low power and low vacuum

[Herb1949]

I had an over heating problem, flushed the system and now it runs cool but, now there is low power when I open the throttle past about 1/4 under load and when I checked the balance on the carbs, they are all the same, but it only has about 11 inches of vacuum. When the throttle is wide open it seems to surge slightly, like it wants to go.

The engine starts and sounds great, when there is no load it winds up great, but on the road it just kinda stagnates.

I pulled the carbs and cleaned them out good, every passage seems to be clear. I can't find a vacuum leak.

Any suggestions???

 

[Jim Van]

Remove the air filter cover and start the engine. Then occlude each air intake snorkel in order. See if you can find one where that has less effect than the other three. That might help find where a vacuum leak may be at, if you have a vacuum leak.

If that doesn't help, just for S&G's you might try doing a compression test. Make sure all plugs are out and the carb slide for the cylinder you are testing is pulled up.

 

[TerryS]

I am faced with similar running symptoms on my 92 ST11. I am resurrecting it after 8 years off the road, and like Herb I have been right through the carbs and unblocked jets, checked diaphragms, removed the vacuum petcock, replaced a fuel pump and replaced plugs. Carbs are perfectly synched, and the bike starts easily, idles beautifully, and under about 4000 rpm it runs really well. Give it more throttle and it starts to misfire and stumble. I inspected the carb boots and they are all in good order and the clamps are snug.

By the way Herb, 11 in Hg vacuum sounds pretty normal to me.

 

[Brant]

I am faced with similar running symptoms on my 92 ST11. I am resurrecting it after 8 years off the road, and like Herb I have been right through the carbs and unblocked jets, checked diaphragms, removed the vacuum petcock, replaced a fuel pump and replaced plugs. Carbs are perfectly synched, and the bike starts easily, idles beautifully, and under about 4000 rpm it runs really well. Give it more throttle and it starts to misfire and stumble. I inspected the carb boots and they are all in good order and the clamps are snug.

By the way Herb, 11 in Hg vacuum sounds pretty normal to me.

Actually, sea level up to 2000ft. elev. should be 21-22in. of vacuum. My location at 5000ft. elev., vacuum level is 18in. of vacuum. At 10,000ft. elev. vacuum drops toapprox. 15-16in. of vacuum.

 

[Jim Van]

I am faced with similar running symptoms on my 92 ST11. I am resurrecting it after 8 years off the road, and like Herb I have been right through the carbs and unblocked jets, checked diaphragms, removed the vacuum petcock, replaced a fuel pump and replaced plugs. Carbs are perfectly synched, and the bike starts easily, idles beautifully, and under about 4000 rpm it runs really well. Give it more throttle and it starts to misfire and stumble. I inspected the carb boots and they are all in good order and the clamps are snug.

By the way Herb, 11 in Hg vacuum sounds pretty normal to me.

Have you considered plugged mufflers ??

 

[Brant]

AlsoHerb1949, if idle mixtures were not re-set or incorrectly set PRIOR to carb-sync, this will show a low vacuum reading.

 

[Jim Van]

AlsoHerb1949, if idle mixtures were not re-set or incorrectly set PRIOR to carb-sync, this will show a low vacuum reading.

Hmm .. That may be true, but would it cause his main complaint of not running well above 4,000 RPM ?

 

[TerryS]

Plugged mufflers??? Sounds like you're suggesting an Italian tune-up, i.e. just rev it until it blows clear!

 

[TerryS]

Actually, sea level up to 2000ft. elev. should be 21-22in. of vacuum. My location at 5000ft. elev., vacuum level is 18in. of vacuum. At 10,000ft. elev. vacuum drops toapprox. 15-16in. of vacuum.

I'm not sure I agree with this; are you mixing your units and talking cm Hg rather than inches? All the carb synch videos I've checked on Youtube show a level right around 10" or 25 cm Hg.

 

[Herb1949]

Just a little more info to answer some of the posts.
The PO was a friend of mine and he said he changed the cam belt at 95k miles.
Prior to the flush it was running really good, at all speeds. Except for the over heating issue.
While I had the carbs off I ran the idle jets all the way in and counted the turns, then pulled them out to clean them. While I had them out I used the dremmel to cut a slot in them to be able to set them better. When I counted the turns they were all set at the correct turns out, 2 5/8 for the CA model, according to the Honda Service manual that I got with the bike. They should be pretty close to correct. The bike starts and runs good at low speeds so it shouldn't be the idle jets.
I live outside San Diego, at about 500ft asl. My Suziki 1400s have always held abouit 18 to 20 inches of vacuum, as do my cars. I find it odd that the ST is that much different than other 4 stroke engines.
I did end up with water everywhere when I did the flush, but had the air cleaner on and it should not have got in the carbs.
I was going to do a compression test but my gauge doesn't have the right adapter for these small plugs, I will try to find the correct adapter. My book doesn't really say what the vacuum is supposed to be.
This bike is driving me crazy. Anyone want to buy a ST1100?

