low rpm issues

graydog8josh · May 9, 2014

i have dax iv motor with rt carb 66 jet
bp6hs plug
new cdi
torquer 2 pipe
crmachine 7cc head

and it runs real bad off idle and seems to clear up after getting up to about 20mph. its missing really bad. what should i do next?

crassius · May 9, 2014

I'd first try moving the needle clip to see if a diff setting helps - if it does, then you will want to recheck the float level & main jet to be sure the needle change didn't make you too lean at higher slide openings.

2door · May 9, 2014

The RT carburetor almost without exception needs a smaller jet than what comes in it. You might be seeing an over rich condition at low rpm. By the way, any Chinese 2 stroke will buck and jerk if you try to ride too slow with the clutch engaged. Anything below about 10 mph and we recommend that you squeeze the clutch lever, disengage the clutch, and pedal. Same for starting from a dead stop. After the engine starts don't engage the clutch for a few moments and never below 10 mph.

Tom

graydog8josh · May 10, 2014

would a leaky crankcase seal cause low rpm roughness? i opened up my crankcase to find my coil and magnet had a little oil in it. I sprayed it out with electro contact cleaner but the roughness persists.

maniac57 · May 10, 2014

Oil in the sidecover is a good sign for seal replacement. It's too cheap to risk a lean mix and blown up engine.

graydog8josh · May 10, 2014

never replaced magneto side gasket before but going to go from the ground up on this to see if the problem goes away

Ive already replaced plug, wire, coil

Im going to replace
magneto, magnet, magnet side crank seal.
additionally im going to go with the manic mechanic intake, maybe ill get it to run correctly

maniac57 · May 10, 2014

I'd start with the seals. Coil either works or it doesn't, same with magnet, unless you have a bad magnet keyway. Search for thread to find which you have.

graydog8josh · May 11, 2014

i dont think it fixed it but i reseated the seal and now it only has a big hesitation about 18mph and then it is just 4-stroking at full throttle. also discovered teh very bottom case screw could be tightened about a quarter turn, i dont know if it stripped or if it was just loose from Dax reassembling the case with the black allen bolts. Im about to say this is the best its going to run. I guess this motor is a dud.

Shame, this is my first "new generation" dax motor and it had a bad head (pitting on sealing surface of head) and bad crank seal. Guess my tastes have gotten as such that i need to buy more expensive motors that have been gone over more thoroughly.

maniac57 · May 11, 2014

Simply reseating a seal might not cure a leak due to wear from being in wrong. New seals are cheap and easy to do. Tighten ALL the case bolts as well, including the three hidden under the large clutch plate.
Four-stroking at full throttle indicates too big a main jet.

graydog8josh · May 15, 2014

Got seal in the mail gonna see if that was it

Davezilla · May 16, 2014

graydog8josh said:
i dont think it fixed it but i reseated the seal and now it only has a big hesitation about 18mph and then it is just 4-stroking at full throttle. also discovered teh very bottom case screw could be tightened about a quarter turn, i dont know if it stripped or if it was just loose from Dax reassembling the case with the black allen bolts. Im about to say this is the best its going to run. I guess this motor is a dud.

Shame, this is my first "new generation" dax motor and it had a bad head (pitting on sealing surface of head) and bad crank seal. Guess my tastes have gotten as such that i need to buy more expensive motors that have been gone over more thoroughly.

If the bottom case bolt threads are stripped, this can easily be fixed by using a slightly longer bolt and putting a nut on the other side, helicoils also work good there, but putting a nut on the other side is the quickest and easiest way to fix it. If you got a case leak there it would cause the same type problem as well.

graydog8josh · May 17, 2014

replaced magneto seal, i think this is the problem.

