Wildguzzi.com
General Category => General Discussion => Topic started by: Redmist on June 23, 2026, 10:18:30 AM
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Hi Guys/Ladies,
I am finally nearing the end of the rebuild I started some time ago.
The electrics are all good and accurately timed, no problems there.
The carbs are VHB30C's, which from what I have picked up from the manuals are not the originals but my guess is that they did work at some time. They were 'off' the bike when it came in to my ownership. I have cleaned them and put them back together correctly, as much as I can tell from diagrams I have come across online. Here the problems start, I have been unable to find any really specific info on whatever is the base line setting up of the carbs. Most manual troubleshooting sections assume that you have an established set-up and require some adjusting of one or more screws to get them running ok. My problem is that I don't have this initial set-up. I have set the carbs with the C screw (as shown in the manual photo) to 1+1/2 left carb, 1+3/4 right carb and adjusted the cables via A to give a bit of a gap at the bottom of the slide as a a starter. Screw B I don't understand. Info suggests it is an idle speed adjuster, but upon looking in the top of the carb it is just a bevelled 'point' that doesn't appear to bear on any internal part? Anyhow the bike will, occasionally, start but doesn't really respond to the throttle. Opening it fully, when it runs, just results in the engine dying. Most of the time it doesn't start at all. Either with the choke levers operated or without. It doesn't have a cable type choke.
I checked Greg's 'bible' for any help there. The nearest was Charlie's setup suggestions which would possibly have worked? if I had been able to use the throttle stop screws (B) to fix the height of the slides but I couldn't figure out how they would then move if I wedged the slides in place with this point.
(https://i.ibb.co/9HJKPKrR/guzzi-carb.png) (https://ibb.co/9HJKPKrR)
I am open to all helpful suggestions.
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could your slides have been installed backwards?
Rick
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The point on screw B goes under the slide in a beveled spot to lift slide as screw goes in. Best I can do. I set the screw up a hair from closed, gap of play in cable. You could even sync the cables if you raise slide & use a feeler gauge on edge so they feel same going in & out the throat.
This is how I do my V700 cause no holes in manifold for vacuum gauges. I sold the carbs on 2 of my 700's, SSI are not to good for unleaking reliability. No power from them, not even with the accelerator kit for them. VHB's are good for the bike.
Make sure your timing is good, hard spot to see w/timing light.
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For vhb carbs, I do a very similar prep. Holding carb up to a light and looking through throat (as fuel will flow), back out screw B completely. Slide should be closed and it should be blocking all light from passing through carb throat. Turn screw B until you see a tiny amount of light under the slide. As soon as you see light, stop and leave it there. That’s how I was taught and it works very well as long as carbs are clean and the rest of the tuning is in order.
Balance of adjustment is as Steve says.
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Rick, I already checked this one, but thanks for the pointer.
Steve, thanks for the info regarding how the point works. This will be tomorrows investigation :-).
Cliffrod, thank you for your input, much appreciated. It will join Steve's suggestions tomorrow.
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What jetting to use is largely dependent on what number of slides you have. If they are 60s, then I would use Ambo/Eldo specs: 45 idle jet, 145 main, V5 needle w/clip in the middle slot, 265 atomizer. If they are 40s, then I would use 850-T jetting 50 idle, 142 main, V9 or V5 needle (virtually identical). I normally start with the idle mixture screws (C in the photo) out a bit more, around 2 turns.
Screw B is the idle speed adjustment. Before turning it in, one should always raise the slides, otherwise it digs a trough into the slide over time. My initial slide height setup also depends on what slides you have. With a number 60 slide, I turn Screw B until I can slip a 9/32 drill bit under the slide. If number 40 slides, then I use a 7/32.
If you have pod filters or more free flowing mufflers, then a slightly large idle jet may be necessary.
To sync. the carbs when there are no vacuum ports, I open the throttle slightly and use the friction screw or some other means to hold it there. Slip a larger drill bit under each slide and act on the cable adjuster on the carb top to get them the same. Make sure you still have a little slack in the cables afterwards.
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A really big thanks to all you guys, problem solved due to a combination of the advice offered.
Duncan
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A happy ending, enjoy! I like mine, 1 of 3 that's running. I was buying them in 90's when everyone was wanting Eldo's & Ambo's. My 67 started right up 25yrs ago.
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So what was the problem and how did you solve it?
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TKelly, the problem was the positioning of the slides and not knowing how the B 'pointer' worked on them. Having stripped them I found the pointers had graunched a bit of a groove and swelling on them both, so a bit of a rub with a watchmakers file sorted that. Then the setting up of the slider to give the initial small opening, sorted thanks to the previous comments.
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So, it starts now? Got it dialed in?
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So, it starts now? Got it dialed in?
Yes Steve, it fired almost straight away! It will have to wait a few days until I have sorted out the paint on my tank :-) I found that the gas resistant lacquer sold by my local hardware shop isn't gas resistant, and having spilled a few drops when I was filling it I now have to a major -ish repaint. It is all part of the fun they tell me, but I'm not sure if they are telling the truth :-) Hey ho!
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Great, now try paint on another piece of metal then put on drips of fuel to test instead of tank. Good Luck.