Stumble and die... Get running again then stumble backfire and die

[Mark]

So measure fuel into a pint jar for 45 seconds and it should be full.

My math is left to the most casual observer...

 

[sofawizard]

also worth a punt try checking the feed wires to the pump are sound at the pump I had 1 snap off recently when I had the pump out also check the feed wiring to the coils its connector in to the harness can be suspect its the white 3 pin plug taped into the loom bellow the left glove box pull it out the tape n give it a wiggle while the engines running may prove to be at fault im currently running down a poor running stumble around the 4k rpm ill let you know what I find in case it helps you

 

[IpswichST]

SO... sorry I have stalled fixing my problem... do some of you have the same problem I have? which is that I want to tinker and ride all the time but my better half doesnt share the same desire that I do? With burning season and cleaning the yard a priority, in order to keep the peace I have not pressed my luck by keeping my distance from the bike and resisting my desire to tear the plastic off and doing all the simple tests that others have suggested. Dont worry.. I will get there and will post my findings.

In the mean time I have continued to read and search possible causes to my stumble and die. One find was that there is a Sub Filter in front of the main air filter. When I took the air filter off I noticed that little filter and when I went to take it out it totally denigrated into my hands. Last night I purchased a filter for a lawn mower and trimmed it down to size. The original makeshift filter I put in possibly could have restricted air flow and caused some issues... maybe? Ill also look and make sure all the air connections are clean and tight.

Just wanted to throw that out there...

 

[sofawizard]

well I finally think I have it sorted my problem was an vacuum leak on the tap control line all sorted and seems good ill report back once ive had a chance of a test ride but static tests were perfect:bow1:

 

[IpswichST]

Control line? When I open mine up I'm gonna look all around. How did you find it? Run the engine then spray something to see if the engine reacted?

 

[sofawizard]

I took it off and found a split replaced with new section of tube n hey presto but as I say not road tested yet

 

[C901]

vacuum leak.........

 

[IpswichST]

Here is what I did today... just being curious.

I pulled the fuel pump to have a look see. I expected it to look a little different. Ill post a pic I took tomorrow. In the tank filter looked clean and good.

I replaced the pump and ran a flow test. Hmmm.. I jumped the pump straight from the battery and filled a measuring cup. I expected to fill 2 cups in 45 seconds but as my son was watching the stop watch he said that the measuring cup would overflow. Indeed, 2 cups filled up in 28 seconds. I ran the test from the service manual... ran the pump for 5 seconds and multiplied my result by 12. The result was about 1200ML? Ill check the actual measurement and report back. Bottom line is that it was more than enough. Is that bad?

Ok.. fuel tank and gas cap. I think that it is not venting properly. When I crack the cap I should expect some noticeable sucking ... right? but I think maybe it is too much.

Question.... When I pull that vent hose from the fuel cap and blow into it... shouldnt it breath pretty easily?

After I put it all back together I went for a nice ride. She ran nice.. no stumble....

OH.. and I replaced the subfilter.

 

[bdalameda]

A plugged subfilter or one that is severely restricted will cause big problems. Usually major hesitation but could cause stalling.

 

[bdalameda]

Just for giggles - pull off the LH side cover (over the battery) and take a look at the 4 pin connector plugged into the main relay. Unplug the connector and see if there are any signs of melting. This is a common failure point on the St1100 and worth taking a look at. If there are signs of overheating and melting this can easily be fixed befor it goes too far.

Dan

 

[IpswichST]

So frustrating... After last night's ride with no problems I went home a lunch to ride the bike back to work. Couldnt go 100 yards before the problem started. Here is what I did then...

I got it running again and went for a ride down the street (one mile). I kept the RPMs up and when the problem started I would REV it to power through the stumble. It would recover by wanting to take off and then TALKING off! This was all done at around 4,000 rpm.

Honest.. Im kinda ruling out a vacuum leak thinking it would happen all the time (Ill pull the air filter and spray some WD40 on the vacuum hoses to see what happens) . After reading other posts Im leaning maybe towards spark and coils? Something of that nature? Is there a way to test?

 

[sofawizard]

A plugged subfilter or one that is severely restricted will cause big problems. Usually major hesitation but could cause stalling.

and where would I find this sub filter thingy?

 

[bdalameda]

and where would I find this sub filter thingy?

The subfilter is located in the small rectangular housing just in front of you air filter housing. It has large hoses running up from both sides into it. It just snaps off to get to the filter.

Dan

 

[IpswichST]

Ok... Took it all apart again... Sprayed WD40 on the vacuum lines around the carbs.. No reaction by the carbs.

I also pulled and tugged on lines and found the line on the right rear carb to be loose. I replaced the hose and went for a ride. Ran fine. Could THAT be my problem? (I have a pic of the hose. Ill post later)

 

[FieSTa45]

Can someone tell us what the sub filter is needed for? It looks like a evap
line or am I missing something?

 

[IpswichST]

So.. the perpendicular hose was loose. It slid right off. The others were tight. I figured, what the hell... Ill replace it with some fuel line I had. Could that loose hose have caused my problem?

 

[sofawizard]

well to much air will make her stumble duno if it would kill it tho been over mine again decided to take the air scoops off the carbs and run her up found I had 1 slide sticking up loobed it n cleaned it up seems ok for now changed the scoops as they were split and some ape before me hadn't put them in properly the bottoms were deformed where they meet the carbs seems to be running a little better road test in the morning

 

[bdalameda]

Can someone tell us what the sub filter is needed for? It looks like a evap
line or am I missing something?[/QUOTE

The Subfilter allows the top of the CV carb diaphragms to vent as the slides move up and down. Without proper venting as the slides are pulled up by vacuum either pressure or vacuum can build up above the diaphragms and the slides will not move correctly. This can cause the engine to hesitate badly and act very strange.

 

[IpswichST]

i thought I was all set...now wondering if a slider may be stuck or torn. Question... do I have to take the carbs all the way out to check/replace them? Thanks

 

[sofawizard]

rear 2 you can get them out on the bike but the front pair will require the carbs taking out you can check them to see if there sticking or not lifting fully on the bike by removing the air filters and the trumpets you will be able to see the carbs and slides at work with the engine running
ive been out this morning and its much better but still a little stumble on hard throttle openings I think this will clear up on its own tho as it was starting to improve on the way home good luck and happy trails