CB450 Is back together, but won't start now...

Emerikol · 05-09-2020, 02:58 PM

Finally got around to getting the overhauled engine back in the CB450 frame. That was an odyssey by itself, but it's in, and all the mounting plates are reinstalled and tightened up. I hung the carbs, did a basic set on the points, and put the exhaust pipes on. I hooked up some jumper cables to the starter and to the coils, and turned the bike over with the plugs pulled. I have spark! Then I put some long tubes on the carb inlets and fill them with gas. Carbs hold, the level in the tubes stayed stable. Put the plugs in, turn the bike over with the starter, and after fiddling with the choke for a bit, it starts up and runs pretty smoothly. A little smokey from all the assembly lube burning off, but it runs!! So I keep filling the tubes for a bit, and let it come up to temperature. Now this is where things get a little weird. The bike popped through the right hand exhaust pipe once, and then quit. I've tried everything I can think of to get the bike running again, but all it does is pop and backfire in the exhaust. I've held my hand over the carb inlets, and it's definitely not coming back through the intake. The bike won't run no matter what I do, it just pops and backfires out the exhaust, usually the right pipe. So with that info put out there, is there anyone that has any idea about why the bike would start behaving like that after the rebuild? Any help or advice would be greatly appreciated. -E

Essayons · 05-09-2020, 03:40 PM

Did the timing chain skip? Maybe verify timing and points. Are you getting a strong enough spark?

You can also check with the facebook group:
Vintage Honda Motorcycle Owners of America
https://www.facebook.com/groups/185595442016587/

Emerikol · 05-09-2020, 03:50 PM

Spark is very strong, but the plugs were a little wet when I pulled them out to check when this all happened a few days ago. I tried again this morning, and got the same thing. That's when I decided to reach out to the collective wisdom of the internet. I'm going to pick up some new plugs and try that, then take the covers off and verify timing. Here's what I put on one of the other forums I'm a member of when they mentioned about carb boots and points:

Points are still tight, and set on my original setup. I don't have the clamps on the carb boots, but it ran just fine for more than 15 minutes without them. I suppose it could be a bad rebuild. Stranger things have happened. I'm going to take the valve covers off and check the timing again. I know the valves are still moving, and not banging into the pistons, so that's a start. Everything sounds normal, it just pops off in the pipes. The plugs are wet when I take them out after trying to crank it for a while, too. Don't know if that makes any difference or not.

Megadan · 05-09-2020, 05:36 PM

wet plugs and a sudden run issue that is timing related with after firing in the pipe on one side. Sounds almost like a coil issue on that one cylinder. I would try swapping coils, leads, plugs, etc. To either try and move the problem or see if it resolves it.

Sounds like it failed to fire, or was very weak, raw fuel gets into the exhaust, manages to fire or the fuel hits a hot spot, bang in the ehxuast, .

Just my 2 cents.

Emerikol · 05-09-2020, 10:49 PM

I put new plugs in, and the pipe backfiring is 10 times larger now. Seriously sounds like a shotgun going off in my garage. I think that the engine may have skipped time. I'm going to take the camshaft covers off tomorrow or monday and check the timing marks. That's pretty much all that's left.

Emerikol · 05-10-2020, 01:47 PM

This morning I verified that all the timing marks were correct, and reset the valve clearances and reset the points, both gap and timing. No effect on the symptoms I'm chasing. Still backfiring in the exhaust pipes. I held my hand over the carb inlet boots (the carbs are pulled off for right now) and I'm getting strong suction impulses when I turn the engine over. I really think that the only thing left to do is pull the engine back out and tear it down again. This is my not happy face.

I can't really think of anything else it can be except a mechanical failure of some sort.

Emerikol · 05-10-2020, 07:09 PM

How does line go? Something like "Nothing is ever as bad as it seems?" The issue was simply the drive pin on the points advance plate. It runs off a driveshaft from the exhaust cam, and it came out. Meaning that the advance was always out of time with the static timing of the points. So I could time the points all day long, but as soon as I turned the engine over the advance would throw all the setting right out the window. Now the bike is running again, but I'm not able to turn the idle down below 3,000rpm. I can back the idle screws out all the way until they lift off the seats, still nothing. I have the idle air mix screws about a turn and a quarter out, and the carbs are drinking a ton of fuel at that rpm. I'm obviously getting more fuel going in than I need, but I'm not sure what to make of it. I haven't really dug into the carbs since I got the bike, what with the engine being the main issue. Guess that's going to be the next project. In any event, the engine is running again, and I can continue on with bringing this one back from the brink.

