Repair of Evap Control System-Solution to Rough Running at High Speed ( ST1100 )

[KoTAOW]

Repair of Evaporative Emission Control System
Causing Rough Running ST1100A at High Speeds

My ST1100 ABS model started running rough at higher speeds but it was an intermittent problem and didn’t always occur.

As time went on I tried running a couple of tanks of gas with Techron added and it didn’t change things. It felt like it was running on two cylinders when I got very much over 80 Mph. I could downshift and go full throttle and most of the time this would overcome the condition. Once it had, I could upshift and then resume speed. But it would reoccur at some point and time, never knew when.

But as time progressed, it got worse, even slower speeds 75 Mph or so. On the return trip from WeSToc I changed out fuel filter and plugs, but still had the problem. So just ran slower speeds. I was riding by myself and sometimes became concerned out in the desert in the middle of nowhere. It sure improved my prayer life anyway.

Upon return home talked to a friend of mine who lives close by and is a Honda factory trained mechanic. He thought it might be something simple like venting of the gas tank.

I checked the vent line and it was clear, then pulled the gas cap apart and found that it had a bunch of sticky fuel residue inside. Cleaned and reassembled and still had the problem.

I decided to disconnect the vent line at the gas cap. Did a test ride and the problem no longer existed. (Hey! I’m on to something!) Could reconnect and the problem would come back.

Dug into the Service Manual and studied up on the Evaporative Emission Control System, that was where the fuel tank vent went. Down to the charcoal canister and back to the carburetors.

Found that the Service Manual doesn’t tell how to troubleshoot the Evap. Emission Control System or even the valves in it. But the common service manual does as located for me by John Oosterhuis.

All the Service Manual says is how the system works: (quote from Service Manual)

Fuel vapor from the fuel tank and the carburetors is routed into the evaporative emission canister where it is absorbed and stored while the engine is stopped. When the engine is running and the evaporative emission purge control diaphragm valve is open, fuel vapor in the evaporative emission carburetor air vent control valve is open and air is drawn into the carburetor through the valve.”

Did find in the Common Service Manual (as pointed out by John O.) that the Evaporative Emission control valve vacuum is tested at: 250mm (9.8 in) of Hg. See pages 7-10 and 7-11.

In researching how to remove the Evap. Emission Control System I found a statement that that also gave me a clue. It said that the vents off the carbs that are vented to open air are needed in order for the carbs to work. Seems like if the carbs aren’t vented the diaphragms in them don’t operate (open/close) properly. The standard model of ST’s don’t  have the Evap. Emission Control System and are vented to open air at the front of the engine.

This led me to think that the two way valve, called the Evaporative Emission Carburetor Air Vent (Evap Cav) Control Valve possibly was defective, (Honda P/N: 17300-MT3-730) as the carburetors vent line runs through the valve.

I even had a wild idea that somehow the vacuum was going back through the canister and pulling a vacuum on the fuel tank and thus overcoming the fuel pump. (But I have since ruled that out)

I didn’t like the cost of a new valve from Honda. So was able to obtain a used one from Don Cortez (Calif).

Upon receipt of the valve I was able to compare mine to his replacement. When I applied vacuum to the intake of the valve I could hear a distinct click of the valve. When I did this on mine sometimes it clicked and sometimes it didn’t. Sometimes it was like it was just frozen up. This was how my bike was also reacting. So I had high hopes that replacement of the valve would solve the problem. I didn’t check the vacuum pressure to the specs as I didn’t have a vacuum pump. If and when I can locate one then I can test the old valve. I applied the “old mouth vacuum test”.

Final Solution and Cause:

After I replaced the defective valve and reconnected all the vacuum and vent lines the problem was gone. I have ridden it for two weeks now and no more problem. I think that the carbs were not operating due to lack of venting and I was suffering from fuel starvation. Again the “standard models won’t experience this unless they are a Calif. Model.” What was happening when I was downshifting and going full throttle when this occurred was actually generating more vacuum from the manifold and overcoming the stuck valve. Once the valve became unstuck then it allowed venting to the carburetors and them to operate again.


Here’s a picture of the location of the valve. It’s right behind the radiator cap and has four lines hooked up to it. It has white lettering UKL04. They are just a mfg. no. so don’t worry if yours is different. It is held in place by a rubber retainer. All of the ABS and Calif. Models use the same emission control valve per the parts lookup list.

NOTE:  Left click on below photos for larger resolution view.



The hose on top side that others are tied to, comes from the carbs and is the vent. . (In the case of a standard model this hose vents direct to open air at the front of the engine.)
The hose to the rear or left of this pic is the outlet side that vents to open air. The bottom hose is attached to the purge control valve. Even though it doesn’t show in this pic, the vacuum source hose, from manifold, is at the front of the valve towards the radiator and is the smallest line attached to the valve.

This is a picture of the valve removed from the bike. (see below)

The fitting at right is the vacuum line source that wasn’t visible in above photo.



I’m posting this to the Archive of Wisdom in hopes that it might save someone else in the future some head scratching and troubleshooting time. The common service manual says to check this valve if you have trouble restarting the engine. But in my case, when the valve malfunctioned the carbs couldn’t vent to open air. If they aren’t able to vent, then no gasoline is supplied to some or all of carbs. Didn’t really see this mentioned in the Service Manuals.

Don Grimes #1285
8/30/2008



John OoSTerhuis added the following info from the Honda ST1100 Service and Common Service Manuals. (click the images for large size copies)

NOTE:  Left click on below photos for larger resolution view.



This schematic is from the ST1100 Service Manual.

And also this info:

Here are the Honda Common Service Manual pages covering testing of their Evaporative Emissions Control Systems, including Purge Control Valves, Carburetor Air Vent Control Valves (Don Grimes' apparent failure part), and Pulse Secondary Air Supply Systems ("Air Suction Valve" {ASV} on the ST1100, which has the reed Check Valve built in).

The ST1100 Service Manual has the tests for the ST1100's Purge Control Valve and Secondary Air Supply (PAIR) Air Suction Valves (page 5-17 in mine, ©'92), but not the ones for the Carbuetor Air Vent Control Valve (see the 2nd and 3rd attachment below from the CSM for those).








The next/last two pages from the Honda Common Service Manual covering Honda's PAIR systems.

[KoTAOW]

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I have added the above photos as attachments for anyone wanting to copy and\or print them.