Vacuum guage vs mercury manometer

[Guest]

I'm looking for opinions on what type of manometer to buy. Traditional mercury, stick or vacuum.

I like the look of the Morgan Carb Tune unit from Limey land but it is a might pricey at about $150 in our cash. On the Z1 site they have a couple of vacuum guage type, one very pricey and one for around $50. This cheaper one appeals to my frugality.

I've beeen trying to research the effectiveness of the different types with no great luck.

Can anyone provide any real world experience?

Cheers,
Spyug

[Griffin]

Mercury sticks have been around forever, and have worked forever. For $50 or so they are hard to beat. I own a set, and between that set and my brother's, I've been using merc sticks for twenty years, no problems. Some are concerned about the toxicity of the mercury. I doubt if it'll ever be a problem since once you buy them, presumably you'll have them as long as you have a bike. You can eventually sell them to someone else if you don't need them, and they can use them then sell them ad infinitum...

Individual gauges all have an accuracy range of +/- a certain %. So if the % is +/- 5%, you could conceivably be 10% off in your readings from one carb to the next, and show them perfectly matched. For general street tuning, this may not be such a big deal, but it is something to consider.

The carbtune gets rave reviews from those who own it, but like you said, it is some hefty $$.

[jpaul]

If you go with gauges, you'll want to to hook all the gauges up to a common vacuum source. There should be a small screw on the back of the gauge so they can all be set to read the same.

[Tom MLC]

Ditto, jpaul. If you "calibrate" all four gages to the same cylinder before doing the sync, you'll get much more accurate results.

I own a mercury stick...and one of the cheapo gage sets from Z1...AND one of the CARBTUNE tools (RenoBruce & I split the cost). Yes, the CARBTUNE is by far the best. The gage set is easy to use & pretty accurate. I do not like the mercury stick. It seems like the columns bounce too much, even with the little restrictors installed.

Hope that helps.

[rapidray]

Also, with the mercury set up if you wing the throttle, when it comes back down, the vacuum sucks the mercury out of the carbsticks & shoots it out your exhaust. Do NOT ever rev the bike using carbsticks! Ray.

[Jethro]

If you ever get a fuel injected bike you'll be happy you bought the Morgan. My mercury sticks don't work well with the FZ1, so I bought a Morgan just recently.

[bwringer]

The Carbtune is worth every last penny.

Buy it. You'll be happy.

Mercury sticks do the job, but the Carbtune is many times easier to use and much more precise.

[Captainkirk]

Well, IMHO the carb sticks do the trick....and well. That being said, if the Morgan Carbtune is what these guys say it is, it would be worth the investment. I've tuned five sets of carbs this summer alone, probably enough to easily pay for a Carbtune. I might consider it in the future. Although I must say, the sticks do a bang-up job; no complaints other than the bouncing of the mercury columns.\\/

[jeff.saunders]

With the limitations on shipment of Mercury in most states, it is now illegal to ship Mercury filled products without a special permit. CA, CT, NY & PA all have Mercury shipment bans / restrictions with more states following suit.

Companies like Motion Pro have discontinued selling the old Mercury filled Manometers. You may still find old stock sitting around, but generally they are no longer available. Motion Pro does have a new product to replace the Mercury filled Manometer. They have not released what the liquid is due to 'Patent Pending'. We've sold a fair number of the new MP units, so far most of the comments are very positive. One nice feature is you can lay the unit down and the fluid will not flow out (unlike the Mercury ones).

[RageZro]

I considered all of the options and decided to go with the TwinMax unit. I got it from RL Motorcycles for $88, not cheap but I like the concept of it better than the other designs. The thing that some don't like about it is thet you only have to vacuum lines out of it. I think that actually is a plus as you are balancing #2, #3 & #4 carbs individually to match #1 carb exactly .

Here is the link to where I got it, you can look up the company that makes them if you want but this was the best price I could find.

http://www.rlmotorcycles.com/home/accessories/TwinMax.htm

I intend to use this and a Morgan Colortune I picked up om my bike soon, I'll let you know how it worked out.

[spyug]

Thanks for all the input guys. It seems that all different units have their supporters so I'm not much further ahead:?. The carbtune seems to get the nod but I wonder if its that much better than the motion pro unit.Also, I hadn't heard of the TwinMax electronic differential guage and I wonder how well it works relative to the others.

I'm going to have to think on this a bit more.

Thanks agtain all.

Cheers,
Spyug

[jeff.saunders]

To sync or not to sync...

For the most part they all do the job of helping to set the carbs for a smooth idle - the issue is that's not always where you want the carbs sync'ed.

Something to ponder...
If you have a set of worn old carbs, you can set the vacuum at idle to be equal, but end up with the slides at different heights - then you get erratic mid-range throttle response.

With mechanical carbs (non-CV type), I bench sync the carbs to set the slide heights using a special tool (a 1" paperclip that's uncurled - these end up being about .8mm - a reasonable starting point for the carbs). I then check that all 4 slides will clear the top of the bore fully and at roughly the same time. After this I fit them to the bike and vacuum sync the carbs. I will adjust the air screws (or fuel screws) in / out small amounts to see if very minor changes (+/- 1/8th turn) will sync the idle rather than mess with the slides. I will ONLY make very small adjustments to the slides and not even attempt to get the vacuum equal is it means setting the slides at different heights. I can live with the idle being a little rough as long as the throttle doesn't 'hang' and take time to settle down.

[Steve]

I think that actually is a plus as you are balancing #2, #3 & #4 carbs individually to match #1 carb exactly .

That depends on what carbs you have.

With VM carbs, I will look at all four to see which is the lowest vacuum and raise it to match the rest. The lowest vacuum will be the carb that has the largest throttle opening, so I will adjust it to close more to match the others.

With BS (also called CV) carbs, your 'master' carb is #3. My book says that you adjust #2 to match #3, then set #1 1cm higher, then also put #4 1cm higher. This is if you have stock pipes with the crossover. If you have a 4-into-1 pipe, set them all the same, but use the same sequence.

Something to ponder...
If you have a set of worn old carbs, you can set the vacuum at idle to be equal, but end up with the slides at different heights - then you get erratic mid-range throttle response.

This may be true of VM carbs, but BS (CV) carbs don't work that way. Although I have found that the book suggests doing the sync at 1500-2000 rpm, I have always done mine at the 1100 rpm idle speed. The short amount of time I spend in the 1500-2000 range is very small compared to the time spent idling at a stop light. And, the small amount of time in that speed range is usually done with the throttle about half open while accellerating, so I feel it really does not matter. I also rev the engine to check the sync at larger openings, but the results seem to change every time the throttle is opened, so I only do my sync at idle.