New to The GSR and my 81 550GS

[Guest]

So far this forum has been a great help as I sifted through a number of bikes. I just purchased an 81 550. Overall it is in great cosmetic and mechanical shape, except the engine has issues.

I have been riding and wrenching on bikes for over 40 years but this is my first 4 cylinder machine. I am also a professional marine mechanic, mostly with the 2 strokes but also have some 4 stroke experience on multi-carb models too.

Here are facts I have gathered so far. Some of these were evident at time of sale.

At initial cold start would not idle and off idle was very poor. Idle stop was set quite high at about 2000+ rpm. If stalled it would not hot start with starter. The only way it might start would be with a push start. Exhaust crossover pipe has holes. Did do a road test and it did run what I would call fair. The louder exhaust made it sound a bit ratty.

In post road test checks pulled choke for hot start to check for a fuel starvation issue but no response. Pulled plugs and they were dry and all the same with very light brown centers. The engine was charging and battery had ample power to crank engine.

**********

Once home I installed a new AGM battery and ran a compression check 110-120 psi. Saw figures in a search of threads that indicated 135-145 was normal. Do I have a problem here?

Fired up engine running on separate fuel source with vacuum line to tank valve plugged. Stopped engine and attempted restart, would not start. Used my timing light to verify spark, yes.

Pulled carbs, some light rust staining in bowls but no fouling, debri, or corrosion. Suspect possible idle /off idle circuit issues but overall they looked fairly good. Will clean carbs and examine/replace intake tract components.

Signs of activity (RTV sealant) regarding camshafts but have not inspected yet.

Probably next week will perform a leakdown test.

Any thoughts?

Thanks

Steve

[Big T]

110-120 cold is great

You need to clean the carbs and all the other stuff

[tkent02]

110-120 cold is great

Especialy if the valves haven't been adjusted yet.

[GSX1000E]

Where are you located? There may very well be another GSR member nearby that could help out a bit.

[steve gs]

I'm in the NE subs of Detroit.

In my marine experience it doesn't take too much to mess up a 4T carbed outboard engine especially in the idle and off-idle circuits. That is why we have seen a quick jump to EFI (marine 4T outboards) down to near 25hp. We are plagued with constant fouling of idle and off idle circuits. Must be that good fuel.

A bit surprised compression figures are acceptable/normal at 110-120 (4T marine is 140-160 and more) but that is good news. It's a start.

Thanks for the guidance. Onward.

[tkent02]

I'm in the NE subs of Detroit.

In my marine experience it doesn't take too much to mess up a 4T carbed outboard engine especially in the idle and off-idle circuits. That is why we have seen a quick jump to EFI (marine 4T outboards) down to near 25hp. We are plagued with constant fouling of idle and off idle circuits. Must be that good fuel.

Is this because marine engines tend to sit idle for long periods? We have trouble with the same circuits on bikes that sit too much. EFI is a lot better at this.

A bit surprised compression figures are acceptable/normal at 110-120 (4T marine is 140-160 and more) but that is good news. It's a start.

These are not high compression engines, and the compression test will be low if the valve clearances are too tight. They normally get tighter as they wear, and most owners never check them. As you know, running valves too tight will burn them. That's why checking the valves should always be the first priority when you pick up an old GS. I have bought a lot of these bikes, only one of them had all of the valves in spec. I bought that one from a GSR member who actualy did his maintenance.

[steve gs]

Is this because marine engines tend to sit idle for long periods? We have trouble with the same circuits on bikes that sit too much. EFI is a lot better at this.



Most likely the same situation. The ethanol just compounds the situation by being a moisture magnet. At a certain point when phase separation is reached all the fun really begins. The only problem with EFI and ECM engines is that they are generally out of reach in terms of owner servicing. They also suffer from the effects of fuel degradation too. The VST tanks often suffer greatly from aged and contaminated fuel.

We also have the recommendation from the engine builders to run stabilized fuel year round especially with ethanol blended fuels

One thing we have in my area is ethanol free marine/recreational fuel at 91 octane. It is available at marine dealers and a few roadside stations. It is priced about $.50 more than premium roadside. I also have several DR's and use this fuel in them as well as all my 2T's.




These are not high compression engines, and the compression test will be low if the valve clearances are too tight. They normally get tighter as they wear, and most owners never check them. As you know, running valves too tight will burn them. That's why checking the valves should always be the first priority when you pick up an old GS. I have bought a lot of these bikes, only one of them had all of the valves in spec. I bought that one from a GSR member who actually did his maintenance.



Thanks for the pointers on the valves, makes sense. I am more of a 2T guy than a 4T so I'm working on my learning curve.