ST1100 Misfire/Stumble just off idle....

[Gymbo]

My ST1100 has developed a miss from just off idle all the way up through the RPM range. We have synched the carbs with a SK Flowmeter, changed spark plugs (NGK Iridium), changed fuel filter...and still a misfire/stumble persists. It is most noticeable just off idle with light throttle. It misses all throughout the RPM range, worst under light throttle. The bike has good power and accelerates well.

The bike has a K&N air filter, but I don't think it's a factor since it ran like that with the air cleaner off synching the carbs.

The bike is a 1996 ST1100ABS with 31,500 miles.

I am thinking it may be a vacuum leak. Where do I begin to figure out where?

 

[TearlessTom]

Possible a bad plug wire?

 

[DeSTy]

does it still miss under full or mid throttle?

 

[saaz]

Apart from a plug lead or coil problem (of which I have not heard of many, most due to not taking the plug caps off properly), it could be either a blockage in a jet, the vacuum valve cutoff (try bypassing it, failure result in a vacuum laek and possible rich running - how did the plugs look?) or blocked fuel filter (one recent case where that was the cause of problems).

 

[BigTom]

My first thought was/is coil. Second, plug lead. Third fuel filter. Very distant 4th is torn carb rubber. One.

I'm not saying that's the order to check, just the order I thought of when I read your post.

#3 would be cheapest and easiest to check. Very standard fuel filter...#2 is pretty easy with a multi meter. #1 is straight forward enough, a little hard to get to.

You know what? From your description I'm thinking not coil. Each coil has 2 plugs, you'd not describe 2 dead holes as "slight". I'd say move coil to the back of the list.

 

[Dalton]

I would expect a vacuum leak to dissappear with a good throttle unless is was really big. If that's the case, I would think it would have a difficult time idling.

How about the pulse generator? Do you have a manual where it explains how to check the coil, pulse generator, wires, etc?

I hope you rid this gremlin soon!

Dalton

PS - I believe I've got some carb boots that are not all bad on my bench. I replaced them in my 1100 without seeing the ones on the bike. they're yours if you want them, just pay the shipping.

Dalton

My ST1100 has developed a miss from just off idle all the way up through the RPM range. We have synched the carbs with a SK Flowmeter, changed spark plugs (NGK Iridium), changed fuel filter...and still a misfire/stumble persists. It is most noticeable just off idle with light throttle. It misses all throughout the RPM range, worst under light throttle. The bike has good power and accelerates well.

The bike has a K&N air filter, but I don't think it's a factor since it ran like that with the air cleaner off synching the carbs.

The bike is a 1996 ST1100ABS with 31,500 miles.

I am thinking it may be a vacuum leak. Where do I begin to figure out where?

 

[Gymbo]

The misfire seems to have improved after adding a bottle of Techron at my last fill-up. I am hopeful that it will continue to improve as I put a few more miles on tomorrow. I'll add another bottle at my next fill-up also.

Dalton - I have the Honda manual, does it explain in there how to check the pulse generator, coil, and wires? Wires, I believe are checked with an ohmmeter? I may take you up on the boots if the misfire is not gone and I can't figure it out otherwise.

 

[BigTom]

Hey.

From the Honda manual. Section 18 is the ignition section, Section 24 is the over all troubleshooting section. Pretty straight forward stuff.

Keep us informed....

 

[Gymbo]

Re: ST1100 Misfire/Stumble just off idle....FIXED

Sure enough, after riding from south Portland to Roseburg this afternoon it is running excellent...probably the best it has since I have owned it. I had run a bottle of Seafoam through it last month, because it was running a little rough without much difference. The Techron made a difference so quickly I was almost unsure if I was imagining the improvement.

After having such success on my ST, I thought I'd try a bottle of Techron in my '91 Nissan Maxima that had developed a bad miss last week. I was expecting that I had a bad injector, and was pricing them last week. I added a bottle of Techron Concentrate Plus and within 4 blocks it was running WAY better and within 10 minutes, it was running perfect...perhaps better than it has in a while. I ran a bottle of Seafoam through it last week without any improvement.

Needless to say I am sold on Techron.

