G1 lean plug reading

[dezrcr822]

Originally Posted by mikeasis

Is this the pilot (mixture) screw? How should I proceed with adjustment, 1/4 turn at a time?

What you are pointing at with the pencil is the pilot jet. The screw with the spring below that is the pilot adjusting screw and should be 1-3/8 turn out from lightly seated. Turn adjuster screw in until just lightly seated, dont go any tighter or you can damage the tip. Also a good idea to count the number of turns in it takes for it to seat just for reference. Then turn it out to 1-3/8 turns out. You should get the engine up to operating temp and then fine tune the adjuster screw. The other screw with the spring above the pilot jet is the idle adjust screw. And yes 1/4 turn or less at a time for adjusting the pilot screw.

[mikeasis]

Originally Posted by dezrcr822

What you are pointing at with the pencil is the pilot jet. The screw with the spring below that is the pilot adjusting screw and should be 1-3/8 turn out from lightly seated. Turn adjuster screw in until just lightly seated, dont go any tighter or you can damage the tip. Also a good idea to count the number of turns in it takes for it to seat just for reference. Then turn it out to 1-3/8 turns out. You should get the engine up to operating temp and then fine tune the adjuster screw. The other screw with the spring above the pilot jet is the idle adjust screw. And yes 1/4 turn or less at a time for adjusting the pilot screw.

I was tinkering with it today. I had exactly 1/4 turn before the screw bottomed out, so I figured I shouldn't even mess with trying to setup from there and after I pulled the intake hose off the carb and noticed while pulling on it that there was cracking in the intake boot on the head side. I don't know if they go all the way through but I ordered a new J17 intake boot and gaskets so ill let you know how it goes after the parts arrive.

[mikeasis]

Originally Posted by dezrcr822

It does look lean. Here are a few shots of my plug. Note it is a NGK BP5HS and I see you are running a 6. Im running on my J17 a J10 carb and exhaust with jets from a Mokini chinese J10 knock off carb which are smaller than the J10 but bigger than the J17 jets which I think richens it up to tune for the carb and exhaust. I run Yamlube 2R premix mixed at 80:1 with 92 pump gas. I just really got my crate running and I am stoked as it runs great, pulls nice to redline and I surpassed my goal of 20mph with this setup.

what pilot jet # are you using? one of my j24 jets is a 32.5 and my other has a 42.5 and my mokuni has a 38.8. Its weird because looking at the bottom of the 32.5 pilot there doesn't appear to be a hole in it like the others. I may try the 38.8 mokuni jet but ill wait till I get my intake boot and gaskets.

[dezrcr822]

Originally Posted by mikeasis

I was tinkering with it today. I had exactly 1/4 turn before the screw bottomed out, so I figured I shouldn't even mess with trying to setup from there and after I pulled the intake hose off the carb and noticed while pulling on it that there was cracking in the intake boot on the head side. I don't know if they go all the way through but I ordered a new J17 intake boot and gaskets so ill let you know how it goes after the parts arrive.

If those cracks go all the way through it will lean it out for sure. You could spray some starting fluid on and around the boot while running and see if rpm increases. You want one full revolution and 3/8 more out from lightly seated for a starting point. 1/4 out may not be enough.

[dezrcr822]

Originally Posted by mikeasis

what pilot jet # are you using? one of my j24 jets is a 32.5 and my other has a 42.5 and my mokuni has a 38.8. Its weird because looking at the bottom of the 32.5 pilot there doesn't appear to be a hole in it like the others. I may try the 38.8 mokuni jet but ill wait till I get my intake boot and gaskets.

Im using the Mokuni pilot jet 38.8, it has a hole on the bottom and three staggered holes around the side of the jet. The 38.8 hole is tiny so 32.5 may be even harder to see. I like to boil my carbs and jets and have a welding tip cleaner set to push through the holes. The pilot hole looks so small I would pull apart some copper stranded wire and run one piece through or just compressed air after making carburetor stew.

[mikeasis]

Im not really sure where to go from here. I swapped jets on the J17 carb a few different times with no real changes. I even cleaned up another J10 carb and tried that thinking something was wrong with the J17 carb. The plug color still makes me think its running lean. The engine does seem to run hot but other than the plug color the thing runs really well. starts right up with very little choke with good acceleration. I replaced the crank seals, the intake boot and gasket and im running a stock air cleaner with good piping so im pretty sure its not an intake leak. Seems odd that different jetting doesn't seem to help. Then again maybe im not running it enough. After changes ive just went around the block a few times and rechecked the plug.

Any pointers appreciated.

[mikeasis]

Installed a larger pilot jet today. Stock was 32.5 and the mokuni I tried after was 38.8 I think? Anyway I installed a 42.5? pilot and went out cruising with no other adjustments. It ran good for awhile then sputtered and missed , I whipped it around and tried to head home but it died 3 blocks from home. Thought for sure id fouled the plug but had no tools or plug on hand. Called the wife and she brought the 84 with a chain and pulled me home. While being towed I kept smelling something, bye the time I got home the belt was smoking. The comet clutch doesn't have the "idle bearing" like the stock clutch. Gotta say I wasn't expecting that. Turns out I had run out fuel

after the embarrassment and refueling nothing seems to have changed. It starts and runs great but im still at odds with the plug reading.

[dezrcr822]

The pilot jet is really only used to about 1/4 throttle or so. After 1/4 all the way to WOT is where the main jet comes into play. How are you doing your plug checks? You may be reading the idle circuit and a larger pilot air jet may make that area of the carb leaner. On my bikes I get it into third gear,open the throttle and ride to WOT and redline the engine then pull the clutch in and kill the engine. Ill coast with engine off and clutch in until I get to my driveway then pull the plug and read it. The object is to get all the way on the main jet under load then read the plug and not be on the idle or pilot circuit of the carburetor. On the golf cart I drove to the end of my street, turned around and matted the throttle driving towards my house. Once as far as the engine will rev I turned the key to off and coasted to a stop then read the plug. Its been my expirence that two strokes run great lean and then they melt down

[mikeasis]

Originally Posted by griffo002

What are the carb jet settings?....How many turns are you at?....like some run theirs at 1 turn others prefer 1 and a half....I think the book says 1 for old motors and 1 and half for new...In is rich ...out is lean.
Here is a link for tuning Mikuni carbs..

http://www.iwt.com.au/mikunicarb.htm

Griff

I broke out the service manual and found this. tightening the screw is leaner and loosening the screw is richer. I doubt this is my issue though as ive tried any where from 1/4 turn to 1 and a half. Tomorrow I'll try 2 full turns out and see what happens.

[mikeasis]

Originally Posted by mikeasis

I broke out the service manual and found this. tightening the screw is leaner and loosening the screw is richer. I doubt this is my issue though as ive tried any where from 1/4 turn to 1 and a half. Tomorrow I'll try 2 full turns out and see what happens.

2 full turns and still lean as I suspected. pulled the plug and shined a light in the hole and the top of the piston is also white. I ran a compression check while the pug was out this time for giggles. 90 psi. Good for the ole j17. I installed the biggest main jet I have 97.5 and the biggest pilot 42.5 and swapped out the main nozzle just in case. I think my next step is to make a block off for the intake and exhaust and fill it full of compressed air and check for leaks.

Could my ignition timing be that far off causing it to be lean? could the after market CDI box be the cause? I really think id have other issues it that was the case but im really not sure.