1982 CB450SC Very poor fuel economy and some other symptoms

[davecmu]

I want to preface this by admitting my complete noobhood when it comes to carbs and carb-based engine performance.  I own a 1982 450sc, and yesterday I had to switch to reserve on the side of the road after getting only about 50 miles on a full tank.  Clearly, this is a problem.  The bike does seem to leak fuel very slowly when the petcock is left on (I tested it last night after refueling, and this morning the garage smelled heavily of gas, but there was not pooling), so I always turn it off when parked.

Strangely, this post by Bumblebee describes almost exactly what I have experienced on my bike so far. 

Cracked/leaking T connectors will get you:
1. Mileage drop from 52-57mpg to about 32-36mpg. (early symptom of a cracked T connector between the carburetors)
2. Power dropout when over about 40-60% throttle. (The actual dropout point is dependent on the airflow rate through the venturi)
3. Acceleration difficult above 40mph.
4. Top speed around 45-48mph.
5. Primary mechanical symptom is around 35mph with the throttle opened beyond a certain point. The vacuum pistons start jumping up and down making a kind of crazy metal on metal vibrating sound that you can feel by putting your hand on the vacuum piston covers.

BTDT with cracked hoses and also experimented by pulling them out just to see what would happen.

I'm 6'1", 189lbs, so my 450 should be able to propel me faster than 48 mph, but it really doesn't, and it takes forever getting even to there.  I know I do not have T-Connectors.  What could possibly cause these same types of issues in a 450?

Let me tell you what I've experienced so far in trying to work on the bike.  I replaced the spark plugs when I got it.  As soon as I fired it up afterward, the idle jumped to 3k - 4k and the exhaust headers started smoking from the outside while the right side backfired continuously.  I removed the plugs, and the left was fine but the right side one had become white as a ghost.  The old plug that came out of that side was entirely crusted over with an oily black filth.  Putting the old plug back in the right side cylinder made all the problems go away, and that has been my temporary fix.  Gap seems right on the right side replacement plug.

So far, no gas in the oil. 

Any and all advice will be very appreciated and thoroughly executed.

[jerjohn]

usually a white plug indicates that the plug is too hot. You may have predetonation on that cylinder and that would cause backfiring. You said puting the old right plug in seemed to fix your problems. Are you refering to gas mileage/top speed etc or just the backfiring problem...Maybe you got a bad plug I havnt personaly heard of it but like any other mass produced part Im sure a bad one sneaks through quality control every now and then. Get a new rightside plug.

have you cleaned your petcock and carbs? How sure are you on the 50miles per tank? If the bike is running extremely rich you would have crap gas mileage and with out an increase in airflow a rich mix would effect performance...Maybe the PO switched out your jets for larger ones, or tried to clean them with micro drill bits...I say start with the carbs cause your obviuosly getting good spark

[windrider]

Probably running on one cylinder.  When you put a good plug in that cylinder, right side, you found out it has other problems.  By putting the old plug back in, you killed that cylinder again.  Take the plug from left side, put it in the right side, and put the other new plug in the left side.  Run it, and see what you get.  As for the idle, previous owner may have adjusted due to fouled spark plug.  Don't be afraid to turn it back down with the new plugs.  As for the fuel leak, could be a sticking float on right side carb causing problems.  keep us posted.

[davecmu]

I should have been more specific:  putting the old spark plug back in the right side stopped the backfire/very high idle situation, but has not helped performance. 

A carb breakdown/cleaning is definitely next.  I am hoping people might have insight into whether specific parts might be broken or out of whack that might not be covered during a typical carb cleaning so that I can minimize the downtime on the machine by having the suitable replacement parts on hand.  Tuscaloosa, as you might imagine, is not a hotbed of vintage Honda motorcycles, and as such, I have a long lead time on parts ordering from the Internet.  Having the carbs out of the machine and in pieces on the bench for a couple of weeks will be difficult.

I actually got 49 miles from reserve switchover to reserve switchover.  Two days of driving.

