Blackjack Top End Rebuild - bogging under throttle

Jaylinb · Post by **Jaylinb** » Tue Oct 09, 2012 2:16 am

I just had my top end rebuilt on my Racerjack Maverick (Swtiched from the racing 4-valve head back to stock two, new cam chain, new seals) and now it's bogging under full throttle. Idles fine.

I have a video of what it's doing, how do I post it?

Post by **jrsjr** » Tue Oct 09, 2012 2:52 am

Jaylinb wrote:I have a video of what it's doing, how do I post it?

Post it on Youtube, view it on Youtube, hit the "Share" button, hit the "Embed" button, copy the code, paste that here. Done!

Jaylinb · Post by **Jaylinb** » Tue Oct 09, 2012 3:03 am

Gotcha. Hope you can link to this:

http://youtu.be/XwJ_ir6v5xw

I don't have all the vaccuum tubes hooked up, i.e. the crankcase vent and all. And I have a K&N on it with stock jets and stock exhaust (waiting on the right parts). But it still shouldn't be that bad, right?

Post by **jrsjr** » Tue Oct 09, 2012 4:49 am

Jaylinb wrote:I don't have all the vacuum tubes hooked up, i.e. the crankcase vent and all. And I have a K&N on it with stock jets and stock exhaust (waiting on the right parts). But it still shouldn't be that bad, right?

It might be a carburetion issue and nothing more serious. According to your comments in the video, you are running the stock jets with a K&N, right? The K&N lets in a lot more air than the standard filter/box. It could just be running way too lean when you give it throttle. You did readjust your valves on the stock head after you reinstalled it, right? And double-checked that the timing chain was reinstalled so that the valve timing is correct? After everything you went through at Bonneville, I bet you could rebuild that motor in your sleep...

P.S. Don't forget to snug up that throttle nut.
P.P.S. All vacuum hoses, too.

Jaylinb · Post by **Jaylinb** » Tue Oct 09, 2012 6:42 pm

I removed and cleaned the carb over lunch today, checked and cleaned both jets and reinstalled. Snugged up that throttle retaining nut and ran it on the center stand. Seems to be doing a little better. The main jet is a 92, is that the stock one? Idle says 32.
I didn't readjust the valves, I'm hoping the shop did all that when they did the swap. If not, how do I do that? And how can I check the valve timing?

Guess I'll need to wait for the stock parts to arrive before I can say for sure.

SYMbionic Duo · Post by **SYMbionic Duo** » Tue Oct 09, 2012 7:36 pm

yes 92 is the stock main. if you have a pod air filter, you need to seriously upjet, like 105.

or you could put some tape around the pod to restrict air flow. then you can stay with the pod and not have to upjet so much. but since this is your racerjack upjet away my friend.

-duo

Jaylinb · Post by **Jaylinb** » Tue Oct 09, 2012 8:32 pm

Would that explain the roughness under throttle, though? I think it's something more than just leanout causing that alternate bogging and surging....

SYMbionic Duo · Post by **SYMbionic Duo** » Tue Oct 09, 2012 8:47 pm

do you have the stock air box still? hook that up quickly and see how it runs under throttle.

EDIT: just saw in the FS/WTB section that you are looking for stock intake.

too much air can cause bogging around mid throttle (right when the main jet comes on line) because there is too much air and not enough fuel to properly combust. Then as you increase throttle and more fuel is available, the extra air stops being an insulator and instead feeds the combustion, but generates too much heat, and you are likely to get surging then.

srsly, you are too lean. accept it and move on, or don't and keep ef-ing around with the engine, pulling your hair out.

-duo

Jaylinb · Post by **Jaylinb** » Tue Oct 09, 2012 11:42 pm

Not sure where you got that I'm pulling my hair out my friend, just asking some advice if anyone's encountered this problem before. I haven't. When I pulled the spark plug it looked good, though I didn't do a cut on it for obvious reasons.

I have a new Prima exhaust and intake coming later this week. Now, I gotta go back out to the garage and eff-around with my motor some more... :+)

Post by **jrsjr** » Wed Oct 10, 2012 12:20 am

Hey, Jaylinb, here is a link to a page you might want to read from top to bottom, however, Section 3, "Re-jet your carburetor" is a discussion of what you want to know. Bear in mind that this information isn't gospel, but you are improvising carb jetting which is kind of a black art. The good thing about this article is that it will give you some numbers that should get you in the ballpark. Once you get it running well enough to ride, it should be a lot easier to go from there to dial it in.

Good luck. Please let us know how it goes.

SYMbionic Duo · Post by **SYMbionic Duo** » Wed Oct 10, 2012 2:59 am

Sorry, I was a little snippy, cuz it seemed that you were asking for help and disregarding advice from two people who told you the same thing.

From your Bonneville thread, I figured that some of this would be elementary to you, and that you had done all the modding of the engine yourself. Sounds like you are still learning these engines.

I can get brusk or downright rude, when things don't make sense to me and it seems that people don't listen. My bad.

-duo

Jaylinb · Post by **Jaylinb** » Wed Oct 10, 2012 3:49 am

Yeah man, still learning as I go. Just because I can do one thing doesn't mean I can do everything! Unreasonable to expect that of anyone. If I could, obviously I wouldn't be asking.

I don't have the special tools to swap out heads and install new cam chains, so I took it to a shop to do that. When jrsjr asked me if I'd ajusted the valves and timing chain, of course I hadn't because the shop hopefully did that when I took it over, and again no I have no special tools.

Stock carb, ugly old 125 pipe since my Prima was cut all to hell for racing and I'm ordering a new one. My stock air box was cut all to hell too, so still running the K&N from the race while I wait for parts like I posted earlier.

I can, however, clean and re-jet my carb over lunch...

buddyguy · Post by **buddyguy** » Thu Oct 11, 2012 2:47 am

Jaylinb wrote:Yeah man, still learning as I go. Just because I can do one thing doesn't mean I can do everything! Unreasonable to expect that of anyone. If I could, obviously I wouldn't be asking.

I don't have the special tools to swap out heads and install new cam chains, so I took it to a shop to do that. When jrsjr asked me if I'd ajusted the valves and timing chain, of course I hadn't because the shop hopefully did that when I took it over, and again no I have no special tools.

Stock carb, ugly old 125 pipe since my Prima was cut all to hell for racing and I'm ordering a new one. My stock air box was cut all to hell too, so still running the K&N from the race while I wait for parts like I posted earlier.

I can, however, clean and re-jet my carb over lunch...

I posted a question on your youtube, maybe it will help out. On another note, I'm curious of what you did to your prima, could you post pics?

lovemysan · Post by **lovemysan** » Fri Oct 12, 2012 4:39 am

Stock jetting will not play nice running an open k&n filter. Id guess you need to step up to 98-105 range on the main. You might get away with just adjusting the low speed mix screw. Anything more than 2.5 turns out and you need to upjet the pilot. You can get jets from the honda dealers too. Honda number is 99101-116-098 for a 98 jet or 99101-116-105 for a 105, etc. they come in 95,98,100,102,105, 108 not sure if thru have the 110,115,120. They have the pilot/slow jets also but I don't have the number anymore.

Modern Buddy

Blackjack Top End Rebuild - bogging under throttle

Blackjack Top End Rebuild - bogging under throttle

Re: Blackjack Top End Rebuild - bogging under throttle