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Discussion Starter #1
Greetings!
I've got a CL450K3 that sat for 10+ years. I've got it running but not well. I replaced coils, condensers, points, wiring harness and spark plugs. I also cleaned and installed rebuild kits in the carbs. The stock airbox was missing and it had UNI oiled foam pod filters on the stock carbs. The bike will now start and idles beautifully but will not rev up. Opening the throttle even a tiny bit causes it to die. If I give it about 1/2 choke, and I carefully work the throttle, I can get it to rev up but not consistently. I double checked valve clearance, timing and float levels with no improvement. Running with pod filters off makes no difference. I did notice, with the filters off, that the slides do not rise when the throttle is opened.
I read mixed things about the stock airbox and pod filters. Some reviews of the filters make them sound like they can work but the info I find on these forums counters that. Also wondering if I overlooked an air or fuel passage when I cleaned the carbs. Looking for some advice from folks that are more familiar with these than I am.
Thanks in advance for your help!
 

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Many pod filters block direct air flow into the air jets, because the step in the rubber boot is too tall. This causes irregular fuel mix entering the air flow from the main and pilot jets, because there is not enough bubbling above the jets. There are a few with a smaller step from the sealing surface to the inner wall, so some do work.

Now, running with the pods off and the CV pistons not rising is a different problem. Either the rpm don't rise enough to increase the airflow enough to lift the pistons, or you have some other blockage in the air passages, or just sticking pistons.
carb_operation.jpg
 

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To add to what WintrSol said, there is a straw test to check if the floats are sticking. The video I linked below shows the idea. You can search for more infor by searching Honda CV carb straw test. On the DOHC carbs the principal is the same but the sensor hole is smaller and round. the slides must move freely. Some pods will block the sensor port.

You did the right things for the ignition. New everything is the way to go.

I'm not a fan of pod filters. My CB450K5 has the stock filters. I have replaced the paper with foam. The bike has stock exhaust. It runs great.

 

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Discussion Starter #4
Thanks! The diagram and video help, gives me a place to look for a problem. The slides move freely in the bores so I'm hoping for some blockage in that air passageway, that seem like an easy fix.
 

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After sitting that long, you could have spider webs in the air inlets, or other insect nesting stuff. Might be a good time to shine a light up the tailpipes, too; you never know.
 

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Discussion Starter #6
Well, it's better but still has a long way to go. Thanks for the "straw test" tip! The air passages were clear but the vacuum slides wouldn't pass the straw test. I worked on them until they would, which improved the throttle response but it's still not running well. It dies as soon as you open the throttle the smallest amount. Giving it some choke helped and then I could rev it up but it wouldn't idle. Pods on or off did not seem to make a difference. I'm stumped at the moment so if anyone has a suggestion, please let me know.
 

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You have a vacuum leak. Could be the rubber boots between the head and carbs, the rubber O-ring on the pilot screw, or the throttle seals. Get some starting fluid and spray around these places with the engine running and listen for RPM changes.
TOOLS
 

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Discussion Starter #9
Tested for a vacuum leak. It's likely I have a small leak around the throttle seals on the right hand carb. I got a pretty consistent rise in RPM when sprayed in that area. Strong mixed opinions on replacing the seals. I think I'll try to bring them back with some grease first. I'm going to tear the carbs down again searching for something else. it dies very abruptly with the smallest opening of the throttle. The vacuum leak seems minor and it's only on one carb, so i'm skeptical it's the only problem I've got.
 

