HT Bicycle Engine Spark Plug Gaps bigger then .022 possible?

Re: HT Spark Plug Gaps bigger then .022 possible?

I run mine in the range of .020 to .025 and it runs fine I have been told that if you run yours gaped to far out it can be very hard on your coil and or cdi . but don't hold me to it im still somewhat new to this I hope that helps some I know theres a thread In the forums about gaping .might help u out more that way

Re: HT Spark Plug Gaps bigger then .022 possible?

Some coils are better than others. Go with the gap YOUR motor likes.
Might consider swapping coils if it really bothers you. They are fairly cheap to buy and you might get a better one. All the ht's I've built ran fine around .020-.030.
I see no point in going any bigger since large gaps DO stress the marginal ignition systems on these engines. Why overwork it for such marginal gains?
As far as the black stuff in the cover...might be seal material signalling a coming failure?
Might simply be smutz from running. Clean it out and see what happens.

Re: HT Spark Plug Gaps bigger then .022 possible?

i run .30 on my motor

Re: HT Spark Plug Gaps bigger then .022 possible?

You might try one of the Iridium or platinum plugs. I hear good reports from people using them.
I use platinum in my high-perf engines normally, but not on china girls.
I'm just too cheap to bother on my Pig. It's all about the cheap for me these days.

Re: HT Spark Plug Gaps bigger then .022 possible?

When I had my B7HS I ran a .035 at one point, backed it down to a .025 and the bike didn't like it. Went back up to a .030 and it ran good so I left it there until I got my Iridium.

Re: HT Spark Plug Gaps bigger then .022 possible?

dodge dude94 said:

When I had my B7HS I ran a .035 at one point, backed it down to a .025 and the bike didn't like it. Went back up to a .030 and it ran good so I left it there until I got my Iridium.

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I'm waiting for a BPR8HIX from SBP, and other goodies, it's listed as easiest starting plug.
I thought i might try 0.022" to start off, Does a bigger gap advance or retard ignition timing,???

At this point in time, i have Heaps of Questions, I'm sure the Forum will Help clear up the Grey areas of my knowledge.!!

The gap doesn't affect the ignition timing, but it does have an effect on how well it can light off the fuel since these coils aren't exactly the best out there and if you add more compression to the engine by changing heads or milling or sanding down a stock head for more compression it might be just enough to cause a missfire if the gap is too wide.
Basically, the more compression pressure the tighter the gap needs to be to continue to run without missfiring.
Another cause to this is carbon buildup which can also raise the compression ratio over time. Try to keep this buildup as minimal as possible by cleaning it off the top of the piston and the cumbustion chamber when you see it starting to accumulate. You can inspect thru the exhaust port or thru the spark plug hole and cleaning is possible without removing the head thru the exhaust port using carb &choke spray and some Q tips, but cleaning is most effective by removing the head and using carb & choke spray or brake cleaner spray and some rags, the head can also be dipped in berryman B9 chem dip to get rid of carbon buildup if it's really severe.
Spray in some WD40 or inject some marvel mystery oil or even motor oil when finished cleaning to prevent any scuffing from the rings from lack of lubrication.

I personally run my gap at .025" just because these stock coils aren't the best and I don't want to put too much strain on them. If you got an aftermarket CDI with a CR80 or similar coil you can run a .030" or even .035" gap with stock compression but keep the gap below .030" if using a higher com ratio.
Keeping the piston top and cumbustion chamber clean and free of deposits will help prevent missfires and detonation too. I polished my piston top before assembly and the fred head's combustion chamber is also very smooth and won't collect carbon but the stock head can and polishing the combustion chamber will prevent this buildup.

I also use the cheaper Autolite 275 plugs during break in and tuning and setting up proper jetting then put a better plug in after all tuning is done, but the Autolite plugs do perform way better than stock and they're a cheap enough to just throw out and replace if they get fouled by running too rich.

The bigger gap does help with the fuel burn but it first needs a coil and ignition power to support that size gap, this is why we need to keep our gaps small, because the stock ignition can't support a bigger gap.

Re: HT Spark Plug Gaps bigger then .022 possible?

GeeBeeN said:

I thought i might try 0.022" to start off, Does a bigger gap advance or retard ignition timing,???

Click to expand...

In theory, a larger gap retards the ignition timing by increasing the electrical resistance to jump the gap, requiring extra voltage to build up in the capacitor before it 'avalanches', releasing all the voltage in one burst. However, this delay only amounts to a few milliseconds. At 9000 RPMs, you'd be lucky to see 2° of retard. Not to mention those extra volts will stress the CDI circuitry, the coil windings of the magneto & solder joints, possibly leading to early failure.

If you want to adjust your ignition timing, invest in a HD Lightning or Jaguar CDI, they offer different settings to taylor the ignition curve. Or use a rocket key to physically move the rotor in relation to the crankshaft position.

I personally run an NGK B8HS plug modified as a side gap(top of ground electrode is cut off, exposing more spark to the piston, an old racer's trick), gapped to .025". When outdoor temps get over 90°, I use a B10HS plug. Yes, that's a cold plug, but I live in Florida at sea level, with a shaved jug, a Puch70 hi-hi head AND an expansion pipe exhaust, so I'm seeing very high cylinder pressures. I've learned that in order for this engine to run right with these parts in this climate, I needed the coldest plug possible plus 10° retard on the rotor to keep it from self destruction/meltdown. So far I have warped a head & jug, blown thru a dozen head gaskets and melted a hole in the piston. My education was earned the hard way, and it has been expensive.