Topic: 1975 Honda CB400f Project - Beginner

[gjunkie]

Your throttle cables are probably set to far, therefor holding up the throttle and not letting it return to where it will hit the idle screw. What rpm is your idle at? Should be around 1000-1200 I think. I wouldn't worry too much on what reading you are getting on your carb sync gauges as long as they are all in sync and reading the same. 4000 rpm isn't very high for these bikes. My 350f doesn't make full power till like 5-6k and red line is at 10k. But you can check your sprockets and see if you have the stock number of teeth on there, front and back.

That's something I noticed. The top throttle cable is taught, the bottom one is a bit loose. How do I get more slack from the top and tighten the bottom?
I see what you're saying about the high red line, which would then make the 4000 rpm ok... But it feels like once I get to around 50mph there's no way ill go any faster. What's that all about?

As for the jets. I have no idea. I haven't set them, and I don't know what they're set to now. I'm gonna have to take it in to fix the oil valves, should I ask them to jet it as well? Or is that something I can handle? If so I'd prefer to do it myself to learn.

I have not done anything electrical wise yet, but I did ride it home today, about 45 min or so, and had no battery issues. Perhaps a wire was loose and it was fixed when I hooked everything back up? What are the odds of that?

Also, idle is at about 1800 right.

[hondamatteo]

Ya that's too high for idle, the throttle is not coming down enough. I don't have any pics to show you but if I remember correctly there is a locknut, loosen it then the base of the cable you can screw down or up to adjust. Pretty self explanatory once you play with it. You have a multimeter? Check to see what voltage you are getting across your battery when you rev it up a bit. Should be more then 13v. Have the carbs been cleaned? I always clean the carbs on a new bike that way you know for sure they are not going to be a problem. Check the number on the jets at the same time. That should always be done before a sync. Also I suggest spraying a copper coat on your new head gasket. This I think helped on my head leak. There are a few topics on the cb400f/350f head leaks.

[gjunkie]

I have a multimeter. That will be my next thing since the bike is now very close by!

I didn't fully clean the carbs. I was focused on getting to the source of the leak. But it shouldn't be too hard to get those cleaned. How do I check the number on the jets? I know nothing about jets.

[hondamatteo]

I have a multimeter. That will be my next thing since the bike is now very close by!

I didn't fully clean the carbs. I was focused on getting to the source of the leak. But it shouldn't be too hard to get those cleaned. How do I check the number on the jets? I know nothing about jets.

Should be stamped on the head of the jet. The 400f has a #40 for the slow and #75 I believe for the main.

[gjunkie]

Here's a question tho. How could 4000 rpm at 40mph (in highest gear) be right, if my bike is supposed to be a 60MPH @ 2240RPM ratio. How does that work?

[hondamatteo]

You are not making enough power. I would figure this out (ex. Dirty carbs, incorrect jets for pods, charging issue) then you can worry about your top speed.

[MexiChriS]

Lots of troubleshooting. Hope you resolve issues soon. If not, well more reading and learning for me to take in as others chime in!

Nice buy though, seems like you got a good deal... but curious as to how much you've spent so far in repairs/parts??



Its crazy, as I've been on a hunt for a Honda CB550 and can't find much of a deal in CA. I remember seeing so many CB400/450 on sale super cheap past 2-3 months in California. So I settled for that as my choice. Now I see nothing but $2.5 - 4 grand price tags!!!

Makes me want to stick to finding a CB550 as planned now.
Your dedication makes me want one to find a nice buy and start tearing one down... Anyways, hope to see more updates!

[gjunkie]

Lots of troubleshooting. Hope you resolve issues soon. If not, well more reading and learning for me to take in as others chime in!

Nice buy though, seems like you got a good deal... but curious as to how much you've spent so far in repairs/parts??

Its crazy, as I've been on a hunt for a Honda CB550 and can't find much of a deal in CA. I remember seeing so many CB400/450 on sale super cheap past 2-3 months in California. So I settled for that as my choice. Now I see nothing but $2.5 - 4 grand price tags!!!

Makes me want to stick to finding a CB550 as planned now.
Your dedication makes me want one to find a nice buy and start tearing one down... Anyways, hope to see more updates!

Thanks for the kind words! As for cost, well, the bike itself I got for $1200 USD. As for how much I've spent up to now on labor/parts, here's a rough breakdown including labor:

Timing/axle fix ($140): When I took it apart and put it back together, I wasn't able to set the timing right. I had to have a guy time it for me at a shop near San Fernando Valley (auto shop city). Also, a guy that was helping us out was trying to get the rear axle off, and since it had probably never been taken off and was near to impossible, he decided to hammer it out... ruined the tip and threads, so I had that same shop grind down the tip and rethread it.

