My very first engine build, but........

[Kart Simpson]

As to my expectations, I can't get it started. It is a Harbor Freight Predator w/ Hemi head 6.5hp. Here is a list of mods.

Removed governor
Removed low oil sensor
Billet conrod
Billet flywheel w/ 32* advanced timing
18# valve springs
0.35 main jet
.022 pilot jet
GX-140 emulsion tube
Autolite AR3910X spark plug
High flow air intake
High flow exhaust
walbro fuel pump

I have stock cam
I have stock crank shaft


It seems to be getting fuel into the cylinder and I have good spark right at the plug spark but it doesn't even attempt to fire. Thinking maybe a timing issue? I dunno. What's really weird to me is that when I give it a little throttle as I try to start it, I can hardly pull the rope. If I don't give throttle, I can pull it normally. Why is that?

 

[justinlogue5_0]

Someone will be along here soon with probably the right answer for ya. All I can say is that it sounds like a timing issue. Any and all motors have to have fuel,air, and fire at the right time. If any of these items is off its not going to run. Since you said its getting fuel and fire, and I can see its getting air, it has to be the timing. I have never used a advanced timing on these motors so I dont know what the proper setting on that should be.

You could always put timing back to factory specs to make sure it cranks and then go back to playing with timing after its running.

 

[Poboy kartman]

Did you properly align the cam/crankshaft timing marks with the piston at TDC?????

What did you set your valve lash to????

Sounds like a timing issue.....to me as well....but checking valve lash is easy enough.....re-algning the cam....not so much.....

Edit: Just realized you said you have the stock cam and a 32° advanced flywheel.....IDK that much about these motors....but that doesn't sound right to me.....you may need to get an offset key and install it backwards.....but....to start with...I would put the old flywheel on and see what happens.....that's a lot of advance....to my way of thinking.....which in itself is an arm breaker......

 

[2SlickNick]

Did you properly align the cam/crankshaft timing marks with the piston at TDC?????

What did you set your valve lash to????

Sounds like a timing issue.....to me as well....but checking valve lash is easy enough.....re-algning the cam....not so much.....

Edit: Just realized you said you have the stock cam and a 32° advanced flywheel.....IDK that much about these motors....but that doesn't sound right to me.....you may need to get an offset key and install it backwards.....but....to start with...I would put the old flywheel on and see what happens.....that's a lot of advance....to my way of thinking.....which in itself is an arm breaker......

That helped my problem too. I had a hard time on the pull start too. Soon as I did this my Briggs roared......
to life. your lash might be different since you have a stock cam. so use your specs

https://www.youtube.com/watch?v=W2iDgU2RF3o&list=UUSbDT6palA3JlXuoQcxUhnQ

 

[Kart Simpson]

Set my valve lash to .003
Set coil gap to .030

Thats why I wanted to mention that I have stock cam. Matbe messing up timing. I dint jnow how to fix that myself so that why i want to ask the pros here. : )

But what exactly would be causing the very very hard pull while giving it even a little throttle???

 

[2SlickNick]

I am not sure, but if I had to guess it would be the timing advance.

 

[Kart Simpson]

Does anyone know what the coil gap should be with the stock flywheel??

 

[justinlogue5_0]

I was thinking its .010

 

[2SlickNick]

I was thinking its .010

same as my briggs....

 

[OzFab]

0.030" seems a little wide... some say "a business card" sets a perfect gap...

Having said that, +1 for a timing issue; whether it's a valve timing or ignition timing issue remains to be seen... more information needed...

 

[Half-breeder]

Alil curious as to the method of thinking... an offset flywheel (w/ that kinda offsetness?!?!), w/ a stock cam.... hmmm. I get a mental pick of the spark occurring wwwwaaaayyyy to late, which in turn doesnt create enough 'oomf' to push the piston to the next rotation.

This is 'just' my opinion but...

"Hard to pull when given gas" indicates (to me, w/ those mods) what I just explained above. "If no gas given, easier to pull"... indicates (to me, w/ those mods) w/ the lack of the internal explosion (fired off late), no 'back pressure' is created, so a normal, nonrestrictive rotation is allowed.

Take a business card, loosen the bolts holding the coil, so that the unit slides. Sandwich the card between the coil unit and the flywheel contact point... tighten coil unit down, and remove card.

Valve lash's are different for the intake and exhaust(most of the time)... just FYI.

 

[Poboy kartman]

Tihm....advanced means it fires sooner.....hence why it's hard to pull....it tries to fire when the piston still has a ways to go to TDC......

 

[Half-breeder]

Tihm....advanced means it fires sooner.....hence why it's hard to pull....it tries to fire when the piston still has a ways to go to TDC......

Hmmmm.... I did say 'late' instead of 'soon', didnt I... "DOLT"!!!



...another thing that popped in my head, was maybe the plug gap is off?... maybe?

 

[Kart Simpson]

Thanks for the ideas guys and please keep them coming. I installed the ARC6626 billet flywheel and it says to set the coil gap at .030 for that flywheel. As far as the valve lash, I did set them both the same at .003 As far as the spark plug gap, there is no gap to be set with the plug I mentioned earlier.

