fine tuning 40c

[Swawpy]

I have about 3 hrs on a fresh rebuild and am still tweaking here and there trying to get rid of an intermitant miss and fine tuning. Just curious how others adjust there carbs and looking for any guidlines and such. Mine seems to like quite a bit more timing so Im curious if others run advanced timing and how much? Also any favorite spark plugs, gaps, or other "secrets"? Thanks!

[Ray III]

When we put metallic core spark plug wires on the 420 it made a huge difference in how it runs. Also make sure you have the same spark plugs in each cylinder, sounds obvious but we found 2 different wires and 2 different plugs so no matter what you did one cylinder was out of tune.

[Swawpy]

Thanks Ray III- I do remember buying new wires that I believe were called copper core or something. I also replaced cap, rotor, points, cond, and plugs. It starts and runs/pushes well but Im getting hicups and a miss. Im guessing my timing and carb adjustments need a more well trained "ear". My valves are adjusted at .012 cold, very cold. When I adjusted it was about 10 degrees outside. There must be a difference between adjusting valves below freezing and doing it at say 75-80 degrees even though the eng is "cold" in both cases. Maybe they are tight? No, I guess that would increase the lash when the weather warmed. Anyway just thinking out loud probably makes no difference. Thanks for the input

[Tigerhaze]

If you have any question about the condition of the coil, I would replace it too. Many people think that coils either "work" or "don't", but I have found in the past coils that work but produce weaker spark.

Out of curiousity, there are aftermarket kits to convert older points distributors to electronic ignition through a module that goes within the distributor base. These kits recommend that the solid core spark plug wires not be used. Does anybody know why is that? I guess you would just substitute with larger diameter automotive-type plug wires?

[Swawpy]

Thanks Tigerhaze- the coil is about the only component that I have not changed. I hate to change parts just because, but I guess its worth a try. I think first I will drain the carb then drain the fuel tank into a clear jug to settle and check for water. I did rebuild the carb but I never flushed the tank (looked ok with a flashlight) maybe thats worth a try too!

[Tigerhaze]

Hey Swampy-

Water in fuel (at least in my experience) causes more problems than just an intermittent misfire; usually it makes the engine hard to start and very erractic idle. If there is just a bit of water, you could just add some ISOHEAT to the tank to treat it- if significant water you should be able to see it in the sediment bowl.

Rust in tank is also a possibility, but again in my experience that usually clogs filters and screens to the point of hard or no starting and very rough idle.

[Ray III]

My valves are adjusted at .012 cold, very cold. When I adjusted it was about 10 degrees outside. There must be a difference between adjusting valves below freezing and doing it at say 75-80 degrees even though the eng is "cold" in both cases. Maybe they are tight? No, I guess that would increase the lash when the weather warmed. Anyway just thinking out loud probably makes no difference. Thanks for the input

Engine parts only reach 150-200 degrees during operation, so 70 degrees is probably a significant temp difference. If the pressure of the valve on the seat is even just barely beginning to be relieved, it can do some pretty screwy things.

Also since you are running it in the cold, put some fresh gas in it. You know how the government likes to monkey with gasoline from season to season. Cars can tolerate the differences pretty well, but these crawler engines are only 7:1 compression and more sensitive to gasoline that is not volatile enough.

[Swawpy]

Sounds like Ill get this bug worked out one way or another with all this help. Out of curiosity... does anyone think that there would be a measurable difference in "hot" valve lash if say one machine was adjusted cold at say 10 degrees, and another machine from the South was adjusted cold at say 100 degrees? If both were run up to operating temp would there be enough difference to make a difference?

[Swawpy]

Sounds like Ill get this bug worked out one way or another with all this help. Out of curiosity... does anyone think that there would be a measurable difference in "hot" valve lash if say one machine was adjusted cold at say 10 degrees, and another machine from the South was adjusted cold at say 100 degrees? If both were run up to operating temp would there be enough difference to make a difference?

[Lu47Dan]

Swampy , I have been thinking about your question on valve lash , I don't think that I would change the dimension enough to hold a valve open. If there was a problem with it than the service manual would state 0.012 @ 60 degrees F. If you had a valve laying around you could measure the overall length at 100 degrees down to 0 degrees and see what happens . Dan

[Swawpy]

Well I had a chance to work it today and pushed about a 40 yd pile of clean dirt over and back again. Got up to only about 170 with the rad 2/3 covered with cardboard and this was pushing real hard with it for about 3 hrs. Anyway I believe a got my load needle set correctly at first it would smoke realy bad pushing, I got that cleaned up turning out and runs and sounds alot better. It smokes and runs rich at high idle (like backing) but cleans out when you push again? I tried a few timing adj and it still seems to run better everywhere advanced a bit. Then it started runly poorly and would barely run so I headed for the shop. I checked the plugs and they were very black, not a wet like plug foul , but almost heavy dry soot. These where ngk's and I think I will try the autolite 216's, but this was a bit discouraging. This is a fresh motor and was the first time it was really worked and broke in. I checked compression and found 135 and 130.

[CELSESSER]

Swampy,

It sounds like you are still running rich. Is the choke opening all the way? As I remember from the copy of the carb info I sent you(did you get it?) with the engine warm and choke open at slow idle adjust the slow idle needle untill she idles smoothly. (the starting piont is 2 turns off the seat). now go to the load needle (also has its starting point 2 turns off the seat) and at high idle under load keep adjusting leaner untill it starts loosing power or missfires and open slightly till it runs smoothly, then open it an additional 1/2 to 1 turn depending on the carb number.
Needless to say the load adjustments means a lot of getting on and off the machine, don't do it moving!( you would have to be a contortionist anyway)
You might check your float (or fuel level) setting, too high and this could be messing you up.

Chuck

[Swawpy]

Yes, I did get the carb manual- thank you very much. With new autolite 216 plugs and some more adj it is running well. It runs strong and clean for now, Id like to get a few hours on it and see. Now the gen stopped charging so the battle never ends. I tried to polarize and didnt take and thats where I left off. Thanks for all the helpful replies.

[Swawpy]

Another point to add is that it will only idle cleanly without missing a beat when the idle screw is within 1/2 turn "out" off its seat. But at high idle or under load it runs best and cleaner about 2 turns out. Load adjustment about 3 out. I sprayed starting fluid around all flanges and such trying to find an air leak and could not. Got temp up to 210 and and just could not find that happy medium between idling well and burning clean while working, so I adjusted where it will run strong and clean but has to have fast idle and still kind of lopes when idling. Seems to push very well here and burns clean but at idle seems to be lean, backfires, pops, and stumbles unless idled around 1000-1100. Carb is a TSX 641 which I think was offered on a 420 so if so it may be a bit much for a 40. Also It was just gone through with a new throttle shaft and carb kit. The felts to seal the throttle shaft kind of suck but thats what is offered, I think if anything I have a leak there. The autolite 216 plugs gave a big improvement and I set timing spot on @2025 according to manual to eliminate whether advanced a bit helped or not. Not sure what else to do but either live with it or go through the carb again....any ideas?

[Lavoy]

Idle jet really should not have any effect at high speed, only at idle.
Lavoy