low power and low vacuum
- Thread starter Herb1949
- Start date
Honda makes one of the most reliable motorcycles made. Others are reliable too, like Yamaha , but OEM Honda parts are a lot less, and it's a heck of a lot easier to check & adjust the valve clearances on both the ST1100, ST1300 than a FJR, Kawasaki, or Triumph Trophy.
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ST1100Y
Site Supporter
I suggest studying the w/shop manual first... no need to pull the valve covers there...
I have the Honda shop manual and it shows the timing marks ON THE CAMS, not on the sprockets. It also shows pulling the cam covers to access the timing marks.
My manual is for a 91, did they change the procedure?
To answer a few of the other questions.
When balancing the carbs I could tell right away when I had one out of sync. I have tried pulling one plug wire at a time and I got a definate drop in rpms each time, at least at idle. Maybe I should go back and pull them at a higher rpm and see what happens.
I agree that the idea of the cam belt jumping is far fetched, but I am grasping at straws folks. any and all ideas, no matter how far out are welcome and I will try them.
One of my friends said I should hook up the vacuum gauges and ride it to see what it is doing under load, I think I will try it. His idea was that I have at least one slide sticking.
I forgot to mention that I have already pulled the vacuum fuel valve off, and put a new fuel filter in, neither one made a difference.
I thought it might be a bad fuel pump, but with carbs I should still get good accell until the float bowls get too low, shouldn't I? Besides that, the fuel pump check in the manual, checks good.
One last thing, My old 82 GS1100 is much easier to maintain, has about the same power, gets the same gas mileage. My 99 1400 intruder has over 200,000 miles on it and had never required a valve adjustment, had a problem with over heating, required a cam belt change, and the stator is less than a 2 hour job to replace, at a cost of about $100.
The St is smoother, handles better, looks better and is really nice to ride, when it runs correctly. I am begining to think the advantages of the ST are not worth the disadvantages.
After you finally figure out your problem, your feelings may change.
BTW, it's not too hard to remove the slide covers ( after removing the air cleaner housing and airbox under it ) and remove the slides to see if you do have a sticky slide , or bad diaphragm. You may have a leaky diaphragm - don't think this was mentioned yet. That would definitely cause your symptoms ( low vacuum at idle & low power at high speeds ) . I have some old diaphragms that are still useable ( I think ). Let me know if you can use one.
BTW, it's not too hard to remove the slide covers ( after removing the air cleaner housing and airbox under it ) and remove the slides to see if you do have a sticky slide , or bad diaphragm. You may have a leaky diaphragm - don't think this was mentioned yet. That would definitely cause your symptoms ( low vacuum at idle & low power at high speeds ) . I have some old diaphragms that are still useable ( I think ). Let me know if you can use one.
+1 on the possible bad diaphragm. They're not cheap, but they last a long time if they do go bad.
ST1100Y
Site Supporter
Dunno, always worked after page 8-13 showing the marks on the pulleys...
But on a bike with unknown history it seems a safe procedure to also check proper cam setting anyway...
My ST-mech was once confronted with an ST which must have been moonshine serviced, idle like a bag of cloth-pins, hesitant in accepting throttle, etc...
Long STory short:
belt was off 2 notches on the RHS pulley, plus both cams badly off their markings on the reduction gear (apparently in an attempt to "correct" the fault during installation of the t/belt...)
See what can happen without a guide plate on the RHS pulley .........
I found that you can check whether the slides are working by blowing air into the diaphragm air vents, which are the large bore plastic T piece between the carbs. If you leave the rubber hoses attached to the vents you can just use your mouth and blow. You will need the carbs off the bike for this as you have to be looking back up the throttle bore with the throttle plates open (unless you can bend the rubber trumpet far enough to see straight in). Because each air vent connects to a pair of carbs, you can visually see if they are moving together or not.
Can you determine if the diaphragms are leaking that way , too ?
Has anyone ever had a problem with the timing advance not working? Could overheating have damaged this? Without going out to the shop and checking my manual is there a way to even check it?
Interesting to know, gonna have to try it.
For jim van, I can't get to the 2 bottom screws on the slide covers with the carbs on the bike, the frame rails cover them. Since I will have the carbs off to check this out I will see what I can find out.
Although when I was cleaning the carbs I had the slides out and didn't find any problems with the slides or diaphrams.
Trying to figure out what those hoses are for. My other bikes, and many others I have worked on, have vacuum carbs and don't have that kind of setup.
Has anyone tried to run these without the air horns on? What happens if I run it without the air horns?
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I've been all over my ST carbs in the last few days, so I think I know what all the hoses do.
Fuel inlet is pretty obvious, and there are a matching pair of fuel overflow hoses that terminate in a bracket at the front of the carbs. Tiny hoses off the bottom are just for the floatbowls. The very big hoses from the small air filter are air supply to the carb diaphragm chamber.
There are four small vacuum hoses that terminate on the inlet manifolds, these are for synching the carbs with vacuum gauges, and one of these hoses is normally used to open the vacuum petcock. There is a liquid drain from the bottom of the airbox.
Given you are in CA, you might have additional fittings for PAIR and evaporative emissions. The PAIR system allows filtered air to be drawn from the airbox and dumped into the exhaust ports, to reduce unburnt hydrocarbons. PAIR normally has a big bore pipe going to a vacuum/solenoid operated valve and from there to the exhaust manifolds, so there will also be a small vacuum pipe running from the PAIR solenoid valve. My bike doesn't have this system, and it is pretty common to remove it and plug the various ports.
An evap system if fitted will connect to the fuel tank breather and trap vapours in a charcoal cannister. These usually have a purge system to draw air through the cannister and into the airbox, so some more rubber hose will be needed for that.
