Engine bogs on low end, then cranks up...

  • Thread starter Thread starter Keith81
  • Start date Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.
K

Keith81

Guest
I got an obr 27.2 full mod... Its bogging on the low end but once the RPMs build up its a god damn rocket... Would timing be an issue here, I don't think I did the credit card thing when I installed the coil... I've tried tuning and tuning and tuning and to no limit, this thing idles right, runs right, starts on the 2nd pull and seems to do what its supposed to do... I just can't get rid of the low end bog... Its got a brand new walbro wt-990 on it, and it did the same thing with a walbro wt-668... I prefer the choke but I know once its warmer out the wt-990 is a must have...


I need help to get this bad boy running right....


Please save me!!!!
 
I would agree. The idle screw should be set just past the tip. When you lean the L needle it should start to rev.
 
So lean it out, and let the idle come up... then use the idle screw and bring the idle back down ??
 
Yes. The idle screw is normaly touching the throttle just past the tip of the screw. No more than 1/4 up from the tip of the screw.
 
I tried and no good results come outta this....

Could the timing be playing an role here ? (coil/flywheel gap?)

I just want this bad boy to scream all through the rpm's like it does on the top end....

Otherwise I'm just gonna sell the full mod and put the 23cc pro back on it and then maybe sell it..

No fun when it don't run like it supposed to!
 
well I think I narrowed it down to a loose spark plug ?

it was loose to my hand being able to unscrew it off...

either way I put the 23cc pro back on it with the jet pro pipe and tgn stack/filter, was having a lot of fun doing donuts n stuff, runs 110% better now...

Anyone interested in a OBR full mod 27.2 cc ???? That needs to be tuned correctly ?
 
Keith81 said:
I got an obr 27.2 full mod... Its bogging on the low end but once the RPMs build up its a god damn rocket... Would timing be an issue here, I don't think I did the credit card thing when I installed the coil... I've tried tuning and tuning and tuning and to no limit, this thing idles right, runs right, starts on the 2nd pull and seems to do what its supposed to do... I just can't get rid of the low end bog... Its got a brand new walbro wt-990 on it, and it did the same thing with a walbro wt-668... I prefer the choke but I know once its warmer out the wt-990 is a must have...I need help to get this bad boy running right....

Please save me!!!!
Click to expand...
sounds like a bad carb diaphram. I bought two 990's new and both were junk out of the package, so I'll stick to my 813's
 
Its not a brand new 27.2 cc so I dunno if it is the long rod then, I do know it SCREAMS on the top end like no other I've seen or had...

I've to two 990's myself, both did this, and so did a 668.... so I dunno... I think I suck at tuning...
 
I reconize the engine due to I have one myself, as for the carb issue, the 668 could do the same because of the diaphram or the top plate warped like I've had one do. As for the 990 I really think there is a bad batch floatin through DDM
 
my 668 works perfect on my 23 cc pro... So I dunno... Maybe it is the carb... Ya got me though... What model is your 27.2 cc ??

I am gonna strip it down to a long block and sell it that way I think so its a bit cheaper...
 
sounds like you needed tighter clutch springs,the higher modded engines rev higher but trade a lot of bottom end power,you need to clutch the engine to engage where the power band hits,if the clutch engages before the engine gets on the pipe it will bog .I see so many engines sold by HP ratings but never a torque rating ,HP means very little with out the torque curve.HP is work over time ,torque is the force that can be applied by the engine .

Think of HP this way .you have a little fast kid with a spoon and a big slow guy with a shovel ,they both move the same sized pile of sand the same distance in the same amount of time .They would have the same HP rating .There you have it, work over time=HP. It means nothing really without torque.that 27 motor you had most likely has way less torque all through the rpm band then your 23cc but the 27 does more work at the top end because it revs higher so it has a higher rated HP. Engines are air pumps and can only be made to pump best at a given RPM. Roger
 
Back
Top