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Discussion Starter #1
Alright guys, this is a bit difficult to describe so please bear with me.

My bike will run great for 10-15 minutes, no hesitation, bogging, etc. with an idle at stoplights around 1k. After those 10-15 minutes the idle will start to drop lower and lower until she wants to stall at idle. Once this starts, the bike still runs well on throttle and part throttle all the way to redline. However, it's still not pleasant to ride because on slow corners she wants to die when not on the throttle.

Ok, so I'll get back home and let the bike sit for a bit - another 10-15 minutes. Start her up and she idles fine! WTF!

The back story on how I got the bike and the previous owners description of the problem - they said the plugs would foul after riding for around 45 minutes. I checked the plugs and they were indeed carbon-fouled. The carbs have since been completely gone through, the coils have been checked, new points and condensers have been installed, and the bike is timed correctly (as far as I can tell).

Any insights you could share with me? While I'm a noob with bikes, I'm fairly competent with mechanics and do my own wrenching on my old Volkswagens.

TIA!
 

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sounds like you have a rich condition with your fuel metering

trash in tank or float bowls?

float and/or needles faulty?

idle jet too large or even missing?

air bleed too small?
 

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or maybe you just need to adjust the idle mixture screw?
 

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Discussion Starter #4
The tank and float bowls are completely clean and functional. Idle jet is stock. I wasn't aware that the air bleed could be modified...

It does seem like it's running rich, but I can't tell if it's rich at idle or the upper-end. Guess I'll just get out the notebook and start turning screws!
 

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sometimes people that drill jets forget to mark them in a manner that would indicate the jets have been drilled

unlikely it's an air bleed since it would affect metering from idle to wide open throttle

you do not mention if the air box and exhaust is stock
 

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Discussion Starter #6
You're right about the jets, they might have been drilled. Exhaust is stock and the air boxes were stock. I've installed some velocity stacks with the though that they might lean out the mixture a bit, but haven't been able to take the bike for a spin. I know it's not good to throw another variable in there, so more than likely I'll put the stock air boxes back on.
 

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Check the things the previous guys said to and then do this.

I have a friend who recently had the same problem as you. But on a 1969 Norton. Fresh motor, and new mikunis. Great at mid and high rpm. Sucks at idle and fouls after 30 to 45 minutes. Coils were the problem. Over time the oil that is inside the coils either leaks out or burns off over time. Old coils work fine when the engine is making plenty of juice at higher rpms. They don't get enough juice for low rpms and cause a rich condition at low rpms resulting in fouled plugs. Get some decent aftermarket coils.
 

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Discussion Starter #8
Thanks Imlost, that validates a thought I had.

I was thinking that maybe the spark plugs just weren't getting enough juice so I modified the stock charging system to run as though the headlight was always on (because the cb450 bumps up the charge with headlight on). That obviously didn't work. I'll have to throw on some new coils and see what that does.

Since Honda coils are non-existant or super pricy I've seen some people use coils for an XS650. Anybody have any experience with that?
 

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you're changing too many things at once and have likely lost any functional point of reference (i can't beleive one of the old timers haven't stepped into to say as much though i think they're simply holding their tongues) reduce variables, don't create more. good god man, installing stacks to address what you think to be a lean condition! without a solid baseline, you're throwing darts at a board, blind folded, in the dark, standing on one leg.

one thing at a time. take it SLOW. be methodical.

and regardless who says what, you get what you pay for with free advice regarding online trouble shooting help. you have the bike in front of you. nobody else does.
 

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Discussion Starter #10
I totally agree with you about the variables, catboy. That's why I put that little disclaimer after I mentioned the stacks, which were installed to possibly correct a RICH condition. The stock filters are fairly dirty, which may be restricting air flow.

The plugs were carbon fouling, suggesting too much fuel or incomplete burn, possibly caused by bad spark. Don't worry, I'm only changing one thing at a time - it just might sound like I'm not because I'm throwing some ideas out there.
 

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Everybody always goes for anything but the electrical stuff. People don't understand it so they don't check it. They assume it is good.

An engine needs two things gas and a spark. A strong spark all the time, not an intermitent one or weak one. My friend thought the same as you guys and would not go buy new coils. But, he relented, bought some and it fixed his bike. It won't fix all fouled plug problems. But, do not forget to check coils. They do go bad. Age kills everything.


ejand22 please let me know if the coils help the problem.
 