New Front Tire Tube ($35)
Lot's of oil ($30)
Spark Plugs (~$8)
Uhaul tow ($20) 
Master Chain Link Remover ($30) - ended up being the wrong one, hence taking off the rear axle to get the chain off.
New set of jets (~$75) - I bought these as a precaution. They're relatively cheap.. about $4 each, but I bought a couple sizes up and down to really get it right.
Carb Sync Kit ($80) - It's a good tool to have.
Multimeter ($20) - another must have.

That's all I can think of right now. These are all things that I've HAD to spend money on. I've also bough parts for things I want to replace, so from there the cost goes up... clip ons, triple tree, speedo/tach mounts, etc. Without these parts, and including a few things I'm sure I'm forgetting, it comes to roughly $350-$400.

However, I need to take it back in soon to fix my oil leak issue, which I'm told that it comes from the Oil Orifice Valves being faulty in the CB400's. There's an old thread about this here: http://forums.sohc4.net/index.php?topic=99363.0. They push too much oil up and create too much pressure. Unfortunately, to fix this it means taking the heads back out, which means everything has to be timed again.... I'm hoping I can keep the cost of that visit under $200, but considering I'm probably gonna have it done in the Santa Monica area this time I'm not keeping my hopes up. We'll see. Hope this helps!

[gjunkie]

I'm trying to lay this issue to rest. After doing a lot of reading on these forums, I keep finding conflicting reports.

Oil Orifice Valves: I get it. These are the problem. That much I can understand. From what I'm also reading, the gasket set that I used came with replacement o-rings for these little suckers, yet were too small. So the problem persists. This thread has a number of different attempts at fixing the dreaded leak: http://forums.sohc4.net/index.php?topic=111517.0

Can anyone tell me if I was to get OEM o-rings if that would actually fix the leak? Or are these valves just part of the problem? Some people say use sealant on the head gasket, others say no (I did not). I just can't make out what the best solution for this problem is...

[gjunkie]

More Updates:

Wow.. I went ahead and tried to clean the carbs thoroughly to make sure to eliminate this as a potential issue with power. Boy was I in for a nice surprise! I took them apart one by one to make sure to not mix up any of the parts. Everything looked pretty clean except for the pilot jets, which I couldn't see through the pin hole... No problem, cleaned those right up and put them back... then I got to the third carb:











As you can see there's some pretty bad corrosion. The setting for the main jet literally has pieces missing at the top. The floats have a rust coloration to them, and the float pin is impossible to remove. It looks like something pooled in there and sat for a while.

The pilot jet, size 40, was impossible to clean. I soaked it in carb cleaner for about 20 min, used a small paperclip to try to clear the jet, but nothing... any tips on getting that clear?

Since I can't remove the floats, I'm unable to check the condition of the valve seat (if i have the name correct). I was able to remove the main jet and confirm that it is not clogged up. Same goes for the others. All jets, except for this pilot jet, are now unclogged. All the pilot jets were clogged, albeit not too bad, so that's part of my idle problem right there. I'm planning to getting this last one cleared up (or get a new one) and see if the bike performs better...

My question is, how do I know if I should even be using this carb? How much corrosion is TOO much corrosion? As for removing the float pin, I keep reading reports of people lightly tapping it out, others saying never to do that... The float itself has a bounce to it, so it isn't jammed which makes me think I could be ok without removing the pin for now. But I do have to check the float level to make sure all floats are even. Here's a couple more images, sorry for the poor lighting.

[Vinhead1957]

I would spray some good penetrating oil on it and let it sit over night.   Then I would tap on it with a very small pin chisel ever so slightly. It should be free there is really nothing to hold it in there.
The key word is finesse! Be gentle, tap it from both sides

[iron_worker]

Be careful!!! Penetrating oil and heat and ever so gentle taps. I know my cousin has broken off one of those little float legs before and had to find a new set of carbs.

IW

[gjunkie]

OK!

I got the pin off with a few very light taps. Turns out it wasn't fused... it was bent! Not much,  but enough to get it stuck. I straightened it out as much as I could.

Also, got the jet cleaned from the corroded carb!! My trick, a sewing needle, the smallest I could find. I poked through on each side, then soaked in carb cleaner. I repeated the process twice and it worked.

One thing I noticed as I double checked all the main jets was that two of them were VERY easy to take off. The O-Rings were essentially flat, which made me think that too much fuel would get through. Regardless, I wanted to at least hear this thing after cleaning everything out, so I put it all back together.

Wow, what a difference! She idled pretty much immediately. In fact, with the choke ON it would struggle. I was just so used to having to use the choke (not enough fuel getting through) that I instinctively turned it on... Turns out that with clean jets I don't need it as much. Who knew....

So I took it for a spin around a long block to see if I could get to some higher speeds and see what it felt like. Pick up was MUCH quicker. I could feel a lot more power! After taking it around the block a couple of times tho, she finally flooded. I should be getting some new main jets soon, I'll replace them, and then take it for a real ride. With my leaks and all

Side note: The battery is still totally good! Last time I charged it was for about an hour on Sunday. I'm still getting full brightness on my lights.

