Topic: Increasing Idle

[Harsh]

I followed some sync advice from DYSKORD and all seems right in the world.  I did have to go back an re-bench sync the carbs after I fiddled with them the first time.  I realized that I never backed down the idle from 1500, which might have put things out of control of the idle circuit.  No big deal as bench syncing is easy to me know.  For all watching this was his advice

You need to constantly adjust your idle screw when you are doing the sync.  When you adjust them the idle will be directly effected. You MUST keep the idle between appr. 800-1300. Letting the idle get too high will negate the adjustments because your carbs will be operating outside of the idle circuit. Adjust one, wait a few seconds for the idle to differ, then adjust idle back up/down to range previously mentioned, then continue with syncing adjustments constantly bringing the idle speed into the appropriate range when necessary.

1. set all nuts on the carbs where you were adjusting during the sync so that 2-3 threads of the screw are showing above the nut.
2. Adjust number #1 carb to #2. Make sure to adjust idle speed after back down/up
3. Adjust #4 carb to the same vacuum as #3 carb. Adjust idle.
4. Adjust #3 to #2. Adjust idle.
Repeat sequence until they are all reading the same vacuum. Adjusting in this sequence will keep you from going in circles since adjusting one will effect the others.

I did all of that and this was the result.



I know it looks like the idle is a bit high, but it is just the angle of the gauge.  It is sitting at 1100 rpm.  Anything lower than 1K and it felt like it was struggling a bit and sounded like crap.


Thank you for all of the help and advice.  I learned some valuable information and now have some more knowledge in my tool box.

[crazypj]

You would need a special camera to get rid of parallax angle on tach 
Glad you finally got it worked out

[kghost]

So.....one or more carbs set higher than the rest?

Too many threads showing on the top of a couple carbs?

[70CB750]

Before you attempt to synchronize, you should calibrate gauges against #2 carburetor.

[Harsh]

So.....one or more carbs set higher than the rest?

Too many threads showing on the top of a couple carbs?

I am going to say yes to both initially.  Now not so much 

[iron_worker]

1. set all nuts on the carbs where you were adjusting during the sync so that 2-3 threads of the screw are showing above the nut.2. Adjust number #1 carb to #2. Make sure to adjust idle speed after back down/up
3. Adjust #4 carb to the same vacuum as #3 carb. Adjust idle.
4. Adjust #3 to #2. Adjust idle.
Repeat sequence until they are all reading the same vacuum. Adjusting in this sequence will keep you from going in circles since adjusting one will effect the others.

What happened to 1 to 1-1/2 threads?

IW

[crazypj]

As long as everything works properly the details can vary

[strynboen]

Before you attempt to synchronize, you should calibrate gauges against #2 carburetor.

there are not a marster kaburator on the erly set up...so no nr 2 vitaut adjusting

[70CB750]

true, but calibrating of gauges is still important.

[strynboen]

yes...like you. i test all gauges on one kaburator to thek they shoves same resultat

[Harsh]

1. set all nuts on the carbs where you were adjusting during the sync so that 2-3 threads of the screw are showing above the nut.2. Adjust number #1 carb to #2. Make sure to adjust idle speed after back down/up
3. Adjust #4 carb to the same vacuum as #3 carb. Adjust idle.
4. Adjust #3 to #2. Adjust idle.
Repeat sequence until they are all reading the same vacuum. Adjusting in this sequence will keep you from going in circles since adjusting one will effect the others.

What happened to 1 to 1-1/2 threads?

IW

That is the only step I didn't completely follow.  I left mine at the bench sync level of 1-1.5 threads showing.

No I did not calibrate the gauges.  However, the buddy I borrowed them from is a calibration tech so he calibrated them where he works.  I am very confident they are accurate.

[iron_worker]

Ah good. I thought we might be going in circles there for a bit. lol

IW

[kghost]

Makes you miss the old mercury sticks....all this talk of calibration

[Harsh]

I have a set of mercury sticks that I initially tried, but they were jumping all over the place making adjustments virtually impossible.

[crazypj]

Fit restriction into vacuum line, 4 old jets, around 100~150

[gregripko]

A little confused with this method:

1. set all nuts on the carbs where you were adjusting during the sync so that 2-3 threads of the screw are showing above the nut.
2. Adjust number #1 carb to #2. Make sure to adjust idle speed after back down/up
3. Adjust #4 carb to the same vacuum as #3 carb. Adjust idle.
4. Adjust #3 to #2. Adjust idle.


my question is....step 3.....why adjust carb 4 to 3 if 3 is going to be changed in step 4? If 4 is sync'd to 3....and then 3 syncs from 2....then 4 isn't syncd to any carbs....

