Hi! My son recently got a 99 Blaster. It has a Pro Circuit full pipe, Vforce 4 reed assy, pre-mix, 155lbs compression, airbox lid removed, K&N air filter, timing advanced, 93 octane 32:1, jetted with a 290 main, and plug chop looks great with the help of some amazing people on this forum. My issue is that at very low throttle in any gear it makes a sort of banging sound and what I call "bucks". It just wants to go faster or slower, not maintain a slow speed This Blaster idles perfect and revs flawlessly throughout the entire RPM range. I can't figure it out! It only happens at about 1/8 throttle in gear. Also did a pressure test that it passed as well. Can anyone think of anything to check that I might have missed, short of pulling the engine apart? Could this possibly be a timing issue? It runs incredibly well other than about 1/8 throttle..
Hard to ride slow
- Thread starter BlueBlaster99
- Start date
1/8 to 1/4 throttle is where it transitions from pilot to needle jet circuit
I'd be looking at carb related first....
have temps changed ?
airscrew may need a slight adjustment ? what turns out are you now ? is that where it achieves highest idle ?
it may rev clean in neutral, but under load may need a slight adjustment
what needle clip setting ? should be middle slot
needle jet removed and all the little holes cleaned ? after the main is out and cap/needle out, the needle jet pushes up into the throat and out (don't lose or forget the brass washer under the main jet)
oil injection port blocked off on the carb ?
electrical .... B8ES plug ? check plug boot and wire, all connections especially at the coil and that ground
I'd be looking at carb related first....
have temps changed ?
airscrew may need a slight adjustment ? what turns out are you now ? is that where it achieves highest idle ?
it may rev clean in neutral, but under load may need a slight adjustment
what needle clip setting ? should be middle slot
needle jet removed and all the little holes cleaned ? after the main is out and cap/needle out, the needle jet pushes up into the throat and out (don't lose or forget the brass washer under the main jet)
oil injection port blocked off on the carb ?
electrical .... B8ES plug ? check plug boot and wire, all connections especially at the coil and that ground
Thank you both for your responses! After reading your suggestions I have discovered that the washer under the main jet is in fact missing. I have no idea if this alone would cause my issue, but it is a good place to start. To answer a few of your questions.... The spark plug cap was recently replaced, the air screw is set at approximately 1.5 turns out, the air jet is the factory size, the clip on the needle is set to the middle position. the oil injection port is plugged with a small piece of hose with a screw in it, and I am running a B8ES plug. A washer will be here in a few days and hopefully, that will be the issue?????
Awk, a question for you. You mention a needle jet. All I see is the main jet, the washer that I just received. the needle with the clip to adjust, but nothing else.... Where exactly ids the needle jet located? is it the brass piece that seems to be pressed into the center of the carb that the main jet screws into? If so, how does it come out? I can look through the carb from under the main jet through and I don’t see anything. Could it be missing????
Last edited:
Also noticed turning the air screw in beyond 1.5 turns slowly kills the motor, however turning the air screw out beyond 2 turns makes little if any difference. Could this mean something? The air jet is stock, needle clip in the middle. Thank you so much for helping me with this. This atv is slowly killing me. lol
yes, I find the correct size socket and gently tap it up into the throat of the carb and out
it has tiny holes in it that may need cleaned out, it pushes back down in and the main jet and washer hold it there
for the airscrew, are you giving it 1/4 turns and waiting 20-30 seconds between turns to see how the engine reacts, turning it too fast will indeed produce what you describe
Okay, I've done everything I could, and made things better in one aspect, but...... The rough running a low throttle while going slow has now been accompanied by an increasingly getting louder knock. Can anyone think of something with the engine that would make it jump/buck/run rough at low throttle as well as make a knocking sound? It seems to get worse when hot and does it more when riding slowly than idling. I am thinking of pulling the cylinder tomorrow just to take a peek at piston clearances and rod play. Any suggestions on what to look for? It really sounds like it's coming from the piston more than the gear train, but it is so hard to tell since its hard to duplicate at idle.
I WILL WIN! LOL Thanks everyone
I WILL WIN! LOL Thanks everyone
Well hell... I did not know that about the needle jet. Been riding Blasters for years. Learn something new everyday!!
I'm pretty sure you wouldn't have 155psi compression if there was excessive piston/cylinder clearance.
the only other knock I know of would be detonation, but 93 octane should prevent that with 155psi.
how did you achieve 155psi. ?
turn the timing back to zero and see what it does. it's only adding a slight increase at lower rpm's, but taking away from higher rpms.
Last edited by a moderator:
It does indeed have a blue plastic ring. I did not notice any type of spacer, and the head looked stock to me anyway. I just bought this engine from Ebay, and have had a hell of a time figuring out the odd noises, and rough running of this thing. I did contact the seller that I purchased the engine from, and he agreed to let me return it for a refund. Now I'm back at square one. A Blaster with no motor. If anyone out here has a good problem-free engine with good compression for sale at a decent price, let me know, please.
I have a crank, rod, piston, rings, cylinder and head, all a package, that came from a perfectly running motor for sale if that would help you out. 120 psi compression before removed to go to a 240, stroker kit.
Is the plastic melted? Even on a computer I couldn’t see clear enough. It’s been so long since I’ve worked on an engine I forget how much room is between rod and piston.
We’re it me unless you find an engine from someone that’s reliable I would just rebuild what you have. DO NOT buy a Ching Chong cylinder. Have your’s bored to next useable size over. It needs to be measured, piston bought, then bored/honed to fit THAT piston.
We’re it me I’d get the Vito’s 3mil. Nice easy power increase and not much more than stock crank.
JMHO
We’re it me unless you find an engine from someone that’s reliable I would just rebuild what you have. DO NOT buy a Ching Chong cylinder. Have your’s bored to next useable size over. It needs to be measured, piston bought, then bored/honed to fit THAT piston.
We’re it me I’d get the Vito’s 3mil. Nice easy power increase and not much more than stock crank.
JMHO
Do any of you think that that crankshaft might be fine to use in its condition? Not sure what that plastic does on there. I think the main issue was the pretty significant play around the rod bearing. The piston slid back and forth quite a lot
IIRC, they were referred to as crank stuffers, a way to reduce volume in crank area. Believe it’s to increase secondary compression ratio.
