Background
When installing the primary fuel rail on my
20B, I noticed a gap between the primary fuel rail and the diffuser (air
bleed.) One of the original air bleeds was damaged when the rebuilder
was removing. He could not locate a replacement. He supplied new
air bleeds designated for a 93-95 13B, which he was informed were usable in
the 20B. The gap between the fuel rail and the diffuser seems to be
between 0.110" and 0.145". This measurement was determined by inserting
the diffuser and measuring its depth. Then the fuel rail was bolted in
place. Through the intake port, the injector was pushed up until it
contacted the fuel rail. The fuel rail was then removed and diffuser
depth was measured. The difference between the measurements was between
0.110" and 0.145". The original diffuser returned by the rebuilder has
no apparent seal, the replacement has a rubber seal molded into the
top.
I took some measurements and drew up the primary,
fuel rail / injector /diffuser (see attached pdf.) It looks like there
are 2 differences between the diffusers that came on the 20B and the
replacements recently purchased. The height of the diffuser above the
seating surface is much lower on the replacements and the length of the area
that projects into the port/air stream is longer. The extra length
extending into the port is probably not an issue.
The shorter height of the replacement seems like
it will be a problem, the problem being a vacuum leak around the
injector. A secondary issue from a vacuum leak in this area may be an
effect on fuel droplet size. By looking at the injector, it appears that
a metered amount of air is intended to flow into the pintle cap, presumably to
aid in reducing the fuel droplet size. A vacuum leak in this
area may reduce the air flow through the pintle cap and the resulting
droplet size reduction.
I would speculate that at medium or higher power
levels the vacuum leak would probably have little noticeable effect. I
would expect that the most significant effect would be at or near idle
conditions. Since smooth idle seems to be difficult to attain in many
installations, it would certainly be prudent to try and eliminate this issue
(not to mention that it would be good practice to get it right.)
Questions
1. There seems to be a very small gap
(~0.010") between the fuel rail seating surface and the top of the original
diffuser. It looks like there should be a grommet that makes up the
difference and provides a positive seal. To anyone who has disassembled
a 20B, is there a grommet/seal the sits on top of the diffuser?
2. Same question as 1, for anyone who has
disassembled a 93-95 13B (13B-REW, I believe)?
3. Anyone have a source for the proper 20B
diffusers?
Any opinions and/or remedy suggestions are appreciated.
Thanks,
Joe