Can't get it right (carb)

MTN13

MTN13

New Member
Oct 24, 2008
150
2
0
Michigan/ Ohio
this damn carb is angering me beyond belief, and i need someone to help please.

I can't figure out why it is bogging down at the top of 6th gear, it runs great from low through the mid range, and even in the top in some gears but when i get to the top of 6th it bogs down and wants to die

i have tried bumping up the main from a 150 to a 160 (PWK 28mm carb) but now it just wants to overload with fuel and break up through the mid range into the top

I also can't get it to idle right. I can adjust it to idle when i first start it but then it will idle and surge once it gets warm. Then i will turn it down and once it cools down it will not idle.

Like i said its a Keihn 28mm carb, 48 pilot, 150 main needle at most lean spot (have tried it in all positions this is only one it will run decent), air screw 1 1/2 turns out, the engine has 180 lbs of compression not sure if that matters, running cam 2 110 octane race fuel mixed 32:1 with klotz.

looking for any type of help or suggestions, all my engine mods are listed in my sig, im just lost on what to do i have tried everything to no results, im just ready to throw this carb in the damn woods and start over

anything i'm missing just ask
 
1997blaster said:
have you tryed doing plug chops ?
Click to expand...


yea i was just going to ask how his plug looked after a wot run. if it boggs on top that kinda sounds lean but hard to say with knowing what the plug looks like.. as for the idle i would warm the quad up and them mess with the idle. you may need to mess with the airscrew and the idle screw to get it right..
 
well after i made this post i went out to try a plug chop and it looked good nice amber color, maybe a little on the lean side, but it started knocking real bad so i pulled it in and shut it down. It did it before but never this bad just a slight tick but it did that before i built it, so i assumed it was normal, but i was wrong, i ended up making a bad mistake. I forgot to put the spacer in between the case and the jug, luckily i caught it before it blew to pieces, so i took it all apart about 20 mins ago and the piston looks good, the head has a slight nick in it but it should be fine, i called my stepdad back home and he said that the spacer was sitting in the box with my stock crank so itll be shipped out tomorrow and i need to order some gaskets to put it back together.

i feel stupid for forgetting that spacer, but i guess sh*t happens. i was thinking that may be the cause of the problem, i called a builder back home and he said that the .060 spacer will throw everything off so it may not be a carb problem at all.
 
I bet you had high compression and maybe a bit of slap...Hopefully your prob is solved, but I noticed you talking about your needle being in the most lean position. That should be telling you that your main is too fat. That is consistent with bogging at high RPM. I currently have a 45 pilot and a 145 main, mid position on needle. Seems ok so far, for what it's worth.
 
so i got the whole top end back together with the spacer in there this time and it runs a lot diffrent. I took it out for a spin and it does really good up top but doesn't like to run down low, i can get it to idle but when it goes up in rpm it doesn't want to come down and it also bogs going into first gear, i think its just that the pilot jet is just to lean so i ordered a new one this morning. It has a 48 in there now and i ordered a 50 and a 52 just in case a 50 is still to small.
 
well i took it to the track again last night. It ran a lot better but i still have a couple problems with it.

1- I need a new clutch in a bad way its slipping really bad
2- i need to richen up the pilot jut its running real lean down low
3- my main prob is that i can't figure out why at WOT in top of 6th gear the blaster will rev all the way up and when it reaches peak rpm it falls on its face and trys to die. Then it will surge in and out, could this be because of the fatty pipe?? i know there not great for up top, just waiting on some money for a new pipe, or is it because of the carb, maybe it can't get enough fuel to the bowls when its that high in the rpm?? i tried re jetting the main and it didn't help, please someone help, any ideas???
 
did you check your float height i thing its supposed to be 19mm from the bowl gasket surface to the top of the float but you have to hold the carb at a slight angle so the float is just touching the needle pin not pusing the springy pin in. cause if your float isnt set right the bowl will start running out of fuel and if it is set right then check your petcock in your tank for any debris clogging it
 
thats what i think is happening, is that at WOT at peak rpm its sucking the bowls dry. anyone have an idea to fix that prob?? or should i just look for a bigger carb.
 
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