Topic: Carb-fu question

[xenoscr]

Hello,

I've read the FAQ's and I think I know what my next move should be. I guess I'm looking for validation that I'm on the right path. Here is my setup:

1975 CB750K5
#40 Slow Jets
Needle Jet clip on middle notch
#120 Main Jets
Pod air filters (airbox didn't come with the bike)

I had #115 Main Jets installed and at highway speed the bike would hit about 70-75mph and would not accelerate any more. I'm thinking I should be able to get a little more out of it than that. Rolling the throttle to full would result in power loss. I'm thinking that the #120 main jets will help that. Am I wrong? I installed the #120 main jests and re-synced my carbs and took it for a very short spin (Raining and 38F). It idles steadily, it seems to loose some power around half throttle and then the power would kick back in around 3/4 throttle. Based on what I've read I think I should try lowering the needle jets one notch and try again. Am I on the right track?

I'm also curious as to what settings others are using with similar pod setups. In searching the forums it seams that most end up using the #120 main jets but there isn't much mention of the needle clip position. Any help would be appreciated.

XenosCR

[ekpent]

Did you route any new fuel line or are you useing any inline filters.These bikes are a little picky on that.Tank filter and tank nice and clean for good fuel flow.

[xenoscr]

New fuel line, no in-line filter. Tank was Kreemed last year. When I was installing the new main jets I didn't notice any debris. The lining seems to be holding on from what I can see.

XenosCR

[ekpent]

Doesn't sound like it may be starving for fuel at higher rpm. Make sure fuel flows downhill though, Timing is spot on right.   next

[xenoscr]

I installed a dyna-s unit last year. I haven't checked the timing since installing it. I'll recheck and go back to the #115 main jets. It sounds like that's what you're recommending ekpent?

XenosCR

[ekpent]

Doen't hurt to make sure all the other variables are in tune before concentrating totally on the carbs.Sure you will get other chiming in who have been there on that big flat spot you got.Floats are set to spec also.When you start it up again put a wet rag to the header pipes up by the engine and compare the "sizzle" to see if they are all running the same-good and hot.

[Bodi]

You should do a plug chop to get an indication of the mixture. Just changing jets on guesses is going to get you really good at pulling and replacing the carbs, but getting the engine running well will be a matter of luck.
There are several threads here about carb jetting. You can either use a dyno and EGA or do plug chops. The Kreskin approach has never been recommended.