Suzuki DT100, compression low

viktor_89

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May 17, 2011
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Hi,

I recently bought a Suzuki DT100 and I felt it was quite weak, so I tried to measure the compression on it. The result for all four cylinders were 8, 8, 7 and 5 bar. So I suppose that explains the weak engine.
What do you think, is it worth trying to repair it? I suppose the error causes can be piston rings or cylinders most likely? I can not feel any air leakage around the cylinder head sealings..

Thanks in advance for advice

/Viktor
 

99yam40

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Sep 7, 2008
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I would pull the plugs and look in to the cylinders to see if scoring can be seen.

if no scoring then do a deep de carboning.
rings maybe stuck with carbon
 

viktor_89

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May 17, 2011
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I would pull the plugs and look in to the cylinders to see if scoring can be seen.

if no scoring then do a deep de carboning.
rings maybe stuck with carbon


Thaks for answer.. I tried to look into the culinders but was really hard to see anything without the piston. I also tried to put some 2-stroke oil into the cylinder and measured compression again after that. The compression increased temporarly by ~0.6 bar.

Deep de carboning, do you mean disassemble and clean or using any chemical through plug holes?
 

ondarvr

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Apr 6, 2005
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Depending on the year, there may be very few parts available for it, so if a de-carb doesn't help you may be out of luck.

​A de-carb is running a product in the fuel that's formulated to remove carbon, you should be able to buy something locally at the auto parts store.
 

rjcamel2355

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Apr 22, 2015
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221
One cylinder is a little low (5bar), do a decarb on the engine, 3/4Gallon of gas, 1 can of seafoam or another combustion chamber cleaner, ringfree etc, and 3.2OZ of oil. Mix it in a gallon junk, put your fuel tank hose into this container and run the engine off this mix, run 1/2 of mix through engine, shut it off, and let sit at least 15 mins, then take it to the lake and run it. Or run it on the muffs or in a tank at high idle. Repeat with other 1/2 of mix. That should clean it up if it's a carbon issue.
 

viktor_89

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May 17, 2011
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Today I tried a decarb with seafoam, but unfortunately no compression improvements :/ Now I am thinking about disassemblying it to see the condition, starting with removing cylinder head to see condition of cylinder walls.

To be continued..
 

viktor_89

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May 17, 2011
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No Title

Today I disassembled the cylinder head in order to see the condition of the cylinder and gasket. (see pictures). According to me it looked surprisingly good, no obvious scoring etc. With that in mind, do you think it is reasonable that the piston rings should be so much more worn than in the other cylinders, resulting in such significantly lower compression? (I'm not so interested in disassemble the cylinder)
What would you think is next step? I will for sure buy a new gasket. Were also thinking about disassemble carburetors and clean them. Can carburetors affect compression?

Thanks
/Viktor
 

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ondarvr

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Carbs have nothing to do with compression, but cleaning them isn't a bad idea.

​You never mentioned the year of the motor or if parts are available. If there are no parts available, or you don't want to work on it, then just run until it stops, that might be in 10 days or 10 years.
 

viktor_89

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May 17, 2011
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The engine is from 1995, and it is possible to get spare parts for it, but are quite expensive. I don't want to put too much money on the engine, but I want to understand the reason for the low compression on especially one cylinder. Looking on the gasket, there is a wet part in bottom, can that be a potential leakage?
 
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