V-Twin Forum banner

1 - 12 of 12 Posts

·
Poser .....
Joined
·
101 Posts
Discussion Starter #1
I have been chasing a slight off idle bog with my bike. If you crack the throttle hard from an idle it will noticeably bog maybe 4 out of ten times.

Adjusted the acc pump so it kicks in as soon as it can. As a matter of fact the spring on the screw is so loose I am afraid it may vibrate out. The bog gets worse if I set the acc pump to come on later. I have increased the pilot from 22.5 to 25 - no change.

Someone suggested it may be timing so I went up and down the settings ( advance and initial ) and really felt there was no change. I don't have the s/w for the Hi4 to dig deeper, but I did put the stock ignition back on and it didn't seem to change much if at all.
I sprayed around the intake to head connections with WD-40 and heard no change in engine idle so, I don't think there is a leak there.

So, I am back to thinking it is a carb problem. Once it gets off idle it rips and no hesitation is there. Thought about putting my CV-40 back on just to see if it goes away.

I realize going from an idle to WOT is not a normal occurance during most riding, but the bog bugs me ...

Any suggestions would be appreciated.

My build info is in my signature in case it helps ..
 

·
Poser .....
Joined
·
101 Posts
Discussion Starter #3
Acc pump change ??

Wouldn't putting the #50 in give me less fuel ? It seems like it wants more. ( meaning I start the pump earlier and it reduces the bog )

I guess I am not sure why you are making the recomendation. Have you see this problem before ? I am not questioning your help just need a little more info to understand it.

Thanks for any insight you can offer. :thanks:
 

·
Registered
Joined
·
798 Posts
I cant see where your build would need that amount of fuel that the #70 nozzle dumps into the motor every time you twist the wick.. Although my build is using the Mik. 42 and the #50 nozzle, 165 main &22.5 pilot jet I just thought its easy enough to change out and why not give it a try. BTW Im running 9.8-1 comp with the Andrews 37G cam putting out 104 ft lbs of torque and 100HP and it pulls like a freight train. Good luck
 

·
Poser .....
Joined
·
101 Posts
Discussion Starter #5
Nice numbers ..

You're right it is easy to change. I just need to order one. I haven't found anyone locally that has parts for the Mikuni. Those numbers are nice. I wish I had went with different cams - but at the time the sticker shock of the build was still in effect. Now I want more.

Think Andrews TW-55s. Are you happy with the 37Gs ?
 

·
Registered
Joined
·
798 Posts
Yes I am very pleased with this build. I went an extra step and had my piston domes coated with a thermal barrier coating(Dart Coatings in Sterling Heights). The motor runs cooler and I am able to set my ignition advance to its max with no detonation at all(Zippers ignition).
 

·
Registered
Joined
·
1,991 Posts
Softail_1, remember that the slide in the Mikuni is connected directly to your throttle cable. Whacking it from idle is likely to cause a bog. I had the same build in a Dyna and used a 22.5 pilot, 50 pump nozzle, 98 needle with clip in the middle, 165 main and pump adjusted per the tuning manual.
 

·
Poser .....
Joined
·
101 Posts
Discussion Starter #8
Thnaks for the Info.

I am going to order a #50 a pump. Overall I am happy with the way it runs with respect to throttle response. Just wanting it all - as usual.

Murphdog - Did you ever have your Dyna - dyno'd ? Just curious what I might see as far as HP and torque.


:thanks:
 

·
Registered
Joined
·
1,991 Posts
softail - no, I never had the Dyna on a dyno. It wasn't a big improvement over the CV with a Sporty needle, but I got it for nothing and wanted to try it. I had a little hesitation just off idle with a 20 pilot, which is what most folks recommend. A 22.5 pretty much took care of it, but I could still feel it once in awhile. I adjusted the pump every which way, changed needles, but never got rid of it completely. I liked the Mikuni but decided to trade bikes soon after I put it on, so took it off and sold it.
 

·
Registered
Joined
·
228 Posts
I have the 42 on a 1200 sporty. I think it is too big of carb for the motor. Iv been up and down with jetting.
It will run smoothly off idle. It will hit hard off idle but not wot.
When you twist the wick on a CV it takes a sec for the slide to rise.
And honestly it will only rise with the motor as it builds vacuum. Just because you have vacuum that don't mean its effective. Think about a vacuum cleaner. If you put a larger hose on it it will have less power to pick up dirt. If you put a smaller hose on it the power is stronger.
When you whack the wick on the mikuni it completely opens the port for the vacuum of the motor to pull through.
I have got it to run like a raped ape, but I have to roll the throttle till about 3-4 grand. If I'm rolling about 3 I can go wot and it pulls.
Try moderation off the line.

I also went with a richer needle.

People with cars do the same thing.
Have a stock or mild build and put a 750 cfm carb on. It like **** off the line and pics up with higher rpm.
Pull the 750 off and put on a 600 and they rock.
 
1 - 12 of 12 Posts
Top