The backfiring is usually caused by screwed-up timing.
When you say "runs well" between 4000-6000, do you mean
you can actually drive it, or you can just push
on the gas pedal in neutral and rev it up that high?
A few days ago I reassembled my engine after changing
the head and cam. It ran sort of like you describe,
and I started to worry how I might have messed up.
It turned out that I got a couple of spark plug wires
switched...
Did the car run OK before the HS2s were installed?
Are there any unconnected vacuum ports?
Any potential leaks around the manifolds?
Are you blocking the vent holes on the sides
of the front flanges where the air filters attach?
Do the pistons move freely?
If there is no gas dripping out from the carb bowls,
I doubt that a somewhat incorrect pressure setting or
float setting could be the real cause of your problem.
HS2s have 0.900 jets, BTW. If you screw up the jet adjusting
nuts all the way and beck them off about 2 turns, that
should be fairly close to the correct setting, in my experience.
I put HS2s on my '72 and after fixing several problems, they
run just great. The trickiest problem what that a PO of
the carbs had installed much stronger non-stock piston
springs.
Doug Braun
'72 Spit
At 09:26 PM 8/29/00 -0700, you wrote:
>Hey list need some help,
>
>Buddy of mine is installing 1 1/4 " SU's on his 77' Spit and we cant
>seem to get it to run. Here is what we know: need to choke to keep it
>running
> appears to run rich
> idles at 1500 stalls below
> runs well between 4000-6000 rpms
> backfires thru carbs
> poor power
> no markings on needles
> electric fuel pump 2-4 psi
> pressure regulator set at 2 psi
>
>Has anyone done this conversion?
>what needles are you running?
>jet height? diameter .090 or .100 dia.
>Timing of engine?
>float setting?
>general suggestions
>
>Look forward to everyones suggestions.
>
>Chris
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