swap Keihin carb for Mikuni?

A

andymeadors

New Member
hey guys,

i recently bought a 72 CB350.

it starts cutting out and loosing power at around 5 to 6k rpm. i believe this bike was tuned for sea level and i live in 6,500 altitude. running too rich is probably what's happening.

so should i re-jet the Keihin or buy a Mikuni? or what?

thanks for your help!
 

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the problem is not the altitude it is the pods :(
unless it ran marvelous at sea level ? can you verify that ?
6500 feet is def enough to make a dif but should not make it fall on its face in my ho
oh and put some kind of mufflers on that preferably with some longer pipes
what you have, that is hurting perf and it is not cool to run staright pipes
 
And please remove those "clown shoes" and fit decent tires. The tires on it are a thirties tire shape and don't handle very well in the dry and are hopeless in the wet. If you live in the mountains, there are probably some great twisty roads to ride on and you want a bike that handles as well as possible to be safe and to have fun - even at legal speeds.
 
Very common, most likely, in fact, it is the points. Check your voltage from the battery at the ignition switch out put to see if there isn't any issues with supply voltage. You can get a decent spark from your ignition coil and still have bad points with a static test. Point bounce or float is common with this year of battery ignition. You should have between 500-750 grams tension. Also make sure the point pivot is lubed with light oil and the felt brush also has lube of silicon grease. Almost any grease will work though. Last test is to ohm it out with the points closed. Should read 001 or 000 depending on your meter. Just touch the probes together to see which reading is closed. Any reading above your infinite/crossed lead, setting is bad.
 

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scroll down to the begining and do it to your pods

then see where you are at

also check your coils for proper resistance

http://cx500forum.com/forum/cx-customization-modifications/14114-pods-plug-atmospheric-ports-7.html
 
Simple test is to remove the pods, it can be the problem. In my experience pods actually flow more air if the right ones are selected. Check your point gap also, the rubbing blocks wear down. You also have a mechanical advance, make sure it can rotate. Setting the points is easy. Adjust the gap to .015" on the left point set, with the back plate in the middle adjust position. Rotate the plate so the points open at the "F" mark. Lock it down, then adjust the right point gap to the timing mark on that cylinder's "F" mark. It may be .012" or in the neighbor hood, should be in the range though.
 
it COULD be weak points springs, just another bit of handy troubleshooting info there,
easy to check for, i don't have one of those slik gram scales tho that is cool,
but i could improvise 8)
 
I've only seen weak springs 6 out of a hundred. A couple times new points didn't pass muster. Bad points that look good, can make you chase your tail whilst pulling your hair out trying to find the problem. I was working in a Honda shop during 1972 as a mechanic. Did that in Germany also. Had the privilege of uncrating the first Honda 750 in Frankfurt, think it was 1969? I had at that time a Honda 450 with Weber stage II and Venolia high compression pistons. It was underwhelming, the performance of the CB750, thought it would scream.
 
FYI, the CV carbs do compensate for altitude a bit....The thinner air doesn't allow the slides to rise as quickly.

The pods block air passages on the inlet, and are lower flow capacity then the stock airbox, and cause turbulent flow, messing up the vacuum slides.

So the advice you received in earlier posts are right on....If the altitude was the problem, even Idle would be a problem....Much more likely ignition or pod setup.
 
hey Teaser - "clown shoes." that's pretty funny. advise well taken!
Scooter Trash - thank you very much for all your time on this.
mydlyfkryzis - thank you!

i came from the custom chopper industry - so this cafe racer culture and bike is totally new to me. i love it - everything about it. stoked to be on a fun (affordable) bike.

i appreciate everyone's advise. i have a head full of trouble shooting starting points.
- pods (take them off and see if it runs better)
- ignition (test voltage)
- points (lube, gap)

thanks a ton!

a.
 
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