VHB 29 Carbs

Shajota

Shajota

Hero member
Location
Whitsundays Qld
Ok, about to cut the slide springs on my carbies. I have searched on here and info seems to be mainly on the roundslides.
I imagine it will be similar so will start with about 30% off and go from there.
Anyone done it on the squareslides and have some contrary advice?
I am doing it because the throttle action is very heavy (and I have a dodgy right wrist). twist grip, cables and cable runs are all good.
Have spent plenty of time trying to improve but definitely needs softer springs. (Very painful on long days)
From what I understand standard springs are 2kg and I have looked for softer springs but appear a bit thin on the ground.
(MG Cycle offer a 1.1kg spring but postage is about $40US so thought I'd try the cut option first.)
Thanks for any help.
 
Spring man here in Sydney made them for our 32 dells, jota wonderful now as good as the modern carbs on the 3c and 3cl. If it doesn't work cutting them chat to Chris Pritt, spring man is in the same complex as his workshop
 
I use a Throttle Rocker, one of those $15 plastic gadgets you clip on around the grip with a blade attached that you rest your Palm on. Helps 100% on long trips. The weight of your hand holds the throttle open.
 
Thanks Vince and Marty, buuut....
My Jota throttle is featherlight compared to the (my) VHB's and I have used one of those throttle rockers on the triple for years to ease my wrist on long trips. (along with grip puppies!!)
Tried it on the Eagle but wouldn't hold. The snap back was too strong. (Also the throttle has a much shorter action than the triples)
Edit - Of course the QA throttle means you don't have to take that 2nd handful to get into the happy zone like the triples:D
Interesting thought about getting some made Marty. Definitely worth a look into.........
 
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Start at 20-25% off... these slides apparently have far more friction due to vacuum than the round PHB/F items. Take off too much, the slide may not return fully, it then takes a few seconds to drop to the proper idle.

piet
 
Shajota said:
Ok, about to cut the slide springs on my carbies. I have searched on here and info seems to be mainly on the roundslides.
I imagine it will be similar so will start with about 30% off and go from there.
Anyone done it on the squareslides and have some contrary advice?
I am doing it because the throttle action is very heavy (and I have a dodgy right wrist). twist grip, cables and cable runs are all good.
Have spent plenty of time trying to improve but definitely needs softer springs. (Very painful on long days)
From what I understand standard springs are 2kg and I have looked for softer springs but appear a bit thin on the ground.
(MG Cycle offer a 1.1kg spring but postage is about $40US so thought I'd try the cut option first.)
Thanks for any help.
Click to expand...
I'll be doing it over winter to make my S a rider for trips of several days or weeks. Along with a longer clutch actuating arm.
I intend cutting one spire at a time.
I believe that standard springs are readily available so no big deal if you go too far.

Have you tried looking if springs for VHBs on other marques, Guzzi, Ducati and others are lighter?

Paul
 
sfcpiet said:
Start at 20-25% off... these slides apparently have far more friction due to vacuum than the round PHB/F items. Take off too much, the slide may not return fully, it then takes a few seconds to drop to the proper idle.

piet
Click to expand...
Thanks Piet. I had actually come across the comment about needing strong springs for vacuum on some Guzzi forums but as always there was those that said a softer spring works fine so I was curious if this would come up here. Slow as she goes I guess.......
Paul Marx said:
I'll be doing it over winter to make my S a rider for trips of several days or weeks. Along with a longer clutch actuating arm.
I intend cutting one spire at a time.
I believe that standard springs are readily available so no big deal if you go too far.

Have you tried looking if springs for VHBs on other marques, Guzzi, Ducati and others are lighter?

Paul
Click to expand...
Yep Paul, I actually had ordered some standard springs (for back up) and now that they have arrived I was going to start;)
As per my reply to Piet most info I found was related to Guzzis however could not find another source for the lighter springs.
MG Cycles in US were the only ones I could find with stock of the 1.1kg version. Most of the Guzzi riders who fitted the lighter springs were happy.
I will try cutting them and see how that goes.
If no good might just have to bite the bullet or maybe someone will come up with another source.
 
Ok - update (I can hear the cheering and feel the excitement from here:LOL:)
Took the old springs out and first thing noticed was the new springs were one coil longer and felt softer!! Old springs are very firm. (pic attached)
Had originally intended to cut the old springs but decided best to cut the new ones due to length and feel.
First put the new ones in and tried them as they were. They definitely felt better but still too strong.
So, (noting Piet's comments) cut one and a half coils and replaced. Action felt markedly better although was still tempted to cut another coil. Took it for a ride and the action is far far better, not having a continual fight with it, so at this stage will ride it for a while before deciding whether to cut anymore off.
The slides still snap back when throttle released and no other issues detected, although wouldn't expect it with the minimal cut off.
(The action when riding felt a lot more comfortable than just twisting it in the shed, so this may be enough)
Anyway, happy with the effect and will improve the ride enormously.................
 

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Paul Marx said:
I'll be doing it over winter to make my S a rider for trips of several days or weeks. Along with a longer clutch actuating arm.
............
Paul
Click to expand...
Paul: "Along with a longer clutch actuating arm."

That´s how it starts - next step will be an electronic ignition instead of the loved contact breakers!

