Calibrating your synch gauges

[dbeardslee]

I built my own set of synch gauges, and like many others I put them all on the same cylinder at the same rpm to calibrate them. I found them all to be a little off using this method, so I labeled them and used that calibration for synchronizing carbs. DGXSER was over last week, and said that he had calibrated his gauge using a vacuum bleeder pump that also had a gauge. That got me to thinking (talk about being on foreign ground ) so this morning I went over to Harbor Freight and bought a vacuum bleeder. I didn't get the Harbor Freight brand - I bit the bullet and got a genuine Mity Vac cause I wanted as much accuracy as I could get - besides they were out of the house brand . I put it on my synch gauges, and what do you know - they all read dead even. I put the synch gauges on Betsy and adjusted her synch, and it made a difference. I was already pretty close, but not dead on it. Now I am, and it leaves me with this conclusion about using the vacuum from the motor to calibrate your gauges - it's not a terribly accurate way to do it. It'll let you know if they're way off, but I just don't think the tach is accurate enough to really calibrate them well. Just passing it along.

[bikerphil]

Yep, that's how I calibrate my cheapo JCW carb sync guages, with the HF brake bleeder pump/guage. Good tip, DB.

[DGXSER]

Hey Doug, that is VERY intriguing as I would have anticipated your method of synching your gages to be fairly accurate.

As to my method, what I intended to tell you but must have got it wrong, is that I use my Mity Vac gage (just the one gage) hooked to a PVC pipe dampener to do my synching. I just hook it up to one cylinder at a time and adjust moving it back and forth. I get them within a 1/4" of each other across the board from what I read.

[Ivan]

I use the 4 way spirit level. Simple, accurate, cheap, easy. Well, mostly easy. it is almost too sensitive. Just the pressure of the screw driver on the synch screw makes one cylinder jump about an inch. So I tweak and wait about 10 seconds.

I think the vacuum gauges would be easier to use since it is measuring the difference between atmosphere instead of the difference between cylinders. Probably not so sensitive, which I really don't think would be an issue.

[dbeardslee]

Don - As Bill's coming over this afternoon, I went out and really took my time calibrating the gauges. I made sure the gauge on the vacuum bleeder was exactly on 10 which produced a reading of 24.5, 25, 25, and 26 on the synch gauges. I used that reading for calibration purposes as most XS's I've done pull about 22 at 1000 rpm's with my gauges, and I wanted them calibrated at the right spot. Don't know that it would make that much difference where you calibrate, but it made sense to me.

Ivan - I love my little home-made setup. I used Harbor Freight combination gauges and some needle valves from Ace Hardware for dampening. They work great - just dialing them in so they work perfect . Here's what the finished set looks like -




.

[DGXSER]

Sound slike you go them spot on Doug. Good luck with Bill's bike and synching. Hope the afternoon cruise up the little river is a great one!

[sam98177]

Don - As Bill's coming over this afternoon, I went out and really took my time calibrating the gauges. I made sure the gauge on the vacuum bleeder was exactly on 10 which produced a reading of 24.5, 25, 25, and 26 on the synch gauges. I used that reading for calibration purposes as most XS's I've done pull about 22 at 1000 rpm's with my gauges, and I wanted them calibrated at the right spot. Don't know that it would make that much difference where you calibrate, but it made sense to me.

Ivan - I love my little home-made setup. I used Harbor Freight combination gauges and some needle valves from Ace Hardware for dampening. They work great - just dialing them in so they work perfect . Here's what the finished set looks like -




.

What's the reason for dampening? I lost my Merc Sticks (I think someone forgot to give em back to me) and thought I'll go to HF&T and make a setup like these.

Sam

[dbeardslee]

Sam - if you don't dampen them with something they'll bounce around so much you won't be able to read them. I used needle valves on mine because they allowed for a very fine adjustment of the needle-bounce. You could probably get adequate dampening by inserting something in the line - like a piece of plastic hose with a very small ID, or old pilot jets. If you go that route the dampening device should be relatively close to the carb taps. On mine I had them closer to the gauges, but with the needle valves they still work well. If you look on the carbtune site there are some instructions for making the dampers for a carbtune. The same principle applies to the gauges, although this setup will not take all the bounce out of the needles. Personally I like the needle valves better, but they cost about $4-5 each, so it depends on the budget.

