Plug gap help

#1
Hey guys I need help with a spark plug issue. I keep fouling out the plug. Here's my problem I can start the bike with choke on and giving it some throttle it stays on a bit. Turn the choke off with throttle it sputters to stay on. My mods list
Predator 212cc hemi
92 non ethanol gas
Mobil one racing 4t 10/40 oil with zinc added.
Bpr6es currently gapped at .040
Flame thrower 8.0 coil high performance
Slip stream billet flywheel 28 degree advance timing currently set gap at .050 with motor at TDC
18# valve springs set valve lash at 0 when installed.
Governor by pass.
Stage one go power sports kit with .038 main jet.

I'm not sure of I got my plug gap wrong or what but I do know with this current set up it gives the most horsepower I went my personal best speed of 62 mph today. Do I need to set my valve lash to .003 I'm tired of fouling my plug out. Or should l try a different plug gap? I've read .035 gap is the most common for high spark set ups but I set one plug to that and lost lots of power my motor is way happier at .050 I know these come stock with a plug gap of .016 and the margin is. 008. But I figured with this coil and flywheel set up I have .035 and up is better. Maybe I should try .039 on a new plug? I'm at a lost any advice will help. Or Maybe I'm just not tuning my carb correctly. I read to get the best plug reading is hold it at half or full throttle for 5 secs then kill the motor and check plug then adjust fuel mixture from there. Lately I been running real rich. I can't figure it out.
 

I74

Well-Known Member
#2
I gap all small engine stuff pretty much @ .030, & that's right around ball park spec for those NGK copper plugs.
Run stock coils though.
Performance coils ect. on classic Harley's & Hot rods,, have always pretty much run copper NGK'S on those also , with mostly .030 - .035 gaps.
Gap specs on misc. GM's ect. ect. & misc. newer cars,, are ''a lot'' wider though.
Think the set of ''expensive'' NGK Iridium's I recently put in my 2015 2.4 Dart,, gapped @ around .050.
Also,,
NGK's ''if you didn't know'',, the lower the number, the hotter the plug.

Looks like .050 that you set your coil air gap at, is about right for those type of flywheels & coil.

Lastly,,
Setting your valve lash @ ''0'' though, throws up a ''big'' flag !
I would definitely set those @ .003 ''ASAP''.
Remember, when valves get seated in & worn, the lash generally decreases anyways,, unless you have a lot of carbon build up ect. . And with those valve springs,, that will probably accelerate it.
I''ll bet your lashes are probably negative now when you check them, especially when cold.



I
 
Last edited:
#3
I gap all small engine stuff pretty much @ .030, & that's right around ball park spec for those NGK copper plugs.
Run stock coils though.
Performance coils ect. on classic Harley's & Hot rods,, have always pretty much run copper NGK'S on those also , with mostly .030 - .035 gaps.
Gap specs on misc. GM's ect. ect. & misc. newer cars,, are ''a lot'' wider though.
Think the set of ''expensive'' NGK Iridium's I recently put in my 2015 2.4 Dart,, gapped @ around .050.
Also,,
NGK's ''if you didn't know'',, the lower the number, the hotter the plug.

Looks like .050 that you set your coil air gap at, is about right for those type of flywheels & coil.

Lastly,,
Setting your valve lash @ ''0'' though, throws up a ''big'' flag !
I would definitely set those @ .003 ''ASAP''.
Remember, when valves get seated in & worn, the lash generally decreases anyways,, unless you have a lot of carbon build up ect. . And with those valve springs,, that will probably accelerate it.
I''ll bet your lashes are probably negative now when you check them, especially when cold.



I
Thanks for the reply. Update I ditched the ngk plug and put in an autolite 3910x race plug and the bike is way better. Also I learned I was tuning my carb wrong. When turning the mixture screw so user error smh. But I got the fuel mixture about perfect. As far as my valve lash I simply followed go powersports install video on the full stage one kit as mine and they set the lash to 0. My bike runs good seems like with no issues. But I will set my valve lash to .003 to see what happens and if I notice any difference.
 