Greetings from Thomas aus LAU (in great concern)
 
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Shajota said:
Ok - update (I can hear the cheering and feel the excitement from here:LOL:)
Took the old springs out and first thing noticed was the new springs were one coil longer and felt softer!! Old springs are very firm. (pic attached)
Had originally intended to cut the old springs but decided best to cut the new ones due to length and feel.
First put the new ones in and tried them as they were. They definitely felt better but still too strong.
So, (noting Piet's comments) cut one and a half coils and replaced. Action felt markedly better although was still tempted to cut another coil. Took it for a ride and the action is far far better, not having a continual fight with it, so at this stage will ride it for a while before deciding whether to cut anymore off.
The slides still snap back when throttle released and no other issues detected, although wouldn't expect it with the minimal cut off.
(The action when riding felt a lot more comfortable than just twisting it in the shed, so this may be enough)
Anyway, happy with the effect and will improve the ride enormously.................
Click to expand...
It's not only the spring rate itself, the preload plays a major part in this. Reduce the preload a bit and you're almost there. You're actually increasing the spring rate by shortening it!

piet
 
Hi Peter. Just to add to Piet's comment a bit...

The high preload is required to overcome the maximum forces on the slide, which occur when the trottle is almost closed, but the engine is on the overrun (the bike is pushing the engine). Here the engine is trying hard to draw air past the slide and the slide is being pushed forward. Increasing friction between slide and body.

So - this is where you should test whether the spring is still up to it's job > under hard overrun conditions, to make sure it shuts all the way. If you want to be pedantic, do it on a cold day, before the carbs have warmed through.

I reduce the spring length on all my Lavs - a coil or 2 at a time - then road test.
 
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Haggis said:
Hi Peter. Just to add to Piet's comment a bit...

The high preload is required to overcome the maximum forces on the slide, which occur when the trottle is almost closed, but the engine is on the overrun (the bike is pushing the engine). Here the engine is trying hard to draw air past the slide and the slide is being pushed forward. Increasing friction between slide and body.

So - this is where you should test whether the spring is still up to it's job > under hard overrun conditions, to make sure it shuts all the way. If you want to be pedantic, do it on a cold day, before the carbs have warmed through.

I reduce the spring length on all my Lavs - a coil or 2 at a time - then road test.
Click to expand...
Thanks for that. Had no issues at all when I did test run including on over run, will give it a couple more targeted tries, but might have to wait a while for a cold day:LOL:
 
sfcpiet said:
It's not only the spring rate itself, the preload plays a major part in this. Reduce the preload a bit and you're almost there. You're actually increasing the spring rate by shortening it!

piet
Click to expand...
One of the reasons I thought it best to use the new longer spring which also (apparently) had a softer spring rate.
Cutting one and a half really only lopped off slightly more than the first (flat) coil. I then reformed the top coil to original shape as best I could and with this minimal change I am sure all is fine.
I had also previously read that the square slide springs push (pull?) the slides forward to assist vacuum* (in line with Hag's comments) and these springs still feel plenty strong enough although I will test further as per above. (* as with anything, there was some debate on this:eek:)
Operation is far better so hopefully won't need to take anymore off, don't want to push it.
Thanks for your input Piet.
 
I’ve used lighter springs in my Guzzi VHB carbs for tens of thousands of miles with no problems - it’s essential to have good condition cables though. The VHB’s fitted to the Guzzi have an accelerator pump built in to the main jet holder which is pushed down and primed by the needle, this is an added force holding the slide up so a VHB fitted to a Laverda should need less spring force to hold the slide down. It used to be possible to get the lighter springs from Dellorto but they are no longer available, some Guzzi people use a lighter spring from a round slide Dellorto carb instead but I can’t remember which one. Could someone on here who lives in the USA buy the MG cycle ones for you and post on more cheaply?
 
Normski said:
I’ve used lighter springs in my Guzzi VHB carbs for tens of thousands of miles with no problems - it’s essential to have good condition cables though. The VHB’s fitted to the Guzzi have an accelerator pump built in to the main jet holder which is pushed down and primed by the needle, this is an added force holding the slide up so a VHB fitted to a Laverda should need less spring force to hold the slide down. It used to be possible to get the lighter springs from Dellorto but they are no longer available, some Guzzi people use a lighter spring from a round slide Dellorto carb instead but I can’t remember which one. Could someone on here who lives in the USA buy the MG cycle ones for you and post on more cheaply?
Click to expand...
Most of what I read on the VHB's was from Guzzis. At this stage I am happy with how things are and am confident all is fine. (Cables all new btw)
I just originally posted to see if anyone had any comments in regard the VHB's on the Lavs (and perhaps for interest of others?).
Will see how it goes, thanks for the suggestion.
 
Thomas aus LAU said:
Paul: "Along with a longer clutch actuating arm."

That´s how it starts - next step will be an electronic ignition instead of the loved contact breakers!

Greetings from Thomas aus LAU (in great concern)
Click to expand...
Next thing you know, you will put new high friction brake pads, and then new tires, and then.........LOL!!!
 
SFCRex said:
Next thing you know, you will put new high friction brake pads, and then new tires, and then.........LOL!!!
Click to expand...
Changed 3 sets of tyres this year and they get worn to the cord. They're ready for winter riding.

The exception is the SFC. Last time out at Francorchamps, I realised that the front tyre was 17 years old but that was ok, I was taking it easy because of the leaking fork seal spewing oil onto one of the discs when I braked.

I'm still waiting for an offer of a riders Vincent twin in exchange for a restored Electronica.

Paul
 
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