Three years later, still having problems with idle

[Long_Road]

When in doubt, draw a picture. The movement of the rear plate is stiff and rotational rather than lateral, but can't be helping.

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I checked the earth wire is still soldered on the pickup and also retimed the ignition to ANT at 6500rpm before making a couple more videos.

Vid 4 https://youtu.be/WziH-_HWce0 - A demo of the engine behavior in general with much better sound

Vid 5 https://youtu.be/BqecfQOkxtc - A timing light demo. Watching it again it is a little retarded now, I'll have to readjust it

Again thanks for your help with this, I owe you all a pint. Steve Brown and 72 Degrees, I may just take you up on your kind offers. There's a red pickup and rotor on Ebay at the moment for a 250 which I'm considering - are they compatible with a 350?

[72degrees]

Again thanks for your help with this, I owe you all a pint. Steve Brown and 72 Degrees, I may just take you up on your kind offers. There's a red pickup and rotor on Ebay at the moment for a 250 which I'm considering - are they compatible with a 350?

Yes, as are the transducers, I robbed the 250 of its ignition pickup for the racer 350 before I sold the 250 engine.

[mbmm350s]

The advance appears to be working. As you can see the advance range is not very much on a Morini the sachse system fixes this but even so it should be possible to achieve reliable idle at 1500rpm indicated.

It's difficult on the early engines to see precisely the marks you need a helper to open the throttle and build the revs up to 6000rpm not blipping the throttle. Some strobe guns aimed at car markets don't work at this rpm.
As you say it's a little over advanced .
Hanging revs just off idle have these causes 1) over advanced ignition or 2) a too small pilot jet.

The strange tinkling has gone away and that's good.
Otherwise it's sounds good. There is a background whirring like the primary drive perhaps. Hard to say.

I saw one pickup on eBay for a 250 single it's not any use. It only has the sensor for the front cylinder. If it's for the 250V then make sure it comes with the rotor as the 250V uses the second series (Same as 350 from 1978) and needs a different rotor to the one you have.

I think that rapid throttle opening if it's on a cold engine may be a little unkind. Does it do still do this after 10 mile warm up if so then there is something wrong.
Inadequate fuel delivery or loss of spark?
Mark

[Canuck750]

I have a several 1970's Italian motorcycles on the road, all with Dellorto carbs. I have fully rebuilt each of my bikes and in each case replaced the carb internals. Half of them, especially my Moto Guzzi's with flat slide Dellorto's have very poor idle characteristics, sounds like the same symptoms you have. Even my bikes with round slide Dellorto carbs (Ducati 860 GT and Laverda SF1) idle poorly, the problem is Dellorto carb bodies and slides just wear out to the point the air leaks are so pronounced an even idle is unobtainable. This year I replaced the carbs on my Ducati and Laverda with new Dellorto carbs and the difference is night and day. I am going to replace the VHB Dellorto carbs on my Moto Guzzi's with new Dellorto round slides, Stien Dinse makes a kit with carbs and manifolds to replace the square slide Dellorto's on 750 / 850 / 1000 cc Moto Guzzi's. The Dellorto's on my Moto Morini 500 are ok but just so, and I will probably replace them with new ones in the future.
From now on going forward when I restore a bike I am replacing the carbs with new ones rather than sinking a lot of money into old worn out carb bodies.

[72degrees]

I saw one pickup on eBay for a 250 single it's not any use. It only has the sensor for the front cylinder. If it's for the 250V then make sure it comes with the rotor as the 250V uses the second series (Same as 350 from 1978) and needs a different rotor to the one you have.


Mark

Thanks for the clarification Mark. When someone says 250 I tend to assume 250 2C V twin - sorry for being cylinderist . My offer of a substitute is for a complete red type 2 pickup with rotor.

[72degrees]

From now on going forward when I restore a bike I am replacing the carbs with new ones rather than sinking a lot of money into old worn out carb bodies.

Not a bad strategy. I treated the 'racer' to a new pair of PHBH28s. I'm looking forward to having them on the road 2C/350 in future. I found the old pair were not too bad in respect of slide wear, and once treated to new needles weren't too bad.

One gotcha with new PHBH Dellortos, however, is the cheap nasty floats they come with. I've had two split, with comedy results at a hill climb start line. I'm not the only one to have experienced this I think. I may go to the trouble of transferring the old style floats to the newer carbs.

[3potjohn]

My PHBH carbs had white floats. Whilst chasing poor running issues I spoke with Eurocarb who supplied me with amongst other things a set of black floats which I gather are better. I tried submerging the old white ones in fuel then weighing them and detected no differences from a dry float.Perhaps an unnecessary purchase? My slides do have some galling marks so likely could do with replacing at some stage , when I am feeling flush.

[72degrees]

My PHBH carbs had white floats. Whilst chasing poor running issues I spoke with Eurocarb who supplied me with amongst other things a set of black floats which I gather are better. I tried submerging the old white ones in fuel then weighing them and detected no differences from a dry float.Perhaps an unnecessary purchase? My slides do have some galling marks so likely could do with replacing at some stage , when I am feeling flush.

When they do split there's not usually much doubt about it. When mine went, the carb flooded like Niagra falls. You could see fuel inside the white float. I squeezed it , and it clicked. I shook out the fuel and then 'welded' the seam with a soldering iron that luckily someone had in the paddock (I had a 12v/240v convertor in my campervan). Then the next day the one on the other side did the same. The new replacements I got from Eurocarb seem to have survived since then, so perhaps it was just a bad batch.

[mbmm350s]

From now on going forward when I restore a bike I am replacing the carbs with new ones rather than sinking a lot of money into old worn out carb bodies.

