Help Please - ST1300 #2 & #3 plugs carbon fouled, #1, #4 Normal

So - the bike started running a little rough at lower rpms about 3 wks ago. Then the idle speed started dropping a bit and got rougher.

Prepping bike last Thursday to go to an Advanced Rider Training Course in UT last weekend. Pulled plugs and discovered #2 (right front) and #3 (left rear) plugs substantially carbon fouled. #1 and #4 looked pretty normal. There were NGK "7" heat range plugs installed (1 step hotter range than OEM), and the specs call for an "8". I put the OEM 8 plugs back in. The new plugs smoothed the idle and brought speed back up to former setting. Bike seemed to run fine at the class (about 70% pretty aggressive track riding). Have not had time to pull plugs to see how they look.

I've given it some though, and cannot come up with any commonalities between #2 & #3, that would also be isolated from #1 & #4. I have not studied the induction system that thoroughly, so could be missing something - need to get into the manual I guess.

Fuel economy seems pretty consistent with what others have suggested for predominantly around town riding.

Anyone have any ideas - vacuum hose leak, stuck valve, etc....?

Thanks in advance for any thoughts you might have.

Randy

When is the last time you changed the air filter? If the air filter is clean, then check the 5 way vacuum tee connected to the throttle bodies... it is known to become clogged and can have an effect on the throttle bodies performance.

You may also want to put some type of fuel injector cleaner in the fuel tank like SeaFoam or something to combat the ethanol problems that today's fuel causes.

From the NGK site:

"5. Heat Range selection
Let's make this really simple: when you need your engine to run a little cooler, run a colder plug. When you need your engine to run a little hotter, run a hotter spark plug. However, NGK strongly cautions people that going to a hotter spark plug can sometimes mask a serious symptom of another problem that can lead to engine damage. Be very careful with heat ranges. Seek professional guidance if you are unsure.

With modified engines (those engines that have increased their compression) more heat is a by-product of the added power that normally comes with increased compression. In short, select one heat range colder for every 75-100 hp you add, or when you significantly raise compression. Also remember to retard the timing a little and to increase fuel enrichment and octane. These tips are critical when adding forced induction (turbos, superchargers or nitrous kits), and failure to address ALL of these areas
will virtually guarantee engine damage.

An engine that has poor oil control can sometimes mask the symptom temporarily by running a slightly hotter spark plug. While this is a "Band-Aid" approach, it is one of the only examples of when and why one would select
a hotter spark plug."

Had similar running problems. Changes #3 HT plug and HT lead which is much more kinked than the other three. Slight improvement but still a little lumpy on cold start. Decided to renew all vacuum pipes together with 3 way and 5 way connector. The 5 way was blocked. Problem sorted.
Watch those screws that hold the air filter pan against the throttle bodies. I had to take an impact driver to get #4 out which are damaged and will need to be replaced next time I am doing a filter change.

Thanks for the feedback. I know all about sparkplug heat ranges - used to build race engines (automotive). That was just a point of information.

The plug heat range has zero to do with engine coolant temperature. The plug heat range has to do with the rate of heat transfer from the center electrode/insulator out to the plug body where heat is extracted out to the cylinder head. If you have higher combustion chamber temperatures, you need to run a colder plug. And yes, if you have oil issues (rings or valve guides/seals) a hotter plug can help reduce the rate of oil/carbon fouling.

I am seeing zero oil consumption, and this did not have the appearance of typical oil fouling. I am pretty certain it was an over-rich fuel mixture condition.

Air filter was new last fall. I did buy new vacuum tees along with other stuff last fall, but haven't had the air box off the top of the TBs yet.

I do not run ethanol-containing gasoline. Non-ethanol premium only. I did add the appropriate amount of Seafoam to the tank at following fill-up just in case there were partially clogged injector nozzles somewhere.

Haven't pursued new plug wires, but I need to replace the boot on #4 as the PO/his mechanic had torn the edge of the rubber cover flange taking the plastic cover off the cam cover - probably for oil change.

I'm not sure if that 5-way tee is likely to be clogged at 25k miles and 5 yrs old, but will get in there and check/replace it and a anything else that looks suspicious. I'll probably go ahead and put in the spring-loaded hose clamps to prevent the potential cold leak problem.

I need to get in there to adjust the lower adjuster on the throttle cables anyway, as I am out of adjustment on the top end and there is still too much freeplay in the throttle.

Thanks for all the advice. I'll let you know what I find when i get in there to check it out.

+1 on the correct explanation of spark plug heat range and heat dissipation.

RandyIdaho said:

The plug heat range has zero to do with engine coolant temperature. The plug heat range has to do with the rate of heat transfer from the center electrode/insulator out to the plug body where heat is extracted out to the cylinder head. If you have higher combustion chamber temperatures, you need to run a colder plug. And yes, if you have oil issues (rings or valve guides/seals) a hotter plug can help reduce the rate of oil/carbon fouling.

Click to expand...

RandyIdaho said:

25k miles and 5 yrs old

Click to expand...

Have you done a valve clearance check yet?

The valve clearance service interval according to the Honda Service Manual is 16,000 miles.

On the ST1300 I have completed 5 of them, 3 of them on my motorcycle. Each of the checks on my bike required at least one shim change. The last shim change was an intake valve that had too much clearance. Wondering if the clearances are off on some of your intakes.

