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Discussion Starter · #1 ·
I posted about this same issue a few days ago. Today I tried squirting some starter fluid into the left cylinder from behind the carb and it would fire up and then immediately sputter out. Is this indicative of a carburetor or fuel issue? Any help is appreciated, thanks.

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Pretty much yes, carb/fuel issue. If compression is decent (150+), there's spark thru the sparkplug and there's no vacuum leaks then that does mean carbs.
So how is the compression? Do you have spark? Are the carbs fully inserted into good carb insulators?
Are you using NGK D8EA plugs? Is the resistance of the plug end cap 5K ohms? Are the insulators pliable or fairly new?
 

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That would indicate that the affected cylinder is not getting fuel but does have spark and compression. Could be no fuel is getting to that carb. Could be the throttle plate is closing too tightly. Could be the idle passages in that carb are plugged.

If that cylinder does not "catch" when you open the throttle there's a good chance there's no fuel getting to the carb.
 

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Discussion Starter · #4 ·
I think I've ruled out it being a spark issue. The right cylinder will always fire, regardless of which plug or wire is connected.

Fuel will drain from the bowl if I open the drain, and I've thoroughly cleaned all jets and passageways twice now. Would a bad air cutoff valve possibly do this? It wasn't in great shape. The insulator boots aren't in the greatest condition either, but I don't think that they're leaking.

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You've swapped wires w/o change so the ignition system is pretty well eliminated other than maybe a bad sparkplug.
That leaves you with fuel. The bad air cuts I've dealt with have affected a mixture adjustment, almost impossible to get it set. Those do create a vacuum leak when torn. The insulators seal to the head with an O-ring which could be leaking. The insulators themselves should allow you to dent them with a thumbnail if they are reasonable to use. The acid test for those is remove the air box boots leaving everything else tight, then lean on the carbs as hard as you can then lift as hard as you can. If they are bad they will separate at the flange where the rubber is bonded. If they pass then you're going back into the carbs, something is keeping fuel from the idle circuit
 

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Discussion Starter · #6 ·
I went through the jets in the carbs again and there was slight improvement. The cylinder does not fire up or stay running, but if I give it a lot of gas then it ignites. It backfires and sputters like crazy, but it does fire when I twist the throttle back a bit. I'll look into the insulators some more as well.
 

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There are 3 idle ports in the floor of the carb throat, one is exposed when the throttle is closed. It sounds like one or more of those is plugged. Removed the mixture screw and spray carb cleaner in that hole, seal as best you can. You should see fluid spray out of the first hole and if you block that with a finger it should spray out the other 2. DO NOT try poking anything into those 3 holes, they are specific sizing for metering the fuel. If those are clear then the slow/idle jet is plugged, that's a pressed in jet and almost impossible to remove.
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Discussion Starter · #8 ·
There are 3 idle ports in the floor of the carb throat, one is exposed when the throttle is closed. It sounds like one or more of those is plugged. Removed the mixture screw and spray carb cleaner in that hole, seal as best you can. You should see fluid spray out of the first hole and if you block that with a finger it should spray out the other 2. DO NOT try poking anything into those 3 holes, they are specific sizing for metering the fuel. If those are clear then the slow/idle jet is plugged, that's a pressed in jet and almost impossible to remove.
View attachment 199985
Perfect, I'll give that a shot. Thanks!

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Gents:

This thread is timely for me...Our 1982 cm450A Hondamatic was put away running reliably for winter storage last season and when taken out of storage, etc. hasn't run all season alas. I've pursued several of the issues discussed here. Some troubleshooting data on mine:

Bike fires/runs on both cylinders at idle and runs at full idle happily whilst warming up. mounted up now for a ride around the patch, it bogs out on the right cylinder as soon as throttle is applied. If I plow through mid rang rpm to full throttle the right cylinder kicks in and it pulls as per normal.

Earlier in the season I pulled the carbs sprayed the jets etc and felt everything was gorgeously clean inside... I did find my two new air bleed diaphrams from two seasons back were totally broken up. Despite studying and learning their very limited impact on running, (backfire control etc..) I dropped a silly large amount for new bits..

Now, studying that excellent carb cut away I wonder if it wouldn't hurt to pull them again and soak them in my card bath..hoping to clear those tiny ports...

.O rings under the intakes seemed pliable and uncompressed, however I was so vexed I dabbed on some hi temp silicone. maybe ill order fresh ones...No filter...in fact two seasons ago I had it professionally serviced and my shop removed my filter..a new one is on the bench..lesson learned.

