Running rough, just off idle

[rodneya]

There is a lot of conflicting information on the internet about pre-ignition and detonation.

Wait until somebody tries to tell you that you have pre-dotonation going on

[2TFool]

Well, maybe I do?
I switched to a 32.5 pilot and dropped the needle one (now all the way down)
and experimented with the air screw.
I also adjusted the throttle slides and idle stops as best as I could. It's best at 1 3/4 out (air screw)
It starts right up and idles fine but put a load on it as you pull away (and (I'm going to try to use words) it sounds like it's four stroking (?) the exhaust tone is sharper, almost a clack sound (way too lean?)in the chamber. That scenario when pulling away on an incline. A lighter load less severe.
Perhaps the idle circuits are slightly gummed up but would it start and idle the way it does if they were)
I did blast brake cleaner through them. Perhaps I should put them in a ultrasonic cleaner?

Main jets  300
Pilot jets 32.5
Needle jet .158 P-8
Slide      2.5
Needle     6F8 (clip in top groove)

Appreciate your consideration!

[m in sc]

you def need to start with fresh clean carbs. so def take them all apart and clean them. blow thry every hole.

then start over w clip in the middle. im guessing the pilot is ok. it really is based on throttle position. idle to 1/4 pilot. 1/4 to 3/4 needle, and wot is main. there is of course some overlap but its about throttle position. p8 is a relatively rich jet tube but not ridiculous.  seems like your issue is primarily there. but a clogged jet tube or air jet will cause a rich condition

[1976RD400C]

How my bike with 34mm carbs reacts to different needle jets: P4-needle must be in position 1 (full lean)   P2-needle in position 2-3  P0-needle in position 4 (rich). I would try smaller than P8.

[automan]

There is a lot of conflicting information on the internet about pre-ignition and detonation.

Wait until somebody tries to tell you that you have pre-dotonation going on

I heard that at work, many times.
(one of the Big Three)!

[m in sc]

had this on the other day. even though its a big block ford, later in the video he goes into a good vut basic ignition timing and definition of detonation,  pre ignition, ping etc. worth a watch if you aren't familiar.

https://youtube.com/watch?v=ze2CROQ34sM&is=GtXol_QzxU7rlBo7

[2TFool]

Ok, a couple of things,
I asked AI about what's going on with my carburetion and it suggested that my slide at 2.5 was a little big and that 2.0 might be more appropriate. The idea being too much air was flowing initially and a smaller pilot jet couldn't keep up. If you didn't want to buy two new slides go up pilot jet size.
Again that's what AI said, what do you think?
I'm about to make a trip over to a bike shop and see if they have any larger pilots. If not, I have to buy them online. Can I buy Chinese? I can certainly get a large selection for a lot less money.
I see online that correct float height is 24 mm from the body of the carburetor to the top of the brass pivot that the floats engage on. Is that correct?
The afore mentioned brass pivot is held in with a pin that is peened over on one end. I've tried tapping it out to remove the float needle assembly but it doesn't want to move. Is there a trick?

[m in sc]

stop relying on ai for this.

a 2.5 is fine. look into the needle issue clean the carb 1st. as far as the pin be careful, i tend to use a small set of needle nose and put one on the pin leg the other on the pin, pushing the pin out

[RDnuTZ]

agree with Mark on this- Stop using AI. If you look closely under the information presented by an AI bot it gives a disclaimer "AI can be wrong, please cross reference with other sources" WTF? Useless! If you have to verify with other sources- get a good RD manual that has all the OEM specs in it as your baseline reference.

Also, beware Chinese jet assortments on-line. I once bought a kit for my KDX220 and they came UNMARKED. No way to tell what sizes they were. Again, useless 

[2TFool]

Well, I tried a whole variety of pilot jets from 17.5 to 45 and throttle slides 2.5 and 2.0.
I tested it on an incline right outside my house and all at less than quarter throttle, the zone where it does not run well.
I think I could hear it knocking on the 17.5 and the 45 was super smoky and bogged down maybe 27.5 was the best, but none of these settings, cured it of its unhappiness at less than quarter throttle.
I don't think it's pilot jet size. I've thoroughly cleaned the carburetor and there are two orifices that are fed by the jet and they are clear.
Once I'm past quarter throttle (I calibrated the twist grip) it seems to be running fine (there may well be some fine adjustment to be made there but nothing like below quarter)
I have posted Engine and carburetor details elsewhere but as a quick recap, it's an aggressively ported 350 with 34 mm mikunis, 152lbs compression and 100 octane gasoline. It was a race bike that came to me, and I saw fit too resurrect it and put it on the road. Steep learning curve in regards to jetting and tuning and I really appreciate this forum!

[m in sc]

sure the carbs are synched off idle really well? also, race bikes don't really perform well under partial throttle, especially old school porting.. there's a cost to all that porting. and that's it.. pretty sure you found it. 

remember, to over simplify it. at lower rpms, until you really get the gases flowing, aggressive porting is going to 'bleed out' mixture to a degree.   this will cause it to be sort of sloppy. I think you've done all you can.

go w the pilot jet that gives best performance at 1.5 ish turns out on the airscrew. this is about where its optimal for air speed in the pilot circuit.

[1976RD400C]

I installed the UFO inserts in my 34mm carbs and WOW, they transformed them to be ultra smooth and crisp. You really notice the improvement at 1/4 throttle. I got them from Niche and they came with the slide. You can get them without the slide, but you must modify the cutout to match the insert.

[2TFool]

I was beginning to wonder if the problem wasn't the pilot jetting but a function of porting, pipes, compression, the way it had been tuned.
The best pilot jet still doesn't make it run very well, it doesn't sound or feel right until the throttle is opened to just past quarter, probably of little concern on the racetrack.
I have ridden it "on or off" no throttle or quarter throttle. Any danger of starving the top end of oil riding it like this?
I'll look into those UFO inserts,