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Old 08-11-2011, 03:11 PM   #4411
mito-nx
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Location: The Netherlands
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What kind of compression do you guys have?
I am doing some work on my 1988 MD21 engine and found out that I only have 175PSI.
When I put some oil on top of the piston I get 205PSI still to low.
So my piston rings are worn out and the valves do not shut properly.
But my engine runs great, it has a top speed of 140km/h and has more power than Original.
Has someone here ever measured there compression?
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Old 08-11-2011, 04:01 PM   #4412
larry31
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Carb. problem

Amishmotorscoot

Could it be you have air leaking in the boots going in and out of carb.?

Try tightening the clamping screws on the boots. Also check the air filter for dirt and blockage.
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Old 08-11-2011, 06:28 PM   #4413
RollingJ
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There is a high probability I am full of crap about the Shinko 16" rear tire. I thought I had tried the 244 while I still was running the 16" rim, but it was after the swap to a 17" rim.

You can quote me on that.
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Old 08-11-2011, 06:32 PM   #4414
Grestil
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Quote:
Originally Posted by amishmotorscoot View Post
My one troubleshooting act was to spray starting fluid on the carb while the choke was open- immediately the hesitation and stutter went away -
If I were you, I would repeat this test with wd-40. Starting fluid is highly volatile and vaporizes too quickly for this test. When you apply starting fluid to any part of the intake, it will vaporize very quickly and if there is a vacuum leak close to where you spray it the vapors will be sucked into the intake through the leak making it nearly impossible to pinpoint. Penetrating oil won't vaporize nearly as fast and it is good at "finding" leaks because it will temporarily seal the leak due to its viscosity. Use the little red tube to apply a small amount right where the intake boot mates with the head. Just a little dab will do. In my experience it's almost always the o-ring in the boot and not the boot itself. I am assuming that your boot shows no visible cracking or damage. If there is a leak and it is small, the engine will respond. If the leak is large, the penetrating oil will be injested and burned producing light smoke and funny smells. Keep in mind that the object of this test is to use light oil to temporarily seal the leak, not to provide the engine with another fuel source such as starting fluid.
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Old 08-12-2011, 12:09 AM   #4415
az2002
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Quote:
Originally Posted by mito-nx View Post
What kind of compression do you guys have?
I am doing some work on my 1988 MD21 engine and found out that I only have 175PSI.
When I put some oil on top of the piston I get 205PSI still to low.
So my piston rings are worn out and the valves do not shut properly.
But my engine runs great, it has a top speed of 140km/h and has more power than Original.
Has someone here ever measured there compression?

13 bar cold engine, 14 bar hot, 15 with oil, 16+-1 in service manual. >67500km
Common gauges have very poor accuracy, they are for cars engines. If you have no compression at all, it is a problem.

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Old 08-12-2011, 06:24 AM   #4416
mito-nx
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Those pressures sound okay, But they are all 1bar lower with me.
But as writen over here I do not know accuracy of the guages and yes I modified one ment for car.
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Old 08-12-2011, 09:37 AM   #4417
amishmotorscoot
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Larry31 and Grestil,
thanks for your feedback, I checked the boot clamps and they are tight, when I removed the air filter (it is a bit grubby) there was no improvement in poor running. I applied WD40 as suggested but there was no change, I then used your suggestion to apply small squirts strategically - I very carefully used the red tube and sprayed tiny amounts of starter fluid to sections of the carb- when applied to the boots there was no change, the only place I sprayed fluid that impacted how it ran was when I applied the fluid to the black cover at the top of the carb - might this indicate a poor gasket seal? Any other place I applied either WD40 or starting fluid caused no change-perhaps a gasket kit is in order?
Thanks much for pointing me in a productive direction in sorting this out.

BTW there is a 1989 listed here in Central Oregon,

http://bend.craigslist.org/mcy/2542527397.html

regards,
AMS
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Old 08-12-2011, 01:57 PM   #4418
amishmotorscoot
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carb issue ID'd

found the carb issue: while poking around, tightening and checking I noticed one of the screws holding the black plastic cover on the top of the carb was loose, after removing the carb from the bike I discovered that the screw was more than loose, the threads in the hole were stripped. I just cleaned, dried and filled the hole with JB Weld and hope drilling and tapping a new set of threads will do the fix -
anyway - thanks for the troubleshooting helps

regards,
AMS
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Old 08-12-2011, 05:38 PM   #4419
Grestil
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I'm glad you found your problem! I have put alot of time in tuning the carb on my NX and I'm only too happy to help others do the same.



Quote:
Originally Posted by amishmotorscoot View Post
I just cleaned, dried and filled the hole with JB Weld and hope drilling and tapping a new set of threads will do the fix -AMS
I have heard of this being done but have never tried it myself. Let us know how it works out!
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Old 08-13-2011, 07:54 AM   #4420
amishmotorscoot
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I have heard of this being done but have never tried it myself. Let us know how it works out![/QUOTE]

I've never done it either! but on paper it's a sound process - I'm away from the bike for a bit, but when I get back to it and finish the job I'll let you know how it went-
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Old 08-13-2011, 12:55 PM   #4421
larry31
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Carb. threads stripped

Amishmotorscoot

They make Helicoils to repair stripped threads. A new hole is drilled and a small coil is installed to make new threads. I haven't tried to do it but it's a common repair for stripped threads.

Check with your local auto parts shop or maybe a local machine shop.
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Old 08-13-2011, 02:46 PM   #4422
007monkey
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Thinning the herd

Sold.
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007monkey screwed with this post 08-15-2011 at 11:47 AM
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Old 08-13-2011, 03:28 PM   #4423
Velocipede
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CDI Repair

Help,can anyone someone save me a whole lot of time and give me the name and phone # for the guy in Eastern Canada who does the CDI repairs.I know its in this thread somewhere.

Thanks John
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Old 08-13-2011, 04:14 PM   #4424
007monkey
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cdi repair

His name on the board is techforlife. Dont have his number though.
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Old 08-13-2011, 04:41 PM   #4425
Velocipede
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CDI Repair

Quote:
Originally Posted by 007monkey View Post
His name on the board is techforlife. Dont have his number though.
Thanks 007,thats all I need. John
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