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So I'll preface this by saying that I have perused the shop manual for the necessary specs, and I've been given a good heap of information that way; however I believe I'm now in need of the knowledge of how to apply such information.

The story goes like this, I purchased a 1973 Cl175 for $500, in decent shape, bored out .50 over with new pistons, rings and some other upper end work. It ran alright albeit on one cylinder the majority of the time. It had a bit of work done to it at a shop and when it came out it flitted in between one and two cylinders without the air filters attached. It idled around 3-4000 without air filters and at points went up to 6000. Every once in a while it would manage to hang on at around 1500 and I was able to take it out. She hit 60 mph in 4th so I can assume she was doing pretty alright for a 40 year old. I took some time off from starting her up so I could fix and replace other sketchy items (rear wheel, speedo/tach, headlight, rusty gas tank). I completed that laundry list a couple days ago and started her up again. She did pretty decent, idling around 1500, yet she still putted along on one cylinder. Compression and spark were and still are mint, so I figured the only thing holding her back from running on two again would be the carbs. Naturally I pulled them off, soaked them in a seafoam and gas mixture overnight and pieced everything back together.

I pulled the air screw out about .8/.9 turns and the idle screw about 3.5 turns out. I put the carbs on and attempted to start her again, however she would only start for a second every once in a while with the choke on and then sputter out when I tried to give gas. Compression and spark are still great. My only guess would be that one or more of my carb variables are off, possibly because of the bored cylinders. Here's a more practical list of symptoms:
• Engine turns but fails to start unless choked and then only for a second
• Pretty dry spark plug tips
• Very little fuel in the float bowl

I appreciate the viewing and apologize for spinning such a long tale. I'd love to answer anymore specifying questions if you all have them.
ps. I have no mechanical experience other than this venture
 

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Hi and welcome
First off set the timing, charge the battery
The carbs need to be set correctly, the best way to do this is with every thing as close to stock as you can get it
The carbs, if clean, should be set and idle at 1200 rpm
Set the carbs will take a bit of time
You need to set the float height, sync the slides, then set yge idle screw and slide stop correctly
Look for Steve's (66 sprint) carb setting here on Honda twins
 

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I've got this exact same issue. I've got the timing set, compression is great, tons of spark, I thought I had good fuel going from the carbs but I can't even get it to turn over,just the occasional sputter. Did you figure this one out or if not any ideas on what to do
 

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I am coming here to the forum with the same issues and would love to begin a discussion, if someone is so inclined. I feel pretty motorcycle savvy, but this bike has got me frustrated at this point.

1973 cb175. carbs cleaned/rebuilt. valves adjusted. timing set. compression is 125psi both cylinders. stock airboxes, no mufflers @ this time.


this video is from a few weeks back...it started and ran fine enough after the carb rebuild, but then this week it was hard to start. brought it to my shop (instead of my home garage) and put new control cables and new brake shoes on and rebuild the petcock. now it's harder than ever to start. performed a full tune up (valves and timing checkups). spark is very healthy on brand new spark plugs.

left the shop frustrated, and unable to start the engine. Spark? Check // Air? Check // Fuel? Must be the issue.

going to do some research for Sprint66's carb setting info
 

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Soaking the carbs isn't enough. Blow out all passages with compressed air, remove the jets and hold them up to the light and make sure you can see through them. The carbs have to be perfect. Set the float height. Clean the petcock. Replace the intake manifold O-rings. You guys are describing dirty carb issues.
 

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my carbs were cleaned and rebuilt proper. disassembled, soaked, blown through all passages with 75psi, float height set to 21mm, new intake o-rings, and using an external fuel cell for testing. flow not an issue.

strange thing is that it wouldnt even fire with starting fluid... not even a single pop!

currently resetting carburetors to baseline and seeing if it helps...
 

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Curious how the original problem turned out. Oh well.......................

As collector says, you need to thoroughly clean the carbs. There are any number of discussions offering recommendations, browse the forum for ideas.

If it won't fire on starter fluid you've got more troubles than the carbs. Compression and spark at the right time are the other possibilities.
 

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re: starter fluid and having bigger problems.... I AGREE!!!

Brand new spark plugs failed. began the day by resetting carbs to spec, syncing throttle cables, tried to start, nothing. starter fluid, nothing. checked spark @ the plugs... no spark. put old plugs back in and it fired up immediately.

wow. dumb to assume that new plugs would be good, i guess.

so it's better now, but still needs a better tune. it dies slowly, won't keep an idle. revs fine, and will stay steady at about 2k if i hold the throttle grip open just a touch. but strangely, trying to use the idle screws on the carbs to achieve the same thing (slightly increased idle) doesn't work. 1/2 turn in, still dies. another 1/2 turn in, still dies. another half turn in, idle runs up to 4k and sits there. 1/2 turn back out, won't idle.

thinking float height could be a culprit.

set height at the gasket base of the carb body, instead of the upper rim of the carb body. so it's 2-3 mm off.

