Boiling bowls

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Boiling bowls

Triumph Trophy mailing list
My last bike had a V-twin engine, and it had aluminum shielding between the cylinders and the carburetors.  this shielding appeared to be there to keep the carbs from getting too much heat off of the engine.  My trophy doesn't have any shielding for the carbs.
I mention this because I have seen an pattern of behavior in my bike.  I mentioned this in a previous thread, but here's a thread specifically on this subject.
Back when I was playing around with different fuel line routings and easily removable fuel filters, I noted that there were frequent air bubbles percolating through my fuel lines, particularly the extra-long one that I had routed to feed carbs 1 & 2.  This line passed between the carbs and the cylinder head, before looping back up around carb 1, through a fuel filter, and then into the H.  I had re-routed the H to flow in from the side instead of from above in order to make all of this work.  I noted pretty quickly that I could frequently see gas bubbles percolating up through my fuel filter, and I assumed that some fuel was boiling in my fuel lines on the way to the carbs.
At the same time I replaced my original Gill coils with PVL coils, I re-routed the fuel lines to stock (rear outlet of fuel tap passes under the fuel tap and proceeds to carbs 1 & 2, side outlet of the fuel tap proceeds around the back of the spine and around to carbs 3 & 4, both fuel lines are the same length), and removed the extra fuel filters because the extra line length.  My goal was to eliminate what might have been a fuel starvation issue (but was likely caused by the failing coils).
Fast-forward to today...  

I've noticed over time that my bike starts much faster if:- The last time I started it, I didn't warm it up fully.- The last time I started it, I ran the engine for at least 10 seconds at 1000rpm.- This is independent of whether or not I engage the enrichment circuit, but of course, the enrichment circuit is needed for cold-weather starting.
I interpret this to mean that the gas in the carburetor bowls is somehow either low at the time I attempt to start the bike, or it's gone bad in some way.  When I say gone bad, this could mean that the gas simply isn't the correct density, as-if the lighter components of the gasoline have evaporated out of the carb bowls while the bike was sitting, and the remaining gasoline doesn't atomize properly in the carbs.
I have noted that there is some gasoline in my carb bowls when I drain them a few days after the a longer ride, so I don't think that all of the gas is boiling out, but it's possible that there is still some change.
Hitting the starter button would then do one of two things.1. It would draw (possibly overly dense) gasoline from the (possibly empty or low) carburetor bowls, causing weak starting performance.2. It would send some initial vacuum pulses to the fuel tap, dumping some fresh gasoline into the carb bowls, eventually resulting in a start.
It sure feels this way.
My bike has new PVL coils and Johnson Jolt, so I'm going to state that the voltage to my coils shouldn't be an issue.  My battery is also strong.
I'm implementing a further test of this potential issue.  I set up a fan in my garage next to my bike to blow fresh air across the carbs after I stop the engine.  If the fuel in the carbs is boiling out, this extra air should cool them down quickly and keep them cool.  I would expect the engine to start more quickly, just like it does if I had started and stopped it while still cool several hours or days before starting it to ride.
This could be a red herring.  There could be other issues that cause my bike to not kick right off, but I wouldn't expect for them to depend so much on whether I ensured that there was fresh fuel in the carbs after the last time I ran it.
So, my questions: - Is my bike missing a heat shield that should go between the carbs and the engine?  - Has anyone else seen similar behavior?
I've started toying with the idea of adding insulation between the engine and carbs. Any thoughts?
- Dave
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Re: Boiling bowls

Triumph Trophy mailing list
Well I agree with the need of heat shielding. But mainly due to exposure at
the vacuum takeoffs and the coils. The vacuum ports o-rings and rubber caps
do prematurely breakdown. These I've taken to wraping in reflective
aluminum tape. Which has helped extend the rubber lifespan. And the coils,
especially being located at the top of the area. Are exposed to too high of
a heat load. Not to mention all of this heat finally boiling out directly
upon ones jewels. All of which rapidly becomes a critical issue in hot high
humidity climates at slow speeds. I now do whatever is necessary to avoid
traffic jams. And if encountered take to the shoulders to clear out. As for
boiling petro etc. I did notice an occasional bubble. But at the moment
suffer none of the potential related issues. So I've chosen to leave well
enough alone. At least except for the coils. Last time I replaced them they
got wrapped in fiberglass tape and  sealed with glyptal. Which I hope will
slow down the heat soak.

Best,
Samuel


My last bike had a V-twin engine, and it had aluminum shielding between the
cylinders and the carburetors.  this shielding appeared to be there to keep
the carbs from getting too much heat off of the engine.  My trophy doesn't
have any shielding for the carbs.

I mention this because I have seen an pattern of behavior in my bike.  I
mentioned this in a previous thread, but here's a thread specifically on
this subject.

Back when I was playing around with different fuel line routings and easily
removable fuel filters, I noted that there were frequent air bubbles
percolating through my fuel lines, particularly the extra-long one that I
had routed to feed carbs 1 & 2.  This line passed between the carbs and the
cylinder head, before looping back up around carb 1, through a fuel filter,
and then into the H.  I had re-routed the H to flow in from the side
instead of from above in order to make all of this work.  I noted pretty
quickly that I could frequently see gas bubbles percolating up through my
fuel filter, and I assumed that some fuel was boiling in my fuel lines on
the way to the carbs.

At the same time I replaced my original Gill coils with PVL coils, I
re-routed the fuel lines to stock (rear outlet of fuel tap passes under the
fuel tap and proceeds to carbs 1 & 2, side outlet of the fuel tap proceeds
around the back of the spine and around to carbs 3 & 4, both fuel lines are
the same length), and removed the extra fuel filters because the extra line
length.  My goal was to eliminate what might have been a fuel starvation
issue (but was likely caused by the failing coils).

Fast-forward to today...

I've noticed over time that my bike starts much faster if:
- The last time I started it, I didn't warm it up fully.
- The last time I started it, I ran the engine for at least 10 seconds at
1000rpm.
- This is independent of whether or not I engage the enrichment circuit,
but of course, the enrichment circuit is needed for cold-weather starting.

I interpret this to mean that the gas in the carburetor bowls is somehow
either low at the time I attempt to start the bike, or it's gone bad in
some way.  When I say gone bad, this could mean that the gas simply isn't
the correct density, as-if the lighter components of the gasoline have
evaporated out of the carb bowls while the bike was sitting, and the
remaining gasoline doesn't atomize properly in the carbs.

I have noted that there is some gasoline in my carb bowls when I drain them
a few days after the a longer ride, so I don't think that all of the gas is
boiling out, but it's possible that there is still some change.

Hitting the starter button would then do one of two things.
1. It would draw (possibly overly dense) gasoline from the (possibly empty
or low) carburetor bowls, causing weak starting performance.
2. It would send some initial vacuum pulses to the fuel tap, dumping some
fresh gasoline into the carb bowls, eventually resulting in a start.

It sure feels this way.

My bike has new PVL coils and Johnson Jolt, so I'm going to state that the
voltage to my coils shouldn't be an issue.  My battery is also strong.

I'm implementing a further test of this potential issue.  I set up a fan in
my garage next to my bike to blow fresh air across the carbs after I stop
the engine.  If the fuel in the carbs is boiling out, this extra air should
cool them down quickly and keep them cool.  I would expect the engine to
start more quickly, just like it does if I had started and stopped it while
still cool several hours or days before starting it to ride.

This could be a red herring.  There could be other issues that cause my
bike to not kick right off, but I wouldn't expect for them to depend so
much on whether I ensured that there was fresh fuel in the carbs after the
last time I ran it.

So, my questions:
- Is my bike missing a heat shield that should go between the carbs and the
engine?
- Has anyone else seen similar behavior?

I've started toying with the idea of adding insulation between the engine
and carbs. Any thoughts?

- Dave



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