Honda 1972 SL125 Project

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milesoffun
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Honda 1972 SL125 Project

Post #1 by milesoffun » Thu Dec 26, 2019 5:28 pm

Hi folks - I'm working on this to ride with my grandson on some trails but I've been stumped for a month or so. I thought I would at least run it by the mechanics on this site!

Background: the bike was locked up when I got it but I got the crank moving again by pouring acetone and transmission fluid in the crankcase after taking the cylinder off and realizing the head was not the problem.

Put new rings in and put her back together and back in the bike. Decent compression - about 125 or higher. Timing was interesting since I had not worked on "points" bike in while - but finally got it.

She fires on the first kick and runs but will not take throttle. As soon as you give it the least bit of throttle, she dies.

I've been searching on the internet a good bit and of course I'm thinking carb and floats and such but no matter what I try, she will not take throttle. She will idle pretty good, maybe a little rough but not bad at all. I have the service manuals but they have not been much help to me at this point.

I've set the float many times with no change. This was the original carb so I ordered a new one (china I'm sure) and put it in. The jets are new obviously in the new one and I was able to clean the old carb jets just fine but none of that has ever helped. No real smoke issue either.

Same exact issue with the new carb. I have noticed that the air mixture screw in both carbs seems to have little effect, which is interesting. The plug become sooty and somewhat damp in 5 minutes of idling. I understand that should be a "too rich" condition but I cannot seem to lean it out. Working with the float does not seem to matter until I set to where it's no longer getting any fuel and then it stops:). I've tried several plugs to no avail.

I'm missing something - if you have any ideas, please shoot them my way!

Thanks!
MilesOfFun
80 GL1100 - Yellow
83 GL1100I - Blue
80 GL1100I (In Waiting!)
68 CT90 - perfectly simple one kick wonder
69 CT90 - very rough but working on it
72 SL125 (In Waiting)
65 Allstate/Vespa (In Waiting)
77 Bianchi Snark in pieces

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ritalz
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Re: Honda 1972 SL125 Project

Post #2 by ritalz » Thu Dec 26, 2019 8:14 pm

Been a long time since I've dealt with something like this. I would start with the timing advance. There should be some kind of centrifugal mechanism connected to the points/timing. Especially since you get the same results with two different carbs.
Al

1975 Goldwing 'Max'
1976 Goldwing 'Grocery Getter' Sold
1985 Goldwing Interstate 'NCC-1985'
1981 Silverwing Sold
1982 Goldeing Project
1973 CB500F Long Gone
1966 CL77 First Street Bike
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flyin900
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Re: Honda 1972 SL125 Project

Post #3 by flyin900 » Thu Dec 26, 2019 10:26 pm

I would go back and look at the timing on both the cam chain and the set up for the points too. If the timing is off it is going to cause running issues too. If it is a single carb then make sure all the jets are clean, especially the slow speed jet and it’s associated very small hole. Set the float to the correct spec and double check this spec as it can show as different spec settings in different manuals.
Current Bikes:
1967 CL175 Low production number with #802 as engine serial- winter 2019/2020 project.
1978 CB550K Very original bike with only 7499 klms from new- light cleanup and refresh pending.
1981 GL1100 Standard model - Sept 2018 start of cosmetic refresh, nice original condition.
1983 CB1000 Custom-Low mileage full cosmetic restoration back to factory new.
1984 GL1200 Standard model in showroom condition-two owner bike.
1984 CX650E Restored summer 2017 - a rare Eurosport model-excellent one owner bike.

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milesoffun
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Re: Honda 1972 SL125 Project

Post #4 by milesoffun » Sat Dec 28, 2019 11:23 am

Thanks guys - timing has been my "fun" with this project - but I'm happy to try again. I had found the common "if timing is not right, the engine will not run right" comments but jumped to the conclusion that idling meant it was running OK. I used a light bulb to set the timing and thought I had the chain lined up with the mark on the flywheel - regardless, I'll dig in to it later today and see if I can make some progress!
MilesOfFun
80 GL1100 - Yellow
83 GL1100I - Blue
80 GL1100I (In Waiting!)
68 CT90 - perfectly simple one kick wonder
69 CT90 - very rough but working on it
72 SL125 (In Waiting)
65 Allstate/Vespa (In Waiting)
77 Bianchi Snark in pieces

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flyin900
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Re: Honda 1972 SL125 Project

Post #5 by flyin900 » Sun Dec 29, 2019 5:47 pm

There is a large dot on the cam gear on a CL175 which maybe the same design given the year similarity too. The T/F mark on the rotor is set to the T mark on the rotor and aligned with the pointer marker on the outer case. The O dot on the cam gear should be at the 12 o'clock position very top of the gear. You then join the cam chain with the master link in the top of the gear area. It doesn't matter if the chain when joined is forward or backward of the top position. You are aligning the O dot mark at 12 o'clock on the top of the cam and the rotor T mark and the pointer marker for correct timing.
Loosen the valve adjusters off completely too if there is resistance from a valve spring, although the cam lobes should be in a neutral position on most of the valves when the O dot is at 12 o'clock.
These two pics show a very close up of the O dot on the side of the top of the cam gear and the master link for the cam chain. The other pic has the pointer marker near the upper left hand hole in the outer case for the T/F mark alignment on the rotor.

P1060827.JPG
P1060614.JPG
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Current Bikes:
1967 CL175 Low production number with #802 as engine serial- winter 2019/2020 project.
1978 CB550K Very original bike with only 7499 klms from new- light cleanup and refresh pending.
1981 GL1100 Standard model - Sept 2018 start of cosmetic refresh, nice original condition.
1983 CB1000 Custom-Low mileage full cosmetic restoration back to factory new.
1984 GL1200 Standard model in showroom condition-two owner bike.
1984 CX650E Restored summer 2017 - a rare Eurosport model-excellent one owner bike.


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