Topic: Dry black deposts on spark plug... help

[ramstsk]

This is my first real post, I have been lurking around for awhile now. So here is my question....The bike is a K4 750, it starts up fine with a couple of kicks but at idle and low reving all 4 pipes are blowing smoke light in color. I used the search feature and it points out that i might be running rich. New plugs are comming out black and dry. I pulled the carbs, and jets are 120 and 40 on all four, and a/f screw at 1 turn out. PO had the bike sitting for about 10 years until I started it just recently. New oil and filter. Valves are set. I changed the oil twice first was after initial start of about 10 min and oil came out runny dark black. Second change was after about 20 minutes at idle and very low reving and a few restarts to check plugs. During kick starts... the bike feels like it has good compression. BTW PO said he couldnt get it started when he aquired from his brother and law. It turned out to be that the spark plug caps were loose.

Thanks in advance

[ramstsk]

forgot to mention that the oil after the second change came out pretty much clean

[Gordon]

If all the engine is doing is idling, I'd expect the plugs to come out sooty.  A plug chop at speed will give you a better idea of the fuel mixture.

Did you change the air filter, too?   

[Spanner 1]

Plugs will always be black and sooty looking with the bike only being run @ idle and light revving in the garage. The test must be a decent ,say, 1 hour ride at different speeds.... bet when you get back there is no more smoke and plugs are a tan color...!!

[ramstsk]

I really would like to take it for a ride.... but im really worried about fogging everybody behind me.....Plus I live in california smog police capital of the world!!! haha. I guess I could take it out for a spin at night.

[ramstsk]

Would this stop the motor from blowing smoke?

[domer]

if it sat outside for 10 years, god only knows what could have settled in the pipes and could be causing your light smoke...  plug chop for sure!!!

[HondaMan]

Like Gordon said: air filter first, after that long sleep in a garage.

That year of 750 at sea level should have 105 mainjets, not 120. The 120 was only found in  the K0 with the open pipes known as "HM300" pipes: by 1970 the K0 had 115 and all K1 had 115 jets. Someone was apparently thinking they could hotrod the engine by just increasing jet size...that will make for smoke, soot, and eventually water buildup and rust in the pipes.

Check: the emulsifier tubes' air bleed port in each carb after that long of a sojourn (look in the Thoughts of Hondaman were Steve D posted my fix for those passages). They are probably partially blocked with a white powdery substance that needs to be removed with a wire: soaking and carb spray simply will not fix it.

Check: needle settings on the carbs. If the PO decided "richer is better" for the mainjets, the needles may be set wrong, too. The clips should be on the 4th groove from the top of the needle, each carb, with 105 jets. They would have to be lower than is physically possible if someone tried to use 120 jets in those carbs...

Check: when you have the needles out to see their clips, make sure there is a tiny "27201" engraved on the needles, every one. If not, they are not Honda needles, but Keyster. Those will be constant trouble, if so, running rich and fouling plugs: the only fix is to replace them with Honda needles. There's dozens of posts here about that issue... 

Try using different sprakplugs: the ND X24ES-U will stay much cleaner in those engines. Sparkplugs.com sells them. 

Check your ignition timing and points gap. If the gap is less than 0.012", the spark will be weak at low engine speeds. If the timing is overly advanced, it will foul plugs at low engine speeds. Also, trying running on only Regular gas: today's Regular meets the slow-burn characteristics of the 1973-1978 premium grade fuels. Regular will generate a little more heat and help burn off the carbon.

[ekpent]

All of my K1's I have had 120's. I think the K0-K1 had 120's,72 and 73 110's and 74 and later 105's. Just bought my 3rd this week but to coooold to dig into it.

[HondaMan]

All of my K1's I have had 120's. I think the K0-K1 had 120's,72 and 73 110's and 74 and later 105's. Just bought my 3rd this week but to coooold to dig into it.

I hear you about the coooold: I've had a '75 F1 apart on the patio for over a month, working on a simple tranny problem: can't touch the gears! 

