Skip navigation

Whilst driving, car revs high whilst changing gears...

Post

Back to the top
All,

Today whilst driving I noticed the car after changing gear begins to rev high until I quickly changed the gear. Or when I stop the car, I can see sometimes the rev goes higher on its own when at standstil.

It's a cabby with a Webber Carb that has a manual choke (and yes the manual choke is all the way down)

Had a look at the and I can't see any cables getting caught…

Last edit: by optimusdub

Post

Back to the top
Have you checked the throttle cable at the carb and see if the return spring is weak and not pulling it back to the idle position, Rev the car at the carb and push it back to the throttle stop.
Next pop the air box of the top of the carb and see if anything is stopping the butterfly valves from moving.

1988 Mk1 Golf GTi Cabriolet 1.8cc DX, K-jet. Daily drive. 317,000 miles and counting
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.

Post

Back to the top
IMG_20200124_141632.jpg

Sorry which bit should I push?

Everything looks intact. However I did notice the screw to hold the manual choke was lose. I just tightened it

Before I tightened it, I took it for a drive and whilst driving at standstill it was below 1000rpm and the red light appeared. So I pulled the choke cable to 1500rpm. But notice it was going down and down at standstill.

Post

Back to the top
Could be any number of things.

When you take your foot off the accelerator when the car is in gear, does it still accelerate? Or continue to drive as though you are still on the gas a bit?

If so it could be the mixture is off or the butterfly is sticking.

Is the air filter clean?

Might be worth giving the carb a good clean with carb cleaner first.

Might be something simple.

Ian

Cornish Host.
1980 VW Derby
Clive the Cabby
Ujum the Invisible
Mynx the  Tintop

Post

Back to the top

borednow said

Could be any number of things.

When you take your foot off the accelerator when the car is in gear, does it still accelerate? Or continue to drive as though you are still on the gas a bit?

If so it could be the mixture is off or the butterfly is sticking.

Is the air filter clean?

Might be worth giving the carb a good clean with carb cleaner first.

Might be something simple.

Ian

Hi Ian,

Thanks for the reply. When I take my foot of the accelerator, then change gears it seems to rev itself….but since I've tighten the manual choke cable on the Webber Carb. It doesn't seem to do it.

However, when the car is started and I reduce the revs via manual choke. Below 1000rpm it seems like it's struggling. So I pull the choke back up until it's abit more stable.

But today whilst driving as I was coming to a standstill it did the same thing and the engine stopped. So I parked up and restarted the car and pulling the choke again and reduced it slowly.

I can't seem to put my finger on it.

Mark mentioned the spring I believe this is fine.

Is there a particular Webber Carb spray you recommend? How do I apply this?

Post

Back to the top
It may possibly be the idle needs lifting a bit. When it's warm does it idle ok? If so at what revs?

Any carb cleaner will do the trick. Take off the air box (to remove it, take the lid off, remove the filter and there should be 2 nuts that are easily visible. Remove these and lift the entire air box away) Then spray liberal amounts of carb leaner in around the carb itself. Feel feel to spray into the bowl and move the butterfly by hand and spray in everywhere you can see. Also spray around the outside of the carb to remove any road dirt build up as this may effect return springs etc.

Might help. If not check the airbox is sealing nicely and the air filter is clean.

Let us know how you get on

Ian

Cornish Host.
1980 VW Derby
Clive the Cabby
Ujum the Invisible
Mynx the  Tintop

Post

Back to the top

borednow said

It may possibly be the idle needs lifting a bit. When it's warm does it idle ok? If so at what revs?

Any carb cleaner will do the trick. Take off the air box (to remove it, take the lid off, remove the filter and there should be 2 nuts that are easily visible. Remove these and lift the entire air box away) Then spray liberal amounts of carb leaner in around the carb itself. Feel feel to spray into the bowl and move the butterfly by hand and spray in everywhere you can see. Also spray around the outside of the carb to remove any road dirt build up as this may effect return springs etc.

Might help. If not check the airbox is sealing nicely and the air filter is clean.

Let us know how you get on

Ian

Hi,

Thanks for the reply.

When it's warm it usually idles stable at 800/850rpm. But lately it goes down and down and the car stops….probably at the initial start up or up to 15 mins.

Also, during a cold start whenever I would start the car and pull the choke. It would be stable at whatever rpm….for eg I tank the choke cable and it's at 2000 rpm. Unless I touch the choke cable it would be consistent at this level…..however recently it's nots been stable, just goes down and down until I press my foot on the accelerator.

I've ordered a cab cleaner spray. Should arrive tom. Will give it a spray and see any improvements.

Post

Back to the top

borednow said

It may possibly be the idle needs lifting a bit. When it's warm does it idle ok? If so at what revs?

Any carb cleaner will do the trick. Take off the air box (to remove it, take the lid off, remove the filter and there should be 2 nuts that are easily visible. Remove these and lift the entire air box away) Then spray liberal amounts of carb leaner in around the carb itself. Feel feel to spray into the bowl and move the butterfly by hand and spray in everywhere you can see. Also spray around the outside of the carb to remove any road dirt build up as this may effect return springs etc.

Might help. If not check the airbox is sealing nicely and the air filter is clean.

Let us know how you get on

Ian

Hi Ian

So gave the carb a thorough clean, and the air filter is fine and fit snug. But the carb still feels lumpy….and when I start the car and crank the choke, the revs is normally maintained…..but it goes down until I put my foot down on the pedal….

Post

Back to the top
At a bit of a loss on that one then.

Erm, I was wondering if it was a bad seal or a vaccum leak somewhere. But normally, I think, this causes the revs to rise rather than drop.

The point of the weber is that it's simple so when they stop working it's probably something else. Apart from lifting the idle a bit, say to 950 and see if that works I'm stumped TBH.

Sorry mate

Ian

Cornish Host.
1980 VW Derby
Clive the Cabby
Ujum the Invisible
Mynx the  Tintop

Post

Back to the top

borednow said

At a bit of a loss on that one then.

Erm, I was wondering if it was a bad seal or a vaccum leak somewhere. But normally, I think, this causes the revs to rise rather than drop.

The point of the weber is that it's simple so when they stop working it's probably something else. Apart from lifting the idle a bit, say to 950 and see if that works I'm stumped TBH.

Sorry mate

Ian

No worries mate, thanks for the reply.

I drove it out today and it seems to be fine now…..I'll keep an eye over it but (touch wood) seems like it may have worked!
0 guests and 0 members have just viewed this: None.