 

[vinny]

How bad was the overheating? Any damage to the heads or head gaskets? Was the timing belt installed correctly... improper timing can cause and engine to run inefficiently and possibly overheat. Just putting it out there for consideration....

 

[Jim Van]

I think he said it was running fine after he acquired the bike. The problem started after the flush , not right after the timing belt was changed.

 

[Jim Van]

Herb :

Just curious, how bad was the overheating ??? How long was the bike run overheated, and what was the temp gauge reading during the overheated event ?

BTW, I'm kinda surprised only a flush cured the overheating.

 

[Herb1949]

The overheating wasn't that bad, I never let it get all the way up to the red.
When on the highway, above 40-50mph it stayed down at about 1/4, idle or running in slow traffic, the temp would continue to rise, even after the fan came on. A couple of times I got into traffic jams and even splitting lanes at 20-30 the temp would keep going up and I ended up having to pull off the road and shut it down. NEVER had to do that with my aircooled bikes.
I have considered the possibility that the cam timing has somehow slipped and is now late, I bought a 6cyl chevy once that acted a lot like this, started great, sounded good but lack of power at higher rpms, low vacuum. Just before I got it the PO had installed a new cam and lifters. After a lot of hassel I pulled the cover off of the cam and discovered the cam was 1 tooth late on time.
I have been doing almost all of my own maintenance since I was 9 years old, bicycles, motorcycles, cars and trucks. I have never seen something like this happen as quickly as this did, without being able to find it.
I rode it 150 miles on on the east county back roads on 1 day, the next morning I flushed the system and rode it around the block a few times but had something else to do that afternoon. The next day I finished putting the body work on and took it out on the freeway and it doesn't run worth crap.
Since I am new to this type of bike I was hoping that someone had seen this type of behavior before and the fix would not require a major amount of work.
I can't believe how much of a pain in the butt having to keep pulling this body work off is.
I find it stupid that I have to pull a bunch of body panels just to check the coolant level.
I am not impressed with Honda's engineering and design.

 

[dwalby]

Actually, sea level up to 2000ft. elev. should be 21-22in. of vacuum. My location at 5000ft. elev., vacuum level is 18in. of vacuum. At 10,000ft. elev. vacuum drops toapprox. 15-16in. of vacuum.

I'm not sure I agree with this; are you mixing your units and talking cm Hg rather than inches? All the carb synch videos I've checked on Youtube show a level right around 10" or 25 cm Hg.

My Suziki 1400s have always held abouit 18 to 20 inches of vacuum, as do my cars. I find it odd that the ST is that much different than other 4 stroke engines.

I agree with TerryS, typical vacuum levels at sea level are in the range he stated. In fact, the very top end of my CarbStix is 50cm, which is 19-20" so I don't know how you guys are getting more than that unless you're using dial gauges that are way out of calibration. Typically, the mercury level on the CarbStix is around halfway up the tubes, or around 10-11". I haven't used mine in quite a while, since it tipped over and lost enough Hg to not work properly any more, but for 25 years before that, I remember it about halfway up.

 

[dwalby]

The overheating wasn't that bad, I never let it get all the way up to the red.
When on the highway, above 40-50mph it stayed down at about 1/4, idle or running in slow traffic, the temp would continue to rise, even after the fan came on. A couple of times I got into traffic jams and even splitting lanes at 20-30 the temp would keep going up and I ended up having to pull off the road and shut it down. NEVER had to do that with my aircooled bikes.

The ST has a fan that should turn on at just over halfway on the temp gauge and prevent it from going any higher. Make sure that is happening, if not, then that's something you'll have to troubleshoot, but its pretty easy. BTW, its normal for the temp needle to climb at speeds below 40-45mph steady cruising, so your lane splitting scenario seems normal other than the temp not stopping at halfway or so when the fan kicks in.

The next day I finished putting the body work on and took it out on the freeway and it doesn't run worth crap.
Since I am new to this type of bike I was hoping that someone had seen this type of behavior before and the fix would not require a major amount of work.

Does it feel like it could be a fuel starvation issue? There's a vacuum valve in the fuel line that is a common failure item. Mine's still going so I haven't experienced the symptoms of its failure, but from what others here have described it could explain your problem.

I find it stupid that I have to pull a bunch of body panels just to check the coolant level.

yep, couldn't agree with you more.

