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Discussion Starter #1
Hey Guys,

new to the forum here and I just got my first bike. I got a 1981 Honda CB400T. I paid $300.00 and it is running.
The kid who owned it before the guy I bought it from took the air box off and put on air filters. which now makes it bog at a certain range or at lease that's what the guy i bought it from said. I know I'm going to have to get new jets, but any of your advice will help a lot regarding this.

Also, the tank doesn't have a lid. Now I looked into finding one on Ebay. The only ones i'm finding when I type in my bike are square type ones. Now I may have bought a bike that doesn't have the original tank? not sure, could happen, or i'm just not seeing how these square lids go on my tank.
i have a few pictures of my tank on my profile and the bike.

Thanks in advance.
 

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The OEM air boxes do a good job of filtering the air and also a good job of delivering the air in a linear fashion. On my old bikes,even if one air filter is dirty as compared to the other,a balancing tube of sorts delivers to both carburetors at equal vacuum pressure.
Pod air filters change the air-fuel ratio. I will admit that some honda bikes' air boxes are pretty difficult to mess with to the point of wondering what the engineers were thinking. Some Hondas as a group [Nighthawk as an example], are said to be nearly impossible to get running the same once the OEM air box is removed.

I cannot see your tank picture . Once you have 15 posts,you will be able to post pictures to your threads. A moderator can post pictures for you,but you would have to contact them to get it done. If I am looking for a Honda part on the 'net, I get the OEM honda part number and feed it right in to the Google search engine and usually get plenty of results. Honda parts fiches are easy to find on dealer websites,so that is how you access the part numbers....
 

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Discussion Starter #3
Slumlord, thanks for the reply. Ya I'm really hoping I can figure out the whole jetting issue on my own. I call the Honda dealer yesterday and they said they charge $100.00 labor per hour and it takes an hour each jet they try. They could get it the first time or it could take them 5 tries. So if I took it in to them it could run me $500.00 maybe. I don't want to spend that kind of money right now. Jets are cheap and I've got the time so I may try to tinker with it myself.
I uploaded the pics to my profile and I thought they were there, but they're not anymore. Hopefully soon I can upload them so you can see the tank. Thanks for the help.
 

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"which now makes it bog at a certain range or at lease that's what the guy i bought it from said."

It would help if you described under what conditions it bogs down. What RPM range? Does it do it if you're sitting still, or when it's under load, or both?
 

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Discussion Starter #5
Eye M No Angel, great question. When I purchased the bike, the seller didn't have the tank hooked up, but he had some type of gas bottle that was connected so I could hear it run. He started it up and revved it a few times then let it idle. during when he was revving it, he said hear it bog down a little? this is when he explained that it's running rich and thinks it needs to be re-jetted. I should have the tank back on my the end of this week. I just ordered the petcock for it, then I should be able to start it back up here at home and listen to it a little better.
Thanks for asking that question, I'm new to this sport and not sure if i'm giving you guys enough information when I'm trying to explain something i'm curious about.
I'll report back to you guys in the next day or two with my results.
Thanks.
 

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I'd say get the tank on it, get it running, then see what it's doing. Try reving it while standing still, and go through the throttle range while you're on the road too and see if there's any difference. (Put fresh plugs in it before you start.)
 

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Discussion Starter #7
got new plugs, and plan on changing the oil and the oil filter as well this afternoon before I even start it up. The Petcock for the tank should be at my house when I get home from work. Hopefully I'll have it running by this evening.
Thanks for advice guys.
 

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Discussion Starter #8
I also bought a Clymer manual for the bike as well. I was told that they are a must have for anyone who wants to work on their bike.
 

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Discussion Starter #9
So i had the Honda dealer look up the parts numbers for me for my tank lid.

17620-469-000 cap, fuel Filler - available $55.00
17530-443-305 lid, fuel tank - not available - discontinued part.

I check a lot of websites today hoping to track down a lid, but everyone says its discontinued. I'm assuming the only way i'm going to find one is check on Ebay every day to see if one pops up or check salvage yards.

Anyone else have any ideas?
 

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Hey Guys,

new to the forum here and I just got my first bike. I got a 1981 Honda CB400T. I paid $300.00 and it is running.
The kid who owned it before the guy I bought it from took the air box off and put on air filters. which now makes it bog at a certain range or at lease that's what the guy i bought it from said. I know I'm going to have to get new jets, but any of your advice will help a lot regarding this.

Also, the tank doesn't have a lid. Now I looked into finding one on Ebay. The only ones i'm finding when I type in my bike are square type ones. Now I may have bought a bike that doesn't have the original tank? not sure, could happen, or i'm just not seeing how these square lids go on my tank.
i have a few pictures of my tank on my profile and the bike.

Thanks in advance.
The square part you are looking at is actually the lock for the gas cap, which is a separate item it fits over the cap. I may be wrong, and hopefully someone will correct me if I'm mistaken, but you can use just the cap right? I would be worried about easy access to the gas though, I like having the locking gas cap.
 

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Discussion Starter #11
That square part is the wrong cap for the tank that I have. I agree it is a locking cap, but the locking cap I need is actually a long finger like locking cap, which like I stated in the above post seems to be pretty much impossible to find at this point.
 