Emerikol · 05-12-2020, 10:06 PM

$300 later at 4into1.com, and I'm off to the races! Ordered complete (and I mean complete carb overhaul kits, a couple odds and ends, and everything should be here early next week. Which is great because I have a week off starting Wednesday. Once I get the bike making the right noises and such, then it's just a matter of stuffing new rubber on the rims, and then finally going to get the registration an tags. Its all coming together to bring this one back!

Megadan · 05-13-2020, 05:32 AM

Glad to see the motor back up and running. My instincts on the ignition were right, just not on exactly where the problem was. Discovering that little tiny issue probably was equal parts joy and anger. I hate those moments where I feel like a dunce, but it works so I don't care.

Be careful of soaking those carb bodies or using harsher chemicals, Keihin carbs of mid 70's and older vintage had felt shaft seals that will get eaten alive by more aggressive cleaners. I usually either "boil" (hot distilled water soak) or ultrasonic clean them to try and preserve said felt.

Also be aware of the slide caps having a potential vacuum leak issue if they have the white plastic centers. They usually tend to cause subtle run issues when they start losing their seal.

**cheesy** · 05-13-2020, 07:10 AM

+1 on the ultrasonic cleaning.

Emerikol · 05-13-2020, 07:59 AM

Quote:

Originally Posted by Megadan

Glad to see the motor back up and running. My instincts on the ignition were right, just not on exactly where the problem was. Discovering that little tiny issue probably was equal parts joy and anger. I hate those moments where I feel like a dunce, but it works so I don't care.

Be careful of soaking those carb bodies or using harsher chemicals, Keihin carbs of mid 70's and older vintage had felt shaft seals that will get eaten alive by more aggressive cleaners. I usually either "boil" (hot distilled water soak) or ultrasonic clean them to try and preserve said felt.

Also be aware of the slide caps having a potential vacuum leak issue if they have the white plastic centers. They usually tend to cause subtle run issues when they start losing their seal.

Quote:

Originally Posted by cheesy

+1 on the ultrasonic cleaning.

Regrettably, the Harbor Freight Ultrasonic Cleaner that has such great reviews is too small to do the carb bodies. Otherwise I'd make a trip up there to go broke buying bargains. The set of carbs I have on there now do indeed have the white plastic centers, however a trick I saw on one of the forums said to smear a thin coat of clear silicone on top to prevent that issue.

As to feeling like an idiot, I literally looked at that tiny shaft pin laying in the bottom of the points tray and said "No F'ing Way!" The points plate and mechanical advance unit both had to slide off the points driveshaft to discover that pin had come out. That's something that would have taken me weeks to figure out, and probably had the engine out again. So yeah, I felt kind of dumb on that one especially considering how careful I was during the rebuild to make sure I didn't lose anything and everything was bagged and tagged to prevent mix-ups.

On a side note, I'm going to be dividing a little bit of time between finishing up the CB and getting started on one of the other engines I have laying around. I'll break the engine down, assess what all I'll need, and start the rebuild so I can maybe make some progress getting the Scrambler back up and running. It's a frame sitting on a rolling tool cart now, but I'm pretty sure I have all the parts to get it back together.

**cheesy** · 05-13-2020, 07:32 PM

I abuse the snot out of my HF ultrasonic. Besides carbs, I do bicycle hubs, and most anything I can cram in it.
I managed both the Keihen VB carbs on my CX and the Urals’ CVK carbs. Yes, it’s small. Only one body at a time, and yes, you will need to flip the body. And maybe cycle each one a couple of times. The amount of crud that comes out of a carb body is amazing, though.

Emerikol · 05-14-2020, 07:03 AM

Well, that settles it... I guess I'm just going to have to make a trip out to Harbor Freight to pick up an ultrasonic cleaner. I mean, it'll be an inconvenience and all, but I'll take one for the team and make the trip.

