Surging engine...

[CrazyClown]

Hello one & all,

It's been a while since I posted a thread. I prefer to sit back & watch the show! However, I have stumbled upon a problem which has me somewhat stumped.

I have recently aquired a nice little Kwak Z650 of 78 vintage. I have done a chop/bobber job on her and the plan is she will be my daily work runner. :rolleyes: Having gone over the engine & carbs, she is now fully serviced & fires up quite nicely on the first kick (binned the electric start!). She idles a treat & when revved/ridden, pulls smoothly & strongly through the revs. It is only when you try to maintain a constant speed anywhere over 40ish that she "surges". Almost like a lack of fuel..... If you open the throttle, off she goes again - smooth as you like. Just wont run smooth at a constant speed.

Now I have checked all ponts, plugs etc & all seems good. No air leaks on carb rubbers etc.... I am stumped!:confused::confused::confused:

All ideas/suggestions will be gratefully received!

[trikerdrew]

No air leaks,twas me first thought.You sure?Patronizing git ain't I?Smear silicon sealant yadda,yadda and the hairspray test?Not easy when cruisin though.

Next thing would be the cap on't tank causing vacuum.Other thing would be are carbs running standard filters/jets etc

regards

drew

ps arse, is the tank fuel cap standard?

[kiffer38]

what filters you using on carbs ? souds like your runnining weak on the idle mixtre, try a bigger pilot air jet

[jcb]

sounds like main jets are worn out or the needles as per.

carbs perhaps also out of balance,only take one to be ahead of tothers to cause surging.

also,lol,perhaps a ht lead braking down

good luck :thumbu:

[John Hopkins]

I'm with Drew on this If you open the throttle in neutral and let go do the revs keep going longer than they should? if so the part that mounts the carb to the engine, sometimes rubber sometimes metal is not tightened up enough and is letting too much air in. (inlet manifold).

John

[CrazyClown]

Thanks for some top suggestions.

Its not carb balance - that was done.:D
Carb rubbers (airbox to carb & carb to motor) are all good.:D
Running standard airbox & filter. Slight exhaust mods but just fitted bigger main jets to compensate.:D
Cant be vaccum caused by fuel cap as that leaks!:(
The pilot jets are inactive after 1/8th of throttle opening. Only in the equation at idle & initial throttle operation. So they would not affect fueling at the speeds this occurs.

As for the bike running, it revs smoothly & the revs drop back to idle smoothly (stationary or moving).

So that leave HT lead breaking down. That thought had occured to me. Did have problems of No. 3 Cylinder not firing. Turned out to be dodgy cap so suppose it makes sense that leads dodgy too.

Will check that out & let you know how goes it.........

Thanks again! Any other suggestions still welcome

[kiffer38]

does it pop through the exhaust when throttling down ? i still would look at pilot jets, you problem sounds identical to mine, and changing the pilot jets, and adjusting the mixture screws sorted it. as for main jets, they only make a difference at over 3/4 throttle !

[jcb]

lol,strangely enuff,yesterday i had a sort of flatness/surge/flatness whilst riding,,thought shit in fuel as id run tank dry but it turns out that id cut the ht lead back earlier and that left the lead tight to the plug,this then slowly pulled itself off the plug and was the cause of my surge,using full throttle was feeding enuff lectric stuff down the string to jump the gap but even throttle didnt it seems.
hopefully is all thats wrong with yours n all.also worth crimping the coil connections for a tite fit.

[Sir Ewok]

What about the clips in the HT lead caps, sometimes if they are not gripping the plug top tight enough vibration can cause a misfire......

[Borg]

Is the fuel tap allowing enough fuel out ? Are the pipes big enough and not kinked.

Float hight correct ?

Plugs need changing ?

[Blackjack]

The pilot jets are inactive after 1/8th of throttle opening. Only in the equation at idle & initial throttle operation. So they would not affect fueling at the speeds this occurs.



Not true.

The motor relies entirely on them up until about 1/8 throttle or so, but they don't mysteriously stop working at that point. Everything else is in addition to whatever the pilot jets are doing.