R100RT Running Roughly

Hi Everyone,

I have a 1995 R100RT that started the season with a couple of issues. I've had the bike for about 10 years. It has 101,000 miles at this point with an upper end refresh at about 75,000.

The last couple of rides at the end of last season I though it was possible it wasn't running as smoothly as usual. I know I had a few stalls however they were easy to chalk up to rider error rather than mechanical.

The bike was winterized as usual. Gas tank was almost full and had Sta-bil added. Petcocks off, fuel run out, and float bowls drained.

This season when I went to start it it started and ran normally at first but at the first ride it quit after about 50 yards. I found that the fuel lines were significantly dry rotted and the tank was dry. I replaced all the fuel lines and put 2 gallons of fuel in. No leaks evident and it started and ran.

Today I started it again and rode it up the street for a shake down ride. It ran as normal at first but after about 100 yards started running roughly. Eventually it stalled once. Restarted easily but increasingly ran rougher and I had to give it more throttle to keep it running. I then noticed significant blue smoke in my mirrors so I returned home. Total ride maybe a mile. by the time I got home it would not idle and was almost unrideable.

I confirmed that there was still gas in the tank. Pulled the spark plugs, both of which appeared clean and looked the same.
After about 10 minutes I restarted it. I started and idled normally. I ran the RPM's up and down a few times and at first it revved normally. However soon it started running roughly again and would no longer idle. There was a noticeable infrequent miss at lower RPM. No blue smoke this time. With the exception of the smoke from the first time the symptoms of this start seemed to mimic what happened when I rode up the street.

Spark appears strong and even on both sides. Intake and exhaust seem clear. Oil level is full. My Dad and I checked valves and timing last year and it was running smoothly after that for the rest of the season. From what I recall we did not make significant changes at the time.

My Dad might chime in if he remembers something I forgot.

Any suggestions on where to go from here appreciated.

Jason

Have you checked your valve clearance lately? When your motor is cold you may have enough clearance for it to start and run but as the motor warms up it may be going away causing your valve(s) to remain open, not allowing compression and causing rough running or stalling. Another reason to consider this is that you were saying that before you parked it for the season you thought it was starting to run rough. Good luck finding a solution. This weather is too good not to be riding.

So you checked valves and you have spark
Have you checked timing?
When's the last time your carbs were overhauled?
Is the gas tank clean?
How about the petcock valves - you can remove the fuel line and turn on the tap and get a visual on both sides to see how the fuel is flowing - it should be a steady stream.

I think crud from deteriorated fuel lines might be messing up the carburetors. I would pull the float bowls and make sure there is no black crud floating around.

Right at the point were it stalls drop the fuel bowls and check if they are still full.

If they are not full check the copper mesh on top of the petcocks. they might be clogged with flakes of paint from the inside of the tank.

And how could a full tank be empty and you didn't smell/see a thing?

/Guenther

Gas loss

Check oil make sure not funky from possible gasoline contamination

PGlaves said:

I think crud from deteriorated fuel lines might be messing up the carburetors. I would pull the float bowls and make sure there is no black crud floating around.

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Ditto. I had similar problems with my R90S and found red jelly/slime in my carbs. I had to reline the gas tank to fix it.

Wild Guess #1: Mouse nest in air intake;
Wild Guess #2: Need new heat sink paste on ignition control unit

khittner1 said:

Wild Guess #1: Mouse nest in air intake;
Wild Guess #2: Need new heat sink paste on ignition control unit

Click to expand...

Good guess. There had been one in there briefly. I found some mouse droppings in the filter when I replaced the it while replacing the fuel lines but it looked like it moved on quickly before making a home.

Guenther said:

Right at the point were it stalls drop the fuel bowls and check if they are still full.

If they are not full check the copper mesh on top of the petcocks. they might be clogged with flakes of paint from the inside of the tank.

And how could a full tank be empty and you didn't smell/see a thing?

/Guenther

Click to expand...

That's the mystery about where the gas went. All my ideas are pure speculation and so far I haven't noticed a leak anywhere. It was stored in a detached garage and I only went in occasionally to get the snowblower over the winter so if it was leaking I never noticed it.

When I removed both petcocks the first time it wouldn't start maybe about a cup of gas was left to drain out. I didn't actually measure it but it was very little.

Thanks for the suggestions everyone. I'll got a list and I'll start going down it this week and see what I come up with.

Besides all the front-end checks you plan to do, also include checking the mufflers for nests or food storage locations. Maybe pull the mufflers and see if anything comes out. Mice like to store corn, bird seed, dog food in such places.

