carb problem

[5lab]

ok, so when i put my foot down from nothing, the car waits a second, then the power 'jerks' on. i dont have to put my foot all the way down, just a bit. doesnt happen my foots already half down, and does happen reguardless of revs (so its not 'choking' the engine) any ideas?

[Tumble]

after the initial jerk, doe sthe power come in cleanly? or does it feel like you should get out and push?

[Crazy Cricket]

Sounds like 'boost circuit' problem, carbs tend to have an enrichment device which cuts in when you floor it, to prevent such power loss.

Not sure what carb the ren lump runs tho, solex?

[Russ]

is it a recent problem 5lab? or you always ahd it?

[5lab]

think its a solex. i've always had the problem.. its all very mechanical, i doubt it has a boost cirtuit (no electrics at all in there).

power comes on cleanly after the jerk, its just initially there. i've not done the valve clearences when i served it - could this be the problem?

[Big RICHARD]

How old is the car? If it's fairly new it could be a 'fly by wire' car and this is fairly normal. If it's this it is the engine management system catching up.

[Zak33]

does it tick over nice and cleanly and stable? COs sometimes, when you get a delay like the one you describe it is because there is an air leak into the inlet (cracked gasket maybe on the inlet manifold) and when you put your foot down, the delay is caused while the mainfiold is "sucked" into position.....and then a split second later, once the gap is closed, of ya go.

Thats only an idea tho.

Also....it MIGHT be the Advange and retard pipe from your DISTRIBUTOR to the MANIFOLD......look for a pipe that has just air (or in this case vacuum) gpoing from one to the other....the idea is that as revs rise, the timing is changed to get the spark to go earlier......cos the piston is going so damnfast it must start a spark earlier to get it all burned.

However...if its BLOCKED it causes a delay on throttle down..so maybe ...

try uplugging it and revving it...is the delay gone?

You CANT drive it like that cos the timing is all gonna be wrong at revs BUT it might need a clean out

[Jiff Lemon]

340's have a known problem for the carb bases to warp.
Extra air gets suck in so to compensate (and get it through the MOT) the idle mixture gets wacked up.

However, it's now overfueling on throttle...

[Zak33]

good oneJiff.....thats quite likely

[5lab]

ok update..

the carbs pretty knackered, it was VERY loose, only 2 of the 5 screws that hold it together work (which werent tight anyways), but its still idling erattically. im gonna give it a 24k service, see if that helps (might be contact breaker points or something) - if not i'll get a new carb and bolt that on instead.

[Zak33]

thats a lot of dough for an old car mate

Cant you google it and find out what other cars have the same one.....and go to a scrap yard and try to get lucky.

[5lab]

nagh £25 for a decent one from my friendly volvo breakers

by new i meant new to me. not new overall. im going to try some retapping screws before i do thou, i mean if they shag the carb then i've not lost anything..

[Jiff Lemon]

I'd be tempted to simply get a S/H carb anyway - Throw that straight on and then look for an overhaul kit for yours. That way you're hopefully:

a) still mobile
b) Have the problem fixed
c) Have time to clean up the old carb and have it on standby to change at lesuire.

[5lab]

ok this is how knackered the old carb is..

all the screws that hold the top half to the bottom half have had their threads ripped off. only held together with gravity (now added some self-tapping screws till i get the new carb)

the diaphragm/gasket thingy that covers the float and stops petrol going everywhere and generally seals everything together (made of something that looks a bit like cardboard) is half missing, so fuel/air can go in and out as they please. god knows where the other bits gone, probably floating round a cylinder somewhere..

the mixture screw is missing (never seen it) - the screw i thought was the mixture screw was actually the volume screw. so the mixture runs *really* rich. old sparkplugs are blacker than coal.

so all in all, im getting a new carb. fitting it might be fun. heh. not.

parcelshelf is nearly finished thou. quite proud of it so far, will get piccies soon..