Author Topic: First timer top-end rebuild gone wrong, yippee! Ugh... (Read 21993 times)

markreimer · « **Reply #50 on:** August 21, 2015, 08:08:14 PM »

Here's a quick video of the bike running

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70CB750 · « **Reply #51 on:** August 22, 2015, 03:01:57 AM »

Check your coil by swapping 2-3 for 1-4 and vice versa. If the problem moves to 1-4, its the coil or power to the coil.

markreimer · « **Reply #52 on:** August 22, 2015, 12:55:39 PM »

How would you do that? My 2/3 spark plug wires aren't long enough to reach 1/4.

I went out again this morning to go for a ride. Started up fine, but as it was warming up #2 cut out. I drove around the block and it got worse. Came home and it would hardly idle, then died and wouldn't start up again.

I removed the plug from #1 and #2 to check for spark. #1 had good spark. Then I put #2 plug into #1 wire, no spark. So that would confirm it was a fouled plug problem, not a coil problem? Or is that misguided... would it be possible the coil is failing to the point that the plug gets fouled from fuel after not firing, which would mean my little plug swap experiment didn't prove anything?

markreimer · « **Reply #53 on:** August 23, 2015, 01:38:56 PM »

Just went out for a ride and discovered two new variables, one of which is a bit embarrassing.

Tried to start the bike with the electric start - engine barely turned over. Gave it a couple kicks and it sprang to life, but within a block or two it sounded like one or two cylinders cut out and I was loosing power. Five blocks later the engine totally died. I pushed into a parking lot and the electric start had no juice, so a few kicks and it started up, but died a shortly after. WTF?

I looked in the tank, there wasn't much gas in there, but there was some. The gas lines also looked like they were full. I dropped three carb bowls - all bone dry. Ah ha... that's not right.

Pushed it ten blocks to a gas station (for shame!) and filled it up. Once the tank was full, I could see the gas flowing through the lines. Carb bowls all filled up.

Seems like I've got something wrong in my gas lines or maybe petcock screen. One kick and it ran perfectly on all cylinders. It makes me wonder, perhaps my #2 not firing properly is actually a fuel supply issue?

Then when I finished my ride, I tried the e-start again since it should have been charged by then. Still nothing! I checked the voltage:

Killswitch in 'on' and highbeams on - 11.7V
Hit the starter button - 5V...... that's not right!
kickstarted the engine, 13V at idle
Held revs at 4k - 15V

Soooo...it's charging, but the battery still doesn't have the capacity to start the bike - it's about five years old. Time for a new battery? What should the voltage drop to when hitting the starter?

mrbreeze · « **Reply #54 on:** August 23, 2015, 04:15:25 PM »

Without rereading this thread I would say time for a new battery. 5 years is longer than I would expect one to last. The battery just sat there while all the rebuilding was going on and usually does the same through the winter months. I usually get 3-4 years tops out of them.

markreimer · « **Reply #55 on:** September 09, 2015, 01:23:12 PM »

You were right, definitely a battery issue. I left the bike on a battery tender for about two weeks while I was riding my other bike. I decided to take it for a ride, disconnected the tender and hit the starter - the starter turned normally for about 5 seconds but the engine wouldn't 'catch', and the starter quickly slowed down until it stopped completely. It lasted maybe 30 seconds.

I put a multimeter across the battery - 12.3V or so. All the lights worked, but I couldn't get it to start up. Weird. Checked the battery...Ahhhhh...it's dry! Time to drop the new battery in.

1 minute later with the new battery installed, hit the starter - instantly starts up and settles into an idle right away. Nice!

I took it for a ride around the block. About a minute into the ride, cylinder 2/3 stop firing. Dammit, what's up with that? I lug it back to the driveway and let it idle while I think through what might be happening. A minute later, they kick back in! Hmm, weird. I rode it for 15 minutes problem free, then parked it.

Came back two days later, started up instantly again with no dead cylinders. Went for a 20 minute ride.

A day after that, same thing. No issues.

So it looks like my starting issue was battery related, but I still have the occasional 2/3 cylinders acting up. I'll go over the wiring to the coil, maybe I've just got a weak connection there. My original dead cylinders were caused by fouled plugs, but this time its 2/3 cutting in and out together, at the same time, which sounds like it must be a wiring problem. I'll figure it out soon enough.

