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Slow Throttle Response, What To Do?

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#1 90anlu92

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Posted 13 June 2018 - 08:59 PM

Hey guys!

 

I have an Austin Mini 1000 from -74, and i just put a stage 1 tuning kit on her. Problem is, throttle response is very slow... Listen to this:

 

 

0:20 and forward. Those two rev-ups are both instant full throttle, foot hard down, and THEN she revs up like a few seconds after... Reving up is really slow as you can hear, and settling down to idle is also quite slow...... Can anyone help diagnosing why it's reving so slowly? What can I do about it? What can I do carb wise, is there an air screw i can adjust or what?

 

I was thinking maybe it's the throttle dampening oil in the carb.. I tried reading up oin what oil to put in there, but I got very mixed results. Everything ranging from ATF-fluid to 20w50 mineral oil... I put in some standard 10w40 as I had that at home ready to go, but maybe that's the issue?? I can't tell at all...

 

Please ignore the paint scheme, that military paint is the work of a previous owner and I'm in the middle of mending rust and getting her prepped for a proper paint work so...

 

Any and all assistance is greatly appreciated, thanks in advance!

 

Regards,

Anton.


Edited by 90anlu92, 13 June 2018 - 09:01 PM.


#2 johnR

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Posted 13 June 2018 - 09:07 PM

What colour are the deposits on the plugs - could it be running too rich causing it to bog?



#3 cal844

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Posted 13 June 2018 - 09:14 PM

Use a 20/50 mineral (engine oil) you may need to richen it up a bit too

#4 unburntfuelinthemorning

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Posted 13 June 2018 - 09:19 PM

Did the stage one kit come with a new carburettor needle?  Regardless you ideally need to visit a rolling road to get the fuel mixture dialled in properly.



#5 90anlu92

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Posted 13 June 2018 - 09:21 PM

What colour are the deposits on the plugs - could it be running too rich causing it to bog?

I haven't been running it long enough to get a reliable plug read, but I will check that first thing once I get some driving done. I just thought if I could somehow determine how it's running before putting miles on it I might spare my engine in the long run...



#6 90anlu92

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Posted 13 June 2018 - 09:22 PM

Use a 20/50 mineral (engine oil) you may need to richen it up a bit too

Ok, that viscous huh? I thought that'd be a bit much, but in that case maybe I should change uit... But won't that slow the throttle response even more??



#7 90anlu92

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Posted 13 June 2018 - 09:26 PM

Did the stage one kit come with a new carburettor needle?  Regardless you ideally need to visit a rolling road to get the fuel mixture dialled in properly.

Yes, that's the one I'm currently using. The setup is a maniflow LCB exhaust manifold, minispares aluminum inlet manifold, KN air filter (the conical one that sits offset upwards behind the carb) and stage 1 needle. I also cleaned the carb out, but I havent really done anything to the carb settings since I'm not even sure how one goes about tuning the carb... Is there an air screw or any other such settings one can experiment with? I did notice a thin hose running from the carb down to the distributor, and that assembly had some sort of tuning screw on the bottom that i tried turning but that didn't really do anything...



#8 unburntfuelinthemorning

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Posted 13 June 2018 - 09:38 PM

There will be a mixture adjustment but this is mainly for the idle speed mixture.  The needle profile is what controls the mixture through the rest of the engine speed range.  The needle supplied will be to get you close to the correct mixture but every engine is different.



#9 90anlu92

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Posted 13 June 2018 - 09:40 PM

There will be a mixture adjustment but this is mainly for the idle speed mixture.  The needle profile is what controls the mixture through the rest of the engine speed range.  The needle supplied will be to get you close to the correct mixture but every engine is different.

Well I did pick the needle recommended for the rest of my setup, so I was hoping that would work... Maybe I should change back to the old one and see if it improves things...



#10 cal844

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Posted 13 June 2018 - 09:45 PM


Use a 20/50 mineral (engine oil) you may need to richen it up a bit too

Ok, that viscous huh? I thought that'd be a bit much, but in that case maybe I should change uit... But won't that slow the throttle response even more??

I use 20/50 in my carbs, they all run well, even without a rolling road tune(not needed IME... we don't even need a timing light.)

If you do wish to try the 20/50 you won't need much, the carb should take a capful of oil to fill from dry.

If your engine is fully topped up with oil you can use some of that, pull the dipstick out the engine and let it drain into the carb dashpot.

I have stage one kits on 3 minis, one car has had a 998 and 1275 engines fitted, they all use AAU needles as supplied in the kits, with fuelling set up roughly by feel on the road, then once I'm happy I get it put on the gas analyser at the MOT station (a few beer tokens may be needed) to 3.0% CO.

#11 unburntfuelinthemorning

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Posted 13 June 2018 - 09:49 PM

I've just stuck a stage three head on an otherwise standard 998 engine.  The old needle was AAC so I tried a AAU which has made a big difference but I'm still going to get it on the rollers otherwise you never really know what's going on with it.  You can do a lot by seat-of-the-pants feel but you can't beat a rolling road tune. 



#12 cal844

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Posted 13 June 2018 - 09:53 PM

I've just stuck a stage three head on an otherwise standard 998 engine. The old needle was AAC so I tried a AAU which has made a big difference but I'm still going to get it on the rollers otherwise you never really know what's going on with it. You can do a lot by seat-of-the-pants feel but you can't beat a rolling road tune.


What did tuners do before rolling roads? Use the same section of road to run the car upto a fixed speed then tune as needed.

#13 90anlu92

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Posted 13 June 2018 - 09:56 PM

 

 

Use a 20/50 mineral (engine oil) you may need to richen it up a bit too

Ok, that viscous huh? I thought that'd be a bit much, but in that case maybe I should change uit... But won't that slow the throttle response even more??

I use 20/50 in my carbs, they all run well, even without a rolling road tune(not needed IME... we don't even need a timing light.)

If you do wish to try the 20/50 you won't need much, the carb should take a capful of oil to fill from dry.

If your engine is fully topped up with oil you can use some of that, pull the dipstick out the engine and let it drain into the carb dashpot.

I have stage one kits on 3 minis, one car has had a 998 and 1275 engines fitted, they all use AAU needles as supplied in the kits, with fuelling set up roughly by feel on the road, then once I'm happy I get it put on the gas analyser at the MOT station (a few beer tokens may be needed) to 3.0% CO.

 

Thanks for the tip, I'll try sucking the oil out of my carb and putting the 20/50 in :)

 

This is the needle I have currently by the way:

https://www.minispar...17.aspx|Back to

 

Are there any other settings I need to be aware of? I read somewhere that you can somehow set the nozzle by turning a screw, how does this work and where is that screw??



#14 Ethel

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Posted 13 June 2018 - 10:53 PM

It didn't sound that bad to me.

 

Some tune up basics:

 

Always start with the ignition - the engine doesn't need to be running to gap the plugs and points and set the static timing. You can also check the dynamic timing against the specs independently of how it's running.

 

It's pretty much a waste of time trying to tune a carb if the ignition isn't up to scratch and it's not got up to running temperature.

 

Similarly, any other fault will have you chasing yourself in circles adjusting the carb if not fettled first. Clogged air filters, manifold air leaks, worn throttle spindles, dodgy float valves....



#15 unburntfuelinthemorning

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Posted 14 June 2018 - 06:45 AM

Good advice from Ethel - it's no use trying to tune the engine if the basics aren't up to scratch.







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