First post... ressurrecting a K100RS after a long idle period

[Andy FitzGibbon]

Hi All,

This is my first post.  Recently, I've been looking for an inexpensive bike that would be better for long trips than my DR650, and I ran across this 1985 K100RS on craigslist:



When I bought it, it wouldn't even try to start... but the owner swore up and down that he had started it a year ago.  The price was very, very cheap, so I bought it anyway- figuring that, if it turned out to be financially impractical to get it running, I could probably get my money back out of the side cases and the Corbin seat.

A replacement fuel pump got it running, well enough to warm it up and do a compression test.  It quickly jumped to 150 psi in all four cylinders, which is pretty good, according to the shop manual.  That encourages me to continue working on it, rather than parting it out.

However, though it runs, it doesn't run well... rough idle, missing, ect.  I suspect spark plugs, injectors, fuel pressure, or maybe a vacuum leak.  Anything else I should be looking for right off the bat?

Thanks for any advice!  The short ride I took on the bike was really enjoyable, and got me excited about putting the effort in to get it back on the road.

Andy

[Laitch]

I suspect spark plugs, injectors, fuel pressure, or maybe a vacuum leak.  Anything else I should be looking for right off the bat?

Welcome, Andy!

Next, definitely replace the fuel filter soon. Check the air filter and air box soon. The air filter can be cleaned if not dilapidated. Be certain all spark plug connections are tight. The electrode insulator tips of all plugs should be neither sooty or oily if the engine has been run recently. If you don't know the age of the plugs and the gap is out of spec, replace them. Older Bricks might temporarily smoke after starting when parked on the side stand for a while—no problem. Check the condition of the vacuum take-off caps along the throttle body assembly.

Manuals are available in the Technical Library card catalog here.

[Andy FitzGibbon]

Thanks!  I should have mentioned that I replaced the fuel filter along with the fuel pump, and I flushed the tank out as well as I could.  The air fiter and air box are both in good shape.

No idea on the age of the plugs- they may even be original (bike has 47K on it).  I plan to replace them.  They have oily crud on them, but they are not wet with oil.  Makes me think that they are maybe just old, and have suffered through a few too many oily K-bike startups.  The guy I bought it from related the story of when he bought it, and the guy had it parked on the side stand... it smoked so much that he almost didn't buy it.

Having seen what the ethanol gas did to the fuel pump, I'm speculating that the injectors may have received the same treatment... but I'll replace the plugs first and check the fuel pressure (need to get a gauge) before going that route.  Good tip on the vacuum caps, too.

Andy

[The Mighty Gryphon]

Welcome!  That is a sweet looking K you have there.  I would suspect that beside some perished rubber bits(everything rubber should be closely inspected), there is a fair amount of varnish in the fuel system, especially the injectors that keeps them from opening properly. 

Get some Techron fuel system cleaner and throw some in the tank with ethanol-free gas.  Run the engine for a while to get the Techron circulated through the system.  Run on this Techron mix for the first 1000-2000 miles, and you will notice the performance improving every time you ride.  If you don't want to wait that long, you can pull the injectors and clean them on the bench.  There are many YouTube videos showing ways to do this. 

Good luck with a fine bike.

[Laitch]

Thanks!  I should have mentioned that I replaced the fuel filter along with the fuel pump, and I flushed the tank out as well as I could.  The air fiter and air box are both in good shape.

No idea on the age of the plugs . . .Makes me think that they are maybe just old, and have suffered through a few too many oily K-bike startups

Having seen what the ethanol gas did to the fuel pump, I'm speculating that the injectors may have received the same treatment... but I'll replace the plugs first and check the fuel pressure (need to get a gauge) before going that route.  Good tip on the vacuum caps, too.

It's helpful to respondents if you give a complete picture of maintenance, procedures or conditions in your primary posts.

The plug's electrodes erode with use, eventually widening the gap and weakening the spark.

My experience tells me gasohol in the proportions sold in the US has no effect on the condition of any equipment if it is run through that equipment regularly. It effects equipment that is idle for long periods and that's why it should be conditioned with stabilizer in those cases.

Because you don't seem shy around equipment, you should just resolve to do a tuneup—check and adjust valve clearances, balance throttle bodies—after you've ascertained that all hoses are in acceptable condition.

How many miles are on the bike? That will complete the picture of this critter for the readers.

[Andy FitzGibbon]

It's helpful to respondents if you give a complete picture of maintenance, procedures or conditions in your primary posts.

The plug's electrodes erode with use, eventually widening the gap and weakening the spark.

My experience tells me gasohol in the proportions sold in the US has no effect on the condition of any equipment if it is run through that equipment regularly. It effects equipment that is idle for long periods and that's why it should be conditioned with stabilizer in those cases.

