NGK plug # are reverse from others. 6 would be colder. Looks lean to me. White insulator should be gray/tan. Plug reading should be done after full throttle blast and immediate shut down. Should be a little color band on ground strap. Location of that is important. HowTo - Kuidas: Spark Plug Reading
Here's some pictures of the ur5 plugs i took out. Only # 4 cylinder plug looks different. Last pic w inspection camera still shows a ton of carbon buildup still on #4 piston top.
use a squirt bottle of water and shoot it down the carb while keeping the rpm at about 1000 or so and this will help clean out that crap off the piston. you didn't have to get crazy just keep squirting it in and see if this makes things run better. or just go out and give it a good 2nd gear thrashing to the top end of the gear smash it into 3rd and go to about a 100 mph then let it settle down and drive normal for the night. Looks like 5 gal of race gas wouldn't hurt either, would at least keep the engine from destroying itself if that is what is going on That plug does look hot and the timing mark is all the way around the J strap better back it down a couple degrees. That plug reading chart above is a good read. Looks like a couple readings there. Ever look at a piston after the head gasket blows it is nice and clean lol.
Passing water through the carb was taught to me by an old timer a long time ago. I was 14 just starting working for my godfather after school thought he was nuts. Lol
you can learn a lot from the geezer.. So that means you young boys need to step up to the plate and put this 350 on the map like in track time dyno time and just plain spinning it in 3rd gear till it runs out of motor.....just to see if it can hold up. I passed, what say you all he he lol lol
Update: I used a bottle of seafoam down the carb 3 weeks ago after I changed the valve seals and just before I changed the oil. I believe it helped clean out buildup a bit. Yesterday I misted/squirted about a cup of water down the carb with engine warm at about 1500 rpms then drove 75 miles. The worst piston (#4) has a couple clean spots on it now. Before and after pictures attached. Spark plug in #4 is still a bit dark and a bit of oil on those threads. I'm thinking that its rings are possibly still not fully or unseating seated. Possibly a hair too advanced. Running 20% race gas w premium for now. 3rd picture is #2 piston. They seem to be getting cleaner. Maybe water again? Maybe a professional paint gun slowly misting water down the carb? Or maybe not. She runs REALLY good now with the freshened carb!
The #4 plug is hotter than the other plugs? Remember the NGK plug numbers are opposite from the others. Smaller numbers are hotter, larger colder.
Use the misting type seafoam into the carb while its running, till the bottle is empty. Then shut off the engine immediately and leave it to soak overnight, that oil and carbon is stuck on there good but this will help. Then drive it hard the following day.
Yes VERY oily and/or LOTS of carbon. That is how all the pistons looked with bad seals when it was burning a quart every 200mi! They are slowly getting cleaner. Maybe 175 miles on the new valve seals so far. Down a few ounces of oil only so far. I put a ur5 in #4 now.
I think that is a great idea but I'm not sure of leaving the oil unchanged for very long after that. It's seems like a whole can down the carb would contaminate the oil a fair amount. I probably only have 200mi on this oil so far.
I use a plastic squirt bottle comes out in a stream and use the rpm to keep it up 1500 good just give less water when it bogs down too much. I would change the oil all this junk can contaminate the oil plus it is still kinda burning so gas is getting in too. Change after this second round then drive for a while and leave it alone at that time give it 500 miles to settle down. Get on it some in second gear put it in 3rd and wind up a little try to get to 3/4 throttle to give this pistons a good push. don't have to floor it just a good push in 2nd and 3rd gear then go back to cruising for the hour then maybe do it again, it will come to ya give it time.
The sea foam is safe to put right into the oil to help clean the oil covered surfaces no worries there. Still change the oil after trying to burn out the carbon.
