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Bike Won't Go Past 4000 RPM

11K views 51 replies 10 participants last post by  longdistancerider 
#1 ·
Hello all,

I have a 1982 CB450SC. I recently changed the oil on it since the previous owner probably hadn't changed in about 5 years, but I didn't change the filter. I added Castrol 10W40. Now I'm having a few issues that I wasn't having before.

When the bike idles, everything seems to be fine. I'm able to run the bike for a few minutes like normal, shifting gears down the road perfectly fine, but then all of a sudden the bike seems to have trouble getting above 4000RPM and also doesn't want to go faster than 60Km/h.

When I stop the bike, there seems to be a bit of smoke coming from somewhere and when I remove the dipstick there appears to be smoke coming from there too.

Anyone have any suggestions that may be causing this?

Cheers!

Jarrod
 
#2 ·
Remove the gas cap and see if that solves it. The tank can go into vacuum if the cap bleed hole gets plugged. If that doesn't fix it then I would check the petcock filter inside the tank and also the small screw cap filter at the bottom of the petcock.
Doesn't sound like an engine issue.
 
#4 ·
Close your petcock (it should always be closed when the bike is shut off anyway).

Disconnect the fuel line at the carburetor and place the end in a suitable container.

Open the petcock. There should be a steady stream of fuel.
 
#6 ·
Yes, you should close the petcock when not riding. Otherwise you may end up with fuel in your oil.
 
#7 ·
You may want to smell the dipstick for oil, it's an easy check that gives a lot of peace of mind
To get to the petcock filter you will need to empty the tank at least halfway, then tip to the opposite side of the petcock (on a towel so the paint doesn't get scratched), keeping in mind that the gas cap does not keep gas in even when shut, then undo the nut on the petcock and the filter should come out. If it doesn't it is most likely stuck in the tank and you may be able to get it out with an easy out that matches the inner diameter or a drill bit in reverse (be gentle)
 
#9 ·
You may want to smell the dipstick for oil, it's an easy check that gives a lot of peace of mind
I haven’t had a chance to get the petcock out yet, I’ll be doing that after work this afternoon.

As for smelling the dipstick, I gave it a quick sniff this morning and it didn’t really smell of gas, but it didn’t smell like the oil from the jug. I’m assuming right now that’s just from being run a bit through the engine, or is that a horrible assumption?
 
#11 · (Edited)
Ok good. I just changed the oil and nothing leads me to believe something is up and I need to change it again.

I drained the tank and removed the petcock but nothing seems out of place there. It seems like the bike loses power as soon as it hits 4000RPM and then stalls. It happened once on a test drive and once while in neutral in my driveway. It's showing same signs that a car I once owned showed the problem there was water in the gas tank. I left some of the gas aside to see if maybe that was the case here but it didn't show signs of anything in the gas other than gas. Could there be an issue with the carbs? Could them maybe need a clean? Could this also be caused by me adding too much/not enough oil? I only added 2L but I'm wondering if the information I was given about oil amount may not have been correct.
 
#12 · (Edited)
Update on the situation:

Bike still won't rev above 4000RPM. I've tried slowly getting up above 4000, and also gunning the engine and either way it gets to 4000 and that's the end. If I don't throttle down slowly the engine stalls on me. I've done this while in neutral on the centre stand, and while attempting to ride the bike.

I've adjusted/cleaned the spark plugs and they are firing fine.

I've also noticed that the engine seems to be at a lower pitch than it used to be. It wasn't a high pitch whine before, but it definitely seems to be a lower rumble to it.

I'm wondering if there is an issue with the carburetor? Or perhaps an issue with the amount of oil (all this started after I changed the oil)? I've also read that maybe airflow could be an issue, would a dirty air filter cause this?
 
#15 ·
Why don't you tell us a bit more about the bike. Are you running with stock airbox and filters or pods? What carbs? Did you rebuild or replace any carb parts at all?
I noted that you said you used Castrol 10W40 for oil. Are you sure you used the right oil? It must be rated for JASO-MA or JASO MA-2 for wet clutches.
 
#16 ·
As far as I know everything on the bike is stock. I haven't rebuilt anything on it. The castrol says its for Motorcycle and from what I saw online this was listed as an oil for this bike. It's SAE 10w40. Could this be the entire problem? Did I ruin the bike with this?
 
#17 ·
Castrol 4T 10-40W oil is fine. Even if you put auto oil in it won't ruin the engine.
You might check the timing. Pop the left cover off and fire up the engine. Timing light should hit on the F mark and when rev'd should advance to towards the 2 l l marks. Full advance hit at 4500-5350 rpm originally but you'll be later than that.
 
#19 ·
Got the thread re-named for you. Hopefully won't confuse folks too much. In any case, pay attention to what Longdistancerider suggests. You won't find any better advice.

You need an inductive timing light. Many auto parts stores will let you borrow one.
 
#25 ·
So I wasn't able to get my hands on a timing light to test that out. I'm heading off island tomorrow for a few days so I'll be able to pick one up and get that checked out.

