74 Z50 Stumped

B

Beretta

Member
K-- Boys- Here's the deal !
Runs perfect without the Air cleaner Rear Housing and Filter.
Put the Filter and Rear Housing on and it Misses Mid range on up !
Too Rich -Right ? Plug looks black !
Next- New Plug- Exchanged Carb off my other Z that runs perfect !
Exact same Mid to full throttle seems like the choke is on !- Plug Black
Next- Hoist up on the Bench- Checked the Points gap-- Perfect .014,
Next- Checked Valve Gap- Perfect .003
Any Ideas ?? Before I set this on Fire ?
 
6

69ST

Well-Known Member
Seems fairly obvious where the problem is...the airbox assembly. Only a question of whether it's the foam element or rear housing. How's it run with the housing assembled, sans foam?
 
B

Beretta

Member
I changed Air boxes and Filters- As soon as I put on the rear Cap with out the filter the same symptom mid-range to WO stumbles.
As soon as I remove the rear Cap it'll go wide open- No Problems.
 
Clayton

Clayton

Active Member
I have the EXACT same problem with my K5 (74) Z50, if I use a “sock” filter it runs great but with the factor air box and filter it bogs down. I hope your find the answers because I have been fighting this issue for months now with no luck. Iv posted about this before and will add my links so you can read the replies I received.
 
B

Beretta

Member
I'm going to take a different approach and start with the basics-1st is a compression test- New Gauge set will be here today.
If that test ok- I'm trying a 3rd Carb from My Grandsons Z50 (72) That worked fine on His Tired Old Engine-His is torn down for a full Restore anyhow.
New Plug
Check Points again
Check Valves again
I'll check back in later today

Thanks
 
B

Beretta

Member
Rich Stumbling with Air Cleaner on !

Compression Test---150 lbs---Eng warm Throttle full open------- I'm good with that --- Specs call for 170 lbs- must have been at Sea Lever and No Barometer -- That will make a difference to the numbers- 10 to 15 %
Put the 3rd- Older Carb on with the Air Filter and Housing - Adjusted to Specs- Perfect-- No Stumble at all through full open Throttle. Took it for a test ride and Wow -- Really Runs Nice.
Carb # 3 has a 55 main Jet
I need to look into Carb # 2 and Carb # 1 the Aftermarket Carb to confirm Jet size- Maybe Someone upped the Main Jets= Pulling too much fuel.
 
B

Beretta

Member
Rich Stumbling with Air Cleaner on ! Conclusion and Observations.
Carb #2 the Orig Carb has a 55 Jet but No O-Ring for sealing- Also a Minor Clog- Float level looked ok- I suspect it was permitting Fuel up past the non-existent O-Ring - Therefor too Rich
Carb# 1 the Aftermarket Carb --Main Jet has No number on it- as best I can measure the Hole -looks to be .060 -using different strands of copper wire to measure.
Well that's it for now--Until the next unfamiliar challenge arises.
Learning as I go !
 
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