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Discussion Starter #1
hey,, bike idles fine, and pulls good up until 7000rpms wont go any higher,, i just rebuilt the engine last fall less than 200kms, all new rings gaskets, oil & filter, new carb boots, new clutcb and clutch springs, new plugs, and i have cleaned the carbs,, i just put new rpm gauge and speedo on the bike this weekend took it out for a ride and it wont go past 7000rpm, thenni parked it went to go for another ride and it wouldnt stay going i checkdd the plugs and theh were black and wet, i heated them with torch and bike was fine again but still wouldnt go pass 7k, i chdck compression and its 160psi both sides... any help would be awesome the bike has got me puzzled at the moment. i got the owners manual when i bought the bike, but i still wasnt 100% sure about the timing when it come to the advance part of it
 

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There's an ignition diagnosis sticky. I would go through that and post your results.
I would also try and trim the spark plug wire or consider a NEW coil. I have had good results from the GM coil mod.
I suspect your cdi, but best run through all the other stuff first.
Do yo have the stock air box and exhaust setup?
Are your carbs vacuum syncd?
 

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Discussion Starter #3
i have stock air box, and stock exhaust with baffles removed,, i had the bike out the weeked
There's an ignition diagnosis sticky. I would go through that and post your results.
I would also try and trim the spark plug wire or consider a NEW coil. I have had good results from the GM coil mod.
I suspect your cdi, but best run through all the other stuff first.
Do yo have the stock air box and exhaust setup?
Are your carbs vacuum syncd?
i have stock air box, and stock exhaust with baffles removed,, i had the bike out the weeked, even thouugh it was new plugs i put in er the fall with less then 100 kms on them inhad to heat them up with torch and put them back in, they looked wet and black, im going to get new plugs,, whats best spark plugs for bike??
 

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i have stock air box, and stock exhaust with baffles removed, ...(So therefore, the exhaust ISN'T Stock).... i had the bike out the weeked, even thouugh it was new plugs i put in er the fall with less then 100 kms on them inhad to heat them up with torch and put them back in, they looked wet and black,.....(So, NOT New plugs, and apparently fouled by 60 miles of improper carburation, or faulty ignition) ......im going to get new plugs,, whats best spark plugs for bike??
The best spark-plugs normally would be those specified by the manufacturer, (See shop or owner's manual), but until you RE-BALANCE the engine's intake to compensate for the changes to the exhaust, even that is a moot point.......
It never ceases to amaze me that people think that any one modification would have zero detrimental effects to the entire system to which that change is associated......IF you want the bike to perform as well as stock, put it ALL back to stock specs......End of rant......
 

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Discussion Starter #5
The best spark-plugs normally would be those specified by the manufacturer, (See shop or owner's manual), but until you RE-BALANCE the engine's intake to compensate for the changes to the exhaust, even that is a moot point.......
It never ceases to amaze me that people think that any one modification would have zero detrimental effects to the entire system to which that change is associated......IF you want the bike to perform as well as stock, put it ALL back to stock specs......End of rant......
the bike was doing it before i removed the baffles even worse honestly
 

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Does it quit at 7,000 rpm in all the gears or just in the higher gears? Does it start to misfire at that speed or does it just stop gaining rpm? If you close the choke partway at that speed does it get better or worse? Does it blow black smoke out the exhaust? Is it actually turning 7,000 rpm, the replacement tach having the same cable drive ratio?
 

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Discussion Starter #7
i notice it in 3rd gear and higher, rigjt upto 7k has good pull but at 7000rpm just starts tk backfire and wont go any higher, i installed new speedo and rpm gauge the rpm hooks up to the coil, i just installed it this weekend but the bike was doing it before i installed the new gauges
 

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Classic CDI failure on these is that the engine will rev fine parked, run up thru the gears sort of ok and then when in top gear, 5th or 6th depending on model, the bike slows down until the trans is downshifted.
Your symptoms don't match that but you may still be looking at a CDI.
Replace the plugs with NGK D8EA gapped at .026". Non resisted version of the DR8ES-L. Don't use any other plug.
Run thru the ignition diagnosis Ignition Diagnosis for CB/CM 400/450 and CB450SC manual trans 1978-1986
 

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D8EA is actually the stock plug for the early 400's, switched to the DR8ES-L in '81 and also used on all the 450's.
If you're running below 5* C or 41*F then you can run the DR7ES which would be considered a hotter plug
 

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Discussion Starter #11
i have the 450 engine put in the 400 frame.. a couple ppl told me to go with the hot plugs but i wasnt sure what number to get.
 

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The 2 choices are CDI Magician on eBay or Rex's Speed Shop in the UK. Rex's has the complete harness and new plugs. CDI Magicians requires soldering the new unit wire to the old harness.
I can't find the eBay listing
 

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Discussion Starter #14 (Edited)

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Discussion Starter #15
i just thought about this i put the camshaft and sprocket out of the 1980 honda cm400t in the 1982 450 motor are both of them the same? they looked identical to me
 

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I can't believe you are asking this "after the fact" rather than simply looking-up the part numbers in the fiche prior to "making the unverified swap" as "Looked identical" is not always sufficient........
Fortunately, in this case you were lucky, the 450 camshaft is the superseded part to the 400 shaft, so they are essentially interchangeable.......
 

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Steve, that's not the right one. Not sure where that seller got the idea it would work on the 400/450 series. His look like a black box with a bunch of wires w/o connectors. here's the picture he always uses
303760

This is Rex's unit
303761
 

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Regarding cams. There is only 1 cam for all of the SOHC 400/450 manual trans engines 1978 thru 1986. The A model uses a different cam, not interchangeable. There is 1 other cam that was used primarily in Germany for the low output bikes, 27hp vs 43hp. Germany and a couple other countries have laws that beginning riders are limited on horsepower.
 

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Discussion Starter #19
Classic CDI failure on these is that the engine will rev fine parked, run up thru the gears sort of ok and then when in top gear, 5th or 6th depending on model, the bike slows down until the trans is downshifted.
Your symptoms don't match that but you may still be looking at a CDI.
Replace the plugs with NGK D8EA gapped at .026". Non resisted version of the DR8ES-L. Don't use any other plug.
Run thru the ignition diagnosis Ignition Diagnosis for CB/CM 400/450 and CB450SC manual trans 1978-1986
heyy,, i took my bike out again today, and it dose the same thing in every gear even first gear wont rev past 7000rpm, every gear is the same idles good and pulls really good right til 7k then just stops wont rev any more, i done the reading with the multi meter and everything seems good,, i might be wrong but im thinking carbs,, might be a stupid question but how can i tell if the slides are opening? or opening all the way??
 

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Did you post the multimeter results? I don't recall seeing them?
Could be carbs. Did you adjust your jetting?
 
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