Intermittent revs drop and stall.

Technical advice Q&A
User avatar

Topic author
H7OB
Posts: 268
Joined: Wed May 10, 2017 3:42 pm
Location: Warwickshire
Great Britain

#1 Intermittent revs drop and stall.

Post by H7OB » Sun Nov 22, 2020 3:51 pm

Hello all. I wonder if anyone could suggest any tips for an unusual intermittent stalling issue?

I started the car this afternoon and let it warm up nicely. On occasions when I’ve blipped the throttle and take my foot off the accelerator the revs drop right off and it stalls. It will then start with no problems and idle but the fault seems intermittent.

As far as the engine goes it’s been recently rebuilt, set up on a rolling road and runs beautifully. It’s on a 123 distributor that has never been a problem. The coil looks a bit elderly.

Electrics are not my strong point and I’m thinking this might be more likely due to the fact that carbs etc have been set up and not touched since. It’s running beautifully other than this occasional dropping of revs and stalling.

Any tips from those more experienced than me would be gratefully received! :scratchheadyellow:
Paul
'68 Series 1.25 2+2

Link:
BBcode:
HTML:
Hide post links
Show post links


christopher storey
Posts: 5077
Joined: Sun Mar 09, 2008 3:07 pm
Location: cheshire , england
Great Britain

#2 Re: Intermittent revs drop and stall.

Post by christopher storey » Sun Nov 22, 2020 5:29 pm

Paul : how warmed up was warmed up ? CMC reckoned at one of the E type days I went to , that it takes 35 miles - yes there's not a decimal point error - to fully warm up an XK engine, mostly because of the vast oil capacity . Now that ambient temps are dropping the stalling after a blip of the throttle doesn't really surprise me unless not only the water, but also the oil temperatures have risedn to operating levels

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

Topic author
H7OB
Posts: 268
Joined: Wed May 10, 2017 3:42 pm
Location: Warwickshire
Great Britain

#3 Re: Intermittent revs drop and stall.

Post by H7OB » Sun Nov 22, 2020 5:40 pm

Hi Christopher. I hear what youre saying, it was very warm but not fully hot. I then took it for a spin c10 miles and it stalled a couple of times when coming to a halt with no accelerator. It will restart perfectly and tick over smoothly at about 700 rpm but it’s definitely a new phenomenon.
Last edited by H7OB on Sun Nov 22, 2020 9:04 pm, edited 1 time in total.
Paul
'68 Series 1.25 2+2

Link:
BBcode:
HTML:
Hide post links
Show post links


gtjoey
Posts: 26
Joined: Tue Jan 22, 2019 4:11 pm
United States of America

#4 Re: Intermittent revs drop and stall.

Post by gtjoey » Sun Nov 22, 2020 8:33 pm

Just for giggles ADD a half turn to each jet setting....meaning clock wise, sounds like your a little low on fuel.
Then see if you race to about 900 after you blip it....If so then turn the slow idle screws clock wise a half and your done.
good luck
gtjoey1314

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

keithmac
Posts: 103
Joined: Sun Jan 22, 2017 2:54 pm
Location: Peterborough,On.
Canada

#5 Re: Intermittent revs drop and stall.

Post by keithmac » Mon Nov 23, 2020 1:49 am

I confirm gtjoeys findings on my car. same symptoms, same cure.
Regards
Keith
Early 1967 S1 OTS, 1952 MG TD

Link:
BBcode:
HTML:
Hide post links
Show post links


Joes66
Posts: 246
Joined: Sun Apr 26, 2020 7:16 am
Great Britain

#6 Re: Intermittent revs drop and stall.

Post by Joes66 » Mon Nov 23, 2020 7:32 am

Yup
Sounds like it's a bit lean at idle
Joe
1969 series 2 2+2

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

Topic author
H7OB
Posts: 268
Joined: Wed May 10, 2017 3:42 pm
Location: Warwickshire
Great Britain

#7 Re: Intermittent revs drop and stall.

Post by H7OB » Mon Nov 23, 2020 8:19 am

Many thanks for your inputs chaps, I’ll take a look.

I’m just surprised that it seems to have suddenly started happening when, separate to this, it’s ran beautifully since it was set up on a rolling road in July last year. Cooler air maybe?
Paul
'68 Series 1.25 2+2

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

MarkRado
Posts: 307
Joined: Fri Jan 26, 2018 9:13 am
Location: Graz
Austria

#8 Re: Intermittent revs drop and stall.

Post by MarkRado » Sat Nov 28, 2020 5:24 am

I had the same problem. I found that one of the throttle discs had a resistance to close completely (fractions of a mm), which was overcome when blipping. This could not be adjusted with the slow running screw, since either I got high idle without blipping all the time or stalling. Slight play in the bushes plus dry cork throttle shaft seals were the reason. As a quick non-rebush remedy I oiled the seals via the shaft and mounted the return spring differently. In a second step I readjusted the disc (carb off obviously). In the end I had the carbs rebushed.
Mark
1963 OTS 880436

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

malcolm
Posts: 1945
Joined: Fri Jan 03, 2014 10:44 am
Location: Fleet
Great Britain

#9 Re: Intermittent revs drop and stall.

Post by malcolm » Sat Nov 28, 2020 9:52 am

MarkRado wrote:
Sat Nov 28, 2020 5:24 am
I had the same problem. I found that one of the throttle discs had a resistance to close completely (fractions of a mm), which was overcome when blipping. This could not be adjusted with the slow running screw, since either I got high idle without blipping all the time or stalling. Slight play in the bushes plus dry cork throttle shaft seals were the reason. As a quick non-rebush remedy I oiled the seals via the shaft and mounted the return spring differently. In a second step I readjusted the disc (carb off obviously). In the end I had the carbs rebushed.
Beat me to it! I was going to say "a sticking throttle"
I've often had cars where the throttle sticks a little open until you blip. Means if it's adjusted when open a little, it ticks over great until you blip and you no longer have a tickover.
Malcolm
I only fit in a 2+2, so got one!
1969 Series 2 2+2
2009 Jaguar XF-S
2015 F Type V6 S

Link:
BBcode:
HTML:
Hide post links
Show post links


Joes66
Posts: 246
Joined: Sun Apr 26, 2020 7:16 am
Great Britain

#10 Re: Intermittent revs drop and stall.

Post by Joes66 » Sat Nov 28, 2020 11:20 am

One other thought
Don't know about the larger su carbs but a common problem on MG's su carbs was throttle spindle wear
The ends of the throttle spindles wear out the hole they go into
They go oval and air is sucked in to the carb through the enlarged hole
This negates the butterfly to control the air flow through the carb and can cause what you are having a problem with
It also causes running on
Joe
1969 series 2 2+2

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

Topic author
H7OB
Posts: 268
Joined: Wed May 10, 2017 3:42 pm
Location: Warwickshire
Great Britain

#11 Re: Intermittent revs drop and stall.

Post by H7OB » Sat Nov 28, 2020 12:02 pm

Many thanks for all your inputs chaps, much appreciated. It’s given me a few things to go at.

Now the only other thing I could do with help with is a kick up the exhaust to get me out of the house and into the garage on a damp grey Saturday! I might just need another large strong tea to contemplate that! :bigrin:
Paul
'68 Series 1.25 2+2

Link:
BBcode:
HTML:
Hide post links
Show post links

Post Reply Previous topicNext topic