#4
I gap all small engine stuff pretty much @ .030, & that's right around ball park spec for those NGK copper plugs.
Run stock coils though.
Performance coils ect. on classic Harley's & Hot rods,, have always pretty much run copper NGK'S on those also , with mostly .030 - .035 gaps.
Gap specs on misc. GM's ect. ect. & misc. newer cars,, are ''a lot'' wider though.
Think the set of ''expensive'' NGK Iridium's I recently put in my 2015 2.4 Dart,, gapped @ around .050.
Also,,
NGK's ''if you didn't know'',, the lower the number, the hotter the plug.

Looks like .050 that you set your coil air gap at, is about right for those type of flywheels & coil.

Lastly,,
Setting your valve lash @ ''0'' though, throws up a ''big'' flag !
I would definitely set those @ .003 ''ASAP''.
Remember, when valves get seated in & worn, the lash generally decreases anyways,, unless you have a lot of carbon build up ect. . And with those valve springs,, that will probably accelerate it.
I''ll bet your lashes are probably negative now when you check them, especially when cold.



I
Also I learned that I have the updated version 2 slip stream flywheel which is 34 degree advanced instead of 28. Not sure if that makes any difference..
 

I74

Well-Known Member
#5
Thanks for the reply. Update I ditched the ngk plug and put in an autolite 3910x race plug and the bike is way better. Also I learned I was tuning my carb wrong. When turning the mixture screw so user error smh. But I got the fuel mixture about perfect. As far as my valve lash I simply followed go powersports install video on the full stage one kit as mine and they set the lash to 0. My bike runs good seems like with no issues. But I will set my valve lash to .003 to see what happens and if I notice any difference.
About the only engines I ever adjusted to around ''0'' lash, would have been old Harley's, with solid lifters.
Basically a ''feel'' thing, with the pushrods spinning ''free without drag'' when the valves closed,, but no noticeable up & down play.
An engine does ''grow'' some when heated up though, especially aluminum.
 

I74

Well-Known Member
#6
Added,,
My hands down fav. plugs are NGK's, & from experiences with Autolite's over the years, is that once they foul ''one time'',, they are pretty much done.
Worked in a race engine shop ect. for a stint years back,, & all we ran in everything was NGK's.
 
#7
Gotcha. I just set my lash to .003 on exhaust and intake before I take off to work. And I know. I think my setup prefers the spark from the autolite. Plus I high Rev a good bit more than idle time. If this plug fouls I'll try the ngk again got a few on hand. Will update how she rides when I get to work. Purple one is mine green one is my buddies.
 

I74

Well-Known Member
#8
Gotcha. I just set my lash to .003 on exhaust and intake before I take off to work. And I know. I think my setup prefers the spark from the autolite. Plus I high Rev a good bit more than idle time. If this plug fouls I'll try the ngk again got a few on hand. Will update how she rides when I get to work. Purple one is mine green one is my buddies.
Could you spin the push rods with the valves closed before adjusting ??
 
#12
Could you spin the push rods with the valves closed before adjusting ??
So bike lost top end with lash set at .003 and some acceleration mid to full throttle. Ran exactly the same though as last set to 0. Topped out at 58 mph otw to work. Then again this is lousiana with really humid weather imma see how it does today at 5pm when I get off.
 

I74

Well-Known Member
#13
So bike lost top end with lash set at .003 and some acceleration mid to full throttle. Ran exactly the same though as last set to 0. Topped out at 58 mph otw to work. Then again this is lousiana with really humid weather imma see how it does today at 5pm when I get off.
I seriously doubt if setting your lash to .003 caused that.
 

I74

Well-Known Member
#17
Was also thinking about,, what was the temp & humidity ect. when you had your fastest run, compared to the conditions of your last run ??
Was the air ''cooler'' on your fastest run ?
 
#18
Yesterday evening between 6 6:30 pm. Was about 85 out not sure on humidity. This morning at 6:40 when I left for work it was around 75 70% humidity. Around 5pm when I off its 90 degrees but 50% humidity
 
#19
So I just got off the phone with go power sports and they basically said with my application I'm running setting lash at 0 should be fine since they do loosen a bit after riding. So what immma do is when I get off today ima ride home and see what my top speed is and see if I'm still feeling the power loss threw mid and full throttle. If so imma set the lash back to 0 go ride and if I gain my power back with my top speed of 62mph. Imma check the lash gap to see what it's sitting at. And go from there.
 
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