Ke70 Lunging Forward When Decelerating

[Mybowlcut]

Hey.

 

I only really get this in the morning going to work, but I go down a highway that is easily a few kms long and it's a descent the whole way down. The speed limit is 80... so I'm going 80 and I gently let my foot off the accelerator and the car kinda lunges forward repetitively until I accelerate again... what could this be?

 

Cheers.

[DearmanKE]

tailshaft needs tightening/balanceing?

[Trev]

Does it have a backfire, Sounds a bit like retarding.

[towe001]

  DearmanKE said:

tailshaft needs tightening/balanceing?

I don't reckon it'd be that. You would tend to notice it regardless of accelerating or decelerating.

 

It sounds more like surging.

 

How about after work ? I guess you wouldn't really notice it since your going back up hill.

Does it still do it after motor has warmed up to operating temp or just while its still cold/cool.

Auto choke or manual ?

Could be a few things ranging from fuel flow, ignition, to an air leak.

[KE30_KE35_KE55]

also check vacuum lines, throttle butterfly's for wear and check secondary butterfly springs. increased vacuum down a hill could amplify any problems.

[Mybowlcut]

  Trev said:

Does it have a backfire, Sounds a bit like retarding.

IT doesn't backfire but when I'm slowing down for a traffic light the exhaust does pop but it's not loud, you know? :)

  towe001 said:

I don't reckon it'd be that. You would tend to notice it regardless of accelerating or decelerating.

 

It sounds more like surging.

 

How about after work ? I guess you wouldn't really notice it since your going back up hill.

Does it still do it after motor has warmed up to operating temp or just while its still cold/cool.

Auto choke or manual ?

Could be a few things ranging from fuel flow, ignition, to an air leak.

Surging was the right word I think! Haha. Yeah, doesn't happen going up hill. I'm pretty sure it happens even if it's at operating temperature, but will double check today as I am going down the hill at about 10 o'clock and car should be pretty warm.

 

Manual choke.

 

Well I did post a thread about my dizzy leaking, maybe that has something to do with the ignition? Haha.

 

  KE30_KE35_KE55 said:

also check vacuum lines, throttle butterfly's for wear and check secondary butterfly springs. increased vacuum down a hill could amplify any problems.

My vacuum lines are all over the place, so that could be it as well. I had one look at that vacuum hose pic and said "forget it". Haha. I'll try again today!

 

Cheers guys.

[Mybowlcut]

Yeah, it does it when it's hot. Also does it in lower gears when I'm going at a slow speed.

[towe001]

I'd hazard at a guess that either your manifold's a little loose or the carbies a little loose.

Spray a bit of carby cleaner or wd40 etc around the carby, vacuum hose connections, etc while the motors running, it'll help in showing up any air leaks if there's any.

 

Could even just be crap in the carby jets causing the lean out.

 

With the dizzy i don't really think that could be the problem unless its causing the timing to swing all over the shot. Then i'd be getting that fixed before any attempt is made at stripping the carby.

 

In all reality whats happening is that the motor is leaning out then going rich again

[ke70dave]

  towe001 said:

I'd hazard at a guess that either your manifold's a little loose or the carbies a little loose.

 

ill second that

 

my carby was all loose a while ago

 

and the accelerator cable was pulling the carby appart from the manifold and causing a HUGE vacume leak

 

it would idle fine cuase there was no force pulling it away.

 

and it was fine when accelerating slowly, but if you did any thing quick with your right foot it would surge and splutter.

 

after you make sure everything is tight id do a quick tune up, reset the timing and plug gaps/points dizzy, spray some carby cleaner down the throat of carby. should run pretty good after all that.

[Mybowlcut]

  towe001 said:

I'd hazard at a guess that either your manifold's a little loose or the carbies a little loose.

Spray a bit of carby cleaner or wd40 etc around the carby, vacuum hose connections, etc while the motors running, it'll help in showing up any air leaks if there's any.

 

Could even just be crap in the carby jets causing the lean out.

 

With the dizzy i don't really think that could be the problem unless its causing the timing to swing all over the shot. Then i'd be getting that fixed before any attempt is made at stripping the carby.

 

In all reality whats happening is that the motor is leaning out then going rich again

Hmmm ok. My question is, how will carby cleaner show air leaks?

 

I am getting a weber soon which I'm presuming will f^^^ off most of the vacuum hoses and any issues with leaning out etc.

 

 

  ke70dave said:

ill second that

 

my carby was all loose a while ago

 

and the accelerator cable was pulling the carby appart from the manifold and causing a HUGE vacume leak

 

it would idle fine cuase there was no force pulling it away.

 

and it was fine when accelerating slowly, but if you did any thing quick with your right foot it would surge and splutter.

 

after you make sure everything is tight id do a quick tune up, reset the timing and plug gaps/points dizzy, spray some carby cleaner down the throat of carby. should run pretty good after all that.

When you say vacuum leak, does that mean ANY air leak? Or a leak from one of the vacuum hoses? I sprayed some carby cleaner down recently, but I guess it can't hurt to do it again. :jamie:

 

Cheers!

[towe001]

The carby cleaner or wd40 (rp7, inox, lanox, etc) acts as a "fuel" and if there's a vacuum leak the stuff will enrich the fuel supply bringing the revs up while your spraying in the general area of the leak.

[ke70dave]

  Mybowlcut said:

Hmmm ok. My question is, how will carby cleaner show air leaks?

 

I am getting a weber soon which I'm presuming will f^^^ off most of the vacuum hoses and any issues with leaning out etc.

 

 

When you say vacuum leak, does that mean ANY air leak? Or a leak from one of the vacuum hoses? I sprayed some carby cleaner down recently, but I guess it can't hurt to do it again. :jamie:

 

Cheers!

 

a vacuum leak is just a place where air can get into the system where is not supposed to be.

 

on carbys yeah it can be one of the matrix of pipes, or more major like a blown intake manifold gasket or in my case loose components coming appart.

 

I'm pretty sure the reason that its bad for the engine is that the air hasnt had the appropriate amount of fuel mixed with it and thus creates a uber lean mixture and thus runs poorly

 

or in the case of an efi system it stuffs up the map/afm sensing and does the same thing.

 

your best bet is just to go around with a few spanners and make sure everything is tight, then fire up the engine and get it to idle. then start spraying some sort of flamable spray (wd40, rp7) and this flamable gas will make its way through any vacuum leaks (if they exist) you have and you will hear an audible change in revs of the engine.

[Mybowlcut]

Cheers guys. Will try this soon.

[KE30_KE35_KE55]

can you hear a vacuum leak when idling?

[Mybowlcut]

I haven't checked hey haha. When my car idles, it does it BADLY... as in it's not stable... the revs are very tumultuous. It's been like this since I got I'm pretty sure.