Topic: CB400F - Running Lean & Ejecting Bolts

[.RJ]

Hi SOHC brain trust, I've got a stack of issues I'm working through on a new (to me) bike and looking for some guidance.

Backstory - I bought this 400F off of ebay with 26k miles, seemed to be everything in order the guy was a motorcycle nut and had gone through and replaced a lot of things to get it on the road - brakes, tires, cleaned the carbs, and a few other things.  Supposedly he ran out of some motivation to get it perfect - it was running a little rough and needed a carb balance, valve adjustment and some small things to finish up, so I thought easy enough.



I get the bike home, put fuel in it and it ran like #$%* and seemed to have an air leak downstream of the carbs - idled too high (2-3k rpm) and would hang on the revs.  So I start getting into it - pulled the carbs, replaced the manifold & airbox boots, cleaned the carbs out (pilots were clogged), bench sync'ed and double checked everything there.  I also installed & timed a dyna ignition, adjusted the valve lash, they were all a hair tight.  The bike had also come with a new set of exhaust gaskets and when I took the pipes off to figure out why there appeared to be a leak from the #1 pipe I figured out why - there werent any gaskets at all.  I'm not sure how long the bike was run like this.  So, installed those as well.

At this point I'm feeling pretty confident I've gone through everything and I'm ready for spring - this isnt my first rodeo at getting an old honda running - put fuel in my remote fuel can and fire it up and the idle is way worse - 4-5k rpm and the right side (#3/4) pipes got hot very quickly, plus the plugs looked black and sooty after only a minute of running.  Thinking that I've got a worn out clamp or pinched the manifold boot o-ring somehow I figured the leak would reveal itself spraying brake cleaner around the boots and I come up empty - no amount of brake cleaner anywhere around the boots, either front or back of the carb, airbox, etc has any effect on the idle - so.... where is my leak coming from?  Checked compression and had 115/110/120/120psi - 1-4, cold, dry so seems good there.

There was also black liquid - I'm guessing just condensation from short running time - dripping from where the #$%*ty aftermarket clamp is holding on the #$%*ty aftermarket muffler on.... I guess I am in for a new set of pattern pipes from david silver spares here, too. 

Then as I'm trying sort this out I hear "clunk" and oil pouring out of the clutch cover....  keep in mind this bike has been run for maybe 5 minutes total since bringing it home and hasnt left the garage. 









The clutch basket nut also doesnt look like what the shop manual supplement says it should, either - so I wonder if someone replaced this nut along the way with something other than OEM for easier servicing?



The bolt and primary shaft threads and primary gear all appear to be undamaged so I can probably loctite and reinstall the bolt and be good there and grab another clutch cover off of ebay.  Does this have anything to do with my air leak?  I'd think not as the primary shaft is effectively a blind hole and wouldnt leak through the crankcase up to the cylinders. 

Where do I go from here?  This was not supposed to be a project, but I'm afraid that I'm going to have to pull the top end & jugs off at minimum and I'm guessing good, used CB400F engines are in short supply these days.

[bryanj]

A lot of bench synced carbs rev too high because they have been "adjusted" too high up the thread and  the mechanism can not close properly, if unscrewing the tickover adjust screw has no effect this may well be the cause. Having done them before right does not mean they are right this time-----i been doing them as a living over 40 years and still make the occasional cock up that way!!! Have a read at some of the 400 threads on the UK site as a few people have found pilot screw setting makes a big difference to even tickover.

As to the primary bolt and clutch nut, that would make me do a total strip and check as how can you be sure anything is correct now and the 400 camchain tensioner is always worth checking out.

Finally, at least here in UK, 400 engines are getting rare especially in complete running order.

Best of luck with your quest.

[.RJ]

I was worried about setting them 'too high'.  What should the closed clearance of the backside of the slide be?  I set them with a slight drag on a a 2.5mm t-handle wrench and the idle screw screwed in halfway thinking I'd give myself some adjustment both ways.  Too much?  I know others here seem to like the round end of a 1/8" drill bit.  I also set the air screws at what I think is the factory setting of 1-7/8 turns out from closed, although looking here I should be 2-1/2 turns out - http://manuals.sohc4.net/cb350/service_manual/SM350400_3.pdf .  The 'carb kit' was aftermarket but I bought them from 4into1 and have had good results in the past with their products.

The primary gear bolt spitting itself out makes me very suspicious of who was in there before doing what.  I dont think the cases have been apart as there's some red paint looking stuff dabbed on a lot of bolts, I'm guessing someone was trying to seal up a leaky engine. 

[.RJ]

From here - http://forums.sohc4.net/index.php?topic=91467.0

Make sure the slides are in correctly - the cutout must face the choke. You can reverse them in pairs since the keying slots are opposite sides with 1 & 2 different from 3 & 4.

I think I may have found my problem.  Time to dig some more today.

Still doesnt explain the primary gear issue.  I wonder if the previous guy installed new clutch plates and didnt torque the bolt in properly though it doesnt need to be removed.

[.RJ]

Yep, slides #3 & #4 were backwards.  That problem is sorted.

On the primary gear bolt.  It will thread in to the input shaft and seems that it will hold torque - so it seems like the easiest course of action is some loctite and torque that guy back in, with new clutch cover & oil seals.  Anyone got a clutch cover sitting around?