Actually, I think I'm going to get one of those pull down electrical cords, too. My garage is a nice size and all, but I don't like having to run extension cords across the floor all the time. The carbs should be the last major mechanical item to sort, and then it's just a matter of putting the old girl back together.

05-09-2020, 02:58 PM	#1
Emerikol Join Date: Oct 2016 Location: Carrollton, GA Posts: 1,465	CB450 Is back together, but won't start now... Finally got around to getting the overhauled engine back in the CB450 frame. That was an odyssey by itself, but it's in, and all the mounting plates are reinstalled and tightened up. I hung the carbs, did a basic set on the points, and put the exhaust pipes on. I hooked up some jumper cables to the starter and to the coils, and turned the bike over with the plugs pulled. I have spark! Then I put some long tubes on the carb inlets and fill them with gas. Carbs hold, the level in the tubes stayed stable. Put the plugs in, turn the bike over with the starter, and after fiddling with the choke for a bit, it starts up and runs pretty smoothly. A little smokey from all the assembly lube burning off, but it runs!! So I keep filling the tubes for a bit, and let it come up to temperature. Now this is where things get a little weird. The bike popped through the right hand exhaust pipe once, and then quit. I've tried everything I can think of to get the bike running again, but all it does is pop and backfire in the exhaust. I've held my hand over the carb inlets, and it's definitely not coming back through the intake. The bike won't run no matter what I do, it just pops and backfires out the exhaust, usually the right pipe. So with that info put out there, is there anyone that has any idea about why the bike would start behaving like that after the rebuild? Any help or advice would be greatly appreciated. -E __________________ First Rule of Aviation: -Never Pass Up The Opportunity to Pee I was struggling to get my wife's attention; I sat down on the couch and looked comfortable. That did the trick! My wife says I only have two faults. I don't listen and something else... If at first you don't succeed, try doing it the way I told you to... The Stable: 2005 Yamaha V-Star 650 - SOLD 2015 Suzuki DR 650 2015 RPS Hawk 250 - SOLD 2016 Ural Gear Up
	0

05-09-2020, 03:40 PM	#2
Essayons Join Date: Mar 2018 Location: fontana, california Posts: 333	Did the timing chain skip? Maybe verify timing and points. Are you getting a strong enough spark? You can also check with the facebook group: Vintage Honda Motorcycle Owners of America https://www.facebook.com/groups/185595442016587/ __________________ 2018 TT 250 2016 RX3 1979 CB750K
	1

05-09-2020, 03:50 PM	#3
Emerikol Join Date: Oct 2016 Location: Carrollton, GA Posts: 1,465	Spark is very strong, but the plugs were a little wet when I pulled them out to check when this all happened a few days ago. I tried again this morning, and got the same thing. That's when I decided to reach out to the collective wisdom of the internet. I'm going to pick up some new plugs and try that, then take the covers off and verify timing. Here's what I put on one of the other forums I'm a member of when they mentioned about carb boots and points: Points are still tight, and set on my original setup. I don't have the clamps on the carb boots, but it ran just fine for more than 15 minutes without them. I suppose it could be a bad rebuild. Stranger things have happened. I'm going to take the valve covers off and check the timing again. I know the valves are still moving, and not banging into the pistons, so that's a start. Everything sounds normal, it just pops off in the pipes. The plugs are wet when I take them out after trying to crank it for a while, too. Don't know if that makes any difference or not. __________________ First Rule of Aviation: -Never Pass Up The Opportunity to Pee I was struggling to get my wife's attention; I sat down on the couch and looked comfortable. That did the trick! My wife says I only have two faults. I don't listen and something else... If at first you don't succeed, try doing it the way I told you to... The Stable: 2005 Yamaha V-Star 650 - SOLD 2015 Suzuki DR 650 2015 RPS Hawk 250 - SOLD 2016 Ural Gear Up
	0

