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