Should I re-do the valve lash, if so then what to set them at?
How can I fix the timing issue with the billet flywheel, do I need a new cam??

I think I will put the stock flywheel back on and set the coil gap at .010 and see if it fires up. What do you think about that?

 

[zbuck]

Should I re-do the valve lash, if so then what to set them at?
How can I fix the timing issue with the billet flywheel, do I need a new cam??

I think I will put the stock flywheel back on and set the coil gap at .010 and see if it fires up. What do you think about that?[/QUOTE]

Stock valve lash should be, IN: .007, EX: ,008 with a +/- .001. That 6626 flywheel has a 8 deg. timing advance built into the key way, 32 degrees BTDC. Way to much advance for a stock cam, I would contact ARC and see what cam they advise for that flywheel. In the mean time, I would put the stock flywheel back on and see what happens. Keep us informed.

 

[Kart Simpson]

Should I re-do the valve lash, if so then what to set them at?
How can I fix the timing issue with the billet flywheel, do I need a new cam??

I think I will put the stock flywheel back on and set the coil gap at .010 and see if it fires up. What do you think about that?

Stock valve lash should be, IN: .007, EX: ,008 with a +/- .001. That 6626 flywheel has a 8 deg. timing advance built into the key way, 32 degrees BTDC. Way to much advance for a stock cam, I would contact ARC and see what cam they advise for that flywheel. In the mean time, I would put the stock flywheel back on and see what happens. Keep us informed.[/QUOTE]

Are you sure on those valve lash specs? I was looking around in the forums and got the impression that the intake was .002 and exhaust was .003

I will put stock flywheel back on later today/tonight and also contact ARC about a cam.

I was also thinking about that billet flywheel. I remembered when I ordered it it said that it has a 8* timing advance built into keyway. But then when I received it, it says 32* timing advance stamped into it. I wasn't sure what to make of it.

 

[Poboy kartman]

Ok...did a little checking.....so. .003" is correct fot the intake and exhaust.....they should be set at TDC on the compression stroke though....

.030" is the correct gap for the coil.....

A stock flywheel has 24° BTDC of timing built in....the flywheel you have has the key cut in with. 8° of advance......so 32° total.....

Still.,..8° is a pretty healthy advance...which is why I suggested you might need an offset key....(like a 4°advanced key) and put it on backwards ....tp retard the timing 4°......giving you 28° of advance....

So I would make sure your valves are set on the compression stroke...

And I already recommended trying the old flywheel....

If you still have problems.....then you may need to double check your cam/crankshaft orientation.......

 

[OzFab]

Umm, hang on Doug, your math is perfect but, your theory is flawed; an 8° timing key will mean it fires 8° closer to TDC, not 8° farther away:

Advance = closer to TDC
Retard = farther from TDC

So, with 8° of advance, it will be firing at 16°BTDC...

 

[Poboy kartman]

Umm, hang on Doug, your math is perfect but, your theory is flawed; an 8° timing key will mean it fires 8° closer to TDC, not 8° farther away:

Advance = closer to TDC
Retard = farther from TDC

So, with 8° of advance, it will be firing at 16°BTDC...

I beg to differ......TDC is 0° ...anything firing BEFORE TDC.....is advanced timing.....after.....retarded timing.......

So a stock flywheel fires 24° Before Top Dead Center......firing another 8° BTDC adds another 8° of advance......= 32°BTDC.......

It's pretty easy to understand when you consider PRE-ignition....or "pinging"....that happens in engines with too much advance in the timing....the piston is still heading up on the compression stroke towards TDC when the charge fires......causing a slamming effect on the piston.....RETARDING the timing.....allows the piston to get closer to TDC....eliminating the problem......

My math is not the only thing that's right.......

EDIT: Kart Simpson......this same phenomena makes advanced timed engines harder to crank.....but...the charge has to be firing for it to come into play.....but why so many aftermarket ignition systems have "Start Retard" to keep from burning up starters......FWIW......My stock Tecumseh almost broke my arm.....because the cam and crank were misaligned.......

 

[Poboy kartman]

Stock valve lash should be, IN: .007, EX: ,008 with a +/- .001. That 6626 flywheel has a 8 deg. timing advance built into the key way, 32 degrees BTDC. Way to much advance for a stock cam, I would contact ARC and see what cam they advise for that flywheel. In the mean time, I would put the stock flywheel back on and see what happens. Keep us informed.

Are you sure on those valve lash specs? I was looking around in the forums and got the impression that the intake was .002 and exhaust was .003

I will put stock flywheel back on later today/tonight and also contact ARC about a cam.

I was also thinking about that billet flywheel. I remembered when I ordered it it said that it has a 8* timing advance built into keyway. But then when I received it, it says 32* timing advance stamped into it. I wasn't sure what to make of it.[/QUOTE]

I'm going by what people who have run the 18lb. valve springs say they set their lash to.......003" on both.....stock is different.....and while it seems weird to me....I'm not going to argue with the majority that do it without any problems......