lean: air vs fuel

so, i took my seca for a spin to get her warmed up for a carb synch and colortune.

parked in the barn and proceeded to hook up the vac. gauge. (i bought a motion pro 4 tube manometer)

i started it up with the gauges attached and the bike immediately raced up to 3500 RPMs or so.

i killed the engine, but not soon enough to stop the engine from drinking most of the fluid out of one of the tubes

anyhow - i used 2 of the tubes that were still ok and synched the carbs, put the caps and vac. line back on and proceeded to try to colortune.

i couldn't get any color other than blue on cyl. number 1, proceeded to get frustrated and quit. i set all my pilot screws to 3 turns out and called it a day.

i took the bike for a ride yesterday and, at higher RPMs, the bike performs great. tbut what i notice now is that i seem to have no engine braking - especially at lower speeds - i have to use the brakes to get the engine to slow down from 3k to idle.

so: i'm figuring i have an air leak - probably from the vacuum port cap(s) not re-seating due to their age and they are leaking now that i messed with them. makes sense, right?

question: is it right to say there's 2 possible causes for running too lean and they are diagnosed as follows:

1) not enough fuel, lack of power, stumbling at particular RPM ranges

- or -

2) air leak - bike seems to have good power but rpms won't come down.

make sense?

 

Do your carbs pass the "clunk test" ? If your carbs arent quite synced properly then you will have an engine that keeps on running on and not dropping RPM immediately you drop the throttle.. I bought the Morgan 4 barrel - synced today - no fluids to suck in at all - steel sliders and really accurate.

 

no, lean is lean the spark plug sees the same thing weather it comes from the carb or a leak
1 could be a lot of things
2 sounds like the sync is off

 

carbs definitely clunk. i follow what you are saying that on out of synch would cause this - however, i just barely turned any screws when synching as the vacuum levels were so close to begin with.

i did adjust my idle up right before i hooked up the vac gauges - it was idling around 900 RPMs and i turned the screw to get it up to around 1050.

the thing that has me thinking air leaks is that the bike NEVER did this until i hooked up the vacuum gauge - then it raced up to 3500 rpms and held there.

the only thing i changed on the bike was pulling the caps off and hooking up the gauge.

i had good engine braking and color on my plugs before i did that.

 

Hey Skeeter,

Your idle jumping up to 3500 rpms seems strange since you turned the screw up to 1050 right before you hooked up the vac gauges. It would only jump like that if...

The piston slides got hung up or stuck (when did you last polish the bores? SEE footnote*), the choke was applied, throttle linkage was affected in some way, or you had a surge of extra air IE: airbox lid popped open or a boot came loose. If anything your idle should've dropped once the vacuum gauges were hooked up.

*I clunk tested/polished the pistons and bores only a few rides before I put my bike away for the winter. I just got back from my 3rd ride of the season and noticed the slides are not returning lightning fast like they were in October. When I rev the engine at a stop light, it takes a second to come back down to idle speed. I will polish them again ASAP!

 

Don't just Polish them again, ...

Mark the Bottoms 1,2,3,4
Then, try ALL of 'em in every Hole until you find a combination that gives you the BEST Performance.

Its OK to SWAP Holes if it helps.

 

Have you tried some temporary form of vacuum cap till you get new ones?
At least that could rule them out as th problem.

 

i had my carbs off this spring - maybe 2 weeks ago now -and they all went clunk. i'm gonna try to "improve" the seal on those caps and see what happens.

after sleeping on it - i'm wondering if it's possible that i have some sort of partial clog in one or more of my pilot circuits that was causing the low idle - and now my idle is actually set too high - sometimes it unclogs and rev's up? kinda sorta makes sense to me. . . i dunno. i had some color on my plugs before i messed with it. . . <grumble>

 

question: i was under the impression that i do not need to oil my air filter - but i've been reading up on air filters and now i know that some filters need to be oiled periodically. i have stock air filter - looks like it's made of some sort of paper type material. i don't need to oil that filter, do i?

(just trying to leave no stone unturned)

 

If your consistently at a high rpm, and you know that you turned up the throttle screw, That would be an easy check. And I don't trust those little intake caps as far as I can throw them. I make my own caps out of vacuum hose with black RTV plugging one end of it.

 

no oil on paper filters

 

have you recently purchased your intake boots? if they're old, maybe when you pulled the caps it was all it took to finalize a crack on the outside making its way all the way through to the inside. The replacement caps from Len are trust worthy no doubt (I have them but bigger problems lol) & i'm sure davstarks idea works too.

 

yeah - i'm thinking i have a crack around a vacuum port. i RTV'd my boots last summer and there was some that got partially removed when i pulled the caps off - luckily, the wife has a bunch of folks coming over to watch twilight movies tonight, so i'll have something to do while i'm exiled to the garage.

 

Ya, I never thought that Twilight would be a good thing.

It's one of the best things to happen in a while

 

i think i got it fixed. initially all the plugs were almost white. they had a kinda pink shade on one side of the insulater. #3 showed the most color - but was still to white for my liking.

i swear - i started out working extremely methodically, doing one thing at a time and checking every plug - then i got impatient with that and decided to do one thing at a time and just check the outer plugs. then i got impatient and did two things at one time and the good news is that one of those things fixed (i think) the problem. i lowered the idle back down to 900 RPMs and i put a hose clamp on #4 vacuum port.

i don't really understand how too high of an idle would cause a lean situation - so i'm guessing it was the vacuum port that really did it. now i'm wondering if my tachometer is off - reading lower than actual - causing me to set my idle too high.

gonna do some plug chops today and see what i see.

 

no luck - ran the bike at 4500 rpms in 5th gear and plug chopped: all plugs are white on one side and have a pinkish shading on the other side.

started if up and let it idle for 3 or 4 minutes - no choke. plugs look the same.

checked again when i got home - after riding 3 miles at around 3k rpms - plugs look the same.

i've never been able to find an air leak with propane, carb cleaner or WD-40.

i notice if i turn the pilot screw all the way in - the engine stalls out - so that tells me there's fuel going through the pilot circuit when the screw is out, right?

question: when air filters get old, to they flow better? i thought old filters got dirty and caused a rich situation and a new filter would allow more air flow. am i wrong?

 

here's the outer 2 from my 750 seca with 126 mains 4/1 pipes supertrapp muffler(9) disks, stock air box without the snorkel and a filter as old as the hills, about 300 miles on them the other side is white
now let me ask you, would you change anything?

 

The rider.

 

are you telling me to quit worrying? from what everyone else has to say about plugs - i'd say those are way too lean - mine look about the same . . .

 

those look about like my plugs. 8k last season riding it like I stole it, didn't burn up yet, pistons look great valves look good, I'm not worried about it unless it starts slowing down :lol:
James