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Discussion Starter #12
I would add a picture of my tank for everyone to see, but it's still saying I can't. Is there a moderator out there that can help me out with this?
 

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Try calling JP Cycles at 800-318-4823. Ask for their metric tech support line, not the Harley tech line. (Obviously.) Tell them what you're looking for, year, model, and give them the part numbers that you have. If a replacement is made anywhere they will be able to find it. They will also know if any of the common multi-fit replacements can be made to fit your bike. They have shelves full of parts catalogues, Tucker Rocky, Mid America, Tedd's, you name it.

If they can find something make sure you write down the company that makes the part and the part number, if you don't want to order it through JP. If it's a company that sells to the public you can look around and try to find that part number yourself. If it's a vendor you might have to go ahead and get it through JP, but they will generally have a good price on something like that.
 

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Discussion Starter #14
eye M No Angel, Thanks for this info. I will call them first thing in the morning. Hopefully I have some luck. I was on and off the phone for almost an hour with quite a few different companies that I thought may have what I need. no such luck.

Thanks again.
 

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So I got the petcock and hooked my tank up. new plugs, oil change, fired her up....... she won't idle, anything below 1000rpms she dies. between 4000-5000rpms she boggs down. I ran it for about 5 minutes. shut it down and started her back up. she would jump from 1200 to 4000 rpms for a bit. I thought that maybe something was wrong with the throttle, but I don't think there is. I'm assuming this is a carb issue? I'm happy I have it running, but now I want to get it running right. I really hope since the guy who owned it before me by taking off the air box hasn't screwed the machine up for good. It has pod filters on it now and from what i'm reading online a lot of people who have put these on all have the same bogging issues.

Any help or advice would be great.
 

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So I got the petcock and hooked my tank up. new plugs, oil change, fired her up....... she won't idle, anything below 1000rpms she dies. between 4000-5000rpms she boggs down. I ran it for about 5 minutes. shut it down and started her back up. she would jump from 1200 to 4000 rpms for a bit. I thought that maybe something was wrong with the throttle, but I don't think there is. I'm assuming this is a carb issue? I'm happy I have it running, but now I want to get it running right. I really hope since the guy who owned it before me by taking off the air box hasn't screwed the machine up for good. It has pod filters on it now and from what i'm reading online a lot of people who have put these on all have the same bogging issues.

Any help or advice would be great.
Hopefully someone here that's familiar with that type of bike can be of more specific help, but I can offer some general guesses. It does sound like carburetor issues, yes. The no-idle problem could be an idle screw adjustment or a clogged idle circuit. The bogging problem could be an accelerator pump problem, a slightly clogged off-idle circuit, or a jetting issue. Both could also be caused, or made worse, by an air leak in the intake manifold. (That's rather common in older bikes as the rubber seals and gaskets start to get brittle.) It doesn't sound like you were able to keep it running long enough to get any read from the spark plugs.

Jumping up from 1200 to 400 rpms? If the throttle was open that could have been related to any of the above causes, if that's what's going on.
 

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Another thing to look at would be your ignition system, especially if that bike has points. If your timing advance is not working correctly or sticking somehow that could also cause problems similar to some of what you're describing.
 

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Discussion Starter #19
Slumlord, Thanks man, I appreciate the effort on this but click the link again and look under the price. It says not available, and further down the page it says product obsolete.
I spent half of last week and most of this weekend looking for that lid, it's not available anywhere. I have to find an old one sitting in a barn or behind someones house that they're be alright with parting with. It could take me years to find one, which sucks, but i'll keep looking.
Also, took the carbs apart and cleaned the hell out of them, had to replace a gasket, put them back on, was a bog for a while, but since i've changed oil, changed plugs and ran it for awhile. I took it out for a 20 minute putt yesterday and it seems to be running "a lot" better then as of friday. No bogg at this point. I think it had just been sitting for so long that it had a lot of crap in it and I just needed to flush a lot of the old stuff out and get some new clean oil in it. I'll keep you guys posted on how things continue to go.
Thanks.
 

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So here's the latest update of my project CB400t.
I've got it running fairly good. for some reason, after about 5-10 minutes of idling it does not bog down and running pretty darn good. When I first start it cold, it does not want to idle. It wants to die unless I mess with the idle screw and keep the RPM's above 2000. during this time is still wants to bog down between 4-5000 RPMs when revving. after it's warm, no bog and it idles great. Is it me or is that not weird? I am new to bikes, but maybe it runs rough cause it's cold and over 30 years old?

I've had it out on the road a handful of times and it rides and runs great. I've very happy with my progress so far. I'm waiting for plates to arrive and some turn signals. I still plan on ordering some different size jets and hope that that may cure my running rough issue when cold. I think it's running lean or rich because there is a strong gas smell when i get back from a short drive. My clothes reek of it. It's going to be a trial and error thing with the jets from what I hear. we'll see.
I have put new handle bars and bar end mirrors on and changed the whole exhaust system from chrome to flat black. I'm currently building a fiberglass seat pan right now.
I've been having a blast with this project and i'm excited about how it's going to turn out when finished.

Ted
 
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