Pipe header colour puzzler !

[tomo]

Been out and about on the GS750 a few times since her tidy up and she runs ok touchwood. A few teething problems, had oil dripping out the airbox which had me worried there was blowby and oil going up the crankcase vent, but looked in the airbox and only a bit of oil at the very bottom, the top section where the vent comes in is bone dry. Think maybe I soaked the new filter too much and did`nt squeeze enough oil out . The new exhaust sounds good, but bit puzzled by the colouring. N0 1 & No 2 have that golden colour for the first 6" or so, but No 3 & No 4 have gone past that to a kind of mottled matt bluish colour. Thought it must be running lean on those two, so checked the plugs. Nos 1 & 2 are a nice mid brown/tan, so ok I think. Nos 3 & 4 I expected to be white, but are actually a dark brown, almost black, but not sooty like when over rich. Has me a bit puzzled, so thought I would see whether anyone has any thoughts on what is going on there.

[GregT]

Is the new pipe stainless or chrome ?

[tomo]

Its a Delkevic 4-1 stainless steel system.

[TxGSrider]

Mine are the same, and I know that my a/f is spot on thruout the rpm/throttle position range (except from about 5000-6500 or so, then it's rich...durn 4-1 header flat spot). The Delkevic uses a rather thin tubing which colors pretty quickly, and by nature of airflow the cylinders 2-3 will run hotter. Also, as a carbureted motor gets warmer it needs less fuel due to vaporization and air density. So it's possible your middle cylinders can be a little richer and a little warmer.

[Rob S.]

...about 5000-6500 or so, then it's rich...durn 4-1 header flat spot.

"Hmm..." I thought, "Maybe he's talking about a smaller cc bike." Because I don't recall any such flat spot. Then I see you're an 11EZ rider, just like I was. First with V&H "Street Megaphone" and stock airbox, then APE pods (and rejetting), then V&H "SS" exhaust.

Of course, curve got steeper at 6.5k, but by no means flat from 5 to 6.5k. I'll dig out Dyno printout later to verify that.

[tomo]

Think I could understand it if it were the inner downpipes, but it is one inner (3) and one outer (4) that are discolouring faster. I might be wrong with my numbering system, but when sat on the bike I number the cylinders working from the left as 1 to 4. I did wonder at first about timing, but that would`nt make sense with one coil serving 1 & 3 and the other 2 & 4. It is a bit puzzling.

[Rich82GS750TZ]

, but that would`nt make sense with one coil serving 1 & 3 and the other 2 & 4. It is a bit puzzling.

This statement is incorrect and may be part or your problem. You have correctly identified the cylinders as 1234 from left to right as you sit on the bike. However, One coil fires Plugs 1 & 4, the other coil fires plugs 2 & 3.

[tomo]

Rich, thanks for pointing that incorrect statement, don`t know where my brain was when I typed that !. As you rightly say, the LH coil fires 1 & 4, the RH 2 & 3. Thought after you pointed it out (even though the bike runs well and smooth, which it would`nt if it was wired up as I stated ) I had better check in case I had somehow cocked up the order when putting the bike back together, but no, the coils are connected up correctly. So still not sure what is going on with those headers. I did wonder whether a leak at the exhaust gaskets might be a possibility, but no sign of one, certainly no smoke from there or sooty marks. So still puzzled as ever !.

[gs11ezrydr]

If I understood...You said #1 and #2 cylinders the plugs look good #3 and #4 looked dark and a little sooty.I would check the Sync.of the carbs. Kinda sounds like it's running on the right 2 cylinders a little more at idle... Possibly...And your right #1 and #4 run cooler then #2 and #3..Most stock machines I have seen jet the inner 2 cylinders just a little different.. Blue pipes as far as I have seen is due to a rich condition,(unburned fuel igniting in the pipes)Over choking in cold conditions (Rich),Air leaks (Hot),or out of sync.(Not running in unison) At times ignition can factor in. Plug caps,timing,weak coils, ect... Also thin wall tubes on aftermarket pipes the inner #2 and #3 get hotter..There for discoloring sooner.