Advancing Ignition

[jak stoll]

Hi
From personal experience with na and forced induction cars
Air and water cooled
Most power was made retarding the ignition
I asume these china engines come preset for fuel economy, not power
That means as much ignition advance as possible
I would try to retard it
Peace

I dyno tune cars for a living.....
timing for fuel economy & power are one & the same
you want the timing as advanced as you can get it without causing damage to the engine
check out Jak Stoll Performance
I dont mean to be a ****e I just wanted the information strait
take care
JAK

 

[velardejose]

Hi
I know that as much advance as possible with lean af ratios are for economy
And for power the minimum advance for the max power is the best (safe af ratios)
I tuned a number of megasquirt ecus
Not trying to compare it to your work, just sharing what I learnt
Peace

 

[velardejose]

A car ecu responds to engine parameters
Our china girls have fixed advance/af ratio
Peace

 

[skipu]

how many degrees btdc are these ht motors ? has any body used a dial indicator and a degree wheel to detirmine this because with the poor quality of these motors all in all i find it hard to believe they would all be exact if you had a baseline to go buy you could safely do it in 1 degree increments and find the sweet spot and then we could all try to optimize timing for our different applications but the truth lies in the baseline timing we need to know this before moving forward

 

[velardejose]

Hi
Would be interesting to have data from the factory or see the original drawings...
Peace

 

[Norman]

I 've put a timing light on one of my engines and I do know the timing changes as you rev it up I believe it advances but that's as far as I've tinkered with it sometime when I'm bored I might put the degree wheel on it and find out exactly where it fires and where the advance is when wide open also where the ports open and close. but I got to get in the mood and lately I've not been there.

 

[jak stoll]

I played with my timing considerably
Id have to agree with Jose above
when you advance the timing on these engines they just kind of flatten out with maybe a tad more up top
more retarded gives more torque
I set mine in the middle of the slop available in the key thats there which is considerable

I think shaving the head a tad & leaving the timing alone is probably the best option
take care
JAK

 

[skipu]

i think the transfer ports are to low just an opinion when in comparison to a couple other 2 strokers im playing with in relation to bore and stroke if i can find just a cylinder some where i would love to play with it and if you bring up the comp. then the motor may be able to run a little more timing but at a low comp. standpoint timing may not be an issue ive been pondering a interchangeable combustion chamber simaliar to a pro design cool head just to play with ratios but its a lot of work and results may vary it is what it is sometimes ! !

 

[Egor]

I raised the transfer ports about one tenth of an inch. I didn't notice any improvement in the way it ran. I think long port timing on the compression side is intended for a high revving engine. I took a Honda CR250 apart a few weeks ago and took a few pics of the ports, they are very aggressive. It is not what these engines need, this engine is not intended to spin above 7,000 rpm. It would be interesting to hear about someone that was able to get one of these engines up near 10,000. It is interesting to hear that these engines may have an automatic advance in the ignition! I would suspect that we would see a very loose timing caused by the small rotor. Have fun, Dave

 

[JoeJ]

I had a puch moped many years ago; all mods,ported,tuned pipe, bigger carb,gearing...Had the same problem with advancing timing even though it had a points system..Had the breaker plate maxed over...didn't help until I took the key off the magneto and moved it almost 2 keys worth..Than it really came to life...By the way didn't even use a key just set it and Torked the heck out of it with a long breaker bar....

 

[JoeJ]

By the way.Yes the engine got finicky and ran alot hotter and lost alot of bottem end tourqe,...but the top end was amazing..I did richen the fuel but I was using products I can't even find today..Such as "Castrol R racing oil" which I think made all the difference in the world in sustaining a 49cc at well over 10,000 rpms. The shorter stroke helped alot versus the 70cc we are using now.

 

[jak stoll]

i think the transfer ports are to low just an opinion when in comparison to a couple other 2 strokers im playing with in relation to bore and stroke if i can find just a cylinder some where i would love to play with it and if you bring up the comp. then the motor may be able to run a little more timing but at a low comp. standpoint timing may not be an issue ive been pondering a interchangeable combustion chamber simaliar to a pro design cool head just to play with ratios but its a lot of work and results may vary it is what it is sometimes ! !

what the heck are you using to work on the transfer ports, lil tiny guys with picks & shovels?

I have an extra cylinder here if you have something to work on the transfer ports with '
I think matching the case to the cylinder would help allot
I dont like the idea of raising the exhaust port as it shortens both the compression & power strokes
Ive heard that most pros turn down the base to effectively lower these ports
take care
JAK

 

[JoeJ]

Jak I failed to mention that the cylinder on my puch had open channel transfer ports, which made it pretty easy to get a long reach porting bit on them... but it still was a chomed bore cylinder like the chinas we run.... I've found the best way to get top end speed on these things is by using a tuned expansion chamber and changed gearing.. I am really interested in the SBR gear set up. Has anyone besides the sellers have some reports on the top end performance achieved with this kit? I have some concerns about the derailer holding up under those conditions.

