September 7, 2015 at 2:48 pm #53940
Just got back a comer I had a new piston and ring job done. Fired it up spent some time getting it broke in -all good. Took it out to get some practice on it and the motor will only turn 11660 max at 375 temp down the straight. The motor I was using just before I swapped them out would run 12750 rpm down the same track. Using the same gears what could be going on and what can be done to get the rpms up on the new motor?September 7, 2015 at 10:03 pm #53960
Carb is the most likely issue. Try swapping the carbs.September 8, 2015 at 5:32 am #53962
Everyone I’ve talked to say to lower my axle gear, would this help? The rpms I list were at the end of the longest straight.September 8, 2015 at 7:17 am #53964
I have learned that the Comer 80 works best when max RPM is in the low 12k range depending on the drivers ability throught the tight sections to carry speed.
If its same chassis, day, and driver, with a different motor I would look to the carb.September 8, 2015 at 7:46 am #53967
There are many ways the kart, tires and the track could be slowing you down. Trying reaching out to your engine builder for help.
LAD Specialties customer / tony kart / rotax / kt100September 8, 2015 at 9:10 am #53970
Thanx for the replies. I pulled off the carb to clean and kit it and noticed that the idle screw was turned in some not allowing the butterfly valve to close fully. Could that be a possibility?September 9, 2015 at 9:31 am #54048
the throttle stop keeping the butterfly from closing is not going to have an effect on the max rpm’s from the motor. While you have the air cleaner off, check that the butterfly is opening completely. Also check that the throttle pedal stop will not allow the throttle to try to get past full open. That will put undue stress on the carb. Are the other carb settings now the same as when you sent the engine in?
LAD Specialties customer / tony kart / rotax / kt100September 11, 2015 at 6:38 am #54116
Yes the carb settings are the same and nothing has changed on the pedal movement. I hear these motors are temperamental and just won’t run right if they are not built right. I’ll try another carb and if that doesn’t help, it’s going to the dyno shop.September 11, 2015 at 4:12 pm #54148
Another thing to consider is:
If the driver is not setting up for the last corner before the straight away, and does not come out of the corner fast enough, it will never reach the desired RPM, there isn’t enough time, or enough track left.
Most of us struggle at the horse shoe, if we don’t set up for it we won’t come out of it fast and right, we cannot recover latter and we won’t get the speed or the RPM we want. Just a thought. Fast Freddy 😉September 11, 2015 at 4:43 pm #54149
Thanx Freddy. That’s a good thought but when he’s consistently running low 32’s and even a 31 last race and now he can’t bring down below a 33.5 all of a sudden with a motor change I don’t believe it’s in his driving. Something’s up lookin at the mychron when it hits 9000 it still climbs, it never tops out, but is slow to get to 11650. Hopefully a different carb or going up a tooth will help get us thru this race.September 11, 2015 at 4:50 pm #54150
Is the motor still fresh/ too tight? Try a new plug
Are you running the same rear sprocket and same clutch driver?September 11, 2015 at 5:17 pm #54151
Only thing changed was the motor. Fresh top end lots of compression 1% leak down. Your saying it make take a bit for the ring to seat before it comes up to where it should be?September 11, 2015 at 6:19 pm #54153
if you were getting considerably more rpm with everything identical but the motor and it’s getting full throttle then it’s likely carburetion or and internal engine issue like stuck ring.
BUT the first thing I would do is check and make sure the clutch has the right gear on it. It’s a common problem I see all the time when swapping engines and forgetting to make sure it has the same clutch gear. If that’s not it and putting the carb off the previous engine on doesn’t work then send it back to the original builder and tell him it has a severe issue he needs to figure out.September 13, 2015 at 10:16 am #54176
Ok got it figured out….Whew! Well turns out the flywheel nut was loose and throwing the timing off. Thanx everyone for the help!September 14, 2015 at 3:53 pm #54247
I was too busy repairing Dave’s kart and my own kart during the race, that I missed your kid’s race, and from what I understand he did a great job! Could you please send me some videos?
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