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Author Topic: Won't pull strong in 5th  (Read 711 times)

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Offline brett_bike

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  • '73 CB500 Four K2
Won't pull strong in 5th
« on: July 13, 2009, 10:01:33 PM »
So...

Done a bunch of work to my '73 CB500 (talk about it here somewhere), and I have a new "issue".  Bike runs well after recent carb sync and pulls hard in 1st through 4th gear.  Once I get into 5th it doesn't pull at the same rate as the other 4, it will reach about 6,000 rpm's but won't pull above that.  I can hit redline if I want in 1 through 4 so why won't it go higher in 5th?

It will hold at 70 mph comfortably at about 6,000-but at cruising speed, it will sputter a tiny bit.  It does it at cruising speed in any gear.  Maybe a slight mis-adjustment with the carbs, or something worse like loss of compression?

Also, it tends to drop speed slightly if going up hill in 5th gear on the freeway.

Slightly confused.
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Offline TwoTired

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Re: Won't pull strong in 5th
« Reply #1 on: July 13, 2009, 10:11:15 PM »
It's all stock?
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline brett_bike

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  • '73 CB500 Four K2
Re: Won't pull strong in 5th
« Reply #2 on: July 14, 2009, 06:40:05 AM »
Mostly stock except three items...

1. I have a Mac 4 into 1 exhaust

2. I have the needle set in the carbs to the number #3 position, I think it is supposed to be in the #4 position.

3. Uni air filter in the stock air box (per your suggestion, and it definitely helped).

All else is stock, and I have done the timing but can't quite seem to spin the point plate base enough to line it up perfectly.  I  also have done the points, valves, carb clean and sync. 
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Offline TwoTired

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Re: Won't pull strong in 5th
« Reply #3 on: July 14, 2009, 11:38:37 AM »
D7 or D8 plugs?
 What do you spark plug deposits look like?
Can you do a plug chop with new plugs while the engine is sputtering?
Can you do a plug chop with new plugs while the engine is power limited in 5th gear?
Are the carb internal components sourced from Honda or after-market?
Are the carbs marked 627B and retain their original parts?
Is the oil level above the mark?

Wouldn't hurt to have the points set correctly, particularly the dwell or point gap.  Have you read the FAQ about shimming the plate during adjustment to restore the adjustment range?

Have you done a sprocket tooth count?  500's should have 34T rear sprocket, not 37 T like the 550's.

These engines do need good compression to make peak horsepower.  Would be nice to know the compression health.

Cheers,
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.
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