Should I re gap spark plug for stock motor?

[Bill Hilly]

As most know, I had a cam follower fail on my fairly hot CG Hawk motor, and it took the timing gears out in the process. I quickly slapped a stock motor on it , from a parts bike I bought, which was showing around 700 miles, but probably abusive miles. It runs good for internally stock, and I am running a VM26 with 110/25 jetting . I had installed one of the Nibbi Yellow coils, not long ago, and gapped my plug to .9 mm. I used this same plug for the current stock motor. Should I reduce the gap to about.7mm, or leave it at .9mm ? Thanks

[Fast_Freddy]

I'd stick with 0.9mm gap.

[red2003]

It isn't going to make a difference either way.

[krat]

Originally Posted by red2003

It isn't going to make a difference either way.

Anyone that would worry about +- .2mm spark plug gap has never watched ItchyBoots being passed by a Chinese motorbike, axle deep in the mud of a west African dirt track, while being chased by elephants and pigmies.

[buzz]

so true ,should not ride a at all

[Megadan]

You can leave the gap alone. I ran the Iridium plug with it's .9mm (.036") gap on my first Hawk for 4400 miles, and that bike only had an exhaust and the same carb. The fine point iridium plug creates a more focused arc point, so they are much more likely to jump a wider gap and with a consistently hotter spark.

Now, if you can hear it missing a hit or two, especially at idle, then you can definitely shrink the gap a bit. Running a .028" gap (.7mm) is perfectly acceptable. That is still wider than the factory plug gap (.6mm). You can also compromise and split the difference between the stock gap and the iridium .9mm gap and run a .030" gap, which is between a .7mm(.028") and .8mm(.032") gap.

[Bill Hilly]

Originally Posted by Megadan

You can leave the gap alone. I ran the Iridium plug with it's .9mm (.036") gap on my first Hawk for 4400 miles, and that bike only had an exhaust and the same carb. The fine point iridium plug creates a more focused arc point, so they are much more likely to jump a wider gap and with a consistently hotter spark.

Now, if you can hear it missing a hit or two, especially at idle, then you can definitely shrink the gap a bit. Running a .028" gap (.7mm) is perfectly acceptable. That is still wider than the factory plug gap (.6mm). You can also compromise and split the difference between the stock gap and the iridium .9mm gap and run a .030" gap, which is between a .7mm(.028") and .8mm(.032") gap.

The bike is running good, and making the power I expect. . I was surprised at how small the jetting was in the VM26 carb that was on the motor. The main was a 100, and the pilot was a 20. The pilot also had a thicker stem than the other Mikuni pilot jets I have. I went ahead and used the 25 with the thinner stem, and it seems to work fine. The largest Mikuni main I had were two 110s, and I used one, and it seemed to do fine, but I got a little worried that it may have been a little lean, because of the pod filter, and exhaust, so I found a torch tip cleaner that fit a 115 small headed main, and forced though the 110 Mikuni main, and the bike didn't like it. I put the other 110 in, and it's doing good. The needle in the carb is very blunt in this carb , but I am running it. I looked at the needle in another VM26 that I have, and it's also blunt, but I don't think it's as blunt. I am still wondering why it seems to be happy with a 110 main , and wondering if this heat wave we have had since I installed the motor has anything to do with it. The power is not lower than expected, and actually it was a little better than I expected. It obviously won't be a powerhouse on the long fast hills, but it seems to be a hair better than it was when the original motor was stock. I had tried the 17/46 on the bike with the stock motor, and ended up putting a 16 tooth front on, because it lost too much steam on the long fast hills. I could not find my 16 tooth the day I put the motor on, so I used the same 17 tooth from the "hot" motor, and I think I will stick with it, because the bike holds it's own a little better than it did running a 17/46 on the old stock motor. I figure it's due to the 4.60x 18 rear tire that's on it now , and the fact that before I was running the stock knobbies.

[ProDigit]

Smaller gap only if your compression ratio is 9.5:1 to 10:1 (water cooled).

For air cooled, especially if you are running close to stoic ratios, the stock gap will do.