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Moped Riders Association • View topic - Honda Express NX50 - need some help

Honda Express NX50 - need some help

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Honda Express NX50 - need some help

Postby Breaze » Thu Nov 20, 2008 7:08 pm

Just aquired 1981 Honda Express SR NX50 as a winter project having no experience at all in this area and could use some help. I did what I could reading the forums and using the on-line manuals for similar Expresses but I need some help specific to the NX50. I got the bike running by reading forums and doing all the basics:

- cleaned carburetor
- cleaned muffler
- changed transmission oil

It starts easily, runs ok, then starts to have problems when warmed up and won't re-start when hot - sounds like the auto choke/bystarter concerns I've read about.

Three problem areas I need help with:

1) Petcock: The upper fuel line flows freely even when the engine is not running and creating a vacuum through the bottom port

2) Carburetor: Last time I started and ran the bike, after turning it off, the fuel flooded through the carb and out (slow drip) as if the float and float needle weren't sealing off the fuel intake - not sure if this has to do with the petcock problem - seems like the float should shut down the flow anyway

3) Before doing too much trouble shooting I wanted to make sure I had the main lines mapped correctly (weren't all connected originally)

Line 1: runs from port on left side (bike left) of the intake manifold to the port on the left side of the control box (I'm assuming the auto choke control box feeds thru where it is attached to the cylinder head so not sure what this line does)
Line 2: runs from left side port on carb to middle port on control box (maybe feeds fuel mix to auto choke from carb)
Line 3: runs from right side port on control box to bystarter assembly (maybe feeds air to auto choke)
Line 4: runs from top port on carb to bystarter assembly (unsure but must feed air to carb to allow output from carb thru line 2)
Line 6: runs from upper petcock port to fuel intake of carb
There was another disconnected line which I am guessing runs from the bottom petcock port to the right side port on the intake manifold to create the vacuum to activate fuel line - it was unmarked - maybe line 5

Sorry to write a book - didn't realize I would get into this project the way I have. Any help would be appreciated.
Breaze
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Location: Atlanta, GA

re: Honda Express NX50 - need some help

Postby Breaze » Sat Nov 22, 2008 8:30 am

Quick (maybe not so quick) update- I believe I have verified the mapping of the lines, although I am still not sure if the #1 line feeds the mix into the manifold or is just used to power/activate the mechanism by supplying the vacuum (suggested by Sean L. in another topic) and the feed is directly to the cylnder. I took the carburetor apart, cleaned again, and it is not leaking anymore - must have been sticking. I'm not worrying about the petcock - ordered a screen/filter for it and will put it in today and check out the vacuum valve workings. If it still flows freely afterwards, it shouldn't affect the performance - can find way to shut off later.

The next things on my list to address the lack of power and uneven acceleration:

1) I'm looking for a compression tester to see if I need new rings, head gasket, etc.

2) Probably need to check for vacuum leaks

3) Need to set carburetor mix and test the autochoke/bystarter mechanism - in order to do these items I plan to cap off (using vacuum port caps) the entire autochoke/bystarter assembly, start and warm up the engine, and then attempt to set the carburetor mix properly. If I can get it running well this way, I'll know I have good compression and no big vacuum leaks. Then I'll deal with the mechanism.

Anyone know the recommended starting point of the mix and throttle screws? When I got the bike they were set:

throttle (upper) screw: about 1 7/8 turns out
mix (lower) screw: about 1 1/8 out
Breaze
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Posts: 30
Joined: Thu Nov 20, 2008 12:50 pm
Location: Atlanta, GA

re: Honda Express NX50 - need some help

Postby Breaze » Sat Nov 22, 2008 4:12 pm

Latest - checked compression - almost 120 so I should be ok.

Capped off the autochoke/bystarter mechanism but still running weak - accelerates slow and choppy. Carburetor adjustments seem erratic at best. Would like to rule out the carb but just don't know enough - would really like to know factory/manual starting adjustments for screws.

One thing, when cleaning, I came up with a small silver washer that had dropped from somewhere - I checked the parts fiche and noticed that there seemed to be a washer and a gasket maybe on the air mix screw. That is where I used the washer but didn't seem to have the gasket. I am planning to order the gasket kit thru service Honda and see what comes with it.

Also am not using stock air filter element (using B&S sponge filter element) - ordering one to see if that makes a difference.

I'm really hesitant to get into the transmission because the weak acceleration and choppy running occur even with the rear wheel elevated.

Any suggestions out there?
Breaze
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Posts: 30
Joined: Thu Nov 20, 2008 12:50 pm
Location: Atlanta, GA

re: Honda Express NX50 - need some help

Postby Breaze » Sun Nov 23, 2008 2:55 pm

Breaze
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Joined: Thu Nov 20, 2008 12:50 pm
Location: Atlanta, GA

re: Honda Express NX50 - need some help

Postby John » Sun Nov 23, 2008 3:32 pm

John

"Plan your life like you will live forever, and live your life like you will die the next day!"
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re: Honda Express NX50 - need some help

Postby Breaze » Mon Nov 24, 2008 9:24 am

Breaze
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Posts: 30
Joined: Thu Nov 20, 2008 12:50 pm
Location: Atlanta, GA

re: Honda Express NX50 - need some help

Postby John » Mon Nov 24, 2008 9:37 am

John

"Plan your life like you will live forever, and live your life like you will die the next day!"
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re: Honda Express NX50 - need some help

Postby Breaze » Mon Nov 24, 2008 8:38 pm

Breaze
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Posts: 30
Joined: Thu Nov 20, 2008 12:50 pm
Location: Atlanta, GA

re: Honda Express NX50 - need some help

Postby Breaze » Tue Nov 25, 2008 8:30 pm

Breaze
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Posts: 30
Joined: Thu Nov 20, 2008 12:50 pm
Location: Atlanta, GA

re: Honda Express NX50 - need some help

Postby John » Wed Nov 26, 2008 6:19 am

John

"Plan your life like you will live forever, and live your life like you will die the next day!"
User avatar
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Posts: 4445
Joined: Tue Nov 18, 2003 9:52 pm
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re: Honda Express NX50 - need some help

Postby Breaze » Wed Nov 26, 2008 8:38 am

Breaze
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Posts: 30
Joined: Thu Nov 20, 2008 12:50 pm
Location: Atlanta, GA

re: Honda Express NX50 - need some help

Postby John » Wed Nov 26, 2008 8:47 am

John

"Plan your life like you will live forever, and live your life like you will die the next day!"
User avatar
John
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Posts: 4445
Joined: Tue Nov 18, 2003 9:52 pm
Location: Caledonia, Ontario, Canada

re: Honda Express NX50 - need some help

Postby Breaze » Thu Nov 27, 2008 11:15 am

Latest:

I was able to straighten the front forks - finally a positive (essentially used brute force)

Turned the reeds over as suggested, put everything together, checked compression, and still only 120

Used PBblaster as suggested and was able to remove cylinder. Piston and rings look good visually but I don't have micrometer or ID bore gage to perform measurements. Should I just replace rings (cheap) or get the equipment?

One comment exposing my ignorance again - I was running an oil/mix fuel along with the injected oil (until last compression test) and wondering why the plug was getting so oily. Would that effect compression?

OK, after compression woes solved, I'll be inspecting the transimission and the drive (clutch, etc.). I'm hoping everything will run well and I can get by just doing the specified maintenance.
Breaze
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Joined: Thu Nov 20, 2008 12:50 pm
Location: Atlanta, GA


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