 

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Try running the bike on one cylinder at a time to isolate the issue. Remove one plug and ground it to the head. Start the bike. It should sit and idle at 1200 even on one cylinder. Repeat process with the other side. Easy way to figure out what's going on.

I'm assuming your points are gapped correctly and you've replaced the condenser? Does it ride good even with the idle issue or does it cut out? Sounds like when the revs get low that one cylinder isn't firing.
 

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Try running the bike on one cylinder at a time to isolate the issue. Remove one plug and ground it to the head. Start the bike. It should sit and idle at 1200 even on one cylinder. Repeat process with the other side. Easy way to figure out what's going on.

I'm assuming your points are gapped correctly and you've replaced the condenser? Does it ride good even with the idle issue or does it cut out? Sounds like when the revs get low that one cylinder isn't firing.
 

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I would suspect dirt in the idle circuit if the mixture screws have no effect.
 

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i havent adjusted the MIXTURE screws at all. they've been set at the 7/8 turns out setting.

Condenser is original, but seems to be working. it's a "works or it doesn't" part, correct?
Once i get back to the shop next week, I'll see what I can diagnose.
Spark plug leads on this bike are probably long enough to swap between cylinders... thats encouraging.
 

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Even so, try adjusting the mixture screws, if they don't make a difference it suggests that the idle circuit is still dirty, despite cleaning the carbs.
 

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Mine runs super rich at 7/8 out. Richard is correct, a 1/4 turn of the mixture screw should make a noticeable change in revs. If they have no effect on revs your carbs are still dirty. Run one side at a time to isolate the problem. Try shooting some carb cleaner on the intakes while it's running to make sure that your o rings are sealing. If you didn't use metric o rings it's very possible. Condenser is not a fail/pass part but probably not what's wrong either.
 

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So I'll preface this by saying that I have perused the shop manual for the necessary specs, and I've been given a good heap of information that way; however I believe I'm now in need of the knowledge of how to apply such information.

The story goes like this, I purchased a 1973 Cl175 for $500, in decent shape, bored out .50 over with new pistons, rings and some other upper end work. It ran alright albeit on one cylinder the majority of the time. It had a bit of work done to it at a shop and when it came out it flitted in between one and two cylinders without the air filters attached. It idled around 3-4000 without air filters and at points went up to 6000. Every once in a while it would manage to hang on at around 1500 and I was able to take it out. She hit 60 mph in 4th so I can assume she was doing pretty alright for a 40 year old. I took some time off from starting her up so I could fix and replace other sketchy items (rear wheel, speedo/tach, headlight, rusty gas tank). I completed that laundry list a couple days ago and started her up again. She did pretty decent, idling around 1500, yet she still putted along on one cylinder. Compression and spark were and still are mint, so I figured the only thing holding her back from running on two again would be the carbs. Naturally I pulled them off, soaked them in a seafoam and gas mixture overnight and pieced everything back together.

I pulled the air screw out about .8/.9 turns and the idle screw about 3.5 turns out. I put the carbs on and attempted to start her again, however she would only start for a second every once in a while with the choke on and then sputter out when I tried to give gas. Compression and spark are still great. My only guess would be that one or more of my carb variables are off, possibly because of the bored cylinders. Here's a more practical list of symptoms:
• Engine turns but fails to start unless choked and then only for a second
• Pretty dry spark plug tips
• Very little fuel in the float bowl

I appreciate the viewing and apologize for spinning such a long tale. I'd love to answer anymore specifying questions if you all have them.
ps. I have no mechanical experience other than this venture
Sounds like the throttle stops are open so far in that the engine is trying to run on the main circuit instead of the idle circuit. Both slide needles in place with the clips in the correct groove? With the air cleaners off, watch the slides and back the idle screws out until the slides are bottomed out all the way. Adjust the cable adjusters on the tops of the carbs so that both slides lift off the bottom at EXACTLY the same time when you open the throttle. Once the cables are synced, run the throttle stop screws in until the slides just barely start to move then turn them evenly in 1-1/2 to 2 turns to start. Start with the air screws 3/4 of a turn out and re-adjust air/throttle screws to suit after the engine is running.
 

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This! You can look at one slide with your eyes and put your finger in the other to make sure you have them perfectly opening at the same time. Critical.
 

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Almost forgot, make sure the slides are not in backwards, reversed side for side. The lower, beveled edge, faces the air cleaner. The carb tops are handed(left and right), they need to be on the correct side also to hold the cables in line.
 
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