I can't even get my air trumpets off (chewed out plenum screws) but their purpose is to tune the air inlet to provide good torque at the expense of lots of top end. I doubt it will cause any problem but I don't think the bike will carburate well with them off.
Fuel inlet is pretty obvious, and there are a matching pair of fuel overflow hoses that terminate in a bracket at the front of the carbs. Tiny hoses off the bottom are just for the floatbowls. The very big hoses from the small air filter are air supply to the carb diaphragm chamber.
There are four small vacuum hoses that terminate on the inlet manifolds, these are for synching the carbs with vacuum gauges, and one of these hoses is normally used to open the vacuum petcock. There is a liquid drain from the bottom of the airbox.
Given you are in CA, you might have additional fittings for PAIR and evaporative emissions. The PAIR system allows filtered air to be drawn from the airbox and dumped into the exhaust ports, to reduce unburnt hydrocarbons. PAIR normally has a big bore pipe going to a vacuum/solenoid operated valve and from there to the exhaust manifolds, so there will also be a small vacuum pipe running from the PAIR solenoid valve. My bike doesn't have this system, and it is pretty common to remove it and plug the various ports.
An evap system if fitted will connect to the fuel tank breather and trap vapours in a charcoal cannister. These usually have a purge system to draw air through the cannister and into the airbox, so some more rubber hose will be needed for that.
I can't even get my air trumpets off (chewed out plenum screws) but their purpose is to tune the air inlet to provide good torque at the expense of lots of top end. I doubt it will cause any problem but I don't think the bike will carburate well with them off.
It will detract big time from your mid-range power. They literally "tune" the intake.
This thing couldn't get much worse on the midrange, and still run. If I run without the air horns and the air filter I would be able to see if the slides are opening. Or would they not open because the air horns are not on it?
Herb I'm pretty much stuck with the same running symptoms as you. If I just cruise quietly with small throttle, my bike runs great. But as soon as I give it more throttle in the midrange it starts stumbling and bucking. I've been into the carbs 3 times and am 98% sure every jet and air passage is clear, I have a new fuel pump and filter and have confirmed flow, the air filter and plugs are new, and the plugs look very normal after use.
I wonder whether water in the electrics could cause this? I washed my dead bike pretty aggressively as it had 8 years worth of accumulated dirt from being parked in a concrete contractor's yard. Maybe we've got water in a coil connection or somewhere? I have tested the impedance of the coils, ICM and plug leads as per the manual and they check out well, has anyone got another suggestion?
And to answer your question, I'm sure the slides should rise without the air horns and filter as long as you have some intake vacuum past the end of the slide.
I wonder whether water in the electrics could cause this? I washed my dead bike pretty aggressively as it had 8 years worth of accumulated dirt from being parked in a concrete contractor's yard. Maybe we've got water in a coil connection or somewhere? I have tested the impedance of the coils, ICM and plug leads as per the manual and they check out well, has anyone got another suggestion?
And to answer your question, I'm sure the slides should rise without the air horns and filter as long as you have some intake vacuum past the end of the slide.
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Terry.
If we keep working on this one of us is going to find a reason. When we do we can post it here to try to help the other person. Good Luck to you, and me.
Unfortunatly I have a lot of other stuff going on and don't have the time to devote to the bike that it really deserves.
I really wish that the Honda manual had done a better job of explaining the principles of operation of these systems.
Reading on other sites, and the manual, I am starting to think it is a problem with the emissions system. One place says that the air vent control valve can cause the problem, but according to my book it is only on California models, which I have, I don't know if your model has it. I am going to try to check it out today, if I have time.
If we keep working on this one of us is going to find a reason. When we do we can post it here to try to help the other person. Good Luck to you, and me.
Unfortunatly I have a lot of other stuff going on and don't have the time to devote to the bike that it really deserves.
I really wish that the Honda manual had done a better job of explaining the principles of operation of these systems.
Reading on other sites, and the manual, I am starting to think it is a problem with the emissions system. One place says that the air vent control valve can cause the problem, but according to my book it is only on California models, which I have, I don't know if your model has it. I am going to try to check it out today, if I have time.
John OoSTerhuis
Life Is Good!
That's pretty well done in the Honda Common Service Manual, Herb. I got mine years ago and it's been a very valuable resource for me. IINM, there is (was?) a downloadable digital version (PDF?) some where out there in the ether.
John
via new iPad Mini 2
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Yes I agree that the Honda CSM has a good explanation of carb function, I downloaded mine a few days ago.
Here's a clip of my bike I made this morning, not sure if this will give any clues? It's not exactly high speed running but was about 1/2 throttle and bogging.
[video=youtube;oMN5OTobtRc]https://www.youtube.com/watch?v=oMN5OTobtRc&feature=youtu.be[/video]
Here's a clip of my bike I made this morning, not sure if this will give any clues? It's not exactly high speed running but was about 1/2 throttle and bogging.
[video=youtube;oMN5OTobtRc]https://www.youtube.com/watch?v=oMN5OTobtRc&feature=youtu.be[/video]
I think I fixed my problem. I did pull the carbs down and cleaned them again, but while I had all the bodywork off I went through some electrical connectors, tracing the power from battery to ICM and coils. I think I had low voltage due to corrosion in the big red connector, right behind the steering head. Terminals in here looked powdery, so I cleaned them and applied some contact cleaner. The bank angle sensor relay terminals were perfect.
Anyway I have had a test ride and for the first time my ST has midrange and the stumbling has gone, the bike seems to be running well now, so I'm off for a decent ride to check it out.
Herb, I hope this also works for you, take a look and see what you find.
Anyway I have had a test ride and for the first time my ST has midrange and the stumbling has gone, the bike seems to be running well now, so I'm off for a decent ride to check it out.
Herb, I hope this also works for you, take a look and see what you find.
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