Flasher relay and LED indicators

The CB350 had this weird issue when using the turn signals. When you switched on either side, the signals on that side would stay lit for a few seconds, and then verrrry slowwwly flash on and off. You wouldn’t think this would be such a big deal, but when you’re trying to change lanes or signal when approaching an intersection, a turn signal lit without flashing just looking like a broken parking light.

So I went looking for solutions and found that I could use a modern flasher relay to replace the ancient mechanical one. I decided to replace the flasher entirely because I was thinking of replacing the indicator bulbs in the gauges with LEDs, and the turn signal indicator required an LED-compatible relay anyway. I ended up with the LF1-S-PIN flasher from superbrightLEDs.com.  I’ve used superbrightLEDs.com for replacing bulbs in my last two cars, and their stuff is always high-quality (even if on the expensive side).

A picture of the flasher is below.  It’s got two prongs, just like the stock mechanical relay.



I already had the tank off, so I went ahead and removed the old flasher from the left side of the bike.

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I removed the metal bracket that provided the mount for the old rubber relay holder, and threaded the new plastic relay onto the bolt that supported the old mount.

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Clean and stable.  And turn signal indicators now flash properly as well!

Oil filter cleaning

The main reason that I decided to restore a CB350 instead of any other bike is that it is a simple, uncluttered machine that has very little weirdness to its upkeep.  One exception to this is the oil filter cleaning.

The oil filter on the Honda CB350 is not of the spin-on/cartridge type that you can find in pretty much every modern car/motorcycle application these days.  It’s actually a steel cylinder whose centrifugal motion (driven directly by the crankshaft) pulls heavier particles to its outer walls while allowing oil through its central outlet.  This is the first weird thing about the oil filter.

You can gain access to the oil filter by first draining the oil from the crankcase and then removing the oil filter cover on the right side of the crankcase.  Do not lose the o-ring on this cover.  My cover was actually pretty tight in its bore, and I had to wiggle it out using a long flathead screwdriver.  Although the cover is cylindrical and unmarked, it can only be re-attached to the crank case in one of the three possible positions (three because of the three equidistant screws supporting it).  That’s the second weird thing about the oil filter. Make a mark on the crank case and cover so you know how it will re-attach.  The three screws are the same.  2015-07-05 09.33.02

In order to remove this filter, Honda recommends that you use special oil filter removal tool.  People on hondatwins.net recommend using a M6x1.0 bolt instead. This seemed to work fine.  Just get the longest M6x1.0 machine screw that you can find.  The fact that Honda didn’t just recommend that in the first place is the third weird thing about the oil filter.

First you’ve got to carefully remove the circlip holding the outer piece onto the filter barrel (not shown) by squeezing the two holes towards each other with a needlenose pliers.  Honda recommends replacing this circlip with each oil change, but you can re-use it if you’re careful.  Also, it’s not a cheap part.  (I was not careful and broke one of the two circle tabs — still usable but about ten times more annoying to use.)

Once you’ve got the circlip off, simply thread the M6 bolt into the threads at the back of the filter barrel as shown, and then when it bottoms out, pull the barrel out using pliers.

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All that’s left is to clean out all the muck in the filter barrel.  It may look like there’s nothing in there, but believe me, once you start scraping a towel around with some WD-40 on it, there will be layers of gunk coming off.

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Mine wasn’t too bad, but I’m planning to run some Marvel Mystery Oil in the next change of oil so I plan to see some more muck at that time.  Luckily there were no metal shavings or rust.

Anyway, assemble in reverse order and re-fill the oil, and you’re good to go.


Left carburetor rich, unaffected by idle air screw

If you’ve been keeping up with my progress, you’ll remember that I recently rebuilt my carburetors and re-installed them on the CB350, but that I was having some trouble tuning them, and that some lightish smoke (with black condensate) was coming out of the left muffler.

