Norbert,
Great knowledge
Some where all this mountain of knowledge needs to be stored!
There are also variants of the VHBZ 25 HS, the early ones don't have the brass vent tubes, but do have the vacuum port.
The VHBZ 25HS with the brass vent tubes , first had metal caps then black plastic.
The brass vent tubes are most likely for emissions reasons - as the tubes attached to them go back
to an air box or collector box for recycling of vapours.
On Moto Morinis the overflow doesn't work and instead the inlet tract or worse the cylinder
or even worse the whole engine fills with petrol if the pertrol is left on and the float valve doesn't seal.
I have perfectly running standard 77 sport with VHBZ 25 HS carbs with 260BD, E17 middle, 48, 115 jets
I connect the vacuum ports together with a tube. So these carbs work fine on sports! mine will idle at 1000 -
but I choose to idle at 1200-1300 .
By the way the first 350s up to 76 or so had VHB 25BS carburettors - these have a different shaped float chamber,
different floats and a non removable float valve seat.
Mark
Three years later, still having problems with idle
Re: Three years later, still having problems with idle
I´got no VHB left, but a float chamber 
I guess they can be interchanged.
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Re: Three years later, still having problems with idle
A long day at work meant that I didn't get much Morini time. I purchased some brake cleaner and just now warmed the bike up and started spraying.
I got the same results as with the GT85. Spraying the cylinder/manifold seal, specifically at the bottom of it's circumference, stopped the engine, same result on both sides.
I expected the revs to increase with this stuff, so as an experiment pulled off the carb/airbox joints and sprayed a little toward the intake. Again, instant stop - even just a bit of overspray when I was spraying other areas, when sucked in would kill the engine.
I still have a lot more inspection and testing of other areas mentioned, when I can.
I really appreciate the effort and information you guys are giving me, and it's a good read too!
I got the same results as with the GT85. Spraying the cylinder/manifold seal, specifically at the bottom of it's circumference, stopped the engine, same result on both sides.
I expected the revs to increase with this stuff, so as an experiment pulled off the carb/airbox joints and sprayed a little toward the intake. Again, instant stop - even just a bit of overspray when I was spraying other areas, when sucked in would kill the engine.
I still have a lot more inspection and testing of other areas mentioned, when I can.
I really appreciate the effort and information you guys are giving me, and it's a good read too!
Re: Three years later, still having problems with idle
Checked the ignition rotor and it looks in good condition with the cupped washer present and correct - no play.
The cam belt seems a bit slack. I don't know when it was last changed. When I put a spanner on the cam pulley I can move it about 2 degrees without the flywheel moving - does this sound like enough play to cause timing issues?
*To add, I was definitely going to change the cam belt and I appreciate how important this is, but only once I was confident in the bike being worth spending out on*
Removed the plastic collars on the carb manifolds and tightened the jubilee clips, with no effect.
I have the feeling I'll be buying a new cam belt tomorrow.
The cam belt seems a bit slack. I don't know when it was last changed. When I put a spanner on the cam pulley I can move it about 2 degrees without the flywheel moving - does this sound like enough play to cause timing issues?
*To add, I was definitely going to change the cam belt and I appreciate how important this is, but only once I was confident in the bike being worth spending out on*
Removed the plastic collars on the carb manifolds and tightened the jubilee clips, with no effect.
I have the feeling I'll be buying a new cam belt tomorrow.
Re: Three years later, still having problems with idle
A cam belt is cheap (see multiple other posts) and the cost of potential damage much greater. Besides, it gives an opportunity to check things over and is not onerous. Check out Paul Compton's Youtube 'how to' videos.
Re: Three years later, still having problems with idle
Thanks Ming. Just ordered a belt and flywheel puller.
Re: Three years later, still having problems with idle
Fitted new cambelt and rechecked ignition timing - both spot on. Also checked valve clearances. Bike ran the same as before.
Swapped carbs over, but had to fit BS internals into the HS bodies (lack of spares). Slides do not look unusually worn, jets are clear. O-ring for idle screws present. Ran engine and checked carbs were in balance, and adjusted mixture screws. Bike runs same as before.
Sprayed rubber manifold seals with brake cleaner - carb to manifold, then manifold to inlet. Also sprayed carb to airbox seals. All places with jubilee clips in other words. Every time the engine would stop. I tried raising the revs slightly and then spraying, and the relevant cylinder would misfire, the other cylinder keeping the engine spinning.
