Box Stock

Stock Predator RPM issues

H

Hobby87

Member
We are running a sealed stock predator class - only modification is removal of governor and added weenie pipe. Noticed my kid was only turning 2700-2800 RPM's the first two nights and figured he just taking it easy since he is just starting out but he said he had it floored.. so I put kart on the stand and ran it wide open and sure enough, maxed out around 2800 rpm. I figured either the valve's are floating or the rockers are waaay loose.. so I unsealed it, and yes, rocker's loose / lash was off, set lash and was able to get to 3300 RPM but no more. Thoughts? We have to run stock springs, but it seems they are either floating at 3300 or the stock carb setup is keeping us from getting anything else out of it? OR the tach is not working correctly (Mychron 4)

Thanks, Matt
 
Who seals it is the person too speak with .
Tach would have to be either 2 cycle or four cycle . So it would be 6600 if it was set on 2 cycle . 3300 if set on 4 cycle . You might have a dud .
2 cycle is the correct setting . It fires every stroke .
 
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flattop1 said:
Who seals it is the person too speak with .
Tach would have to be either 2 cycle or four cycle . So it would be 6600 if it was set on 4 cycle . 3300 is probably correct. You might have a dud .
Click to expand...
It needs too be on 2 cycle by the way .
Fires each revolution not every other like a chevy v8.
 
Hobby87 said:
the tach is not working correctly (Mychron 4)

Thanks, Matt
Click to expand...
If your tach wire is wrapped around the the plug wire try connecting it to the kill switch wire. Don't wrap it, put a connector on the tach wire and plug it in. My clone motor and mychron 4 have to be run that way. For test purposes just skin the wire back and tape
 
The other question.
Was it a dog in the race ?
If it was totally slow its obviously not doing its thing rpm wise .
 
271mac said:
If your tach wire is wrapped around the the plug wire try connecting it to the kill switch wire. Don't wrap it, put a connector on the tach wire and plug it in. My clone motor and mychron 4 have to be run that way. For test purposes just skin the wire back and tape
Click to expand...
can I see pics of what this looks like? Seems simple but not 100% following
 
not in the fight, but again, only 3 races in, so had assumed he was taking it easy - gets lapped in heats and feature. I wouldn't say it matched RPM exact, but within 200-250 rpm's, would you assume under load (on track) it would have alot lower RPM's? total weight is 266 lbs, so not pushing alot of weight.
 
Hobby87 said:
can I see pics of what this looks like? Seems simple but not 100% following
Click to expand...
The rpm wire on a mycron uses an inductive pickup on the back of the gauge. That's the posts the wire is threaded around.
Wrapping the other end of the wire around the spark plug wire does the same thing.
Clones sometimes do not produce a big enough energy field to work 2 such connections.
So connecting one end directly to the kill wire eliminates one inductive pickup.

You are not sending spark voltage thru your gauge.
 

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Hobby87 said:
not in the fight, but again, only 3 races in, so had assumed he was taking it easy - gets lapped in heats and feature. I wouldn't say it matched RPM exact, but within 200-250 rpm's, would you assume under load (on track) it would have alot lower RPM's? total weight is 266 lbs, so not pushing alot of weight.
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most stock winning karts in the pred class are only running around 4800rpm. that is the torque sweet spot. If a kart is running in the front with the max rpm of 5500 i would be suspicious of that engine !
 
So I have an update - I went through the Mychron4 and for some reason it was set to divide RPM by 2 SMH.......:rolleyes: So he's actually maxing out the RPM around 5400.. no wonder it is floating the springs!! Time to reduce the gearing to get closer to 4800-4900 range. I have no answer for how others are lapping him, but suspect they are no stock/legal, but we'll focus on driving and our program before caring what others are doing.
 
Jusy checked mine again. Let it warm up good. 5432rpm on the stand with governor hooked and motor surging. What i worry about is if I come of the track and they check me right then will the motor be over our 5500 on the stand rule. I worked hard to get it where itis at. I hate to change anything. My max rpm the other night was a little over 4700 on the track. I know it sounds like a goofy question but if i gear on the track to turn 4900 will it effect rpm on the stand. I don't think it should but i get confused thinking about it.
I do know i can make it turn more than 5500 on the stand with the governor on it
 
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