I did some further investigation today, using the old pull-one-spark-plug-lead-off method to run the bike on one cylinder. While running on the right cylinder alone, the bike’s idle was in fact controlled by the idle speed screw on the right carb. However when I ran the bike on the left cylinder alone, the idle speed was entirely unaffected when I manipulated the screw. I could screw the idle screw all the way in or remove it entirely and the bike ran either way.
This would seem to indicate that there’s some sort of condition on this carb that is causing fuel to make it through even when the idle air jet is pulling nothing but air. There’s likely a rich condition.  That COULD also explain the smoke from the left muffler.
Because I’m not seeing anything coming out of the overflow tube for this carb, I have a hunch that the floats are set too high in that carb. When I have some free time I’m going to try adjusting it downward to see it that helps.

Carburetor rebuild

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Rebuilding carburetors a carburetor for the first time is a lot like having sex for the first time.  You pull off the cover and find a whole bunch of parts, tubes, and pieces that you’ve heard about before and maybe even seen some illustrations in textbooks, but the moment you start prodding around you instantly feel like you missed a step and you’re in way over your head, and that carburetor knows it.  All your friends are going to laugh at you when they find out you tried to stuff a secondary jet into the idle jet hole.  Compounding this difficulty is the fact that Honda used at least three different carburetors during the 4 production years of the CB/CL350, so online information is often incomplete and unclear.


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And oh yeah, it’s filthy down there.  Note how the old float bowl gasket is actually flattened and bonded to the groove of the float bowl.  This is the reason that gas was seeping out of the sides of the carburetors before I took them off of the bike.  2015-07-02 17.19.34

I used a set of K&L carburetor rebuild kits to rebuild my carburetors.  They contained the right replacement parts for the primary and secondary main jets (#68 and #105), needles, float bowl gaskets, and float valve assemblies.   I was afraid that I’d crack the ancient brass floats if I attempted to pop out the float hinge pivot, so I never got down to the float valves to replace them.  I really wanted to replace the slow jet from the left carb, but the kit had the wrong size jet included.

When you remove the three jets, you should be able to see straight through the primary/secondary holes to the throat of the carb (two larger holes on the left), but not through the slow jet hole.  This is because the slow jet feeds fuel through a passage that makes a turn towards the outlet side of the carb where it lets out just on the engine side of the throttle plate.  2015-07-02 23.02.57


So I didn’t get a chance to replace the slow jet or float valves, and because I didn’t detach the floats, I didn’t soak the carb body in carb cleaner.  I did set the float levels by eye.   I also pulled the slide and replace the needle.  In hindsight, it probably would have been a good idea to lubricate the slide with some WD40 or something as well.   I just didn’t think of it.


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There are three passages that connect to the area under the diaphragm.  I am not sure what these are for, and I did not clean them either.  I will likely have to do that in a future rebuild.

I painted the top covers because they were rusty and disgusting, and then reassembled the carbs.  I installed them on the bike and sync’ed the throttle cables.  The bike started right up.

I am finding that the bike has lost the problem it had before of holding revs after the throttle is closed (probably due to cable synch issues), and that power is greatly improved.  Tuning was still not possible however because the idle screw on the left carb doesn’t seem to have any impact on the idle speed of the bike.  I will probably have to tear that carb apart again and thoroughly clean the idle jet and/or idle screw.  Hmm.

Much like my first time having sex, I did pretty much what the books told me to do and conquered some of my fears in the process, but I ultimately left the job less than satisfactory and will need to do another job to really clean things up.




Valve clearance adjustment

Honda’s factory service manual (FSM) lists as 150-170psi as within specification for cylinder compression.  I did some measurements when I first got the bike and found the right side firing at 170psi and left side at 119psi when warm.  I let the bike sit for a week with Seafoam Deep Creep in the cylinders, topping them up every couple of days.  I got the bike up to running temperature and did another measurement.

Right: 165.  Left: 119psi.