 

[Jim Van]

The overheating wasn't that bad, I never let it get all the way up to the red.
When on the highway, above 40-50mph it stayed down at about 1/4, idle or running in slow traffic, the temp would continue to rise, even after the fan came on. A couple of times I got into traffic jams and even splitting lanes at 20-30 the temp would keep going up and I ended up having to pull off the road and shut it down. NEVER had to do that with my aircooled bikes.
I have considered the possibility that the cam timing has somehow slipped and is now late, I bought a 6cyl chevy once that acted a lot like this, started great, sounded good but lack of power at higher rpms, low vacuum. Just before I got it the PO had installed a new cam and lifters. After a lot of hassel I pulled the cover off of the cam and discovered the cam was 1 tooth late on time.
I have been doing almost all of my own maintenance since I was 9 years old, bicycles, motorcycles, cars and trucks. I have never seen something like this happen as quickly as this did, without being able to find it.
I rode it 150 miles on on the east county back roads on 1 day, the next morning I flushed the system and rode it around the block a few times but had something else to do that afternoon. The next day I finished putting the body work on and took it out on the freeway and it doesn't run worth crap.
Since I am new to this type of bike I was hoping that someone had seen this type of behavior before and the fix would not require a major amount of work.
I can't believe how much of a pain in the butt having to keep pulling this body work off is.
I find it stupid that I have to pull a bunch of body panels just to check the coolant level.
I am not impressed with Honda's engineering and design.

If it never got up all the way into the red, I doubt you have a serious problem with a head gasket or valve, etc. caused by the overheating.

But I thought you said it ran fine before the flush, which was after the timing belt was replaced. So why do you think you may be a tooth off ?? Please confirm it ran good after you first acquired the bike, or not.

Something isn't making sense here. Do all the plugs look good ? Maybe you have a dead cylinder ? The problem may be unrelated to the flush, the "timing" just may be a coincidence.

Hope you can figure this out. I would hate to hear that you sold the bike because you were getting frustrated. The ST1100 is a great bike to own.

BTW, mine started running like crap on the highway and it turned out to be a sticky rear brake caliper piston. The week before, the rear wheel would spin freely, but the next week it had a problem.

 

[Herb1949]

If it never got up all the way into the red, I doubt you have a serious problem with a head gasket or valve, etc. caused by the overheating.

But I thought you said it ran fine before the flush, which was after the timing belt was replaced. So why do you think you may be a tooth off ?? Please confirm it ran good after you first acquired the bike, or not.

Something isn't making sense here. Do all the plugs look good ? Maybe you have a dead cylinder ? The problem may be unrelated to the flush, the "timing" just may be a coincidence.

Hope you can figure this out. I would hate to hear that you sold the bike because you were getting frustrated. The ST1100 is a great bike to own.

BTW, mine started running like crap on the highway and it turned out to be a sticky rear brake caliper piston. The week before, the rear wheel would spin freely, but the next week it had a problem.

Before the flush the bike ran really good, just seems wierd that it happened like it did. I have pulled the plugs and they all look good and I had replaced them after I got the bike.

The only reason that I think it might be a timing belt is I did have water all over the place and it could have got on the belt, causing it to skip a tooth. I really hate to tear it all the way apart and find there isn't a problem.

BTW, The way Honda makes you pull the cam covers to replace the belt is another stupid bit of engineering. I have replaced a LOT of car timing belts and EVERY ONE of them had the timing marks on the cam sprocket. STIPID.

I really like riding the bike, when it runs correctly.

If there were a dead clinder I should have been able to see it with the vacuum gauge.

As for the vacuum, it is a lot lower than I am used to but from what I am hearing here it is about right. Not sure where to go from here.

There is no reason for all of the problems with this bike.

I have put over 200 K on my VS1400 with no where near the problems. That this one has with less than 140K.

I doubt that I will ever buy another Honda.

 

[dwalby]

The only reason that I think it might be a timing belt is I did have water all over the place and it could have got on the belt, causing it to skip a tooth. I really hate to tear it all the way apart and find there isn't a problem.

the belt is covered well enough that significant water entry isn't likely, and even if a little water did seep in, there's enough tension on the belt that nothing is going to skip. Was what you did any different than riding in the rain?

 

[TerryS]

The cam belt is a toothed design, water or other lubricant can't cause it to jump a tooth, only low/no belt tension would do that.

Regarding the vacuum levels, all these show is that the amount of air being sucked in past the intake butterfly is the same, so the each cylinder must be sucking the right amount, so the valves/rings must be sealing well. I think even with a dead cylinder you'd still suck air through the intake, but getting a smooth idle would be difficult.

It was very obvious when i was balancing my carbs when they went out of line, the idle became rough and then engine vibrated more.