Acceleration Cut Out

[Scoobasteve7]

Hi foum,

So finally managed to get the red mini running. I bought a gunson colortune to tune the carb, the timing is right.

However, whenever I go to accelerate, the engine dies.

I did a bit of tuning different parts to see if they would make any difference such as choke idle speed and the main carb adjustment screw.

now I have the engine in a state where it will run fine, but a bit high on revs by itself at idle, but when I keep the acceleration on constant it will rev, almost die and rev again.

Any ideas?

Thanks

I have a short video taken of it and I'll link it here once it uploads to somewhere I can store it online.

[Scoobasteve7]

https://www.youtube.com/watch?v=cehEINM ... e=youtu.be

Link to engine running.
notice how I don't move my hand at all, the engine revs/almost dies...then revs again and then dies...still no change to hand.

Any ideas??

Thanks

[keith]

have you got oil in the dashpot? needs a light oil there.

[Scoobasteve7]

Yep, there's fresh oil gone into the dashpot.
Brand new rubber seal at the top pf the pot too!

This is really confusing me...

[D Seven]

Had similar problem, changed condenser and points and it was ok.

[keith]

assuming its the correct needle for the car, fitted flush to the bottom of the carb-piston, and that the timing is roughly correct...

from the youtube clip it sounds like its leaning out for some reason... blocked fuel delivery? air leak? - air leak would explain high idle speed too... with the throttle closed you should be able to have it tick over at about 600rpm.

ignoring the colourtune for a minute, turn the jet under the carb to fully lean, ie: fully clockwise, (jet should be flush or nearly flush with venturi) with then back it off 2.5 turns. that's 15 "flats" - it should start and run, you may need to tweak the throttle screw for it to idle.

try removing the breather hose at the carb and block the hole with a plug of paper or the like...

[woody]

I agree with Keith,look for an air leak. Is your carb on tight and is the manifold tight?
Your vacumn advance tube leaving the carb seems to be heading for the drivers wing, is it connected to the dizzy? Check that the vacumn advance is working, its job is to advance timming at idle to make it smoother.

[Scoobasteve7]

Thanks for the reply lads.

There's brand new contacts and points in it. Spark is really strong now with it.

Timing is definitely set right.

Definitely the correct needle for the carb. Must check the flatness to the piston.

I did have an air leak by the manifold to exhaust bracket. I removed the exhaust, reshaped it and now it's perfectly smooth.

I'll try the adjustment tomorrow.

Yep, vacuum pipe is connected between dizzy and carb.

I'll let ye know how it goes! thanks

[Scoobasteve7]

Still no joy.

Took the carb off. Needle didnt look the best so I put in one out of the same type carb.

I noticed the manual choke cable was a bit short so cut it back to allow the cam to rotate fully.
This was stopping the bottom section moving up and down.(part that connects to the jet).

Put it all back together and back into the car.

Checked the fuel and spark again...both very good.

Now it wont even start! .

Just reread the jet adjustment part. Is that just turning the direction of the jet itself or is there a screw?

The adjustments I've been using are the big nut under the dashpot and the throttle adjustment screw.

Thanks

[keith]

not all carb needles are the same.... you need the right profile for your set-up. however the wrong needle wont prevent the car from starting.

the needle profile is stamped on the mounting boss of the needle. if your original needle is bent, replacement needle can be ordered from a mini supplier.

have a read of this handy guide for setting up a single HS carb.

http://sucarb.co.uk/technical-hs-type-c ... ing-single

also:

[Scoobasteve7]

The two I have are the same type and same length so I'd imagine it should be OK.
I will check the stamping though jsut to be sure.

Super link! Thanks

[woody]

All HS4 needles are the same type and lenght, its the diameter that changes but this isn't visable with the naked eye. Check the float chamber for dirt in the bottom of it and blow out the tube between the float chamber and jet. Wrong needle shouldn't stop engine from starting but set the bridge as Keith said 2.5 turns down. I would block off the breather inlet untill I had it running right.

[Scoobasteve7]

Hey guys,

Still no joy.

The needles are both ABB.

I have two carbs at the moment, one that I took apart and rebuilt with an SU rebuild kit so no dirt or anything in the bottom of the bowl as I cleaned the entire thing out with white spirits. I tried the other one and it seemed to run lovely and then I turned off the car. turned it again and no joy either. Seemed very strange.

I put back on the original rocker cover too in case the alloy one wasnt gripping enough and letting air in/out somehow (not that it should make a difference).

To be honest, there isn't a whole pile in them to go wrong with the carbs as far as I can see.
Fuel is definitely good, strong battery, great spark...Starting to wonder if it could be something else causing it.

I'm going borrowing one off an engine that is currently running during the week to eliminate it altogether.

I'll keep ye posted.

[woody]

Too much air getting into the carb via the engine can be a problem thats why I said to block off the breather inlet pipe. If the engine ran ok and then failed to restart you may be right to look in other places, namely the ignition system. You may need to check how strong the spark is.

[Dilogoat's Gruff]

As a general point I would recommend changing to electronic dizzy and get rid of the old unreliable inners. To me it sounds like a badly setup carb. They can be a pain to diagnose because there are a few small parts in the float that can cause issues. You said you have fuel? But at what point? Have you popped out a plug and seen the fuel and air drawn in? Are the plugs wet when you remove them? They should be fairly damp with fuel if it's not starting.

[Scoobasteve7]

Thanks again for the replies guys.

I got another carb from a 998 that was already set up and running. It starts the car and now runs well.

At first though, it wouldnt start as there was air being drawn in where the carb connects to the manifold..the nuts just werent tight enough.

Also, I just put in new gaskets but no gasket sealer so I reckon that could be where the air was getting in on my own ones.

going to get gasket sealer tomorrow and try my own carb again to see.

Still it was nice sitting in the garage well ago being able to hear the proper rev from the engine again!

[woody]

Well done you've narrowed the problem down to the carb. In all my years I've never had to put sealer on a carb gasket. With the original carb off you can examing it for the fault.
Make sure it is clean inside and that all leavers are moving smoothly and fully.Use carb cleaned.
Place the piston in the dashpot without the spring and check that it moves up and down smoothly under gravity.
Check the needle in the flootchamber is closing at the right level, if not it may flood the engine.
Check that the main fuel needle is dead straight.
Check that the jet is moving freely up and down on the choke and that the hose between it and the floot chamber is clean and not kinked.
Set the bridge down 2.5 turnes.
Once there cleaned and set up properly at the start SU carbs give very little trouble.

[keith]

Well done you've narrowed the problem down to the carb. In all my years I've never had to put sealer on a carb gasket. With the original carb off you can examing it for the fault.
Make sure it is clean inside and that all leavers are moving smoothly and fully.Use carb cleaned.
Place the piston in the dashpot without the spring and check that it moves up and down smoothly under gravity.
Check the needle in the flootchamber is closing at the right level, if not it may flood the engine.
Check that the main fuel needle is dead straight.
Check that the jet is moving freely up and down on the choke and that the hose between it and the floot chamber is clean and not kinked.
Set the bridge down 2.5 turnes.
Once there cleaned and set up properly at the start SU carbs give very little trouble.

+1 what woody said.