Fuel System Testing

Ok, need some advice. I picked up a 2002 ST1100 that had been sitting for a while. She wouldn't idle and needed the choke on all the time to run. Thought it was old gas/dirty carbs, so I ran several tanks of sea foam through her with only marginal improvement. Checked the plugs and found that one was very fouled and traced the problem to the associated ignition wire. I replaced the wire and then, no spark to any of the plugs.... Went through the troubleshooting diagram in the service manual and everything was ok, so I replaced the ICM with a used module. Still no spark, but all the trouble shooting tests were still ok. Took everything apart, put in the original ICM, coils, and wires, and made sure all my connections were as tight as could be. Put her back together and now have spark to all plugs. But still no start.

With all this testing/replacing I've had the ignition coils pulled out several times and run the battery down trying to crank her over (so now I'm using jumper cables to make sure I've got good battery voltage).

And then it came to me. Even with all the cranking I'm not smelling fuel. She never has that flooded smell.

So, starting to think I've done something that has impacted the fuel system. The fuel pump still whines when I turn her on and she'll fill the fuel filter, so I'm thinking it's not the pump.

What next? There is no handy trouble shooting guide (measure this at this location, kind of thing) in the service manual.

Is there something obvious that could have become disconnected with all the times I've pulled the airbox and ignition coils?

Is there a way to test the vacuum system using basic tools in my parking lot?

Any help would be greatly appreciated.

Could be a vacuum leak somewhere (thus needing the choke on to keep running). I'd bypass the fuel cutoff valve in case that is the source of the vacuum leak first.

Check to see that the #3 carb intake vacuum port hose is connected to the auto fuel valve. If it is, bypass the auto fuel valve and plug the hose.

Edit: which plug was fouled?

John

Forgive my ignorance folks, but a lot of this is new to me.... Initially it was the #1 plug that was fouled. After much back and forth I narrowed it down to the plug wire, and after much more back and forth I got spark to all plugs.

During this process I had pulled the tank to try to get a better look at the carbs, had pulled off most of the plastic to try to get at the ignition coils, and had pulled the plug wires and coils out a number of times. It was when I finally got spark to all the plugs that it wouldn't start and I started looking at the fuel system (before I only had one plug fouled and she would start and run on choke)

Today I went back trying to find where I had probably disturbed a vacuum line, but I didn't pull the tank to get at the underside of the carbs. What I did verify was the fuel pump pumps gas to the input of the fuel valve through the fuel filter, and that at the fuel tube joint assembly I had good gas flow when cranking the engine.

I could not find an obvious vacuum hose that was disconnected, but I didn't get under the carbs. And I'm not sure how to identify the #3 carb intake vacuum hose... Thee is not a good diagram in the service manual.

And, verified again today. After sitting for a while (a week this time) apparently enough gas gets into the float bowls that she tries to fire up at first but then asfter just a few seconds goes back to acting like she is fuel starved.

... I'd bypass the fuel cutoff valve in case that is the source of the vacuum leak first.

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Did you try this?

The vacuum powered fuel valve is hanging on the air filter by the fuel filter. Disconnect the hoses and reconnect them coming from the tank to the filter. No extra parts are needed. Plug the vac. line with one of the screws holding the valve bracket to the air filter. Try to start and run the motor. You can keep the vacuum valve bypassed or hook it back up at your discretion. This is a quick simple test to check the fuel valve. A diaphragm inside it gets ruptured and it doesn't work correctly.

If needs the choke on all the time to run, your idle jets are clogged up. Pretty simple to fix other than the work. Pull the carbs, flip them over, remove the bowls carefully to preserve the gaskets. You'll see the jets so you either replace them or gently clean them out.

Not sure if I'm being clear. She does not run with the choke on now. After she sits for a while (a day?) she will fire for a few seconds, and then nothing. Like she is getting no fuel.