05-09-2020, 05:36 PM	#4
Megadan Join Date: Apr 2017 Location: Omaha, NE Posts: 8,053	wet plugs and a sudden run issue that is timing related with after firing in the pipe on one side. Sounds almost like a coil issue on that one cylinder. I would try swapping coils, leads, plugs, etc. To either try and move the problem or see if it resolves it. Sounds like it failed to fire, or was very weak, raw fuel gets into the exhaust, manages to fire or the fuel hits a hot spot, bang in the ehxuast, . Just my 2 cents. __________________ Hawk Information and Resource guide: http://www.chinariders.net/showthread.php?t=20331 2018 Hawk 250 - Full Mod list here. http://www.chinariders.net/showpost....62&postcount=1 2024 Royal Enfield Shotgun 650 https://chinariders.net/showthread.php?t=34124
	1

05-09-2020, 10:49 PM	#5
Emerikol Join Date: Oct 2016 Location: Carrollton, GA Posts: 1,465	I put new plugs in, and the pipe backfiring is 10 times larger now. Seriously sounds like a shotgun going off in my garage. I think that the engine may have skipped time. I'm going to take the camshaft covers off tomorrow or monday and check the timing marks. That's pretty much all that's left. __________________ First Rule of Aviation: -Never Pass Up The Opportunity to Pee I was struggling to get my wife's attention; I sat down on the couch and looked comfortable. That did the trick! My wife says I only have two faults. I don't listen and something else... If at first you don't succeed, try doing it the way I told you to... The Stable: 2005 Yamaha V-Star 650 - SOLD 2015 Suzuki DR 650 2015 RPS Hawk 250 - SOLD 2016 Ural Gear Up
	5

05-10-2020, 01:47 PM	#6
Emerikol Join Date: Oct 2016 Location: Carrollton, GA Posts: 1,465	This morning I verified that all the timing marks were correct, and reset the valve clearances and reset the points, both gap and timing. No effect on the symptoms I'm chasing. Still backfiring in the exhaust pipes. I held my hand over the carb inlet boots (the carbs are pulled off for right now) and I'm getting strong suction impulses when I turn the engine over. I really think that the only thing left to do is pull the engine back out and tear it down again. This is my not happy face. I can't really think of anything else it can be except a mechanical failure of some sort. __________________ First Rule of Aviation: -Never Pass Up The Opportunity to Pee I was struggling to get my wife's attention; I sat down on the couch and looked comfortable. That did the trick! My wife says I only have two faults. I don't listen and something else... If at first you don't succeed, try doing it the way I told you to... The Stable: 2005 Yamaha V-Star 650 - SOLD 2015 Suzuki DR 650 2015 RPS Hawk 250 - SOLD 2016 Ural Gear Up
	0

05-10-2020, 07:09 PM	#7
Emerikol Join Date: Oct 2016 Location: Carrollton, GA Posts: 1,465	How does line go? Something like "Nothing is ever as bad as it seems?" The issue was simply the drive pin on the points advance plate. It runs off a driveshaft from the exhaust cam, and it came out. Meaning that the advance was always out of time with the static timing of the points. So I could time the points all day long, but as soon as I turned the engine over the advance would throw all the setting right out the window. Now the bike is running again, but I'm not able to turn the idle down below 3,000rpm. I can back the idle screws out all the way until they lift off the seats, still nothing. I have the idle air mix screws about a turn and a quarter out, and the carbs are drinking a ton of fuel at that rpm. I'm obviously getting more fuel going in than I need, but I'm not sure what to make of it. I haven't really dug into the carbs since I got the bike, what with the engine being the main issue. Guess that's going to be the next project. In any event, the engine is running again, and I can continue on with bringing this one back from the brink. __________________ First Rule of Aviation: -Never Pass Up The Opportunity to Pee I was struggling to get my wife's attention; I sat down on the couch and looked comfortable. That did the trick! My wife says I only have two faults. I don't listen and something else... If at first you don't succeed, try doing it the way I told you to... The Stable: 2005 Yamaha V-Star 650 - SOLD 2015 Suzuki DR 650 2015 RPS Hawk 250 - SOLD 2016 Ural Gear Up
	4

05-12-2020, 10:06 PM	#8
Emerikol Join Date: Oct 2016 Location: Carrollton, GA Posts: 1,465	$300 later at 4into1.com, and I'm off to the races! Ordered complete (and I mean complete carb overhaul kits, a couple odds and ends, and everything should be here early next week. Which is great because I have a week off starting Wednesday. Once I get the bike making the right noises and such, then it's just a matter of stuffing new rubber on the rims, and then finally going to get the registration an tags. Its all coming together to bring this one back! __________________ First Rule of Aviation: -Never Pass Up The Opportunity to Pee I was struggling to get my wife's attention; I sat down on the couch and looked comfortable. That did the trick! My wife says I only have two faults. I don't listen and something else... If at first you don't succeed, try doing it the way I told you to... The Stable: 2005 Yamaha V-Star 650 - SOLD 2015 Suzuki DR 650 2015 RPS Hawk 250 - SOLD 2016 Ural Gear Up
	4

05-13-2020, 05:32 AM	#9
Megadan Join Date: Apr 2017 Location: Omaha, NE Posts: 8,053	Glad to see the motor back up and running. My instincts on the ignition were right, just not on exactly where the problem was. Discovering that little tiny issue probably was equal parts joy and anger. I hate those moments where I feel like a dunce, but it works so I don't care. Be careful of soaking those carb bodies or using harsher chemicals, Keihin carbs of mid 70's and older vintage had felt shaft seals that will get eaten alive by more aggressive cleaners. I usually either "boil" (hot distilled water soak) or ultrasonic clean them to try and preserve said felt. Also be aware of the slide caps having a potential vacuum leak issue if they have the white plastic centers. They usually tend to cause subtle run issues when they start losing their seal. __________________ Hawk Information and Resource guide: http://www.chinariders.net/showthread.php?t=20331 2018 Hawk 250 - Full Mod list here. http://www.chinariders.net/showpost....62&postcount=1 2024 Royal Enfield Shotgun 650 https://chinariders.net/showthread.php?t=34124
	3

05-13-2020, 07:10 AM	#10
cheesy Moderator Join Date: Jul 2010 Location: Elburn, IL Posts: 5,839	+1 on the ultrasonic cleaning. __________________ Cheesy ______________________________________ 07 Hi Bird Enduro-Flown the Coop 07 Ural Gear Up 79 Honda CX500 77 VeloSolex 4600 V3 73 VeloSolex 3800 I'm making this up as I go.-Indiana Jones Telling me something 'is for my own good', is a fast way to a fat lip.-Me I don't even care about my own problems, why should I care about yours?-Quote on one of my favorite t-shirts
	2

05-13-2020, 07:32 PM	#12
cheesy Moderator Join Date: Jul 2010 Location: Elburn, IL Posts: 5,839	I abuse the snot out of my HF ultrasonic. Besides carbs, I do bicycle hubs, and most anything I can cram in it. I managed both the Keihen VB carbs on my CX and the Urals’ CVK carbs. Yes, it’s small. Only one body at a time, and yes, you will need to flip the body. And maybe cycle each one a couple of times. The amount of crud that comes out of a carb body is amazing, though. __________________ Cheesy ______________________________________ 07 Hi Bird Enduro-Flown the Coop 07 Ural Gear Up 79 Honda CX500 77 VeloSolex 4600 V3 73 VeloSolex 3800 I'm making this up as I go.-Indiana Jones Telling me something 'is for my own good', is a fast way to a fat lip.-Me I don't even care about my own problems, why should I care about yours?-Quote on one of my favorite t-shirts
	6

05-14-2020, 07:03 AM	#13
Emerikol Join Date: Oct 2016 Location: Carrollton, GA Posts: 1,465	Well, that settles it... I guess I'm just going to *have* to make a trip out to Harbor Freight to pick up an ultrasonic cleaner. I mean, it'll be an inconvenience and all, but I'll take one for the team and make the trip. Actually, I think I'm going to get one of those pull down electrical cords, too. My garage is a nice size and all, but I don't like having to run extension cords across the floor all the time. The carbs should be the last major mechanical item to sort, and then it's just a matter of putting the old girl back together. __________________ First Rule of Aviation: -Never Pass Up The Opportunity to Pee I was struggling to get my wife's attention; I sat down on the couch and looked comfortable. That did the trick! My wife says I only have two faults. I don't listen and something else... If at first you don't succeed, try doing it the way I told you to... The Stable: 2005 Yamaha V-Star 650 - SOLD 2015 Suzuki DR 650 2015 RPS Hawk 250 - SOLD 2016 Ural Gear Up
	4