List,
Long time since I've posted but I need some help diagnosing a problem I am
having with a new Dual HS4 SU conversion I made on my 77B.
First, thanks to David D. for the parts. He was generous with his time and
engenders everything that is right with our hobby/sport.
The conversion went along just fine. I had a couple of roadblocks such as a
leaking needle connection and some other stuff that were pretty easy to
overcome. I still have the following two issues.
1. The carbs backfire like crazy. Here's the story. After setting the needle
height to be even with the bridge in the carbs I backed them down 12 flats.
Then conducted an air flow test where I lifted the pistons (at the same time)
ever so slightly (about 1/8") and got a slight rise in RPMs, indicating a rich
mixture, so I went up by one flat until the idle did not change when slight
lift was applied. So far, everything is by the book but I can't get the carbs
to stop backfiring. When cold, they backfire like crazy but quiet down
substantially when the engine is warmed up - but still backfires especially
when accelerating slowly (a heavy foot almost eliminates the backfiring).
Also, when the choke is applied, the backfiring stops. Sounds like it's
running too lean right? So I make the mixture richer and still get
backfiring. Anyway, I trust this is something easy that I'm overlooking for
which you all can suggest a remedy.
2. I have an exhaust leak at the head-exhaust manifold connection for #2 / #3.
I have used a single gasket that burned right through after 10 minutes and
over the weekend put on a double gasket but it also burned right through. Any
ideas on how to get rid of the exhaust leak? Is it possible that the exhaust
manifold needs to be milled straight? If so, who does this work? Are there
torque specs?
Other that this, life is great and I'm looking forward to another season of
shows and seeing some of your butt ugly mugs over the summer (Speaking of
which: Macy, don't you still owe us all some beers or something???).
Dr. Doug
BTW, an elderly gent in my area is looking to get rid of a 58 or 59 Jag 150s
that has been sitting in his garage since 1972. Also has a tranny with OD for
an AH 3000. If you are interested drop me a note.
BTW BTW - I'm on the digest so please CC your reply to the list to me at
dr-doug@msn.com - thanks
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