5 replies to this topic

[MB1380]

Hey guys, I have an ongoing problem with my mini. Basically When it gets up to temperature after about 5 miles it starts running very rough and becomes un-driveable. It also trys to run on for a few seconds when switched off.

I have Changed the Carb and Coil and it has made no difference. 

I bought this engine in parts and assembled it myself. The spec is as follows:

 

Bored to 73.5mm (1380cc)

Decked by .046" to flush pistons.

73.5mm Powermax pistons with 10cc dish

12G940 11 stud, Stage 3 Head

17cc chambers

1.5 Roller Tip Rockers/shaft

MD286 Camshaft

 

As far as i know this will give a high compression setup so do i need to run Octane Booster? different Plugs? Timing?

It runs perfect until it gets up to temperature.

 

Thanks in advance!

 

[Scott@minispeed]

What gaps are you running at the tappets?

[jaydee]

If CR is higher than 10.5:1 you'll probably need to run on premium fuel

Did you take this to a rolling road to have it tuned?

Its also a slightly lumpy spec so it definately needs fine tuning otherwise it will run very rough.

[KernowCooper]

What type of carb ? if a SU whats the needle?

[Da11yn]

From what I can recall over running can be caused by hot spots from carbon deposit build ups or hot plugs and some other things like timing and pre detonation. Therefore getting fueling and timing are important. The risk of pre detonation is increased by higher compression ratio and so everything becomes more crucial. Based on your your piston dish, head volume and 1380 you CR must be around 11.5, so you should probably be running on at least premium pump fuel and octane booster such as Castrol Valvemaster plus. 

 

mine used to over run considerably when i first built it, after i took it to be set up at a rolling road it was considerably better. It does still over run on occasion, but is noticeably worse if i have to run on non premium fuel or forget to put the additive in. 

 

I also think the metro had an anti over run valve which i imagine does what it says on the tin

[MB1380]

What gaps are you running at the tappets?

 

Not sure, will check it out! what should it be at? 15 thou?

 

What type of carb ? if a SU whats the needle?

 

Hif44 I tried a BDR a few months ago but it did not run well so it is on the original one, must check what that is.

 

From what I can recall over running can be caused by hot spots from carbon deposit build ups or hot plugs and some other things like timing and pre detonation. Therefore getting fueling and timing are important. The risk of pre detonation is increased by higher compression ratio and so everything becomes more crucial. Based on your your piston dish, head volume and 1380 you CR must be around 11.5, so you should probably be running on at least premium pump fuel and octane booster such as Castrol Valvemaster plus. 

 

mine used to over run considerably when i first built it, after i took it to be set up at a rolling road it was considerably better. It does still over run on occasion, but is noticeably worse if i have to run on non premium fuel or forget to put the additive in. 

 

I also think the metro had an anti over run valve which i imagine does what it says on the tin

 

Thanks I will try to get colder plugs and additive today and try it out!