I did however take apart the carbs to check them out, somewhat anyway. I just wanted to see if there was anything that jumped out at me with the jets. I didn't notice anything wonky with them. Put everything back and the bike is still running like it was, gets up to 4000 RPM and won't go any higher.

Hopefully I'll have a better update next week when I'm able to work on the bike again.

Thank you everyone for helping me out with this. Really appreciate all the advice.
 
#26 ·
Here's the relevant thread for the ignition https://www.hondatwins.net/forums/6...400-450-cb450sc-manual-trans-1978-1986-a.html
There are 2 choices for a CDI replacement. 1) CDI Magician on eBay and 2) Rex's Speed Shop in the UK
Biggest difference in them is Rex's is a plug-n-play while the other is a cut and solder your old connectors to it.
UK vs. US customs may come into play also since this is a Canadian destination

Timing can only be "adjusted" by swapping in different stators and CDI boxes,you're playing with resistance values.
If one wants to actually have adjustable and accurate timing, Honda's version isn't either one, then you would go with the Ignitech DCCDI-P2 unit
 
#27 ·
Timing can only be "adjusted" by swapping in different stators and CDI boxes
So I get my hands on a timing light, test it to see if it’s out, if it is I pick one of these two options for purchasing one to replace the bad one on the bike?

Then later down the road if I feel like being able to adjust the timing I switch to a different system.
 
#28 ·
I played with 3 CDI's and 3 stators and the advance was late on all combinations.
In checking the timing you're going to be looking for it to advance with the throttle. If it doesn't advance then it likely is the stator, not the CDI. Use your VOM and run thru the ignition tests in the thread I linked earlier.
 
#31 ·
I thought that might be the case too since my choke cable is stuck. But when I took the carbs off I just never bothered to reattach the choke. I’ll take another look to make sure it is seated properly and completely closed though.
 
#33 ·
The stator is the large set of windings mounted on the lower left side of your engine primarily under the magnetic dome shaped rotor......
It contains both the alternator windings (to recharge the battery), and the ignition pick-up coil (exterior to rotor) and advance coil (within rotor) that trigger and control ignition timing........
Failures to rev past 4K are often due to the advance coil/winding failure...This is not a separate part and the stator is replaced as a complete unit......
The stator can be tested by verifying the Ohm readings are within the specific ranges listed in the factory service manual.......
Jim, (longdistancerider) has provided a good discussion topic detailing this procedure, and it can be found in the SOHC electrical section.....
 
#34 ·
Jim, (longdistancerider) has provided a good discussion topic detailing this procedure, and it can be found in the SOHC electrical section.....
He’s posted the link to it for me already, I just wanted to make sure I knew which part we were talking about and I was definitely not thinking the right part. Thank you for clarifying this for me!
 
#36 · (Edited)
So the bike engine will not rev past 4 to 5 k revs and it seems like a fuel issue, or a ht coil breaking down..........you have used the red neon plug caps so you can "see" the spark ( the red neons flash as they pass ht to the plug ) or spark loss.

The engine seems to surge at about 4 to 5 k revs and slows down a bit then re revs etc.etc.etc.

Have you check for proper ignition advance?

Have you checked acv outputs of the genny ign system wires?? as a rule all acv values should rise with increase in engine revs, rate of change.

disconnecting the cdi black/white wire will disconnect the cdi from the rest of the bike. earthing this cdi black/white wire kills the ign. Sometimes the handlebar dedicated kill switch can cause problems, especially when wet.

cdi's have been know to "die over night" which has happened to my sons 400, then a few months later the genny stator died.........

a multimeter will show acv and a pulse to the ht coil, but a scope will show much much more.....

you have a wiring diagram and know that the genny ign windings are on the same stator as the charging system coils but are completely seperate........the reg/rec is the black finned unit by the fuses........3 yellow, a black and a red/whiter from memory.......
 
#40 · (Edited)
Now the question becomes what is your idle RPM?....

AND YES, EXACTLY on the F mark alignment......
Sounds like you are starting out partially advanced at idle, and thus it can't fully advance the necessary number of degrees beyond that initial setting......

Have you checked for a damaged (crank to rotor) key or key-way?
(Which would shift advance timing slightly. making it difficult to smoothly increase in RPM, with incomplete fully advanced position causing the peak RPM limit/stoppage )

While the rotor is off to check that, look at the advance pickup coil to check for overheating as a short there would "read" erroneously to the CDI...(Although your prior Ohms readings SHOULD have told that tale......)
 
#42 ·
The crank keyway should be a nice slot, while the rotor key should be a nice fit in that slot. If you look up the parts diagrams you should be able to find what it normally looks like.

Pickup coil overheating I'd guess would be melted wires, black soot marks, blued steel (hopefully not). You can always get opinions on here about pictures as well.
 
#43 ·
The woodruf key should be a very tight fit in the crankshaft, you literally have to drive it out with a punch. Remove it and check the fit in the rotor groove if you see any signs of wear, it should just slide in. If there's any deformity then replace it. They get deformed if the rotor wasn't torqued properly.
 
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