Balancing and adjusting carbs? Moto Guzzi V50 Help!

[Willber]

Hi Guys,

I have a Moto Guzzi V50 (v-twin) which I am trying to set the carbs up on properly. I have bought a Morgan Carbtune II and hooked it up for the first time tonight. I have followed the instructions on both the Carbtune and also the V50 workshop manual however it will only show a reading on the left hand carb. Tried shifting the tubes round on the gauge (i bought the one with 4 levels on incase I use it in the future on a 4-cyl) so I know that all the gauges work but it just won't show a vacuum on the RH carb.

Anyone got any ideas or had this problem before? It's a bit odd as the RH carb seems to have more pressure from the exhaust than that of the LH carb but it won't show a reading.

Bit stumped to be honest!

Any help much appreciated.

Cheers

Will

[RizzoTheRat]

Are you sure you're getting a good seal where you're attaching the pipe to the carb? It only takes a tiny leak to throw them way out.

[Willber]

Hi thanks for your reply.

I am pretty positive that the seal is ok, it was screwed in finger tight and I also tried two of the different nozzle adapters, the o-rings are in good condition (brand new)

Seems very odd I can't get a reading at all!

[Rubin215]

Right, first things first; the vacuum reading at the carb has nothing to do with pressure from the exhaust. What you are trying to measure here is how much air is passing through each of the carbs while the engine is ticking over (or alternatively, how hard each cylinder is "sucking").

With the vacuum tubes connected to the take-off stubs, you adjust the idle setting for each carb so that the vacuum readings are as close as possible (i.e. the same amount of air is passing through each) and the engine ticks over at the correct rpm.

It is very unlikely that the RH carb is flowing no air through it at all, or the engine just would not run well at all. However, over time, the vacuum take off from the carbs can become blocked, which leaves you without any reading.

Try connecting one of the rubber hoses to the RH take off stub and blowing through it; if you can't, then it's blocked, and you need to get busy with the carb cleaner spray.

[Willber]

Thanks Rubin, by take off stub do you mean the screw on the intake pipe which I remove to connect the pipe to the carb?

What does it mean if I can blow through it but am still seeing no reading?

[Rubin215]

Willber said:

Thanks Rubin, by take off stub do you mean the screw on the intake pipe which I remove to connect the pipe to the carb?

What does it mean if I can blow through it but am still seeing no reading?

Yes, the screw on the intake pipe is the take off stub.

If you can blow through it, and are still not getting a reading, then it is a miracle the bike runs properly...

Do you still get a zero reading if you open the throttle to rev the engine?
If you suddenly get a reading, then you need to adjust the throttle stop on the problem carb until you start to get a reading (this will normally make the engine run faster), then back the throttle stop back out on the other carb to bring the revs back down to tickover.

Once you have a reading on both sides, and the engine is more or less at tickover, it is just a case of fine tuning.
Every time you make an adjustment, snap the throttle open and closed a few times, then let the revs settle before you adjust again.

[Willber]

Ok i'm starting to get my head round this a bit better now, the manual is a bit vague and also its a photocopy so some of the parts of the diagram it refers to I can't see properly.

The carbs are Dellorto VHB 24's. As I understand it the idle speed screw has a spring on it and is located toward the top of the carb, and the mixture screw is at the bottom left of the float bowl. Does this sound about right?

I guess even if the screws are not wound in/out exactly the same amount it can still be set up properly? because in my case it seems that the screws will be at all sorts of levels!

Thanks again.

[Rubin215]

Willber said:

Ok i'm starting to get my head round this a bit better now, the manual is a bit vague and also its a photocopy so some of the parts of the diagram it refers to I can't see properly.

The carbs are Dellorto VHB 24's. As I understand it the idle speed screw has a spring on it and is located toward the top of the carb, and the mixture screw is at the bottom left of the float bowl. Does this sound about right?

I guess even if the screws are not wound in/out exactly the same amount it can still be set up properly? because in my case it seems that the screws will be at all sorts of levels!

Thanks again.

I can't comment on those carbs in particular, but the generic advice I have given is pretty much standard for all twins where the carbs aren't linked together. Try looking for the diagrams on the t'internet.

If the mixture settings have been adjusted at some stage, then you need to get them both to the same settings again, or one carb will be letting more fuel into the engine than the other (or less, if you would prefer it that way round...).
Ideally, this should be with a CO meter (which very few home mechanics have...), but if you go for the recommended settings in the manual this is normally a pretty good base setting.
Normally, you screw the adjustment screw in gently until it seats, then back it out so many turns. The emphasisis is very much on gently; if you overtighten it, you will distort something.

Ideally, balancing the carbs (which is what you are trying to do) should be done at the end of a service with the valves adjusted properly.

Beyond balancing, very few carbs actually "go out of tune" other than getting worn out over time, or gummed up from lack of use, so once you are happy with them again, then leave them alone!

[Willber]

Thanks very much for your help.

I will report back once I have had another play with it tomorrow!

Cheers

Will