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if the coils were weak any problems they would cause would be more pronounced as engine revs and load increased

but if you are gas fouling at idle

and every where else and everything else (including the ignition) is fine like you originally posted

you have a low speed metering problem

but by all means check the ignition at least twice and if you really want to know how to check the ignition reserve

just whistle

but again, if the coils were laying down they would generally become worse with engine speed, heat and load..... not better

it's not fun to start chasing jetting when you have poor ignition or compression

have you done a leak & compression down test and also made sure the valves are adjusted correctly?

leaking rings or poorly sealing valves are more pronounced at slower engine speed due to the fact the engine is turning slower and there is more time for their failings to bring about the resulting affect
 

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Discussion Starter #13
I just got a compression tester so that's on my list of things to check along with the valves. Probably won't get to it until this weekend.

What is this ignition reserve you speak of?
 

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Ignition reserve refers to how much "spunk" the system has

one method of testing it is to drop the supply voltage to the coils in increments until a misfire develops

doubt there is a published spec for your bike for that procedure

another way is to simply note full charged battery voltage and incrementally open up the plug gaps which are firing in open air until they refuse to jump the gap

useful on a two or more cylinder engine having a coil for each cylinder since you can find out if one side is stronger than the other


kick that about and maybe one day you'll find it useful
 

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oh and you can determine if you really have a rich condition by inducing a controlled vacuum leak

maybe there is a nipple with a plug on it?

open and allow a tiny controlled amount of air to leak in and if it's truly rich

the engine will pick up and run better

just simple logical stuff
 

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Discussion Starter #16
Ok, I started the bike up this afternoon. Turned on a box fan and let her idle to see how long it would be before she fouled out. Well, 20 minutes later she was still holding idle at roughly 1200rpm, but was stumbling a bit. I pulled the plugs to find this:



The plug on the left is from the left bank and you can guess where the other one is from. Left one looks ok, but the right one looks a bit wet...

Tested the compression (dry test) next and got 140psi on the left and 135 on the right. I searched the forums and couldn't find what a good number is, so are those numbers good? 3.5% difference between the two seems ok.

I didn't have time to do a wet test or check the valve adjustment, but thought I would post up what I found so you guys to give me any pointers.

PS. Here's a video of my bike at idle. The top end sounds a bit noisey and clattery. Normal or not?
 

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my guess is you have a valve guide shot

that sure looks like oil fouling to me

does it puff any blue smoke at all?

grab the valve tips with a pair of angled needle nose pliers and wiggle them still keyed up

compare both sides

you may find your problem that way

wear should be fore and aft but I've seen some weird ones that had some funky geometry and wore the guides from side to side

the clattery noises could be a valve trying to do somersaults in the guide, adjustment of course, or even detonation as oil in the chamber increases that tendency

but really could be just about anything

hard to tell from that very good pic but did that plug come out smelling like raw fuel?

after it sat for a while did it become not glossy/shiney

dull and flat black?
 

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Discussion Starter #18
Update: Changed the coil this weekend, checked compression again (warm this time), and checked the valve adjustment. Valves were good (after I figured out how to check the cam alignment - thanks guys) and the compression was 175 on the left and 170 on the right. I forgot to mention in my earlier post that the test was done cold prior to this one. Changed the coils too. Didn't get rid of the fouling issue...

I think I'm going to have to go through the carbs again and just make sure it's not an issue with them, then off comes the head.

Any other ideas on what it might be?
 

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I'm with hack - that looks like oil fouling. Valve stem seals on the CB450 are kinda mikey-mouse anyway...

What's the answer to his questions above? Was that right plug smelling like gas? Is it now dull or still shiny?

The top end noise you are hearing is more or less normal for a CB450, especially one with the cam sprocket dampers missing like yours are. Make sure the cam chain is adjusted.
 

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Discussion Starter #20
Yeah, it seems like oil fouling to me too... I just don't want to give in to pulling the head just yet. That will mean it probably won't get ridden for the rest of the season. Which would suck.

I rode it a bit after putting in the coils, checking the valves and installing new plugs. Pulled the plugs while still warm and they just smelled hot, I couldn't discern between oil or gas smell. The right side plug wasn't as wet looking as the photo above - it looked at bit wet, but not as wet as the photo above.

It doesn't seem like the valve guides would be difficult to install, but I'm a bit worried about the reeming required to get the new guides to match the valves. I'll probably just take it to a machine shop.

I agree with you about the noisey top end, especially since it's missing a damper. If (when) I pull the head I'll replace that while I'm in there.
 
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