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Mini Struggling When Accelerating - Suggestions Please......


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#1 dorchard1978

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Posted 30 June 2020 - 06:09 PM

Hi All, 

My first post to this group and I really hope you all can help. 

I have a 1978 998cc factory standard mini that has suffered some issues since respraying and re-commissioning after almost 4 years off the road. The mini is now presenting a feeling of loss of power – almost like missing – as you accelerate. On idle it seems almost normal. The car was running beautifully before being locked away all that time ago, and it was started occasionally to keep it ticking over. 

 

To give you some background I have done the following: 

  • - All ignition parts replaced 

  • - Basic service 

  • - 2nd hand distributor fitted. (this solved a large proportion of the overall issue, but the current issue still persists) 

  • - Carb jet replaced, clean and refitted. This did not resolve the issue so then a 2nd hand carb was brought, cleaned, and the same new waxstat jet and existing needle fitted from the original carb. New gaskets where required – still no real noticeable change. I have ordered a new needle but that is not fitted. 

  • >One thing to note was that float chamber in the carb had lots of obvious rust residue – I have replaced the needle valve in the carb as it came in the same kit as the wax stat. 

  • - New manifold inlet gasket fitted 

  • - Fuel tank removed to remove any rust build up (there was quite a lot) and refitted 

  • - All Fuel line from tank to the fuel pump replaced. 

 

I think that’s it.  

On a previous older vehicle, I had a similar issue where an air leak through a gasket at the point which joined the carb to the inlet manifold. However, I have replaced all the gaskets from anything post carburation through to the engine itself.  

Has anybody had any issues when they replaced gaskets to do with the inlet side of things? Is it normal to have any problems with new gaskets? I am 99.9% sure that I have nipped up all the bolts to a suitable torque. 

Is it advisable that I remove the inlet gaskets and add some anaerobic curing silicone sealer to help ensure that all gaskets have sealed up nicely? 

Also if anybody may be able to suggest anything that could help me in my quest to solve this issue then please let me know. 

 

Thanks 

 

Darren 

 



#2 cal844

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Posted 30 June 2020 - 09:04 PM

Get the float bowl clean then make sure the jet and pipe from the float bowl isn't blocked.

You should also set the timing by ear.

Did you put oil in the dashpot on the carb?

#3 dorchard1978

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Posted 30 June 2020 - 09:41 PM

Get the float bowl clean then make sure the jet and pipe from the float bowl isn't blocked.

You should also set the timing by ear.

Did you put oil in the dashpot on the carb?

Hi cal844, 

 

Thanks for your thoughts - much appreciated taking your time to reply. 

 

The bowl was cleaned first of all, and the kit carb rebuild kit I brought had a new jet in - that was fitted once the carb was fully clean. I will probably end up checking this once again now you mention it though.

 

Timing has been set by ear now I have the new distributor in it. 

 

The dashpot oil was changed and replaced with SU dashpot oil. The piston is not sticky either.

 

Still sounding like I am a little stuck with this :(

 

Darren



#4 cal844

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Posted 30 June 2020 - 09:47 PM

Ok great to hear another user who doesn't use a timing light. I'd now try a thicker dashpot oil, just use half a cap of the mini engine oil, maybe even mix the SU and a small amount of engine oil .

I use 20/50 oil in my carbs, they're perfect for the car

#5 DamoMini

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Posted 30 June 2020 - 11:19 PM

You could spray some carb cleaner on the gasket interfaces and see if the idle speed changes - can help troubleshoot air leaks / gaskets.

Is the vac advance connected and have you checked that the vac line is leak free and the distributor responds to the vacuum?

#6 luismx123

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Posted 01 July 2020 - 07:56 AM

as stated above, check for air leaks in the manifold-head flanges and manifold-carb. 
A good way to check if it has to do with the carb/oil/spring is to get the car up to temp, and accelerate very slowly and hold a certain rpm/speed. For example, 2nd gear 2000rpm, then try 3000, then 4000. Just keep the speed and rpms constant so that the carb has time to settle. If this works well, then what you are experiencing is stuttering or bogging caused by quick accelerations and changes in the carbs piston. This could be down to the wrong carb dashpot oil/spring setup which is quickly remedied. If the opposite is true, and the car is having problems holds steady rpms, then it has to do more with the needle and carb setup. i.e being too rich or lean. 
Do you know which needle is currently installed? 
Fault finding is trial and error. My upgraded 998 has a flat spot once I floor the pedal so I installed an AFR gauge to find out whats happening. Oil was too thin, causing leanness. Thickened the oil a bit and that has solved it to an extent. It takes time...and patience. 


Edited by luismx123, 01 July 2020 - 07:58 AM.


#7 PoolGuy

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Posted 01 July 2020 - 08:15 AM

This “ Fuel tank removed to remove any rust build up (there was quite a lot) and refitted“ jumps out at me. How did you clean it, how do you know it was spotless once it was done? Fuel tanks are notoriously difficult to clean and very rarely stop rusting once they’ve started.

