Jet advice

[armyofda12mnkeys]

Hey guys,
My bike runs pretty well (1978 XS400E, basically stock but with 2-in-1 pipes)...
But I feel like in the low end (1st-2nd gear) there is not much power.
If feel like I go through the gears pretty quickly to get at 25-30mph (prob @ 6th gear when I hit 30mph). Usually I like to cruise at 3-4rpm's and not allow the engine to get 'too loud' while riding (so I'm never really going above 5/6 rpms while going 50/55mph in 6th gear I think).

Taking off in 1st gear feels kinda 'weak' on the bike versus other bikes I've ridden. If Im on an uphill, and I have to brake and try to let the clutch out smoothly, i think I feel it more that the bike just doesn't pull strong like I'd want.
The clutch plates and springs were new and measured the right size. I've also done many clutch adjustments and kinda got it to where I like it (making the clutch too 'smooth', seems to cause alot of false/stuck nuetrals, so most of the action currently happens mid to the end of 'letting the clutch out').

Also more background, I used a Colortune to set my Fuel-Air mixture. Did a decent job. Lets say 3.5-4 turns out and no issues with high idle rpms or other things that seem to plague other peeps.


Anyway with all that background... I thought I need to maybe play with jetting to possibly give the bike more power in the low-end since I think I can possibly rule out clutch and fuel-mixture screw settings.
My current/stock? settings are:
Pilot Jet: 42.5
Main Jet: 132.5

I upgraded yesterday to:
Pilot Jet: 47.5
Main Jet: 137.5

The bike now runs high at idle, like high rpms then goes too high and I turn it off.
This is with the choke not out. and Fuel-Mixture screws at a relatively conservative 1.5 and 2.5 turns out with the same result. and no air leaks Im guessing since bike ran fine earlier with old jets, and sealed the carb and air intakes pretty well.
Just curious where you guys I should go back to... the same sized pilot jet to control that idle rpm's, but with a larger main jet for more low end power? I was hoping to give it more power without trying to use shims to optimize the needle jet which seems harder than just playing with main/pilot jets.

Any ideas?,
Thanks!,
Ari

P.S. if anyone ever wants to come over if they live in Philly and help me figure out simple jet settings, I'd pay ya help me jet my bike .

 

[16VGTIDave]

Where to start? If you were closer...

This may sound harsh, but I've posted a link numerous times to a great page that explains exactly how to get your carbs dialled in. Check one of the other threads. Read, learn, stop guessing, stop playing.

If you aren't willing to rev the engine, you will be forever disappointed and will never get the carbs setup correctly. A 400cc twin has to be revved to make power. It was designed that way. They aren't torque motors, they are revving motors. They aren't a 1400cc v-twin and never will be. You will have to learn to rev it well past the point where a Harley motor would explode, or just buy a Harley. Yeah, that sounds real harsh, but the truth often is.

 

[armyofda12mnkeys]

Hey 16VGTIDave,
That wasn't harsh at all.
I've read a few jetting guides but was hoping for the 'Easy Button' .

Well, I shall give her some more gas than I have been giving her and see how she holds up.

 

[Unkle Crusty]

What Dave said.
I bookmarked the CV carb tuning guide. Also did a search on jet sizes on this site. And I bought a bunch of jets. The PO of my bike had it wrong. Was fine to about 3/4 throttle, but at WOT it did not run right.
At 45hp (DOHC) these bikes are making about the same horsepower as a 650 Bonneville. Only way to make more horsepower is with bigger bangs or more bangs. These bikes have to do it with more bangs, which is revs.
I go from 1st to 4th fairly quickly. Have to. And down the highway the engine is buzzing. Has to.

Unkle Crusty

 

[armyofda12mnkeys]

The old stock pilot jet helped get the bike back into riding mode.
Will tune/jet the carbs when the weather gets warmer next spring .

-Ari