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

IpswichST

IpswichST

Joined
Jan 5, 2013
Messages
191
Location
Ipswich MA
Bike
1994 ST1100 ABS
Ok... Im sad Im already posting in this section and I have read some posts but now I have some questions. Here are the symptoms and what led up to them:

Riding home from an appointment... my fuel light was on so I stopped and purchased some fuel. I cracked my fuel cap... vacuum sound (normal?), filled it up (6 gals) and checked my mileage (this is my first mileage check and I only got 30 MPG.... maybe that is a factor? keep it in mind if it is). Driving home was fine... maybe it had some hesitation moments but made it home.

I worked 2 hours then went back out and thats when it really started to run poorly. It started fine then I rode maybe 100 yards and it felt like it either was starved or had too much fuel. I pulled over and figured it needed to warm up. I rode another 100 yards and the same thing. Another 100 yards and again the same thing. Running at high RPM didnt help. Eventually I heard and felt some backfires.

Im thinking I need to clean my carbs but that may be too simple. Any suggestions where I should start will be appreciated.

Also... I want to balance my carbs. My question is... can the vacuum balance tool also be used for other tests? fuel pump pressure... or other tests?

Thanks
 
IpswichST said:
Ok... Im sad Im already posting in this section and I have read some posts but now I have some questions. Here are the symptoms and what led up to them:

Riding home from an appointment... my fuel light was on so I stopped and purchased some fuel. I cracked my fuel cap... vacuum sound (normal?), filled it up (6 gals) and checked my mileage (this is my first mileage check and I only got 30 MPG.... maybe that is a factor? keep it in mind if it is). Driving home was fine... maybe it had some hesitation moments but made it home.

I worked 2 hours then went back out and thats when it really started to run poorly. It started fine then I rode maybe 100 yards and it felt like it either was starved or had too much fuel. I pulled over and figured it needed to warm up. I rode another 100 yards and the same thing. Another 100 yards and again the same thing. Running at high RPM didnt help. Eventually I heard and felt some backfires.

Im thinking I need to clean my carbs but that may be too simple. Any suggestions where I should start will be appreciated.

Also... I want to balance my carbs. My question is... can the vacuum balance tool also be used for other tests? fuel pump pressure... or other tests?

Thanks
Click to expand...

Well, looks like maybe your overthinkin' the issue a bit......just sayin'. Was it runnin' fine prior to issue?. If so, would replace fuel filter if ya' already haven't(OEM only). Second, check function of fuel shut-off diaphram. Important to do just one thing at a time and test results. As for carb sync........why? 'Just cause' or is there something related goin' on that makes you think it needs it done? Helps to not be guessin' and just throwin ideas at it. The above two mentioned would be a good place to start;)
 
Fuel cutoff vacuum valve probably quit working or your fuel pump. Try bypassing the cutoff valve and see if the bike will run correctly without it.

Dan
 
Hey... I was reading another thread and when I go to page 4 I read this...

Also, as a safety feature, a running engine is safer than a non-running engine. That valve is double redundant 'cause the tip over relay shuts off the engine, which shuts off the fuel pump.

Which made me remember.... When I got back from my appointment and went back to work, where I park my bike is a tight turn around so that I can back it up into a safe spot. Today I got careless and slowly tipped it down onto the tip-over wing on the right side. I quickly picked it up... literally wasnt on the wing for more than 5 seconds (hoping no one saw me... a little careless, pissed and embarrassed). SO.. could it have anything to do with this relay?

And.. as my quote above states... is the fuel cutoff vacuum needed? do most people disconnect them when they fail and just leave them off?

Thanks
 
I routed around the shut off and have not regretted it...

30mpg is pretty low... how does/did the bike run over 5000rpm before the 'new' gas?

I might put some seafoam in to see if the gas had water in it too...
I hope you are using regular not premium fuel too... the bike doesn't need the extra octane.
 
I think I will route around the shut off and see if that is the issue. AS a matter of fact, the post I quoted was I think YOUR post Mark. I recall you broke down on the hiway in OK, tore your bike apart and did the re-route and got up and running again? Interesting post!

