Author Topic: My CB450 Came With 500T Carbs (First Post)  (Read 854 times)

Offline NickGiumenti

  • Posts: 4
My CB450 Came With 500T Carbs (First Post)
« on: Jun 01, 2017, 00:21:05 »
Hey all, recently bought my first vintage bike a couple weeks ago and just joined this forum. Got a 1974 CB450 from a guy who owned and was selling several. Been going through the bike fixing any issues I find and I came to realize the bike has 500t carbs on it.

From what I understand these carbs are close to the late year 450s, but have some differences. He also sold it to me without any air boxes on it. (didn't realize this at the time.) I called him and had him send me the filters and covers. I cleaned them out and replaced the paper with 5/8 uni foam as I've seen people do. After installing them, I had some trouble getting the boots to really sit well on the carb intakes. They also don't line up perfectly flush with the metal passage in the frame that links the 2 air filters. From what I know, you want these filters to create a tight seal, so that the right amount of air enters only at the correct place.

Anyhow, I'm currently on the issue of checking for vacuum leaks and syncing the carbs. After looking at the carb boots on the engine side they definitely look worn. I know thats a fairly common theme with older bikes and Im going to use some carb cleaner to check for leaks tomorrow.

I was hoping you guys could tell me which carb boots are currently installed? I assume since its a 500t carb it would be a 500t boot, but after googling Im not so sure. Also hoping someone could tell me if these are the correct air boxes for a 74 CB450, or if they're from an earlier year?

Any special considerations I need to know rocking these carbs on a 450? Pics below. Thanks for any replies, cheers.

Offline Luugo86

  • Posts: 741
  • '73 CB350, '78 XS650 Cafe Killer
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Re: My CB450 Came With 500T Carbs (First Post)
« Reply #1 on: Jun 01, 2017, 10:48:42 »
The carb boots are the same between the two models. Did the bike run well when you bought it? If so I wouldnt start dismantling things, especially if you arent experienced with working on these bikes. If I were you the first thing I would do is get a Clymer manual for your bike, as well as a factory shop manual, they aren't too hard to track down and Im sure someone on this forum would help you find one if you ask.
It looks like a very clean, nice bike, if you need something installed and arent sure what youre doing the best thing to do would be to take it to a honda bike dealer.
Live to Die, Die to Live

Offline coyote13

  • Posts: 1199
Re: My CB450 Came With 500T Carbs (First Post)
« Reply #2 on: Jun 01, 2017, 11:57:58 »
Getting the carb boots and filters to fit properly should clear up whatever issues you're having, but if it does not please heed the advice below...

I have had varying degrees of unsuccess at the dealers here in Dallas (and I've tried a few).  I would not recommend that route, as they are typically lacking in knowledge regarding anything built pre-2000's (i.e. with a computer).  With a Clymer or factory manual you can do just about anything you need to do to get this bike running tip top.  Get yourself a manual and go through a full tune up to ensure you have a good baseline for performance (plus it's a fairly quick and easy process and cheap insurance).  Keep this thread posted as you go through everything, it will help you track what adjustments you're making.  If you are still having trouble after tuning up let us know and we can work through it.
Half the fun's in the get there...

Offline Turnturtle

  • Posts: 76
Re: My CB450 Came With 500T Carbs (First Post)
« Reply #3 on: Jun 01, 2017, 12:21:54 »
If you don't have a Factory Service Manual you can download one here:

Offline NickGiumenti

  • Posts: 4
Re: My CB450 Came With 500T Carbs (First Post)
« Reply #4 on: Jun 01, 2017, 16:08:56 »
Thanks for the replies everyone, I have downloaded a few manuals from what I can find online. I have the factory one from common motor collective, and another from, as well as some essays from Bill Lane's website.

Would you say the Clymer one is better than the factory manual? 

The bike ran ok when I got it, however with old gas and no airboxes it definitely needed work.

So far I have:

Drained old gas (very stale) and cleaned all rust from inside tank with muriatic acid
Changed Oil and spark plugs (didnt mess with the oil filter yet)
Fixed a choke issue (choke plates wouldnt open all the way because they were linked with the wrong bracket)
Cleaned and rebuilt air filters and boxes with Uni foam and installed em

Im new to old bikes but I really enjoy wrenching on mine. I feel like it's part the experiences of owning an old bike and caring for it, plus its helping me learn my machine better.

Going through the tune up procedure is definitely what I need to do, as Im sure there are things Im forgetting to check.

Offline coyote13

  • Posts: 1199
Re: My CB450 Came With 500T Carbs (First Post)
« Reply #5 on: Jun 01, 2017, 16:11:49 »
Sounds like you're on the right track.  The factory manual is basically the bible, the Clymer or Haynes would be next best but still good.  From what I understand the aftermarket manuals have a tendency for better English but also may have some discrepancies from the factory book.  If possible I'd go with the factory, but whatever you can find should be good.
Half the fun's in the get there...

Offline NickGiumenti

  • Posts: 4
Re: My CB450 Came With 500T Carbs (First Post)
« Reply #6 on: Jun 01, 2017, 19:31:45 »
Well, I'm going through the tune up procedure in the factory manual. Figured it'd start simple with the 1st step compression test. Was trying to do it on the engine cold first (was gonna do warm after and compare the 2) and I'm already slightly confused.

I've removed both plugs and threaded and seated my gauge into one spark plug opening. Choke is fully off and wide open throttle. I've tried to kick it a few times. 1st kick will go fairly easy and I can hear air escaping from the other cylinder and what sounds like the exhaust. 2nd kick however won't even budge. The bike will lean up off the kick stand and the kick start lever will stay put. I'm afraid to kick it any harder cause it feels wrong that the lever won't move. Ignition is off, gas is off, and kill switch is off. Can't think of what Ive done wrong?

Offline spotty

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Re: My CB450 Came With 500T Carbs (First Post)
« Reply #7 on: Jun 02, 2017, 00:24:16 »
check that the compression tester extends no further down the spark plug hole than the orig spark plug did (compare length of threads) if its longer (which it sounds like it is) then you have contact with the top of the piston. this is far from a good thing.

don't try and turn it over again until you have pulled the tester

 if it turns over after that then that's your problem solved

if you can't get a shorter tester then pack it with washers to lift it further up the plug hole

you may also want to check whether any damage has been done to the piston crown (not easy to see but try looking down the plug hole with a torch and mirror or endoscope if you've got one ) or the tester itself. it would seem unlikely as the tester should just be a tube of some sort with a hole in the end but check anyway
« Last Edit: Jun 02, 2017, 00:29:39 by spotty »
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Offline NickGiumenti

  • Posts: 4
Re: My CB450 Came With 500T Carbs (First Post)
« Reply #8 on: Jun 02, 2017, 00:39:46 »
Thanks so much spotty, if the tester is longer it wouldn't have been by much but that's definitely possible. I'll check tomorrow when I'm back at the garage. I didn't try cranking without the tester but I should have. To be honest after I kicked it and it didn't move I wasn't eager to keep trying until after I got a second opinion haha.