RD03 carb diaphrams

[holla]

Hi all,

I'm still trying to get to the bottom of my misfire.

I've heard mentioned the 2 sets of diaphrams in the carbs are prone to damage. I took both sets out of both carbs but there was no signs of damage. Is it possible that the diaphrams could be worn without showing a tear or hole in them or if they look ok they will be ok???

The problem seemed to start after i had replaced the air box connector (big rubber tube that connects both plastic parts of the air box) as it was badly mis shaped and wouldnt connect properly

Is it possible that the carbs have been balanced with this air leak from the damaged rubber and now i have fixed it, the carbs are now out of balance ??

would a badly balanced pair of carbs give a splutter/ misfire at 3/4 to full throttle ??

If so i'll try to balance the carbs and see what that comes up with.

thanks

[Kjell Lindberg]

When I bought it, my bike had a sticking choke wire, badly adjusted valves, a clogged airfilter, and carbs out of synch.

You know what? I did not miss a beat!
Sure it was gulping fuel like a 747 dodging missiles over Iraq,
but no missfire during that month of everyday driving I did before I set it all right.

What about the HT-leads or the Spark plug caps?
Have You checked them?

//Kjell

[BobA]

Out of balance carbs will not make the bike misfire.

If the carbs are out of balance, the bike might run/idle a bit lumpy, and be quite vibey at higher revs.

Balancing the carbs is a REALLY basic thing, and a small screw just adjusts the the differential on the carb linkage, making each carb suck the same amount of fuel/air.

I have to say, my opinion is the 650 engne is MUCH smoother than the 750, so unbalanced carbs may not be as obvious as on a 750 bike.

A damaged diaphragm could make the bike seem like a misfire, but a visual inspection would have revealed this. There are another set of diaphragms in the carb which are the air cut-off valves (I've never replaced these) but from memory if these have failed you will get exhaust popping on the overrun, very similar to a leaky exhaust.

Think back. How many things did you change before the misfire manifested itself?

I know from experience it can be REALLY annoying. I had a tatty but super smooth and reliable RD03 that was cleaned up, modified, and rebuilt for a TV programme, and it came back running badly. I tried a few things but lost interest, as I didn't really like the result, and I then sold the bike to Fergus1964 who seems to have excellent RD03 knowledge, so he may have cured it and have a few more ideas on your dilemma.

Good Luck, persevere, because you have the best AT ever made.


Bob

[holla]

Thanks Bob, the bike always popped on overrun from when i got it, i did a complete service, oil,oil filter, plugs,air filter, fuel filter. At this point i noticed the air box connecting rubber was off at the bottom and looked like it had been for years as it was all mis shaped. i put it back as best i could and it was ok for a week then the popping came back.

at this time i snapped the bolt that holds the exhaust heat shield off and in drilling it out then snapped a drill in it !!!!!. i just loosened the exhaust off enough to pull off the rear downpipe from the system ( i didnt completely remove the system as the front nut was a b!sta*d to get at.

whilst i was picking the new air box rubber i picked up some new honda heated grips and so fitted them as well as the rubber. It seemed ok with no more popping but i dont really think i'd really opened it up yet ( full throttle) and it was then i noticed this misfire.

There were no trapped fuel pipes, I've put 4 new exhaust gaskets on, new choke cable as the other one was a bit stiff, taken carbs off stripped and cleaned and its still no better.

I'm going to check CDI, ht caps and leads and coils now............................................... ...... the search continues.

Thanks

[AIRWOLF]

Does the missfire start at a certain RPM or at a certain throttle opening ?

Put some tippex spots on twistgrip so you can see throttle position.

make a note of TP and RPM in top gear. then in 2nd or 3rd gear run it up to the RPM where it started missing, the thottle opening will be less in the lower gear,so this will point to either ignition or fuel.

I will pm my phone number in case i hav'nt explained it well.