GT550 - Surging off throttle - educate me on carb removal

[TRC]

Hello again. If you've seen a couple of my other threads, I have a GT550 that I bought at the end of summer last year and so the bike is new to me. I'm currently working through the issues with it.

From those threads the prior problems fixed were hanging throttle due to air being sucked from SRIS lines that were partially connected (WTF? I plugged them), and fouling the left plug which I attribute to the float for that cylinder being way off and the timing not being set correctly. So you might be asking, "how did he fix the float if he didn't remove the carb?" Well, I removed all three as the bundle so I could get to the float bowl of the one.

The bike is certainly running 150% better - no more hanging RPMs or fouling plugs but this brings me to the next problem. The bike surges when cruising or off throttle. It's bad enough that I often have to pull in the clutch to stop the surging on a long downhill for example and am constantly in a cycle of on the throttle and off, awaiting to pull in the clutch when off throttle. Obviously this isn't ideal!

First thing I'm planning to do is to try lowering the clip a notch on the jet needle to richen it in the 1/4-3/4 throttle zone and thus the need to remove each carb. First, does that sound like a good plan of action or would you do something else first to fix the surging? Assuming I should proceed with this, what do I need to know about removing the carbs from the...don't know what you would call it specifically...the hanger plate that the three carbs are connected to? I'm unfamiliar with this style of setup for the carbs and am afraid of screwing something up when disconnecting the top portion where the boots are specifically. Any advice? For example, the little screw at the very top, what specifically does that adjust and how do I get the three back into proper adjustment when reassembling them back onto the bar/plate that holds the three?

Hope that makes sense. I couldn't find any information specifically about removal / reassembly of the carb from the carb hanger plate doohickey. BTW, what is the plate doohickey called?

Any wisdom appreciated before I go really screwing it up. Thanks in advance!!

[GTandcbr]

Can't help you about the gang carbs, I have the early separate carb set up. These triples are prone to surging it is a very common problem.have you tried turning your airscrews in to make the mixture richer?
Here is the carb manual link to help you http://www.3cyl.com/mraxl/gt/manuals/su ... /cover.htm" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;
This may help too http://www.iwt.com.au/mikunicarb.htm" onclick="window.open(this.href);return false;

[TRC]

Yes, I've been down that road somewhat but admittedly I could certainly spend more time there first. I'll do the "run it a bit uphill for a while then kill it and pull the plugs test". I should mention the bike has air filter pods and custom pipes so it isn't stock. Unfortunately I have no idea if the jetting is stock or if it had been adjusted for the air filter / pipe changes. I won't know until I pull the carbs and take a look so still interested in what I need to know to get them off and back on properly.

But yeah, I'll do that tomorrow and see if going richer on the idle end makes a dent in the issue.

[TRC]

Ah, thanks for adding those links. Brilliant!! Just what I needed.

[yeadon_m]

TRC,
A properly set up GT550 does not surge, at all. That trick is reserved for the GT750!
I have one of each of the triples, and the bigger they are, they less smooth. But 550s classically don't do the snatch and lurch show.
I would remove, clean, replace or clean the brass and carefully set every aspect of the carbs. If your ignition & battery is good, and running gear well fettled, it'll be the carbs that are the cure. Do take particular care on the pilot circuits, there are two, tiny holes in the carb to engine mouths and they must both be perfectly clear and spray out carb cleaner sprayed into the pilot air intakes identically across the three carbs.
In due course, let us know what jet sizes you have. Suzuki messed around with the jetting on 74-77 GT550s more than with any other triple and it can be downright confusing and manuals can be contradictory.
Cheers and good luck!
Mike

[GTandcbr]

Have a look here viewtopic.php?f=2&t=12241&hilit=Surging" onclick="window.open(this.href);return false;

[TRC]

Thanks all for the info. I have read through that other thread about surging several times as there's great info in it. I think I've got the info I need now to remove them from the mounting bracket confidently.

