Ignition issue

[Clats97]

I have a Skyhawk GT5A w/ expansion chamber, mikuni "cns" type carbeurator, high performance CDI & the head was shaved and compression is at 130-137psi.

For the last week or so it takes at least 3 attempts to start, then it finally starts chugging and eventually fires properly.

The engine runs amazing, low vibration, smooth acceleration, good power band. I have tried cleaning the carb, checking for leaks, just about everything. I ordered a "super magneto" which should arrive soon so maybe that will fix the problem, but assuming it doesnt- what could be going on?

Spark plug is reddish brown perfect. I've done basically an inspection of everything.

What's going on lol

 

[Street Ryderz]

I have a Skyhawk GT5A w/ expansion chamber, mikuni "cns" type carbeurator, high performance CDI & the head was shaved and compression is at 130-137psi.

For the last week or so it takes at least 3 attempts to start, then it finally starts chugging and eventually fires properly.

The engine runs amazing, low vibration, smooth acceleration, good power band. I have tried cleaning the carb, checking for leaks, just about everything. I ordered a "super magneto" which should arrive soon so maybe that will fix the problem, but assuming it doesnt- what could be going on?

Spark plug is reddish brown perfect. I've done basically an inspection of everything.

What's going on lol

How old is this engine?What performance cdi are you using? I ask this to help us understand what's going on,the compression you describe is very low for that engine under 140 p.s.i and start up will be difficult as it's struggling to pull a/f into it.

 

[Clats97]

How old is this engine?What performance cdi are you using? I ask this to help us understand what's going on,the compression you describe is very low for that engine under 140 p.s.i and start up will be difficult as it's struggling to pull a/f into it.

Engine is 2 months old, cdi is the "Thunder CDI" (15 turns, 10°tdc).

Stock the compression was about 110psi and I am under the impression that is the average compression in a stock China girl. So I shaved the head and managed to get it up to around 140. Concerned about going any higher until I figure out this ignition issue. Considering it is harder to start since adding compression I don't wanna end up completely screwing my engine

 

[Clats97]

Ah I made a mistake. After you told me that compression is way low, and considering I noticed a power increase post mod, I thought something was up. I called my friend (he has some sort of tester that checks the compression) to verify the reading and he said it was 30-37psi higher than "normal". He also told me the avg engine is 100psi so I assumed mine is 130~. He doesn't remember the baseline but told me that the final reading was 195psi

 

[Street Ryderz]

195 psi would

Ah I made a mistake. After you told me that compression is way low, and considering I noticed a power increase post mod, I thought something was up. I called my friend (he has some sort of tester that checks the compression) to verify the reading and he said it was 30-37psi higher than "normal". He also told me the avg engine is 100psi so I assumed mine is 130~. He doesn't remember the baseline but told me that the final reading was 195psi

195 p.s.i. would make way more sense if you shaved the head as a stock Grubee is usually between 170-180 p.s.i. .Thunder cdi is ok but not sure what you mean by 15 turns or 10 degrees tdc,the engine's crank timing is at 20 degress btdc and the cdi will retard the advance but it still goes off the base timing only the jag and super charged cdi's have a lower base timing from what I've seen and that's not necessarily a good thing.

 

[Clats97]

195 psi would

195 p.s.i. would make way more sense if you shaved the head as a stock Grubee is usually between 170-180 p.s.i. .Thunder cdi is ok but not sure what you mean by 15 turns or 10 degrees tdc,the engine's crank timing is at 20 degress btdc and the cdi will retard the advance but it still goes off the base timing only the jag and super charged cdi's have a lower base timing from what I've seen and that's not necessarily a good thing.

Those were the measurements provided by another member on this site. Not sure if it is correct but I threw it in there in case it helped at all.

So.... Any ideas as to what's going on?

The super magneto should arrive by Canada post around 12pm EST.. Assuming that changes nothing

 

[Street Ryderz]

Those were the measurements provided by another member on this site. Not sure if it is correct but I threw it in there in case it helped at all.

So.... Any ideas as to what's going on?

The super magneto should arrive by Canada post around 12pm EST.. Assuming that changes nothing

Where in Canada are you? It sounds like it's just too rich at start up!

 

[Clats97]

Otta

Where in Canada are you? It sounds like it's just too rich at start up!

Ottawa. How do I fix that? It's not too rich when I give it throttle..

 

[Street Ryderz]

Otta

Ottawa. How do I fix that? It's not too rich when I give it throttle..

Cool I'm in the gtha 5 hours away LOL,so if you had said it was hard to start but ran properly as soon as it did,that would make me think lean but you said it chugged and then ran properly so that makes me think it's rich and having to clean out as it warms up to run properly.As the throttle is opened from idle/start up position the fuel metering changes if it's a cns carb you can solder the pilot jet closed and re drill it slightly smaller with a numbered bit micro bit set.

 

[Clats97]

Maybe if you PM me I can send you a video of me starting it