j_freak

Member
Feb 7, 2004
169
0
After I got my 1975 Honda MR175 running, it ran great and had a lot more power than it used to. (new used piston and cylinder) Well, after about an hour's worth of riding, I stopped, put it in neutral, and let it idle for 30 seconds or so while I adjusted the preload on the shocks. As soon as I started riding again, I realized something was wrong. It now has less power than it did and sounds different. I parked it and pulled the pipe off to look in at the piston. It looks fine, compression is the same, so I figure it didn't sieze. Next I took off the sidecover to check the flywheel (for those of you who haven't heard, I had to lock-tite a chunk of the crankshaft back into place, right next to the woodruff key.) and it looked ok, though I did not pull it off to really check it carefully

I figure what must have happened is that the flywheel shifted slightly on the crankshaft, changing the timing. (I think that would retard it slightly, but I'm not totally sure) The bike idles fine, though with slightly more piston noise. (very slight) When accellerating, the bike sounds and acts normal at low rpms. when the revs start getting up there (it doesn't have a tach,but I'd guess 3000 rpms and higher) it starts sounding really crappy. Instead of revving smoothly to a nice "scream" sound, it has a dead spot as far as power goes, and I can hear a loud(er) sound from the back of the muffler every time the piston fires. basically it just sounds rough. It sounds a lot better (almost normal) when under a heavy load, like accellerating in 3rd and 4th.

Is this a timing problem, or should I look elsewhere?
 

elf

Member
Jun 7, 2003
695
0
If your timing retarded it would have less power throughout the rpm range. Pay attention to throttle position. if it runs good at idle and wide open but not at half throttle you might need to lean out your needle. Try raising the clip one notch.
 

j_freak

Member
Feb 7, 2004
169
0
I thought of that, but if it's running too lean then why would this happen all the sudden?

It does have less power throughout the rpm range, it's just not as noticeable at low rpms, probably because the bike has always had a ton of power at low rpms, so the loss is not as noticeable
 

elf

Member
Jun 7, 2003
695
0
I guess I didnt quite understand your original post. I think you should make sure your timing is good first, take off your flywheel see if your repair is holding up.
 

j_freak

Member
Feb 7, 2004
169
0
The timing is dead on. I ran it a little, and the plug isn't firing every time at high rpms. I figured I had better change the plug (duh) so I bought some more plugs, got them home, and discovered that they're the wrong size. They're NGK BR8ES instead of B8ES...

I tried raising the needle up one (to the last spot), and it made the problem worse.

At this point I would guess it's either the plug or the points. When I was checking the timing, I noticed that the points were arcing a lot. I sure hope it's the plug, because it'll take me at least a month to find someone who has a set of NOS points for this bike.
 

elf

Member
Jun 7, 2003
695
0
Those two plugs are the same the R stands for resistor. You can litely sand the contacts on your points to make them work better. check the point gap, if the point gap is to big it can cause misfire at higher rpms.
 

j_freak

Member
Feb 7, 2004
169
0
The BR8ES is slightly less than 1/16 of an inch shorter than the B8ES.

I'll check the point gap. I just cleaned the points a few days ago, but I'll do it again.
 

j_freak

Member
Feb 7, 2004
169
0
oops, turns out the plugs my brother bough that were supposed to just be one step hotter are also a little longer. The plugs I bought are the right size.

Put a new plug in, it ran like a scared rabbit for a minute, then started acting funny, then ran great, etc.

Decided I had better check the carb, pulled the float bowl off, and guess what was in there? About a teaspoon of water. had to clean the carb and drain the gas tank, haven't gotten a chance to ride it yet, but I'm 99.9999999% sure that was the problem
 

elf

Member
Jun 7, 2003
695
0
Glad to see you figured it out. I was running out of ideas. Its been about 20 years since I worked on a motor with points.
 

j_freak

Member
Feb 7, 2004
169
0
Boy, you're really missing out. Just think, if you had bikes with points for those 20 years, you could spend about 5 days out of those 20 years filing and replacing the points :eek:

Oh well, at least they're cheaper to fix and replace than cdi's. Thanks for your help.
 


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