Mike, funny you mention the battery. It isn't holding a charge well and I have a new one on order. I did adjust the chain as it was a bit loose but that made no difference in the surging. Good to know that the 550 shouldn't surge much if at all if proper as I was starting to wonder if it was just part of the nature of the beast. Sure, I don't expect it to cruise like a Goldwing lol but it's pretty bad currently. In the short term I will try setting to 1 1/4 out on the air screws and keep going in a quarter of a turn regardless of idle and see if that helps at all in regards to the surging. At some point though I'll be pulling them apart and yes, will report back what I find.

[yeadon_m]

Given the battery info, its possible that your ignition is marginal. Do you know if the bike is charging as you ride? if you measure battery voltage with ignition off, then compare with ignition on only and motor stopped, then motor idling at say 1300rpm and 4000rpm, what do you see? if voltage is low, it will miss on one or more pots and that might be part of the issue?
see here...viewtopic.php?f=2&t=12291" onclick="window.open(this.href);return false;
note that voltage at the points/coils is often another volt or so below battery voltage due to losses in the loom even when new, and this can be 2v or more on crusty old looms.
Cheers,
Mike

[TRC]

Mike thanks again. I haven't measured it but I certainly will. Here is what I do know - I take it off the battery tender and it starts right up. The battery is good and strong and I ride it to work. Then, eight hours later I go to start it up for the ride home and the battery is really weak and it's 50/50 if it will have enough juice to start the bike. If not, I kick start it.

When I bought the bike, the starter motor turned over just fine but it had eaten a gear so it didn't do anything to start the bike. I fixed the gear and now the starter works fine but it means the previous owner had been kick starting it for some time which leads me to believe he probably didn't care much about having a battery in good working order. On the other hand, though I haven't pulled the battery yet, it doesn't look to be ancient either.

I'll measure the voltage and the new battery should arrive any time now.

I do have other fish to fry on it as as well - the rear brake is nearing the wear limit according to the markings so it's time to replace the shoes. At some point I'll be done with the "must fix now" list on it.

EDIT: BTW, I did order a conventional battery for it: 12N11-3A-1.

[Alan H]

Too late now, but a Motobatt battery is as good as you can get.

[TRC]

Note taken! I'm sure this won't be the last battery ever to go in it.

BTW, the bike came with BR8EIX iridium plugs in it and as I've been working through the issues I've been running standard B8ES plugs in it (was fouling the left side prior to the float level and timing set properly fixes). However, the Clymer manual lists B7ES as the standard plug. I did do some tests yesterday where I started the air screw at 1 1/4 out and and then turned all carbs in a 1/4 turn, ride some more, repeat. I will say that I do think it helped the surging. Totally solved? No. Better? Yes. However, when I got home I pulled the plugs and the bike was definitely running too rich but that was after going all the way in to just 1/2 turn out. So for now I set it back to factory 1 1/4 turn as the point was to glean some information if making the air screw richer would help the surging and it did. Makes me wonder though if I should try the hotter B7ES plugs in it? My thinking is with a hotter plug the carbs can be set richer but with less potential for fouling. Correct? I live in an urban area with plenty of stop lights and sometimes getting stuck in traffic is unavoidable so if set towards the more rich side to reduce the surging, in turn it increases the risk of fouling.

[Alan H]

So called surging is a strange one to me.
A 2 stroke naturally fires occasionally on the overrun, and if the tickover is set too high and/or the mixture is out at bottom end, this causes the situation to be worse.
What is the engine ticking over at? Should be 1000rpm or less.
The timing must be set correctly and the battery must be on top line as if it gets discharged while running, it will affect the general performance anyway. Take the air filters out and give them a wash in warm soapy water, then dry completely and put a little oil on the foam and squeeze it so no oil comes out. That may make the carburation better. A 7 plug is hotter and if you're only doing short hops, lots of traffic and no constant high speed runs, it 'should' be OK. If you're going to do long runs 6000rpm plus for a time, then stick to 8s. I still run SRIS lines in my 550s, Suzuki knew what they were doing when they built these bikes, and if you're doing lots of stop start work, the oil will build up in each crankcase and needs a good long fast run to get rid of it if you don't have SRIS. If you do have SRIS it's less of a problem as the oil is recycled into another cylinder and burned during normal riding. (SRIS stands for Suzuki Recycle Injection System.)
Also make sure the pump is set correctly at tickover so that it doesn't over oil during normal running.
What 2 stroke oil are you using?

