• Enter the March CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!

wont rev above 4000rpm after work done

markm

CB750 Enthusiast
Messages
36
Reaction score
0
Points
6
Location
michigan
Hello, posting this question for my son who is doing a cb750 k2 cafe racer. First let me say that he has just got his bike back from a honda dealer who re jetted the carbs and tuned the bike. It starts and runs fine but on the road it will not advance above about 4000 rpm. He had installed a new 4 into 2 into 1 exhaust and put pods on it for the intake and then took it to a honda dealer for the carb work. They did not have a dyno and just rode it around the parking lot and it ran fine. He got it home and took it out on the road and thats when he found it dead above 4000 rpm. Any suggestions on what the problem is? any help will be appreciated. thanks.
 
what pods? emgos are worse then crap. actually almost any pods will have a negative effect on a street ridden bike.
A rejet will help but more often then not it take a few sets of jets to get it right, and the time to tune it. most people buy cheap pods and then dont spend the money on the two or three sets of jets that is needed to tune.

Lets start with the basics though.
Was it running well before the "mods"?
-Check the fuel to make sure that its not separated due to ethanol
-is the bike timed right?
-Good spark?
-What do the plugs look like after a plug chop test?
-and intake leaks?

Also there are a million factors that go into jetting so no one can just say...."put these in and go"
 
what pods? emgos are worse then crap. actually almost any pods will have a negative effect on a street ridden bike.
A rejet will help but more often then not it take a few sets of jets to get it right, and the time to tune it. most people buy cheap pods and then dont spend the money on the two or three sets of jets that is needed to tune.

Lets start with the basics though.
Was it running well before the "mods"?
-Check the fuel to make sure that its not separated due to ethanol
-is the bike timed right?
-Good spark?
-What do the plugs look like after a plug chop test?
-and intake leaks?

Also there are a million factors that go into jetting so no one can just say...."put these in and go"

Yes and no on running right. It had power and would idle with the stock air box and mufflers but leaked gas as the floats were set wrong.
good new fuel
hopefully the mechanic set the timing right
we will have to check spark and check the plugs color and for intake leaks.
 
Always start with a good running stock bike, as its easy to tune based on the manual....you do have a manual right?

If you mod before hand you are adding alot of variables that make things harder to tune if you dont know what you are doing.
I dont mean that in a bad way....as everyone has to start some place but what im saying is you have walk before you can run
 
While riding and in the "dead" spot in the power you can start to close the choke slowly. If it starts to run better then it is lean, if gets worse or no change then it may be rich. Just be careful so it doesn't catch you off guard if it starts to run better and you only have one hand on the bars. This was an old trick I have used for many years just to get an indication of where the jetting is. But.....if it ran good before taking it to the shop and all you really needed done was the floats set, I would put the jetting back to where it was before they messed with it. I run pods on all of my 750's and they can be jetted to where they run good. I don't know your honda shop so I can't say if they know how to actually set timing on these old bikes or not but it is easy to get the marks confused. On the jetting....if it flat out seems like it just falls on its face it sounds like lack of fuel.....rich will still run but low on power and seems choked. Pull a couple of plugs and see if they are very white or very black will give a clue.
 
We have manual and will double check timing, and will also try the choke at the dead spot. thanks allot for all the help and suggestions.The reason for the rejet was for the pods and new exhaust system. My son has went north hunting mushrooms for a couple days and will do these things this weekend. thanks again.
 
Cut up an old T-shirt and wrap the material around your pods. If you get an improvement in power, the main jets are too small.
 
I will pass the on to him and we can try this out also. he did not have time to do any thing to it yet.
 
Take it back to the shop and have them deal with it (for free I hope). Re-jetting a bike and only testing it in the parking lot is unacceptable.

If you tackle it yourself, I'm going to guess that they have way too big of mains in there and you're way rich on the upper end. :shrug:

Good luck and keep us posted!
 
Back
Top