Per the FSM, I added a tablespoon of motor oil to the cylinder with low compression and re-tested.  I got the same result: 119psi.  This indicates that the compression issues were caused by something in the head of the engine and not in the piston rings.  Possible causes include the head gasket, valve timing, clearance, or seals.  I didn’t see any leaks around the head gasket, so I decided to try my luck with adjusting the valve clearance.  I didn’t see any reason to check the right cylinder because it was running well already.  Don’t fix it if it ain’t broke.

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There’s three things you have to do in this operation: Hold the crank at top dead center (TDC) for the cylinder you’re examining (“LT” mark on the generator rotor) with one hand, and with the other hand alternate between slightly adjusting the tappet clearance adjuster screws and checking the rocker arm clearance with feeler gauges.

This is harder than it seems because the appropriate clearance is measured in thousandths of an inch, and even a couple thousands off will cause problems.  The adjustment screws only need to be turned a thousandth of an inch in order to translate that change to the rocker arms.  It took about an 30 minutes for me to adjust each of the two screws.  That’s half an hour sitting on the ground, resisting the inertia of the cylinder falling from TDC, trying to turn a flathead screw a thousandth of an inch and accidentally going a few hundredths in the wrong direction each time.  Ugh.

Once I got the valve clearances into spec, I did a quick compression test on the cylinder and read 155psi, up from 119psi!  That’s with the carburetors off the engine, so the engine was cold.  With the engine warm, it’s likely that that number would be a bit higher.  Either way, the cylinder is now in spec for compression.

Carburetor removal

My carb rebuild kits came in earlier this week, and I figured that it might be a good time to actually take the carbs off the bike to clean them. It was pretty scary. The carbs were so gummed up that even when I unscrewed the drain screws at the bottom, gas came out from the drain screws themselves (and not the drain holes!). When I turned the left carburetor sideways to remove it, gas started leaking out through its gasket. These things need a serious overhaul.

Here’s a picture of the bike with the air filter removed.  The fuel petcock was turned off, but I think that the fuel lines were still flowing a little bit of fuel.  I’ll have to check that out sometime.  I want to get some nice chrome filters, anyway. You might also notice that the right carburetor is missing its choke plate.  I know, pretty lame.  I’ve got the plate on the left carb, but I might just run with that if I can get the bike to agree.

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Next a look down the intake manifold form where the carburetor was attached.  I sprayed some deep creep into each manifold for good measure.  Can’t hurt.

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This is a picture of the bike with the carbs and air filters removed.  Yeesh.

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And the stars of the show, the carburetors.  Ready for a good cleaning.
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Tachometer oil seal

When I first took the bike out for a 5 mile ride at about 45mph, I noticed a new feature: hot oil gently spritzing my right pant leg with the fury of a tiny sun. When I stopped to take a look at it, I found that oil was seeping slowly from the port where the tachometer drive cable entered its housing on the right side of the engine head.  The cable was secure in the housing, but there was a couple millimeters of play in its seating against the oil seal.  This is probably why there was a leak.  I think that over the 40 years since the bike was assembled, the seal had hardened and shrunk.  honda-cb350-super-sport-350-k4-1972-usa-cylinder-head-side-cover-breaker-advancer_bigma000148e02_d4ae

I ordered new Honda part 91211-286-003 to replace the oil seal that was apparently failing.  That’s part 19 in the schematic above.

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At first, I had a lot of trouble getting that oil seal out of there.  It was apparently fused to the aluminum of the housing.  I tried using combinations of penetrating oil (Seafoam Deep Creep), dental picks, wood screws, and tweezers, but nothing worked.  I looked to www.hondatwins.net for guidance and found a recommendation to just pull out the whole tachometer drive element (#5 in schematic), and the oil seal would come with it.


After some wiggling and gentle but firm yanking, the whole assembly dislodged.  I had pretty much destroyed the old seal while trying to remove it earlier, as you can see.

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I replaced the seal and re-assembled the connection.  The play in the seating of the cable is now almost gone, and the leaks appear to have almost completely gone away.