John - just a quick question.  Does your 450 perform well?  What gear are you typically in at 45mph?  55mph?  I guess I have to start from scratch in trying to determine if it's really a performance issue (outside the TERRIBLE MPG) or if it is typical that a 450 wouldn't get over 45mph despite pushing hard on the bike.

[davecmu]

Probably running on one cylinder.  When you put a good plug in that cylinder, right side, you found out it has other problems.  By putting the old plug back in, you killed that cylinder again.  Take the plug from left side, put it in the right side, and put the other new plug in the left side.  Run it, and see what you get.  As for the idle, previous owner may have adjusted due to fouled spark plug.  Don't be afraid to turn it back down with the new plugs.  As for the fuel leak, could be a sticking float on right side carb causing problems.  keep us posted.

You posted while I was replying - awesome!

You have written down all the ideas that have been swimming around in my head.  I'll be swapping around the plugs tonight to test that very thing.  I, too, think it might be running on one cylinder.  Because we have a crossover piece on the exhaust, it's not possible to tell if one is dead.  I also suspect a stuck float causing the leak, or possible bad o-rings between the fuel tubes going to the right side cylinder, which may explain why it might not be running or running extremely lean.

Thanks!

[jerjohn]

Your performance is indicicating a problem. I wiegh 230 at a squat 5'9" and my little hawk is able to get me up to 75 easliy. I have maxed out the speedometer at 85 and kept increasing speed. At 45 Im usually in 4th and 55 im typicaly in 5th with rpms around 5000. In 6th i usually go about 70 with rpms around 4500...this isnt exact because shifting changes per enviroment ya know...higher rpms on twisties, lower on flat straight aways etc. Im not a very agressive rider. if your pushing the bike hard you should esaliy be over 45.

Also Im not sure about the crossover tube effecting the headerpipes temps. I mean im sure it would eventually i guess, but not at start up. When you start up are boths pipe hot or is one cold? So have you observed a leak? If your mileage is that bad you should be able to see where that fuel is leaking out...or its in your oil, but you said it wasnt. what plugs did you install? you should be using ngk dpr8ea-9 or its equivalant.

[davecmu]

   I was only thinking about holding my hand at the rear of the exhaust when I mentioned the crossover - touching the header is a great idea.   

I'm using the -9 NGKs, and I'm going to double check my oil for gas.  Going to the garage now to swap spark plugs.

[davecmu]

Alright, here's the scoop:

- No gas in the air box, pooling on the crank case or dripping anywhere.

- After filling up to the brim this morning, there is half a tank of gas remaining after only 20 miles.

- Swapping the left cylinder spark plug (known good) with a spare, identical one produces no change (spare now known good).

- Swapping the right cylinder spark plug (oil fouled) with a known good spark plug causes the idle to soar to 4k immediately upon start up and the right exhaust to begin smoking whispy white smoke instantly from the tailpipe.  Also, a thin, shiny film of oil or gas covers the spark plug tip in less than 3 seconds of running.

- Running the engine with the oil-fouled spark plug in the right cylinder (same condition as it has been for a week or more) returns idle to 1,200 - 1,500 (nominal).  In this configuration, I can grab the right header with my full palm without any pain after 1 minute of idling.  Left header is too hot to touch within 10 - 15 seconds.  There is a very slight warmth to the header, but it is obvious the cylinder is not firing normally, if at all.


Conclusion:  The oil-fouled plug is not firing the cylinder, causing the performance issue.  When replaced with a known-good plug, the idle immediately rises to 4k and the exhaust begins smoking while the spark plug tip itself becomes instantly fouled.  Excessive fuel is getting through the system somewhere, most likely having to do with either a severely increased idle or some failure in the right cylinder/carb.

At this point, I have no idea what would cause the right cylinder to smoke and pop and bang when it actually begins burning fuel. 

Also, there may very well now be gas in my oil.  I checked it before starting it up (after sitting for 3 hours) and it is in a overfilled position on the dipstick and smells sharp, not fully of gasoline but certainly not just motor oil.

