Ignition issue

Clats97

New Member
Jul 21, 2019
25
9
3
23
Hey guys I have a 2 month old skyhawk engine. I use a mikuni carb, expansion chamber, 36t sprocket, supercharge cdi and a few other minor mods.

I recently shaved some of the head to raise compression, and ended up raising it by about 30psi.

Since then, my motor has become a bit more difficult to start, however this issue preceded that.

What happens is it takes about 3 or 4 tries until the engine kind of slowly chugs then slowly fires up. Once she's running, it runs really well.

Just a bit annoyed with this ignition problem. I have a super magneto on the way hopefully it helps.

Any ideas?
 
  • Like
Reactions: indian22

Clats97

New Member
Jul 21, 2019
25
9
3
23
I'm positive this problem isn't your ignition! (there's such a thing as too much compression) :(
Using cheap gas with high compression can also cause problems...
This happened before and after I raised the compression. In terms of fuel I use shell ethanol free 93 octane, redline full race oil, lucas upper cylinder lube.

This issue literally sprung itself upon me out of random... It would have been much easier to diagnose had I just put on a new carb or something. Not the case.
 
  • Like
Reactions: indian22

Clats97

New Member
Jul 21, 2019
25
9
3
23
What spark plug are you using (& what's the gap)?

How much oil are you adding to the gas?

Just got the oz super megneto & bullet train spark plug. It didn't fix the issue.

My ratio is 32:1 +5 parts lucas upper cylinder lube.

Gap is .025, but I have experimented with different sizes. Above a 45 it will not run.

I'm not sure I noticed a difference going from the plug I had on yesterday (. 40) to today (. 25)
 

Clats97

New Member
Jul 21, 2019
25
9
3
23
Just got the oz super megneto & bullet train spark plug. It didn't fix the issue.

My ratio is 32:1 +5 parts lucas upper cylinder lube. I have tried slightly leaner and richer mix's but it appears most people are using that ratio

Gap is .025, but I have experimented with different sizes. Above a 45 it will not run.

I'm not sure I noticed a difference going from the plug I had on yesterday (. 40) to today (. 25)
 
  • Like
Reactions: indian22

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
6,620
429
83
Los Angeles, CA.
Try a NGK - B6HS gaped at .025"

Also... drain the gas & mix a new can (without the upper cylinder lube), & see if those work.

it also helps to get the engine real hot before judging performance (because many of these engines can be very cold blooded)
 
  • Like
Reactions: indian22

Clats97

New Member
Jul 21, 2019
25
9
3
23
Try a NGK - B6HS gaped at .025"

Also... drain the gas & mix a new can (without the upper cylinder lube), & see if those work.

it also helps to get the engine real hot before judging performance (because many of these engines can be very cold blooded)
Will do. Same ratio?

The thing is, when I started putting the upper cylinder lube in, it was a much smoother ride less vibration and I swear it improved the power band. But I'm not one to ask for advice then ignore it. I'll try that plug. I was actually going to order that one but the way bike berry described the bullet train one made me think it was the best choice for my cdi and magneto
 
  • Like
Reactions: indian22

Clats97

New Member
Jul 21, 2019
25
9
3
23
Try a NGK - B6HS gaped at .025"

Also... drain the gas & mix a new can (without the upper cylinder lube), & see if those work.

it also helps to get the engine real hot before judging performance (because many of these engines can be very cold blooded)
One more question - why are you suggesting keeping the gap at 25?i was under the impression that because I have a super magneto, and magnet and upgraded CDI that a wider gap will = more spark and better combustion.

Can you weigh in on this
 

indian22

Well-Known Member
Dec 31, 2014
3,855
4,629
113
Oklahoma
You say the problem started when you raised compression by 30 psi. I'd try installing a thicker copper head gasket to eliminate the power modification of added compression as a source of your problem.

Bikeberry sells stuff and some is good, but hype is what it is. How can one beat the research of NGK on plugs with a catchy "bullet train" name from an unknown manufacturing source?

In my book Norm's advice is golden & too much compression can be the cause of other problems as well. 12 lbs. of torque on the re-install of head bolts.

Rick C.
 
  • Like
Reactions: Venice Motor Bikes

Clats97

New Member
Jul 21, 2019
25
9
3
23
You say the problem started when you raised compression by 30 psi. I'd try installing a thicker copper head gasket to eliminate the power modification of added compression as a source of your problem.

Bikeberry sells stuff and some is good, but hype is what it is. How can one beat the research of NGK on plugs with a catchy "bullet train" name from an unknown manufacturing source?

In my book Norm's advice is golden & too much compression can be the cause of other problems as well. 12 lbs. of torque on the re-install of head bolts.

Rick C.
I said the opposite - my bad if there was a misunderstanding. I said it happened before and after raising the compression
 
  • Like
Reactions: indian22

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
6,620
429
83
Los Angeles, CA.
One more question - why are you suggesting keeping the gap at 25?i was under the impression that because I have a super magneto, and magnet and upgraded CDI that a wider gap will = more spark and better combustion.

Can you weigh in on this

I know these engines don't have anywhere near the compression of larger engines, but I've read that high compression can actually stop the spark if the gap is too big.... plus .025" is what's recommended in most of the old Honda motorcycles & VWs that I work on... (& those are 12V systems).


Honestly... your problem could be something as simple as a lightly fouled plug, (because of too much oil, incorrect heat range or too large of a gap)?
 
  • Like
Reactions: indian22

Clats97

New Member
Jul 21, 2019
25
9
3
23
I know these engines don't have anywhere near the compression of larger engines, but I've read that high compression can actually stop the spark if the gap is too big.... plus .025" is what's recommended in most of the old Honda motorcycles & VWs that I work on... (& those are 12V systems).
I know these engines don't have anywhere near the compression of larger engines, but I've read that high compression can actually stop the spark if the gap is too big.... plus .025" is what's recommended in most of the old Honda motorcycles & VWs that I work on... (& those are 12V systems).


Honestly... your problem could be something as simple as a lightly fouled plug.
I know these engines don't have anywhere near the compression of larger engines, but I've read that high compression can actually stop the spark if the gap is too big.... plus .025" is what's recommended in most of the old Honda motorcycles & VWs that I work on... (& those are 12V systems).


Honestly... your problem could be something as simple as a lightly fouled plug, (because of too much oil, incorrect heat range or too large of a gap)?
That's what I assumed right off the bad. But when I swapped the plug it did nothing, I read the one I installed yesterday and it's perfect, reddish brown.

To update u on this - the problem has been somewhat fixed. Since the new magneto and plug was in the bike it doesn't chug then start anymore--it just takes a few tries (3 max) to turn over.

Maybe I'll order one of those extra strong magnets and see if that does anything?
 
  • Like
Reactions: indian22

indian22

Well-Known Member
Dec 31, 2014
3,855
4,629
113
Oklahoma
Greg I've one modified engine that still hasn't really come to life after 300 to 400 miles, and it's not the first to be recalcitrant. Straight mineral oil is in my opinion the best for the break-in period and I'm quite certain I used the mix I'd prepared for my other bikes and it's the Lucas semi-synthetic...wear in just hasn't occurred at it's normal pace.

Your remark is so true.

Rick C.