Honda NU50 NU50M Urban Express Starting Problems

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Honda NU50 NU50M Urban Express Starting Problems

Postby adamsjd » Tue Apr 27, 2010 1:35 pm

I recently bought a 1982 NU50M and cannot get it to start.

Compression: Good ~ 180psi
Spark: Good ~ New plug
Bystarter: Clean and working
Electrical: All working
Reeds: Cosmetically good looking
No carbon buildups on head/cylinder ports
Carburetor: All ports/jets cleaned

Im fairly experienced with two cycle engines but i cant figure this one out. I was able to get it to start by putting gas strait into the choke tube that goes from the choke control box to the intake tube. It runs smooth until that gas is gone. The throttle/carb dont have any effect on the way it runs in any way. It seems like the carb is doing nothing or that there is not enough vaccum pulling air and gas into the intake. When I kick it or get it running off the choke gas I can put my hand over the carb air-inlet and there is also effect on the way it runs. There seems to be very little if any suction at the intake of the carburetor. If there a gasket or a seal somewhere else in the engine that is allowing air into the cylinder while bypassing the carb all together?

If anyone has any ideas please let me know. Thank you.
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re: Honda NU50 NU50M Urban Express Starting Problems

Postby adamsjd » Wed Apr 28, 2010 7:38 am

Im starting to think that the compression may not be so good. I couldonly get the 180psi after the engine went through 10-12 cycles. It seems to me the pressure buildup should be much faster. Also, The 180psi is only with the muffle off. as soon as I put the muffler on the highest i can get is 140-150psi and it wont fire at all. Again, this is after going through 10-12 cycles. Does this sound like the signs of bad rings? I think that is giong to be my next thing to attack.
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re: Honda NU50 NU50M Urban Express Starting Problems

Postby supercub » Thu Apr 29, 2010 1:21 pm

Does it run without the muffler? Is it clogged?
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re: Honda NU50 NU50M Urban Express Starting Problems

Postby adamsjd » Fri Apr 30, 2010 11:57 am

we have gotten it to run a little with the muffler on. however, just like before it only works when gas is put strait into the intake. as far as i can tell the muffler is good. There is nothing rattling around and i can blow right through it without a problem. We should be getting the new rings today or tomorrow so i will be sure to update the results... if anyone can think of anything else i can try let me know. Thanks :)
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re: Honda NU50 NU50M Urban Express Starting Problems

Postby supercub » Fri Apr 30, 2010 2:42 pm

Trial and error.
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re: Honda NU50 NU50M Urban Express Starting Problems

Postby adamsjd » Tue May 04, 2010 12:07 pm

I think I may have solved it....

The crankshaft bearing on the tranny side is shot. The seal is also shot which is letting airflow in through the crankcase through the bearing. Hopefully this will solve the lack of vacuum problem. Ill throw a note up here when i finish it all up if it solves the problem.

Thanks for the responses so far.
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re: Honda NU50 NU50M Urban Express Starting Problems

Postby adamsjd » Wed May 26, 2010 4:03 pm

Solved.

It was the crankshaft bearing. After a long time and a complete rebuild of the engine it is up and running. the lack of a seal on the crankshaft was allowign the vacuum to be pulled from the side case and eliminating the vacuum through the carb.

Now it just needs a little bit of tuning and it will be good as new.
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