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Discussion Starter #1 (Edited)
Hi All,

Really hoping someone can help me out here as I have hit a brick wall. I will send virtual beer. I rebuilt the engine and cleaned carbs and now I am losing power at around 5000 rpm in every gear. I have read just about everything on line and I am running out of ideas. I should point out I have a pretty large leak in the muffler that sounds like a Tommy gun that I plan on welding. So far:

Checked power to coils
Changed sparks. Carbon foul fast due to the current issue I believe
Checked diaphragms on carbs and slide movement
Put stock air filters back on
Made sure choke was not engaged
Starts ok and idle seems to be ok
Compression on left side was 120 but throttle wasn’t open - would this be caused by hole in muffler?

I am wondering if I maybe have an issue with the advanced cam. Could it be 180 out? Would the engine start in this state. Point and valves were set to spec.

This forum is a god send. Can’t thank you enough for all your help.
 

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Discussion Starter #2
Update. Changed a spark plug that was shorting and idle has improved. Still no response above 5000 rpm. Exhaust starts to pop at the hole louder but not acceleration. Thanks
 

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Discussion Starter #3
Cam advancer also appears to be lined up correctly and I do not see any arcing at the points. Power to both coils and getting spark. Still no power at 5000 rpm and above
 

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Do you have good fuel flow to the carbs? Are you sure your ignition advance is working? Is your battery FULLY charged?
 

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Thanks for the response. Yes battery appears good and is charging through new stator rectifier set up from ricks (verifies with a meter). I don’t believe there to be a fuel issue as there wasn’t before rebuild. I am leaning towards a carb issue though maybe with the jets.
is there away to verify the advance operation the cam is on ok and the spark advancer plate is rotating normally with cam shaft.
Could running too rich cause such a problem.
WOT and the rpm just sits at 5000rpm
Would the exhaust leak cause this?

thanks again everyone!
 

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Do you have replacement diaphragms, and if so, are you positive the slides are oriented correctly, with the holes to the rear? How about the rubber jet passage plug inside each carb - are those in place?
 

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Discussion Starter #7
Yes I replaced the diaphragm on the right side. All appeared ok in terms of vacuum. The slide moved up and down when moved manually. I did check that the holes were at the choke plate also. I am going to check the other side position tonight but it had a marker and I assumed that it would be in the correct position but I will check again. I noticed one side also bleeds a little from the overflow after running. I am going to pull jets again and verify that they are ok, clean and in position.
Thank you!
 

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If it’s running extremely rich, it may not want to run at higher rpms, but that would be a function of the largest jet and the slide needle. I’d make sure your needles are secured in the slides to stay in place, and check your jet sizes. Are you using your OEM jets, or replacements from a kit? What do your plugs look like?
 

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Discussion Starter #9
Plugs are sooty and black and pretty fouled but I think that’s a lot to do with running a little rich and not being able to get gas or bite at higher rpm. The jets are stock and I’m running stock air filters. There is a hole in the exhaust that would cause some loss of power but not to this extent. I am going to pull the carbs again and rebuild making sure that everything is seated correctly. Hopefully weld a plate to the exhaust at some point this week too see if there is much difference. Left side seems to run a little colder also, not sure if this could be related but could also be the exhaust again. Going to try and find a timing light to check advance also (never done this before).
One thing I did notice on the new diaphragm is that when I lift it with carb lid off it doesn’t drop on its own straight away. It slides free though if I move it up and down. Thanks for the feedback. It’s much appreciated. I have totally hit a brick wall here. Everything else seems to be ok
 
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