Topic: No power above 5k rpm

[ramjdmcmm]

1975 Honda 400four SS
She idles ok about 1100 rpm, I can rev it no problem above 5k rpm when not under load. Get her on the street and she just bogs down above 5K rpm. carbs manifolds are in great shape, no cracks or signs of any. Any ideas???

[ramjdmcmm]

bump

[Mantree]

Sons like fuel flow to me

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[links56]

Could be condensers for the points. I would check the points as well. Its only 20 bucks to replace the points and condensers.

[mrfish2]

Could be condensers for the points. I would check the points as well. Its only 20 bucks to replace the points and condensers.

If it was a condenser then 2 cylinders wouldn't be firing at all.

Check for spark at all cylinders, it's the easiest thing to do. If good spark is verified then you're looking at a fuel flow issue.

[przjohn]

Sounds like it can't breath. Is the inlet clear, no mouse nest, etc?

[flybox1]

what is your current jetting, airbox/stacks/pods, and exhaust?

[rb550four]

Have you adjusted your valves, syn'c your carbs ?
 Are sure that your floats are set to the correct height in all 4carbs.?
X        Do you have one cool pipe..... have you checked for spark at each cylinder through the caps?
X        Have you removed your spark plugs to see how each cylinder is burning ?
Did you use a light when setting 1+4, and 2+3  and you are sure the spark is spot on?
Yes       Did you use quality points or the cheap ones that won't hold adjustment?Or are they old ones that have been cleaned or     filed        filed. STILL SUSPECT     

Yes         you running filters on your fuel line?
Yes       Do you have clean air filters?......... Stock
X       Are they pods?
Yes    Are you running stock exhaust or a header?.......Header
       Are they baffled? You have stock jets.
X       Have you upgraded the jets or used the kit stuff instead of cleaning out the Honda stuff ?......Stock jets
      But are they really really clean?
X       How does your clutch feel ?
X       All of your fuel line is on the top side of the venturi right , none fuel line dips below the float bowl.
last question...does your carbs have vents? and are they clear of debris?
   Sorry...needed more information.

Oh Oh 3 more questions  ...  all related , so it's kinda like one question .Did you clean the carbs ? emulsion tubes.... do the carbs have them? Did you remove them to clean them or just blow air through them?

[ramjdmcmm]

I was wearing a full face white helmet.
I'll go through the checklist and report my findings. Here's what I know now.
Plugs have good color.
all pipes hot.
Yes, i have an inline filter. Fuel line does not dip below bowls.
Good stock air filter. It does the same thing with no air filter.
The carb jets are stock.
New condensers, points were in good shape so I just cleaned, no pitting.
Running a header.
Clutch feels good. It was replaced 1 yr ago. Not much road time since then.

That's all I cam remember.

[rb550four]

Excellent! Did this white full face helmet have a visor?
Why do you have inline fuel filters?
Rusty tank?
Have you cleaned the petcock really well, is there stuff in the screen?
how old is your gas?
Have you checked to see how the fuel flows from the petcock lately?

Did you rebuild your carbs.............yourself or sent them out?
            clean the emulsion tubes
            Clean the vents
            Set all floats to correct position
            Sync the carbs
            Check the valve clearances
I figured these are questions you may know the answer to off hand so we can take them off the list.