It was an exceedingly popular mod to change the K1's 115 jet, with the needle in the 4th position, to 120 with the needle in the 3rd position, because it noticeably increased the midrange torque (while also noticeably increasing the plug fouling tendencies!). This was born of the K0 and K1 guys exchanging notes, because the K0 could whip the K1: at the dragstrip these two models were almost a half second apart. I heard so much arguing (over beer) about the jetting being the whole Honda "problem" that I started measuring and recording every 750 I touched from those days (summer, 1970) forward, hence my pile of notes. It turned out to be that Honda was reducing cam dwell and lift to reduce warranty costs, and the reduction in jetting was their move toward reducing plug fouling. So, some riders were partly right: the 120 jet would increase the power somewhat.

In stoplight racing, the 120 jet was king: in daily riders and touring bikes the 115 reigned. Many rider went to the Dyna "green" (3 ohm) coils to control the fouling a little better with the bigger jets, unknowingly giving up power above 6500 RPM in the process, though. I, too, have seen a lot of K1 bikes over the years with 120, even 125 jets (from low-altitude areas), but they came out of the crates with 115 only, starting in June of 1970 when I started this 'vendetta', on every one I personally assembled at the shops. If the pipes got switched (over the years) to the HM341 type, these jets will foul the plugs in 100 miles! 

You are SO fortunate to find K1 bikes! I'd love to. Out here in the West, they were ridden to death and most are gone. There are a lot more K3 and later versions out here than the earlier ones. I 'convert' them to K1 when rebuilding, to recover the lost power in the later engines, and the riders really like the results. Heck, by the time of the K4, we measured 41-45 HP on the rear wheel, which was more than 60 HP on the K1. The HM341 pipes "cost" about 3 HP at 7500 RPM compared to the HM300 pipes, but boosted the (touring) midrange torque at 5000 RPM almost 10% because of the backpressure. The HM341 allows leaner jets and cleaner plugs, too.

[ekpent]

Good info Hondaman. Yes, here in the midwest we are lucky to have so many old Honda 750's around. Thanks to the harsh winters they just get put away for very long periods,kind of forgotten about as the older guys who owned them move on to different toys.  PS-Congrats and look forward to your book 

[ramstsk]

I hear you guys about the cold.....it like 68 degrees here in San Diego

Thanks for all the replys..  as of now I was starting the bike with out filters , PO had some rotted foam pods on there. I took those off and gave the carbs a cleaning. But I didnt check those passages too closely. The bike was pretty much a basket case...Wires were a mess , for example the fuse box was missing and the PO hard wired everything together, Some wires had melted. I Fixed all of that stuff, and all the electronics work good with the exception with starter. Im guessing that thing is fried. The solenoid clicks but the starter doesnt spin..... I will address this in a later thread.

[HondaMan]

I hear you guys about the cold.....it like 68 degrees here in San Diego

Thanks for all the replys..  as of now I was starting the bike with out filters , PO had some rotted foam pods on there. I took those off and gave the carbs a cleaning. But I didnt check those passages too closely. The bike was pretty much a basket case...Wires were a mess , for example the fuse box was missing and the PO hard wired everything together, Some wires had melted. I Fixed all of that stuff, and all the electronics work good with the exception with starter. Im guessing that thing is fried. The solenoid clicks but the starter doesnt spin..... I will address this in a later thread.

It's not unusual for those solenoids to have a burnt spot on the copper bar and bolt contacts inside. This causes the voltage to drop too much for the starter to turn as the result. Try taking it apart and see if cleaning up those contacts help before going after the starter itself. I think I've only seen 2 bad 750 starters in 40 years. 

[ramstsk]

Well I tried to lay a screwdriver across the terminals and still got nothing but sparks. Would I be able to take the wire from + wire from the starter and place it dirrectly to the batt. or would this be a bad thing? I will be on the look out for jets this weekend.
I will post pics of my project soon

Thanks again for all the replies!!!!!!