Bad plugs or too lean?

[chef1366]

Ah, CV carbs. They run so smoothly with an airbox! :-)

Bill, I think that you need to check the operation of the diaphragms. If they're lagging too far behind the engine air/fuel demand, you will have a lean stagger until they open at the right rate. Make certain that part of your pods are not blocking off the vacuum ports.

You can compensate with needle shape, or the diaphragm spring rates.

The pods aren't blocking the vacuum port. I have the needle set at the bottom notch. Can't raise it anymore unless I lose the plastic spacer or at least shave a little off it. I have four extra ones. Maybe I'll try that if the spark plug cap trim doesn't work.
The 1150 springs are shorter than the 1100s. Can I shorten them, Ian?

I'm also going to invest in a Dyna S and green Dyna coils.

[salty_monk]

Bill,

If you are getting a nice fat spark at the plug I wouldn't bother.... on mine when the ignition went you could clearly see it was weak. You could also test it per clymer's, mine failed that too.

Could the problem be the other way? Too much fuel when it's coming onto needle?

Dan

[49er]

The pods aren't blocking the vacuum port. I have the needle set at the bottom notch. Can't raise it anymore unless I lose the plastic spacer or at least shave a little off it. I have four extra ones. Maybe I'll try that if the spark plug cap trim doesn't work.
The 1150 springs are shorter than the 1100s. Can I shorten them, Ian?

I'm also going to invest in a Dyna S and green Dyna coils.

Bill, I didn't realise that you had the needles on the bottom notch. Seems a bit extreme but so are the engine mods!
If you were rich on the needles at transition, that should carry on through the mid range and show up on your plug chops.

You need to compare both sets of springs along with the weight of the diaphragms. Your vacuum levels at 1/4 throttle will be different to what you had before you fitted the larger valves and enlarged the porting.
Dont cut your 1150 springs just yet.

If your plug chops are good in the mid range, try leaning your pilot air screws a tad and see if the transistion improves. If it gets worse, then you are definately leaning at transition. If it improves your pilots are too rich.

Because of your radical tuning, you may never get it to run perfectly, especially at the bottom end of the rev range. But don't stop trying just yet.

[chef1366]

I richened the needle with washers in place of the spacer. Too fat! I couldn't even get it to run at WOT.
The heat range on the plugs is showing up and I have one thread on 2 and 4 and none on 1&3. I think I'm fat all around.

[chef1366]

Lowered the needle one notch from the bottom and put in the 137.5s. Issue solved. I guess when I jetted these carbs in the cooler weather it was borderline rich and the heat just but it over the edge.
Plus those plugs threw me for a loop! I guess they were just bad plugs:-?
They certainly didn't melt from being lean!

[49er]

Lowered the needle one notch from the bottom and put in the 137.5s. Issue solved. I guess when I jetted these carbs in the cooler weather it was borderline rich and the heat just but it over the edge.
Plus those plugs threw me for a loop! I guess they were just bad plugs:-?
They certainly didn't melt from being lean!

If your plugs didn't melt from excessive leanness, their heat range number was incorrectly marked on the plugs. Melted electodes are bad news and are usually followed by holed pistons. You're one lucky Dude!

Redo your plug chops to make sure you've got it right. Even better, do a dyno check of your AFR's throughout the rev range.

[chef1366]

The right way would be to get it Dyno'ed.
What would I do with all my spare time??

[49er]

The right way would be to get it Dyno'ed.
What would I do with all my spare time??

You could prepare an exceptional Independance Day feast for your GSR buddies :-)

[chef1366]

You could prepare an exceptional Independance Day feast for your GSR buddies :-)

I wish! One thousand reservations. YIKES!

[TheCafeKid]

Ok...total newb question when it comes to this, but after reading this thread, and knowing some of the symtoms that chef was experiencing (not the plug problem, thankfully) kinda got me starting to look more at my plugs. They LOOK good, good colour. The response in the throttle is the same as Chef was having, that slight stagger when you wack it, then being blasted out of a cannon when the slides/throttle caught up. Anyway, i see this about heat range reading with the threads, WHAT exactly am i looking for with this?

[chef1366]

On the outside of the plugs count the threads that have color. Lecroy stated that 1.5 threads is a good temp.
Looking at my plugs I'm wondering if the color is heat or oil? These are the same plugs I put after new rings were installed. I don't think I was running hot because I was rich and you run cooler rich.

[TheCafeKid]

On the outside of the plugs count the threads that have color. Lecroy stated that 1.5 threads is a good temp.
Looking at my plugs I'm wondering if the color is heat or oil? These are the same plugs I put after new rings were installed. I don't think I was running hot because I was rich and you run cooler rich.

K, thats kinda what i thought, but then started thinking that it COULDNT possibly be THAT simple...lol

[Shaughn]

K, thats kinda what i thought, but then started thinking that it COULDNT possibly be THAT simple...lol

Thanks for asking TCK, it was a new concept to me as well. Is this an old
racer trick? I've never heard of it and want to know more. Is 1.5 threads always what you want? Or only for this engine? So many factors in this, plug construction, head construction, plug thread pitch, plug base material, it seems like it would be hard to find a standard line to draw in the sand as to where/what/why.

I know I could just google it, but I'd love to hear people's experiences with it, if you all are willing to share

[lecroy]

I posted quite a bit on this. Try a search.