Because you don't seem shy around equipment, you should just resolve to do a tuneup—check and adjust valve clearances, balance throttle bodies—after you've ascertained that all hoses are in acceptable condition.

How many miles are on the bike? That will complete the picture of this critter for the readers.

As I mentioned, 47K miles.  Sorry I didn't mention the air and fuel filters right off- checking such things has become second nature to me, but obviously nobody here knows that.

The fuel in this bike supposedly had stabilizer in it.  However, areas of the aluminum fuel pump can were corroded by the fuel, in the same way as I have seen it do so to many small engine carburetors.  I've always chalked this up to increased amounts of ethanol in gasoline, as I can't remember seeing it with near as much regularity ten or fifteen years ago.  But, perhaps it's caused by some other additive.  Anyway, the bike definitely sat unridden for a long time, as the guy got a Harley and didn't ride it for the last several years.  He claims he started it occasionally.  So, even with stabilizer, I'm not surprised to see some damage.

Plugs will be the first step.  I guess I just wanted to run the situation by other K bike riders, in case I was overlooking something major.  I want to make sure the bike will run well for a minimum of investment, before I do things like tires, ect.

Andy

[Laitch]

The fuel in this bike supposedly had stabilizer in it.    Anyway, the bike definitely sat unridden for a long time, as the guy got a Harley and didn't ride it for the last several years.  He claims he started it occasionally.  So, even with stabilizer, I'm not surprised to see some damage.

Stabilizer is only effective for 1 year. It's not embalming fluid for gasoline. :giggles

[Andy FitzGibbon]

Stabilizer is only effective for 1 year. It's not embalming fluid for gasoline. :giggles

True, that, although it's a popular belief in certain circles. Not sure when this last had fuel put in it. It was nearly empty when I brough it home.

[Andy FitzGibbon]

An update... the bike, predictably, runs better with cleaned plugs, and even better with new plugs.  Replaced the broken left hand combination switch as well.  Would have taken it out for a ride this week, if the place I ordered a new front tire from had shipped me the 100/90-18 tire I ordered, instead of the 100/90-19 motocross rear tire that they for some reason shipped instead.

We are swiftly running out of good riding days here in WV, so I'll have plenty of time to do valve adjustment and TB syncing.  I don't have a syncronizing tool, but have seen recommendations for the Morgan Carbtune.  Any suggestions are appreciated.

Thanks,
Andy

[Laitch]

I don't have a syncronizing tool, but have seen recommendations for the Morgan Carbtune.  Any suggestions are appreciated.

Carbtune is a good choice. F14Crazy made a competing style from tubes and a 2x4; Gryph uses Snapple bottles. Those seem more like Mountaineer tools that would fit in down there.  :hehehe  Here's a useful thread.

[Andy FitzGibbon]

Carbtune is a good choice. F14Crazy made a competing style from tubes and a 2x4; Gryph uses Snapple bottles. Those seem more like Mountaineer tools that would fit in down there.  :hehehe  Here's a useful thread.

I won't pretend like I haven't rigged up similar things!  But, for $100, I'll forego all the tubing, ATF, and 2x4s.  I have an R75/5 here that needs syncing as well, so it's a worthwhile investment.

Andy

[Laitch]

Where have the all bold frontierspeople gone and went to? eBay!

[Martin]

Once you have got it tuned there good little trick that seems to be only applicable to the Bricks. With the engine running and idling at 1000 RPM press the green starter button ( kid you not, it will do no damage), if the mixture is correct the revs should rise slightly. If they drop or rise significantly the mixture will need adjusting. You can do this using the lean drop method posted on this site, or beg borrow or steal an exhaust gas analyzer. After having 4 different workshops stuff it up, I  bought my own Gunson Digital Gas Analyzer cost me about $300.00 Au 19 years ago. It has now proved to be a cheap investment. The mixture is adjusted by inserting a Allen key into the hole on top of the RH front cover of the air box, it will require you to carefully removed the rubber grommet. Lube the grommet with rubber grease on replacing it, it will help fitting and it will extend it's lifespan.
Regards Martin.

[jakgieger]

Welcome to the asylum.   Looks like a good project.  My bike sat longer ...The Z hose is a common leak http://www.motobrick.com/index.php?topic=3968.0  The injectors will be suspect.  You can swap them with newer 4-hole variety  or clean them.  CHANGE BRAKE FLUID and check the splines.  Moly powder in transmission will smooth shifting.  Good Luck.

[Andy FitzGibbon]

Just a brief update. Bad weather and other projects have mostly pushed the Brick to the back burner, but I was able to get a ~50 mile ride in just after Christmas. Though it still needs work, the bike ran well, which encourages me to continue putting money into it.

The rear master cylinder is leaking, so that's the next project. Haven't disassembled yet to see if the bore is rusty or not.

Thanks for all the help so far,
Andy

[billday]

Beautiful K, congratulations on a great find.

More pictures!