Help on jetting issue

[Deano10972]

Hello everyone, this is my first post..

I recently built a 212 Predator with the Hemi head and need some help tuning

Here is what I did to the build-

Removed the govoner
Removed the low oil Spenser
Installed air filter and adapter
Minibike header
18lb valve springs
Racing spark plug
ARC RuiXing carburetor
GX 140 E tube
.038 main jet
.022 idle jet
Top plate and fuel pump

Before anybody starts bashing I'm not finished yet, I'm planning on getting a conrod and flywheel before I start riding, I'm just trying to tune what I got

Anyway my jets are not right.. I get a lot of backfire when it comes off idle. It's hard to get a plug reading when the motor isn't mounted on anything( but the plug looks good). The motor seems to be running too hot, I think that's a sign of being too lean.
With that new carb should my jets be larger? Also I hooked up a cheap RPM meter and its reading almost 2500 on idle, seems too high, when I idle it down it wants to cut off.

Any help on my set up would be appreciated.

 

[minibikin']

Before looking at jetting, when you installed the valve springs, did you check for coil bind? The 18# springs seem to have that issue in a hemi unless you cut the spring pockets. Since you didn't mention doing that, I figured I'd ask. You need .080-.100" clearance between the coils at max lift.
The jetting you have with those parts should be ample. Possible vacuum leak?

Sent from my Texas Instruments Speak and Spell...[emoji2]

 

[OND]

I'm with minibikin on the valve spring coil bind on the hemi head...I used 26# springs. Make sure you Installed the carb gaskets right, especially the one behind the carb and the one between the af adapter to carb. When you get the ARC flywheel you will gain about 6 to 8 more degrees of timing to.

 

[Prowler08]

If sitting there revving it up it should pop/backfire when you let off... Even racing it on a track and you let off suddenly it will backfire.
The left over fuel from a shut down leaves un burnt fuel that is why it is popping...

And yes watch for coil bind with those springs in a Hemi Head...
On gas it is normal for the temps to be in the 350-375*f range...
Also I see you have not replaced the flywheel... So the timing is still stock? For a good running motor timing should be in the 28-32* range.
Double check your valve lash also should be set to 0. To .003.

 

[Deano10972]

Before looking at jetting, when you installed the valve springs, did you check for coil bind? The 18# springs seem to have that issue in a hemi unless you cut the spring pockets. Since you didn't mention doing that, I figured I'd ask. You need .080-.100" clearance between the coils at max lift.
The jetting you have with those parts should be ample. Possible vacuum leak?

Sent from my Texas Instruments Speak and Spell...[emoji2]

Thanks for all the suggestions,
I've built a few of these motors (not Hemi) and work on small engines all the time but I'm not sure what coil bind is? I was also told by somebody else that since I dont have a good rod than stay with the stock springs so a least ill have valve float around 5000. I was thinking about putting them back in..
I'll take the carb off today and check the gaskets

 

[Deano10972]

If sitting there revving it up it should pop/backfire when you let off... Even racing it on a track and you let off suddenly it will backfire.
The left over fuel from a shut down leaves un burnt fuel that is why it is popping...

And yes watch for coil bind with those springs in a Hemi Head...
On gas it is normal for the temps to be in the 350-375*f range...
Also I see you have not replaced the flywheel... So the timing is still stock? For a good running motor timing should be in the 28-32* range.
Double check your valve lash also should be set to 0. To .003.

Thanks Prowler,
I'll double check the value lash, I set it at .002 and .003' when I installed the springs, again not sure what coil bind is.. Should I order an advanced timing key?
Thanks again

 

[minibikin']

Coil bind is when the valve spring coils contact or come too close to contacting the next coil during a cycle of the engine. When the cam/valve is at full lift, you should have a minimum of .080-.100" between the coils with a feeler gauge.


Sent from my Texas Instruments Speak and Spell...[emoji2]

 

[Deano10972]

Coil bind is when the valve spring coils contact or come too close to contacting the next coil during a cycle of the engine. When the cam/valve is at full lift, you should have a minimum of .080-.100" between the coils with a feeler gauge.


Sent from my Texas Instruments Speak and Spell...[emoji2]

I learned something new today, I'll check:thumbsup:
Thank you..

 

[Deano10972]

Just a update;

I took the valve cover back off to check the lash it was .003 and .004, so I just left it at that,
Took the carb off to check the gaskets everything looked good
While I had the carb off I checked the jets, idle jet was .020, so I went ahead and drilled it to .022
The main jet was .038 so I took a spare jet I had and drilled it to .039 ( just to see if anything would change)
Cleaned the racing plug up( thought about putting the stock plug back in but stayed with the four prong one)
I backed the mixing screw out to two turns
And so it wouldn't be just straight flow I installed a muffler on my minibike header.

