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Discussion Starter · #1 ·
Hey guys I'm a tech at a small shop in Cocoa, FL. During my down time I'm working on my bosses 72 cl175.
A comp test revealed 50-60 psi from both cyl's. Pulled it apart cleaned everything, looked at the valves and piston rings and they looked fine, replaced all the gaskets and Bam 130-140 both cyl's.
Timing is set perfectly and she makes great spark.
My problem lies in the carb tuning, or lack of correct carbs. She fires up and idles ok, but I'm finding it difficult to get her to hold a steady idle, giving it a blip of throttle the idle will hang and hold unless I give it some choke to force the idle back down (no the cables are nice and free), and even with a/f screws all the way in the idle hang almost goes away but she still wants to idle around 2k and sounds like she's gonna stall if I get her back down to 1200. Needle set at it's lowest point and no air cleaner's plug come out pitch black after 20-30 seconds of idling.
The carbs have slide covers with 20 on them, the butterflys on the choke plate have 18 on them, from what I can tell the air jets look like the ones from the 200 carbs (I'm not super informed about these old Honda's, I just have a couple of old crappy shop manuals that cover all the cb/cl range), and both carbs are running 35 and 90 jets. I don't have a great way to measure the Venturi size reliably. I'm just curious to know the slide and needle dimensions for the stock bike and whether or not these seem to be the correct carbs. ANY suggestions at this point would be an awesome and much needed help. Thanks
 

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It might not be carbs... if the spark advance isn't retarding properly at low engine speed and the timing isn't set right (maybe a bit retarded, points gap a bit narrow) the engine will want to stay advanced once there and it will make it drop down to idle slowly. Check the springs on the advancer, and make sure the timing is correct at idle as well as full advance if you haven't already
 

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If it helps with the carb ID, here's a pic of CB200 and CL175 carbs.


DSCF2727.jpg
 

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Discussion Starter · #6 ·
Timing is dead on.
The reason I question the carbs is because of how black the plugs come out after a little bit of idling and the best shop manual I have for it says it should be running a 38 slow and 90 main, so I should be under jetted at idle.
Correct me if I'm wrong but the 72 cl175 should be running carbs with the 20 mil Venturi.
On my choke butterflies it has an 18 stamped on it, is this the Venturi size?
I'm thinking that the carbs on it now just can't provide the air flow to accommodate the amount of fuel going in.
 

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Timing is dead on.
The reason I question the carbs is because of how black the plugs come out after a little bit of idling and the best shop manual I have for it says it should be running a 38 slow and 90 main, so I should be under jetted at idle.
Correct me if I'm wrong but the 72 cl175 should be running carbs with the 20 mil Venturi.
On my choke butterflies it has an 18 stamped on it, is this the Venturi size?
I'm thinking that the carbs on it now just can't provide the air flow to accommodate the amount of fuel going in.
Idle jets are pressedinto the carb body , afaik they're all #100 having a 40/100 or 35/90 or 38/98 ( or any other combo) set up won't affect idle because idle is a completely different circuit
Needle setting and float height will
At idle the carbs shouldn't matter if they're 18 or 20 since 18's should only choke out WOT
There's a little bit of disagreement about the cb175/200 carbs and what actual Venturi they have
Most of the info saying the cb200 had 18mm Venturi is based on a couple of reviews written in the 1970's but there are ads from the same time saying they're 20mm
I've seen mesurments but they seem to indicate a 19+mm Venturi when extrapolated to the area of the oval which isn't that far from the 20mm of the cb175 ....
Black plugs wet ? Or black plugs dry?
 

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CB200 carbs in the UK

cb200 carbs.JPG

cb200test1.JPG cb200test2.JPG

I'm actually running CB200 carbs ( mounted on CB175 manifolds ) on my CL175. Runs fine, maybe a trifle rich, on the stock 88 mains of the CB200. I'm personally convinced that the venturi size is the same on 175 and 200 carbs, as is the relative performance of the two bikes.
 
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