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Discussion Starter · #1 ·
I recently came into possession of a very cosmetically intact scrambler that, upon closer inspection had seen better days in terms of internal maintenance. This bike is giving me the most perplexing issue I have ever had. It is fine at low revs and holds a healthy idle of about 1200 and will feel fairly high in torque at near-idle speeds, but once you rev over about 3,500 - 4500 while under load, it becomes completely anemic and struggles to accelerate. When I attempted to tune and synch the carbs shortly after I got it home, I noticed that the right cylinder (with the left plug out of the hole and grounded to the fins) revs all the way to redline absolutely fine and with no hesitation, but the left cylinder under the same conditions will stop right above 3k and then sound like I just turned the bike off. I have already swapped out a dead condenser that was resulting in only one piston firing, and I dropped 100 bucks on a brand new AGM battery. I also have replaced the FUBAR'ed float bowl gaskets, cleaned every brass part in the carbs, made sure the diaphragms are intact, and that there were no more air leaks. While initially cleaning the carbs, I discovered that one side (the one that won't rev past 3k) had a 105 main jet while the right side had a 110. I just finished reinstalling everything, thinking that a new 110 jet from CMC on the bad side would fix the issue, but it still persists. I have a nice blue spark on both plugs, both pipes are hot, the OEM airboxes are still there (though I haven't yet checked the Filter elements themselves), and I know for a fact that I am getting fuel to both carbs. The only thing I can think of at this point is either bad compression that is entirely localized to the left cylinder, or maybe a float height issue? The overflow on the left carb occasionally drips gas, and the plug from that side is black, so maybe there is too much gas in the float bowl causing a rich condition? Any suggestions are more than welcome, as this is only my second vintage bike, and my fist Honda twin, so I still have a steep learning curve ahead of me.
 

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Compete engine number and the letters and numbers off both carbs. I'm showing too many combos of this series. I'm assuming K5 is late, but better we match both engine and carbs to said engine numbers. Why the main jets are off is more thinking two different carb numbers?

Back in your court.
 

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It's not a compression issue. Put a timing light on that side, then rev it up and watch the flash, should tell you if it's electrical or a fuel problem.
 
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Discussion Starter · #4 ·
Compete engine number and the letters and numbers off both carbs. I'm showing too many combos of this series. I'm assuming K5 is late, but better we match both engine and carbs to said engine numbers. Why the main jets are off is more thinking two different carb numbers?

Back in your court.
You are spot on about the carb numbers;
Right Carb: 722A
Left Carb: 726A
Engine #: CL 350E - 5047164
Both carbs look identical to me other than the jetting, and both have the later style drain plug
 

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Check your numbers ... 726A isn't a number I can find that looks like the correct 722A. Post a photo.

I would suggest be cautious using Common Motors for information. Look around for a Factory Service Manual. I set my floats to 26mm .... tip carb so float tang is just touching the float valve .... it is spring loaded so check it isn't stuck....
Did you push emulsion tubes out when cleaning carb? Honda brass pieces are best ... aftermarket parts have been found to be inconsistent.

Pull plug cap and check for 5K ohm resistance. Trim back spark plug lead by 4 or 5 mm and install cap. If plug is fouled replace .... it must be a non resistor plug ... don't believe CM. NGK stopped making the 8ES plug. I have gone to non resistor cap and resistor plug.

Avoid running on one cylinder or on the side stand.... oil pickup is on rhs can run dry if oil level gets low.

Check voltage at coils, should be very close to battery voltage, check KOEO, at idle and 3500 rpm at which point you should be seeing 14 plus volts if charging properly. Key switch, wiring in headlight and kill switch are all areas of high resistance.

Make sure the mechanical advance for the points is moving smoothly, haven't found one yet that didn't need cleaning and lube.

Some aftermarket points, read CM again, have issues and someone may have used them. Make sure the wiring to the points isn't grounding on the cover.
 

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Discussion Starter · #7 ·
Check your numbers ... 726A isn't a number I can find that looks like the correct 722A. Post a photo.

I would suggest be cautious using Common Motors for information. Look around for a Factory Service Manual. I set my floats to 26mm .... tip carb so float tang is just touching the float valve .... it is spring loaded so check it isn't stuck....
Did you push emulsion tubes out when cleaning carb? Honda brass pieces are best ... aftermarket parts have been found to be inconsistent.

Pull plug cap and check for 5K ohm resistance. Trim back spark plug lead by 4 or 5 mm and install cap. If plug is fouled replace .... it must be a non resistor plug ... don't believe CM. NGK stopped making the 8ES plug. I have gone to non resistor cap and resistor plug.

Avoid running on one cylinder or on the side stand.... oil pickup is on rhs can run dry if oil level gets low.

