GT550 issues, thoughts first step, and some questions!

[TRC]

First of all, since this is my first post, hello!!

Ok, right to it. My bike is a '75 GT550 which I've had for 3/4 of a year so it's pretty new to me.

ISSUES:
1. After high RPMs, the RPMs linger momentarily when releasing the throttle before it returns to idle
2. It just started fouling the left plug. The others look fine. Leaned out the carb, new plug, same thing.

MY THOUGHT:
Crank seals going bad? Ugh!

Ok, then I started poking around and discovered the SRIS return line to that left cylinder appears to have broken! I barely touched it and it just came out and the line does look broken on the end. I took that as good news as I would much rather have it be an air leaking from that causing the issues instead of bad crank seals!

I then removed the left SRIS line at the front of the case and a bit of black oil dripped out. Not much, a few drips. Here's where my questions begin...

What are the SRIS valve filters? Does my bike have them and if so, are they inside the crank case? I didn't notice anything when I removed the valve but then read on here about them. I intend to remove the SRIS valves and lines and plug them so do I need to worry about removing these filters when I remove the valves? Sounds like bad news if they are there and end up floating around inside!

Thanks in advance! I plan to report back after plugging the SRIS lines if my issues are resolved or not and if not, ask for advice on next steps. Thanks!!

[GTandcbr]

Welcome to the forum. Firstly your revs lingering is almost certainly down to an air leak. How old are your carb rubbers? Best way to test for air leaks is to spray starter spray around each carb at idle see if the revs pick up. If they do air is getting in!. The sris hoses are fairly cheap and easy to get hold of I would replace them as they do go hard over time. The filters are an afterthought by Suzuki not necessary I ditched mine years ago and are difficult to source anyway. They slot on the end of the valve before it is put in. Its not possible for it to get into the crankcase.
The spark plug fouling is more likely to be electrical is the bike misfiring?
The only way to confirm your crank seals without an engine strip down is by what is called a leakdown have a look here https://youtu.be/Pdh_HkeQYIM" onclick="window.open(this.href);return false;
Good luck

[TRC]

Thanks a ton! I picked up some bolts this morning to plug the SRIS line holes this evening when I get home from work but still need to source some seal washers today. I may end up rebuilding the SRIS lines but plugging the holes should rule out one potential air leak source.

I haven't inspected the carb rubbers thoroughly but I will do so and will also do the starting fluid test. Thanks for that suggestion!

It's a bit hard to tell if it's misfiring or not but the bike was converted to an electronic ignition by the previous owner so it isn't bad points for that one cylinder. I guess I would suspect that if it was out of wack I'd be having issues with all cylinders, not just the left one. Does that sound like a correct assumption or am I off base thinking that?

Yes, had doing a leak down test on my list of trouble shooting things to try but will do the simpler things first. I've never done one before so if it gets to that I'll learn something.

Again, thank you and I'll report back with good or bad news...

[TRC]

One thing I forgot to mention. I keep the battery on a trickle charger and it's fine when I start it up but there's been times when I go to start it to leave work and the battery is very weak. In other words, the battery isn't holding a charge very well. You mentioned you though that the fouling plug was electrical so do you think an old battery that needs to be replaced could potentially be the source of the fouling plug? This fouling problem is new and wasn't happening until just a few days ago but is happening consistently now.

[GTandcbr]

I was thinking along the lines of a broken HT lead that works itermitently. Try cutting a few cm off the end of the cable and re screw in the cap. Removing your sris system is done by lots of owners but it may not help your plug fouling as the sris valves are designed to eject unwanted oil from the bottom of the crankcase.
However if the electrical side does work out okay have a look at the float level of the offending carb. If it is set too high it will make the mixture too rich and foul the plug preventing it from firing properly.

[TRC]

Yeah, I figure plugging the SRIS lines is a long shot but worth trying, especially considering the line leading to the top of the left cylinder is broken anyway.

OK, thanks for the suggestion on the HT lead as well. I'm only asking about the battery as I had read somewhere that on these a weak battery can cause issues, though I'm pretty skeptical. Might go ahead and replace it as it needs replacing anyway if I can find one locally this weekend.

Again, thanks!

EDIT: Thanks - will also check the float level of that left carb.

[TRC]

Back to your misfiring question. Prior to fouling the plug, when on the throttle there is no sign of misfiring. All cylinders are running consistently, not intermittently. Then, after riding for a good while the left cylinder cuts out and upon pulling the plug, it is fouled.

[GTandcbr]

Of course if the plug stops firing it will foul up. Just had another thought. Check that the choke piston for that carb is returning as it should. It does happen that they stick in the bore flooding that cylinder. A quick spray with carb cleaner will do the trick.

[TRC]

Good thought. Will do.

[TRC]

OK, the SRIS valve bolts in the front of the engine have been removed and solid bolts installed. But..

There are only two SRIS lines on the back of the engine? The lines were a mess so I couldn't tell where they were going accept for the two on the back side of the engine but where did the third line connect? Makes no sense. At any rate, the SRIS lines are no more. Confused...

In addition, much to my surprise the two SRIS line nipples on the back side of the engine are press fit and not bolt-style valves like the front? How should I plug these? I'm thinking I'd take a short piece of the line and try to re-attach them to the nipples and JB Weld the other end or something? Those suckers are hard to get to though and I still don't know where the third line fed back to the engine.

The choke piston on the left carb isn't sticking. With a flashlight I can see it doing it's thing through the little hole it opens and closes. Hope that makes sense.

EDIT: Ok, here's why I couldn't find the third SRIS nipple on the backside of the engine. Previously someone had just clamped a piece of fat rubber tubing to the nipple for the middle cylinder! I didn't know they were right next to each other until I pulled that fat rubber tubing off LOL.

Ok, going to proceed with JB Welding off the ends of some SRIS line that will act as the plugs for the back side.

Update on the carb: I removed the float bowl on the left side carb and the float was at about 0.7". Well that's not good if the Clymer manual is correct at 1.01". I removed the float and bent the tang until the float sat at an eye-balled-with-a-normal-ruler 1". Ok, not exact but certainly way closer and the best I could do for now. Hopefully this is the fix for that cylinder's plug fouling and should be close enough to find out as it was way off. I'll set it to exactly 1.01" later.

More to come...

[GTandcbr]

The sris pipes are held on both ends by a metal spring clip normally and the tube is soft when new but goes hard fairly quickly.
You are going to need to set that offending float very accurately as a little bit over or under will have a big effect on the cylinder.it needs to be bang on. Have a look here for help
viewtopic.php?f=9&t=11588&hilit=Setting+float+level" onclick="window.open(this.href);return false;

[TRC]

Started the bike up and did some test rides this morning and lots of good news!

1. No more hanging RPMs! The SRIS lines were so mucked up with a quarter of it not even connected and I'm convinced was causing the air leaks. Plugging them resulted in a bit more smoke at initial start up but I'm not worried about it. Now I'm thinking I'll just leave the SRIS system plugged instead of rebuilding the lines.
2. First ride was for about 20 minutes and then pulled the left plug. NOT fouled!!
3. Took another ride for about 45 minutes and then pulled all of the plugs. They all look great! In fact, I decide to richen it up a tad on all three carbs.


So there you have it. Do I dare say she's fixed?

[GTandcbr]

Great news! Hopefully your problems are behind you .