engine cranks, no start after 2 min riding

Hi everyone,

I recently replaced a cylinder stud on my 1977 R100RS, got the bike to start, but noticed that the throttle response was laggy. I also noticed it was struggling to idle and at a stop light, the engine died and it hasn't been able to start since. This is after riding it for 2 minutes. I checked the battery and somehow it was dead. It's a new battery as the PO replaced it before I purchased the bike in May. It also wasn't able to charge on a slow charger.

The bike sat for a week or two while waiting for the part and in that time we got a lot of rain. I also replaced the valve cover gasket, purchased a new Panasonic battery, tightened the bolt from the airbox that goes down to the tranny (as it leaked a bit) and cleaned the carbs . I re-checked the points, valve clearances, spark and throttle cable play. The engine cranks but does not start.

Some other things I noticed: a brown liquid coming from the coils and dripped down to the engine case, nothing excessive. Could water have gotten in the tank and spoiled the gas? I'm stumped as the bike was working fine before.

Brown liquid

Yes, water could have gotten into the gas.

Was the bike outside in the rain while it was sitting? I am going to proceed with the assumption it was sitting outside because you brought up the rain. Water can't get into a gas tank unless the gas station has water in the gas or as I assume, the bike sat in the rain.
I myself find water getting into the tank during rain pretty slim. Unfortunately, I have gotten water mixed with gas at gas station pumps.

So one of the possible sources of brown liquid may be from the rain. In the gas tank there is the filler neck. The gas cap fit flush with the top of the tank. In the recess around the filler neck, is a catch basin with a drain in it. One purpose is to catch water and drain it via a tube down onto the ground in front of the swing arm. It also catches any over flow of gas and directs it down the tube onto the ground rather than on to the top of the engine. If the tube is not there to direct the flow of water or gas, there is a chance the water from a rain storm could dribble onto the top of the engine. Now, forgive me, I don't have my bikes in the office with me so If the drain without the tube does not dribble on to the coils, don't beat me up. That is a possibility of the brown liquid.

Pull the float bowls off of the carbs, if there is water in the gas for sure it will show up in the bottom of the bowls. If there is water, put the petcocks into the reserve position and drain into something you can see into to check for further water.

I have never cut a coil apart nor seen one broken or split, so I am taking a wild guess the brown liquid might be from inside a bad coil. Again for the rest of the responders, don't beat me up on this, I really don't know what is inside a coil other than windings.

Enough water could be in the system to cause a no run problem.

Is it a totally no run at all, cranks over and there is nothing? Or does it cough and sputter but won't start?

One thing I say frequently is always assume the last thing you did to the bike might be the first thing causing the new problem. Check your work on the points. I personally hate points and got rid of them on my 78 as fast as I could. Closed points, won't let the coils charge to produce spark. On your bike, assuming it has no added gizmos, to the ignition system, you should be able to pull a spark plug out crank the engine over with the plug grounded and see if there is in fact a spark and if it is bright white or weak.

I know others will chime in with things I may have missed or may be wrong about. Meanwhile, check your work again. Cheers. St.

Since the cylinder was off, a recheck of the valve regulation may be prudent.

Doug

On your brown liquid issue, if you still have the under tank brake cylinder check it for leaks, it may me wicking back enough to drip on the coils. I have had the similar event on my R100S. Just a thought.

Step one is to remove the tank and identify the source of the liquid. It may just be rusty water but it could be brake fluid. If water identify the location where it was captured and held hostage.

So STEVENRANKIN was right about the brown liquid. There isn't a tube from the drainpipe so that explains the brown liquid on top of the case. What problems could arise if water got into the case?

The engine cranks but doesn't cough or sputter. The sparks look a bit weak/white and I rechecked the points and inspected them further and it turns out they aren't in great condition either.

In the process of removing the tank, I also found white gunk in the fuel filters.


I checked all this stuff maybe a month before all of this went down, and it was running fine. I guess these bikes really need to be ridden. I'll probably be switching over to an electronic ignition and get new Bosch sparks are mine are NGK. Will keep you posted

PS I tried uploading photos but the uploader doesn't work.

EDIT: I was told that the brown liquid is actually insulating fluid in the coils

jerko said:

PS I tried uploading photos but the uploader doesn't work.

Click to expand...

Can you reduce the size of the photos so they are around 1Mb big? I think you're photos are too big...they won't upload when too big.

water in the case

To be honest, even if water gets on top of the engine from the gas cap catch drain. Not much is going to happen. I mean, riding in a hard rain, the engine is going to get wet. The main purpose of the drain under the flush gas cap is to catch any overflow of gasoline and to direct it via the tube and a hose down onto the ground rather than have it spill or cover the tank. The hose that is missing, keeps the gas that overflows from landing on a possibly hot engine and perhaps causing a fire. Water from a rain storm can also collect in this Catch and drain down to the top of the engine if the hose is missing at the bottom of the tank.

One point brought up was the master cylinder leaking, I have seen this happen but it shouldn't cause a problem with the bike starting and running unless I really leaks bad into the starter relay which is under the tank.

I see the Edit, the coils contain a brown insulating fluid. I know older transformers used to have oil in them, as I said, I have never cracked open or cut a coil open so I don't know for sure if there is fluid in them. If you have found information that there in fact is brown liquid in them then, you may well have a bad coil. That could cause the no start problem.

Plugged fuel filters will also cause a problem.

To me, it sounds like you are on the right track with replacing and rechecking your points. Before you invest in an electronic system to solve your problem save a few bucks and work with a new set of points to see if the bike starts running. Check the coils for something weird like cracks or things.

New fuel filters will help.

Once you get the problem solved, then, you can ride until winter decide what electronic replacement system you want to use and install it then. I have an early Boyer system on my 78 RS, So far, it has worked flawlessly and I have never had to set points or timing since it was installed. Two less things to mess with at tune up time.

Personally if I were to install a system now on the RS, I would go for the Alpha system sold by Motorrad Electrik. There are other systems I might be interested in if the Boyer unit I am using now dies. Back when it was installed, there was no other choices.

You will find the problem soon. St.

jerko said:

In the process of removing the tank, I also found white gunk in the fuel filters.

Click to expand...

There should be no “white gunk in the fuel filters”. Fuel, even contaminated with water, isn’t white. Without seeing what you are, the possible sources of “white gunk” that come to mind in a fuel system would be a failing Kreem relining effort, or accumulated “lead substitute” fuel additive. If either are what it is, you won’t get the bike to run well for long without rectifying that situation.

A good point

There should be no “white gunk in the fuel filters”. Fuel, even contaminated with water, isn’t white. Without seeing what you are, the possible sources of “white gunk” that come to mind in a fuel system would be a failing Kreem relining effort, or accumulated “lead substitute” fuel additive. If either are what it is, you won’t get the bike to run well for long without rectifying that situation.


A very good point, if there is no fuel, no go. I said to change the filters but this is a very good catch as well. Most people don't use lead additives, they are not needed, however, if the bike is old enough and in a shape where a gas tank reline had to be done, this is a very possible problem. fuel taps plugged with a failing tank liner is just another no go item.

As the original owner of the bike, you know the history. If you are the second or so owner, well, welcome to the large club of buying used and the possible heartaches it can bring.

I just caught something you said about a leaking bolt in the tranny. If, any water got in, change the gear oil fast! In fact, even if you suspect water got into the tranny via that loose bolt, changed the gear oil. My friend's shop just finished rebuilding a tranny that had water in it. It was not pretty. Another source for water in the gearbox is a bad speedometer cable cap on the tranny might be a good idea to check it.

Having purchased a very pretty looking used bike myself and finding the beauty was only skin deep, I can safely say, it can take a lot of time to sort out age related problems, Previous owner sins, to get the bike running the way it should. Sometimes the cost of this is far more than the bike is worth. the practicality of the cost of repairs is up to you as the current owner and how much you want to spend or invest. Kudos for doing the work yourself, and sorry I can't give a hand.

Once things are sorted, airheads are a joy to ride and own. Not trouble or maintenance free mind you but a joy to own. A long winded note to keep you positive. cheers, St.