Ok.. honest... cant say that I have been cruising with my RPMs up over 5000. Sure sometimes I take off and my RPMs get up there... but I dont readily cruise that high. Are you saying that I should be? that is is normal to cruise that fast? Maybe I need to take some lessons!
 
Yup... I did the re-route on the side of the road... better to do it in your garage... really!

IIRC if the carb diaphrams are torn you get poor mpg and no power in the higher revs.

I like 5000rpm (or above) in 5th; but, I think MA roads have more LEOs than we have on the long beautiful backroads here in the West... :D
 
What about a bad batch of gas? Maybe run a bit of fuel into a glass jar and look for tell tale water and gunk.
Carb clean is maybe a good idea but if you got a bad batch of fuel you it will do little good to clean carbs.
You can do a lot of troubleshooting and swearing over simple bad gas. Maybe empty it into a gas can or 2 and start with known good fresh gas.
I would also pull and check plugs and perhaps replace with known good ones. Simple stuff first.
 
John OoSTerhuis said:
Um... er... Is the choke (stuck) on? KISS
Click to expand...
I live by KISS.... and no, Choke is not stuck. In fact I used the choke to start her up and when I turned it down it definitely responded.

The gas was from a station that gets a ton of business. Im sure it was fresh... not that it couldnt have a bad batch.

Ill pull a plug or 2... check them out. Drain some fuel when I bypass the fuel shutoff.

This will be the first time I pull the plastic around the engine so Ill do a little exploring... familiarize myself with whats behind there. I have a pretty fill punch list of simple tasks I want to accomplish.

Thanks for all the responses. Ill report my findings
 
Was it was running good before you got the gas? Probably bad gas.

30 mpg is pretty low so there could be a problem there.
 
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Do the "really" simple stuff first. I had this same thing happen after a fill up on nearly empty tank. Dose of Seafoam fixed it.

Jim
 
Ok... Pictures.. I love pictures. I took the tank cover off at lunch today to do that bypass of the fuel cut off vacuum valve and low and behold I think the whole valve has been removed! While I was there I noticed the fuel filter which I think is not OEM and.. I also noticed a vacuum hose that has a rubber cap on it which was about to fall off. Now when I say fall off I mean it was cracked and split and possibly was causing some rough running. Experts dont hesitate to chime in and let me know definitively if this line could cause maybe an unsteady idle (which it did suffer from) and ultimately a failure to run.

What I did do is put a wire tie on that cap and added about 6oz of seafoam into my fuel... just as a maintenance step to clean out my carbs.

Thanks

Fuel Cut Off.jpg
 
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Yup, already rerouted.
Yup, not stock.
Yup, a vacuum leak can cause really rough running and stalling.
 
DAMN... After I found that cracked cap... missing fuel cut off, and not OEM filter I took it for a ride... seemed to ride ok. Went to work and when I came out it did the EXACT same thing. Hard to start also. One curious thing... Both times it happened I had left the bike on the side stand. Noooo... that couldnt be a cause.. could it? Could something become drained or overfilled due to it being on the side stand? Im grasping.

Thoughts?
 
IpswichST said:
Ok... Pictures.. I love pictures. I took the tank cover off at lunch today to do that bypass of the fuel cut off vacuum valve and low and behold I think the whole valve has been removed! While I was there I noticed the fuel filter which I think is not OEM and.. I also noticed a vacuum hose that has a rubber cap on it which was about to fall off. Now when I say fall off I mean it was cracked and split and possibly was causing some rough running. Experts dont hesitate to chime in and let me know definitively if this line could cause maybe an unsteady idle (which it did suffer from) and ultimately a failure to run.

What I did do is put a wire tie on that cap and added about 6oz of seafoam into my fuel... just as a maintenance step to clean out my carbs.

Thanks

Fuel Cut Off.jpg
Click to expand...

The capped vacuum line is the line that works the fuel cut off valve. Cracked cap would indeed cause a lean F/A mix and low milage. I have been running the same fuel filter in the pic for 50,000 miles on my ST and it was on the bike when I bought it. I have run that same filter on my bass boat since 1988 without a problem. OEM filter??? If one likes spending more money.
 
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