RD350 Air Leak at high Compression

[Pravin]

Hi guys ,

Long time , am back in trouble  : )

Recently I have installed new top end with 130 PSI compression , Standard sleeved HT blocks with 1A1 Pistons.

Bike ran well during run in on 0.5 turn Air screw as am not crossing 3k rpm ...

Post 500 Km am trying to pull her say by 4 or 5 k mark with air screw opened to 1.5 but the bike doesn't go , if i open air screw to 1.5 the bike overheats a lot and dont want to go even 1 turn .

Same issue happened when I tried China barrels , ran well but when tried to pull the bike she doesn't go ..

My Set up :
Original Points ignition , points gap 0.38mm , timing between 1.9 to 2.1mm BTDC
NGK BP7HS Plugs
Non Resistor Plug Caps
Mikuni Carbs 140 Mains 25 Pilot ---- Tried 150 and 27.5 no luck
Needle 4th from top -- 1 less to Richest position
Changed and sealed intake manifolds , exhaust is well sealed , No head gasket leaks..

Suspecting She's sucking air from some where due to high compression ... crank case ? Exhaust port ? , base gasket ?

she JUST GO PASS 5K RPM ...just screams but too slow acceleration .. and slapping sound comes neat the skirt area ..  if I open air screw more than 0.5 turn

Any guesses ?

Cheers ,
Pravin

[m in sc]

bigger pilot to start off with. I run ~ 140 psi zero issues. its not a leak.. your jetting is off. what's the jet tube and needle you are running? you're describing, for sure, a fueling issue. keep throwing fuel at it till it wont take anymore, then back it off a hair.

on my r5 with reproduction barrels im running stock 74 350 b carbs (0-8 jet tube and 5l1e or whatever the stock needle is) with a 270 main, 27.5 pilot, needle in 4th clip, and FPP chambers with a y boot and k&n. i rode it yesterday and it absolutely rips. Im also running a cdi but that shouldn't matter down low.

[Pravin]

Thanks SC ,

This is a stock set up , am using 5L4 needle and 0-8 I guess but I will confirm , that's the needle jet RD came with in India and we don't have any other spec available  :(..

I tried 150 mains and 27.5 pilot considering the STD Stock Set up but no luck , I will trace the Fuel today right from Fuel Tank to Carbs > Floats> Reeds and see where the bottle neck is ..

I do have bigger jets I can try .

[m in sc]

what color are the plugs? it can be easy to confuse too rich for too lean. i know.. sounds weird but its true.

[m in sc]

riding into work this morning i thought about this a bit more. if its RPM only related, its more than likely ignition. if its throttle position related, then fueling. if you don't think its any of that, pull the exhaust baffles out for a test, see if it gets better. if so, then you have a clogged or mis-aligned (to the pipe baffle plates) baffle.

[Pravin]

Hi SC ,

The plugs are Dark grey rare sight on an RD for me at least ... and when i try to increase the Air screw the Smoke  increased making it more lean  : (

I opened the reeds today and found that I can suck the air from  the reeds the other way , so they are leaking for sure .. cant tell if that IS THE PROBLEM ...

I started testing from Fuel tank > Flow to Carbs > Emulsion tubes are 1750-8 Indian RDs spec I  guess
All circuits are clean , float levels ok ...


Baffel plates are fine am running stock exhausts with all plates intact I checked some time ago ...

[Pravin]

Its RPM and Throttle both --

The bike doesn't rev easy past 4krpm and in 5th gear hardly touches 100KMPH....I tried to pull but just screams and too slow acceleration and lot of vibrations I can hear the sound is lean

Bike runs smooth till 3500 RPM and hits 4k rpm well with 80kmph on Speedo ... but the struggle starts after that . Currently she is  on 0.5 turn if I increase the air the slapping sound comes from cylinder bottom area as I release the throttle... 1.5 it becomes real bad ... again back to 0.5 shes happy touching 4k RPM ..this is the circle ...

I suspect its air leak and Lean both as STOCK bike should run smooth with stock 140 and 25 jets with stock fueling set up -- Air box , air filter , VM28, 140 ,25, Needle on 4th Notch etc etc

even on 150 and 27.5 shes not ready to go pass 5000 rpm easily..

[Pravin]

Plugs and Reed block

[m in sc]

too rich jetting. or weak ignition.

[350GUY]

bigger pilot to start off with. I run ~ 140 psi zero issues. its not a leak.. your jetting is off. what's the jet tube and needle you are running? you're describing, for sure, a fueling issue. keep throwing fuel at it till it wont take anymore, then back it off a hair.

on my r5 with reproduction barrels im running stock 74 350 b carbs (0-8 jet tube and 5l1e or whatever the stock needle is) with a 270 main, 27.5 pilot, needle in 4th clip, and FPP chambers with a y boot and k&n. i rode it yesterday and it absolutely rips. Im also running a cdi but that shouldn't matter down low.

Apologies to the OP, didn't mean to hijack this post.
Mark, on your R5 in the above pic, what reed intake boots are those? Are they a direct fit (bolt to bolt)onto the RD350 cylinders? Would you mind sharing the part #? Are those off the Banshee and also the Vforce reed itself? Thanks.

[m in sc]

reeds are rm100 and intakes are some i had laying around from who knows. the moose ones from economy work well. these may be yambits ones, im not sure. yes the back is sanded flat. https://yambits.co.uk/rd350-ypvs-lc2-inlet-rubbers-p-1699.html

[350GUY]

Great, thanks!