Help me interpret this Carb balancing video

[Guest]

Hey guys, could do with some help with this video. Any experience gratefully received.

https://www.youtube.com/embed/fO9DCXejABM

https://www.youtube.com/embed/fO9DCXejABM

Bike - Its a 1980 GS850, standard airbox - 4-1 exhaust, CV Mikuni Carbs, standard Jetting.

History - I had a problem with cylinder 4 (the furthest right cylinder on the bike, the bottom gauge in the video)

For a while it wouldn't run at all, but it was a mystery,
there was a good spark, and the plug was wet, but wouldn't run, maybe just a second when starting at first, then nothing.

Long story short, I did a full carb rebuild (all new seals, boiled the carbs in lemon juice, rebuilt) and it started working - hurray.

I've taken it out for a few rides and its a lot underpowered at low revs so I thought maybe they needed balancing, bought a gauge and here's the video. I don't really know what I'm seeing, why some jump up more on acceleration and fly further down after decelerating, but most concerning of all is the gauge at the bottom for cylinder 4 - it hardly moves

Questions - Any ideas whats going on with Carb 4
- Why are the others jumping about more than each other,
(also if you have sound on the video you can hear the bike popping on deceleration)

[hampshirehog]

At first look I'd suggest that the damper screw on the gauge is turned in too far on number 4.

[L1ndon]

Any further out and the needle dances around :-( I can try swapping gauges

[hampshirehog]

A little bit of dance is reassuring that the damper isn't too far in. Your idea of swapping over the gauges will show if that is the case.

[londonboards]

I would say the same thing. If it isn't the actual damper valve on the carb synchroniser, physically check the hose is not kinked or trapped under something. Swap over the vacuum hoses for 3 and 4 and you will soon tell.

Apart from that, which I would take as a reading anomaly, looks to me like your carbs are near spot on.

Not like these:

Have to say you bike sounds mighty fine. What sort of pipe are you wearing?

The popping is quite interesting too. I was getting that when the carbs were not in synch and the number 1 cylinder was running too rich. Best way of telling is to take the header off and see which cylinder is spitting at you. Like this:

there is no mistaking that! And in your case if the carbs are balanced the richness that causes the popping will be due to something like; needle height set differently on one carb (if you have adjustable needle heights in your carbs), incorrect float height in the offending carb, choke not completely turning off when running (check the little grub screws in the choke rod are all biting in the indentations and that all chokes move in unison), maybe the air pilot screw (on the top front of the carb is incorrectly adjusted. Did you get the bike running sweetly using these screws before you did the sync?

One other possibility I have just dreamed up is that the no. 4 throttle slide (variable venturi thing that you can see down the throat of the carb from the air filter end) maybe a little sticky or the spring that holds it down may have snagged or something like that that prevents that slider moving up and down at the same speed as the others. If you can access the carb throats again (I'm guessing this would involve taking out the air box) try lifting all the sliders using your finger and see if they all operate in a similar fashion. It could also mean (I'm guessing again) that the diaphragm on that carb maybe holed and therefore does not create the same amount of vacuum to lift the slider as the others. Also these round sliders have holes drilled though them so that the vacuum created in the throat of the carb body is transmitted into the round pancake top of the carb. This creates the suction that lifts the sliders. If that hole is blocked or of a different size (some performance jet upgrade kits recommended drilling out these holes to make them bigger to give a snappier throttle response), you may have an odd sized one in there.

That's given you something to think about! Hope it helps. Well I hope its just an error with the readings!

[Chromedome]

Hi,
iv got a 1980 Gs850L, std airbox, 4-1 Motad exhaust, CV Mikuni Carbs, std jetting and the exact same gauges you have. I expect, pretty sure, like the guys have already said its the damper screws. Try turning the screw on No3 In, as No3 is to sensitive, now, not a quarter turn only a fraction of a Quarter then you should see the gauge slow down or stop, if it stops you turned it in to much if its still erotic sorry erratic you havnt turned it in enough. Then do the same only in reverse with No4, turn the damper screw out, only a fraction, to allow more vacuum. I expect this should help if it doesn't the problem may be kinked or externally fouled hoses.
Id always thought that these Suzukis need re jetted to run properly with a 4 into 1, mines pops ever so slightly on No4, only when cold but not enough even to consider re jetting. Hope this helps.
One more thing, worth a mention! well 2 or 3, londonboards, LOVE the bike, Bike of the month, not only can some of us not read we cant spell or do fractions.
Stephen.


