Q-Jet Problem (Re:Howell Fuel Injection Kits)

[patrick flowers]

>
> By " air door" in the secondary barrels do you mean the twin large
> spring loaded air valves at the top of the carbruretor? I'll follow
> your advice and see if I can locate the allen head set screw on the
> spring tensioner and check to see that the adjustment is right.

Yes, the secondary air valves look like a "choke" over the secondaries.
I thought Roe covered this adjustment in his book, but if you look on
page 166(hoping that your edition is the same as mine), you can see what
looks like a screw behind the secondary block link. That's the
adjustment screw. The set screw is underneath the boss that the
adjustment screw is in. You can't see it, you must feel for it.

Another thing to check is that secondary block link. On the Q-jet, the
secondaries are blocked from opening until the choke pulls off. If that
block link does not move freely, that would also result in
overenrichment and loss of power.

Hope this helps!
Patrick
- --
Patrick Flowers
Mailtoatri63

The GMC Motorhome Page
http://www.gmcmotorhome.com

 

[philip l. stewart]

Patrick, thank you for the reply to my recent posting. I agree that the
fuel enrichment problem I'm having should be fixable on this carburetor,
but there sure seem to be a lot variables one must consider.

I recently found a copy of Doug Roe's 1986 book on Rochester Carburetors
at the bookstore and I'm studying it now. I also found the current
address for Roe, Inc. in Gilbert, AZ if anyone's interested.

I believe that the secondary metering rods are the original ones for the
1976 GMC MH carb, because I took them out and cross-referenced their ID
code (CJ) to the Rochester part number(7040767) in Roe's book (see the
table on page 152) and to the replacement part number that Cinnabar
supplies. They're the same. But I believe this doesn't mean they are
necessarily the correct rods for today's reformulated gasolines we have
to burn. This is where I'm interested if anyone has recently replaced
their orginal secondary rods and what ID number or Rochester part number
they used to get a proper air/fuel ratio. Since it looks like Rochester
at one time or another supplied about 50 different designs of the these
secondary rods for the Q-Jet, I need some idea of where to start if I
want to start changing these to lean out the secondary mixture. By the
way, I re-installed the rods exactly as directed by Roe.

I believe Roe says that the secondary jets (orfices)can not be easily
removed and replaced and that there is just one size anyway. This means
that tuning the secondary fuel metering system requires changing the
rods or possibly the rod hanger. I read that the rod hanger has an
effect on how the rods raise or lower into the jets which in turns
affects the rate and on-set of secondary fuel flow. So, another
question would be has anyone had any experience in changing to another
hanger recently. My carb has the "K" rod hanger installed.

By " air door" in the secondary barrels do you mean the twin large
spring loaded air valves at the top of the carbruretor? I'll follow
your advice and see if I can locate the allen head set screw on the
spring tensioner and check to see that the adjustment is right.

Thanks again, Patrick, for your reply, and any one else who feels like
commenting please jump in let me know you thoughts on the Q-Jet or
Howell fuel injection systems.
PHIL.
Phil