Reviving A -99 Tdm 850

[anda3243]

So, some time has passed and the bike has now done 70 000 kms, the motor 40 000 kms. I will write what has been done to the bike, and what failures have hapened.

I need an outside view on this.

 

During the summer of 2012 a trip was undertaken. Prior this trip some uppgrades and service was done. Most of it is writen above.

 

I cleaned the air filter, and discovered that there is a gap under the filtre element so air can go past the flitre. There are 6 to 7 mm under the filter where air can go past :o. I fixed this with a sponge under the filter element, so all air must pass trough the filter.

 

This of course changes the resistance for the airflow, and therefore the fuel/air mixture. :istupid:

 

Here is a picture of air filter on my bike. It is a washable air filter.



 

The bike run a little differently, but still had power. Over 5500 rpm or full throtle it run a but rough, but i do not use full throttle to often.

I drove with this fix some weeks with no problems, and then headed out on my trip.

 

Outside Kiev the bike started to have problems, at low rpms only running on one cylinder, and runnig quite rough on higher rpms. It was realy hard to strart. This was a difficult and memorable part in our trip. :badgerrock:

 

When strarting it cold I needed to remove the sparkplugs and clean them, put them back and to try again. And repeat this until the bike started.

I suspected the ignition coils and HT leads, these were checked. Then I suspected the carbs, wich were also checked and ok. Cables and spark plug caps were changed, with no noticable result.

The bike was getting worse and worse, nothing I did gave any effect. Now it would not idle, it could onlu be run if the rpms were over 2500.

The tank, air filter and carbs were taken off several times. I did not know what else to doo. I was getting desperate.

All work on the bike was done outside with the tools we brought with us. Sometimes it was raining. :badgerrock:

 

Eventualy we made it to Slovakia where we knew some people and could get help. Bike was brought to a localy well known bike mechanic. He was a bit of a original. He was a little hesitant on taking this on since the motor was not stock, but if I stayed and could answer questions he had, he would attempt to fix the bike.

 

So I was sitting on a chair, while he was fixing with the bike.

 

There compression ratio was measured. 8:1 resp 11,5:1 !!!! WTF, The comnpression ratios was 12:1 on both cylinders when the bike was bought.

Then he declared that the spark plugs are damaged, and must be changed. The spark plugs were the only part that I did not have spare.

Ignition coils, the leads and caps were measured. Those were ok.

 

At this point we found out that the bike was running much to rich. Wich caused the spark plugs to fail and create carbon depisits inside the combustion chamber. The idea was that the carbo deposits were affecting the function of piston rings and maybe valves, wich loveres the compression ratio.

The reason the fuel mixture was too rich was the restricted air filter. The previous owners must have put this filter in and then changed the jetting to get the bike to run. Must have been way to lean with air bypassing the filter.

 

To get the compression back he hed a secret solution that should solve the carbon deposits. He did not want to tell what it was, my guess is diesel and fotogen and maybee brake fluid. This solution was poured down the cylinders and left owernight.

New spark plugs were purchased and put in.

Air filter was washed out to give less resistance.

 

after 20 hours with the secret solution, the compression ratios was 11:1 and 12:1 It worked wonders.  :banana:    He still did not tell what he was using, trade secret I guess.

And with new spark plugs and the washed air filter the bike much better. It could idle and run much much smother.

 

After this I borrowed a garage and could perform a valve check. Valves were within spec. So the low compression was probably due to the carbon deposits and not a mechanical failure.

 

To sumerize this far. The fuel mixture was to rich due to the sponge put in the air filter. The rich mixture made the spark plugs to fail and the carbon deposits to build up. The carbon deposits made the piston rings to fail.

 

I decided to continue the trip despite this mishap. In Budapest I changed the main jets to size 150, the ones that were fitted were way to big. The stock size is 142 I think. Spare spark plugs were bought. Air filter was oiled up again.

After this the bike run well. I wisited Romania, Bulgaria, Turkey, Greece, Serbija, and back to Sweden. And did some riding in Sweden during the autumn. I had no problems with the bike at all.

 

 

This summer a trip to Norway was undertaken. And the bike was again prepeared.

 

I changed the spark plugs and noticed that they are quite white. The bike is running lean.

I kept the main jets. I liftet the needle up one notch and opened up the air screw 2,75 revolutions from bottom. After this the bike had much more power from 4000 to 5000 rpm-

Valves were checked again and was within spec.

 

In Norway, after running in rain and slowly driving down a steep descent using motor brake an low revs the bike started to run rough again. The same simptoms as last summer. Running on one cylinder and running a bit rough on higher rpms. This time the bike could idle, but was difficult to rev up.

My idea was that the mixture at low rpms/idle is ti rich wich causes the spark plugs to fail.

The spark plugs were changed, and air mixture screws set to 2 revolutuion from bottom. Bike run better, but not good. It still wanted to run on 1 cylinder. After some driving it got better.

After driving one hour at 100+ km/h the bike runns good on both cylinders. It idles nicely and has plenty of power.

After idling a minute or so or driving in slow trafic it starts running on 1 cylinder. When giving gas it starts running on both cylinders, and runs good with plenty of power. But maybe not as good as it run before the failiure.

 

My theory is that carbon buildup, possibly on the piston rings gives this effect.

 

My questions to the forum is.

 

What can be done to make it run good?

Is my theory about carbon deposit buildup plausible?

Has someone had similar problems when changing air filters/mufflers and/or rejetting the bike?

Have someone experienced spark plugs to fail? Should a different heat rating be chosen?

Have anyone used any carbon deposit remover? I have read about a product called seafoam, but I am a bit sceptical.

Or is the dissasembling and manual cleaning of pistons, valves and combustion chamber the correct way to do it.

 

Next thing I am planing to do is inspecting the spark plugs and then measuring the compression.