GS550T Stalls when warm, won't restart

[Guest]

Hi all,
I'm new to the gs family, this is actually my first bike, so forgive any ignorance. I recently acquired a 1981 gs550t, the previous owner has previously done a lot of work restoring, I believe he said the electric was redone (R/R & stator) I actually did request an itemized service history from him, so hoping to get that soon. However the bike seems like it runs really well, starts up fine, and idles steadily. But every time I'm out for a mile or two, it will start losing RPMs and will eventually stall out and die. I won't be able to restart it until it cools down, sometimes that's an hour or more, and even then it's weak, and I have to open the choke to keep it alive. At first I thought it was a battery issue because I had gotten road side assistance and they load-tested the battery and said it was bad, so I upgraded it to a new AGM battery. But sure enough took it out today and the same thing happens.

I know I have a lot of things to run through from the noob checklist, valve clearance and petcock and all, but wanted to see if there was anything else I could check in addition, for the next time it happens. The only thing I did try was removing the tank cap and starting with no success. I'll be dedicating all of tomorrow to diagnosing if I can. It seems this is a fairly common occurrence, but with lots of different diagnoses. Here's what I have on my list to do:

• Try running bike on PRIme
• If it stalls pull a plug and check spark (also note wetness? coloration?)
• Going to try running without fuel filter
• Check valve clearance
• Test petcock? (not sure how to test)
• Check gas tank for crud

One thing of note also was that the last time I started stalling I glanced down and the fuel line (it's clear) had air bubbles in it, which made me think it could be a fuel issue, but today there weren't any.
I've also been reading it could be the ignition coils, is there a resource anywhere on how to test those?

Let me know if I missed any pertinent information.
Thanks in advance for any help! The little time I've been able to ride has been awesome, so I'm chasing that feeling again. Hoping to squash this gremlin.

 

[Steve]

You can probably skip everything else, after you ditch the fuel filter.

.

 

[Guest]

It's possible the igniter is going bad. Then when they are going bad, tend to fail when they get hot. I had an 81 850G that had a similar problem and a good used one from a member cure it.

 

[Steve]

It's possible the igniter is going bad. Then when they are going bad, tend to fail when they get hot.

I tend to agree, except for one small detail. :-k

... But every time I'm out for a mile or two, it will start losing RPMs and will eventually stall out and die. ...

Unless he warms it up for half an hour before riding, I don't see where a two-mile ride will overheat the ignitor.

.

 

[Guest]

Thanks for the quick replies! I’ll start with taking out the inline filter and focusing on fuel flow to see where that gets me.

 

[Grimly]

The idea of fuel filters is that they will intercept and trap the pesky little particles that will clog up the teeny-tiny little filters in the carb inlets - you know, the ones you can't get to at the side of the road when they strand you by getting blocked up.
That's why, when an inline filter is fitted, it should become part of the occasional check-out and even replaced every service just to be on the safe side. If the filter looks dirty it's doing its job and saving you from being stuck at the side of the road.
Anyone who's ever been stuck broken down because of bad fuel / rusty tanks etc knows the feeling of impotence and while it's all fine and dandy for those with membership of a towing organisation, it's still a major pain the arris to deal with - because you still have strip and clean the carbs when you get it home.
If you find the inline filter is, in fact, causing a flow restriction then replace it with a clean one or move one size up and get more flow through it.

I'm NOT impressed with the advice to dump them, not at all. Modern gasoline is pretty clean but you never know what you're getting as it pours into the tank and the tank itself, being 40 years old will not be pristine.

 

[cowboyup3371]

Grimly, modern fuel filters are designed for cars and are too restrictive for bikes even with vacuum setups. There is no reason to have one anyway with the filter already on the petcock and the smaller ones in the carbs themselves. If there is a reason to use one at all, get one designed for a lawn tractor as it won't be as restrictive

 

[Nessism]

I'd adjust the valves straight away. Running poor when hot is a classic symptom. Even if it's not the problem it needs to be done regardless.

