craps out at top end

R

radrob

New Member
i got 120 miles on my bike so far. ir is running stronger and smoother than it was to start with.
my only problum is that at top speed (24 mph) it runs very poorly. If i back off the throttle just a bit it smooths out and runs alot better. I havent adjusted my needle in the carb yet. Is that what you would try. If so witch way shouls i go its in the middle right now.
robrmfla
 
Tell us more. Stock spark plug? Change it.

Stock exhaust and no gasket port matching? Check it out. Big power robbers.

I don't think the needle will make much difference at top end, but try one notch each way and see what happens.

Is the intake track well sealed, no leaks?

Check your new plug after several hot hard runs. How does it look?

You may consider the main jet is typically a bit rich. .70mm or so. .65mm is a bit better.

What is your rear sprocket size?
 
i am running a b5hs ngk plug. I switched out the plug wire . 44 tooth sprocket. ( i have a 40 tooth on order) put silicone sealer on the carb to intake connection.
it runs good 20 to 22 mph i was hoping for a little more top speed!
 
What does your plug look like after a hot hard run?

Have you tightened your head nuts lately?

Also at the very least match the exhaust gasket and exhaust flange to the exhaust port outlet.
 
radrob said:
i am running a b5hs ngk plug. I switched out the plug wire . 44 tooth sprocket. ( i have a 40 tooth on order) put silicone sealer on the carb to intake connection.
it runs good 20 to 22 mph i was hoping for a little more top speed!
Click to expand...

Change your jet in the carb....even with a #65 I still ran rich and 4stroke all the time. Your engine is simply taking in more fuel and not enough air. If you can get more air into it, example and intake or change the jet out itll run better. Your plug should be gapped at .018" and .022" any more than that is gonna affect top end speed, not that youre gonna get much top end with a 44T.
 
Does it sputter when you have it wide open, (too rich) or seem to surge and feel weaker? (too lean)

What fuel to oil mix are you running? Go to at least 24:1 or even 32:1.
 
the plug is dark around the outside and light brown in the middle.
I had my gap at 25 i will reduce it.
what is the torque on the head bolts.
it kind uf sputters at top speed
 
Hmm...fuel ratio seems OK by your description.

Torque depends on your stud size. 6mm (10mm wrench) 10-12 ft-lbs. or 8mm (13 or 14mm wrench) 14-16 ft-lbs. Please don't blame me if the stupid acorn nuts strip.
 
i changed the needle to the first notch. didnt help. re gaped the plug to 18 nothing.

I bought another kit for my cruiser bike got it running today and it is already way faster than the one with 170 miles.
 
I just canged my main jet to a 0.80mm and now it screams at WOT. I have the same problem as u to.

Steve
 
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well i havent chainged the jet yet. i have moved the needle up and down . the guy i got the new kit from modified the muffler . so i took mine apart and cut and drilled some holes. put the needle back in the middle.
Got it up to 37 with the stock 44 tooth!! on flat ground
have a 40 tooth on order
usflg
 
I have got a 36 tooth sprocket and it will cruise easy at 36 - 37km/h. Have only done 500km's so I still want to run in a bit more prior to flogging the crap out of it. I took the cap off the muffler and took that pipe out and drilled a 3/4" hole in the cap and then screwed in a barbed socket and put some 3/4" rubber motor water pipe on. Goes great.

Steve
 
I must say though that all these crazy tops speeds I keep reading about make me wonder. With all the tweaking and mods I have done it only makes it run betters or smoother up to 40km/h then it craps out. I think these things are just not made to to do 15000rpm and 100km/h. I enjoy speeding around at 36 or 37km/h without any problems.

Steve
 
Try putting your choke about 1/3 more or less on. If it's worse at WOT then it's too rich. If it's better it's too lean.

BTW: That's right out of the Delorto carb tuning manual
 
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I have my needle on the top slot and after running at WOT its a perfect clean light brown colour. If I put the choke on while running it will crap out.

Steve
 
Ok choke not all the way on, just on a little. If you have that bog at totally wide open it will tell you if your lean or rich. If there's no change put it on just a little more. If the bog gets better your lean, if it's worse your rich. With the slide all the way up your totally running off the jet. The needle shouldn't really be affecting it much. The needle is for controlling mix at mid throttle.
 
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