Gas flow issue??

[DPris]

Having a problem with, I believe gas flow. Bike idles nicely and accelerates nicely to about 3500 rpm in all gears and then begins to balk. Every once in a while it will get just past 4000 but then it seems to be gas starved. I've never done jetting but is this a jetting problem? If it needs more gas, do you go to a higher number on the main jet? the bike is supposed to have 130's but I have not yet checked the size. Had the carbs off and cleaned but forget the jet size. Hoping to look into it this weekend. Petcocks have also been apart and a couple of parts replaced so I don't believe it is the petcocks.

 

[jpdevol]

That could be several things fuel related, but I would first check ignition timing for both sides. Got a timing light?

 

[DPris]

Yes I do and I'll have a look this weekend. Thank you. That would seem to be a good place to start.

 

[5twins]

What you'll be looking for is whether or not the timing advances. It should fully advance by about 3200 RPMs and by the sound of your problem, it may not be. Your mechanical advance unit and advance rod may need servicing.

 

[Jan_P]

I always say this keeping on like a parrot even if it is not needed
I Do it pretty much even if the tire pressure is low ( joking )
According to my main rule
CSF -- rule
As in Cheapest - Simplest -- First

Measure the charging Voltage across battery.. Reason being that a weak spark can be insufficient to ignite
the mixture
And should your main jet be on the large side the extra fuel can make it stumble.

You can do that test in a 3 piece suit with a straight back .. Not getting your hands dirty
5 minutes .. should it be something else -- no harm done

In 40 years I have had few carburetor problems 5 or so
But electrical problems almost every year

Having said that the spark being weak manifests itself mostly at lower rpm and giving gas
letting go it fires again

What setup Stock ?? and Year model.

CSF -- rule

 

[DPris]

Checked the battery - simplest
Did dynamic timing and it made the difference.
I had done static timing and that along with some ill advice from a friend thought it was good.
Did the static again and found the left to be off. Adjusted and then did dynamic. More adjustment.
Also checked it at 3000+and the advance is working.
It now goes smoothly past 4000rpm and on.
Thanks to jpdevol, 5twins and Jan_P

 

[5twins]

Just because it's working now doesn't mean the advance unit and advance rod don't still need servicing. Although it's not something you need do often (maybe every 5 years or so), it is a required maintenance item, and it was never mentioned in any of the manuals. The advance rod rotates back and forth a little, maybe 1/4 turn, between it's retarded and advanced positions inside the cam. There are bushings pressed into each end of the cam to support it. The outer bushing has grooves cut into it's I.D. These are to hold grease and provide a lube supply for the rod .....

So, every 5 years or so, you need to remove the rod, clean out the grooves and pack them full of fresh grease .....

The factory shop manual recommends a grease with moly in it. As I said, none of the manuals make mention of this as a required service, so many of these haven't been touched since they left the factory. They're long overdue for some fresh lube.

 

[DPris]

Thanks. I will keep this in mind for future service. the engine was a new rebuild and I am going to believe this has been dealt with for the time being.
Good pics.