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MG Midget and Sprite Technical - No response when I press the throttle

I have a new problem with my 1979 1500 midget. It runs but when I press the throttle there is no response and takes time for the engine to rev up. It was running OK this problem has just started. I was thinking it was the fuel pump but proberly wrong. This is my first midget and classic car and not the best with machanics but will give it ago. Any help would be good.Thanks.
n Allen


I'd start by checking the carb is working to open up the airflow. Could be the linkages between both carbs have come loose.
Gavin Rowles

try revving the car directly where the throttle linkage meets the carbs. There is a known problem with the throttle cable... could easily be that its getting stuck. If you can rev it easily with your hand... then go read a recent thread on 1500 throttle response.

C L Carter

Have a look at the dashpots on top of the carbs. They need topping up every so often. Have a google on dashpot oil for more info.
J White

I have put a new throttle cable on recently and I have reved the car directly where the throttle linkage meets the carbs the problem still happens so The cable is fine.

I will check the linkages between the carbs tomorrow.

Thanks
n Allen

Topped up the dashpots on top of the carbs. All fine there. Thanks
n Allen

Does that mean that the probelem is now fixed or just that the level of oil in the dashpots is now ok?
Gary & Gaps

Sorry, The problem isn't fixed just that the dashpots are OK.
n Allen

"there is no response and takes time for the engine to rev up."

Can you define this a little more?

You mean there is a delayed response? Then the engine speed gradually increases?

Does it misfire?
Lawrence Slater

topping up dashpots is in the Driver's Handbook :)

and setting carbs is in the Driver's Handbook :)

a few videos explaining the carbs (early on) and two about setting the carbs, one earlier and another more recent - http://www.youtube.com/user/Universitymotorsltd#g/u

carbs are favorite but could be something esle (too)

all will be revealed tomorrow
N Atkins

I presume you did not fiddle with anything after it was running fine, and before the problem started?

Like move the distributor round, possibly accidentally, if the retaining bolt is loose from a previous owners maintenance.

Problems like this are usually the result of a "fiddle gone wrong", in my experience!(Bitter experience)
Un-do the fiddle if that is the case.
JB Anderson

Must admit sounds straightforward because you do not describe and banging or spiting back so one would assume that the engine simply speeds up slowly.

I think the things that can cause this are

As described timing (dissy) slipped badly. check ignition timing.
Or maybe a cylinder is not firing. This will cause slow revving and to the untrained ear would not sound out of the norm. For you to check this it would possibly easiest to simply remove a plug lead from number 1 and try the engine, is it worse?
Then try 2 is that worse? etc etc. If you remove one that makes no difference there is the problem. Let me know what happens please.

A fuel pump problem would not cause this behaviour! it would either stop or start spitting due to extremely weak mixture.
Robert (Bob) Midget Turbo

Thanks for all off your response.

N Atkins - I've enjoyed watching some of them youtube videos. Thanks

JB Anderson - I have just done timming so that is OK. It was fine anyway but thought I check. I wasn't fiddled with anything the car just started doing on a short journey home.

Robert - I Did your check with taking a plug lead out 1 at a time and when I removed number 1 and 2 the car run evern worse but on 3 and 4 Nothing difference happened. Didn't make the car run any worse. Not to sure I like the sound of this.

What is my next move?

Thanks again everyone
n Allen

It'll still go on 2 cylinders... got yourself a little lawnmower =]

You need to find out why 3 and 4 aren't firing... could be loads of things. Interesting that its 3 and 4 though...


its probably the carb that feeds the rear 2 cyclinders... see if your float is full of petrol... the petrol pipes perish and you could easily not be getting fuel into the 2 rears

C L Carter

oh and if its not that... then its worth checking your ignition from the spark plugs... working back to the dizzy cap... before you start dismantling the carbs. Always check the simple stuff first!
C L Carter

Yes it does run on 2 cylinders but my lawn mower is better at the moment. Do you know which carb I should be looking out? I don't want to do any thing to the wrong one. I know I had a spark from 3 I saw that when I took the plug lead off. Not to sure about 4. Thanks
n Allen

Yep thought it was a simple problem so well done so far.

The majority of the time with these symptoms you have a problem with the carb supplying cylinder 3 and 4. As described you need to check the fuel level in that carb (perhaps the inlet valve to that float chamber is blocked or the float is stuck in the up position)? It could conceivably be possible for the head gasket to have totlly gone between cylinders 3 an 4 although I doubt that very very much.