Started on first pull and it runs like a champ, no backfire and smooth off throttle, I removed the muffler. And not so smooth so I left it on.
I have this trail tach hooked up to spark plug wire( don't know how accurate this thing is) but I got it idling at 1500
My only concern now is when I reved it a couple of times it got to 6000' is this safe with the other stock parts' I'm obviously not going to hold it down, but is it ok to just rev it while tuning? When I took the muffler off it goes up to 7500' another reason I left it on..

 

[Stangrcr1]

I am surprised any of us are answering a thread where the OP has bypassed/removed the governor and running it. :shrug:

While I agree with providing info, the OP has not taken it to heart and continued down this path.

 

[Camjamsdad]

I am surprised any of us are answering a thread where the OP has bypassed/removed the governor and running it. :shrug:

While I agree with providing info, the OP has not taken it to heart and continued down this path.

He does appear to know it'll explode at his new rpm levels and he won't/can't take it easy.

Op. Read this http://www.oldminibikes.com/forum/h...governor-engine-OldMiniBikes-please-read.html

Don't ruin your engine and possibly hurt yourself over a couple hundred bucks. The cast flywheel is the weak link. It's the magnets that'll fly off usually and the destroy the flywheel. It's cheap thin Chinese cast iron. The factory rod is also not designed for high rpms. There is no pressurized oil system. It relies on a small slinger to throw oil everywhere. There are no rod bearings. It runs aluminum against a cast iron journal. Once the slightest bit of aluminum sticks to the crank its over with. Aluminum is sticky and every revolution will transfer more aluminum to the crank in a process called galling. The billet arc rod is a work of art. It runs a babbitt bearing up against the cast iron crank. The oil slinger is replaced with a dipper that slings but it's cupped with a small hole the feeds oil right to the crank rod bearing. In a sense its sort of a pressurized oil system. And it's billet aluminum and not cast aluminum. Cast can have tiny unseen bubbles in it from pouring molten aluminum into a sand mold. Or weak spots. Normally its the galling that'll kill the rod.

Whoever suggested valve float as a rev limiter is clueless. I've heard it before but do you think it's a good idea to have your valves not working properly at 6 or 7 thousand rpms? There's a good chance that the piston is going to hit a valve at some point. The valve will bend, then stick, usually open, and the piston beats itself to death and can bend the rod or snap the crank. Your gear ratio can rev limit but what happens if you lose traction,break a chain, or become airborne? These issues can be helped for $150. to $190. depending on your choice of flywheel.

 

[Havasu Dave]

I am surprised any of us are answering a thread where the OP has bypassed/removed the governor and running it. :shrug:

While I agree with providing info, the OP has not taken it to heart and continued down this path.

He says in his first post that he's going to replace the rod and wheel before riding it. Thing is, running at 5-7K with no load, he may not get the opportunity to ride it.

 

[Deano10972]

He does appear to know it'll explode at his new rpm levels and he won't/can't take it easy.

Op. Read this http://www.oldminibikes.com/forum/h...governor-engine-OldMiniBikes-please-read.html

Don't ruin your engine and possibly hurt yourself over a couple hundred bucks. The cast flywheel is the weak link. It's the magnets that'll fly off usually and the destroy the flywheel. It's cheap thin Chinese cast iron. The factory rod is also not designed for high rpms. There is no pressurized oil system. It relies on a small slinger to throw oil everywhere. There are no rod bearings. It runs aluminum against a cast iron journal. Once the slightest bit of aluminum sticks to the crank its over with. Aluminum is sticky and every revolution will transfer more aluminum to the crank in a process called galling. The billet arc rod is a work of art. It runs a babbitt bearing up against the cast iron crank. The oil slinger is replaced with a dipper that slings but it's cupped with a small hole the feeds oil right to the crank rod bearing. In a sense its sort of a pressurized oil system. And it's billet aluminum and not cast aluminum. Cast can have tiny unseen bubbles in it from pouring molten aluminum into a sand mold. Or weak spots. Normally its the galling that'll kill the rod.

Whoever suggested valve float as a rev limiter is clueless. I've heard it before but do you think it's a good idea to have your valves not working properly at 6 or 7 thousand rpms? There's a good chance that the piston is going to hit a valve at some point. The valve will bend, then stick, usually open, and the piston beats itself to death and can bend the rod or snap the crank. Your gear ratio can rev limit but what happens if you lose traction,break a chain, or become airborne? These issues can be helped for $150. to $190. depending on your choice of flywheel.

Thanks for the advice..
Im ordering the ARC Billet Rod this weekend, the one i found is part # 6245 it says it measures 3.308 is this stock length? And would this one be ok for my set up?