Check engine oil level. If your tank had gas in it before you put it in storage, it should still have had fuel. Occasionally a float will stick or 'sink' causing a leaky petcock to drain the tank into a cylinder with an open intake valve.... and transfer the fuel to the engine crank case. Your description tells me that is exactly what has happened. If this IS the case, just drain the oil, change the filter, (add new oil) and go. You haven't run it long enough to hurt anything. Go check now...

He said he had the petcocks closed. So no fuel could have escaped through the carbs. Otherwise...a possibility!

But even then he had the tank topped before so 6 gallons of gasoline would have made it into the crank case unnoticed?

It ran as normal at first but after about 100 yards started running roughly. Eventually it stalled once.

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I had this symptom once: With the SHED (gasoline evaporation limiting) installed the tank vent comes out at the front left side of the air filter box and very close to a hose. If that hose is too close it may prevent enough air to get into the tank at a wider opened throttle. If that is the case it should not show the symptom with the tank cap opened just a bit.

/Guenther

Smell the oil.

Here is the update. Today we started going down the list and checked/found the following.

1. Gas cap off to check for plugged vent: No change.

2. No evidence of contamination in float bowls, gas drained from tank, or in old fuel filters or the new ones installed with the new fuel lines.

3. Strong flow from both petcocks in the on and the reserve settings.

4. Floats both appear to function normally.

5. Oil is clean, at correct level and smells normal.

6. Carb bowels are full immediately after rough running/stalling.

7. Both mufflers are clean and clear.

8. Left petcock leaks intermittently. It only happened once but when it did it flowed as though it was completely open and could not be turned off. I'm assuming it was leaking all winter and that explains the missing gas.

9. The rough running and stalling occurs only at lower RPM's. It is consistent. Upon first starting (choke on) it starts and runs normally and will idle. Once it starts to warm up it runs roughly from idle up to about 2800 RPM. Once above 3000 RPM it smooths out. No hesitation like at lower speeds and no missing.

A casual internet search came up with petcock rebuild kits for years up to 1980. Tomorrow I'll look into it more. Any help in this direction is appreciated.

Early next week we should get a chance to take a look at the valve adjustment and a few other things. If today's details point in any particular direction we'll look into those as well.

Had a similar issue last fall and it turned out to be oil deposits in the main jet area and the idle circuit. You might want to try removing the floats and needle valve. Then you can remove the main jet parts and then remove the air mixture screw. Spray those orifices out with carb cleaner and blow (gently!) some compressed air through those passages if you have air. Make sure they are all clear and the idle screw is nice and clean. This chart shows what part of the carb is used at varying throttle openings. In your case you are having issues with the Air Screw slow jet and maybe just when the needle starts moving up the main jet.

jhorn,

thanks for answering all the questions in your complete update!

My next focus would be the idle jet. Here's why: With enricher(=choke) on, gasoline is funneled through separate openings in the carb straight to the cylinder side of the throttle plate. At low fuel consumption (=idle) it dominates over the gasoline from the idle jet and the main jet. Once the enricher is closed the idling motor depends on gasoline coming from the idle jet.

But this has nothing to do with the occasional misfires. It still does misfire, right? At which RPMs?

How long ago were the carbs checked? Diaphragm, jets, o-rings, gaskets...

/Guenther

As someone who just resurrected an 83 R100RT (among a lot of other vintage bikes), I can tell you the carbs will for sure need attention after sitting so long. My bike sat for 3 or 4 years and the carbs were in bad shape. Jets all clogged, o-rings fractured, and the diaphragms were toast. And it was put up dry.

I would (and did) replace all soft parts, including floats. Once the valves (much more critical than I ever imagined) were adjusted the bike started right up. Now I need to fine tune the timing and balance the carbs. Oh....and the rear master cylinder needed a rebuild. Had nothing to do with the bike running, but having brakes is nice. Sitting long term does nothing for rubber in contact with fluids.

After you get the carbs and the rest of the "typical" stuff gone through - there are several symptoms here that may also indicate a vacuum leak. Note that a small vacuum leak will have less effect as RPM increases.
Examine the coupling tubes and clamps between the carbs and heads, and if your carbs have vacuum measurement ports, verify that their screws (or caps) are in great shape and secure.
If your bike has the old vacuum "crossover/balance" lines, rip them off & cap the ports closed forever; while some claim no effect, they are another place where a tiny crack or pinhole in the hose will cause issues.