BlackJack's rarely 'come on' the high circuit, chokes etc

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baldwin ny
It is possible that the exhaust hose is blocking the holes in the diaphragm covers intermittently. This could cause the symptoms you describe, especially in turns. (They are atmospheric pressure reference holes and essential for proper popoff operation)
You could flip the carbs around if your manifold and throttle cable allow it.
Or you could drill an additional hole into each diaphragm cover. This is what I did. (I drilled them towards the bottom of each plate).

Something to consider.

bing go. i had that happen also. but it made the needles stick open.
 
lol, man If it turns out this simple issue (possible) has been my headache for so long and possible distruction of pistons etc, I'll be kicking myself. I hope it is tho, such an easy fix! haha.
 
Yes, thats what I noticed on the weekend. They are on the current way due to the R&D Manifold, ie it has the setup for the throttle etc that way. Even changing round the shaft in the carbs not sure it would work (will look into it tho).

Does it really matter tho? If the diaphram covers are not getting blocked obviously lol.

The way the fuel inlet pipes are makes it a PITA to hook the hoses up, so it does make sense they are ment to go the other way.
 
Couldn't tell you if it's the 'narrow' version but it's definately R&D.

Hey wax, I noticed earlier on OZfree you do porting etc, also trying to work out if the cyl's have any done, I think the ports been raised for racing. 35mm top of port to the deck (inside) it curently sits at, I've read std is anywhere from 37 to 39 (I guess 61x and 62T's make the difference there).
 
carb's, stripped and inspected. As expected nothing obvious.

Perhaps the circuts are some what different in blackjacks but the return system seems ok.
With the carb stripped I can blow back through the return outlet on both carbs.

Also with the pumps still on I could use my mouth (yes still tasting 2 stroke) to pump fuel through fine (and out the needle/seat). Blocking the needle/seat would see fuel want to come out the return line, which makes sense to me.

I couldn't pick up any leaks in the pumps. All diaphrams are in good nick.

I'll blow through the stripped bodies tomorrow at work with the aircomp.


The idea of the blocked breather holes on the needle/seat diaphram is still plausable. The covers are shinny and rubbed up where the hose has been against them. However the hole is at the bottom not the middle of these covers and it seems the rubbing is just above the holes.

Could be possible with load on the engine combo of engine movement on the mounts plus exhaust hose pressursing some it then blocks the holes, hence why its ok down low before this happens.

I'll dill a second hole at the top to be sure.

ALso can't see any issue with the fuel lines but will replace all, and the filters and 45 cut the pickups.

As for flipping the carb mount around, would involve modifying the manifold. Which given some advice I think I'll be changing anyway.
 

Flash-FX

No Square..No Round..FX-1
Hey, just read thru this whole thread, (a lot of great stuff=all good answers) by chance did you happen to remove the stock waterbox and check it for issues? I've seen baffles break loose and partially clog up (creating weird sounds,run on the trailer good, then hate the water) before.

If you are running a AM box, they normally do not have baffles.
 
Location
baldwin ny
Hey, just read thru this whole thread, (a lot of great stuff=all good answers) by chance did you happen to remove the stock waterbox and check it for issues? I've seen baffles break loose and partially clog up (creating weird sounds,run on the trailer good, then hate the water) before.

If you are running a AM box, they normally do not have baffles.

thats a good one also. the waterbox gets smoken hot when it happens.
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:werd:posted via Mobile Device we had an almost brand new x metal box come apart on us last year. never thought to look at it because it was " new". definately worth looking into
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I originally thought it was the water box, it was getting spastic hot, same with the pipe. I pulled the box out and one of the transfer tubes through the baffle had broken loose. Really I couldn't see how it could block anything but I got it welded back in and back together. I wish it was just that.
 
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