1980 Gs850L
1982 Gs1100L

[phydeauxmutt]

You couldn't find anything stronger than lemonade to clean the carbs?

Dirty carbs might not affect the sync too much, but they WILL affect the running, which could be some of your 'popping'.

Seeing videos like that is why I have other types of sync gauges.

[L1ndon]

Thanks so much for the help guys, I'll get on it next chance I get... (phydeuxmutt - They don't have decent carb dip in WA) I'll check all the below, I do remember one of the slide jobbies being a bit sticky, but I cleaned it...plus I think it was on another carb. Anyway update to come... In the mean time here's a pic of the bike.

IMG_20160219_135711.jpg

[jdvorchak]

I prefer Berrymans Chem dip available in every auto parts store I've been. Bought mine at O'Reilly and used my smart phone to show them Wal-Mart price of $18.54 and they matched the price. Normal price was about $30. On the worst carbs I've seen overnight soak cleans them. But you have to take everything apart. Do one carb at a time and you won't mix up the parts. Also I don't dip the slides and diaphragms. I very carefully clean the slides trying to keep any chemicals off of the diaphragms.

Even with the overnight dip you may have to use a #10 guitar wire on the enrichener jets, located in the carb bowl.

[L1ndon]

I prefer Berrymans Chem dip available in every auto parts store I've been. Bought mine at O'Reilly and used my smart phone to show them Wal-Mart price of $18.54 and they matched the price. Normal price was about $30. On the worst carbs I've seen overnight soak cleans them. But you have to take everything apart. Do one carb at a time and you won't mix up the parts. Also I don't dip the slides and diaphragms. I very carefully clean the slides trying to keep any chemicals off of the diaphragms.

Even with the overnight dip you may have to use a #10 guitar wire on the enrichener jets, located in the carb bowl.

I would have loved some of the Berrymans dip but you cant get it here in Australia, all you can get is the spray cans... I did a full strip, pulled out and cleaned every component with the spray cans and wire (gently) and boiled the bodies in Lemon juice - it actually did a good job in the absence of chemical dip (nothing went on the diaphragms, in fact they didnt get cleaned at all, which makes them top suspect if there is a problem other than just a gauge issue... hopefully I'll get answers on it tonight :-) (I have a house full of little girls who scream when the motorbike starts so opportunities for tinkering are scarce!!)

[jdvorchak]

Ok I understand now. As for the gauge I'm not seeing a problem in the videos. Now one of the brass adapters may not have a fully formed restricter hole drilled in the end. Is there a running issue? Because at idle they look perfect to me. When you rebuilt the carbs did you also replace that O-Ring that goes between the boot and the cylinder head?

[L1ndon]

Update: swapping gauges over alleviated the problem, so maybe it was a kink or the adjustment of the dampers. I set them all to "dancing a little " and all seemed good. Thanks so much for the advice all.

John, I was worried about the sluggishness of cylinder 4. I've never seen carb balancing before so wasnt sure how big a problem that was... It adjusted out with the damper.
I did replace the o-rings on the head, though they looked fine.

All this meddling is because it seems a underpowered at low to medium revs. I tried to lean drop the air mix, but wasn't too sure that helped.

Maybe the 4-1 exhaust needs different jets. I'll keep searching on the forum

[phydeauxmutt]

Maybe the 4-1 exhaust needs different jets. I'll keep searching on the forum

What jets are in there now? Depending on the restrictiveness of the 4-1, you might need anything from 120-130 jets.

If the muffler is a "street" or "quiet" type, you can get by with smaller jets. However, if it is more of a "competition" (louder) variety, along with the larger jets, you could benefit by a different needle to enhance the transition from pilot to main jets.