OzVMX Forum
Clubroom => Tech Talk => Topic started by: Wasp on January 15, 2017, 08:20:05 pm
-
I have some issues with my carby settings on the 32mm round slides . The bike starts easy , it screams top end , but around 5 mm lift the the engine (3 x 250 cc ) starts to four stroke like if it was very rich . But as soon as you go another 2-3 mm in lift , the power band comes in and all is clean . I dropped the needle to the lowest clip and and it improved , but not enough . I think the pilot is OK , but lowest point of the needle is not .Mikuni does not offer different needles for this carb. Could it be the cut away . At the moment it has 2.5 and no others are available . If I turned down the 2.5 Slide by 0.5 mm , would that make approximately a 2.0 and lean it off ? I know its a bit of bush mechanics , but am I on the right track ?
-
Most likely slide cutaway. You need to go to a bigger cutaway not smaller as it sounds rich. Can be filed but need to be acurate.
-
Tried retarding the timing a little?
-
whats the needle jet?,go back one size?, :P
-
Just a question really and I am sure you have it covered. Are they new carbies fitted or at least new needles and needle jets.
It sounds a lot like worn needles and needle jets. The throttle opening you are have problems with probably relates to the point were the bike operated often. If you have new needles and needle jets installed disregard this post.
-
whats the needle jet?,go back one size?, :P
That's the common wisdom. If you are at one end of the adjustment on the needle jet clip position, changing the needle jet one size should put the needle back on the middle clip. According to Mikuni OZ (Obviously then you have the adjustment back.)
-
eggsakery :P
ooh,just looked in my book,they H1,H2's both like O series,yours with 6 to 8 options,so if you have 8's,try 6's?,if you have 6's your'e forked,(pun intended ;) ),needles same,cutaways 2.5, :P
-
Pilot is 45 Main is 110 .Needle seat is new and needle has 5 clips ( needle in bottom position , fully rised . )When I drop the needle it is starting to surge in mid range (to lean) . Plugs are brown and fuel consumption yesterday was 21 liters for 160 km !!!. I have used Dellortos all my life and there you have a great arsenal combinations to cure things . But because those carbies are OEM , parts are limited and not the same as the after market Mikuni . If all fails , I may go to modern half round slide Mikuni if they have one with oil feed in lines for the H2 C . I will try a few things that have been suggested .
-
Pilot is 45 Main is 110 .Needle seat is new and needle has 5 clips ( needle in bottom position , fully rised . )When I drop the needle it is starting to surge in mid range (to lean) . Plugs are brown and fuel consumption yesterday was 21 liters for 160 km !!!. I have used Dellortos all my life and there you have a great arsenal combinations to cure things . But because those carbies are OEM , parts are limited and not the same as the after market Mikuni . If all fails , I may go to modern half round slide Mikuni if they have one with oil feed in lines for the H2 C . I will try a few things that have been suggested .
Put a 0.5mm shim under each clip failing that put 3x 36mm PHBE's on there and forget
-
Lozza , wouldn't lifting the needle more , exaggerate the problem more ?The first 1-5 mm of slide lift , that is where it is too rich , after that it all comes good .
-
I rekon you need to go down 1 size in the needle jet so you can return the needle to the middle clip position which should put you exactly where you are now but then you can lift the clip 1 slot to lean that blubber out....
-
Makes sense , I will give that a try (if they are obtainable ) Thanks
-
This may sound strange but are the needle jets fully home in all the carbies? if one or more is sits even slightly lower than its correct position it will cause richness at small openings.
I know you would have triple checked. Are the carbies exactly synchronised if they don't open off the closed position together it could give the impression of rich as one cylinder tries to accelerate ahead of the others. Just an idea
-
Have you spoken with Ian Williams ( Ian Williams Tuning, Torrens Rd Brompton)? He has given me some good advise over the years regarding sorting out jetting problems with Mikuni carbs.
-
Without yet reading all of them & my ideas might be way off--but-- had a realy unusual problem on my bucket racer years 30 odd years ago which i'd ported to the moon & gave rich blubbery type symptoms at about 1/3 throttle exactly where it was "getting on the pipe", couldn't clean it up by needle or slide etc till some smarty came along & said "Reed Flutter" to which i said "yeah rite", said double up the reeds & bugger me it fixed it on the spot. Also do you have an aftermarket pipe fitted which might be too short overall--if so add some into the header [easiest place] which might spread the power & take the sharp kick out of the powerband so to speak, if a 250 has a powerband!!, in saying that a mate had a 250F "79 which came on hard like a lightswitch & someone had been porting it wildly which was hardly necessary on one of those. Similar story on an IT400 motor i had in something 'dirt' & once again it had been got at & had 190 degrees exhaust port duration so had to add 100mm to the header to cure the flat spot--which wasn't blubbery but just flat--good up to that & crazy wild past it but 'hollow right there' where you needed it for dirt. Ignore all this woffle if irrelevant.
