cant figure out bottom end bogging

[nickf74]

I have a 94 Blaster B1 that I have rebuilt and have been having problems tuning it for bottom end performance. It runs very good on the top end and idles very well. It bogs then cleans up as it gets to full throttle when I punch from low speed or when I am at high speed then slow down for a corner and punch it. I have played around tuning the carb and tuning the pipe jets, but havent figured it out. My blaster is setup with the following:

-stock 701 61x case
-ADA head 35cc domes
-carbon tech reeds
-lightened flywheel
-single blackjack 44 carb
-SJ spark arrestor
-Factory B limited pipe
-jetworks flow control valve
-Solas mag pump
-Hooker 10/16 prop
-bored out stock nozzle (i think about 1mm bored out)
-Worx 201 intake grate
-jet dynamics ride plate

First I thought the pump was getting too loaded up so I got the nozzle bored out, I think it was bored out about 1mm, but it still has the bog. Now I am thinking I just dont have it tuned right. Between tuning the carb, tuning the factory B pipe jet screws and adjusting the flow control valve, I think something is off or a combination of things is off. I have read many things about tuning carbs and tuning the exhaust, but I feel like I just cant get it perfect, unless it is something else. Should I tune the carb first then the pipe, or vice-versa? Should I try a different setting on the pipe jets? And what is most likely causing this bogging? Any help or direction would be a help.

 

[Vumad]

Not sure on that carb setup.

The ski can run good with no pipe adjustment. Tuning the pipe might get more response in one area or another but if you have a significant bog or hesitation then it is being caused by something else.

Be sure its a bog and not a hesitation. Sometime lean and rich feel a lot a like.

Again, not sure on your tuning but try raising the popoff, or lowering the popoff and going smaller on the pilot jet. Again, be absolutely sure its a bog because you're going leaner.

Also research what others are using for props, nozzles and tail cones. Too much prop kills the bottom end. It will be impossible to tune on the bottom if the prop is too steep.

If you don't have a tach, get one. I've been using hardline.

 

[Quinc]

What size jets, seat and spring are you running? You should look up the Factory blaster limited pipe instructions and start with there recommended jetting, pop off and go from there.

 

[nickf74]

Hi guys, I was traveling for work, but got home today and pulled the carb to see what the settings are:

Main jet = 165
Pilot Jet = 130
High speed screw = 1.75 turns out
Low speed screw = 1.5 turns out
pop off = 16 psi
seat = 2.5

I have a blackjack 44mm carb that came with that pilot jet, pop off spring and seat. Im not sure what the size of the spring is, but the pop off is about 16 psi. I had main jets from tuning quads and dirt bikes, but I dont have pilots and springs. I am going to order some pilots and springs so I can get this ski tuned. I have to read up more on tuning and the order to tune things, but what should the pop off be around? I was thinking it would be around 20 psi.

 

[RoscoeJ]

I had similar problem .I thought I had a carb problem ,but found my plug wire ends were corroded.

 

[joeiscold!]

I have had the same situation with my blaster when I got a single carb.... do some reading and it will help alot. I think group k has a great article on carb jetting.

If you are getting hesitations when slamming on the throttle, but then in clears up after a second and takes off quick that is typical lean situation....

If you have a bog that seems to clear up whilst slowly building up revs when you slam the throttle that would be a rich situation.

It is best to jet starting with the low (pilot) circuits and get that crisp then go to the high circuit (main). You will find that your bog if it comes when you "gas it" out of a corner may very well be lean on the high. IDK But 165 does sound a bit lean if you have mods on your engine, maybe someone could chime in with there jetting specs who run similar setup. I have a stock engine with single carb that runs 165 high and 115 low from memory. Good luck...

 

[capitalcrew]

Call art for jetting