Poor running 2003 ST 1300, can’t resolve need help

Joined
Jun 9, 2025
Messages
3
Age
75
Location
Woodstock, ON
Bike
ST 1300
Purchased a 2003 last year after quitting bikes 3 years ago with 30km and put on about 4-5k.

During that time have not been able to nail down the problem. Bike runs ruff when accelerating, does not want to rev freely or smoothly. Engine noisy under load and takes time to get up to rpm, struggling.

Brakes are fine, went over them. Clutch is fine not slipping, adjusted balance shafts with engine running, checked hoses and T splitter which is new in 2022. That year the fellow I got the bike from spent $4000.00 at shop and they went over everything since the bike has been sitting idle. They even took the swing arm off to replace clutch cyl. He damaged his left knee and quit riding 2 years ago. Bike has been owned by seniors since new and has not been abused. That’s the history I know.

This spring I striped the bike down. Bled the brakes properly, checked coils primary – secondary, crank sensor, plugs, etc. All in spec and put it back together. Did not check 02 sensors till this weekend. Left side under the seat there is a 2 pin plug “black white wires” where I get no reading. On the right side similar plug reads around .4-5 ohms. Have not been able to find 02 sensor related problems on the site so asking for guidance. From what I understand that plug supplies 12V to speed up heating of sensor during cold starts for emission reasons. Don’t know exactly where the 4 pin plug for the sensor is located to check the other 2 wires. Correct me if I’m misunderstanding how the sensor works. I also notice at the end of handlebar a very slight what seems like a misfire which was confirmed by a friend of mine the morning. Would a bad 02 sensor cause all the problems. Rode gmtech94’s 2004 bike last year for comparison and what a difference. Smooth, pulls strong and feels like a different animal.


Image of plug. When I puled the wire from underneath the frame rail there was a note wrapped reading “preventing measure” that I assume was placed by the shop that worked on it last.Plug.jpg
I’ve hit a dead wall with this bike and could use all the help I can get.
 
I would start with checking that each cylinder is getting spark and fuel. Have you pulled all the plugs? Post pictures of each one, and note which cylinder they came from.

Is the FI indicator blinking at all? If so note the code that it's displaying.

I would also check the air cleaner and housing to make sure a squirrel or something didn't turn it into a living room.
 
O2 should not cause a running issue, if the ecm doesn't see a signal it should go to a default setting. While idling pull the plug wires off one at a time and make sure each cylinder is firing. Lack of power sounds like a dead cylinder to me.
 
Pull each spark plug cap off clip the plug wires back and screw the caps back on the wires. Could also be a bad plug cap. If the spark plugs were changed check and make sure you did not install counterfeit spark plugs. This has been a big problem lately.
 
Check that your spark plugs leads are routed correctly. I once saw an ST1300 with the #1 and #3 leads backwards and it actually ran pretty good.
Also maybe run it with out the mufflers, maybe one of the cats burned up from a misfire and exhaust can't get through. Good luck.
Has the compression been checked?
 
Had the plugs out several times and all seem to be burning the same. They are original NGK.

Fuel pump is working fine and was out in 2022. I’m pretty sure its not the problem. Not many miles since it was gone over.

New air filter last year, there were mice in there. Had it of recently and its perfectly clean in there.

Checked underneath for any problems with wiring and hoses throttle bodies, ail fine. I did not pull the injectors out to clean them thinking a lot of riding might do the job if they were partially clogged. Maybe I should of done it while in there.

Plug wires are in order and are marked so as not to mix them up. Swapped 1 and 3 just to see how it ran and it ran bad. I did try pulling one at time on 1 and 3 and again ran badly. Have not had the plug caps off so will try, but when I tested the coils through the plug wire it read properly.

Did compression test last year and all 4 were fairly even. There are no lights, codes other than the fuel light at startup for a few seconds.Plugs1-3.jpgPlugs2-4.jpgThrotleBody.jpg
 
Had the plugs out several times and all seem to be burning the same. They are original NGK.

Fuel pump is working fine and was out in 2022. I’m pretty sure its not the problem. Not many miles since it was gone over.

New air filter last year, there were mice in there. Had it of recently and its perfectly clean in there.

Checked underneath for any problems with wiring and hoses throttle bodies, ail fine. I did not pull the injectors out to clean them thinking a lot of riding might do the job if they were partially clogged. Maybe I should of done it while in there.

Plug wires are in order and are marked so as not to mix them up. Swapped 1 and 3 just to see how it ran and it ran bad. I did try pulling one at time on 1 and 3 and again ran badly. Have not had the plug caps off so will try, but when I tested the coils through the plug wire it read properly.

Did compression test last year and all 4 were fairly even. There are no lights, codes other than the fuel light at startup for a few seconds.Plugs1-3.jpgPlugs2-4.jpgThrotleBody.jpg
Did you replace the fuel pump with new or just clean the filter. I had the same issue with my ST1300 and it was the fuel pump going bad once heated up a bit. Checked good on the bench.
 
Those spark plugs' gaps do not look like 0.031- 0.035"- the shop manual's spec. They look more like 0.050" to me.
 
Fuel pump is working fine and was out in 2022. I’m pretty sure its not the problem. Not many miles since it was gone over.



Plug wires are in order and are marked so as not to mix them up. Swapped 1 and 3 just to see how it ran and it ran bad. I did try pulling one at time on 1 and 3 and again ran badly. Have not had the plug caps off so will try, but when I tested the coils through the plug wire it read properly.
So did you pull the spark plug wires on 2 & 4 ? What's the fuel pressure? If you don't know that how do you know the pump is good? Also it sounds as if this bike never ran properly from the day you bought it, correct?
 
Last edited:
Back
Top Bottom