Rough engine poor gas mileage

[MerlF]

Had a 2006 ST1300A which ran so butter smooth, it was a pleasure to ride it. I upgraded and purchased a 2013 ST1300 with 19000km on it and it runs rough and I get pretty poor gas mileage compared to the 2006. Interestingly I find when the weather is really warm, 25° c and above, it runs way better.
Any thoughts anyone?

 

[ToddC]

Read up on cleaning your five way t under the gas tank.....
Just my two cents worth... ToddC

 

[TerryS]

Maybe the thermostat is stuck open (they often fail that way)? That would lead to cold running and the ECU will compensate by making the injection run richer. You can do a quick and dirty thermostat check by starting a cold engine and keeping a hand on the radiator. If the radiator stays cold for a few minutes, then suddenly gets too hot to touch, the thermostat is doing its thing. If the radiator slowly warms, the thermostat is stuck open.

 

[Art Franz]

Also, you should get a full three bars on your temp gauge before the rad changes temp, if all is working as it should.

 

[CYYJ]

Hi Merl:

I'm 99% sure that the problem is caused by either a blocked five-way tee in the midst of the throttle bodies, or a problem with synchronization of the idle airflow into the throttle bodies. There's a 1% chance the problem might be caused by failure of some other part, such as a bad spark plug or bad coil, but that is unlikely.

Here's a link to an article that explains how to synchronize throttle bodies: ST1300 - Throttle Body Synchronization Unfortunately, the photos that were embedded inline in that article are now all down at the bottom, which makes it a bit difficult to follow, but the information there is good.

You will need a manometer such as a Morgan Carbtune in order to synchronize the throttle bodies. I'm pretty sure someone in the lower mainland area or on the island will have one - just throw up a flare in the BC forum here asking for help. Failing that, I am sure that someone who will be coming to the WeSTOC Rally in Calgary in late June will have one - if you plan to go to that rally, post a request in that thread for someone to bring their manometer.

But, before you go to the trouble of balancing airflow into the 4 throttle bodies with the manometer, take the bike apart and clean the five-way tee with a pipe cleaner. There is a good chance that that action alone will solve your problem.

It's not easy to get to the five-way tee. You need to lift the upper fuel tank, remove the air filter, remove the snorkels, and remove the lower portion of the air filter housing. To get the snorkels off without stripping the screw heads, you need to have a JIS (Japanese Industrial Specification) screwdriver. The screws that you think are Phillips head are not Phillips, they are JIS, and if you use a Phillips screwdriver on them, chances are you will strip them. So, before you do anything, order a JIS screwdriver. They cost about $20.

Below is a picture that shows the five-way tee. It connects a bunch of vacuum hoses. This tee gets plugged up over time, and vacuum cannot flow freely and equalize between the hoses. This leads to rough idling. The tee is somewhat fragile - a new one costs about CAD $10 - it might be prudent for you to order a new one before you take the bike apart, just in case it breaks when you are pulling the hoses off. The part number is 17201-MCJ-003 . At the same time, you might want to order a roll (1 meter long) of bulk vacuum hose, in case the hoses that connect to the tee are plugged. You can clean the tee out with a pipe cleaner, but it is a SOB to try and clean hoses - it's a lot easier just to replace them. A roll of vacuum hose, part number 95005-35001-20M , costs about CAD $12. If you replace the hoses, cut the new hoses about 2 inches longer than the original ones - that allows them to sit up nicely in the middle of the throttle bodies, like you see in the picture below, and gives you easy access to the hoses when you do the throttle body synchronization.

Once the five-way tee is cleaned and the hoses are cleaned (or replaced), you can then do the throttle body synchronization. When that is done correctly, you will be able to balance a nickle on its edge on the gas tank filler cap when the engine is idling.

Regards,
Michael

Five-Way Tee with Vacuum Hoses

 

[T_C]

Maybe just some bad gas? Mine ran really rough and mileage dropped an hour after filling up at a little bitty gas station with old premium gas. A can of seafoam and two full tanks it all returned to normal.

Start with easy and work to harder solution is my opinion.

 

[Bikeric]

Check your air filter too - may be old and full of crud!

 

[SupraSabre]

If none of those remedies solve the issue, I would check the wax valve thing there at the throttlebodies.

When I bought my 2010, for the first year or so, it never ran right and if I stopped and within a few minutes to an hour later try to restart it, it would have a problem restarting!

After replacing that wax valve thing, it cleared up.

you can see it in the diagram above, between the fuel rails to the left, between the adjustments for the left side.

Good luck!

 

[David Ammons]

Wax valve thing ? Do you mean the MAP Sensor

 

[sennister]

Maybe just some bad gas? Mine ran really rough and mileage dropped an hour after filling up at a little bitty gas station with old premium gas. A can of seafoam and two full tanks it all returned to normal.

Start with easy and work to harder solution is my opinion.

This happened to me on a Iron Butt Ride. I got a tank of bad gas in Fargo ND and it was very painful and took several tanks of good gas before things got back to normal. The good news is on the way home from that trip I hit the best MPG numbers I had ever seen If I recall it was reading 62MPG. Normal numbers are in the low 40s. Considering I was riding heavy (lots of wet camping gear on the way home from Moonshine) and was running 89 octane I was shocked with the numbers.

Seafoam is one option. I use that for a fuel stabilizer in the winter but I have used Techron as well in the past. When on the trip I didn't stop to take time to find additives, I just kept dumping more good fuel in it and my range kept getting better and better.

 

[sennister]

Wax valve thing ? Do you mean the MAP Sensor

No it isn't the MAP sensor. There is a wax valve that when the engine is cold causes the bike to run in enrichment mode. This will consume more fuel. Think of it like a choke. When the engine warms up, the wax melts and the RPMs will drop. Kind of a neat way to do that if you ask me. At least that is my understanding of how it operates.

 

[MerlF]

Wow, thanks guys. Guess I'll start art the easiest solution and work my way through to the most difficult or until it runs right.

 

[mortenk]

No it isn't the MAP sensor. There is a wax valve that when the engine is cold causes the bike to run in enrichment mode. This will consume more fuel. Think of it like a choke. When the engine warms up, the wax melts and the RPMs will drop. Kind of a neat way to do that if you ask me. At least that is my understanding of how it operates.

My ST1300 commuter consumed a lot more fuel when running in enrichment mode. I tracked my mpg's for 5 years, and it was consistently lower during the winter where I had two cold starts every day. Initially I thought the winter/summer gasoline may have contributed, but I highly doubt that as I don't see this effect on my FJR1300 - I get pretty much the same mpg summer/winter on that. It should be noted that my ST would idle above 3,000 RPMs on very cold mornings - very annoying actually. My FJR may idle at 1,800 RPM for a very short time, but then return to 1,100

 

[sennister]

My ST1300 commuter consumed a lot more fuel when running in enrichment mode. I tracked my mpg's for 5 years, and it was consistently lower during the winter where I had two cold starts every day. Initially I thought the winter/summer gasoline may have contributed, but I highly doubt that as I don't see this effect on my FJR1300 - I get pretty much the same mpg summer/winter on that. It should be noted that my ST would idle above 3,000 RPMs on very cold mornings - very annoying actually. My FJR may idle at 1,800 RPM for a very short time, but then return to 1,100

Did you ever change out your thermostat? That is a symptom of a stuck T-Stat and not getting to 3 bars on colder days.

 

[Bikeric]

May also be worth checking your spark plugs.

 

[paulcb]

My ST1300 commuter consumed a lot more fuel when running in enrichment mode. I tracked my mpg's for 5 years, and it was consistently lower during the winter where I had two cold starts every day. Initially I thought the winter/summer gasoline may have contributed, but I highly doubt that as I don't see this effect on my FJR1300 - I get pretty much the same mpg summer/winter on that. It should be noted that my ST would idle above 3,000 RPMs on very cold mornings - very annoying actually. My FJR may idle at 1,800 RPM for a very short time, but then return to 1,100

On my ST1100, I tracked my mileage very closely for a few years, not so much now. I commute and tour on it. My enricher is manual, so it stays on about the same amount of time every day... for a few miles down the road. I definitely noticed a winter/summer difference (44.3 vs 47.3 mpg) and attribute the difference to winter/summer blends. My calculations only looked at commuting miles, so I suspect some of the difference is due to lighter traffic in the summer. From the Car and Driver link below... "Despite those higher prices, summer gasoline contains about 1.7 percent more energy than winter gasoline. Warmup times aside, that’s why you could measure reduced fuel economy outside the summer months."

A couple related links...
https://www.caranddriver.com/news/a15339380/the-vapor-rub-summer-versus-winter-gasoline-explained/
https://newsroom.aaa.com/2013/06/what-is-the-difference-between-summer-and-winter-blend-gasoline/

 

[mortenk]

Did you ever change out your thermostat? That is a symptom of a stuck T-Stat and not getting to 3 bars on colder days.

It always went to 3 bars and stayed there, so I'm pretty sure my thermostat was good. During winter it would obviously take a little longer to get there, but it would reach 3 bars after 10-15 min and be rock solid. I never saw 4 bars in my five years of riding it. I read that it's possible to adjust the "cold idle" but I never attempted it. I may have been able to reduce the cold morning starts to say 2,000 rather than 3-4,000 RPM - but I was always afraid that I would mess up the warm idle, which was always nice just below 1,000 RPM

 

[mortenk]

On my ST1100, I tracked my mileage very closely for a few years, not so much now. I commute and tour on it. My enricher is manual, so it stays on about the same amount of time every day... for a few miles down the road. I definitely noticed a winter/summer difference (44.3 vs 47.3 mpg) and attribute the difference to winter/summer blends. My calculations only looked at commuting miles, so I suspect some of the difference is due to lighter traffic in the summer. From the Car and Driver link below... "Despite those higher prices, summer gasoline contains about 1.7 percent more energy than winter gasoline. Warmup times aside, that’s why you could measure reduced fuel economy outside the summer months."

A couple related links...
https://www.caranddriver.com/news/a15339380/the-vapor-rub-summer-versus-winter-gasoline-explained/
https://newsroom.aaa.com/2013/06/what-is-the-difference-between-summer-and-winter-blend-gasoline/

1.7% difference in energy is below my level of uncertainty. Small differences in riding style on a few identical commuting days can easily give you an MPG difference in that range. I am talking about a much more substantial difference that I observed during my 5 years of riding it. In January and February (typically the coldest months in Seattle) I would get around 38 mpg. In July and August I would get 43 mpg. So, I basically got 13% better fuel efficiency during warm weather. I'm not totally surprised as it was easy to spot: in the summer when I hit the first red light half a mile down the road, the engine would already be fairly warm and idling just above 1,000 RPM. In the winter I would be embarrassed as the engine idled above 3,000 RPM - sometimes almost 4,000 on very cold days (below freezing). My old ST1100 had a manual choke (as you also point out), which allowed me to control this much better

 

[fnmag]

oh, I forgot to add that my current mpg is a verified 52mpg.. I picked up 10 mpg!!!!!

Excellent mileage!

 

[mortenk]

oh, I forgot to add that my current mpg is a verified 52mpg.. I picked up 10 mpg!!!!!

Wow! At what speed(s)?