94 ST1100 Fuel Pump Issue

[secretoctopus]

Hello all,

Picked up a free 1994 ST1100 with all the plastics and title because the guy was tired of dealing with trying to work on it. I figured for the cost of $0 I could give it a shot.

Came with a note about the issues he was running into and one seemed interesting so I thought I would ask here. Basically according to the note the fuel pump will prime normally when the key is turned to on, but then it says that the fuel pump electrical must be disconnected for the bike to start and it will run until the carb bowls empty. So if the fuel pump will prime it sounds like it works, so maybe the fuel pump relay is the issue? Once the pump stops priming after 3 seconds and is shut off it is then supposed to kick back on when the engine is running, but doesn’t? Also seems weird that it cannot stay plugged in or it will kill the bike. I would just try a new relay but it has to be Honda OEM apparently and they are not cheap as a maybe fix.

I still need to dig into it myself but I thought maybe this was a somewhat common ST issue that others might be aware of. TIA.

 

[Erdoc48]

I can’t comment on the fuel pump vs relay as I don’t know, but very nice score on a free bike- if you do get it running, then you have a nice runner. I’m not sure but as my 94 looked the same (black with gold wheels), I wonder if it’s an ABS1 version. If it is and you’re having issues with the ABS system, the parts are no longer available- with mine, I just disconnected the ABS via pulling the fuses and ABS/TCS dash lights and made it a non ABS bike (and runs fine as such). I could never get it to work properly.

 

[Willsmotorcycle]

Nice score, great that it came with kids too, that won't be cheap. Watch out for the one in front, I can tell from here that ones a handful.

A little patience, smart fellas will be along shortly to help you get it sorted.

Welcome to the forum!

 

[secretoctopus]

I can’t comment on the fuel pump vs relay as I don’t know, but very nice score on a free bike- if you do get it running, then you have a nice runner. I’m not sure but as my 94 looked the same (black with gold wheels), I wonder if it’s an ABS1 version. If it is and you’re having issues with the ABS system, the parts are no longer available- with mine, I just disconnected the ABS via pulling the fuses and ABS/TCS dash lights and made it a non ABS bike (and runs fine as such). I could never get it to work properly.

Thanks for your reply. I am not sure what ABS version this is yet, I need to do some digging still to find out. I don't have ABS on my other bike so maybe I wouldn't miss it if it's not working correctly.

 

[secretoctopus]

Nice score, great that it came with kids too, that won't be cheap. Watch out for the one in front, I can tell from here that ones a handful.

A little patience, smart fellas will be along shortly to help you get it sorted.

Welcome to the forum!

Haha, she did get right in front and twist the throttle immediately. The bike will for sure cost less than the kids do.

I am looking forward to the advice from everyone here, seems like a great group of people!

 

[Erdoc48]

It’s an ABS 1 version as all 94’s were at the time- ABSII didn’t come out until much later (I think 97 or so). It great if you can get it sorted out but the bike will be no less rideable (I’m a fair weather rider and even in some rain, I’ve never had an issue- just take it easy and all is well). There’s a huge degree of information here, so search and all will be known. Plus, it’s a pretty easy to maintain and very reliable bike.

 

[Uncle Phil]

ABSII in 96. Run a fused wire directly to the hot terminal on the fuel pump (the one with the larger white connector) and see if the bike runs.
That eliminates the fuel relay.
If the pump does not work with that, probably a flaky fuel pump - which can be replaced with an aftermarket one.

Article [11] - ST1100 - Fuel Pump Replacement | ST1100 Articles

Well since I have four of these pretties and the chances of a fuel pump failing goes up as the mileage increases (already had 3 stockers fail), I decided I'd see what was available at a reasonable price with the ability to replace the stocker and leave everything as is. This is the link -...

www.st-owners.com

 

[secretoctopus]

ABSII in 96. Run a fused wire directly to the hot terminal on the fuel pump (the one with the larger white connector) and see if the bike runs.
That eliminates the fuel relay.
If the pump does not work with that, probably a flaky fuel pump - which can be replaced with an aftermarket one.

Article [11] - ST1100 - Fuel Pump Replacement | ST1100 Articles

Well since I have four of these pretties and the chances of a fuel pump failing goes up as the mileage increases (already had 3 stockers fail), I decided I'd see what was available at a reasonable price with the ability to replace the stocker and leave everything as is. This is the link -...

www.st-owners.com

Thank you regarding ABS model years, I did realize that later in the day as I was doing more research.