 

[JoeJ]

oops I mean SBP

 

[Norman]

you can change things with a thinner base gasket and if you don't like how it turns out go back to stock same with the head gasket. I have played around with them a little.

 

[Egor]

JoeJ - Those Mopeds are indestructible, my kids had them and it was like a Timex watch. I do exactly what you are talking about with the Briggs engines I run in the mini bikes, and yes it is amazing about moving them two slots forward. I run mine without the keys also. The key is most for standard build you can't miss with the key in there. Have fun, Dave

I had a puch moped many years ago; all mods,ported,tuned pipe, bigger carb,gearing...Had the same problem with advancing timing even though it had a points system..Had the breaker plate maxed over...didn't help until I took the key off the magneto and moved it almost 2 keys worth..Than it really came to life...By the way didn't even use a key just set it and Torked the heck out of it with a long breaker bar....

 

[skipu]

I raised the transfer ports about one tenth of an inch. I didn't notice any improvement in the way it ran. I think long port timing on the compression side is intended for a high revving engine. I took a Honda CR250 apart a few weeks ago and took a few pics of the ports, they are very aggressive. It is not what these engines need, this engine is not intended to spin above 7,000 rpm. It would be interesting to hear about someone that was able to get one of these engines up near 10,000. It is interesting to hear that these engines may have an automatic advance in the ignition! I would suspect that we would see a very loose timing caused by the small rotor. Have fun, Dave

i think lowering the exhaust port would be benificial too you would use more of the cylinder before evacuating the exhaust gasses ive been thinking about designing some kind of port stuffer that would be fixed to the exhaust manifold just to try it but just havnt had the time so many ideas but so little time i wish i could retire young and just build motorcycles 5 this year and motorized bicycles 2 aside from my race car that i have not raced in 5 mths. i should have a little more time this winter when work slows a little hope i get to try some of my ideas and post results (looking for cylinders good or bad) if anyone has old burnt up ones PAECE !!!!!!!!!!!!

 

[Egor]

Skipu - Tell me about it, one of the things I have noticed is that as I get older the days just get shorter. I only have one cylinder extra, I have fooled with the ports leaving the exhaust alone and have found that I could not get anything out of the motor, in the end I had to move the exhaust up to the 1.1" from the top, I think that is still conservative. On the CR Honda there is only about 1/2 of the stroke for power the rest is for scavenging. On some of the newer CR's they have the variable port timing with the little rotary door they invented, that still I think does not get it to the height that we get at a full port job, ours is still lower at 1.1. I have a 29 Ford in the garage I hope to someday get finished, but you know the days that get short. LOL. Have fun, Dave

 

[jak stoll]

Skipu - Tell me about it, one of the things I have noticed is that as I get older the days just get shorter. I only have one cylinder extra, I have fooled with the ports leaving the exhaust alone and have found that I could not get anything out of the motor, in the end I had to move the exhaust up to the 1.1" from the top, I think that is still conservative. On the CR Honda there is only about 1/2 of the stroke for power the rest is for scavenging. On some of the newer CR's they have the variable port timing with the little rotary door they invented, that still I think does not get it to the height that we get at a full port job, ours is still lower at 1.1. I have a 29 Ford in the garage I hope to someday get finished, but you know the days that get short. LOL. Have fun, Dave

I dont understand how moving the exhaust port up helps.... it reduces the effective compression stroke as well as the power stroke
can you explain or post a link to a place that does?
thanks & take care
JAK

 

[Egor]

Jak - I don't have a site that has the formula, but I can explain, I think. There are quite a few ways to formulate a two stroke engine, I know it seems like if you limit the amount of time the charge can push the piston down it would also limit the power produced. The problem is that you also limit the time for the exhaust to blow down the pipe, thus limiting the amount of charge you can introduce into the chamber. Remember the piston is not pushing the charge out, it is the pulse from the expanding gasses. Also if you are using an expansion chamber you have to wait for the ram affect to return from the pipe, so you also want to let some of the charge escape down the pipe to be returned with the shock wave. There is another reason that the ports are manipulated and that is to restrict or enhance the amount of power, this engine is supposed to be at the two HP only to meet some of the restrictions placed on the motored bikes. You can throttle a two stroke at both ends, by restricting the end of the exhaust of a larger engine you can use the torque produced by the larger bore and still limit the top end. I used to sneak a little hole in the muffler of the little Honda's we used to run around on, I never let on and the rest never could figure out why my bike would always run away from there's. I hope this helps, I have built a lot of engines, and I like answering questions. Have fun, Dave