Check voltage at coils, should be very close to battery voltage, check KOEO, at idle and 3500 rpm at which point you should be seeing 14 plus volts if charging properly. Key switch, wiring in headlight and kill switch are all areas of high resistance.

Make sure the mechanical advance for the points is moving smoothly, haven't found one yet that didn't need cleaning and lube.

Some aftermarket points, read CM again, have issues and someone may have used them. Make sure the wiring to the points isn't grounding on the cover.
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I will definitely try that if I ever get my hands on a timing light, is there any way to tell statically with a volt meter?
No, the only way to know if it's firing steady at higher rpm is to use a timing light. That will show up point bounce or overlap, causing the right cylinder to miss.
 
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Float: 26.0mm
Primary jet: #68
Secondary main jet: #105
Slow jet: #35
Idle mixture screw: 1 1/8th turn out
Tappets: IN 0.05mm Ex 0.10mm
Plugs: B-8ES
Compression: 153 - 187 psi

The 'initial' turns out is left alone and kept there.
Both carbs use the same jet numbers above.
Change plugs to new ones and see if it cleans up.
 

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Use of the timing light above 3500 rpm can confirm if full advanced timing is set correctly. It is possible the breaker point gap on the left side is out-of-spec, which could change timing on that side or result in a short dwell time and weak spark at higher rpms tho it might run fine at lower speeds.

The Honda Factory Service Manual for the 350 model:
Spark advance begins around 1800 rpm and is full advanced by 3500 rpm, advancing the spark 35 degrees (page 100). With a timing light, the high rpm full-advanced spark should fire between the two marks on the stator 30 degrees before the F and LF lines (page 149).
Breaker point gap should be clean and adjusted to 0.3-0.4mm (0.012-0.016 inch).

Valve adjustment does have an effect on power in that cylinder. If you have not already, you might run a compression test and leak-down test to compare the condition of the cylinders and valves. Compression should read about 150 psi.
 

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Doing some digging I found the 722A and 726A carbs are the same for all intents so doubt that is your issue.

I will add that many of us have found it beneficial to bump the float height to 26.5 or 27 due to the difference in specific gravity of old vs new fuel.
 

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If you have it available a discount store like Harbor Freight has a inline spark checker. It plugs onto your spark plug then plugs into your spark plug wire. It glows when the plug fires , the price is cheaper than throwing tools thru the garage windows in frustration.

Your symptoms mimic a non advancing spark or a plugged emulsifier tube in the carb. I also have run into rusted and plugged mufflers very rarely. . Also check your air filters you might have a mouse nest in one. The left side is a pain to check on stock bikes so it might not have ever been checked.
 

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Discussion Starter · #14 ·
UPDATE: I just tested voltage at the battery terminals and found that over the span of a few weeks, I drained the brand new battery down to 11 volts. On my ride home from class tonight, I noticed that the headlight was pulsing and the blinkers were dimmer than normal and blinked noticeably slower. This leads me to believe that the regulator and/or rectifier needs replacing. I was wondering if the combo units from common motor are to be trusted, or if I should avoid their products as much as I avoid their tech advice. I trimmed the spark plug wires to no avail, and tried switching the spark plugs, which yielded the same result. I am still waiting on a decent feeler gauge to check the points and valves, and have been asking around to borrow a timing light or a compression tester. Thank you all for the factory specs.
 

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Just a thought....Make sure your coils are well grounded. Sometimes running a wire from the coils to the negative battery post can fix a bad ground. See if there is sparking at the points when running. There should not be any sparking
 

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If its not charging will run lousy i used RICKS regulator rectifer was better right away ...stators and rotors go bad as well you have to be charging solid for those early points bikes to run well thats what its sounding like charging issue hang in there keep plugging.....
 

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Discussion Starter · #19 ·
Update: after installing a new regulator/rectifier, fully synching both carbs, lubing up the spark advancer, and fixing the static timing, all to no avail, I finally went and bought an in-line spark indicator, which narowed it down quite a bit. The spark clearly stumbled after 3k and stopped completely at about 3100. I am now certain that it's an ignition system issue, not a fuel issue. While I've definitely made progress, I am still unsure what else might be causing this. Maybe the coils? Thank you to everyone who has participated in this thread, and any further advice is more than welcome.
 

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switch the condenser wires and se if the spark drops on the other cylinder. Check your point gap, and feel if the points both have equal pressure from their spring when fully closed. While running spray the coils with soapy water to see if you have a cracked or defective coil (don't use contact cleaner like I did with a gold wing once and had everything on fire from a cracked coil) You are closing in and will have a really tip top shape bike when you solve whatever the problem is.......keep all the old parts for spares.
 
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