Check the fuel level of th carb and let me know what you find.
Robert (Bob) Midget Turbo

Bob thankyou very much I will check the float chamber tomorrow and let you know how it has gone.
N Allen

Could be a carb piston stuck, try lifting the pistons using the little lifting pin under each carb.
Cheers John
HALL JOHN

I have checked the fuel level on the float chambers they are both full the pistons are lifting up. Any ideas now anyone?
N Allen

Well - probably a blocked jet...

but I would check ignition circuit first - just to be sure.
C L Carter

You should get the workshop repair manual, it explains how to rebuild the carbs... and you may have to end up doing that by the sounds of things.
C L Carter

I have checked the ignition circuit all seems to be fine. How do I unblock the jet?
N Allen

not a job I've ever done... taking the carbs to pieces scares the willies out of me... although there is no real reason why it should. But you NEED to get the manual before you start dismantling.

Just one thing before you start... Is it really cold where you are... and how long are you letting the engine warm up for. I'd get the engine going... give it some revs for a few mins and get it warm and see if the back kicks in.

C L Carter

Check you are getting sparks from all plugs. Then remove the dashpot caps and see if both pistons rise when you press the acc pedal.
Cheers John
HALL JOHN

Going to jump on the back of this thread with a similar problem 1275 69 Midget,

Car was parked up for almost four years recently liberated it from my ex wife! Brought it back home and it started straight up, brilliant I thought. Ive been running it up and down a local lane for the last week which is 2 miles there n back & over the week have clocked up 150 miles!!

Greased everything that needed it & cleaned/adjusted brakes took it for MOT today and it passed so Ive litrally just insured it & fetched the tax (FOC) Yippee.. went out for a longer journed and it konked!

It ran fine for 20 miles then suddenly lost power & refused to restart. After a mild panic it restarted but ran rough as hell and under 'load' ie trying to move but then burst into life and ran OK for about 2 miles then happened again, I managed to limp it home but it happened again 3x on the way at about the same intervals.

ideas? fuel or electrical? had a quik look when i got in but nothing obviousjumped out and got me
Rob Flint

Not sure the main jet on an SU could block it has a needle passing through it?

However perhaps the pipe supplying the jet from the float bowl is blocked but I assume this problem has just started.

Just for my benefit has this engine ever run right?

Robert (Bob) Midget Turbo

Yep! it used too... Bob.. you know i 'dont do' engines!
Rob Flint

Not you Rob you dipstick but Mr Allen. :)

Rob if you want your car mending then just pop round! LOL but not tonight as I have just been to my daughter's graduation at Huddersfield and I still have my suit on!!
Robert (Bob) Midget Turbo

Rob Flint,

That sounds like an intermittent fuel blockage.
Lawrence Slater

RF,
On a '69 Midget with those symptoms I would suspect the electric fuel pump. The contacts are prone to sticking at which point the carbs run low on fuel. The car then "kangeroos" for a bit and this is sometimes all it needs to shock the pump back into activity and off you go again!

Bob, (& Mr Allen)
I have had a sort of main jet blockage on an SU. There was a lump of crud in the little fuel bowl to jet feed pipe. The fuel flow washed it up to the bottom of the jet. On tickover, when the jet needle was down it pushed the dirt down as well, allowing fuel to flow and the engine ran ok. But on acceleration the needle rose, allowing the bit of dirt up into the jet and disrupting the fuel flow so that the car misfired and wouldn't rev freely. The needle prevented the dirt from simply washing through and clearing the jet. It was easily fixed though by removing the dashpot and piston and allowing some fuel to flow through to wash it clear.
Guy

Knew I would confuse the thread... Sorry.....

Guy,.. new electronic fuel pump fitted last week as last 'old' one was stuck & not working,

Bob... Im sure oil wont show on a black suit.. JOKE!

When are you free?? I will bring beer tokens..
Rob Flint

Crap in the fuel bowls then, -- getting sucked into the jet.
Lawrence Slater

Thanks for everyones help the problem has been sorted. I gave the fuel bowls a good clean took part of the carbs apart then blew compressed air through it all for quite some time and now it is running well again and on 4 cylinders. Thanks again.
N Allen

This thread was discussed between 09/11/2011 and 16/11/2011

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