[swan]

Yeah. As I mentioned CB400F carbs are very sensitive to dirt, rust, corrosion, etc. Put an filter on your fuel line.

[gjunkie]

The fuel filter is the first thing I replaced on this bike. It's brand new. I've ordered a new set of #80 Main Jets to replace the stock ones, and I have a feeling once I do she'll purr like a kitten. After that... tackling this dreaded leak.

Can anyone tell me what is the best way to address the Oil Orifice Valve leaks?

Thanks!

[gjunkie]

I made my way to the Deus Sunday Mass today to check out some of the bikes. I found 4 other CB400f's, so I had to ask them about the leak.

Two of them told me that I had to replace the head gasket, which I did. They said that if that doesn't fix it, the most likely problem is that its warped. If that's the case I would have to machine them flat. Does this sound about right? At this point I think it's the most likely thing. One of them said that they also had a leak which he decided to just leave (which sounds like the "leak" that most people with this bike talk about). But mine is BAD... I mean I have to top off every couple of rides. That's just not right. So warpage seems likely.

Thoughts?

[gjunkie]

SO! In my search for a replacement carb I found that Yoshi's Garage in LA had a bunch. Most were missing pieces, some were in not so good condition, but they let me take home all of them to see what worked. One of them seemed like it was in pretty good condition, and although it was missing most parts, I was able to use the ones from the carb I was replacing.

So I put it all together and tried to start it up. It floods immediately. It seems as if there is no stopping the fuel flow. If I turn off the flow of fuel and try to start it up, I can hear it actually about to start as it burns through the fuel already in the carbs.

All of the jets in there now are at least clear enough to let fuel through. My guess is that the floats are not working properly and not stopping the flow of fuel... would this be a good guess? If all floats seem to have a healthy bounce/spring to them, could it be that the aluminum tab that makes contact with the spring is too closed and not pushing the spring soon enough?

I just received a new set of Main Jets to replace all of them just in case, but my guess is that I'll need carb rebuild kits for at least one carb....

** EDIT **
Or could it be that because the o-rings on the main jets are a bit corroded that the motor is sucking up too much fuel through the jets? Or both??

[gjunkie]

Replaced all the main jets and tried to set the floats to the proper height. I read that they need to be at 21mm. My understanding is that the lower the height the more fuel that goes through. They were all around 24mm (from gasket lip). The floats that came from the bad carb weren't even, so I evened them out. After a few tries it started back up. I was able to ride it around the block a few times, but I can tell the carbs need some major resyncing as it sorta sounds like the Lost monster. Or a typewriter.

I have to accelerate very slowly or else it bogs and shuts off. It also feels like it can't pick up speed very well.

I took a video of it idling for you guys to hear it.
Honda CB400f idling

[hondamatteo]

Kinda sounds like you are not running on all cylinders. Are all the headers getting warm at the same time?

[gjunkie]

Kinda sounds like you are not running on all cylinders. Are all the headers getting warm at the same time?

It's hard to tell it gets warm pretty fast. I know all plugs have spark and when I synchronized the carbs last time it sounded a lot better. Is there another way to tell if I'm not running on all cylinders?

[hondamatteo]

You can pull the plug caps while its running (with some non conductive pliers preferably) Ground the cap to the engine somewhere. You should notice a distinct change in engine rpm and sound when you pull each cap. Or just squirt water on headers?

[iron_worker]

Yes I agree that it is likely missing on one cylinder. When you slow the idle down you can hear it doesn't sound smooth anymore but sounds like it's "chugging" along. The slow rev is likely from it having to pull up a dead cylinder with it. Either than or it's running really lean.

I would check that you're getting spark to all cylinders as Hondamatteo has suggested.

IW

[gjunkie]

Well I know I'm getting spark on all cylinders for sure. That I've checked. I'm gonna try to sync the carbs today and see if that helps. I really don't like my float, pin, and spring situation I've got going on right now. Particularly the bounce on the floats, a couple are a little tougher than others, which would definitely affect the flow of fuel.

[gjunkie]

OK. I took a go at syncing the carbs. The typewriter sound was reduced, but not eliminated. It also now feels like it has no power.

To be honest, I just think the carbs are totally messed up. I think the floats are bad, the springs are bad, the pins are bad. I need to get myself some rebuild kits and start these carbs with as many new parts as possible.

After that, try to sync the carbs again. I'm convinced my carbs are 99% of my problems.

Does anyone know if when you buy new floats for a specific bike if they come set to the height the company recommends, or is that left to the buyer? Thanks for the help guys!

[iron_worker]

The floats are probably preset somewhat close but the tangs are easily bent out of adjustment so would be best to verify. It's not hard to set float height. A lot of guys just use an old plastic card (credit card or similar ... preferably one you don't owe money on lol) and cut a section out of the middle that is the desired float height. Basically you end up with a little C shape. Each leg stands on lip of carb body flange and the cut-out goes over the float height. You want to adjust the float so it *just* touches the back of the c-notch.

If that makes sense.

IW