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High idle with a “tweak” of the throttle is indicative of an air leak. Check around your carb boots for cracks.
 

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Any time you remove the cables from the carbs, you have to go through the whole routine of synching them again. They have to be set EXACTLY the same. Start out with a little freeplay in the cables. Both butterflies need to begin to move at exactly the same time when you begin to twist the throttle, idle speed screws need to be holding the butterflies open exactly the same amount at idle, and the idle mixture screws adjusted to the "sweet spot" that provides the highest idle (but you have to listen carefully for it). If the carbs aren't synched correctly, it never will drop to the nice steady idle you want. The carbs function from intake vacuum, and one carb that isn't right will cause a sympathetic reaction in the other.
 

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Discussion Starter #303 (Edited)
High idle with a “tweak” of the throttle is indicative of an air leak. Check around your carb boots for cracks.
New intake manifolds, but will check for leaks again using a propane torch.
as to resyncing them, I suspect my issue might be there and/or my efforts to seal the felt washers just made matters worse. I do note that there is a lot off difference in available cable on one carb vs the other (a lot more or less adjuster available might be a better way of writing it).
The popping might be a tell-tale of something.
To put it this way, when it come to my efforts, I did not even bother to take the bike for a spin after pulling the carbs and "lubing" the felts.
 

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Discussion Starter #304
Fiddled a little with bike and the fast idle issue not as prevalent. At the recommendation of the Common motor guru, I lowered the idle speed as he made note that I had set it while bike was cold. Got it to 1200 after riding a while. Was rideable.
Pulled plugs. The dirty one is the right plug.
Will be pulling carbs to work on sync. Will wait until I get in new throttle cable.


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Discussion Starter #306
Common Motor guru...?

We have a resident guru here who actually worked extensively in the industry when these bikes were current.
Was visiting with him face to face while exploring the vintage bike show and rally this weekend. Telling him of my current challenges. He still thought it was probably a sync issue, but suggested readjusting idle. First question was does it start real easily and idles like a dream right off the bat. He suggested that idle should be set after bike is warm. A few from their shop made the 300 mile ride from Houston to Luckenback.

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Was visiting with him face to face while exploring the vintage bike show and rally this weekend. Telling him of my current challenges. He still thought it was probably a sync issue, but suggested readjusting idle. First question was does it start real easily and idles like a dream right off the bat. He suggested that idle should be set after bike is warm. A few from their shop made the 300 mile ride from Houston to Luckenback.

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Not sure you got the gist of my point... Brendan is probably a nice guy, but I don't think he compares to Steve (66Sprint) in vintage Honda knowledge. Doubt that he'd offer you his cell phone number and access to his advice anytime as Steve does for everyone.
 

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Discussion Starter #308
I understood your point.
One of the guys there brought up Steve's name without me even mentioning it saying he had been a ton of help for his cl450. Won't doubt Steve, you or a host of others here when it comes to making or keeping these bikes running.
But when one gets a chance to chat face to face with others who definitely know more about these bikes than I, you take advantage of the opportunity. Heck, if I was at an event and you guys were there you would end up running and hiding from me. I would be begging you to hop in my truck and make the trip back to where my bike is to show me in person the err of my ways.
When you are getting close, but not there in terms of running, you look for any resources you can find.

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Discussion Starter #310
I will say, since lowering idle speed, I am not getting near the "high idle" symptoms as before based on a couple of rides. Deceleration is not precise - let off and engine quickly decelerates at idle - but much better. The popping sound seems to be right carb specific. Now, I have ordered new accelerator cable and once I get it in, I will pull the carbs and try to do a better sync. I might pull the top cap on the CVs and see if I can polish the slide and chamber as well on both carbs. Not looking forward to replacing the cable as it requires pulling the tank. But perhaps I will be a smidgen closer to getting this bike running the way I think it should run. Also seriously considering changing out front and/or rear sprocket to improve/reduce rpms at 55/60 mph. If I do increase the front sprocket, will I need to increase chain length or will I get enough adjustment out of my rear wheel alignment.
 

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You will likely have enough chain if you only go +1 tooth up front....If not, that's why the make a "half-link" (Half outer and half inner link with one pin)
 

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Discussion Starter #312
Found a problem that might be contributing to my acceleration/deceleration issues. Torn diaphragm on my left carb.
Was replacing accelerator cable and wanted to check to see if my slide as moving smoothly.
So will be securing one of those. Based on some sticky stuff around the tears, might have been a repair effort previously. Pretty sure I checked the diaphragms prior to reassembling carbs after rebuilds.


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Discussion Starter #313
I could not imagine I missed a torn diaphragm during the carb rebuild. Went back and looked again. A previous owner had attempted a repair using rubber cement on two tears.


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Discussion Starter #314
As to replacing the diaphragm is the procedure documented here http://jbmindustries.com/Yamaha650.html an acceptable approach? This way does it by cutting off the retainer ring at the top of the slide.


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Great work so far. Yours is one of my favourite models of the period.

I have successfully replaced two pairs of carb diaphragms using JBM's product and their excellent instructions. Note that they also have a page dedicated to the Kei-Hin carbs on our Honda Twins:

Keihin CV carburetor diaphram installation page for JBM Industries

Go ahead and cut the plastic ring; the replacement diaphragms will grip the slide very firmly. I didn't feel the need to Super-glue them in place.
 

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Discussion Starter #316
Great work so far. Yours is one of my favourite models of the period.

I have successfully replaced two pairs of carb diaphragms using JBM's product and their excellent instructions. Note that they also have a page dedicated to the Kei-Hin carbs on our Honda Twins:

Keihin CV carburetor diaphram installation page for JBM Industries

Go ahead and cut the plastic ring; the replacement diaphragms will grip the slide very firmly. I didn't feel the need to Super-glue them in place.
thanks for the information. Since the diaphragm acquired does not have a "tab" for alignment, I am thinking the super glue might help retain the proper orientation of the "holes" in the bottom of the slide.
 

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Discussion Starter #317
Went ahead and ordered "both" types of diaphragms for my carb repair. I hope to be able to use the original style, but have the other style in the event I have to tear off the retainer components from the slide.


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