I seem to have a myriad of air leaks, with almost no doubt. What's puzzling is that these are brand-new manifolds, and I can't find any other reports of this being an issue. I'm going to try and seal the suspect areas to see if it makes a difference - how I haven't considered yet.
Swapped carbs over, but had to fit BS internals into the HS bodies (lack of spares). Slides do not look unusually worn, jets are clear. O-ring for idle screws present. Ran engine and checked carbs were in balance, and adjusted mixture screws. Bike runs same as before.
Sprayed rubber manifold seals with brake cleaner - carb to manifold, then manifold to inlet. Also sprayed carb to airbox seals. All places with jubilee clips in other words. Every time the engine would stop. I tried raising the revs slightly and then spraying, and the relevant cylinder would misfire, the other cylinder keeping the engine spinning.
I seem to have a myriad of air leaks, with almost no doubt. What's puzzling is that these are brand-new manifolds, and I can't find any other reports of this being an issue. I'm going to try and seal the suspect areas to see if it makes a difference - how I haven't considered yet.
Re: Three years later, still having problems with idle
A mystery for sure.
Do you have the carb throat reducers fitted?
These were fitted on all rubber manifold bikes from new and when converting from metal manifold, often they are missing on conversions.
Also is the inlet manifold stub secure in the head.
Mark
Do you have the carb throat reducers fitted?
These were fitted on all rubber manifold bikes from new and when converting from metal manifold, often they are missing on conversions.
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Mark
Re: Three years later, still having problems with idle
I just went to the garage and tried using brake cleaner as I just got some, to see if I too could reproduce your symptoms.
On the 350 no effect.This bike has never had any carb issues.I rebuilt them about112 years ago.
On my 507 which has had some chugging/ stuttering at mid rpm, spraying onto the carb to head rubber on the rear cylinder did cause it to stumble so either my (old ?) manifold rubber has a crack or the clips need a tweak.They were pretty tight though. Might try coating it in threebond / silicone and repeat tomorrow.It looked OK recently though.
John
On the 350 no effect.This bike has never had any carb issues.I rebuilt them about112 years ago.
On my 507 which has had some chugging/ stuttering at mid rpm, spraying onto the carb to head rubber on the rear cylinder did cause it to stumble so either my (old ?) manifold rubber has a crack or the clips need a tweak.They were pretty tight though. Might try coating it in threebond / silicone and repeat tomorrow.It looked OK recently though.
John
Re: Three years later, still having problems with idle
Great idea John! to try it on bikes that work fine(ish in the Cougaros case)
Theory is then there is a leak in the inlet tract and its nothing to do with chilling the carb by evaporation.
When it refit, I always make sure that the end of the manifold is snug against the inlet tube, no gap.
By the way there are grooves in the manifold which are supposed to match the ridges on the tube
and some bad ones simply don't fit properly.
I always use the plastic collars but many don't with no ill effect, the plastic collars do stop bad quality hose clips like Jubilee clips
from eating the rubber. I recommend using hose clips without an external thread so they are smooth against the rubber
Mark
Theory is then there is a leak in the inlet tract and its nothing to do with chilling the carb by evaporation.
When it refit, I always make sure that the end of the manifold is snug against the inlet tube, no gap.
By the way there are grooves in the manifold which are supposed to match the ridges on the tube
and some bad ones simply don't fit properly.
I always use the plastic collars but many don't with no ill effect, the plastic collars do stop bad quality hose clips like Jubilee clips
from eating the rubber. I recommend using hose clips without an external thread so they are smooth against the rubber
Mark
Re: Three years later, still having problems with idle
Thanks for the suggestions. The carb reducers/converters are indeed present and tight, as are the inlet stubs (one did need tightening earlier on in the investigation).
I am wondering about the jubilee clips. I remember a long time ago NLM fitted them when I first took the bike to them, so I guess the same did the trick on other Morinis.
May replace them with more sympathetic clips.
I am wondering about the jubilee clips. I remember a long time ago NLM fitted them when I first took the bike to them, so I guess the same did the trick on other Morinis.
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Re: Three years later, still having problems with idle
Update no. 5382!
Moving on with John and Mark's comments about the brake cleaner and the effects of evaporation chilling the carb, I tried spraying parts where I knew there was no intake of air, and it still stalled the engine. The most obvious sign was just spraying the float bowl, shielding the rest of the carb with my hand. I think this particular brand of brake cleaner may be sending me on a false lead and chilling the carb. I'm going to buy some carb cleaner and try that, see what happens.