This weekend I disconnected the fuel line on the carb side of the fuel valve and verified she would pump fuel while cranking.

Today I bypassed the fuel valve, with the same result; she fired for a few seconds and then nothing.

Unfortunately I don't have garage space so I am working in my parking lot. I don't really want to pull the carbs, but if that is the only way to check the vacuum lines I will....

what say you all? Is there something else I can do before pulling the carbs?

Interesting. You have convinced me it's not the fuel pump. And having bypassed the pet cock, you've eliminated the next probable issue.

So...Have you disconnected the fuel line at the carb connection point and cranked over the engine...to ensure gas is getting from the fuel filter, down the hose to the carb? Trust you don't have a blockage in that part of the hose.

If you are getting gas to the carbs, but little to no gas getting in the carb(s), then it's a carb(s) issue.

It appears you have a service manual. Try something different... Drain the float bowls (as per service manual) into container which will be placed under the bike. There should be around 1-1 1/2 US cup of gas, if the float bowls are filled properly. Leave the fuel shut down valve by-passed and the container under the bike. While the float bowl drain screws are open, cycle the key multiple times to see if you have proper flow going THROUGH the carbs. Keep an eye on the container and drain hose for flow. This will determine if the float needles and seats are ok. It will also show if the bowls have trash in them....

Adam has a good suggestion and I'd like to add a bit to it. Someone, Rich??, had a fuel pump that would pump; but, not at the proper rate.
Easy to test while you're playing with the gas lines anyway because you can measure what you get in the 'through the carb' test of Adam's.

I don't know if that would work Mark. I've never tried measuring fuel flow capacity that way. He would have to by-pass the fuel cut relay then check fuel flow capacity per minute as outlined in manual. However, going "through" the carbs would more than likely give false specified readings. The Honda way, measures capacity per minute using an open container.

Looking at capacity per minute going "through" the carbs has many restrictions. Such as, starting flow going through a 3/8" fuel hose, then through 4 float needles and seats, through 4 float bowls, then through 1/8" float bowl drain tube nipples, then exiting the bike through a single 3/16" drain hose. Not a bad idea, but I'm thinking too many restrictive variables to get an accurate reading. I just want to give him a quick easy way to see if fuel is getting up into the float bowls, before tearing STuff apart.

We haven't heard from the OP in a couple of day's. Maybe this is fixed?

I hadn't thought my suggestion through... I agree fuel pressure is meant to push through restrictions; so, measuring at the 'end of the trail' would not let you know if the pump has sufficient output.

If I were the OP I'd test by measuring the flow though because we have seen bad fuel pumps which make it look like a carb issue/s

Still hefe and still not fixed. Just waiting for the weekend to start testing again... What I think im going to do is press the starter to see if she turns over a few times. Then drain the float bowls just to see if fuel is being pumped into them. Then check the flow rate based on the manual. And then maybe I'll have some more data points to work from.

What bothers me is the initial problem was faint spark at the #1 plug. Who h after all my messing with it turned into no spark at any plug. Then spark finally at all plugs, but wont run more than a few seconds, and then only once between days of rest.

Either I have had multiple problems or I have created my problems through taking apart and putting back together. And I'd be willing g to bet it is something I did by mistake.

I would 'verify' the spark (which should be pretty easy - short the plug out against the head or get an inline spark tester), eliminate that then move on to the fuel 'debugging'. Remove as many 'moving parts' out of the fuel system to make sure you are getting fuel (cutoff valve, filter, wire directly to the pump eliminating the relay). If you can pick one up cheap, I'd get an external electric pump just to see if the bike will run with consistent fuel pump pressure. They will suck gas up through the existing pump. Then go back and add a piece at a time until you find the failure. Good Luck!

