Spark plug colour

Hobot · Sep 18, 2014

Rather more on plug chop reading than covered-posted prior , If ya think a Honda expert could advise us on this.
http://honda-tech.com/forced-induction- ... *-3063102/

aceaceca · Sep 18, 2014

I am not too sure I like that fuel line routing going way below the carb inlet. Remember it is gravity feed. When you run low on fuel you may not have enough pressure to move the fuel into the carb bowl. You are also going to pull the high tension leads out of the coils with the routing you have on them below the ex cover cap nut. Have a close look at both plug leads to be sure the wire is connected well to each fitting and then into the coils.

toppy · Sep 18, 2014

aceaceca said:
I am not too sure I like that fuel line routing going way below the carb inlet. Remember it is gravity feed. When you run low on fuel you may not have enough pressure to move the fuel into the carb bowl. You are also going to pull the high tension leads out of the coils with the routing you have on them below the ex cover cap nut. Have a close look at both plug leads to be sure the wire is connected well to each fitting and then into the coils.

The fuel lines shouldn't be a problem as it is the head of fuel in the tank about that together with size of bore in line and taps etc. determines fuel follow. They are not excessively low or long and have nice gentle curves to prevent kinks that would restrict flow. I would however agree that that HT leads should not be touching the head (it looks like they are but may just be camera angle) as they may possibly rub through and short out in time. If they can't be rerouted some type of over braiding or sleeving would be a good idea.

dimitri · Sep 18, 2014

My single VM34 kit had gaskets (manifold to head) that would overlap in the middle. they did not seal very well. I cut a slight piece off each, and the plug colors became even.

Might be worth checking.

acotrel · Sep 18, 2014

I'd be thoroughly checking the ignition system first. If a valve seal passes oil the carbon deposits would usually be sticky. If you are using the carbon type plug leads that might be the cause. I strongly doubt that with only one carb, this is a jetting problem. Another thing which can affect combustion temperatures is the exhaust pipe. If you have one resonating well and the other clogged up with rubbish, however this is unlikely to happen with a well-maintained bike. I doubt it is a faulty plug - you would experience the motor missing, as you ride the bike. If the ignition timing moves it can easily give the same symptoms as a change in jetting.

kerinorton · Sep 18, 2014

aceaceca said:
I am not too sure I like that fuel line routing going way below the carb inlet. Remember it is gravity feed. When you run low on fuel you may not have enough pressure to move the fuel into the carb bowl. You are also going to pull the high tension leads out of the coils with the routing you have on them below the ex cover cap nut. Have a close look at both plug leads to be sure the wire is connected well to each fitting and then into the coils.

the syphon effect will cancel the above suggestion.

RoadScholar · Sep 18, 2014

What are the calibrated parts in your carb?

Main Jet:?
Idle jet: 25
Needle: ?
Needle jet:?
Air correction jet:?
Slide cutaway:?

I'm surprised that you get any off the line performance with a #25 idle jet, is your air trim screw tight on the seat?

Once we know what the jetting package looks like it will be easier to understand what should be going on inside your combustion chambers.

Bill.

Roadrash · Sep 18, 2014

Nice purchase Freefly103. Pretty bike.
From the picture it looks like there is no hose clamp on your crank breather hose. it's cheep insurance to keep a mess from happening.

freefly103 · Sep 23, 2014

After some more fiddling with the mikuni, the rhs plug colour is acceptable but the rhs is still fouled black.

I pulled the head today and found this:

Pistons and rings look good with not much carbon build up at all:

I also pulled the barrels. Barrels are in great condition. Cam followers look good with almost no discernible wear.

Seems I have a intake valve guide leak on the rhs of the head.

The head is now off to confirm if this is the case and if so, to have the guides sorted and head rebuilt.

Hobot · Sep 23, 2014

Might also ask forum about those heat isolating comma slotted pistons to trust any further. Might of saved your self some riding time with just hotter plug on the r side till something really required attending too. Of course that's a shade tree opinion not best practice, which is fix up completely then store in museum.

htown16 · Sep 23, 2014

I believe the short comma slots are okay for street riding, it's the ones with the long slots on the tail of the comma that go about quarter way round the piston crown that you have to look out for. Hard to tell from the picture which they are with oil rings in place

freefly103 · Sep 24, 2014

Thanks for the heads up on the pistons Hobot. Have ordered a new standard pair. Might as well replace these anyway since the barrells are off. Never thought about a hotter plug on the rhs. Head is on its way to Jim anyway to sort out, so when its back, I can ride it like I stole it. Its not a museum piece.

Hobot · Sep 24, 2014

Ugh - wimping out to send major complex stuff off to real experts don't build much machinist self respect but heck I just want to be a pilot anyway too. Here's quick low down I found on taboo type pistons. For about $350 more could have cylindder Bore Tech coated to last for a few pistons and ring sets they claim.

by JimC » Sun Jan 22, 2012 3:37 am
I bought some new Hepolite pistons off eBay a few years ago to replace the JRC pistons I was using. Unbeknownst to me, there are Hepolites with a large oil ring groove cutout. They will fail in a Commando 750. One let go in my Combat. In fact, they are referred to as flip tops. As for an 850, I don't know if any flip top Hepolites exist. All I can say is, all Hepolites are not suitable for a Commandos.

Postby ZFD » Sun Jan 22, 2012 2:04 pm
"Real" Hepolites were quite all right in Commandos- we used them for decades, until AE phased them out and Andover Norton had them made by GPM due to Hepolite stopping production. Again, no problems with GPMs, neither race, nor road.
The "dangerous" Hepolites were for 750s, and the downward slots on these are joined by a horizontal slot each side that runs behind a piston ring (easy to see looking into the piston). these are fit only as ashtrays, but they haven't been made since the early 1970s. If you get them they are still there, new, because the experienced dealers and owners declined to buy and use them!
Real Hepolites have "AE" cast in their piston skirt.

WZ507 · Sep 24, 2014

freefly - May we please see a picture of the tops of the pistons? Thank you.

john robert bould · Sep 24, 2014

I have not had a lot of joy with mikuni carbs, starting a vincent comet was a night mare...it felt like it was not rich enough ..SO i changed it to a amal. now with that lovely tickler! plenty of fuel dripping the Vin fires up first kick :lol: Proberly my settings whern't right with the Mikuni..after all theres about 30 start jets...Amal ONE! screw in or out...nice and easy. Not for a moment suggesting they are bad ..just a bit new for me and old iron.

freefly103 · Sep 24, 2014

Piston tops:

Spark plug colour

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