Other things I can think of:

- spark plug wires or connectors not passing the spark 100% of the time on #2 and #3.

- fuel injectors in #2 and #3 not shutting off quickly enough (unlikely but possible). Maybe previous owner used gasoline with ethanol?

What is the current miles on the odometer?
How long have you owned the bike?

My 07 has 16000 miles. Bought it a year ago with 9000. Around 11000 it started idling rough and throttle tip in was not smooth. I raised the tank, removed the air plenum and stacks, cleaned the starter valves (air screws) which appear to have a dual purpose on this engine. They provide idle air adjustment for each cylinder at idle but because they are movable and hooked to a common thermal wax valve they provide fast idle during cold start and warmup. I synched the starter valve adjusters using an air flow meter. Some use a Manometer type. It is unlikely the throttle body main butterfly linkage would be off but not impossible. This Imbalance could cause a a spark plug color difference if you are doing light driving. Plug read should be taken after a hard run and shut of clean. Heard issues with clogged vacuum lines too but haven't experienced it myself. I have expert knowledge of many engines but IGOFAR is the go to guy for experience on the ST1300. There are several threads here about syncing the starter valves.

Couplers,

25000, owned since last August (21000, bought from original owner).

I have to get in under the airbox to adjust the lower end of the throttle cables (no more adjustment at the top end). I have a 4-cyl manometer. I will check that air valve sync. This is no minor color difference, this was "normal" color on 1 and 4, and wet carbon fouled on 2 & 3. I doubt the air valves are that far out of sync to do that, but will check when I get in there. I haven't pulled the plugs yet since changing them, but will do that when I pull the airbox and so on.

A former Honda shop tech (now independent shop owner, with well over 20 yrs Honda MC service experience) I deal with has checked a number of STs, and according to him has yet to find one at under 30000 miles with any clearances out of tolerance. His advice was to leave it for another 5k-10k, and check then. Maybe just happenstance on his experience, since it seems common to have a few out of tolerance a small amount at 16k based on what I have read. I will get to checking that, probably next winter unless this plug fouling is not corrected through the other adjustments. He has offered me his shim assortment to adjust if needed when I get around to it.

Thanks for your detailed response, and I will contact IGoFar and see if he has anything else to add.

Randy

Very odd to have rear cylinder on one bank and front cylinder on the other bank having this issue. I would have some other ideas if it were one bank or the other. For sure I would run some carbon cleaner seafoam or techron for a tank or two and retest if you havent already tried that.

RandyIdaho said:

A former Honda shop tech (now independent shop owner, with well over 20 yrs Honda MC service experience) I deal with has checked a number of STs, and according to him has yet to find one at under 30000 miles with any clearances out of tolerance. His advice was to leave it for another 5k-10k, and check then. Maybe just happenstance on his experience, since it seems common to have a few out of tolerance a small amount at 16k based on what I have read. I will get to checking that, probably next winter unless this plug fouling is not corrected through the other adjustments. He has offered me his shim assortment to adjust if needed when I get around to it.

Click to expand...

Always good to make sure motorcycle is serviced according to the Service Manual specifications before looking for problems. My motorcycle required a shim change at 16,000 miles and two shim changes at 32,000 miles.

Another thought. Spit balling here. Some here have had the Insulator bands between the throttle body and engine come loose. This may pull some extra air into the cylinders signaling the ECM to run rich. Since O2 sensors are on each bank I might check to see if the Insulator bands on cylinders 1&4 (the normal looking cylinders) are loose. I believe these are hose clamps that need tightening with a screwdriver. Should be fairly simple to check.

Many thanks for the insight.

However the O2 sensors are paired for #1 & #3, the other for #2 & #4. The leaky TB couplers (could be any one or multiple of them) and/or 5-way connector partial blockage seem like promising approaches.

The idle has been a bit uneven and sometimes fluctuates within 900-1200 rpm range (this is after up to operating temperature (3 bars) so should not be involving the cold start air valve system (unless there is some failure - but I think there is only one temperature sensor capsule that connects to common linkage??).

~~~~
Not been a particularly good few weeks for me. Bike in garage with front end off to replace faulty RaceTech suspension parts that I installed last month.

Improperly de-burred adjustable damping and preload caps - factory assembled - cut the sealing O-rings. 5 minutes into the track training course, and I was getting fork oil sprayed onto my visor. Not exactly good use of an advanced track riding training class, having to frequently try to wipe oil off the visor at 80+ mph - rather distracting...

Now fighting a problem with one of the damper retaining bolts. Installed with thread locker and new copper seal washer in accord with RT printed instructions, and their provided thread locker compound (didn't feel good about it so called, and got confirmation via phone to proceed and use it). The lower valve in one fork is now spinning inside the damper tube, about ?-turn loosened.

Have suggestions from a more experienced guy at RT (Terry) on how to resolve. Heat bolt head with MAPP gas torch to break down the thread locker. He is sending new o-rings, since it could get hot enough to degrade the valve-tube sealing o-ring. That's later this week.

Since MiSTerioso is currently down and out, might as well look into the valve clearance check, airbox, throttle body connector sleeves, 5-way connector, etc., etc. and hopefully get it all sorted out so I can get some riding in before Thanksgiving (normal time of first snowfall).

Standing by the white courtesy phone if needed :call: