Need feedback on my carb tuning plan of action

[5twins]

Gary, I think you may be missing a washer on that left carb throttle shaft. It shouldn't stick out that far past the nut .....

 

[gggGary]

I bet you are right.... I did not disassemble it, but the nut was loose and the throttle stop arm wasn't centered on the idle screw. I'll check it out, Thanks!

 

[blackbetty]

Wow, nice eye 5twins!

So, I put my carbs on the bike after adjusting the floats and was able to get it fired up. It idled pretty well and I was stoked. I reset the mix screws to 1.5 turns out, needle is still dropped 1 slot.

Drove it around and it definitely performs better and is not nearly so willing to stall out out of first gear. Needle probably needs to go back to stock position per 5twins suggestion, as I could feel the motor chug a little in midrange.

However, for some reason after I get home and restart, it runs like shit. Left carb is still racing a little off a blip of the throttle, and the idle isn't very smooth.

I'm going to finish dialing in the mix screws and attempt to get my manometer on here to see if syching is off.

I changed out the plugs as well and they looked pretty good after my run.

 

[blackbetty]

So I did some more tuning last night and got the bike to idle steady and drive decently, but it's still not perfect.

Not even a half of gallon of gas through the motor and my plugs are already black

I got a manometer on the carbs and it acts strangely; I can get them to stay steady and even, but the vacuum will oscillate between carbs, so the ATF column in my manometer will jump ab 2" high, hold, then even off, and then switch sides.

Also, after I gas it down the street, I noticed the idle will run high as I come to a stop until I adjust it down on the side of the road.

I have the screws at 1.5 turns out + another 1/8th of a turn on the rich side. If I lean it anymore than that it will stumble when I crack the throttle.

Again, needle position is dropped in slot 2.

Should I go ahead and drop the float bowls another mm? I'm trying to figure out why my plugs are black after such short runs despite conservative jetting and a leaner needle setting.

 

[retiredgentleman]

I hate to tell you this, but if you have puffs of black smoke out the exhaust, the spark plugs blacken quickly, and they appear wet when removed, you may have a passing head gasket. The gasket may be allowing the cylinders to suck oil from the camchain tunnel.

What is the history of the engine...............how many miles (kms) since it was last apart? If the PO had the top end apart, he may not have retorqued the head studs properly.

If you use a white paper towel to wipe the inside of the exhaust pipe, does it appear black?

Use a small LED light to look through the spark plug hole...............is the top of the piston black with carbon build-up?

If the engine is sucking oil, then carb tuning is really of no value at this point.

I just reread your posts. I see you say you already know you have valve seals passing oil into the engine. Does the engine dip stick oil level drop quickly?

All these things point to an engine that has high mileage with worn internal parts. Compression test does not mean much either, because carbon build-up can actually increase compression.

 

[blackbetty]

Well that's the thing, not seeing any black puffs out the exhaust. The plugs don't appear wet, the white porcelain is just blackening quickly, and it seems to be concentrated to one side of the plug.

I will wipe the pipes and see if there's residue inside.

Looking through the spark plug hole, the piston tops do have some grime on them, but it's not caked on carbon. Oil level on dipstick isn't dropping.

But again, I have only had about a gallon of gas through the engine total. I swapped in new plugs since the super rich condition before I adjusted the floats really fouled them. It was sooty residue with raw fuel on the left cylinder plug.

When I got the motor the cam chain and valves were adjusted, a screen type sump filter was installed, points were set, and there was a new gasket on the cam chain tensioner, so the motor had clearly been through before I took it an extra step further with the PMA, new filters, and Boyer.

When I was cleaning the motor I only noticed the stem leak on the exhaust valve, the others were ok.

 

[blackbetty]

Just a quick update....my carbs are possessed. Time to throw more money at them!

Anyway, I was only able to get a decent idle and eliminate pops with the carbs set up with 125 mains and 27.5 pilots and the needle dropped one slot and mix screws right at 1.5 turns, just like the very first day when I posted this thread, except this time I swapped the new float valves with the old Mikunis ones I replaced thinking the new ones could have possibly been leaking, and my floats are properly set at 24mm....

This setup has given me about 100 miles of decent performance (when I say decent, I mean no backfiring, no stalling, etc., but a pretty weak midrange).

Bringing the needle back to the factory #3 position, which would richen the midrange, seems to lean out the pilot circuit? What gives? The bike sputters and pops out the left cylinder and shoots flames on decel; it also will not hold an idle and stall when hot....which would indicate lean, correct? Only when I put the needle down a slot does it start acting right.

However the performance is inconsistent at best. Yesterday was our first day of cold weather in Dallas (48*), and you could really feel the lack of testes in the midrange when opening it up, it simply feels like there should be more. Plus, the idle would run high once hot....I could get it to notch down a bit when blipping the throttle. Strangely, bike has backfired out the right carb 2 times over the miles I've put on the bike.

I went ahead and ordered genuine Mikuni 130 mains and 27.5 pilots to replace the ones that came in the Mikes rebuild kit. I'm also going to go ahead and pull the carbs back down to the screws to see if I can't find any foreign object debris. With the 130 mains I'll leave the needles alone.

The top end is leaking a bit of oil from valve seals, but after running the engine a few miles since I finished my build it seems to have gotten a little better. Since the season is pretty much over for riding I'll pull the engine and send the head to Hoos, but not before I try out the new jets next week.

EDIT: I was browsing the carb guide, and this is an interesting bit I am experiencing with my carbs:

"Too small of a pilot can be indicated by an idle that "hangs" after blipping the throttle or
by having the motor be slow to return to idle after running at higher speeds. Once again,
mix screw settings may help here."

This was happening after my cold weather run yesterday, would a 27.5 pilot jet still be too small for my application?

 

[5twins]

When you set your floats, did you measure off the gasket or the surface beneath it? The spec (25mm) is from the gasket surface. If you measured off the gasket, your levels will be off by a MM or 2. In this case, 25 would be 26 or 27mm in reality and a leaner than spec setting.

 

[blackbetty]

Yes I removed the gaskets and measured 24mm float height off the ungasketed surface, just like the image you posted earlier in the thread. I have checked and rechecked the floats, even swapped sides when I switched out the new float valves for the old ones.