So, I think I'll be pulling the carbs out and giving them a good cleaning (I've read the post on the Pine Sol, and that seems the simplest way).  When they are reinstalled, I'll start the adjustments at factory standard with new spark plugs and a fresh oil change.  That should help eliminate the over-idle condition.

With so much gas in the oil, I don't think it's safe to run it long enough to get warmed up in order to adjust the idle down with a new spark plug in the right cylinder. 

Or, am I better off changing the oil, letting it warm up, swap the spark plug, and then trying to adjust the idle down by hand just to see if that is the only problem?  I don't think this way resolves the "some kind of fluid is splashing on the spark plug" issue.

Could the valves be so far out of adjustment as to let the gas by in the cylinder to mix with the oil and for the oil to enter the cylinder, causing the plug fouling?  It makes a pretty awful mechanical racket, especially on the right side, that may be out-of-whack valves.

Obviously, there is a lot going on here.  Any help will be much appreciated.   

[jerjohn]

Looks like you got it nailed down. I would do three things to work out the kinks
1 pull the carbs soak/clean/set
2 adjust valves while carbs are soaking
3 change oil
just for clarity, the white smoke is indicating an overly rich mixture, so check that side float bowl level and slow idle jets and also the intake valves for that cylinder. Lets hope the backfiring and  what not from the right cylinder is just a misadjusted valve and not valve damage...you did say its loud right. No worries if you got a bent valve, its just a bit more work but its fairly straight foward.
Dont run the bike anymore until you have pulled the valve cover and inspected everything...you wont get an accurate idle adjustment with the valves and or carbs letting that right cyclinder run so rich anyway.
have you got yourself a clymers manual or honda service manual?

[SmokinFast]

Worn rings in the right cylinder are letting gasoline get into your oil. Its commonly referred to as 'blowby'. And oil is getting into the combustion chamber and fouling the right spark plug.

To verify this, get a compression gauge and check for low compression. Remove both plugs. I'd recommend disconnecting the ignition coil so it doesn't burn out during the compression test. And hold the throttle wide open while pushing the start button.

Although the carbs might be contributing to the problem, I think your primary problem is in the right cylinder. I wouldn't mess with the carbs until you correct the source of the oil fouling, which might involve new rings, a cylinder rebore, or a valve job.

Brett

[davecmu]

Guys, this is exactly the type of help and direction I needed.  Amazing! 

I plan to do this this weekend:

Worn rings in the right cylinder are letting gasoline get into your oil. Its commonly referred to as 'blowby'. And oil is getting into the combustion chamber and fouling the right spark plug.

To verify this, get a compression gauge and check for low compression. Remove both plugs. I'd recommend disconnecting the ignition coil so it doesn't burn out during the compression test. And hold the throttle wide open while pushing the start button.

Brett

And follow up with this after the oil fouling is resolved:

Looks like you got it nailed down. I would do three things to work out the kinks
1 pull the carbs soak/clean/set
2 adjust valves while carbs are soaking
3 change oil
just for clarity, the white smoke is indicating an overly rich mixture, so check that side float bowl level and slow idle jets and also the intake valves for that cylinder. Lets hope the backfiring and  what not from the right cylinder is just a misadjusted valve and not valve damage...you did say its loud right. No worries if you got a bent valve, its just a bit more work but its fairly straight foward.
Dont run the bike anymore until you have pulled the valve cover and inspected everything...you wont get an accurate idle adjustment with the valves and or carbs letting that right cyclinder run so rich anyway.
have you got yourself a clymers manual or honda service manual?

Beautiful work, you guys.  Thank you so very much!  I'll keep everyone updated with pictures of the progress over the next couple of weeks.  Of course, this happens to be the busiest three week period of my entire year (I live on an academic calendar, and work in University housing, so August is pretty much washed out with RA training, move-in weekends, and new freshmen issues), so it will be slow going, but this will certainly help keep me sane by giving me something to do with my hands at night.

