Mikuni HSR42 questions
dbh
and perhaps commenting on the following:
I've sifted through Dejanews and finally feel compelled to ask
for help. I just put a new Mikuni HSR42 on my '99 FXDS-CONV
and am left with some concerns. On the left side, above the idle
speed screw and below the throttle is a brass fitting pointing downwards. No
mention is made of this thing in the accompanying
documentation. It doesn't suck when the engine is running but I assume it
must vent something.(?) Anyway my question is what should I do with this
little pipe? I am worried about getting dust or other crud into it I was
thinking of either plugging it or connecting a length of tubing to it and
letting it dangle down along with the float vent. And on the topic of vacuum
lines - I used the VOES fitting (which is supposed to be plugged on the
TC-88) to power the fuel valve. Anyone see any problems doing that?
Next question: The idle speed adjustment has a long floppy extension on it
that just kind of hangs there. I was thinking of just snipping it off, but
maybe someone has a better idea?
Finally: I'm almost positive there is a vacuum leak between the carb and the
manifold. The carb doesn't seem to fit into the seal very snugly (although I
did soap it up first) and even after tightening the air filter backplate
against the carb, I can still rotate it. (It did go all the way into the
seal.) The reason I think there is a leak is that I can screw the pilot air
screw in until it seats and the bike then idles so fast I can back the idle
speed screw right out and it's still at 1200 rpm. I'm hoping a new seal will
cure it but my question: has anyone got any advice on this seal? I'm tempted
to smear a little Gorilla Snot (silicone sealant) around the carb before
stuffing it in next time.
That's all. Thanks for listening.
Barkeep on my tab...
dbh
Mark Howell
>
> Greetings, and beverages of choice to anyone interested in reading
> and perhaps commenting on the following:
> I've sifted through Dejanews and finally feel compelled to ask
> for help. I just put a new Mikuni HSR42 on my '99 FXDS-CONV
> and am left with some concerns. On the left side, above the idle
> speed screw and below the throttle is a brass fitting pointing downwards. No
> mention is made of this thing in the accompanying
> documentation. It doesn't suck when the engine is running but I assume it
> must vent something.(?) Anyway my question is what should I do with this
> little pipe? I am worried about getting dust or other crud into it I was
> thinking of either plugging it or connecting a length of tubing to it and
> letting it dangle down along with the float vent.
In the external components diagram, it says "vent fitting (do not plug)".
Stick a hose on it if you're worried about crud getting in there.
> And on the topic of vacuum
> lines - I used the VOES fitting (which is supposed to be plugged on the
> TC-88) to power the fuel valve. Anyone see any problems doing that?
Nope.
> Next question: The idle speed adjustment has a long floppy extension on it
> that just kind of hangs there. I was thinking of just snipping it off, but
> maybe someone has a better idea?
If you are not going to use it to bump up the idle speed during cold starting,
replace it with the short one, part # 990-605-065.
> Finally: I'm almost positive there is a vacuum leak between the carb and the
> manifold. The carb doesn't seem to fit into the seal very snugly (although I
> did soap it up first) and even after tightening the air filter backplate
> against the carb, I can still rotate it. (It did go all the way into the
> seal.) The reason I think there is a leak is that I can screw the pilot air
> screw in until it seats and the bike then idles so fast I can back the idle
> speed screw right out and it's still at 1200 rpm. I'm hoping a new seal will
> cure it but my question: has anyone got any advice on this seal? I'm tempted
> to smear a little Gorilla Snot (silicone sealant) around the carb before
> stuffing it in next time.
At 1200 rpm the carb is using the pilot jet as its idle fuel source. Drop the
rpm to 1000. If the idle mixture still has no effect, your pilot jet is too
big.
Mark H.
d...@my-dejanews.com
Thanks for your comments Mark, they were much appreciated. I tried dropping
the rpm back after adjusting the idle air screw but here is what happened:
clockwise on the air screw = higher rpm, all the way until it was seated
CCW on the idle speed screw = no effect (already nearly falling out)
When the pilot air screw was all the way in, the idle was highest and
I couldn't lower the idle speed with the idle speed screw ie. throttle
stop. Since the throttle cables were not even connected yet and there
were no obstructions to the carb throttle, I could only conclude that
the slider was fully down and there was a significant vacuum leak.
Thanks again for your comments,
dbh
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Mark Howell
>d...@my-dejanews.com wrote:
>
> Thanks for your comments Mark, they were much appreciated. I tried dropping
> the rpm back after adjusting the idle air screw but here is what happened:
> clockwise on the air screw = higher rpm, all the way until it was seated
> CCW on the idle speed screw = no effect (already nearly falling out)
> When the pilot air screw was all the way in, the idle was highest and
> I couldn't lower the idle speed with the idle speed screw ie. throttle
> stop. Since the throttle cables were not even connected yet and there
> were no obstructions to the carb throttle, I could only conclude that
> the slider was fully down and there was a significant vacuum leak.
>
> Thanks again for your comments,
> dbh
>
> -----------== Posted via Deja News, The Discussion Network ==----------
> http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
Hmmm....that's odd, you should be able to kill the engine with the
idle speed screw all the way out. The problem might be your
enrichener (choke). The cable has a 90deg. bent tube at the end where it
meets the black plastic cable nut that screws into the carb. This tube
should slide *into* the plastic nut. Mine didn't because the tube was too
large and I had to drill (by hand) the plasic nut with a 1/4" drill bit.
This could be your problem: the enrichener is partially on.
Check it out.
Mark H.
Mark Howell
Something else: if you shoved your origional enrichener cable, needle and all,
into the mikuni,the CV needle is smaller in diameter than the mikuni's. This
will pass some gas even though the enrichener is fully closed. Use the
enrichener needle that came with the carb.
Mark H.
d...@my-dejanews.com
Thanks again Mark, I will definitely check that it closes. Following the
instructions packaged with the carb, I used the Mikuni enrichener needle and
spring, but re-used the stock cable _including_ the stock plastic nut. It felt
like the cable went slack when the knob was pushed all the way in. Like you
said, I now need to check that the 90 degree arm fits all the way into the
plastic nut, but I bet you modified the Mikuni's plastic nut instead of
re-using the stock one. Since I can't actually see the cable anywhere after
everything is reassembled, it's hard to know for sure that the valve is
seating. I did notice however that pulling it out required about 1/8" before I
saw a noticeable change in the idling engine. You obviously have lots of
experience dealing with this carb. and I'm grateful for your thoughts.
Cheers!