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| Flat Spot https://www.ausmini.com/forums/viewtopic.php?f=2&t=53169 |
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| Author: | Drexxle [ Tue May 12, 2009 10:32 pm ] |
| Post subject: | Flat Spot |
Ok, done clutch, hardly any shudder left, need to do oil seal. Motor is pretty much reconditioned fully now, rebored, cleaned head, new clutch, reco gearbox. Last few things i did were reco 45d4 with electronic module, new plugs (6's), new leads, new thermostat, new radiator cap. Car sits on idle fine, doesnt vibrate, sits fine. When i go to take off i get power then a really bad flat spot at about 1500rpm, and then when the butterfly starts to open i get power again. Ive redone the fuel/mixture and idle on the carby numerous times to no avail, and have advanced the dizzy about 1/2-1 degree, and it made it better but there is still a flat spot. Pulling the choke makes it go away, and then pushing the choke back in again sort of compensates. The carby is pretty good, probably needs a new disk but the rod is ok. |
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| Author: | sgc [ Tue May 12, 2009 10:34 pm ] |
| Post subject: | |
Dashpot fluid? |
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| Author: | Drexxle [ Tue May 12, 2009 10:36 pm ] |
| Post subject: | |
hmmmm good point, not even sure whats in there at the moment. gary at mini pro filled it up. its supposed to be sae80 isnt it. |
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| Author: | TheMiniMan [ Tue May 12, 2009 10:39 pm ] |
| Post subject: | |
no, It should be some thing like 20w,,, so Auto trans fluid or 20w motor oil is ok,,, even some synthetic is good (depending on the cars needs/requirments) But it sounds more like it has the wrong mixture needle in it to me,,, there`s not many good SU carb tuners around who actually "Know" what they`re doing these days 
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| Author: | sgc [ Tue May 12, 2009 10:40 pm ] |
| Post subject: | |
Drexxle wrote: its supposed to be sae80 isnt it.
Nooo, that's way too heavy. Auto trans fluid is best according to general consensus, I tend to mix my own blend by trial and error though. |
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| Author: | david rosenthal [ Wed May 13, 2009 12:11 am ] |
| Post subject: | |
check if there is any oil in the piston. if there is tip it out and re-fit and try the car. If it is worse the put some thick oil in and try. all you are doing is changing the rate or speed it lifts at. same as diferent springs as Matt said probably the wrong needle. if it runs better with the choke then 1 wrong needle 2 air leak around butterfly shaft |
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| Author: | Drexxle [ Wed May 13, 2009 12:16 am ] |
| Post subject: | |
i didnt put it in there. and im gathering that gary at minipro did the right thing. How full is it supposed to be, ill check it tomorrow morning. I also tend to sort of be a lead foot, i also noticed changing the plugs from 5 to 6 a little power loss. |
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| Author: | david rosenthal [ Wed May 13, 2009 12:32 am ] |
| Post subject: | |
going by the SU bible if the piston damper has vent hole[the black cap on top has tiny hole in it] then the oil level is set at 1/2" or 13mm above the top of the hollow piston rod. That's all ok as long as the piston rod and chamber clearance is not too much. I have a carby here that some -one decided to polish the rod and the inside of the chamber. They used emery paper so the rod is like a ning nong in a shirt sleve. The oil finds its own level to the top of the piston. |
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| Author: | Drexxle [ Wed May 13, 2009 12:50 am ] |
| Post subject: | |
Ok yes it does have a black screw top with a pinhole in it. What do you mean by hollow piston rod. The black bit has the rod on it with a metal bush on it, you mean 1/2 inch above the bush thing on the end of it. |
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| Author: | drmini in aust [ Wed May 13, 2009 8:24 am ] |
| Post subject: | |
No he means 1/2" above the piston rod, which is the hollow shaft you can see inside there when you pull that damper rod out. ie fill it up just to the threads inside the alloy thingy.. |
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| Author: | sgc [ Wed May 13, 2009 8:37 am ] |
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I wouldn't worry too much about the oil level, I just put enough oil in to fill the piston when the damper is installed (i.e. to about 5mm or so below the top of the piston). Any more than that and I find that the oil gets sucked into the carb or blown out the vent in the cap. If there's nothing in there or the oil is too thin, you'll find you have a flat spot at part throttle acceleration. This happens because the piston is allowed to rise faster than it otherwise would, which admits more air into the carb for the same amount of fuel which leans the mixture out. A thicker oil produces a more pronounced 'accelerator pump' action; that is, the piston rises more slowly which keeps the mixture rich for a little longer, producing more power (or erasing the flat spot). Too thick an oil prevents the piston from rising, which chokes the carb and overfuels. |
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| Author: | TheMiniMan [ Wed May 13, 2009 9:40 am ] |
| Post subject: | Re: Flat Spot |
Drexxle wrote: Ok
When i go to take off i get power then a really bad flat spot at about 1500rpm, "If" it was dampner oil problem, then the flat spot would occur almost instantaniously as you apply throttle,,, & as he says he gets power & then it flat spots after soooooo,,, either the mixture needle is wrong or there is a problem with the piston/bell assy, & my guess is the needle not that i`ve been doing this SU carby stuff for very long, maybe only 35plus years
It`s really not hat hard to work out """IF""" you know what you`re doing |
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| Author: | Drexxle [ Wed May 13, 2009 10:18 am ] |
| Post subject: | |
if it was the needle matt, wouldnt it have done the same thing in my previous 998, this carby came off my previously written off mini. I pulled the needle out and its gold, has no markings, no paint dabs, nothing to indicate what type of needle it is. It has a spring on the end of it. would changing the plugs from 5 to 6 cause any of this to happen. i do notice a loss of power. And the car takes longer to warm up, but also doesnt get as hot when a drive it in traffic. The carby is pretty good, got reco a few years ago, but the disc is a little worn in the butterfly. |
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| Author: | simon k [ Wed May 13, 2009 10:25 am ] |
| Post subject: | |
Drexxle wrote: I pulled the needle out and its gold
tee hee hee, that still cracks me up  why don't you buy a standard needle from Midel, so at least you know what's in there and have a known starting point
get a workshop manual, take the carb off, dismantle it, identify all the parts, then put it back together - then you'll see how it all works and will be able to fix it or you could take it back to the guy who set it up and show him it's not working - depending on how long ago he did it.... |
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| Author: | Drexxle [ Wed May 13, 2009 10:35 am ] |
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why dont you buy a red needle like i had in a previous vehicle and THEN tell me all needles are gold. Buying a standard needle is probably a good idea seeing as i cant make this one out having no markings on it. Side Note: ive taken this thing apart more than many times. |
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