PS...I have a theory...that Oregon changed to all fuel having 10% ethanol in it recently. I think that is partially responsible for two of my vehicles developing injector/carburetor problems in such a short time frame.

 

[Mark]

So Jim, how much stock do you own...


Mark
P.S.
I don't own stock; but, I either buy Chevron gas or run techron through about once every 3 months.

 

[Gymbo]

So Jim, how much stock do you own...


Mark
P.S.
I don't own stock; but, I either buy Chevron gas or run techron through about once every 3 months.

No Mark, no Chevron stock, I probably should with their record profits. Weird thing is I tried Seafoam in both my bike and my Maxima and it didn't help. I was surprised that I noticed a difference so quickly on both my bike and my car with the Techron. BTW, I used the Techron Concentrate Plus from the auto parts store, not the Chevron ProGuard, which is available at Costco.

 

[BigTom]

Glad you are back in the saddle, smiling!

 

[Dalton]

Re: ST1100 Misfire/Stumble just off idle....FIXED

GREAT news!!

Sure enough, after riding from south Portland to Roseburg this afternoon it is running excellent...probably the best it has since I have owned it. I had run a bottle of Seafoam through it last month, because it was running a little rough without much difference. The Techron made a difference so quickly I was almost unsure if I was imagining the improvement.

After having such success on my ST, I thought I'd try a bottle of Techron in my '91 Nissan Maxima that had developed a bad miss last week. I was expecting that I had a bad injector, and was pricing them last week. I added a bottle of Techron Concentrate Plus and within 4 blocks it was running WAY better and within 10 minutes, it was running perfect...perhaps better than it has in a while. I ran a bottle of Seafoam through it last week without any improvement.

Needless to say I am sold on Techron.

PS...I have a theory...that Oregon changed to all fuel having 10% ethanol in it recently. I think that is partially responsible for two of my vehicles developing injector/carburetor problems in such a short time frame.

 

[Mark]

N BTW, I used the Techron Concentrate Plus from the auto parts store, not the Chevron ProGuard, which is available at Costco.

Good tip. Thanks.
Mark

 

[Gymbo]

My ST1100 has developed a miss from just off idle all the way up through the RPM range. We have synched the carbs with a SK Flowmeter, changed spark plugs (NGK Iridium), changed fuel filter...and still a misfire/stumble persists. It is most noticeable just off idle with light throttle. It misses all throughout the RPM range, worst under light throttle. The bike has good power and accelerates well.

The bike has a K&N air filter, but I don't think it's a factor since it ran like that with the air cleaner off synching the carbs.

The bike is a 1996 ST1100ABS with 31,500 miles.

I am thinking it may be a vacuum leak. Where do I begin to figure out where?

Well the problem still persists just off idle and with light throttle. It no longer misses under hard throttle and seems to run great once I get the throttle open and roll on it. I have run several bottles of Techon and Seafoam through it to no avail.

I am thinking at this point that I probably have some jets plugged in my carbs. I am planning on pulling carbs to clean them. Other than the carb isolator boots, are there any parts that I may want to have on-hand? Not planning on doing a PAIR-ectomy unless there is a really good reason to do so.....I do need to replace my coolant, so I'll inspect the hoses under the carbs. I can't think of anything else to do while I am in there.

Any experience or advice you can share is most appreciated.

Thanks!

 

[chesthing]

Sounds like the pilot jets, they have extremely small holes and typically adding fuel cleaner to the gas tank does nada. To clean take them out and soak them in carb cleaner for a little while, run a wire from some braided speaker or electric line through the holes and spray the holes really good with carb cleaner. When you see daylight they should be good. While you are in there you may as well spray out the main jets as well.
Before you do all that, I'd check for a cracked vacuum line - this could also cause the symptoms you describe. With engine running spray starter fluid around all vacuum lines, looking for a difference in idle speed.

 

[broc11]

Apart from a plug lead or coil problem (of which I have not heard of many, most due to not taking the plug caps off properly), it could be either a blockage in a jet, the vacuum valve cutoff (try bypassing it, failure result in a vacuum laek and possible rich running - how did the plugs look?) or blocked fuel filter (one recent case where that was the cause of problems).

Thanks,sounds like I'm having the same issues,vacuum valve is the first item check.