[TRC]

So called surging is a strange one to me.
A 2 stroke naturally fires occasionally on the overrun, and if the tickover is set too high and/or the mixture is out at bottom end, this causes the situation to be worse.
What is the engine ticking over at? Should be 1000rpm or less.
The timing must be set correctly and the battery must be on top line as if it gets discharged while running, it will affect the general performance anyway. Take the air filters out and give them a wash in warm soapy water, then dry completely and put a little oil on the foam and squeeze it so no oil comes out. That may make the carburation better. A 7 plug is hotter and if you're only doing short hops, lots of traffic and no constant high speed runs, it 'should' be OK. If you're going to do long runs 6000rpm plus for a time, then stick to 8s. I still run SRIS lines in my 550s, Suzuki knew what they were doing when they built these bikes, and if you're doing lots of stop start work, the oil will build up in each crankcase and needs a good long fast run to get rid of it if you don't have SRIS. If you do have SRIS it's less of a problem as the oil is recycled into another cylinder and burned during normal riding. (SRIS stands for Suzuki Recycle Injection System.)
Also make sure the pump is set correctly at tickover so that it doesn't over oil during normal running.
What 2 stroke oil are you using?

Thanks! The bike is idling at about 1100-1200 RPM. The manual specifies 1100 if I'm not mistaken so I don't think it's extremely abnormally high or something. Timing has been set correctly, air filters were just cleaned and re-oiled. I'm definitely riding on side streets with lots of stop lights and not extended 6000rpm freeway runs. No SRIS lines currently as they were shot and not even connected in 2 out of 3 of them. I may end up rebuilding the lines and re-installing them. The oil pump has been checked and the markings are aligned properly with the dot at the top of the circle on the carb. I'm running Royal Purple HP 2-C Synthetic 2 stroke oil.

I went ahead and picked up some B7ES. I figured for the price of admission they are worth trying given my riding conditions. If no improvement I'll go back to the B8ES.

[TRC]

Given the battery info, its possible that your ignition is marginal. Do you know if the bike is charging as you ride? if you measure battery voltage with ignition off, then compare with ignition on only and motor stopped, then motor idling at say 1300rpm and 4000rpm, what do you see? if voltage is low, it will miss on one or more pots and that might be part of the issue?
see here...viewtopic.php?f=2&t=12291" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;
note that voltage at the points/coils is often another volt or so below battery voltage due to losses in the loom even when new, and this can be 2v or more on crusty old looms.
Cheers,
Mike

Ok, I checked the voltage at the battery:
- Ignition on, bike not running = 12.67
- Idle = ~12.8
- 4000 RPM = ~15

My conclusion from these tests indicate that indeed it should be charging the battery when running. Interestingly enough the bike had sat overnight off the tender but was plenty strong this morning. Why then would it sometimes be weak when leaving work? Same thing has happened after getting gas - battery was weak and had to kick start it. I always turn the headlight switch to off when parked (not sure if leaving the headlight switch on is a "thing" with these or not?). Weird.

Thoughts?

I realized I always run with the headlight on so I'm going to repeat the test with it on as well...

Headlight On:
- Ignition on, not running = 11.87
- Idle = ~12.2
- 4000 RPM = ~14.5

[GTandcbr]

My opinion your battery is duff. Any battery charged over 14.7 volts will gas and boil look here for help.
http://www.w8ji.com/battery_and_charging_system.htm" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;
PS I run NGK B7es plugs