Homemade manometer sync issues

[Nolzb]

So I have had issues with syncing everytime I used my homemade manometer. Which I made from a thread on here. The meter itself worked fine, but everytime I synced it... the bike was always worse off than when I started to sync and I can never understand why. Always bench synced to get back to a baseline and I have wondered/noticed my butteryfly valves are opened a crack and wonder is that would contribute to my hanging rpms slightly during idle, more so when it warms up and even worse when i am actually test riding it. Unfortunately the bikes goes through periods where it sits for a while. But it is a 1980 xs400SH stock other than uni foam pods on the stock H pipe. Jetting is 150 main, with. 50 pilot with stock jet needle & needle jet, air/fuel screw at 5 turns out most recently. Which due to my tinkering and trying to find the right set up changes when I'm able to get my hands on it. As a side note I have been following the the factory pro carb tuning as a guide and it has gotten me much closer to a better running machine. As always any anysight is always appreciated.

 

[amc49]

Likely way too rich at idle with the pilots you are running. All you are doing is providing extra fuel so the idle can hang. If the butterflies are not closed enough where the hanging comes from, they need to be cracked slightly but not enough to allow the hang. You have to crack them more just trying to make up for the richness at idle too. So, partially creating your own problem.

If you even mod heavily like headers and cam the idle pilots still rarely need to be change, I don't get where everybody gets that from. I have modded countless engines and never once changed pilots or what passes for them. The mixture screw usually has enough range to take care of that. Most engines are set slightly rich at idle using the OEM pilots and the mixture screw then cuts back on that, they set up rich due to the slight EGR effect from the engine rolling over slow enough that you get partial exhaust gas residuals due to the overlap in cam. If still running stock pipes and the only mod is the pods then you are too rich at idle with those pilots.

Anybody with a sharp ear can sync carbs on twins perfectly by simply listening to the engine at a slow slight pullaway from an idle stop. You need no sync tools for that, I used to do it all day long.

 

[Nolzb]

hmm, the butterfly valves makes sense. I will re-bench them and adjust the valves so the are just barely cracked. If it was so rich at idle, wouldn't the plugs show and they do not show richness. After reading your reply a few times, I guess they would not show rich because of the valves being cracked more than they should be.. Not disagreeing with you on the a/f screws out, just that I have read on here quite a few times that 3-5 turns is within range. Well I don't have sharp hearing or ear for it to say the least.

 

[amc49]

If you are not running the OEM plug for one you may not see rich but you shouldn't anyway as you do not drive the bike at idle speed only. You see on the plug the most major amount of driving you do if you do not do a wide open run and cut the throttle to check them on the spot.

You can't just adjust the butterflies to just barely cracked as your idle speed may not allow it. They often have to be open more due to engine condition, as ring and valve seal die the engine has to have the butterflies slightly opened more and more, the normal position is an indicator of engine condition. Normal should have them barely exposing the first hole that when 100% shut they cover fully, if the entire hole is exposed you are too far open. There are fixes for that but rarely used, I did it all the time on cars and other bikes when needed. If open to expose too much of that hole that is more rich on top of the pilots.

 

[amc49]

I could be wrong on the screws at 5 turns but I've never gone that high on any bike before. I don't have one of these though.

Here's the thing. The amount of turns you do is directly based on how rich the system is to begin with. To go leaner for EPA emissions the pilots get smaller and if using a fuel/air mixture screw (one up front, instead of air only and one that is toward back or carb) then it has to open more. On a normal non-emission carb you should be able to open or close that screw enough to both lean to die or rich to die (or almost, some get running worse only and that is enough) meaning you have complete control of the entire idle mixture range. When a carb goes EPA you often lose the richen to die because the pliots are then picked lean enough you can never adjust the screw enough to get to too rich. Why the number of turns often goes up on an EPA carb.

After giving some thought I edited the above post with 5 turns too much mentioned in it.

 

[Nolzb]

I am running the oem plug(bp7es), ha yes that is true. Which my dumb self realized that after I had posted. I am sorry, but can't adjust the valves to just barely cracked because engine speed wouldn't allow. Isn't that why they have idle screw underneath, don't mean to be dense.. just i am not sure which hole you are referring to, as there are no holes on the other side of the throttle plate just the main passage. I understand that them being slightly open so not all of the area is allowing air and fuel to pass through, but I am not aware of any hole.. I think we may be speaking 2 different languages here. I appreciate your help and explainations though.

 

[amc49]

http://web.ncf.ca/ag136/cvCarb.jpg

Point 14 not 13 which is way forward of the closed butterfly edge. Transition mixture holes, or can be a short slot. When the butterfly opens the engine instantly goes lean until the main system begins to pullover, it takes a fractional second. The holes act like miniature accelerator pumps for a second to give small bursts of fuel until the main carb begins to flow. If they are exposed too far at idle they feed fuel and overrich then.

On this Yamaha carb they may be on the top of the bore as the mixture screws seem to be if I was looking correctly at a pic last week. Most carbs they are on the bottom.

 

[amc49]

http://www.xs400.com/threads/idle-mix-plugs-stuck.19994/

Yep, on the top. Look at pics in post #1.

 

[Nolzb]

Yes the mixture screws are at the top and i appreciate you taking the time to explain some of these things. I have swapped out my pilot as well as my main for a smaller size on each and I have re bench synced both carbs getting the butterfly valve as so it will not allow so much and have hanging rpms. I will keep you posted as to what difference it makes. Unfortunately it is gonna be a rainy week thanks to the wanna be hurricanes.