I couldn't agree more. But I think the original poster tried some newer (though not brand new later carbs) with little improvement
For sure any air leak past the slide is destroying the weak vacuum that makes the idle to progression work smoothly.

I have original ignition system on my 350 and very low mileage VHBZ 25HS carbs of the last type with vent tubes
regular idle of 1000 rpm is achievable, though I usually set it to 1250. The options to replace VHB 25 flat slides are more limited and
whilst many with tuned bikes have very successfully gone down the PHBH 26 or 28 round slide route my opinion is maybe its not a good solution for stock bikes,
I tried it with 26mm and the fuel consumption was bad but I am not a tuning expert!
Does anyone have a good setup using alternative carb on stock bikes?

The original poster drew the rotor, no good rotor I have has any movement whatsoever of the rear plate, relative to the front.
though I have one where the magnetic material has gone soft - how did that happen?
Sadly I don't have a good rotor of the first type for you to try.

Mark

[AntietamClassicCycle]

Never found the need to replace any Dellorto carburetor due to wear, not even those on my 111,000 mile Guzzi Ambassador. <shrug>

[AndyB57]

Fingers crossed I don't end up having to replace the carbs on mine as well as fitting the Sachse ignition!

[AndyB57]

My carb slides look ok, and I've renewed jets, etc during a good clean up so hopefully they'll be fine.....

[Long_Road]

Really interesting reading the discussion. I was mulling things over at work today and I think one of the reasons I haven't made much progress with this bike is due to an unwillingness on my part to invest a lot of money in it, and instead trying and find what's going on with it using an exhaustive process of elimination. Unfortunately I'm too rubbish at Italian bikes to actually find the bloody problem!

My gut tells me the engine is close to being good, there's just one small thing stopping it from running as Mr Lambertini intended. At some point I'm going to get the rear light working and go out for a cheeky ride, blow out the cobwebs. I don't think I mentioned that it was bored out to 375cc? Once I know it's a good engine I want to spend out on rearsets, suspension etc. but for now I'm trying to be...frugal.

Is it ignition or carburation? Both apparently are acting normally. With the former I re-soldered the pickup to it's wires, replaced the HT leads, went from plug caps to direct clips, and replaced the plugs. This was 3 years ago, and I need to check the quality of the spark again. Retiming it With the ANT mark has improved it, and it does seem The pickup rotor needs replacing.

The VHB BSs have had a lot of attention. An ultrasonic bath, new o-rings, seals (including choke), needles, various sized pilot jets, many float height adjustments and countless mixture screw settings, and quite a few re-balancings too. Settings now are stock except for 48 pilots, and these are getting swapped back to 50 before I ride it. The slides don't look that bad, but then again these are early versions of this carb, with no takeoffs for a balance pipe. Perhaps the bodies are worn where the slide moves? I remember there being a fair bit of play when I wiggled the slides, but don't have a frame of reference.

It's true I swapped the carbs for some HSs but I think these were more worn. I had to swap the internals over from the BSs because they were just empty bodies. They actually ran worse.

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I could photograph the slides I'm using? Like I said, they look okay but no frame of reference. I'm open to trying different carbs, even considered Japanese but it would be tricky getting them to fit. Then of course the long road of jetting... PHBH seems like the easiest alternative. I've seen Dell Orto still make them, mostly for scooters?
Thanks - Chris

[Steve Brown]

Again thanks for your help with this, I owe you all a pint. Steve Brown and 72 Degrees, I may just take you up on your kind offers. There's a red pickup and rotor on Ebay at the moment for a 250 which I'm considering - are they compatible with a 350?

Pints gratefully accepted thank you. If you're being frugal and are still considering spending £250 on an unknown pick up that is at least as old as your is, please give me a ring. I can do it cheaper.
I think the new pick ups from Nuovaray cost less than that, though I haven't checked recently. Also that pick up rotor of yours-the amount of movement your excellent drawing shows is quite significant. It that's 15 degrees at the pick up it's 30 degrees on the crankshaft. That would be enough to make the idle rpm drop or rise, depending on which way it was shock loaded when you last blipped the throttle. Left to it's own devices it seems to idle pretty well for a bike that hasn't had an Italian Tune up recently.
So I'm thinking when it's idling nicely and you blip the throttle quickly as in the video, the pick up moves and gets left behind slightly so retards it and the revs drop and it stalls.
When you've been holding it at higher revs for a while, again like in the video and release the throttle, it gets shocked the other way and has moved to the over advance position and hence idles faster until the rotor has time to catch up with itself. Maybe why you think the timing has moved from where you last set it?
Also as Mark said, you need to get eye level with the mark on the crankcase when strobing so you don't get any parallax error. Defintely better with a friend to help.
As Pete says my offer still stands, but I wouldn't want to be posting the stuff away, just let you fit it and try it. Also mine is a later black pick up but has the diodes added to allow use with the old transducers.
Another random thought-I think Nuovaray listed the rotor and pick up separately? Worth a check.

[nickst4]

From my experience with the Dart, now long gone, I had carb flooding problems but the floats looked and sounded OK. The problem turned out to be expansion of the nylon float with ethanol-containing fuel, such that the bond joint between the two halves of the floats caught on the side of the metal float bowl when the carb had emptied, preventing the float needle from cutting off the supply. A little work with a sharp knife to trim the excess plastic prevented any subsequent flooding.

I can second the concept of investing in new carbs on old bikes. A pair of new pumper Dellortos worked wonders for the low-speed running of my Cagiva Alazzurra (Ducati Pantah derivative). The only problem was that they'd altered the stub fitting, but I was able to incorporate the newer resilient mounts. Those carbs will now outlast me, for sure!

Nick