Author Topic: Great Carb Sync Video (Read 28813 times)

dagersh · « **on:** February 04, 2011, 06:25:02 am »

I don't know if this has been posted before, but this seems like a good place for it. I think it will clear up the blackmagic of using a carb sync!

Hope this helps, and that it is not redundant!

Gersh

http://www.youtube.com/watch?v=t0qf11BOx6o

sinks88 · « **Reply #1 on:** February 07, 2011, 01:41:33 pm »

so other then dialing them in to the same plane, what else can that do?

OneWheelDrive · « **Reply #2 on:** February 07, 2011, 01:47:48 pm »

Quote from: sinks88 on February 07, 2011, 01:41:33 pm

so other then dialing them in to the same plane, what else can that do?

Else? The goal of syncing carbs is to get the vacuum pressure that pulls fuel into each cylinder even between each of the 4 carbs. This balances the power being imposed upon the crank . With uneven combustion at idle, the cylinders are fighting against each other, usually producing labored idle, clicking or knocking sounds, and ultimately a poorly running bike. A good vacuum tune can do wonders for a bike that is seemingly running poorly.

Also, one very useful addition to that tool is a restrictor valve on each rubber hose. This allows you to eliminate the bouncing needle that occurs at low idle RPMs making it very easy to carefully dial the idle tune. The guy in the video has to tune at what sounds like 3k RPM or so, which really doesn't tune the idle at all.

dagersh · « **Reply #3 on:** February 07, 2011, 05:48:45 pm »

I am hoping that the Morgan Carbtune will alleviate that. It seems to tune at idle as opposed to 3K. I will post video ad how-to when I do my 400F.

Really? · « **Reply #4 on:** February 07, 2011, 08:37:43 pm »

That was one hell of a fast idle, lol. Wonder how in sync they really are? Not really, it is his bike not mine. At most, you get the jist of it.

TwoTired · « **Reply #5 on:** February 07, 2011, 10:35:57 pm »

yes the video was posted before.
http://forums.sohc4.net/index.php?topic=77002.msg861530#msg861530
And I made a comment on it.
http://forums.sohc4.net/index.php?topic=77002.msg861551#msg861551

The video is only a rough "guide" and still has errors/misleading procedure in it.

Flying J · « **Reply #6 on:** February 15, 2011, 07:42:16 pm »

This may sound sarcastic but i mean it honestly. download the manual, read it, and do what it says. You can learn tons about the bike just reading through the manual. Do a search for "manual" to find one you can download.

rm56 · « **Reply #7 on:** February 21, 2011, 11:06:42 am »

Dagersh,

I'm experienced in syncing carbs, I've done several including my 74 CB 750. I have a Morgan Carb Tune which worked well on my bike. I'm working on a friends 74 CB550 which is unfortunately
not as clean as yours. He left it out in the weather for years. Yesterday it took hours just to free up the adjusters. The 8 mm lock nuts were not the problem, the slotted adjuster screws were
frozen due to neglect. We finally got them to move. One thing I wanted to ask you is the location of cylinders 1, 2, 3 etc. You stated that the left piston as your sitting on the bike was the #4.
I believe on Hondas as your sitting on the bike its 1,2,3,4 from your left to right (that is how a CB750 is laid out). I don't have a service manual for Phils 550 so I could be wrong on that. Question?
While you had your bike running it sounded like you had it up to about 3-5000 rpm? I noticed yestersay I had a hell of a time getting 8 inches of mercury reading on my tuner. Is it required to
have the engine running at say 3000 rpm or higher? You mentioned do the #1 and #2 and then the #3 and #4 together as a set. I can see where the adjusters are linked by a thin metal plate.
My friend also has aftermarket pipes on his bike, they are two into ones side flow headers, possiby JC Whitney or Rockys crappy pipes. He also uses K&N pods which are ok. I noticed also on
your bike that you have one fuel hose going from your tank to the carbs. Phils 550 has two just like my 750, I have long hoses but of course when I hooked them up on his bike gas leaks all over.
We used some bailing wires to try and tighten the seal but it did not work too well. Thanks for the video it helped, I was guessing as to the location of his adjusters and luckily was right. In your
video you said PSI, when your syncing carbs you are dealing with vacuum not psi. I appreciate your video it did tell me I had the right adjusters. But it would be more helpful if you had someone
zoom in the camera while your actually doing the adjustments and mention what RPM the engine is at? It sounded like you were redlining the bike? Way too high just to sync carbs.Thanks

Tree · « **Reply #8 on:** February 27, 2011, 02:32:12 pm »

Anyone know if the length of the rubber tubes between the carb ports and the sync gauges matters (i.e do that all have to be the same, or is it irrelevant)?

TwoTired · « **Reply #9 on:** February 27, 2011, 04:11:25 pm »

Quote from: Tree on February 27, 2011, 02:32:12 pm

Anyone know if the length of the rubber tubes between the carb ports and the sync gauges matters (i.e do that all have to be the same, or is it irrelevant)?

Without any bounds on the length, then yes. 100 ft of hose is going to behave differently than 2 feet. But, within a one ft length difference, not really, as long as they don't leak.

AustralianShepard · « **Reply #10 on:** February 28, 2011, 06:43:34 am »

I just sync'd my carbs this weekend with the same tool as in the video. I had the plastic adjusters on each vacuum line and it got all the bounce out of the needles. It was actually very easy to adjust. After that, I tried setting the fuel mixture using the 50rpm drop proceedure. What a pain in the A$$. I ended up just setting all the fuel mixture needles at 2.5 turns out. I've read on here that some guys are setting them up at 1.5, and 1.75 turns out. Any body have any feedback on the fuel mixture screw adjustment?