 

[Grimly]

Grimly, modern fuel filters are designed for cars and are too restrictive for bikes even with vacuum setups. There is no reason to have one anyway with the filter already on the petcock and the smaller ones in the carbs themselves. If there is a reason to use one at all, get one designed for a lawn tractor as it won't be as restrictive

After being caught out the first time, I've had fuel filters on all my bikes and quickly realised the bigger, the better. Admittedly, the big single carb leaves plenty of room to fit a really good filter, but even the XJ and the XS with fairly standard carburettion have enough room to fit one that's not as big as I would like. I keep an eye on the XJ one as it's slightly on the small side, but the bike wazzes up to 120 plus with it on, so it's not causing much restriction that I can see.

 

[Guest]

So I did some testing today, checked the valve clearances, they seemed mainly correct. My feelers only go from .076 to .102 so I wasn't able to dial in more. I also don't have the tappet depressor so I'm not able to switch any out yet. Here are my clearance numbers for record keeping:

#1ex: ~.038mm
#2ex: ~.076mm
#3ex: ~.076mm
#4ex: ~.051mm

#1in: ~.076mm
#2in: ~.063mm
#3in: ~.102mm-.127mm (is this clearance big enough to cause stalling issues?)
#4in: ~.063mm

Side note, can someone tell me how to remove this attachment? It leads to the tach but removing this 8mm bolt didn't seem to do anything: https://imgur.com/NzwcgPb


Before I checked the clearances, I did run the bike on PRIme, and it actually ran for a little while decently. A few times it did start stuttering, but I kept it alive with throttle or using a bit of choke. I thought it might be something with the petcock after that, so I removed it, but it actually looks quite new: https://imgur.com/MANDbRC
There was a little gunk in the tank, but not much.

Unfortunately I wasn't able to test removing the inline filter, because I couldn't find any fuel line suitable for a replacement, I'll have to order some online I suppose.

I now feel more inclined to think the hot stalling issue is fuel related after the PRIme experiment. I'll have to wait for the new fuel line to see if removing the inline fixes it.


Additional photos if it helps get a better picture of what I'm working with:
fuel filter:https://imgur.com/6UUWxuD
spark plug status: https://imgur.com/LF1Yyxy https://imgur.com/0rjotmG https://imgur.com/tLKZKW8

Once again, thanks for all the help!

 

[cowboyup3371]

That screw holds the tach drive in place but you'll have to really pull on the outside to get all of it out; it's also easier to pull the valve cover off and pull/push the drive out. Just know you'll want to replace the O-rings in there (See http://www.bwringer.com/gs/tachcableseals.html)

It sounds like you ran the bike then checked your clearances correct? If so, how long after shutting it down did you do so? If not long at all then you'll also want to recheck your clearances with a completely COLD engine

 

[Guest]

Thanks, I did wait a few hours for it to cool down, but just in case, I checked it this morning with the same results.

I'm going to try to ride today with a coupling in place of the inline filter to see if that helps alleviate the symptoms.

 

[Guest]

For posterity, I'll note:
Took the in-line filter out and no issues at all riding today. I did stall once, but... that was because I ran out of gas

Hopefully I won't have to respond to this thread again!

 

[Steve]

Hopefully I won't have to respond to this thread again!

Please do. ray:

We enjoy hearing what the final fix is. :encouragement:

.

 

[Buffalo Bill]

For posterity, I'll note:
Took the in-line filter out and no issues at all riding today. I did stall once, but... that was because I ran out of gas

Hopefully I won't have to respond to this thread again!

Be sure the fuel line has no upward bends, that it flows downhill continuously from petcock to carb.
Had a problem with mine, just a slight uphill bend in the line gave the engine a slight fuel starvation while riding at continuous HWY speed. Disappeared when I slowed down or idled, because the bowls have time to top off again.