Serious flat spot around 4k RPMs?

[Moespeeds]

Hey guys, since making some changes to my bike I've got a serious flat spot right around 4000 RPM's. It's so bad it's like hitting the rev limiter, but it only pops up during hard accelleration. I made the following changes, all at once:

-adjusted pushrods
-changed ignition to a single fire DYNA 2000i. Tried advancing ignition a little, using curve #3
-Changed air cleaner from a BM spike to a stainless creations "apocalypse"

I'm pretty sure the Apocalypse is letting in more air than the spike did. What do you guys think, play with the ignition or the jets?

 

[johnny2]

I had a similar issue most of it was cured by opening up the tank venting, on the split tank bikes under the dash there is a couple of pipes with caps on them not sure about single tank models but remove these caps and pet a hose on them I also added a check valve for a dirt bike that wiil vent but not let out the liquid. I was also very lean through the middle but never got the poping out of carb over 2500 rpm,with out an o2 sensor or a sniffer you will never get the carb set perfect and that is very hard on any engine. my mid range was so lean that it didnt register on the o2 and after the tank venting was fixed I didnt notice it was lean. You can pull off the fuel line run it out from the bike (longer hose required) keep it at the same level as the carb and let it run into a bucket watch the horizontal to vertical arch of the fuel if it gets shorter you are restricted mine took 30-40 seconds to show up the other thing was the hose touching the engine the vibration causes bubbles to form and the fuel flow slows. good luck

 

[Moespeeds]

I did have to re-route my fuel line because of the new ignition. Plugs looked good but initially but I'll check them again.

 

[05chop]

Hey guys, since making some changes to my bike I've got a serious flat spot right around 4000 RPM's. It's so bad it's like hitting the rev limiter MOESPEED does the dyna ingition have a adjustable top engine limit? Could be your on the low side of the trim pot. This would mean 4000k max rpms?

 

[Moespeeds]

Yeah rev limiter is at 6k. I'm not actually hitting the limiter, I can push through it but I've gotten in the habit of just shifting. I haven't had allot of time to fool with it because of all the other issues I've had recently. Heading to Myrtle Thurs so hopefully I'll have time to beat on it over the weekend down there. Would this be a symptom of an intake leak? The new air cleaner had no gasket between it and the carb.

 

[Moespeeds]

Ha, there is a screen down in there, and a red LED light now

It's cool, at idle you can hear the thing sucking air.

 

[lee]

Jesus - first time I've seen a set up where the intake is almost as long as the pipes have you done all that and not changed the jets at all?

 

[Moespeeds]

No I rejetted 3 years ago when I put the spear intake and first set of short pipes on. 3 sets of pipes later, but they have all been basically the same, really really short, so no jetting changes. I'll pay close attention to where the flat spot is this week and post back. The intermediate kicks in at 2500? Like I said, plugs looks good after the first 50 miles, but I'll check them again.

 

[lee]

you might want to shut off when you hit the flat spot to give you a better reading on the plugs - do it safely though!

 

[Raywood]

The intermediate kicks in at 2500?

No the "main" jet starts coming on at about the 2500 rpm. It can be controlled by the airbleed that you may or maynot have. Stock BD carbs didn't come with them but if you had your carb modified by Triple X then it has the airbleed installed.


Here is a great example from Zippers website just ignore the Thunderjet part of the graph. The rest shows how the intermediate and main jets transition.

:flag:

 

[lee]

has anyone changed from the standard size air bleed??

 

[Raywood]

has anyone changed from the standard size air bleed??

No, I haven't and my bike is tuned pretty good with a 29.5/72 combo with the stock .40 airbleed.

 

[lee]

yeah mine works well too with the .040 - I've never heard of anyone on here doing it

 

[Chopper Dave]

Yeah rev limiter is at 6k. I'm not actually hitting the limiter, I can push through it but I've gotten in the habit of just shifting. I haven't had allot of time to fool with it because of all the other issues I've had recently. Heading to Myrtle Thurs so hopefully I'll have time to beat on it over the weekend down there. Would this be a symptom of an intake leak? The new air cleaner had no gasket between it and the carb.

Damn Moe....that dual stack looks Ignorant!:2thumbs: SIICK!!

 

[Moespeeds]

Now I just need some new pipes, that will be my mission in Myrtle. I'm heading down tomorrow.

 

[CCRainman]

Have fun and taking some pics for us poor working guys.:2thumbs:

 

[ezrstl]

Your flat spot has to do with the "air filter" that is used in that set-up. The "air filter" is doubled-over metal screen and is to restrictive above 4000 rpm. Yep, it's a show piece, not for hard riding. That the filter out, and it will run fine. You will unfortunately have no filtration for the engine.

Tim

 

[P8RIOT]

...you can hear the thing sucking air.

Keep pets and small children away from that thing! It'll suck right in!

 

[Cutter]

It'll suck right in!

Cutter, step away from the keyboard... resist the temptation... do not respond... :nono:
:lol: :roll: :crazy:

 

[T.Byrd]

I would say that your problem could be to mush air and not enough
venting try pulling the allen screw at the far left bottom of your carb.
and see if that helps.