Here's a hottttt video of the bike in action after the new battery..... https://instagram.com/p/7Q3xePB2A3/?taken-by=markreimer

Scroll through and you can see the '74 cb350f I'm rebuilding now!

mrbreeze · « **Reply #56 on:** September 09, 2015, 01:45:08 PM »

Yes clean and tighten all connectors thoroughly. On my bike it turned out to be The power wires to the coil. With the tank off and in front of the coils is a double female. I don't remember the color off hand but it supplies power to the coils. Each coil has a male that connect here. One of mine was loose (turned out to be 2-3). When a connector is loose it arcs and that cause heat which accelerates corrosion. It will start out as an intermittent and when left unchecked will totally fail.

70CB750 · « **Reply #57 on:** September 09, 2015, 03:11:31 PM »

Power to coils come from the Kill Switch, black with white stripe wire in Honda scheme of things.

markreimer · « **Reply #58 on:** September 22, 2015, 08:48:02 AM »

I checked the black w/ white striped wire coming from the coils and one of them was indeed only half-connected. Strangely enough it was the 1/4 coil though, hah! Anyway, I pulled both wires out, cleaned the contacts and re-connected them. The connection was nice and tight. I went over all the connectors to the coils and ignition, making sure they were good and tight.

The bike fired up right away, though it belched out some nasty black smoke for about ten seconds. Weird, that's a first. I've had blue smoke from burning oil, and white smoke after the rebuild, but never black. Any thoughts? It cleared up and idled just fine.

I went for a 20 minute hard ride to get the oil nice and hot, then came home and changed it for the first time after the rebuild. I was happy to not find any large metal flakes. My oil pan magnetic plug was clean, and the filter housing was clean as well. I had about 200km-250km on it since the rebuild.

I also removed and cleaned the oil pressure switch as I was getting erratic performance from the oil light. It wouldn't switch on with the ignition if the bike had sat for a few days. But it would come on after I shut the bike off. A quick cleaning and it's working exactly as it should, shutting off within a second of engine startup.

Also replaced the K&N air filter with a stock filter after hearing some negative reviews of the K&N. Overall the bike is running really well now. It pulls harder than ever and is nice and smooth. Though after riding my dual-disc R80 for the last few months, I was shocked at how HORRIBLE the cb's front brake is

Maybe this winter I'll have to do a dual disc conversion.

mrbreeze · « **Reply #59 on:** September 22, 2015, 07:34:35 PM »

Glad you got it sorted. The black smoke was unburned gas. It always pays to be thorough with the maintenance on these old bikes.

jayowen · « **Reply #60 on:** September 22, 2015, 08:32:01 PM »

i had a similar issue with my cb550 where after riding a bit it would foul plugs. ended up being condensers. when they got hot they began to fail which in turn fouled the plugs due to weak spark. just something to look and and they are fairly cheap.

markreimer · « **Reply #61 on:** October 02, 2015, 11:27:27 AM »

Thanks. I've got a Dyna-S ignition system so I thankfully don't need to worry about that.

I was out riding my bike just now and the middle two cylinders died after doing a minute or so of near-red line acceleration. I pulled over and waited a minute, then shut the bike off. Started it again and 10 seconds later they both kicked back in, and remained running for the remaining 10 blocks to work. Hmmm... So even though I went through all the connections to the coil for 2/3, I still had that problem. I'm thinking that might suggest a coil on its way out. Since it doesn't do this all the time, any ideas how to test the coil? I wouldn't think the typical way using an ohm meter would work since it works fine more often than not.

Also still getting that puff of black smoke on start up. Not sure why I'd have unburned fuel in there though? I checked the petcock and it's not leaking. If I leave it open when parked I don't have fuel pouring out the overflow tubes, so I don't have reason to think my floats are leaking either. How would unburned gas be in there then? Could it be related to the coil problem?

markreimer · « **Reply #62 on:** October 02, 2015, 11:59:01 AM »

Just realized I have a spare set of coils from a '74 cb350F, which I believe are identical to the 750 coils. I'll try swapping the 2/3 coil and go for a long ride, see if anything changes.

markreimer · « **Reply #63 on:** October 02, 2015, 05:07:37 PM »

More weird behaviour. I rode to the shop to pickup my spare coils. When I started the bike, 2/3 wouldn't go. After 2-3 minutes of wiggling wires and staring at the damn thing, it spontaneously kicked back in. I rode to the shop and grabbed the coils, then hit the highway. I noticed a lot of white smoke coming off the engine and out the breather. Looks like I have oil leaking at the valve cover, pooling on the fins and dripping down, and when I stop at a red light and there is no wind to blow it off it starts to burn. It looks like I'm sitting on a bonfire!