TwoTired · « **Reply #11 on:** February 28, 2011, 10:06:06 am »

Quote from: AustralianShepard on February 28, 2011, 06:43:34 am

Any body have any feedback on the fuel mixture screw adjustment?

Any significant feedback will depend on the make model and year of the bike/carbs in question. And, also if any modifications from stock (induction/exhaust/engine) have been made.

Cheers,

AustralianShepard · « **Reply #12 on:** March 01, 2011, 07:18:25 am »

1974 CB750, K&N air filter with the stock airbox, 4 into 1 header with Kerker muffler. Stock motor, stock Kei Hin carbs.

TwoTired · « **Reply #13 on:** March 01, 2011, 10:53:37 am »

Quote from: AustralianShepard on March 01, 2011, 07:18:25 am

1974 CB750, K&N air filter with the stock airbox, 4 into 1 header with Kerker muffler. Stock motor, stock Kei Hin carbs.

With this setup I would guess that you will need to turn your pilot screws inwards about 1/8 to 1/4 less than the stock setting.
You will determine this by how the engine responds to pick up upon throttle twist under load.

Mark your throttle, set pilots to stock position (or leave them where you have them now), and test drive. Top gear at 15 MPH whack the throttle to the one half of total travel position. The engine should pick up smoothly, and predictably without stumble. If it wheezes and loses power, then turn all the screws inwards 1/8 turn and repeat the test drive. Keep turning the pilot screws inward and test drive until the engine does accelerate smoothly and predictably.

Here is why.
Your carbs don't have accelerator pumps. When the throttle is suddenly opened, the carb throat vacuum is mostly lost as it is quickly equalized by the inrush of air. It is the vacuum that pulls the fuel up from the fuel bowls (under these low speed conditions). Lose the vacuum, and although there is plenty of air going to the engine, it starves for fuel. Later carbs overcome this with the accelerator pump, which shoots a stream of gas in the carb bore when the throttle is twisted. Since accelerator pumps are absent on your model carbs, the idle mixture is set over-rich at idle so opening the slides still keeps the mixture in the combustion range, so long as not too much air is introduced. Hench the 1/2 throttle travel twist.

The K&N filter induces less pressure drop across it's membrane compared to the stock item, causing some reduced vacuum and a leaning effect on carb jet flow. Further, the Kerker's lesser back pressure (compared to stock) allows more oxygen to replace the spent gases in the combustion chamber, setting up a requirement for more fuel needed at idle.

It could be, that the filter and exhaust changes also require a main jet and slide needle adjustment. But, that would be determined by a Dyno test, or a test track and spark plug tip reading.

Ethanol blended fuel can also mess up ideal carb settings and make stock to-the-book settings wrong or just "off" a bit.

All this assumes the engine and carbs are working as well as when new.

Cheers,

Messenger750 · « **Reply #14 on:** June 22, 2011, 09:12:13 am »

This is great thanks for the post!

dave500 · « **Reply #15 on:** July 12, 2011, 05:50:33 pm »

thats running too fast to be syncronizing them,you have to have the dampers on the hoses and do it at a much lower rpm,,with an engine out of sync,watch the guages as you increase the rpm,they all appear to go into sync,lower the rpm and watch as the vac guages all show otherwise.

lucky · « **Reply #16 on:** February 03, 2012, 01:56:44 pm »

"black magic" wow. I did not know. LOL...lol...lol

dave500 · « **Reply #17 on:** February 05, 2012, 12:51:53 am »

theres probably heaps of wrong u tube vids on all sorts of stuff.,the problem is learners get the wrong idea and put it into practise.

LesterPiglet · « **Reply #18 on:** February 05, 2012, 04:14:51 am »

Quote from: dagersh on February 07, 2011, 05:48:45 pm

I am hoping that the Morgan Carbtune will alleviate that. It seems to tune at idle as opposed to 3K. I will post video ad how-to when I do my 400F.

I have used the Morgans in the past. Much more accurate than the gauges as they don't bounce around.

dave500 · « **Reply #19 on:** February 06, 2012, 12:49:10 am »

you must have dampers with the gauge type so they dont flutuate heavily.

PurduePete · « **Reply #20 on:** February 16, 2012, 04:38:22 am »

Good info here. I'm going to try an sync my carbs when I get home and get the bike running.

PurduePete

Sent from my iPhone

theitguy · « **Reply #21 on:** June 28, 2014, 06:55:31 am »

I am trying to sync my 73 750 carbs and am adjusting the small flathead screws but it is not moving the gauges can some one help me find the right adjuster on these round top carbs all the videos out here show no adjusting for pre 76

theDQG · « **Reply #22 on:** June 14, 2019, 06:15:47 am »

I got that same carburetor synchronizer.. it didn't come with instructions. What do I have to do to get the needles to stop flickering all over the place? Is this from the carbs themselves or something I am doing wrong?

TwoTired · « **Reply #23 on:** June 14, 2019, 10:01:10 am »

Quote from: theDQG on June 14, 2019, 06:15:47 am

I got that same carburetor synchronizer.. it didn't come with instructions. What do I have to do to get the needles to stop flickering all over the place? Is this from the carbs themselves or something I am doing wrong?

Install and adjust the dampers in the line between carb runner and gauge.

The needles respond to vacuum changes. And the intake runner pulses each time the intake valve opens.

dave500 · « **Reply #24 on:** June 14, 2019, 02:15:35 pm »

read reply #19

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Author Topic: Great Carb Sync Video (Read 28813 times)

AustralianShepard

AustralianShepard