ST1100 starving for fuel / Aux fuel pump

This is a follow-on to my earlier thread about my 1100 starving for fuel and the trouble I had diagnosing the problem.
The short story is that it was the fuel filter and since replacing the filter (OEM) (with another OEM part) I haven?t had another problem in over 1000 miles.

The longer story is kind of interesting:
I didn?t think that it could be the fuel filter because the problem was intermittent. Also I had changed the original filter at about 100,000 miles and the replacement filter (OEM Part) ?only? had about 25,000 miles on it when I started having problems.
I also didn?t think that it could be the vacuum cut-off because I had replaced the diaphragm about 5,000 miles ago (and the problem was intermittent!)

This first time it shut down on me it was 28 deg F and many folks thought that I had carb. Ice. I thought that I may have had a vacuum building up in the tank so I checked the vent line and disassembled and cleaned out the fuel cap.
The problem didn?t re-occur for 1000 miles and then it was on a warm day (no ice). I left the cap loose and continued to have trouble so it wasn?t a vent problem.

I could not reproduce the problem near home. The bike would only shut down after 20+ miles of high-speed freeway riding. I tried to make it run bad by doing lots of full-throttle runs to redline and while lugging but it ran great and never missed a beat.

The ride home in the tow truck after another freeway shut-down was the last straw, and of course, once we got home the bike ran great

By now I was sure that either the fuel pump or the fuel control relay was the problem.
I decided to ?instrument? the bike to help find the problem. I added a Cycle Max voltmeter wired across the fuel pump and a fuel pressure meter on the handlebars so that I could see if the pump had voltage and pressure the next time it stalled. I also removed the vacuum shutoff and installed an auxiliary fuel pump (Facet ?105) in place of the vacuum valve and wired up a switch that I could turn on when needed.

I jumped on the freeway and about 30 miles later the bike started to starve for fuel but the voltmeter and the fuel pressure looked normal! As soon as I turned on the Aux pump the bike smoothed out and ran great! I got the bike home, pulled the hose off of the filter, turned on the in-tank pump and fuel would barely trickle out. I turned on the Aux pump and had great fuel flow. I removed the filter and tried to blow through it and I could but I felt a little resistance. I cut the filter open and didn?t find any debris. But the paper was discolored. Maybe some type of varnish or ???
By the way, I usually run Arco fuel or whatever is handy (87 octane).

What I learned:
? Stock pump has low pressure but good volume. From testing my pump and reading about other 1100 pump problems it looks like our pumps are only good for about 1 psi of fuel pressure. They don?t do well with a restriction!
? Also tried applying a vacuum to the tank and the stock pump quit pumping immediately so make sure your vent line is open.
? The fuel control relay is more than just a dumb relay. It applies power for a second or 2 when the key is first turned on. Then it uses the ignition events (tach signal) from the ignition module to determine if the engine is running, if so it applies power to the pump.

I am going to leave the vacuum fuel cut-off valve off of the bike and leave the Aux pump on for a while. I was going to add a voltmeter to the bike to monitor the alternator output. so I may leave it connected to the fuel pump. It reads a little lower than battery voltage here but I can still tell that the alternator is charging. I?ll also remove the fuel pressure gauge and relocate the Aux pump switch.

Attached are a few pictures of my Aux pump, gauge and switches.

Rick

Did you replace fuel filter with a non OEM first and than changed it back?? Reason I ask is that I just replaced my fuel filter with a non OEM fuel. Wondering if that will make a difference or not?? Non OEM $3 ...OEM was $20 .. I went for non OEM. Has anyone else had that problem or should I just go out and buy an OEM fuel filter???

dmarrier said:

Did you replace fuel filter with a non OEM first and than changed it back?? Reason I ask is that I just replaced my fuel filter with a non OEM fuel. Wondering if that will make a difference or not?? Non OEM $3 ...OEM was $20 .. I went for non OEM. Has anyone else had that problem or should I just go out and buy an OEM fuel filter???

Click to expand...

All of the filters that I changed were OEM. However, someone posted to my old thread that they had a similar problem when they installed a non-OEM filter.

Rick

Yeah...that would be me. Used an Emgo and had immediate problems as Rick has described. I don't know if there is less flow in the Emgo than the OEM....at any rate, I went back to a new OEM and the problem disappeared right away.

Rick, thanks for sharing your experience. For warned is for armed. May have saved many of us aggravating problems down the road at a future time.
Regards, Vinn:ups1:y

Great report, Rick!! Thank you. Amazing bit of 'instrumenting' the bike to help diagnose the problem. Adding this one to my archives of ST wrenching lore. Bravo.

Regards, John

John, please arrange to add the article to the AOW on ST Riders.

John OoSTerhuis said:

Great report, Rick!! Thank you. Amazing bit of 'instrumenting' the bike to help diagnose the problem. Adding this one to my archives of ST wrenching lore. Bravo.

Regards, John

Click to expand...

John, thank you for the links that you provided to me earlier. Those helped motivate me to find the problem.
Are you going to post this to other sites or did you want me to do something?

Thanks again,
Rick

Rick, aren't you registered over on ST-Riders? Just cross poST there, always best to hear it straight from the horse's mouth. If not, I can just post a link to this thread. Dunno about the MY-MC folks, but I'm sure they'd be interested/appreciative of hearing this story.

John

I am happy to post over on my-mc, with full attribution to the author.

Rick,

I did that write-up that John sent you to and it sounds to me like your pump is sticking like mine was when the pump got warm. The method I found to free mine was to blow back through the pump backwards and then it would free up until the next time it got warm and seized up again. BTW, I don't think you can simply monitor the pressure gauge unless you have the gas cap off. We found the pressure was still adequate, even though the pump was runnuing, because there was built up pressure in the tank from the engine heating the fuel.

BTW, did you compare the flow rate to the ones I listed in the writeup? Was it as weak as mine (which still meets the Honda spec)?

STPaulK said:

Rick,

I did that write-up that John sent you to and it sounds to me like your pump is sticking like mine was when the pump got warm. The method I found to free mine was to blow back through the pump backwards and then it would free up until the next time it got warm and seized up again. BTW, I don't think you can simply monitor the pressure gauge unless you have the gas cap off. We found the pressure was still adequate, even though the pump was runnuing, because there was built up pressure in the tank from the engine heating the fuel.

BTW, did you compare the flow rate to the ones I listed in the writeup? Was it as weak as mine (which still meets the Honda spec)?

Click to expand...

My pump could be a little weak but I?m pretty sure the filter was the main problem for me.
After my last episode I tested the fuel flow again (with the bad filter) and found that the pump would flow about 1500-1800cc / min with the filter removed but I could only get about 100cc per minute with the filter installed. My fuel pressure gauge is installed between the pump and the filter and I saw about 1 psi on the gauge with the old filter in-line but the output disconnected from the carbs and just flowing into a container. When I installed a new filter, the pressure fell to 0 psi and lots of flow.
I did most of my testing with the fuel cap loose and you are right that the pressure increases a lot with a warm engine/fuel on a warm day with the cap in place.
I?ve got about 2,000 miles on the new filter with no further problems so far but I am leaving the Aux pump on for a little longer just in case

BTW, thanks for your original write-up it was lots of help and motivation in troubleshooting my problem.

Rick

saaz said:

I am happy to post over on my-mc, with full attribution to the author.

Click to expand...

I'm not worried about getting credit, just want to help others if I can so please post the thread if you'd like to. I don't spend much time on sites other than this one because I don't have much free time.

Thanks,
Rick