#1 to #2. = #1 and #2 Sync'd
#4 to #3 = #4 sync'd with #3
#3 with #2 = #3 sync'd with #1, #2, #3 but now #4 is sync'd to #3's first setting

[bjbuchanan]

A little confused with this method:

1. set all nuts on the carbs where you were adjusting during the sync so that 2-3 threads of the screw are showing above the nut.
2. Adjust number #1 carb to #2. Make sure to adjust idle speed after back down/up
3. Adjust #4 carb to the same vacuum as #3 carb. Adjust idle.
4. Adjust #3 to #2. Adjust idle.


my question is....step 3.....why adjust carb 4 to 3 if 3 is going to be changed in step 4? If 4 is sync'd to 3....and then 3 syncs from 2....then 4 isn't syncd to any carbs....

#1 to #2. = #1 and #2 Sync'd
#4 to #3 = #4 sync'd with #3
#3 with #2 = #3 sync'd with #1, #2, #3 but now #4 is sync'd to #3's first setting

The only one you are syncing too is what you made your master. The main reason to make a master is so you have something to compare to. You can't randomly sync to each other because that won't necessarily mean the lowest opened slide height, it would be an amazing chance that it would be.

The master is the absolute lowest slide that is still open but has the highest vacuum reading. Vacuum reading is counterintuitive, like car gearing. As the master gets lower and lower(slide height) vacuum will go up til it goes ape sh!t. Just before it goes haywire, that is your absolute lowest functional height.

Now you adjust them all til the guages are the same reading. This is why fluid or vacuum works equally as good and measurements don't really mean anything. It is a way to simplify something tough, syncing mechanical objects

[lucky]

The vacuum should be around 8-10 lbs. Your gauges show 20lbs?

In the photo of the carb slide the choke is partway on. Why?
If it is fully warmed up for the sync procedure the choke should be completely off.

[lucky]

I have a set of mercury sticks that I initially tried, but they were jumping all over the place making adjustments virtually impossible.

The dial gauges are so much easier and time saving. Suit yourselves though.

[Harsh]

The vacuum should be around 8-10 lbs. Your gauges show 20lbs?

In the photo of the carb slide the choke is partway on. Why?
If it is fully warmed up for the sync procedure the choke should be completely off.

The gauge isn't pounds it is cmHg.  Going from memory here, but I believe the manual states that you should have between 20-24 cmHg of vacuum.  Again I understand the number to be somewhat arbitrary and that you want the readings to be equal across all carbs.  It just happened that my carbs were happy right at 20cmHg.

If you are referring to the early pic it is quite possible I moved the choke lever when I tried to get a pic of the #1 carb.  I couldn't get a good pic so I swapped over to the #4 carb.

I agree that the gauges are easier, but I tried to use what I had on hand first.


Greg...While I completely agree with BJ's analysis, I was willing to try something.  What was the worst that could happen I would have to pull the carbs and bench sync them again.  I found that when I synced 4 to 3 that the engine settled down quite a bit.  It really seemed to smooth things out and only a minor adjustment was needed to one of the other carbs after I synced 4 to 3 to get all of the carbs in line with one another.  Yes #2 could use a little bit of tweaking, but it is really close to the others and the engine was starting to get a little hot so I called it good.

[strynboen]

you have to have a ventilator running..it takes somtime 5-10 minuts to get it adjusted..if you do it in 60 sekunds it cant be good

[Harsh]

By ventilator I pressume you mean a fan.  I had one blowing on th efront of the engine.  Like you said it does take a little bit of time.  Making small adjustments to one carb then letting that setting take effect either by waiting a bit or as some suggest blip the throttle and when the revs settle back down make your next adjustment.

[crazypj]

The vacuum should be around 8-10 lbs. Your gauges show 20lbs?

In the photo of the carb slide the choke is partway on. Why?
If it is fully warmed up for the sync procedure the choke should be completely off.

 Nope, wrong on both counts.
Slides are too low for choke to have any effect.
Choke lever has to be lifted slightly or you can't fit the vacuum adapters.
You've never done vacuum sync on 750?

 You can also use vacuum gauges to check motor set up by slowly increasing rpm to around 4k.
If everything is good inside all the gauges will move in unison and maintain same level
If one or more 'goes off' you have some sort of issue with the cylinder