R75/6 not picking up

[Whitey]

i have been working on an R75/6 over the past couple of months, it hadn't run in 10 years but I finally got it through the mot. The bike was running really poorly but I did reach 80 mph on it, the carbs hadn't been balanced and I thought one was having a lack of fuel.

I stripped both carbs separately, replaced o rings, floats, ultra-sonic cleaned them. Thought I was ready to go but now the bike won't rev at all. It idles nicely and starts fine, but as soon as I try to open the throttle it dies. I though lack of fuel but this seems to be fine. The timing needs properly setting, although on idle the s mark is in the window, I can't open the throttle to see the advance position though.

Why won't the revs pick up? What should I be checking?!

Ta.

Mark

[khittner1]

You don't mention 10+yr. old carb diaphragms, which would be suspect.

[Whitey]

I have new diaphragms on the carbs

[Kurt in S.A.]

Clogged air filter? Is there about 22-24mm of fuel standing in each float bowl?

Kurt in S.A.

[Bamboo812]

Before messing with the carbs, make sure your timing is advancing (and valves are adjusted). Old grease in the advance unit can cause it to stick and cause bogging.

[Whitey]

I have replaced the points with an electronic ignition kit and a reg/rec instead of the diode board. Whilst the timing isn't perfect if is starting and no adjustment will make it throttle

[Bamboo812]

Try this; remove the intake tubes between the carbs and filter housing and see if the slides are moving. Could be slides fitted incorrectly or binding. Are you sure you installed the chokes right side up and correct side?

[ME 109]

Are the throttle cables accidentally hooked up to the chokes?

[SteveD]

This can be an annoying problem...but I guess you've worked that out.

Equipo5 had a similar problem where his bike hardly ran after 80kph. That problem was resolved with setting the float heights after replacing a bent float pin.

Does it rev ok if you're not riding it?

Other than the diaphragm check, I'd run some fishing line thru the mixture screw holes, then flush with carb cleaner, then run the line again. I understand you've had them cleaned, but unless I was 100% sure those circuits were clear, that's what I'd do. The line is to loosen crud, the flush to remove it. Of course, whilst the screws are out, examine the o-rings and ensure the small springs are there.

One odd thing I'd look at is the carb to head manifold. If they're old and stiff and fuel collects in the gaps, then once the throttle is gassed you might experience a sudden flooding, causing the bike to stop from too much fuel.

Have you added diaphragm springs? If so, maybe try it without them.

As your carbs have recently been removed/replaced, then it might be prudent to ensure the carb to head stubs are well approximated to reduce this. New manifolds might be needed. You want that area of the carb throat to be for well metered air/fuel transition and no fuel "storage" at all.

Then there's whether or not the "choke" mechanism is reassembled correctly. It wouldn't be the first time and it won't be the last.

Are your needles set at the second or third notch? 3rd is richer. The 313/314 BINGS want the 3rd notch according to the book.

[Whitey]

So I tried to run the bike this eve, it would only run on one cylinder again. Both carbs attempted to pick up, both together and tried seperately, the slides attempted to rise but bounced as the bike started to stall. I tried to raise the slide manually and turn the butterfly as suggested but this didn't work.

I feel that the carbs are not the problem. I need to set the idle and mixture but it is impossible to do anything at the moment.

So I suppose I'm moving on to the spark/leads/coils. I don't have spares so before I commit to buying these am I barking up the wrong tree? I fitted an electronic ignition, the wiring is pretty basic so I couldn't have messed that up, the timing needs some adjustment though. I've tried it in all sorts of positions whilst it is idling. I did double check at the wiring.

I also put in a reg/rec, again pretty straight forward.

Not really sure what else I can add! All electrics work fine.

Feeling quite disilusioned with the bike if I'm honest.