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1985 CR125R help/advice

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So i picked up an 85 on the cheap to help out a buddy in need of some cash. Had her running but it only idled well, and would bog once the throttle was opened. I already had cleaned and rebuilt the carb. Compression test came back at only about 90 psi. Which i felt was low but i had a hard time finding the correct spec. Even in the manual i bought i couldnt find I believe it should be around twice that though, at about 180 psi. Correct me if i'm wrong please. I pulled the head and ordered up some gaskets and piston rings as well as new reeds. Hope that takes care of that issue. Once i have it running fairly well and know its viable, i will be ordering up a new piston and sending the head out. I have an extra jug too that my buddy had laying around and gave me. Anyhow,  moving on to the exhaust, the ATAC unit is missing some parts The jug port is capped. I was wondering if i could use an aftermarket expansion pipe and just omit the ATAC system. Has anyone ever heard of this being done? I wouldn't mind losing some bottom end if the higher rpms were decent. Thanks for checking my post out, and thanks for any input. 

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The atac is just about useless. You won't even know it's not working. At one time they made a new piece for the exhaust that eliminated that atac chamber. And 90 psi is way too low . 160-180 should be in the ballpark.

How does the water pump look. Almost every Honda from that era the clutch housing/water pump is eaten away since it's out of magnesium. Both my 85 250 and 500 have been replaced with a newer aluminum cover. The bad news is for the cr125 you can't use a newer aluminum cover. There is a guy in Australia that is making replacement covers but there $400+.

Edited by GreenMT_Rider
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1 hour ago, GreenMT_Rider said:

The atac is just about useless. You won't even know it's not working. At one time they made a new piece for the exhaust that eliminated that atac chamber. And 90 psi is way too low . 160-180 should be in the ballpark.

How does the water pump look. Almost every Honda from that era the clutch housing/water pump is eaten away since it's out of magnesium. Both my 85 250 and 500 have been replaced with a newer aluminum cover. The bad news is for the cr125 you can't use a newer aluminum cover. There is a guy in Australia that is making replacement covers but there $400+.

Ok.  Thanks for that. The water pump had a new gasket but i didnt pull it off yet. I will check it out in the next day or two though. As far as the exhaust/ATAC is concerned, I guess thats pretty good news assuming i can find and/or retrofit an a/m pipe. For now ill run the capped off oem. I thought i read something about losing compression through the atac actuator assembly passages. I may need to take a closer look at all that as well. 

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You cannot just put new rings in your cylinder and expect it to work. The cylinder needs to be prepped with a glaze breaker or ew rings will never have any hope of sealing. Ideally you should have taken the cylinder and had it checked for any possible dimensional issues by a machinist to make sure it's within spec. And if you dropped ANY debris into the bottom end when you pulled the top end you'll need to wash it out really good, or you'll likely toast both the top and bottom end.

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You cannot just put new rings in your cylinder and expect it to work. The cylinder needs to be prepped with a glaze breaker or ew rings will never have any hope of sealing. Ideally you should have taken the cylinder and had it checked for any possible dimensional issues by a machinist to make sure it's within spec. And if you dropped ANY debris into the bottom end when you pulled the top end you'll need to wash it out really good, or you'll likely toast both the top and bottom end.
I honed the cylinder out (ball type) and mic'd it. The piston/wall clearance was within spec as well. I'm not looking for a track bike. Shes almost as old as i am. The guy who worked on her butchered it and I'm almost certain the loss of compression was through the top head gasket. The head I'm working with looks like someone took some time to clean it up though. 20181021_200323.jpeg

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“She’s almost as old as I am...” I had one back in the day which was obviously before your time but back to the issue at hand. I’m not sure how badly you want that bike to work but I found this on eBay:

https://www.ebay.com/itm/ATAC-EX-MANIFOLD-OEM-HONDA-NOS-P-N-18350-KA3-760-FITS-HONDA-1985-CR125R/223171282082?fits=Year%3A1985|Model%3ACR125R|Make%3AHonda|Submodel%3A--&epid=1611859928&hash=item33f60b84a2:g:jKAAAOSwr-Ra66Jd

Those must be extremely rare and no it’s not cheap BUT if your bike is missing that piece then you can get a new one that’s intact and you won’t have to worry about rigging something up that may or may not work. Like GreenMT said the water pumps corroded over time so check that out before you go any further. 

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“She’s almost as old as I am...” I had one back in the day which was obviously before your time but back to the issue at hand. I’m not sure how badly you want that bike to work but I found this on eBay:
https://www.ebay.com/itm/ATAC-EX-MANIFOLD-OEM-HONDA-NOS-P-N-18350-KA3-760-FITS-HONDA-1985-CR125R/223171282082?fits=Year%3A1985|Model%3ACR125R|Make%3AHonda|Submodel%3A--&epid=1611859928&hash=item33f60b84a2:g:jKAAAOSwr-Ra66Jd
Those must be extremely rare and no it’s not cheap BUT if your bike is missing that piece then you can get a new one that’s intact and you won’t have to worry about rigging something up that may or may not work. Like GreenMT said the water pumps corroded over time so check that out before you go any further. 
I actually have two of those ATAC pipes. It's some linkage pieces im missing. I don't mind omitting it. In fact I may sell the extra parts I have to help out someone else looking to do a full resto. I'm just looking to have a something to go out with my buddies with. Thanks for the link though

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