut out get some o rings on the air screws it can only help, take float bowls off and give the jets a good clean if you havent already there is one in the corner that has a o ring on it mine were perished so worth replacing hope iam not repeating what has already been said.

[nicko]

Thanks to everyone for their advice and Paul's great YouTube films.

I have replaced the o-rings on both the mixture screws and throttle stops and upped idle speed to between 1600 and 1900 and it's no longer stalling. Once I've given it a good run I'll readjust and see what happens, now I know what I'm doing.

Cheers
Nick