Broken Starter Valve #1

Blrfl

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It occurs to me that #1 valve could be replaced with an adjustable one and then brought into alignment with the other three assuming those haven't been touched.

I have a Carbtune II that I lend to anyone who'll cover the postage; PM if you need it.

--Mark
 
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YR

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I would bet that it's not really 'calibrated' by Honda.. it's simply a set part that is the same length on all bikes and the other 3 nuts are used to adjust to that... but nothing special about the #1, it's just non-movable.
It crossed my mind as a possibility on my way to the local dealer, who gave me a very good service over the past 8 years. The "master" technician said that he would do exactly the same thing -- try to fit an adjustable start valve and synchronize it to the excising other three valves. He welcomed me to give it a try and get back to him if I get into trouble.

BTW, he already replaced a broken start valve on an ST sometime ago but it was not on #1.
 
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YR

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It occurs to me that #1 valve could be replaced with an adjustable one and then brought into alignment with the other three assuming those haven't been touched.

I have a Carbtune II that I lend to anyone who'll cover the postage; PM if you need it.

--Mark
Mark, this is very kind of you. Many thanks! I'll PM you later, when I get all the parts.

Cheers, Yoed
 
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YR

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BTW, how much would you worry about precise tuning of starter valves?
 

Blrfl

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BTW, how much would you worry about precise tuning of starter valves?
The big thing you get out of it is smooth idle. I have a half-baked theory but no proof that they fine-tune the air intake just a bit off-idle.

--Mark
 
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YR

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Problem fixed. I was lucky to find a Starter Valve at a regional distributor and pick it up before the end of the day.
Here is the broken-thread valve and the replacement valve side by side:
BT05.jpg
Note the new nut design, which is now about double the length and made of brass. I triple-checked the part number. It is the right (only) one.

Here are the valve cylinders:
BT06.jpg
Note the Honda red thread lock, which was unexpected, but I guess that they wanted to make sure that I well understand "do not adjust". Since I do not have means to tune the starter valves, I originally wanted to count turns to fully closed, mark it down, and recover the same setting on the new valve. The unexpected thread lock left me confused about what fully closed actually was.

I measured all dimensions on the valves and the shafts. They are identical--no difference between this part among all starter valves. The original nut is designed differently, such that it would be hard to adjust it once assembled, so I went with the brass nut to keep the adjustment option.

Since I do not have a tuning tool and since the thread lock left me puzzled, I decided to give it a shot with eyeballing the location of the base of the cylinder through the air holes--marked with red arrows:
BT08.jpg
Not very professional but I planned to fine-tune it later, ... if it will work to start with. It worked like a charm, but I may have been lucky. I was able to set the hot idle RPM at stable 1100 (after what I believed to be some additional fine tuning). Rechecked hot and cold (over night) starts several times. All work fine.

BTW, since Honda recommends to put oil on the insulators when placing the throttle body back in place, I figured out that there is no reason why not using oil for a similar purpose when pulling the throttle body up in the first place. A couple of droplets with the assistance of a screw driver did miracles.

Thank you for all the useful advices.
 

Mellow

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Good work! Glad to see you got it all back together.
 

ChucksKLRST

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Great that you got it fixed, But it brings to question, How did it get broke in the first place? Was it the Previous owner or some "Honda Service Tech" Or???? Inquiring minds want to know.
 
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YR

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Great that you got it fixed, But it brings to question, How did it get broke in the first place? Was it the Previous owner or some "Honda Service Tech" Or???? Inquiring minds want to know.
I wish I knew. I am the original owner of the bike since 2006. I do all the maintenance and repairs on my own, and no technician have ever worked on my bike. Last time that anyone has tightened this nut was probably in Japan in 2005. I have been to this general area twice before, once to replace a faulty Map sensor, and the other time to clean a vacuum tube. Both cases were long ago and the bike run with no problems afterwords. The symptoms that led me to inspect the throttle body this time lasted only about 3/4 of a fuel tank (I waited until it got to two bars for a while before removing the empty tank). I was sure that I am about to find a dysfunctional SE Thermal Valve, which would cause similar symptoms.

The broken threaded piece--the starter valve lock nut--is actually made of plastic. The nut's only functions are to be a stopper for the valve spring and to hold the rubber sealing. The clearance between its bore and the shaft of the starter valve is very significant. I cannot imagine that applying any force on the shaft sidewise would brake the nut when the shaft is still held in place on the SE Thermal Valve Link Plate; the shaft would have to be significantly deformed first. Since the Synchronization Plate and the all other parts function properly and non is deformed, there is no possibility to apply any sidewise force on the nut to start with.

Who knows why did it fail after 8+ years. I assume that whatever caused the failure was not dramatic but progressed over time.
 
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Mellow

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I think it's just one of those things.
 
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Good find. plastic got brittle from heat. Something to check when you have an idle problem.
 
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YR

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My guess - that nut probably got over-torqued at the factory, and with time, heat (think brittle plastic), and vibration, the threaded portion just split.
Yeah, could be. Either that or a defect in molding.

Could also be the daemons that mess up with the throttle body when I do not pay enough attention ;)
 
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YR

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...
Since I do not have a tuning tool and since the thread lock left me puzzled, I decided to give it a shot with eyeballing the location of the base of the cylinder through the air holes--marked with red arrows:
BT08.jpg
Not very professional but I planned to fine-tune it later, ... if it will work to start with. It worked like a charm, but I may have been lucky. I was able to set the hot idle RPM at stable 1100 (after what I believed to be some additional fine tuning). Rechecked hot and cold (over night) starts several times. All work fine.
...
Got back from work, some 50 miles today, some on the interstate and some in stop-and-go at various temperatures, all works fine. While the unorthodox synchronization procedure described above worked for the bike, it doesn't do a lot of good to my TCD (tuning compulsive disorder). I am working on that now but if it is still there by the time that I need to replace the air cleaner, I am thinking of tuning the throttle body a little bit better. Using Mark's generous offer to lend me his Carbtune II is one option. Another option is to go old school with a quadruple bypass partially filled with water. I never tried that on the ST and I am not sure how low pressures or pressure oscillations to expect there. It is far more sensitive than the regular gauge system and some measures need to be taken not to suck water into the engine. Anyone tried that on an ST 1300?
 
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YR

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Fast forward three weeks. I connected a Carbtune Pro to the throttle body and the picture before tuning is attached below. The connected cylinders are 1 through 4 from left to right.

Conclusions I had at that point:
1. My crude synchronization of starter valve #1, including tuning by ear, actually worked better than I expected.
2. I now (then) needed to synchronize cylinder #3.

I adjusted the starter valve of cylinder #3, assembled everything back, and was quite happy with the outcome. The cold start on the following morning was unusual. Started at about 1400 RPM, went down to about 700-750 RPM when engine temperature got to one bar, and up to a normal 1000 idle when the engine temperature got to 2-3 bars. It was not the thermal valve, since the thermal valve worked fine before tuning. No error codes was picked up from the map sensor either. When warm, everything worked nice and smooth. It was all about tuning, but it took me two additional weeks to come up with a possible reason.

One possible solution would be to tighten the nut on the thermal valve rod, but it is preset from the factory and instructed not to be readjust. The alternative solution was to tighten all the starter valves at the same amount, which, for cold engine, would give the same exact effect as tightening the thermal valve nut (the starter valves are tightened in the opposite direction to the thermal valve nut on the same plate). For a warm engine it doesn't really matter, since a different mechanism holds the idle RPM.

I tightened all the starter valves 4 clicks, whatever displacement this may result in, and double-checked with Carbtune that the vacuum readings on all cylinders is the same. Now the bike works like new, cold starts, warm starts, runs smoothly, and all is synchronized.

My additional conclusion:
Starter valve #1 is indeed calibrated to a specific length and not arbitrary locked at some generic position. It either has to be calibrated with the extension of the thermal valve rod, or with the specific throttle body after the thermal valve is hooked to it. It may be that for this reason, starter valve #1 is not sold separately from the throttle body. Either way, with some patience, it can also be tuned.
 

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