-
Sorry, not sure what i was thinking--i'm thinking 250 husky 'dunno why' but now see H1 H2 is that a 750 Kwaka sidecar--no doubt piston port anyway--carry on & ignore my woffling.
-
Yes , we synchronized them from bottom up and checked with the mirror to make sure of that . Yes I have spoken to Ian and showed him the carbs . They are made by Mikuni , but for Kawasaki triples only . Slides are different and the shape of the jets are different to the normal Mikuni parts . Of course being from 1974 most Kawa part numbers are obsolete now . With all your blokes input in mind I will redo them again , maybe I have over looked something very little . I will give it one more go , otherwise Ian recommended to go for the new half round carbies and then there would be plenty parts to play with . Thats the fun with those old girls , they are a constant challenge , but soo much fun to ride when they are on song . Some blokes in UK have welded reed valves onto them for better down low delivery , but some how I feel it defeats the purpose of going for that type of bike .
-
Can you give some details on the motor. Is it stock with stock pipes for road use or modified?
-
"normal mikunis",shit most of my bikes run R jets,(ok so they're all early 70's,so thats the norm),my museum pos yamaha YDS R thingy was having b/e issues too lean,banged 60 pilots in (35's),changed the P-0,s for P-4 (availble Hatricks),dropped needles back down,bingo,can now start easier, bonus , motor to start line at a reasonable low rev,actually working on a H1 atm,(500, overthe hill ;))sort ignition,then back to carbie issues,(think they're related), :P
-
Engine is standard , fresh pistons and rings .New Higgs pipes , new Lakeland ignition and timed to the book . The bike is 750 H2 1974 (C)
-
Lozza , wouldn't lifting the needle more , exaggerate the problem more ?The first 1-5 mm of slide lift , that is where it is too rich , after that it all comes good .
So it's at the full rich or position 5? If it is in the initial part of throttle opening your looking at the parallel part of the needle before it tapers. Look at the mikuni needle chart and look for a needle with the same taper dimensions but with slightly fatter end to the needle. Changing the atomiser will only shift the whole fuel curve to the left or right. Mikuni needles are not really designed to run on positions 1 and 5 that means new atomiser. Something you could try is to calculate the annulus area between various needle/ atomiser combinations to find a slightly smaller area, rather than spend a fortune on tubes and needles. I would have said stick 3 PHBE's on there I can tune them from a description :D
-
on your recheck, make sure the needles are seated in the top of the slides and pinned by the spring / clip whatever is there. "floating" needles can cause weird shit to happen in the carb and rich early can be one of the symptoms
-
geezas Lozza,spending a small fortune on needle/emulsifying jets aint gunna cost 3 new effing delortos,i'm thinking N series next ones back x 3 isn't as exccy??,hmmm funny "my" 500 has new chambers from pommyland which richened the motor up too??, :P
-
Engine is standard , fresh pistons and rings .New Higgs pipes , new Lakeland ignition and timed to the book . The bike is 750 H2 1974 (C)
So did it run ok with the stock pipes? My money is still on the slide cutaway if it is rich just as the throttle is opened above idle.
-
I bought is mint from Canada via a agent displaying lovely pics ...... To cut a long story short , ignition , barrel , pistons, clutch and exhaust are new now and it is running at last,now that we fixed all that ... If I can can get that last bug out of it , I will finally have my dream bike that I wanted since a teenager.
-
geezas Lozza,spending a small fortune on needle/emulsifying jets aint gunna cost 3 new effing delortos,i'm thinking N series next ones back x 3 isn't as exccy??,hmmm funny "my" 500 has new chambers from pommyland which richened the motor up too??, :P
I never suggested buying new Dellorto's.
-
I love the Dellortos for the chrome trolleys . They work well there because of of the pumps and many jetting options . But this is a challenge I like to ride out on OEM Mikunis if I can . There will be a way . There must be a way .
-
May I suggest you purchase the Sudco 5th edition mikuni tuning manual and use monometers and or vacume gauges for synchro of the carbs