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If you have the original pilot jets, clean them up and re-fit them. I have yet to see any kit where the pilot's match Kei-Hin spec. Youdid remove primary emulsion/discharge tubes as well as secondaries? The nylon seals under CV pistons the right way up? Uni's are normally easier to use than K&N filters on Kei-Hin 3 jet carbs although rarely will you get away without some modifications. You'll probably need at least 10% larger secondary main jets plus lower needles (shimming them is real bad idea), cheap pods are pretty worthless on almost all CV carbs and engines
 

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Discussion Starter #11
Finally got back to this. Well, the major problem turned out to be my incompetence. Somehow, I omitted the seal under one of the CV pistons when I reassembled the right hand carb. There was my vacuum leak! I'm still using the pilot jets from the rebuild kits but did put the original slow jets back in. When I compared them to the new ones, there was a noticeable difference in the size of the holes drilled into the sides of the tube. The new ones were smaller.
I'm moving on to a rebuild of the front end and a new front tire. After I finish that, I'll be able to ride it and get serious about carb tuning.
Thanks for everyone's help, it's appreciated!
 

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Thanks for getting back to us; sometimes, we never hear the results.:thumbsup:
IMO, unless they are damaged, or you need to change sizes, the brass jets and emulsion tubes never need replacing; gasoline doesn't wear them down.
 

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I do a lot of CB350, CB360 and a few CB450/500T carbs. Trek 97 pointed out the differences in pilot jet OEM and aftermarket a few years ago. I almost always re-used original jets and just swapped out o-rings and shut off valves so hadn't really noticed until then. Now, I check the cross drilling's on everything and modify those with wrong sizes (so far, all aftermarket kits LOL), The 'better' kits come with the wear items, needle and needle jets as well as shut off valves although so far none come with drain screw o-ring so that's the only part I 'stock' I usually contact owners to make sure things are OK (or check build threads) Minor adjustments are all that is usually needed, major 'carb' issues after I've worked on carbs are always electrical or mechanical :D (so far)
 

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Hey everyone! If you are following this thread, you might be struggling with jetting and carb issues because of running some type of pod filter. I would like to suggest that you find a set of stock air boxes and filters...leave the stock jets, etc..and see how great your bike can run.
I have patiently tried many different jets, pods, with only mediocre success. Never could I get full RPM range smoothness. After reading the excellent info on this forum, I "rebuilt" my stock air filters with the UNI-Filter foam..(Green). It now runs like a champ!! Pulls nice from idle to redline. Thank you guys for the contributions! I have three service manuals but have learned more from Honda Twins.

..FYI: My bike is a 73 CB450 rebuilt engine, Electronic Ignition (Shockwave) Stock pipes, etc..
 

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Hey everyone! If you are following this thread, you might be struggling with jetting and carb issues because of running some type of pod filter. I would like to suggest that you find a set of stock air boxes and filters...leave the stock jets, etc..and see how great your bike can run.
I have patiently tried many different jets, pods, with only mediocre success. Never could I get full RPM range smoothness. After reading the excellent info on this forum, I "rebuilt" my stock air filters with the UNI-Filter foam..(Green). It now runs like a champ!! Pulls nice from idle to redline. Thank you guys for the contributions! I have three service manuals but have learned more from Honda Twins.

..FYI: My bike is a 73 CB450 rebuilt engine, Electronic Ignition (Shockwave) Stock pipes, etc..
We try to tell people here all the time, but form over function still wins for those who want to make the bike different... it's especially difficult with CV carbs on our bikes but it's eventually doable, just painstaking and time-consuming. Even buying an old crusty used set of stock filters and covers (as long as the connector tube is still there on the stock battery box), then refurbing them with filter foam as you did, is the best way to get the most out of a stock engine. As you learned, Honda knew what they were doing... you can lead them horses to water but they gotta drink it themselves... and BTW, hope you have better luck with your Shockwave system than one of the Seattle HT members did recently on the group ride up there. His ride ended early with a melted sensor
 

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f you want to use K&N or Uni's (cheap pods are a waste of time and money) I can re-build and modify early carbs (up to 1977) for CB350, CB360, CB450/500 dohc and a few Suzuki GS models. It isn't possible to 'jet out' the problems. Carbs need modifications in various places to minimise the ~4,000 rpm issue
 
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