highly modded predator cutting out

vwfan79

Active Member
#1
First things first here are the mods:
14cc head
milled .030
.010 head gasket
ported and polished
27mm & 25mm ss valves
Locks and keepers
1/4" pushrods
Champion shaft rockers
50# springs
Black mamba cam
Arc rod and flywheel
12° timming
Flat top piston
22mm Mikuni no air filter
Running turbo blue

So here's the problem, bike ran great for about 30 passes the last 3 it started to break up off the line. Not real bad just one little "miss", couple weeks later it was a little worse but seemed to get better by richening up the low end screw. Then today it was real bad breaking up for the first half of the 1/8. I check the lash and change the oil before every race and have not changed anything else. Here are my 2 ideas, there is a piece of dirt in the carb or my coil is taking a crap. I'm pretty good with these motors but looking to do some brain storming with you guys. I did check the plug and it was a little rich but the idling down return road at the strip may have skewed that. It was was spinning over 8k in the 1/8 now it only turns about 6500. Engine idles great and will rev up nicely on the stand but under load is when the trouble begins.
Any of you high performance guys have any thoughts.
 
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vwfan79

Active Member
#3
Because of the high rpms this thing will turn. I've had it to 9700, on accident, but want to be able to turn 8500 in the 1/8 with out worrying about float.
 

vwfan79

Active Member
#5
No, plug is a autolite ar3910x (I think that's the number) racing plug. Was new with the build a month ago and has not been changed, I did clean it in a plug cleaner today before riding.
 

vwfan79

Active Member
#8
Could be the fuel but I'm still on my first 3gal can. I had thought about a seat being lose but thought I would see effects at idle and when reving it, and guides are new but that doesn't mean I don't have a bad one.
 

Neck

Growing up is optional
#10
Reason I ask, if the ignition stops and your still sucking fuel, when the spark starts up again the raw fuel in the pipe lights and it will pop like a machine gun. If for some reason there is an interruption in fuel delivery it'll just lay down and bog. Have you had the bowl off the carb and check for the possibility of water?
 

Neck

Growing up is optional
#12
Try not to dump the contents of the bowl out when you remove the carb, and work over a small container so you can see what come out. Just a small amount of water will really mess with you!
 
#14
ARC and many others use much stronger magnets in their flywheels that the original design spec on the coils were designed for.

Combine this with the much higher speeds these modified engines can turn the induced voltage in the coils is higher.

It stands to reason the cheaper clone coils will have a higher failure rate...

I have observed removing the resistor button from the spark plug boot allows more of this energy to blow through to the plug.
If nothing else you can make some hellish RF noise without it using a plug like the 3010.

I can't say for sure but my gut feeling is these coils fail less with the button removed.
And real OEM Honda coil is probably better made to stand up to these issues.

One of my back burner projects is to find a way to adapt these simple adjustable GY6 ignitions to the clone.
But I will be honest with you this is way in the future ( and have been thinking about this way into the past )

 
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125ccCrazy

Well-Known Member
#15
No, plug is a autolite ar3910x (I think that's the number) racing plug. Was new with the build a month ago and has not been changed, I did clean it in a plug cleaner today before riding.
that's where I'd start..a new plug..just because it looks ok or it was cleaned doesn't mean it's any good... a plug can break down under a load yet run ok at idle... Not saying it's the plug but that is the easiest thing to try in a process of elimination..
 

vwfan79

Active Member
#16
ARC and many others use much stronger magnets in their flywheels that the original design spec on the coils were designed for.

Combine this with the much higher speeds these modified engines can turn the induced voltage in the coils is higher.

It stands to reason the cheaper clone coils will have a higher failure rate...

I have observed removing the resistor button from the spark plug boot allows more of this energy to blow through to the plug.
If nothing else you can make some hellish RF noise without it using a plug like the 3010.

I can't say for sure but my gut feeling is these coils fail less with the button removed.
And real OEM Honda coil is probably better made to stand up to these issues.

One of my back burner projects is to find a way to adapt these simple adjustable GY6 ignitions to the clone.
But I will be honest with you this is way in the future ( and have been thinking about this way into the past )








that's where I'd start..a new plug..just because it looks ok or it was cleaned doesn't mean it's any good... a plug can break down under a load yet run ok at idle... Not saying it's the plug but that is the easiest thing to try in a process of elimination..
I cleaned the carb today and gonna try that, I have another brand new coil to try and a spark plug. Gonna try one thing at a time to figure out what it is. Problem is I don't really have anywhere by the house to try it, I've been looking for one but no luck yet.
 

vwfan79

Active Member
#17
I was out riding the moped today and found a spot I can for a little testing on the drag bike so I went home and got it. The first run went ok didn't miss, then second and third run started missing again, so I messed with the carb a bit and still doing. I change the plug with another AR3910X out of another bike just to try it and she runs like a raped date again, spun 7800 in less then an 1/8 and came out of the hole good. So looks like I need to start bringing some extra plugs with me. Thanks for the brain storming guys and Randi you nailed it.
 

125ccCrazy

Well-Known Member
#18
I was out riding the moped today and found a spot I can for a little testing on the drag bike so I went home and got it. The first run went ok didn't miss, then second and third run started missing again, so I messed with the carb a bit and still doing. I change the plug with another AR3910X out of another bike just to try it and she runs like a raped date again, spun 7800 in less then an 1/8 and came out of the hole good. So looks like I need to start bringing some extra plugs with me. Thanks for the brain storming guys and Randi you nailed it.
good to hear that it was an easy fix... the plugs can get hairline cracks in the ceramic that you can't see and it will cause the spark to jump around and if the outter ceramic is cracked it can jump to ground...

I pulled my db back down that you see last Christmas and started on the forks.....making new trees copied from a ruttman wild goose... this narrows the front end and eliminates that big gap between the trees,,,it also lengthens the wheel base a little..
 

vwfan79

Active Member
#20
I glad to, I'm just happy I didn't have to tear it apart. It was nice to ride it running right after 2 bum race days.
Get that thing finished and come up and race with us.
 
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