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Discussion Starter #1
First let me preface my question with a little background. I have been working on and riding the Honda 350 twins since they first came out new (with a lot of other bikes thrown ). I have always had trouble with the stock carbs on these bikes as most people seem to have. I have a 1973 Honda CL350 now that I have yet to get to run right on the left cylinder. I have built 3 separate left side carbs for this bike and it still will not run on the left side. The compression is 150 psi, the timing is correct, points have been set right, valves have been set and the plug is firing. I am not a newbie to these bikes and I know how to build the carbs and set it up. It obviously sounds like something wrong in the left cyl, but I can assure you I have checked EVERYTHING I can think of. Also the exhaust is stock and the stock airbox is in place. Any ideas?
 

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Assuming you have perfect spark... Perfect compression... And perfect fuel flow the bike should be running. If not it's possessed by the devil himself.

Short of that....What's the running condition? ... not firing at all on that cylinder? Backfiring from that cylinder? Intermittent spark from that cylinder? Do you have a timing light? Did you pour gas / starter fluid directly into affected cylinder?
 

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Personally I would swap any interchangeable parts from the left side with parts from the right side until the problem moved to the other side :|
 

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Discussion Starter #4
Thank both of you guys for your reply. Everything is set right and spark and compression is good. One thing I have not tried is using starting fluid on that cyl, which I will try. Another thing based on Trials Rider's suggestion that I will try is swapping the complete carbs from left to right. I know I can't run the bike this way, but I can set it up well enough to see if that is the problem. BTW the left cyl is not running at all.
 

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Swap or replace the condenser as well as the points if you can, same with the coils and plug wires and caps. Just a hunch.
 

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Discussion Starter #6
Well, I just got the left and right carbs swapped. Started the bike up and as I suspected, the bike ran great on the left side and would not run on the right side. That tells me that it is the carb that is the problem. No idea what is wrong with it. I have changed everything inside the carb that can be changed and it still will not run. I do have the cure for it though. I have a new pair of Mikuni 28mm carbs on order to go on that bike.
 

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Without seeing the carbs it's hard to say, but most likely a blockage in one of the internal drillings in the carb body. It could be a blocked air jet or the pilot jet outlet.

What I would do is to strip the carbs completely and blow through the jets with a can of WD40 or carb cleaner. Do one jet from one carb and then the same jet from the other carb. That way it's much easier to see how they compare. Then do the same with each hole in the carb body. That's an easy way to see which circuit is clear on one and not on the other.
 

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Discussion Starter #8
Well, I have a set of 28mm Mikuni's on the way. Does anyone have any info on the jetting for these carbs on a stock motor CL350? I have found the jetting suggestion for the 32's but assume that the 28's will be different. I know any info will be only a starting point but would be better than starting in the dark.
 

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Well, I have a set of 28mm Mikuni's on the way. Does anyone have any info on the jetting for these carbs on a stock motor CL350? I have found the jetting suggestion for the 32's but assume that the 28's will be different. I know any info will be only a starting point but would be better than starting in the dark.
Are these VM model round slide carbs? You won't be in the dark for long, they will come fitted with jets, roll with those as your start point.
The VM carb has a main needle jet that can be adjusted by moving a cir-clip up and down on the needle and low speed air screw has a range of adjustment, you don't need to venture outside those adjustment ranges until you discover how well or badly it works for your application.

... what you might start shopping for is a set of throttle cables that will work.
 

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It is possible that you will be lucky and the carbs will be fine, but that's not been the usual experience. Genuine Mikuni carbs are usually jetted for two strokes with Primary type needle jets and are jetted rich at the top end and lean down low because that's what two strokes need. Just to rub salt in the wound, it is highly likely that the spigot will be much smaller than the OEM Keihins.

I'd start by cleaning what you have and if you still can't make it run, contact CrazyPJ who is probably the world's expert on crabs for CB350s and 360s.
 

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Speed Moto's set up comes properly jetted and includes throttle cables and Uni filters. Did you buy a kit like that or just the carbs?
 

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Discussion Starter #13
Yea, I know I will have to change basically everything in the Mikuni VM's from the start. If no one has info on setting up the 28's, I will start with the info on the 32's with the understanding that it is only a starting point. The problem with the carb boot being too large can be solved with an adapter made to reduce the opening on the boots. Is CrazyPJ on this list and do you know how I can contact him?
 

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I would strongly encourage you to reach out to XB33BSA on this forum. There is probably very little that he does not know about Honda parallel twins and what works with them.
 

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I believe you will find the aftermarket Mikuni VM is suited to either 2 or 4 stroke applications and the only way you can mess up is to buy one that came off a used bike and where that carb was specifically ordered to suit a particular OEM motorcycle model. Mikuni does make a TMX model carb that is specifically designed for 2-strokes.

source for this and more info: Welcome to Mikuni Power - VM Series Carburetors


... from their FAQ:
"Are all carbs suited for both two and four stroke engines?
Other versions of the same looking TM and VM carbs to ours have through the years been manufactured by the factory for different bike manufacturers and are quite often of slightly different design and intended to only run on a specific application, hence the stories you hear when people have trouble getting old two stroke carbs to work on four strokes. All our VM and TM carbs are both 4 & 2 stroke compatible. Obviously correct jetting is essential for Australian conditions and fuel.
"


This is also a worthwhile read: Sudco Intl. Corp. - Dealer Info
 

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...... Obviously correct jetting is essential for Australian conditions and fuel. "
Most VM carbs come with Primary type needle jets which are designed primarily for 2 strokes. They will work on a 4 stroke but not as well. As long as you have enough time and cash, you can make most carbs work.

Those Dime City or Speed Moto carbs. does anyone have a list of what jets and needles they come with?
 

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As far as I remember, although there are different models of carb for CB/CL/SL 350's there are really only 3 types. mechanical, CV with 'square' brass floats and round brass float carbs. The most common problem I've found is the pilot system blocked or damaged if needle tip has been broken off in the seat. I've only ever seen one with the nylon plug covering bypass drilling was missing but several where the drilling's were blocked or partially blocked. I'm guessing you have CV carbs, diaphragms are good without any pin-holes? ( I have to ask :rolleyes:) Where are the float levels set? I use 26mm on round brass CV, I think the 1square' ones are 15mm. Oh, I've also seen a few mismatched 'pairs' with early and late carbs. Check the model number is the same on both as they may have different requirements (stamped on intake side of carb on section below CV chamber or on mounting flange )
Yea, I know I will have to change basically everything in the Mikuni VM's from the start. If no one has info on setting up the 28's, I will start with the info on the 32's with the understanding that it is only a starting point. The problem with the carb boot being too large can be solved with an adapter made to reduce the opening on the boots. Is CrazyPJ on this list and do you know how I can contact him?
I used the 1970's~80's Yamaha RD350/400 carb specs when I first modified VM carbs for my various CB/CJ250's (various capacities up to 391cc) When Yamaha fitted reed valves they knew bike would operate more like a four stroke at lower rpm so did all the hard work. In the past I have made completely new emulsion tubes (fitted VM32 to my XS650-800cc) No longer have machine to drill the cross holes to 0.8mm
 

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Coo, thanks for link, I had forgotten about that ;)
I'm not taking on any more carbs at present. My step-grandson is now 4 and way too boisterous. Only sleeps about 6 hrs at a time so I'm expecting him up about now (3:00am) He was awake about 19 hrs Saturday which isn't too much problem but also says any tool her picks up is his and demands 100%attention.
 
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