Rough running

[unreal]

Hi all, hope you can guide me in the right direction.

I finally got my '75 Sport MOT'd today (yes just in time for winter!). This is the first time I've been able to run her further than the 20 yards of my garage entrance and have some problems:

Starts first kick, but when running tend to bog down, pops on part throttle around 3000 rpm, if I open the throttle at around 4000rpm it bogs before picking up. I suspect the carbs are out but is there anything else I should check for?

Plugs are new and look a good colour.

Finally the rev counter runs fine up to about 6000rpm then shoots around to the stop!

I know Veglia aren't the best but this is new.

Any pointers really appreciated.

Simon

[stillooking]

have you just re-built it ?

[unreal]

Not totally, it hadn't run for around 6 years, so did all the normal stuff (belt,oil etc) but had to strip the carbs, so that may be my problem.

Si

[72degrees]

Repeat the mantra; Compression, Ignition, Carburation.

Compression - Valve clearances tight?
Ignition - Does it rev up better on one cylinder than the other if you disconnect one HT lead?
If so, if you swap the ignition over does the reluctance transfer with the spark if you see what I mean.
Carburation - Disturbed the float height in the carbs?
Sounds as if a check and fiddle if necessary with the needle height might be worth a try first though.

As to the tacho. I have a nice mechanical drive one. The needle flutters like a floozie's eye lashes, but it gives you an idea when to change up.

[EVguru]

As to the tacho. I have a nice mechanical drive one. The needle flutters like a floozie's eye lashes, but it gives you an idea when to change up.

When to change up?

When the engine stops pulling hard, about 10,000rpm indicated on the main straight at Cadwell.

[72degrees]

As to the tacho. I have a nice mechanical drive one. The needle flutters like a floozie's eye lashes, but it gives you an idea when to change up.

When to change up?

When the engine stops pulling hard, about 10,000rpm indicated on the main straight at Cadwell.

Heh! I've been spoilt by modern bikes with rev limiters and the GFR which just hits the two-stroke 'wall'. To be fair I still have the 250 tacho on which is red-lined higher than a 350. I've also been riding a Morini with hill climb gearing recently. Still never gets in to 5th

[unreal]

I'll try the swop, also any connections. She was running sweet as a nut when put away, so I'm thinking carbs or connections. Considering have JRS overhaul them, anyone used them?

The tacho is an odd one it goes from 5000 to off the clock with no increase in revs... by the way it's electronic.

Simon

[EVguru]

Heh! I've been spoilt by modern bikes with rev limiters and the GFR which just hits the two-stroke 'wall'. To be fair I still have the 250 tacho on which is red-lined higher than a 350. I've also been riding a Morini with hill climb gearing recently. Still never gets in to 5th

Yeah, 10,000rpm is 85mph cruising on the CX and it hits the wall at about 13,500.

[EVguru]

She was running sweet as a nut when put away, so I'm thinking carbs or connections. Considering have JRS overhaul them, anyone used them?

I automatically strip the carbs on a newly aquired bike and drop them in the Ultrasonic cleaning tank for most of a day. That sorts most problems. Oh, and phosphoric acid based toilet descaler brings brass jets up a treat!

[unreal]

Thanks everyone for the advice, I'm sure this is a carb problem now.

I'm going to invest in an ultrasonic tank, and get them really clean to start with!

As to the carbs, how much play is acceptable between the slide and body?

Simon

[Harry]

Don't bother with an ultrasonic baths unless you can afford one big enough to take a crankshaft, just leave in rust remover (phosphoric acid) 'Metalbrite" for half an hour and it will bring everything all up. The cleaning fluids are more expensive than rust remover! Blow through the passages with air and check free by squirting electrical cleaner through the orifices. Your problem is most likely the needle and emulsion tubes are worn and seals under the mixture screws knackered or missing so the carbs not balancing, get in touch with Contact Developments 0118 943 1180 in Reading who will also send you the parts sheet with an exploded view of the carbs.

[3potjohn]

Take one carb apart at a time.Log the jet sizes. Clean out the jets.Even carb spray up them.Ultrasonic bath is good if you have one but spray should work.Mind your eyes and any painted tanks. Then repeat with the other one.Be double sure to log the jet sizes as you might find mixed sizes. Make sure all jets are seated and tightened (not too tight!)
Check any o ring seals,Make sure the slides go in the right way round.Make sure there is no muck or water in the float bowls.Any wet fuel will cause endless misery.Before refitting the airbox tubes you can check they are both opening at about the same time.Do they "click" at the same time as the slides lower?
A blocked pilot causes a misfire at low throttle opening, whereas water in the floatbowl will tend to cause a misfire as you whack it open, in my experience at least.
Eurocarb sold me rebuild kits.

[Harry]

Eurocarb is the same as Contact Developments. The only way to balance carbs accurately is with vacuum U tubes or Carbtune, you can then check at tickover and the progressive opening of the slides as you open the throttle ie are the cables adjusted so that the slack (free play) is equal on both carbs, having one opening before the other. Much has been written about this subject in the eighties and nineties and I think there in a definitive description in the archives by Benjy Straw or our first Chairman.

[72degrees]

I find an ultrasonic cleaning bath big enough to take a carb body is very effective. It was the only thing that sorted the CV Keihin on my wife's CB250. I can offer a postal service if anyone needs it. Dellortos are pretty simple though and shouldn't really need one.

My original Morgan mercury carbtune is great for getting the balance absolutely perfect, but simpler methods (taking the intake elbows off helps to check by eye or the 'dangling rod' method) should get them close enough not to run really rough once well off idle.

[Harry]

Some have suggested using ball bearings! The vacuum method is still easiest - try using rods on three twin choke down draught Webers.