#8 dorchard1978

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Posted 01 July 2020 - 05:30 PM

Ok great to hear another user who doesn't use a timing light. I'd now try a thicker dashpot oil, just use half a cap of the mini engine oil, maybe even mix the SU and a small amount of engine oil .

I use 20/50 oil in my carbs, they're perfect for the car

I will give this a go. Thanks for letting me know!



#9 dorchard1978

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Posted 01 July 2020 - 05:31 PM

You could spray some carb cleaner on the gasket interfaces and see if the idle speed changes - can help troubleshoot air leaks / gaskets.

Is the vac advance connected and have you checked that the vac line is leak free and the distributor responds to the vacuum?

 

Ok, will give that a go - thanks for replying!



#10 dorchard1978

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Posted 01 July 2020 - 05:37 PM

as stated above, check for air leaks in the manifold-head flanges and manifold-carb. 
A good way to check if it has to do with the carb/oil/spring is to get the car up to temp, and accelerate very slowly and hold a certain rpm/speed. For example, 2nd gear 2000rpm, then try 3000, then 4000. Just keep the speed and rpms constant so that the carb has time to settle. If this works well, then what you are experiencing is stuttering or bogging caused by quick accelerations and changes in the carbs piston. This could be down to the wrong carb dashpot oil/spring setup which is quickly remedied. If the opposite is true, and the car is having problems holds steady rpms, then it has to do more with the needle and carb setup. i.e being too rich or lean. 
Do you know which needle is currently installed? 
Fault finding is trial and error. My upgraded 998 has a flat spot once I floor the pedal so I installed an AFR gauge to find out whats happening. Oil was too thin, causing leanness. Thickened the oil a bit and that has solved it to an extent. It takes time...and patience. 

 

So I have just replaced the needle today with a like for like new one. I have an ADF needle in my carb. This made no difference.

 

Thanks for the advice on testing I will give it a try and and report back soon.



#11 dorchard1978

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Posted 01 July 2020 - 05:44 PM

This “ Fuel tank removed to remove any rust build up (there was quite a lot) and refitted“ jumps out at me. How did you clean it, how do you know it was spotless once it was done? Fuel tanks are notoriously difficult to clean and very rarely stop rusting once they’ve started.

 

I removed the tank fully from the car, I rinsed the tank out with fuel that I then filtered through a mesh - hence removing any particles suspended in the fuel. I did this process until no more particles were seen for two rinses. 

 

You could well be correct in saying that the rusting could now have taken hold but in such a short time I doubt it will have rusted significantly enough for to be an issue at this point. I do think that a new tank will be required soon though.

 

Thanks for the comment though as all ideas are very welcome!



#12 Chris1275gt

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Posted 01 July 2020 - 06:28 PM

There was a very fine mash nylon filter in my original 1975 tank on the end of the pick up pipe that even with it out of the tank was impossible to clean as the rust in the mesh had all hardened.

#13 dorchard1978

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Posted 03 July 2020 - 05:57 AM

There was a very fine mash nylon filter in my original 1975 tank on the end of the pick up pipe that even with it out of the tank was impossible to clean as the rust in the mesh had all hardened.

Hi Chris1275gt,

 

Thanks for that - you comment put me to task removing the fuel tank and checking out the filter. I managed to get a clear view (just!) of the small filter and on the pickup pipe and unfortunately

 

 

as stated above, check for air leaks in the manifold-head flanges and manifold-carb. 
A good way to check if it has to do with the carb/oil/spring is to get the car up to temp, and accelerate very slowly and hold a certain rpm/speed. For example, 2nd gear 2000rpm, then try 3000, then 4000. Just keep the speed and rpms constant so that the carb has time to settle. If this works well, then what you are experiencing is stuttering or bogging caused by quick accelerations and changes in the carbs piston. This could be down to the wrong carb dashpot oil/spring setup which is quickly remedied. If the opposite is true, and the car is having problems holds steady rpms, then it has to do more with the needle and carb setup. i.e being too rich or lean. 
Do you know which needle is currently installed? 
Fault finding is trial and error. My upgraded 998 has a flat spot once I floor the pedal so I installed an AFR gauge to find out whats happening. Oil was too thin, causing leanness. Thickened the oil a bit and that has solved it to an extent. It takes time...and patience. 

 

So I have just replaced the needle today with a like for like new one. I have an ADF needle in my carb. This made no difference.

 

Thanks for the advice on testing I will give it a try and and report back soon.

 

So the issues will not give up if I allow the carb to settle, so it could be a mixture issue. The search continues once more!

 for me it looked like new! So the search goes on.



#14 Chris1275gt

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Posted 03 July 2020 - 08:25 AM

When you say the piston isn't sticking did you run your finger around inside the pot to check for any light vertical scoring.

#15 dorchard1978

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Posted 03 July 2020 - 11:08 AM

When you say the piston isn't sticking did you run your finger around inside the pot to check for any light vertical scoring.

I will take another look! Cheers






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