So, bit of an update, the next day after posting this I had some time to check out the bike a little more. The fuel pump will turn on with the key and fill the carb bowls, just like the previous owner wrote on the note. I was able to get the bike to start with the fuel in the carbs, but of course it only ran for a few seconds until the bowls emptied. I did this a few times, but if I twist the throttle at all, the bike immediately dies. Also confirmed that if I fill the carbs and start the bike, no fuel is pumping to keep the engine running.

So, it would seem that the fuel pump works, at least enough to fill the bowls, but something kills the engine if the throttle is twisted. Any ideas with this information??

It’s an ABS 1 version as all 94’s were at the time- ABSII didn’t come out until much later (I think 97 or so). It great if you can get it sorted out but the bike will be no less rideable (I’m a fair weather rider and even in some rain, I’ve never had an issue- just take it easy and all is well). There’s a huge degree of information here, so search and all will be known. Plus, it’s a pretty easy to maintain and very reliable bike.

Appreciate it. I am not too concerned with having ABS either so hopefully things are in working order once I get it running.

ABSII in 96. Run a fused wire directly to the hot terminal on the fuel pump (the one with the larger white connector) and see if the bike runs.
That eliminates the fuel relay.
If the pump does not work with that, probably a flaky fuel pump - which can be replaced with an aftermarket one.

Article [11] - ST1100 - Fuel Pump Replacement | ST1100 Articles

Well since I have four of these pretties and the chances of a fuel pump failing goes up as the mileage increases (already had 3 stockers fail), I decided I'd see what was available at a reasonable price with the ability to replace the stocker and leave everything as is. This is the link -...

www.st-owners.com

I will also try running a fused line directly to the fuel pump when I have a chance to try to eliminate the fuel relay as the issue. I actually (allegedly) found the right fuel pump on eBay last week for $20 and it's being delivered today. Might not need it but it seemed like I couldn't get one shipped to CA from other sites so maybe it will be good to have it as a backup.

 

[Ron]

... I will also try running a fused line directly to the fuel pump when I have a chance to try to eliminate the fuel relay as the issue. ... I rode an 1100 (with a switched on wire) this way for about 6 months.

 

[secretoctopus]

I rode an 1100 (with a switched on wire) this way for about 6 months.

Nice, and you didn't experience any issues doing this? Did you end up fixing the issue after 6 months?

 

[secretoctopus]

Okay, trying to bump this original post as I still have the same issue.

Since posting this I have spent some time trying to get the bike to run. So far here is what I have done:

1. Removed the carbs, cleaned jets, cleaned bowls, installed new gaskets.
2. ATTEMPTED to bench synch carbs, hopefully got it close (Seemed better than when I started).
3. Installed a fused jumper wire directly to the fuel pump.

Now with the key in the On position the fuel pump will pump continuously. With the battery jumped, the key to On, the kill switch to Run, I was able hold down the starter button which cranked fine, and the bike fired up after a few seconds. I was able to rev the motor for a 15-20 seconds or more. After 20 seconds or so the bike died. I could crank it and crank it but got nothing. Eventually I assume the fuel pump flooded the carbs, but the bike never started up again.

This has been consistent so far with the other time I was able to start it. Start it up once, rev it for a few seconds, it dies and won't start again.

I seem to have bypassed the fuel relay by jumping with direct power, correct? Engine basics say air, fuel, and spark to run. Air and fuel seem to be good, possibly a spark issue? Should I look at plugs, or ignition coils/wires?

So, I just am at a loss for what the issue could possibly be at this point. Looking for some advice on what to try next. Thanks all.

 

[Uncle Phil]

Did you by any chance unhook the fuel line to make sure the pump was still pumping after it quit running?
Flaky fuel pumps can do some strange things - that would eliminate a bad fuel pump.

 

[Al st1100]

First of all, the pump can run all day and the carbs should not flood. If the carb bowls are full it will run for at least 10-15 seconds with no fuel pump working. Take a fuel line off and turn on the pump, there should be a steady flow into a suitable container. If this has been sitting a long time, fuel pump strainer could be clogged. fuel is crap. Or lines and fuel vacuum valve were filled with gunk and got into the needles of the carbs. Enrichment valve could be stuck. How are the diaphragms on top of the carbs? Is the fuel getting past the vacuum fuel valve? How can you assume it's flooded? Sounds to me is your not getting fuel. There is a lot that could be going on and it doesn't add up.