After doing a few hard accelerations up to red line-ish, I came to a stop light and the oil light went on

It shut off at 1500 rpm though, so I figured it might be a fluke. It continued to flicker at anything under as I rode straight home, keeping rpm's as low as possible. By the time I got home the engine smoke was really, really bad haha. Guess that new valve cover gasket didn't work out. But now the oil light was staying on all the way up to 2,000 rpm. What's up?!

I had a buggy switch earlier where the light wouldn't turn on with the ignition. I removed it and cleaned it with carb cleaner. It then worked perfectly for a few days. Now it's doing the opposite and coming on at idle.

After I let it sit for 20 minutes and wiped all the oil off the front, I started it again. No more smoke anywhere, including the breather, though I did notice a little drop coming out the hose. The oil light also didn't come on at idle or any other speed, but did light up when I shut the engine off.

What's up, just a sender switch on it's way out? And regarding white smoke from the breather (no, it is not water vapour, I rode for an hour at 50mph and it was still there), could that still be from the top-end rebuild? I've only got about 250km on it so far.

Next steps - see if I can torque the valve cover down at all anymore. If not, I may try replacing the gasket with the engine in the frame. It's worth a try. Sure wish I didn't sell that damn frame kit...

Imago · « **Reply #64 on:** October 02, 2015, 06:55:27 PM »

Your electrical dilemma got me thinking...

I remember in 1981 on our way from Saskatchewan to see Mt. St. Helens right after it erupted, my 1975 CB550K kept dying on 1 or 2 cylinders, just like yours.

A Honda dealer in Montana, as I recall, finally determined it was an intermittent wire in the spark plug caps, or an intermittent resistor in the same caps which I believe the 750's have as well. When they got warm and expanded, no contact.

Up until then I drove on 2 cylinders for WAY too many miles before we figured it out.

Mine smoked too, from all the unburned fuel pouring through the cylinders.

Check the caps out. You never know...

mrbreeze · « **Reply #65 on:** October 02, 2015, 09:23:11 PM »

Did you check the black/white wire connector under the front of the gas tank? That's where my problem was a couple of years ago. That wire branches off to 2 wires. It runs from the kill switch and each wire that branches off supplies power to the coils. The connector on the one that feeds the #2-3 coil was loose and corroded. It started out to be intermittent and finally failed totally. The loose connection caused heat and the heat caused corrosion. After cleaning and tightening the connector...all is well again. I thought I had bad coil also. When you think you have cleaned all connectors...go through and check em again and be thorough!!! Much cheaper than throwing parts at it.

markreimer · « **Reply #66 on:** October 02, 2015, 10:09:23 PM »

Quote from: mrbreeze on October 02, 2015, 09:23:11 PM

Did you check the black/white wire connector under the front of the gas tank? That's where my problem was a couple of years ago. That wire branches off to 2 wires. It runs from the kill switch and each wire that branches off supplies power to the coils. The connector on the one that feeds the #2-3 coil was loose and corroded. It started out to be intermittent and finally failed totally. The loose connection caused heat and the heat caused corrosion. After cleaning and tightening the connector...all is well again. I thought I had bad coil also. When you think you have cleaned all connectors...go through and check em again and be thorough!!! Much cheaper than throwing parts at it.

Yeah that was the first thing I checked, and I DID find a loose connection, but it was for the coil that fires 1/4, hah! I cleaned all the coil connections and plugged it all back together. Still having this issue. Tomorrow I'll do a static test of the coils and see if it shows anything interesting, but I doubt it as it normally works just fine..

Bad news is that I bench tested the two 350f coils I have, and they're both dead. I'm not getting any reading at all through them. Not very surprising, they were free in a box of junk parts. My wife has a complete 350f which I could steal a coil from for a couple days to test though, so that'll be the final test.