As another test I sprayed a bit of WD40 directly into the open carb mouth, and the engine carried on idling like nothing had happened; I was surprised at that. Another false lead.
Also found some wider hose clamps knocking about, which fit the larger area left by removing the plastic collars on the manifolds. After warming the engine I found that it was running richer, and changed the pilot jets from 50 to 45.
The bike idled for a good 3 minutes at a fairly steady 1500 ish, the best it's run with the (slightly grotty) VHB 25 HSs. Still did cut out every now and then when I blipped it but it's progress. I think I'll refit the BSs again as it used run better with those, readjust and try a 2 minute test ride. Petrol-stained fingers crossed.
Moving on with John and Mark's comments about the brake cleaner and the effects of evaporation chilling the carb, I tried spraying parts where I knew there was no intake of air, and it still stalled the engine. The most obvious sign was just spraying the float bowl, shielding the rest of the carb with my hand. I think this particular brand of brake cleaner may be sending me on a false lead and chilling the carb. I'm going to buy some carb cleaner and try that, see what happens.
As another test I sprayed a bit of WD40 directly into the open carb mouth, and the engine carried on idling like nothing had happened; I was surprised at that. Another false lead.
Also found some wider hose clamps knocking about, which fit the larger area left by removing the plastic collars on the manifolds. After warming the engine I found that it was running richer, and changed the pilot jets from 50 to 45.
The bike idled for a good 3 minutes at a fairly steady 1500 ish, the best it's run with the (slightly grotty) VHB 25 HSs. Still did cut out every now and then when I blipped it but it's progress. I think I'll refit the BSs again as it used run better with those, readjust and try a 2 minute test ride. Petrol-stained fingers crossed.
Re: Three years later, still having problems with idle
I would not keep on trying to carburate a bike that has been parked for years on the main center stand, withot moving it a bit.
One thing is if a bike runs or not, another thing if it has a safe low idle or not. Maybe then it would be easier to find the failing spot.
I wonder about your break cleaner results. If you have a leak of false air at the manifolds, aplying the spray, the revs shoud raise. But yours are starving
How many gap you have when the slides are set down?
One thing is if a bike runs or not, another thing if it has a safe low idle or not. Maybe then it would be easier to find the failing spot.
I wonder about your break cleaner results. If you have a leak of false air at the manifolds, aplying the spray, the revs shoud raise. But yours are starving
How many gap you have when the slides are set down?
Re: Three years later, still having problems with idle
I agree. In fact the last thing I did before I started this thread was take the bike for a ride. I can't go far because of Covid restrictions, and the bike is not yet road legal.
On that last ride it seemed to pull well and carburate cleanly. Even the idle was more consistent than it was three years ago, so I was happy to then concentrate on the idle aspect.
I will have another ride later today. The slide gap is approximately 1mm.
The brake cleaner was stopping the engine when it was sprayed into the open carb too. It doesn't seem to the type to cause an increase in revs. Maybe because it's a aerosol?
Are the air mixture screws supposed to have o-rings?
On that last ride it seemed to pull well and carburate cleanly. Even the idle was more consistent than it was three years ago, so I was happy to then concentrate on the idle aspect.
I will have another ride later today. The slide gap is approximately 1mm.
The brake cleaner was stopping the engine when it was sprayed into the open carb too. It doesn't seem to the type to cause an increase in revs. Maybe because it's a aerosol?
Are the air mixture screws supposed to have o-rings?
Re: Three years later, still having problems with idle
The mixture screw should have a spring,then a washer, then an o ring.The washer protects the o ring from the spring end. Eurocarb have these.
On my 350 I found I only had the spring but it made no difference to running.However on my other bike with PHBH carbs new o rings did improve idle and response.One of those had a properly blocked idle circuit, which took some cleaning (carb spray/hot detergent/ultrasonic bath/copper wire / vinegar/ air etc). This caused rough running and a bad tickover.
On another test run it went onto one cylinder but this was the float jet coming loose.
John
On my 350 I found I only had the spring but it made no difference to running.However on my other bike with PHBH carbs new o rings did improve idle and response.One of those had a properly blocked idle circuit, which took some cleaning (carb spray/hot detergent/ultrasonic bath/copper wire / vinegar/ air etc). This caused rough running and a bad tickover.
On another test run it went onto one cylinder but this was the float jet coming loose.
John