Carbed LQ4 Smoke at Idle-Carb Issue?
11-09-2011, 09:33 PM
#1
Teching In
Thread Starter
Join Date: Mar 2005
Location: Cypress, TX
Posts: 22
Likes: 0
Received 0 Likes
on
0 Posts
Carbed LQ4 Smoke at Idle-Carb Issue? I am at wits end on my carbed LQ4. I have a constant amount of smoke coming out of the car immediately upon start up. It appears to be of a bluish/grayish color. It doesn't smell like oil even though it looks a bit blue, but rather of gas and a rich mixture. Here's some basics on my combo:
LQ4 short block-~65k miles
L92 heads-brand new (500 miles maybe-has sat alot for past two years)
XR281HR cam
MSD 6010
Pro Systems 850 (built 5 years ago)
Unregulated Edelbrock 1791 electric fuel pump preset to 6.5 psi
The carb had originally been built for a 414 big block Chevy, and was jetted 76/86 with a 6.5 pv. I've since reduced this to 74/78 and a 5.5 pv to lean it out, and I have accomplished this to a degree. However, the smoke remains and is unchanged in volume no matter what I do to the carb.
The reasons I tend to think it is the carb first is that 1.) my idle mix screws fail to kill the car when screwed all the way in, 2.) the heads are new (purchased from a dealer) and I would tend to think the seals are still good,
and 3.) the carb has sat for extended periods of time since new and I found what appears to be porosity starting to develop on the metering blocks. All of this tells me that I may be having some sort of leak into the engine resulting in my overly rich condition despite attempts to lean it out.
Anybody ever had an experience similar to the above? I don't want to think it is oil that is burning, but the slight bluish hue has me worried. I did drain and change the oil in it, and the oil smelled very much of gas and came out pretty thin.
For the record, this exact combo has run smoke free in the past. Something has changed. Any thoughts/ideas/ridicule will be taken gratefully to help me solve this problem.
LQ4 short block-~65k miles
L92 heads-brand new (500 miles maybe-has sat alot for past two years)
XR281HR cam
MSD 6010
Pro Systems 850 (built 5 years ago)
Unregulated Edelbrock 1791 electric fuel pump preset to 6.5 psi
The carb had originally been built for a 414 big block Chevy, and was jetted 76/86 with a 6.5 pv. I've since reduced this to 74/78 and a 5.5 pv to lean it out, and I have accomplished this to a degree. However, the smoke remains and is unchanged in volume no matter what I do to the carb.
The reasons I tend to think it is the carb first is that 1.) my idle mix screws fail to kill the car when screwed all the way in, 2.) the heads are new (purchased from a dealer) and I would tend to think the seals are still good,
and 3.) the carb has sat for extended periods of time since new and I found what appears to be porosity starting to develop on the metering blocks. All of this tells me that I may be having some sort of leak into the engine resulting in my overly rich condition despite attempts to lean it out.
Anybody ever had an experience similar to the above? I don't want to think it is oil that is burning, but the slight bluish hue has me worried. I did drain and change the oil in it, and the oil smelled very much of gas and came out pretty thin.
For the record, this exact combo has run smoke free in the past. Something has changed. Any thoughts/ideas/ridicule will be taken gratefully to help me solve this problem.
11-10-2011, 06:58 AM
#2
Bluish gray smoke at idle is almost certainly oil being burned. When it happens just at start up my first guess is always valve seals. Continuing to smoke after warming up is more likely rings, but a completely gone valve seal can do the same.
Valve seals sometimes get installed incorrectly. Don't rule out leakage past the valves. Try looking at the plugs and see if one is wet with oil.
Idle mixture screws not killing the motor when closed just means you have other carb issues. Things like excessive float level, bad gaskets can all lead to non-responsive mixture screws.
Do you have a PCV hook up? Try disconnecting that for the time being.
Valve seals sometimes get installed incorrectly. Don't rule out leakage past the valves. Try looking at the plugs and see if one is wet with oil.
Idle mixture screws not killing the motor when closed just means you have other carb issues. Things like excessive float level, bad gaskets can all lead to non-responsive mixture screws.
Do you have a PCV hook up? Try disconnecting that for the time being.
11-10-2011, 07:12 AM
#3
TECH Regular
iTrader: (9)
Join Date: Dec 2007
Location: Ohio
Posts: 460
Likes: 0
Received 0 Likes
on
0 Posts
Blue smoke is oil. If it were valve seals, I would think that it would only smoke on startup for a minute, not consistently. Sounds like ring blow by to me and carb issues.
11-11-2011, 07:45 AM
#4
Teching In
Thread Starter
Join Date: Mar 2005
Location: Cypress, TX
Posts: 22
Likes: 0
Received 0 Likes
on
0 Posts
I may have overstated the amount of blue in the smoke. It's there, but I do have to look for it, looks more gray than blue.
I did do a compression test, all cylinders were close to 140 psi, within 15 psi of each other.
Looking at the plugs, they are sooty black to the point of fouled, and are brand new. No oil on the plugs (no film/sheen), just a dry black chalky look.
I converted the PCV to the LS6 style. Disconnecting it and plugging has no effecting on the smoke volume.
I did do a compression test, all cylinders were close to 140 psi, within 15 psi of each other.
Looking at the plugs, they are sooty black to the point of fouled, and are brand new. No oil on the plugs (no film/sheen), just a dry black chalky look.
I converted the PCV to the LS6 style. Disconnecting it and plugging has no effecting on the smoke volume.