THis spring i dissassembled and and I traced the wiring harness as the PO had left a big look exposed outside the headlight at the head stock pinching the wires at every swivel of the bars.., so I inspected it all and found a broken, pinched off black wire at the CDI box. I reassembled convinced Id discovered the hidden problem only to have all the same issues. Perhaps it was grounded all the same??

Because of the solid high end running I believe I can rule out spark..plugs are correct and re-gapped. intake boots passed my scrutinizing, but if a fresh set were to be found I'd pursue that and fresh o rings for same.

I have studied the carb settings in the manual and those don't appear to have moved..anyway, I put it in storage for winter running well..

Help!!! what have I missed?? My only tack to pursue now as I see it is to remove the carbs: strip again , soak in the carb bath and convince myself that all three of these idle ports are clear of rust etc.. BTW I've had great success freshening and removing gas tank corrosion with a vinegar soak rotating the tank periodically over a few days on my Gold Wing project...went from a rust covered interior to shiny metal...

Thanks for reading

What are your inputs? Im all ears as they say..
 

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I think I've ruled out it being a spark issue. The right cylinder will always fire, regardless of which plug or wire is connected.

Fuel will drain from the bowl if I open the drain, and I've thoroughly cleaned all jets and passageways twice now. Would a bad air cutoff valve possibly do this? It wasn't in great shape. The insulator boots aren't in the greatest condition either, but I don't think that they're leaking.

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There are some excellent posts about the air cut off valve if you Google. Doesn't seem to impact driveability. With the OEM parts stupid priced I went with aftermarket units when I found my diaphrams blown out.. Cheap aftermarket units don't seem to last like OEM.
 

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The air cut diaphragms when leaking seem to mostly affect setting idle mixture. Very true about the aftermarket not lasting as long although there do seem to be some decent ones, K&L comes to mind.
For your particular issue I'd try running some Berryman's B12 or Sea Foam in the fuel for a couple of tanks and see if it's just a case of fuel fouled/gummed up passages.
 

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Discussion Starter · #12 ·
Quick update:

I haven't had much time in the last week or so for bike work, but I did give the carbs a good soak and a thorough cleaning. Upon doing so, I noticed a crack in the air cutoff valve cover on the left carb.

I think I found my vacuum leak?

The crack was on one side of the little hump where the spring rests, with a corresponding dent on the outside. Looks as if the carb was dropped onto something pointed.

I did my best to patch it with some JB weld, and I hope that works until I can find a replacement cover.

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Discussion Starter · #14 ·
Another quick update: after letting the JB weld cure, I mounted the air cutoff cover and it fired right up.

It's not running well, and the right cylinder is sputtering quite a but and there was some ignition in the exhaust pipe. But it's running!

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So Monday last I took out a can of Sea Foam spray with the cool red tube to point down the carb barrel.. dropped and broke off the nozzle [email protected]#$%@#$# Ok so I live an hour from anything... so I transferred the fluid to a pump sprayer, removed the airbox boots ( seem nice and pliable....) and fired the beast up..

So it started and idled perfectly throughout the roughly 20 minute run.. I several times sprayed into the right intake and belched out whitish exhaust like a smoke system on an aircraft.. In neutral I got the impression that transitions were going better.. revving well throughout the range etc...so I mounted the seat for a ride.

Once in gear though the familiar bogging returned...( is this something else)>...?

So I rode up and down my country lane pouring on the coals.. Above idle the right cylinder sputters and isn't firing like its fuel starved.. then after several seconds of wind out it kicks in.. no backfire .. and it pulls hard through 6k.

What next?

BTW. What are the smaller nipples in the middle of each carb unit facing the center? Overflows? How should these be connected up,

Where should I buy fresh rubber intakes?
 

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These are the least expensive carb insulators I know of https://www.siriusconinc.com/pro-detail.php?pid=&product_id=121231
The 2 brass nipples are breathers for the float bowls, they are left open to the air. Don't put a hose or anything else on them.
I'd suggest checking the ignition system per the Ignition Diag thread in the Electrical section. Ignition and carb symptoms are very close to each other and the checks are fairly quick.
I would suggest adding Sea Foam or Berryman's B12 to the fuel per the instructions on the can. This may be a case of fuel fouled jets and passages that the chemicals will clean out.
 

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So its warm in SW WI 88 in the shade...that won't last .. so I went for a ride...and tweeted the right carb mixture a bit. But no joy.. still bogs. I revisited the Carb settings thread... Seems I dont have the specified plugs, nor the wide gap specified. There's a driveability bulletin with a spring ring kit for my year 1982.. I doubt thats installed.

Im convinced the right cylinder is loading up on raw fuel, too rich, maybe ill go reset the mixture screws to the OEM spec and start from there again, maybe recheck the float heights. Anyway too nice a night to not do some wrenching. Cheers.
 

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Thanks for the carb insulator info only my 1982 CM450A model isnt listed ..Drat!

thanks for the tips in the ignition etc. Ill follow through on those firts.
 

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So is this the thread and specs apropros to my 1982 CM450A? I guess I need to read up on the ignition as there are some oddities with the A model yes?

http://www.hondatwins.net/forums/64...400-450-cb450sc-manual-trans-1978-1986-a.html

Ignition Diagnosis for CB/CM 400/450 and CB450SC manual trans 1978-1986
These tests are used to check the CDI system. There are no valid tests for the CDI unit so this is an elimination process. If all these tests are good then the CDI is at fault. Before replacing a CDI all these components have to test good.
Use a multi-meter and set it to measure electrical resistance in Ohms.

Coil Test:primary Side.Measure the resistance between the Yellow and Green wires.
The Yellow and Green wires being measured will be coming out of the spark plug coil.
The resistance should be less than 1 Ohm. Spec is .35 to .55 ohms
Secondary Side: Measure the resistance of the spark plug wires with the plug end caps removed, they unscrew. Insert a probe into each wire. Spec is 7.2K ohms to 8.8K ohms
Plug End Caps: Measure the resistance of the plug end caps. Spec is 5K ohms. Replacement part number is NGK XD05F

Stator Tests:
The connectors used are found under the left side cover
Measure the resistance of the Pink and Green wires.
The Pink and Green wires to measure will be going into the bundle that goes along the frame and eventually to the stator. This is the advancer pickup sensor
The resistance should be about 135 Ohms. New Spec 129 Ohms

Measure the resistance between the White and Blue wires.
These wires to measure will be going along the frame and eventually to the stator also. This is the CDI power source
The resistance should be about 85 Ohms. New Spec 84.2 Ohms

Measure the resistance between the Brown and Light blue wires.
These wires to measure will be going along the frame and eventually to the stator also. This is the primary pickup coil, the aluminum piece outside the rotor
The resistance should be about 207 ohms. New Spec 203 Ohms

The stator ohm readings listed can exceed the old spec by no more than 1 ohm, more than that will have a negative effect on the timing advance.
The New Spec was obtained by measuring 2 NOS stators, fresh unused old stock early model with the bullet Blue and White wire connectors.

Run/Kill and Ignition switch Tests:
Connect one probe to the Black w/White tracer pigtail wire coming out of the main wiring harness that connects to the CDI unit. Connect the other probe to the negative battery terminal. The results should be:
Ignition switch on, Run/Kill switch in Run position: Infinite Ohms reading meaning an open circuit
Ignition switch on, Run/Kill switch in Off position: Zero ohms or close to that showing the circuit is closed/completed to ground
Ignition switch OFF, Run/Kill in any position: Zero ohms or close to that showing the circuit is closed/completed to ground

Alternator Tests: Select/connect to one Yellow wire with a probe. Connect the other probe to one of the remaining 2 Yellow wires, resistance should be below 1 ohm. Repeat twice using a different wire each time. If the readings are good then test each of the Yellow wires with one probe connected to ground. There should be an Infinite ohms reading meaning none of the charging coils is shorted to ground.

NOTE: ​Some VOM's are auto-ranging meaning they switch ohm scales as needed and some are range selectible. If you have to select the range be sure to do that matching the expected ohm range.
 

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I don't get the troubleshooting electrical if you have fueling issues. But I can tell you this, I'll bet a C note that you still have obstructed carb pathways. I don't care how you cleaned it with can carb cleaner, ask any outboard motor mechanic what he thinks of carbs and todays fuel. In many cases an ultrasonic cleaner and some meticulous and diligent handwork is required. Very tiny passages for air bleeds in the venturi , get a magnifying glass, take some time and figure out the passages and clear them. Be sure to remove all screwed in jets and jets behind screw plugs etc...
Ultrasonic cleaners can be found on ebay for small money, or take the carbs to a mechanic with an ultrasonic cleaner or keep chasing this dragon.
 
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