Low Power

[paul1478]

Hello,
I have been trying to find were my power went to for some time now.
When it was done, it was about the same as Chucks bike in power. 63HP on the dyno. When I rode Chucks bike at the gap, I knew I was not just dreaming, it is for sure down on power. 
The bike starts no issues, revs cleanly. It just is way down on power especially one it hits the power band.

Just before the gap this year, I noticed a ripped intake manifold. I was able to get a replacement and it was on for the event.
Still down on power.

Chuck checked the following:
Timing- he said it can use some more but ok
jetting including air jets. we went through many combinations none made a difference you could tell. 
removed the heads to check pistons. heads were perfect no carbon. piston tops looked great. you could still see the hash marks on the cylinder walls.
I changed to a non 0-ring chain but nothing.
When I got home I rented economy cycles leak down checker. It would not hold even 1 PSI, found the crossover was leaking. Fixed that and no leaks but no more power.
I am out of ideas. Do you guys have any? I miss my bike...

Thanks
Paul

[m in sc]

check compression.

[paul1478]

Thank you Mark.
I will do this today when I get home.
I did but it was with the plugs in the exhaust during leak test. I am sure that was not correct.

Paul

[m in sc]

hold throttle wide open, kick it until the needle stops moving up.

i wonder if it was jetted to compensate for an air leak, now that its fixed is running rich? 

[paul1478]

could be. It currently had the jets back in it when it had the power. I have no idea how long that manifold was ripped. Very well could have caused damage to the piston. I know the side with the torn manifolds plug was and still is much blacker that the other side. Even when Chuck was messing with the jetting.

[m in sc]

i had a set of urethane intakes tear once, 2016 or so, luckily i saw it before i had run it for any length of time. just aged out and heavy carbs bouncing around. compression test should tell you where to look.   

[1976RD400C]

After putting new pistons in my bike, I have been messing with the carbs this week. It is important to get the needle set right. With the clip set one notch too rich, it accelerates flat and slower than it should, and doesn't really want to pull up to top rpm. With the needle set one notch too lean, it will have a gasp when it comes off the pilot circuit if the throttle is snapped open, and you can feel the weak power at 1/4 to 1/2 throttle. I was surprised how this was easy to feel while test riding. I would try leaning the needle position and see if it comes back to life.

[Striker1423]

compression is the biggest factor in power loss when everything else is good.

[paul1478]

I have not checked yet, I have my 4 year old granddaughter this week unknown until Monday.
I am going to have her help me do it today. She LOVES helping.
I am honestly hoping to find low compression. That would be great to at know what the issue is and a rather easy fix.

[paul1478]

150 on the side that did not have the ripped manifold
143 in the side that was ripped.
This is on my cheep auto zone compression tester.
But not that different and seems high to me.

Thoughts?

[m in sc]

seems ok to me. 

[paul1478]

Yea thought so. Thanks

[Evans Ward]

I'm hoping you find the issue Paul. Good positive thoughts sent your way for a quick find of the issue with resolution. 

[m in sc]

make sure allt he jets and shit are tight in the carb. etc.

[paul1478]

Thanks Evens. I have been trying to fix this for about 8 months.
Mark,
thanks. we removed every jet including the air jets while trying to change it at the gap. also made sure all passages were clean.

Several months ago I found the plug wire on the left side was hanging on by a thread to the coil. I cut it and put it back (checked today still solid).
we replaced the plug wire caps on the 2 sides
cleaned the airlifters
changed the battery
verified timing
removed heads to check pistons
did a lead down test
brakes to not drag/wheels spin free
new non 0-ring chain
now the compression test
I was thinking coils are week making for week spark but from what I understand they work or they don't work.

Again, it is not that the bike runs bad, it just has noticeable less power. no power wheelies in 1-2 like before.
thanks for all the input. I am sure it will be something stupid when I find it like a bad ground or loose wire.