Another jetting question - round 2

[rdsarefun]

Hello Everyone,
I was looking for some additional feedback regarding jetting.  I posted on here last year and had my bike sorted after correspondence with individuals on this forum.  The bike "was" a 75 RD350 Stock bore with DG pipes,  a K&N filter with a new Y boot and a Dyna S ignition.  I had the carb currently (set up with Dave F mod) 5DP7 jet needle, 169P0 primary needle jet, 30.0 pilot, with 190 mains and the needle clip in center position (#3), air screw 1 turn out from seated. I also added banshee intakes and a crossover tube, 3/8" thick reed spacers. With the spacers, I did not need to cut the ears off the banshee intake, just cleared. The bike was sorted and ran great, just a little tired at 6600 miles on stock bore.  Since then, I acquired another engine from a forum member and sent the top end to Josh at Bill Bune (again a recommendation from a forum member).  I had the following done to the stock 64 mm heads and cylinders I acquired for spare engine per Josh below:

"ProX Banshee pistons. A pair of those are $200. The head we would play it safe and recut the Squish + 2 degrees from the top of the ProX pistons, Then mill for more compression. The cylinders would be "trail ported" Meaning safely raise and widen Exhaust / polish, Raise Transfers, Lower intake, and blend everything in"  - Josh also cut the pistons to be used in this setup.


Prior to putting the new top end on, I replaced the DG's with a set of SS Dogster expansion chambers.  I did not change anything else when i put these on (everything on bike was the same as before), and the performance (seat of pants) was the same as the DG's.

I just got around to putting the new top end on with new setup.  I kept the timing the same as before (need to look at notes for exact value but set with an inductive timing light and it ran great with previous setup). My problem now is that when riding, It ran great until roughly 4K rpm, and then sputtered and popped, could not go above this.  I changed the needle position to # 4 (was # 3) and it seems as if it is getting too much gas as it just bogs and is not happy, could not even ride it in new clip position as needed to give it throttle just to keep running.  I am wondering if I need to up my pilot jet to a 35 or 37.5 with this new machine work done and maybe up the main in addition? Notes from Chuck Q during my last bike (very similar build to where I am now) indicated this pilot jet setting and a 220 main.  Wanted to get some feedback from the group.  As of now it looks nice, but just a garage queen until I get it sorted.  Thanks

[RDnuTZ]

Pump gas or race gas (110 Octane, etc.?) Usually, the builder discusses this with user and how they intend to use the motor and mods tailored for the type of fuel expected. Jetting would be expected to change to harmonize with engine changes. Good Luck!

[rdsarefun]

Sunoco pump gas, 93 or 94 octane, depending on station

[m in sc]

carb slides in backwards? cutouts to air filter. check that 1st. type of fuel wont cause that kind of issue.

[1976RD400C]

I would try going the other way with the needle clip and lean it out.

[rdsarefun]

Carb slides are in correctly with cutout to rear and large angled slot (for idle screw) in contact. Octane question from a response will not make a difference as it is not detonating.  My thought is that the pilot circuit is too lean and I made the primary too rich by moving the clip position, adding other complications.  I only have a 27.5 and a 30 pilot available, thinking of buying a 35 and 37.5 from John at Economy and putting the needle back to middle position, start with pilot changes and see where it leads.

[m in sc]

dave f mod: did you drill the airjet out to 2.0mm?

[rdsarefun]

Yes, this was drilled and tapped for a thread in airjet, Bought kit from John at Economy

[rdsarefun]

I used a a 2.0 Mikuni 4mm X .7 threaded jet within

[m in sc]

ok. just checking.

hows the charging system?

[rdsarefun]

New voltage regulator and gel cell battery. Last time I measured it was putting out a little over 14 volts at 2500 plus Rpm. Now that you mention it I checked the plug against the head and it sparked, just not a hot "blue" spark.

[m in sc]

it depends. if its solely rpm related, not throttle position related, its electrical. if its at a certain throttle position, its fuel related.

[rdsarefun]

I will have to play with it this weekend, in New Mexico for work. I did order some more Jets from John just in case I need them

[2 Smoker]

Maybe pistons in backwards, just a thought

[Hawaii-Mike]

Maybe try putting the needle on #2.  Be very careful, if you hear even one ping, immediately let off the gas.  If not, in a second or two your engine will need a new piston at a minimum.