I'll also check the caps. I trimmed 1/4" off the wires a year or two ago, but I always thought you really had to bend the wires aggressively to get them on the plugs so it's possible the connection is just bad there.

markreimer · « **Reply #67 on:** October 08, 2015, 05:09:21 PM »

So I tested my coils and I'm not sure I'm doing this right...

I disconnected the two small wires to each coil and put an ohm meter set to 200 across it. Both read 4.9, great. But when I tested the secondary circuit, ohm meter set at 20k, I get nothing at all on either coil. Doesn't actually matter what I set my meter to, I get nothing.

Am I doing the test wrong? The bike ran just the other day so I know they work. How do I do the test properly?

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markreimer · « **Reply #68 on:** October 08, 2015, 05:29:45 PM »

To clarify when I'm testing the secondary side I have one lead in the plug cap and one lead on the small colored wire

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markreimer · « **Reply #69 on:** October 08, 2015, 07:23:28 PM »

I guess testing dual output and single output is different. Putting the leads in the ends of both caps yields a resistance of 32 on 2/3 and 33.5 on 1/4, when set to 200K

I believe the caps are 10 ohm resistor caps so that'd be 12 and 13.5 ohm on the coils. Sounds a bit low, but more importantly they're pretty close to each other which is weird given my 2/3 random cut out.

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markreimer · « **Reply #70 on:** October 08, 2015, 08:30:52 PM »

Figured I'd go test ride agin after the coil checked out. Yeah but the wires are cracked. Same thing - handled fine when riding hard. On the highway. Then coming back into the city and slowing down/cooling down 2/3 died. Down shift to raise rpm and they stumbled back to life. Then again after slowing down a few minutes later. When I ride hard with max rpm they are happy. Guess I should buy some new coils.

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mrbreeze · « **Reply #71 on:** October 08, 2015, 08:45:28 PM »

Before throwing coils at it check points and all wiring going to the coil......thoroughly!!! Sounds more like an iffy connection to me. Mine acted the same way and I didn't find the problem right away. It will drive you nuts but will really piss you off if you spend money on a new coil that doesn't fix the problem.

markreimer · « **Reply #72 on:** October 08, 2015, 08:52:32 PM »

Thanks, I did that however. I've got a dyna S ignition and disconnected, cleaned and reconnected all the wires from the dyna and up. I had found one loose connection, but it was for the 1/4 coil! I'm searching for a local coil to swap out to test first hopefully. But haven't had any lucj

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markreimer · « **Reply #73 on:** October 09, 2015, 09:42:22 PM »

Ok, I think I'm making progress here...

I jumped on the bike to ride to the shop. Five blocks in 2/3 dies. Odd... Can't get it to start. Long story short it starts to feel more like a fuel issue. Open the tank, there's an inch of fuel in there. Drop the bowls - dry. Wtf! Fuel wasn't making it down for some reason. I blew into the cap to pressurize it and fuel flowed enough to get to a gas station. Once full it rode totally fine all the way to the shop. Hmm... Maybe my fuel line wasn't routes properly?

Got to the shop and put in a coil from a 350f and re routed the fuel like to what I believe is stock (through the holes in the rack). I have a petcock with two fuel lines coming out. The first feeds 3/4 and is basically straight down. The other feeds 1/2 and has a bit of an upside down U shapes to it.

I fire up the bike, new coil works great. I rode for 40km and didn't have 2/3 die on me. However I thought it was about to die as it felt like it was stumbling at times, just like it did right before dying. Then I realized it was only doing that at sustained high rpm riding- the opposite of when my coil died. Usually high rpm kept it going.

So my theory is that I fixed my coil problem and created a fuel starvation problem in 1/2. Sound plausible? Tomorrow I'll change the fuel line routing to what I had before, a big U shape, and go for a hard ride. If there's no stumbling or dead cylinders this may finally be solved.

Then I focus on my failed valve cover gasket. Still smoking like a chimney as it leaks right by the cam chain, down the plug caps and burns off the head cooling fins

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markreimer · « **Reply #74 on:** October 10, 2015, 09:26:42 AM »

Back to square one. 2/3 died on me after ten minutes of riding with the new coil.

No idea what to do next. This is so frustrating.

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Author Topic: First timer top-end rebuild gone wrong, yippee! Ugh... (Read 21993 times)