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Discussion Starter #1
Hello again
I did a compression test on the 1970 450 today after a thirty mile run,the readings were 115 ibs (8 bar on both sides,is this a bit low or about right there is no smoke from the exhaust,there is slight puffing from the rocker breather,which also smells very much like unburnt fuel.Also when i get up to about sixty after about a mile she starts cutting out as if she is running out of fuel,slow down to about forty and she picks up again,have checked tap filter and tank cap,they are ok,could it possibly be float levels,any help wold be appreciated.
thanks
Dave.
 

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Never hurts to check the float levels. If you're getting raw fuel into the cylinder, it would wash the oil off the cylinder walls and you would get a low compression reading - but you should also be getting grey exhaust smoke (especially on acceleration) and wet/carbon fouled plugs. These carbs aren't very sensitive to a low a float level but run rich with too high a level.
 

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Make sure you take your readings with throttle Wide Open, and No Choke.

Try them again - it should barely run with those readings.
 

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Discussion Starter #4
Hi guys thanks for the replies just checked the compression readings again,this time with the throttles wide open,the readings are now 170 lbs on both pots,did not open the throttles before,have now just got to sort the fuel problem.
thanks
Dave.
 

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WOW :shock: those are some SWEEEEEEET bikes!! I LOVE LOVE LOVE that 750 my friend!! Those are two of the cleanest looking bikes around I bet.. ;)

P.S. What's the little sticker on the lower cases of that 450 for? To remind you it's a 450dohc?? :lol:


GB :mrgreen:
 

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Discussion Starter #7
thanks chaps
dont really know why,the sticker is there,it seems to be factory fitted so i leave it there,the log book states it is a 1970 k2, i need a owners handbook for it,if anybody has one please let me know.
dave.
 

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I just saw one on Ebay (the kind that goes under the seat) not a couple days ago. I do believe it was for a 70 model? Maybe it wasa 71? My memory isn't as good as it used to be.. :p

GB :mrgreen:
 

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Discussion Starter #9
Hi guys
set the floats with the credit card tool,reset the timing,took her for a spin,now running a treat,thanks for your help,a great forum,taking the 750 for a spin tommorow.
Dave.
 

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I've had a sneaking suspicion that my bike had low compression as she blows some black smoke and I always smell like oil when I'm done riding. Also, she sometimes dies while idling and it seems like she should have a little more power. I finally stopped by Autozone and borrowed their compression tester (what a great service!). So I got 130 psi on the left and 135 psi on the right with the throttle wide open and the choke off.

What is the lowest someone can probably ride around on?

I would like to ride it this summer and put new rings on it in the winter. Think she can make it until then as long as I keep topping up the oil and keep a spare set of plugs on the bike?

Mike
 

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Is there ever any blue smoke? Does it actually use any oil?

Hard starting occasionally?

I assume the tests were done on a warm engine?

GB :mrgreen:
 

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i'm in the same boat. my compression measured about 150 on both sides. is that still considered acceptable? autozone is great with the tool loaner program...
 

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On a 450, 163 pounds is the MINIMUM reading before rebuild...... They will run , but not produce good power... At 150 (you tested hot and throttles wide open...right?) you are past due to rebuild.....
 

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Mine was warm but not hot. I had just ridden it for about an hour and a half so I let it cool down for a couple hours while I mowed the lawn. I'll try it again tomorrow when it is hot.

Not usually a problem starting. If I haven't ridden it all week it will take about 3 to 4 kicks on average. The main problem is that is dies when I'm idling at a light for awhile and I smell like oil when I'm done riding.

I'm not really sure what color smoke it is. Yes, it does consume oil, but slowly. I'm also in the process of fixing a small oil leak from the points base so that may account for some of that.

If it should barely be running at 130, it must SCREAM at 170! As I said, I plan a rebuild in the winter.

I just wanted to make sure I wasn't going to permanently damage something by running it with low compression
 

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Average running compression is 185.... It can be as high as 213 right after the new rings seat.....
 

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uhohferris said:
i'm in the same boat. my compression measured about 150 on both sides. is that still considered acceptable? autozone is great with the tool loaner program...
Lotsa of guys keep riding at 150 pounds.
Probably the majority of people (their old Hondas, that is) out there have below-par compression.
It's simply not news that people want to hear, and usually any comments about it get ignored.

But, and this is important - it is a Honda 450, they're incredibly tough, and they'll try to run for you no matter what.

And yes, a 450 with 180 pounds runs like a raped ape.
 

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I wonder if lots of us are running around with 150 psi compression due to questionable replacement parts availability. What do you suggest for a source of pistons and rings (brands and vendors)?

Thanks,

Mike V (who just might be in the 150 psi club)
 

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Ebay seems to be pretty cheap on rings. Pistons too. I remember one guy here really got taken to the bank by a Honda dealer when buying rings. Something like well over $100!! :shock: Ebay has them for cheap.

Just be sure to measure/inspect your bore before buying these parts. ;)

P.S. Welcome aboard Mike! :D

GB :mrgreen:
 

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this may be tooo big of a can of worms to open in this thread, but as a TOTAL new guy here- and a new owner/mechanic of a 450, what EXACTLY would be included in a "rebuild" to get my compression back up to "raped ape" standards? if it's possible to answer here, what kinds of things are possibly causing this low compression. i'm kind of finding that a lot of the other "tune up" checklists i'm running through on this bike now are i'm assuming, being done for the first time- in a LONG time on this bike. i don't really know much about it's history. and just to verify yes, 150psi. at full throttle, hot engine. and yes, still only running on one cylinder i think- sometimes cold exhaust on right side. among other timing problems that i'm addressing, but she rides!

i know, the old saying if i have to ask i probably don't need to know. BUT, the learning curve on this bike has been going straight up ever since two local mechanics have basically told me to go get a new engine after simply hoping to get the bike safety checked and ready for riding. screw that, i'm learning myself. i would absolutely be up for the challenge of a rebuild this winter and my tool collection is growing rapidly.

-seth
(an optimistic member of the 150psi. club)
 
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