Patrick,
Thanks for your offer to help regarding the enrichment problem I'm
having with the Qudrajet carburetor on my 1976 GMC 455. You asked for
more detail, so here goes.
As I mentioned in my previous posting, this carb is producing a sooty
black exhaust whenever I have to depress the accelerator peddle enough
to open the secondary fuel metering system to climb hills, pass, etc.
It performed like this particularly bad with very noticable loss of
power at evelations greater than 5,000 feet on a recent trip to New
Mexico. (Homebase is East TN.)
The carb. is the orginal motor home model and my coach now has 85,000
miles on the odometer. The enrichment problem did not exist until
recently. Because of a hard hot starting problem and 20 years + of gum
and dirt accumulation, 4,000 miles back and before the New Mexico trip I
had the carb "rebuilt" by a very experienced GMC mechanic nearby. The
carb was dissasembled, solvent cleaned and put back together with a
"kit" installed. This fixed the hard hot starting but may have
contributed to current enrichment problem.
I assume, but don't know for cetain that with the rebuild job the float
was either repalaced or verified to be okay and then properly installed
and adjusted. Since the engine starts fine now, both hot and cold,
idling is no problem, and no black exhaust is noticed with only the
primary barrels operating, I'm thinking that the float sysytem is not
the cause nor are the fuel well plugs leaking. (They were supposed to
checked by the mechanic who did the rebuild.) I confirmed that the
power vlave is not stuck, the choke opens fully with a warm engine, and
the secondary metering rods are the orginals (ID code CJ, part no.
7045780).
All this leads me to think that the secondary metering rods probably are
no longer correct and the carb needs to be calibrated with differnt rods
to get the fuel air ratio correct again. However, I haven't yet located
any repair shops in the Chattanooga, Atlanta, Nashville area that say
they can tune this carb using an exhauast gas analyzer to make sure
they get it right. I know I can drive to Michigan and get this kind of
work done at Cinnabar, but that's a "fur piece" to go this winter.
7 to 8 MPG is the gas mileage and I could probably live with that. The
lack of power at moderate altitudes and black sooty exhaust, I can not.
So, there are the details and I would greatly welcome any one's
comments, advice and opinions on this problem. The Howell TBFI system,
admittedly, is a pricey but possible solution, and as they say,
sometimes its time to quit "beating a dead horse" or in this case an old
Q-Jet.
Phil
Thanks for your offer to help regarding the enrichment problem I'm
having with the Qudrajet carburetor on my 1976 GMC 455. You asked for
more detail, so here goes.
As I mentioned in my previous posting, this carb is producing a sooty
black exhaust whenever I have to depress the accelerator peddle enough
to open the secondary fuel metering system to climb hills, pass, etc.
It performed like this particularly bad with very noticable loss of
power at evelations greater than 5,000 feet on a recent trip to New
Mexico. (Homebase is East TN.)
The carb. is the orginal motor home model and my coach now has 85,000
miles on the odometer. The enrichment problem did not exist until
recently. Because of a hard hot starting problem and 20 years + of gum
and dirt accumulation, 4,000 miles back and before the New Mexico trip I
had the carb "rebuilt" by a very experienced GMC mechanic nearby. The
carb was dissasembled, solvent cleaned and put back together with a
"kit" installed. This fixed the hard hot starting but may have
contributed to current enrichment problem.
I assume, but don't know for cetain that with the rebuild job the float
was either repalaced or verified to be okay and then properly installed
and adjusted. Since the engine starts fine now, both hot and cold,
idling is no problem, and no black exhaust is noticed with only the
primary barrels operating, I'm thinking that the float sysytem is not
the cause nor are the fuel well plugs leaking. (They were supposed to
checked by the mechanic who did the rebuild.) I confirmed that the
power vlave is not stuck, the choke opens fully with a warm engine, and
the secondary metering rods are the orginals (ID code CJ, part no.
7045780).
All this leads me to think that the secondary metering rods probably are
no longer correct and the carb needs to be calibrated with differnt rods
to get the fuel air ratio correct again. However, I haven't yet located
any repair shops in the Chattanooga, Atlanta, Nashville area that say
they can tune this carb using an exhauast gas analyzer to make sure
they get it right. I know I can drive to Michigan and get this kind of
work done at Cinnabar, but that's a "fur piece" to go this winter.
7 to 8 MPG is the gas mileage and I could probably live with that. The
lack of power at moderate altitudes and black sooty exhaust, I can not.
So, there are the details and I would greatly welcome any one's
comments, advice and opinions on this problem. The Howell TBFI system,
admittedly, is a pricey but possible solution, and as they say,
sometimes its time to quit "beating a dead horse" or in this case an old
Q-Jet.
Phil
atri63