Dave

[Munkey]

Could the valves be so far out of adjustment as to let the gas by in the cylinder to mix with the oil and for the oil to enter the cylinder, causing the plug fouling?  It makes a pretty awful mechanical racket, especially on the right side, that may be out-of-whack valves.

Valves being out of adjustment is not the cause of gas in the crankcase or oil in the cylinder. Like Brett said, that's going to be caused more more serious issues.

[gammer]

Could the valves be so far out of adjustment as to let the gas by in the cylinder to mix with the oil and for the oil to enter the cylinder, causing the plug fouling?  It makes a pretty awful mechanical racket, especially on the right side, that may be out-of-whack valves.

Valves being out of adjustment is not the cause of gas in the crankcase or oil in the cylinder. Like Brett said, that's going to be caused more more serious issues.

+1
I agree. It sounds like you have multiple issues here. A compression check would be a good idea.

[geemann]

^^^
+2 for good game plane and sound advice

keep us updated!

~G

[davecmu]

Guys, I know I sound like a noob, but I didn't follow the plan specifically.  First, not a single autoparts store in town (damn you, Tuscaloosa!) sells or rents a compression tester with a 10mm fitting, so compression checking was becoming problematic.  Second, it turns out my neighbor is a former motorcycle mechanic (now working on the line at Mercedes-Benz) and has owned two Nighthawk 450s.  When he saw mine, he stopped over and started helping me poke around.

Following his advice, I pulled the carbs and cleaned them out.  Did a complete breakdown and Pine Sol soak, then cleaned and reassembled the pieces, paying special attention to the needle seats.  Set idle screws to 2.25 turns per factory, and got ready to put them on.

While the carbs were off, I pulled the valve cover to adjust the valves.  The left side, which has been doing all the work, was in okay shape, although a bit sloppy.  Got it adjusted to the middle of spec.  The right side, though, was another matter altogether.

Get this - the intake valves were so tight they were pretty much always open when the cam rolled around, even on the stroke when they were supposed to be loose.   I guess the only thing that kept the bike from blowing up under my rear was that the spark plug was so fouled it wasn't firing.  God knows how long it had been running like that.  Must have been sucking enough fuel through the carb at all times to overflow the cylinder, push past the rings, and put it all into the oil.  Ugh.

I adjusted the right side to the middle of spec, installed new, properly gapped plugs, reinstalled the carbs (what a nightmare - no room!), changed the oil to 15w40 Rotella, and fired it up.  For about 20 seconds it ran like it had before:  3k - 4k idle, lots of smoke.  I shut it down, fiddled with the choke lever (just pulled it in and out a bit to try to get it seated) and fired it back up.  It idled at 900 and stayed there. 

After getting it warmed up, I adjusted the idle to 1200 and gave the throttle a couple of quick twists.  It runs!

There is a slight miss that I'm trying to nail down.  It backfires a tiny bit (seemingly more from the left, but who knows) on deceleration.  It sounds like an occasional staccato drumbeat, albeit a quiet one, when it's idling.  I'm going to have my neighbor come back over and help me adjust the valves again and probably adjust the carb as I've never done it before.

So far, 9 miles in, there does not seem to be any gas in the oil.  It smokes a little bit (and smells like an old two-stroke snowblower - burning oil?) when starting it up cold or warm, but that seems to go away during driving.  I think the exhaust valve seals may be worn and will need to be replaced to fix the issue.  For now, I'm more concerned about the problem here:

http://nighthawk-forums.com/index.php/topic,6529.new.html#new

I'll keep this post updated as I find out more about whether its still putting gas in the oil and how fuel consumption is going.

Thanks for the help so far - despite not posting much, I have been reading a ton and it's all great advice!

[detdrbuzzard]

riding around the city where my mph is between say 30 to 45 and in fifth gear i usually fill up every 80 miles. above 45 i am riding in 6th gear ( 45mph - 65mph ) and fill up with around the 110 to 120 miles showing on the odometer. if you haven't drained your crankcase breather do so. it is the capped tube on the right side of the bike near the back of rhe trans

[jerjohn]

Congrats man