[latexeses]

On the Carbtune they tell you to put the dampener about 90 centimeters from the Carbtune on a 1 meter tube.

[dbeardslee]

On the Carbtune they tell you to put the dampener about 90 centimeters from the Carbtune on a 1 meter tube.

Which is about 4" from the motor. They tell you that so there will be a higher volume of air inside the tube so that the vacuum will change more slowly between the carbtune and the dampener. That keeps the carbtune from bouncing too much, but you still get some bounce. Since the dampeners for the carbtune are just small pieces of plastic straw, the only way you can adjust the bounce is by changing the distance from the carbtune to where the dampeners are placed - the farther from the carbtune, the less the bounce. The carbtune has to bounce a little to work properly, while you can adjust gauges down to almost no bounce and still get accurate readings with adjustable dampeners, even when they're up close to the gauges.

I put the needle valves up towards the top of the lines for two reasons. The first reason is that I wanted them up top where I could get at them for adjustment with out reaching around a hot engine. And second, the needle valves I've got are made out of brass and steel and I didn't want them scratching the gas tank. With the four inch Harbor Freight gauges and the backing plate I installed them on, the completed set is big enough that you can just lay it across the speedo and tach. In that configuration the dampeners are suspended in between the handlebars and the tank where they're accessible but don't touch the tank.

I recently bought a carbtune, and when I first got it I used it to check the accuracy of my gauges. I synched with the carbtune, and then put my gauges on it to see what they read. They were dead-on accurate. I bought the carbtune because it's easier to carry since it's smaller than my gauge set and comes with a carrying case. It travels better, and that's the only advantage I could see of the carbtune over the gauges. With the adjustable dampeners I think the gauges are actually easier to use than the carbtune.

[dbeardslee]

Sam - Here's another option for you. If you put together your own gauge set you've got 4 gauges at $12.99 ea. (you can catch them on sale for $7.99 ea., but who knows when they'll be on sale again?) Four needle valves at $5 ea. And another $5-$10 for copper tubing, and odds and ends. That gives you a finished price of around $80. For $99 plus shipping, you can buy this set which comes complete with the gauges, mounting bracket, hoses, dampeners, adapters for working on other bikes, and a plastic carrying case. For $10 more you can get an aluminum carrying case. JAT

[sam98177]

Which is about 4" from the motor. They tell you that so there will be a higher volume of air inside the tube so that the vacuum will change more slowly between the carbtune and the dampener. That keeps the carbtune from bouncing too much, but you still get some bounce. Since the dampeners for the carbtune are just small pieces of plastic straw, the only way you can adjust the bounce is by changing the distance from the carbtune to where the dampeners are placed - the farther from the carbtune, the less the bounce. The carbtune has to bounce a little to work properly, while you can adjust gauges down to almost no bounce and still get accurate readings with adjustable dampeners, even when they're up close to the gauges.

I put the needle valves up towards the top of the lines for two reasons. The first reason is that I wanted them up top where I could get at them for adjustment with out reaching around a hot engine. And second, the needle valves I've got are made out of brass and steel and I didn't want them scratching the gas tank. With the four inch Harbor Freight gauges and the backing plate I installed them on, the completed set is big enough that you can just lay it across the speedo and tach. In that configuration the dampeners are suspended in between the handlebars and the tank where they're accessible but don't touch the tank.

I recently bought a carbtune, and when I first got it I used it to check the accuracy of my gauges. I synched with the carbtune, and then put my gauges on it to see what they read. They were dead-on accurate. I bought the carbtune because it's easier to carry since it's smaller than my gauge set and comes with a carrying case. It travels better, and that's the only advantage I could see of the carbtune over the gauges. With the adjustable dampeners I think the gauges are actually easier to use than the carbtune.

I bought the HF&T Gauges to make my Sync Tool. How far from the gauges did you install the needle valves or is that criticle?

Sam

[dbeardslee]

Sam - I put them close enough to the gauges that I can lay the complete gauge set across the bike's speedo and tach without the needle valves touching the gas tank. They're probably about 3.5" from the gauges, but no, it's not critical with an adjustable dampener.

[sam98177]

Sam - I put them close enough to the gauges that I can lay the complete gauge set across the bike's speedo and tach without the needle valves touching the gas tank. They're probably about 3.5" from the gauges, but no, it's not critical with an adjustable dampener.

Thanks,

Sam