Still got 40+ year old valve stem seals, can those be replaced with the head on & motor in the frame?   Or if I want to refresh the head, does (or should?) the motor need to come out? 

[bryanj]

Head will come off with engine in frame but the bit of camchain tensioner that gets damaged/worn needs the bottom crankcase off

[jakec]

I just bench sync'd my carbs using the smallest drill bit I had, maybe 1/16"? Hope that wasn't too big.

To RJ, I too have run into problems with an ebay purchased 400F. I feel your pain.

[.RJ]

Well I'm certain the carb issues were due to the slide cutout reversed, so I feel better about that one.  First time for everything, I guess, never seen that one before.  I bench sync'ed them with the same 2.5mm t-handle, it was right at the point you could get daylight through from the other side of the carb - I've got plenty of adjustment either direction on the idle screw so I think I'll be OK there. 

Can anyone confirm the correct idle mix screw setting?  2.5 turns out seems like a lot - normally if I'm going that far out I'm going to get a larger pilot jet.  The 400F carbs do not have an o-ring on the idle mix screw, correct?

I think I'd like to get a riding season out of this bike before tearing into the motor - the 455cc Yosh big bore kit is looking nice for when the time comes.  A new repro muffler, clamp and gasket are on its way from DSS, along with a clutch cover gasket, oil seals and new pan-head screws.  Just need to find a used clutch cover now.

[dugsgms]

Cover could be a little tough to find, kinda rare. I looked around a bit and found one in Germany, decent price too.
https://www.cb-four.com/cgi-bin/shop/__Clutch-cover-Honda-CB400F-used__17-8202-09_02.07.html

[.RJ]

Thanks for the lead - if my usual source for parts up in Baltimore doesnt have any I'll have to grab that one.

[ekpent]

 Sorry your off to a rocky start with your new E-bay purchase.Getting some miles on it before doing anything else sounds like a good idea and you may find its all good to go once run in a little. Lets see if it needs fork seals,hopefully has some newer ones in there. Enjoy, those are neat machines.

[.RJ]

Forks dont seem to be leaking but not sure how old the seals are - for my 350 twin project I used 400F forks and rebuilt them with new springs & racetech gold valves, so hopefully I get that on the road soon to see if I want to do the same with this one.  I'd love to keep the original appearance but if I can make it run, go & stop better that'd be great.

[Redline it]

looks to me like someone who sold it to you, knew there was a big problem on the primary shaft. and selling it because of his short supply of motivation apparently was aided in the fact that maybe that primary shaft is toast and being the nut that he is, he knew it was macgyvered together and wouldn't last long. it's ebay, some people will do anything to sell junk. piston rings worn out, transmissions shot, main bearings used, beyond limits of specs for sale. crazy. i bought a rack of carbs for a cb400f and asked the guy to take more pictures before a sent 250 bucks. and he carefully missed the 16 holes that had been bondo'd or jbwelded closed, that was 4 holes in each carb body. someone tried to bore the venturi with a too large of a boring head, maybe they used a hole saw. he returned my money and i kept the carbs and sent him 90 bucks for the jets. the carb was rusted stuck floats etc. 

[BenelliSEI]

RJ...... I you want to “road test”, cut a piece of aluminum to fit and JBWeld it in temp. Glue it in then after doa cover coat...... it will hold for a test.

[.RJ]

To add some closure to this one, I scored another good condition clutch cover off of ebay, in nice shape, with no holes in it.  I pulled everything out of the clutch cover, it all looked as it should I think, and reinstalled with some red loctite on the primary gear bolt.  I dont expect I'll ever have to remove it again.  With a new gasket and bolts it sealed up and good to go.

I wasted a ton of time with Bob's parts in Arizona - they are incredibly disorganized over there, in that it seems only one person will do the shipping, one person will take the payment, one person will pull the parts and none of them will talk to each other or are at work in the same time.  They originally sent me a sprocket cover, and then weeks later I got them to send me the clutch cover, which, also had a hole in it and was gouged to hell by someone removing one of the screws by using a flathead as a chisel.  It may have been salvagable but I moved on and will never deal with them again. 

The carbs were assembled incorrectly, but after correct assembly, we still have some problems.... on to the next thread - http://forums.sohc4.net/index.php/topic,177932.0.html

[Alaxy Galaxy]

I couldn't help but chuckle at these two topics back to back... 

I feel your pain RJ. My problems were fixed with a good carb balance and re-jetting.

[cjespersen]

I need to run over to Bob's parts in Arizona to see what they have for CB350f tanks but its getting hotter then #$%* this time of year.

[.RJ]

I couldn't help but chuckle at these two topics back to back... 

Yeah, its been a rollercoaster ride over here.  I have the carbs apart on the bench and everything *looks* clean and clear and I hope that an assortment of OEM parts in place of the aftermarket stuff resolves my issues. 

The PO I bought it from had a garage full of bikes but he was not a "honda guy" so I cant blame him too much for using aftermarket carb kits and installing slides backwards, but its run me in circles for months now.  When we're done I've gone through everything again and we should be good to go for a long while and better than it was when I started.