While hunting down the performance issue i did the stupid thing and upgraded the motor, so my base tune is probably dead wrong. I thought i just had stock performance because it was a stock motor.

so now my motor is a little different and im trying to get it dialed in right.

that's dax gen iv motor
fred head 7cc combustion chamber
ngk bp6hs plug
manic mechanic intake plenum
rt carb with 68 jet(4-stroking may go down to 66 again)
boygoesfast banana pipe with sickbikepart muffler attached with silicone tubing(probably major exhaust restriction)
running a 32 t sprocket on back with 20" wheel (26" cst cyclops tire in front) for that aggressive feel

Im about to put on the torquer 2 pipe and the 66 jet

I cannot feel much of a difference between the stock intake and the manic mechanic yet but i dont have a speedometer hooked up so i can see any speed changes

Also, i dont really understand teh correlation between compression and plug heat. I have a 6 in there and ive never really had the guts to run a 5 plug even though its been in the 50's for days, sometimes it gets around 80 and hovers there for a while and i dont think i make a habit of changing my plug whenever a cold front sweeps in or it gets really hot outside.

graydog8josh · May 19, 2014

it was definitely the seal. when i removed the seal it was gummy and the mag cover had lots of oil more than before not just a drip. after replacing the seal i felt an immediate improvement. i changed the piston for a fred cut piston with trimmed skirt. now its running smooth all the way up to 7800 rpm. it revs a lot faster.

graydog8josh · May 20, 2014

here is a video of the engine running, wanted to see if someone could tell me what the misfiring is.

https://www.youtube.com/watch?v=Vpwg66-lAMA&feature=youtu.be

maniac57 · May 20, 2014

Mine recently was doing the hiccup thing yours displays a lot worse after I drilled and set my jetting finally. Seemed to me like the spark was being blown out or overwhelmed. Some careful gapping and plug selection helped, but it continued to be very noticeable and annoying.
I never found a fix until I recently installed a HD Lightning CDI.
Now mine pulls from almost idle smooth and clean.
Mine seemed to really start acting up once I had the jetting optimized and after I installed a Fred head so this leads me to believe the stock CDI simply could not produce a strong enough spark, especially with a decent head making the mixture more turbulent with an actual squish effect.
Now it runs like it should considering it's a stock ebay bottom end. It will now also rev farther than I'll ever feel safe running it but I really can't speak if it improves overall speed. All I know is my engine sounds and feel much happier now with the Lightning.
Just my opinion.

graydog8josh · May 20, 2014

gonna try a b8hs plug with a smaller gap and see if that makes it run better

graydog8josh · May 20, 2014

B8hs runs worse

graydog8josh · May 20, 2014

did a compression test, my compression is 110 psi. Thinking i can raise the compression a good bit. (used harbor freight compression tester)

crassius · May 20, 2014

new motors sometimes take 50 miles to get enough seat on the rings to raise compression

sounds like you have enough to run, but may need to adjust carb a bit for more power

graydog8josh · Jun 2, 2014

the gap on my b8hs was wrong, thats what was wrong there. I put it back in and it ran okay, the ignition i replaced wiht the HD lightining coil and now it runs correctly, a little rich even at 66 jet. Im nervous about going to a 64 and i have a 65 jet i got with the rt carb but im also nervous about that because it is not an original dellorto jet and im not sure if it is precise. it will go 35 now and it has no rough spots in the acceleration until it gets to full throttle then its fourstroking a bit. with a 20" wheel and 32t sprocket 34mph is 7800 rpm i think, i dont think that i can ask for much better than that with my current setup
i cant really tell what hot is on my head, so i might order a TTO gauge or something os i can monitor my head temps.

I was pleasantly suprised that a weak ignition was my problem especially after replacing the magneto the coil the plug and the wire, the seal and the head.

low rpm issues

Member

Well-Known Member

Moderator

Member

Old, Fat, and still faster than you

Member

Old, Fat, and still faster than you

Member

Old, Fat, and still faster than you

Member

New Member

Member

Member

Member

Old, Fat, and still faster than you

Member

Member

Member

Well-Known Member

Member