JLamb
1991 ST1100
Can the carb diaphrams be checked without removing the carbs?
Checking diaphrams for damage
- Thread starter JLamb
- Start date
Been a while since I have had the air box off the bike, but I am thinking that it can be done without removing the carbs. It may be advisable to remove them anyway since there is some age on the bike to check and possible replace the isolators. The isolators can harden and crack with age and give you fits. My guess if you are having carb problems, a removal and inspection would be the best bet. Once you have the airbox removed, removing the throttle cable and choke cable, loosen the isolator clamps is all that left... the fuel and drain connections are not difficult.
OP
OP
JLamb
1991 ST1100
Potential damage to the isolators is my main reason for not wanting to remove the carbs - I can check if they leak w/ WD-40 and replace if necessary but its been my experience the old hardened parts often begin to leak after the stress of removal and reassembly. The bike is a 91 w/ 80K miles but only 300 by me. Unknown as to POs maintence let alone the previous PO (ppo?). It runs well, good power and all everywhere. Roll on is good, top speed is good - idle is a little bumpy but milage is terrible at 30MPG. I am planning to do plugs (NGK Irradiums) and a carb balance, inspect the air filter - main and pre both, and thought I'd take a look see at the diphrams and isolators at the same time. Anything else you would suggest regarding the milage problem?
If the idle is a little bumpy, try running some "seafoam" through it to clean the low speed jets. If the bike has set a while, the jets can get gummed up with ethanol deposits. It is a good start if you do not want to remove the carbs. The isolators are about $9 a piece... might be a worthy investment if you plan on keeping the bike for any length of time. It would be a good idea to have the valves checked, or do it yourself if you are so mechanically inclined. If you are uncertain about doing a valve check, find out who in your area knows the 1100 and ask for assistance... some are willing to help out and may even post a "tech event". There are lost of threads about maintenance on the 1100... just go to the technical forums and click on ST1100. Hope you find the information you are looking for.
Vinny
Vinny
OP
OP
JLamb
1991 ST1100
I will try the sea foam before I do the plugs and sync. One other thing - I need to use full choke, no throttle when cold to start the bike - or even if just sitting a little while. It likes the choke untill it warms enough to move the temp needle off its stop. Idle will be about 1000 to 1200. When it gets fully hot - mid way on temp gage - idle climbs to 1400 to 1600 RPM. Normal?
Velves were reportedly done just before I got the bike, supposedly by a dealer shop. I appreciate the info.
Velves were reportedly done just before I got the bike, supposedly by a dealer shop. I appreciate the info.
It doesn't sound like diaphragms to me, it sounds like clogged low speed jets (and maybe the high speed jets too).
It is normal to start the 1100 with full choke. Should not have to run it very long on choke, and the idle should go up past 2K when it starts warming. Sounds a lot like clogged jets.
schlep1967
Bill
Probably wouldn't hurt to balance the carbs AFTER you get all the jets cleaned out.
First, since the bike has good power, there is nothing wrong with the carb diaphragms. If they were torn the bike would have no power above 60% throttle. 2nd, since the bike needs choke to start even when not really cold, this is a symptom of a lean condition. A lean condition will also cause lower fuel milege. I'm guessing that the 1600 rpm idle when warm is with the choke off????? If this is the case the idle is too high and the carb butterflys are too open which can will lower fuel milage. Warm idle spec for US bikes is 1200rpm + or _ 100 rpm.
My fuel mileage on my '91 has always been in the mid 30s to very low 40s . 39mpg is spec on Motorcycle Consumer News tests and othet spec sheets. I've never figured out how some get 50mpg. Larger than stock windshield will cut the milage.
My fuel mileage on my '91 has always been in the mid 30s to very low 40s . 39mpg is spec on Motorcycle Consumer News tests and othet spec sheets. I've never figured out how some get 50mpg. Larger than stock windshield will cut the milage.
OP
OP
JLamb
1991 ST1100
It does have a tall windshield... Yes- full warm w/ choke off idle is 14-16K RPM. I am at sea level in California - its a Cali bike as far as I know. Could be bad jetting but PO had no knowledge of anyone being in the carbs. Likely dirty circuits.
OK - I'm convinced that I should pull the carbs and clean the jets as a minimum. Where do you get the $9 isolators? Doesnt sound like a Honda price!
OK - I'm convinced that I should pull the carbs and clean the jets as a minimum. Where do you get the $9 isolators? Doesnt sound like a Honda price!
So does balancing the carbs cure this lean condition,I think you have just described my bikes exact condition,also at 39,000 miles should I also get the valve clearances checked?
Thanks
Before pulling the carbs I'd run a couple of tanks of gas with carb cleaner.
SeaFoam in the USA (max 2oz per gal), don't know what you use across the pond... I'm sure you have just as many though!
Lean condition can be completely blamed on clogged jets (until the jets are clean!).
SeaFoam in the USA (max 2oz per gal), don't know what you use across the pond... I'm sure you have just as many though!
Lean condition can be completely blamed on clogged jets (until the jets are clean!
).
$8.75 from Ron Ayers
I bought a 91 ST1100 this year that seemed to run well. Took the carbs off and cleaned all of the jets, replaced the carb insulators, (your 99 insulators can be found here> http://www.cheapcycleparts.com/model_years/897-honda-1999--st1100/assemblies/13591-left-cylinder-head, balanced the carbs and get 45mpg doing mostly interstate on my 87 mile round trip daily commute. I still need to adjust the pilot screws and hope to improve on the mileage. I have a tall wind screen, and found that spirited ridding will bring my mileage down some.
OP
OP
JLamb
1991 ST1100
Thanks