Vapor lock or fuel pump problem?

Uncle Phil · Jun 30, 2015

AFAIK, it's purpose in life is cut the fuel flow off after the engine stops. Some think it is critical, some don't. I've run my ST1100s (all three of them) for 100,000+ miles and they have not caught on fire, engine blowed up, or my hair turned purple so far ...

Eagle59 · Jun 30, 2015

You will get many responses on whether to keep it or remove it. It's purpose is to prevent fuel from getting pumped to the carbs in the event of an accident. The scenario being an accident causes the engine to stop running but the ignition is still on, the power to the fuel pump is also still on. Since the engine is not running there is no vacuum. The valve shuts off fuel flow to the carbs. The idea is that this prevents fuel from being pumped out of potentially damaged lines.
This is a safety device but, as you have seen, another point of failure. Murphy strikes again. I have it removed from my ST as do many here. I'm also running an after-market fuel filter and do the Star-Tron treatments. There are also many on the site that hold to your thoughts on the engineer's intent. There are rebuild kits available for the cut-off if you wish to fix and replace. I'm sure others will share their opinions. The final decision is yours.

Mark · Jun 30, 2015

Many of us throw it out after it fails, many of us rebuild it and put it back inline.

If you feel better putting it back inline after a rebuild you can ride the bike until you've rebuilt it.

DonMac · Jun 30, 2015

Took mine off 4 years ago and it's gathering dust in my toolbox.

bikerdrumr · Jul 1, 2015

If that's the case, then it seems as though that when it's actually doing it's job, I'll have plenty of other problems to worry about :hurt1:

....or nothing to worry about for all of eternity. :angdev1:

I think I might keep it off. That way with the weight savings the ST will be the lean, mean and svelte racing machine it was meant to be. :rofl1:

Sorry, I went a bit crazy with the smileys.

Mark · Jul 1, 2015

bikerdrumr said:
with the weight savings the ST

Yeah because it ways so much!!!
I like one of the comments I have seen about these bikes paraphrased:
If you really want to increase the performance of the ST1x00 lose 20 lbs...

Uncle Phil · Jul 1, 2015

Mark said:
Yeah because it ways so much!!!
I like one of the comments I have seen about these bikes paraphrased:
If you really want to increase the performance of the ST1x00 lose 20 lbs...

Now Mark, you've quit preaching and gone to meddling ....

Mark · Jul 1, 2015

Uncle Phil said:
Now Mark, you've quit preaching and gone to meddling ....

Too bad I don't know the difference between 'ways' and 'weighs' though...

And *I* wasn't pointing any fingers!

Uncle Phil · Jul 1, 2015

Mark said:
Too bad I don't know the difference between 'ways' and 'weighs' though...

Well at least they 'sound' the same .... ;-)

bdalameda · Jul 1, 2015

The vacuum fuel cutoff is basically a safety feature and not necessary to operation. Honda designed it to cutoff the fuel supply to the carbs if the bike was dropped - When the engine dies the fuel cannot keep flowing (or overflowing) to the carbs and reduce the chance of fires. Many cars have a similar system.

Dan

davehirst · Jul 1, 2015

Mine went out on a 3 day ride, the first day. Out in the middle of nowhere, I called a tow truck, and had it towed to a stealer. They replaced it and lightened my wallet about $300.00. Never did they suggest bypassing it, I imagine for their liability. Had I checked on this website, I would have saved some moola. Oh well, live and learn. (I now carry a fuel pump just in case that's the next thing to go)

hotrod1 · Jul 8, 2015

I just bought a 94' 1100 abs/tcs. Serviced the entire bike, tires, fluids, etc, carb removal and cleaned, new carb boots, synched carbs, rebuilt vacuum fuel valve. On a small ride the bike quit. I bypassed the fuel valve on the side of the road and everything was back to normal. Took the bike on a thousand mile trip 2 weeks ago, bike dies at 600 miles. I pulled the seat to check for fuel flow, fiddled with the fuel pump wires and it started right up and took me home. No problems for about 500 more miles. Now, returning from a store my bike quit on me again after feeling like fuel loss issue. I started it up and it took me one mile, I could not restart. It would start for a second on full choke, run rough then die. I pushed it home as I was almost there. I am now getting ready to tear into it again and fix this and other issues. Any Ideas to the problem here???? Thanks........Rod

Al st1100 · Jul 8, 2015

Eagle59 said:
You will get many responses on whether to keep it or remove it. It's purpose is to prevent fuel from getting pumped to the carbs in the event of an accident. The scenario being an accident causes the engine to stop running but the ignition is still on, the power to the fuel pump is also still on. Since the engine is not running there is no vacuum. The valve shuts off fuel flow to the carbs. The idea is that this prevents fuel from being pumped out of potentially damaged lines.
This is a safety device but, as you have seen, another point of failure. Murphy strikes again. I have it removed from my ST as do many here. I'm also running an after-market fuel filter and do the Star-Tron treatments. There are also many on the site that hold to your thoughts on the engineer's intent. There are rebuild kits available for the cut-off if you wish to fix and replace. I'm sure others will share their opinions. The final decision is yours.

engine dies the fuel pump will not run. there is pressure in fuel tank that will push the fuel out of the tank // fuel tank is behind the engine and it gets warm, after a ride on a warm day take the fuel line off at the tank or before the shut valve and watch how much fuel come out(make sure key is off.) take the fuel shut valve apart, it's very simple and does not take hardly any vacuum to open it. As long as it is not leaking fuel into the vacuum line it's most likely good.

Al st1100 · Jul 8, 2015

put a fuel pump on and be done with it see https://www.st-owners.com/forums/showthread.php?61246-Mike-Martin-ST1100-Maint-Pages look at last 3 of 4 pages

Vapor lock or fuel pump problem?

Uncle Phil

Eagle59

Mark

Gotta make tracks

DonMac

My backyard

bikerdrumr

David

Mark

Gotta make tracks

Uncle Phil

Mark

Gotta make tracks

Uncle Phil

bdalameda

PaleoCyclist

davehirst

hotrod1

Al st1100

Al st1100