Tuning Engine for More Power / Loss of Performance During Race / My Personal Notes/Ideas/Questions

Arik434

Member
Here are my questions asked in this thread incase you dont want to read my hypothesis/notes/ideas
What color are your spark plugs after a session?
Has anyone experienced a performance difference from changing to a new pump?
Does the type of line make a difference? If so what is the best?
Has anyone experienced temperature differences between these two different style of throttle plates?

Tricks/Tips to gain more performance out of clone engines?




Currently run in a spec clone series (engines sealed from series organizer).

Motor Setup:
-Ducar 196cc
-DynoCam CL2 (https://www.dynocams.com/item/cl2/)
-18LB Springs
-Stock Carb Main Jetted to .038 and Low Speed to .022.

Was fast enough to get pole for my first race this season. We had a caution about half way through. After the caution my motor went from hitting 6100 RPMS before caution to 5500 RPMS after it. After I finished I checked out the spark plug, and it was bad. Carboned up and black. My hypothesis is that I may of fouled the plug when pacing as these engines run rich at low RPMS. Another thing to note is if I held my hand close to he head after the race it felt hot, hotter than normal After the race I went back out on track after cleaning the carb and changing to a cleaner plug and the issue seemed to go away.

What color are your spark plugs after a session?

Another thing to note is I never have the straight line speed compared to other guys, I have been racing for 4 years and this issue has plagued me the entire time. I am great in qualifying, I hate to brag, but I think I am one of the better drivers in the series as far as consistency and getting good times as I am faster in corners. We do a 12 lap average over 3 4 lap sessions and I am always within a tenth of a second delta between all my laps.

I am just trying to check boxes to figure out how to be faster top end wise. With the plug being black, next time I go out on track I am going to try a smaller main jet to attempt to lean it out. This worked for me a few years ago because for whatever reason a .035 main jet in my old carb was crazy fast. At that point it was .003 smaller compared to everyone else.

Another idea came to my mind as well. I have used the same fuel pump for 2 seasons now and have never changed it. Fuel lines get hard over time, so im assuming the rubber, or whatever material that the diaphragm is in the pump has gotten hard, possibly causing a vacuum leak. The pulse line (pump to carb) always has some air bubbles in it. Not sure this is normal or not. I have read cases of people replacing pumps and it making a huge advantage.

Has anyone experienced a performance difference from changing to a new pump?

Yet again while writing this, this came to mind:
I have an older style throttle plate that effectively blocks airflow to the head. Which could lead to higher temps. See image below.
DJ_3146_002__39030.1416842324.1280.1280__12102.1642008211.jpg


Everyone else mostly has this style throttle plate.
DJ-1145-BC_001__35931.1511370186.JPG


Has anyone experienced temperature differences between these two different style of throttle plates?

Finally, my final question. As far as fuel line is concerned, I do have proper line for the Inlet & Vacum. However the OD of the carb does not work with 1/4" ID tubing. I just went to the hardware store and bought regular tubing, I needed to use a heat gun to get it on the outlet for the pump.

Does the type of line make a difference? If so what is the best?


I guess this can be summed at with this question:
What Tricks/Tips do you do gain more performance out of clone engines?
It is so vague, but lets get a discussion going.
Those engines are definitely not all the same. That is why all motor builders blueprint them and dyno test and tune them individually. They may have the same parts, but all the tolerances add up. More than likely, some of the crank gears need to be slightly twisted for them all to be the “same.”

That cam also calls for 10.8lb springs…I think the 18s are overkill…you shouldn’t need to worry about any valve float with those low rpm’s and stock flywheels.
 
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Those engines are definitely not all the same. That is why all motor builders blueprint them and dyno test and tune them individually. They may have the same parts, but all the tolerances add up. More than likely, some of the crank gears need to be slightly twisted for them all to be the “same.”

That cam also calls for 10.8lb springs…I think the 18s are overkill…you shouldn’t need to worry about any valve float with those low rpm’s and stock flywheels.
Forgot to mention, we had PVL flywheels https://www.dynocams.com/item/dc-pv...as issues with valve float with these setups.
 

"J'-remy

Member
my built motor can spin to 7100 with no valve float and 10.8 springs. 18 lb springs are robbing you power your cam has to push through that. heaver springs are for higher RPM . flywheel and the springs have little if nothing to do with each other. put the motor on a dyno it will tell you everything you need to know. these things foul plugs idling all the time. my motor builder wants it back after 20 or so races and if they are local i would get a valve job + springs after 10.
 
my built motor can spin to 7100 with no valve float and 10.8 springs. 18 lb springs are robbing you power your cam has to push through that. heaver springs are for higher RPM . flywheel and the springs have little if nothing to do with each other. put the motor on a dyno it will tell you everything you need to know. these things foul plugs idling all the time. my motor builder wants it back after 20 or so races and if they are local i would get a valve job + springs after 10.
I want to try this. It is a good note now that I am thinking about it.
 
Here’s an update. The main issue holding me back was that a clamp on the axel broke causing the axel to sway back and forth. Once that issue was resolved I experimented with the springs and the 10.8 lbs springs would not get my motor above 6150 regardless of gear. I’m still not there yet, but I’m out of ideas.
 

"J'-remy

Member
Here’s an update. The main issue holding me back was that a clamp on the axel broke causing the axel to sway back and forth. Once that issue was resolved I experimented with the springs and the 10.8 lbs springs would not get my motor above 6150 regardless of gear. I’m still not there yet, but I’m out of ideas.
I had a predator that wouldn't rev on the dyno it was a real dud. Dyno operator said it was likely the valves not sealing properly. 4 seasons sounds like that motor needs a rebuild in a bad way. NKA AKRA all run 10.8 lb springs and turn 6800-7000 all day long so that is not your issue. get it rebuilt its long overdue. cl2 on dynocams site is 6700 target so your not even close to where that cam makes power unless its retarded because of the crank gear not timed correctly (witch is a common problem). Stillwagon at hi tech will take on anything as long as he knows what the rules are and is one of the top builders in the country. or degree the cam and ignition timing, lap the valves and be sure the lash is correct.
 
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