Vapors from carb and other tuning issues
11-22-2003, 01:06 PM
#1
Melting Slicks
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Vapors from carb and other tuning issues
I just got back from a little test run and here are some of my observations.
I've heard of this before but it seems like I might have a combination rich/lean condition. I'm using a Speed Demon 750 and I've heard of this before. One of the circuits is rich while other is lean.....
On easy takeoff there is a very slight hesitation or drop in rpms. If I give it a decent amount of gas it's unoticable but if low rpm then the rpms really try to drop.
Did some hard throttle runs on the highway and then shut it down without idling to check plugs. I checked two of them and they are light tan. Not quite white but very light tan.
On hard acceleration there is a puff of smoke at first (this is where I think it's rich).
My jets are 5 lower than what came stock...from 83/76 to 78/71. I've never messed with pump cam, power valve or anything else on the carb except idle screws and mixture screws. I set the mixture screws where I had the most vacuum and then 1/8 turn in.
Timing is at 40 total ~2400 rpm.
I tell you what though, even still, I have a hard time keeping my mirrors in one place because of the acceleration of this puppy :smash:
EDIT: Oops, almost forgot the vapors. After driving there are vapors coming from my carb....that's where I was thinking maybe too lean or too much timing. Engine runs cool though ~180degrees.
[Modified by tshort, 12:07 PM 11/22/2003]
I've heard of this before but it seems like I might have a combination rich/lean condition. I'm using a Speed Demon 750 and I've heard of this before. One of the circuits is rich while other is lean.....
On easy takeoff there is a very slight hesitation or drop in rpms. If I give it a decent amount of gas it's unoticable but if low rpm then the rpms really try to drop.
Did some hard throttle runs on the highway and then shut it down without idling to check plugs. I checked two of them and they are light tan. Not quite white but very light tan.
On hard acceleration there is a puff of smoke at first (this is where I think it's rich).
My jets are 5 lower than what came stock...from 83/76 to 78/71. I've never messed with pump cam, power valve or anything else on the carb except idle screws and mixture screws. I set the mixture screws where I had the most vacuum and then 1/8 turn in.
Timing is at 40 total ~2400 rpm.
I tell you what though, even still, I have a hard time keeping my mirrors in one place because of the acceleration of this puppy :smash:
EDIT: Oops, almost forgot the vapors. After driving there are vapors coming from my carb....that's where I was thinking maybe too lean or too much timing. Engine runs cool though ~180degrees.
[Modified by tshort, 12:07 PM 11/22/2003]
11-22-2003, 02:50 PM
#3
Melting Slicks
Re: Vapors from carb and other tuning issues (tshort)
All those vapors are from gas dripping into the plenum.
When you turn the car off look and see if you have gas dripping from the boosters. (if this is the case you may have a stuck needle and seat). My mighty demon was pouring fuel because a small aluminum shaving was stuck in the seat.
Also...if you see those fuel vapors one circuit may not be sealed. Most likely the power valve. I know these carbs have the anti-blowout check ball, but apparently it didn't work on mine. After fighting a bunch of tuning issues I pulled the metering blocks and found out the powervalve as blown. To check this suck on the side opposite the spring...if you get air its bad. If the powervalve is bad its going to be releasing fuel at almost any vacuum state, also when you turn it off it is below the fuel level in the float bowl so this will "drain off". I went with a 4.5 PV as I only have 9" idle vacuum and its runnign GREAT.
I would also suggest setting your float level to the lower line.
Check the needle and seat, check the float level, check fuel pressure (6.0-7.5psi), MAKE SURE the idle transfer slot is only .020" exposed, check power valve.
These should get you going good.
:cheers:
When you turn the car off look and see if you have gas dripping from the boosters. (if this is the case you may have a stuck needle and seat). My mighty demon was pouring fuel because a small aluminum shaving was stuck in the seat.
Also...if you see those fuel vapors one circuit may not be sealed. Most likely the power valve. I know these carbs have the anti-blowout check ball, but apparently it didn't work on mine. After fighting a bunch of tuning issues I pulled the metering blocks and found out the powervalve as blown. To check this suck on the side opposite the spring...if you get air its bad. If the powervalve is bad its going to be releasing fuel at almost any vacuum state, also when you turn it off it is below the fuel level in the float bowl so this will "drain off". I went with a 4.5 PV as I only have 9" idle vacuum and its runnign GREAT.
I would also suggest setting your float level to the lower line.
Check the needle and seat, check the float level, check fuel pressure (6.0-7.5psi), MAKE SURE the idle transfer slot is only .020" exposed, check power valve.
These should get you going good.
:cheers:
11-22-2003, 03:51 PM
#4
Melting Slicks
Re: Vapors from carb and other tuning issues (tshort)
c'mon now - fuel vapors are good for you, better than beer and that funny weed stuff...... and free too!
:nono: :sleep:
:nono: :sleep: