Rough starting and running, gasoline smell

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Rough starting and running, gasoline smell

David Webb
I fixed an issue the weekend before last and wanted to share with the group..
My bike was hard to start, hiccuped at idle, smelled like raw gas, and had weak bottom-end power.  It was also getting 33mpg, which is lower than normal.
I had recently purchased a temperature gun online, so when I had time to take a look, I started the engine and pointed the gun at each header, one at a time.
Cylinder 1 was 400+F after a minute of runningCylinder 2 was 400+F after a minute of runningCylinder 3 was 400+F after a minute of runningCylinder 4 was 84F after a minute of running
I think I had a cylinder that wasn't firing at all at idle.
I twisted the grip and all 4 cylinders went up to 500+F.
Normally, I would check compression, then ignition, then carburetion.  In the case of a Trophy, checking compression and ignition involves removing the rear rack, bodywork, and tank, so I went straight for carburetion.
First, I drained all 4 carbs and refilled them using the PRI setting on the fuel tap.  I did this to flush out anything small that might have gotten stuck in the needles and seats, then I started the bike and checked header temperatures with similar results.

5 years ago, I had disassembled and thoroughly cleaned my carburetors, and I took the opportunity to replace the bowl and cap JIS screws with allen bolts.  This has been a good thing for me several times since then.
Since it was the #4 carb, I took an allen wrench that I'd modified and removed the bowl for cleaning.  It had a small amount of fine (not rusty) gunk in the bottom, but nothing that I would be worried about.  After a light scrubbing with a swab, it was cleaned up and ready to reinstall.  I also popped off the float assembly and disassembled it to check the needle and seat.  No issues there either, so everything back together and start the bike - same results, #4 wasn't firing at idle.
Next stop was to look at the top of the carb.  If I needed to take the top off, I'd need to remove the bodywork and tank, but a quick visual inspection might help matters....
With the bike still running I looked at the top of carb #4 and started hearing "psst... psst..." coming from that direction.  A quick probe with my finger found a leak and suddenly, the bike was idling on all four.
The cause of the leak: The vacuum cap on #4 had fallen off.  A previous owner had at some point, but didn't use the right size, so they used a larger one and cinched it with a zip-tie.  It had previously fallen off of a middle carburetor and dropped on top of the transmission case, so when I investigated and found it, I moved the offending cap to the #4 carb where I could easily access it if the cap decided to jump again.  I then promptly forgot about it until I discovered it missing again.
Two trips to the auto parts store later, I had the right size cap to fit snugly on carb 4 and a set of spares in my pannier along with my service tools.
- Dave2002 Trophy 1200 Merlot RedPinellas, FL

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Re: Rough starting and running, gasoline smell

Samuel Crider
Hi Dave,

Good work!! Those vacuum port caps and the little o-rings under them endure
lots of heat being so close to the head. The last time around I wrapped the
rubber caps in aluminum tape. And so far they seem to be lasting longer
this go around.

Glad to hear your back ripping and running.

Samuel
NOLA

On Wed, Mar 6, 2019, 10:07 AM David Webb [hidden email]
[TriumphTrophy] <[hidden email]> wrote:

>
>
> I fixed an issue the weekend before last and wanted to share with the
> group.
>
> My bike was hard to start, hiccuped at idle, smelled like raw gas, and had
> weak bottom-end power.  It was also getting 33mpg, which is lower than
> normal.
>
> I had recently purchased a temperature gun online, so when I had time to
> take a look, I started the engine and pointed the gun at each header, one
> at a time.
>
> Cylinder 1 was 400+F after a minute of running
> Cylinder 2 was 400+F after a minute of running
> Cylinder 3 was 400+F after a minute of running
> Cylinder 4 was 84F after a minute of running
>
> I think I had a cylinder that wasn't firing at all at idle.
>
> I twisted the grip and all 4 cylinders went up to 500+F.
>
> Normally, I would check compression, then ignition, then carburetion.  In
> the case of a Trophy, checking compression and ignition involves removing
> the rear rack, bodywork, and tank, so I went straight for carburetion.
>
> First, I drained all 4 carbs and refilled them using the PRI setting on
> the fuel tap.  I did this to flush out anything small that might have
> gotten stuck in the needles and seats, then I started the bike and checked
> header temperatures with similar results.
>
> 5 years ago, I had disassembled and thoroughly cleaned my carburetors, and
> I took the opportunity to replace the bowl and cap JIS screws with allen
> bolts.  This has been a good thing for me several times since then.
>
> Since it was the #4 carb, I took an allen wrench that I'd modified and
> removed the bowl for cleaning.  It had a small amount of fine (not rusty)
> gunk in the bottom, but nothing that I would be worried about.  After a
> light scrubbing with a swab, it was cleaned up and ready to reinstall.  I
> also popped off the float assembly and disassembled it to check the needle
> and seat.  No issues there either, so everything back together and start
> the bike - same results, #4 wasn't firing at idle.
>
> Next stop was to look at the top of the carb.  If I needed to take the top
> off, I'd need to remove the bodywork and tank, but a quick visual
> inspection might help matters....
>
> With the bike still running I looked at the top of carb #4 and started
> hearing "psst... psst..." coming from that direction.  A quick probe with
> my finger found a leak and suddenly, the bike was idling on all four.
>
> The cause of the leak: The vacuum cap on #4 had fallen off.  A previous
> owner had at some point, but didn't use the right size, so they used a
> larger one and cinched it with a zip-tie.  It had previously fallen off of
> a middle carburetor and dropped on top of the transmission case, so when I
> investigated and found it, I moved the offending cap to the #4 carb where I
> could easily access it if the cap decided to jump again.  I then promptly
> forgot about it until I discovered it missing again.
>
> Two trips to the auto parts store later, I had the right size cap to fit
> snugly on carb 4 and a set of spares in my pannier along with my service
> tools.
>
> - Dave
> 2002 Trophy 1200 Merlot Red
> Pinellas, FL
>
>
>
>
>