Uncle Phil said:

I would 'verify' the spark (which should be pretty easy - short the plug out against the head or get an inline spark tester), eliminate that then move on to the fuel 'debugging'. Remove as many 'moving parts' out of the fuel system to make sure you are getting fuel (cutoff valve, filter, wire directly to the pump eliminating the relay). If you can pick one up cheap, I'd get an external electric pump just to see if the bike will run with consistent fuel pump pressure. They will suck gas up through the existing pump. Then go back and add a piece at a time until you find the failure. Good Luck!

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A BIG +1 to Uncle Phil .. Logical troubleshooting beats "By Gosh & By Golly" and " My cousin said ( fill in the blank ) "

Another Good Luck from me, too. Do some logical troubleshooting and you will be satisfied with the result !!

I'm all for the logical approach.... Verify spark. Verify fuel is getting to the carbs.

Here's where lack of a mechanical background fails me. I have spark as tested by grounding a spare plug to the head for each pug wire. That doesn't tell me the quality of the spark, but it tells me I have spark at all four cylinders.

I verified I had fuel to the carbs by disconnecting the fuel tube at the fuel tube joint and then cranking her to see fuel pulse into a bowl. Just in case I bypassed the fuel valve anyway and as directed plugged the #3 vacuum hose.

I also verified I had fuel in the float bowls by draining them.

So, if I have spark at each plug and fuel in the float bowls, shouldn't she at least try to crank? Yesterday she didn't even try to fire.

What gets me is the bike was running (on 3 cylinders) before I took her apart to chase the ignition problem. And now that the ignition problem appears to be fixed she is not running at all.

Q1: if there is a vacuum problem will the float bowl fill but fuel not be drawn through the carb?

Q2: If there is a vacuum problem is there a logical place I disturbed it by removing the ignition coils, airbox, or fuel tank?

Q3: Is it logical to think the carbs were performing reasonably well, with at least 3 tanks of fresh gas with sea foam run through them before pulling her apart to diagnose the ignition problem, and now they have become so clogged she won't fire at all?

Q4: If it was something like an very rich fuel mixture wouldn't it smell like she is flooded and when I pulled the plugs wouldn't they be pretty fouled (now they are clean when i pull them with only a little fuel moisture/smell)?

Sorry for all the questions, but I'm not working on a poorly running bike, I'm working on one that is not running at all. So the only feedback she gives me when I test something is that she still doesn't fire.

Try replacing the fuel with fresh gas.

Got any starting fluid? Pull the air cleaner cover and give her a good squirt and give her a spin. If it fires consistently while you 'squirt' you can focus on the fuel issue. I have had Sea Foam kill a set of spark plugs where they would barely fire. Starting fluid will ignite pretty much if there is any spark at all. As I said earlier, if you get an electric fuel pump and hook it straight without the filter, you can eliminate the fuel pump either yes or no. You could have multiple issues so you have to eliminate as many pieces of the puzzle as you can to get down to business. Vacuum issues generally will make them run rough but not stop them from running. With the electric fuel pump, you have eliminated the vacuum from the fuel tank to the fuel bowls.

odd that you should suggest that, because that is exactly what I did this morning (thinking to rule out spark or fuel, and maybe diagnose a leaking vacuum hose).

Squirted starter fluid around the hoses with the airbox buttoned up, and as soon as the vapor made it's way intothe back intake vent she fired right up. And continued to run.... with no choke. And she idled.... And I turned her off and went away for a couple hours, and she started right up when I came back.

While this is not the result I was expecting, I'm pretty happy to have something in the plus column.... Going to button her up this evening and take her for a little ride if I can. I can't imagine the problem is fixed, unless something was bound up and getting the started and running was what it took to clear it (some sort of super vapor lock?)

Now what do you all think?

Hmm, sounds like the old fuel pump issue where it works, then it quits, then it works, then it quits ... I carry an external fuel pump 'kit' with me on long trips already wired and with hose clamps just in case (I've had two pump failures - two different ST1100s while on the road). Just glad it's running for you now. Sounds like an electrical issue of some sort because of the intermittent failure that 'healed' itself.