 

[secretoctopus]

Did you by any chance unhook the fuel line to make sure the pump was still pumping after it quit running?
Flaky fuel pumps can do some strange things - that would eliminate a bad fuel pump.

That is a great question, I need to do that the next time I dig into it. Once I put everything away last time I thought damn, I should have made SURE that the pump was still pumping. I will be doing that ASAP.

I also just bought 4 new spark plugs...possibility here with this issue or unnecessary to replace?

Also, another thing I meant to mention before, I have no idea how old the fuel is in the fuel tank. It is probably not THAT old as the guy I got it from was actively working on it, but still, it is old for sure. Should I dump it and add fresh or is that probably not contributing?

 

[secretoctopus]

First of all, the pump can run all day and the carbs should not flood. If the carb bowls are full it will run for at least 10-15 seconds with no fuel pump working. Take a fuel line off and turn on the pump, there should be a steady flow into a suitable container. If this has been sitting a long time, fuel pump strainer could be clogged. fuel is crap. Or lines and fuel vacuum valve were filled with gunk and got into the needles of the carbs. Enrichment valve could be stuck. How are the diaphragms on top of the carbs? There is a lot that could be going on and it doesn't add up.

I plan on popping the fuel line off at the filter and running the pump to see what happens. The filer itself looks clean. It has been sitting for a while as far as I know, but I believe it was being actively worked on somewhat recently.

After replacing the bowl gaskets and after the motor died I did end up with some fuel leaking from somewhere, but I couldn't quite see from where. Almost certainly from the carb bowls at least as far as I could see. This is why I thought the pump might have been filling the carbs up, but maybe not.

As far as the needles, vacuum lines, or diaphragms, I have not dug into those at all yet. Any one of those things could be a possibility it sounds like.

This was very helpful, thank you.

 

[Al st1100]

I plan on popping the fuel line off at the filter and running the pump to see what happens. The filer itself looks clean. It has been sitting for a while as far as I know, but I believe it was being actively worked on somewhat recently.

After replacing the bowl gaskets and after the motor died I did end up with some fuel leaking from somewhere, but I couldn't quite see from where. Almost certainly from the carb bowls at least as far as I could see. This is why I thought the pump might have been filling the carbs up, but maybe not.

As far as the needles, vacuum lines, or diaphragms, I have not dug into those at all yet. Any one of those things could be a possibility it sounds like.

This was very helpful, thank you.

That is the vacuum fuel shut valve if the small vacuum hose has any fuel in it just bypass that valve. When the it goes bad it can leak fuel into the intake causing flooded condition cutting out. Many just eliminate it. Pump running take the small hose off and see if fuel comes out, it's not suppose to.

 

[Ron]

Bypass the vac. fuel valve by connecting the green "X" hose to the fuel filter where the red "X" hose is connected. Plug the vacuum line. I use one of the screws that holds the valve bracket to the air filter housing. Inspect the vac. hose for splits or leaks as best you can. If the hose has a leak, it won't hold the vac. valve open.

I would drain the gas and replace with known "good" gas.

It's OK if the fuel pump runs all the time (when the bike is in use). That is how it operates normally. There is a by pass built into the system, inside the tank, for when the carbs are full.

 

[rwthomas1]

Isolate the fuel system from the engine for troubleshooting. I made, years ago, a fuel bottle with a petcock, that can gravity feed an engine. Buy/make one and feed fuel directly to the carbs. Run engine. If the engine will run reliably on a remote gravity tank then start adding the other components into the system. Keep a fire extinguisher handy if you do this....

 

[secretoctopus]

That is the vacuum fuel shut valve if the small vacuum hose has any fuel in it just bypass that valve. When the it goes bad it can leak fuel into the intake causing flooded condition cutting out. Many just eliminate it. Pump running take the small hose off and see if fuel comes out, it's not suppose to.

Oh, okay interesting, that is great info thank you. I will give it a shot.

 

[secretoctopus]

That is the vacuum fuel shut valve if the small vacuum hose has any fuel in it just bypass that valve. When the it goes bad it can leak fuel into the intake causing flooded condition cutting out. Many just eliminate it. Pump running take the small hose off and see if fuel comes out, it's not suppose to.

Okay I’m working on the bike today and I can confirm that I do not have this vacuum module at all. The fuel runs through the filter and right through to the left and to the carb bank as far as I can see right now. I haven’t taken off the air filter base yet to try to inspect further, but I thought it was weird that I don’t have whatever what vacuum module appears to be.