ausmini :: View topic - Bike carbies on a car

headgasket wrote:

This would be a good place to ask a question that's been bugging me.

When I corner *really* hard, my mini stumbles. What's the cause of that? I have a single SU 1.5 i believe. I think during such right turns the oil light also comes on.

hg.

Fuel surge, what they were talking about happens with the bike carbs.

When you turn right all the oil and fuel goes to the left side of the engine. Due to inertia and circular motion and lots of boring physics stuff.
The oil light would come on because im assuming you dont have a centre oil pickup and all the oil is being pulled to the left side of the gearbox therefore starving the engine of oil. This is very bad so id reccommend you dont do this until you get a centre oil pickup.

The fuel problem is less severe as the fuel still goes to the left of the float bowl but as it is deeper its a less noticeable change, more a stumble than a full on miss. This is part of the design of the su carb, and all carbs are effected by this in some way because theyre pressurised like fuel injection.

Author:	TK [ Mon Mar 08, 2010 6:39 pm ]
Post subject:	Bike carbies on a car
From the current issue of Race. They say that running bike carbs on cars is not a problem until you start corning hard (Minis corner hard). The problem being that the carbs on a bike are not designed for flat cornering (a bike leans into a corner tilting the carbs) and they don't adequately control the fuel in the bowl. This leads to rough running in the corners and the potential for engine damage. So what words of wisdom do we have here? yes or no

Author:	Morris 1100 [ Mon Mar 08, 2010 6:48 pm ]
Post subject:
Maybe yes on the track. Maybe no on the road. Maybe easily fixed with a bit of attention to the float bowls. Do you think that SUs were ever designed for high load cornering anyway?

Author:	JC [ Mon Mar 08, 2010 7:01 pm ]
Post subject:
Seem profoundly ridiculous. A reckon a bike is leaning more into a corner then a car is.

Author:	Morris 1100 [ Mon Mar 08, 2010 7:15 pm ]
Post subject:
There are a lot of stock standard carbies that are useless on the race track until modified. The HIF SU does not like long fast corners. The HQ Holden Stromberg carby can suck air via the power valve in right hand corners. Webers don't like vibrations. You need to set the carby up for the job.

Author:	drmini in aust [ Mon Mar 08, 2010 7:35 pm ]
Post subject:
I ran a pair of Amal Monoblocs on my 1058 way back when, and fuel surge was not a problem.

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Author:	TheMiniMan [ Mon Mar 08, 2010 8:42 pm ]
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well,, going on the amount of continuous abuse, hard cornering & down-right smashing that dirt-bikes get,,, & the fact that the bike carbs (road or dirt) have been sooo well developed over the many many years,,, & that sooo many race cars are actually running bike carbs now (speedway, clubmans, hillclimb cars, & general all-round club cars etc etc etc),,, tells me that there really isn`t too much of an issue--> compared with the dramas that we all know webers/dellortos/solex have with long hard corners & the mods needed to address these issues with them ,,, SUs are`nt really that bad at all but bike carbs are definately VERY VERY good these days The carbs i`m running on one of my twin cam mini engines are fairly late model ZX9 quad-carbs & work a treat, no starving, no flooding,,, Just truely sweetsweet things the Yamaha R! carbs on my Hillclimb special show absolutely no dramas what=so-ever,,, run hard all day, long hard corners & short tight corners alike,,, bumps & jumps are not a problem either,,, they run smooth as silk in all circumstances so there`s at least 2x personal experiences with bike carbs on cars without any dramas for you anyone else running them to add to this thread???

Author:	drmini in aust [ Mon Mar 08, 2010 9:07 pm ]
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The only problem I had with the twin Amals was the throttle slides sticking at idle due to vacuum. The linkage was a Mini cable into a Triumph Bonneville 1-2 slider adaptor. These work fine on a bike, but when you are prodding the throttle with your foot, it's not so good. You either stall it off the line, or leave in a cloud of tyre smoke. Mr Plod (these days) would not be happy Jan.

Author:	TheMiniMan [ Mon Mar 08, 2010 9:44 pm ]
Post subject:
drmini in aust wrote: The only problem I had with the twin Amals was the throttle slides sticking at idle due to vacuum. The linkage was a Mini cable into a Triumph Bonneville 1-2 slider adaptor. These work fine on a bike, but when you are prodding the throttle with your foot, it's not so good. You either stall it off the line, or leave in a cloud of tyre smoke. Mr Plod (these days) would not be happy Jan. now here i thought we were talking about "quality Late Model Bike carbs" sorry Kev,,, i`ve gone over to the dark side & using Carbies that are actually good & don`t have problems at all muckin with ya mate, just muckin

Author:	blue_deluxe [ Mon Mar 08, 2010 9:49 pm ]
Post subject:
I did read that issue, and read it as not working on bikes but working well on cars. (More interested in the FSAE cars, they look better in the flesh and are ballistically quick) But thinking about it, its the opposite. An easy fix would be a bit of the spongy type stuff you use to stop fuel surge in fuel tanks. Or for someone with to much time a free rotating collar that joins it to the manifold, but thats just wank factor.

Author:	headgasket [ Mon Mar 08, 2010 11:11 pm ]
Post subject:
This would be a good place to ask a question that's been bugging me. When I corner really hard, my mini stumbles. What's the cause of that? I have a single SU 1.5 i believe. I think during such right turns the oil light also comes on. hg.

Author:	blue_deluxe [ Mon Mar 08, 2010 11:17 pm ]
Post subject:
headgasket wrote: This would be a good place to ask a question that's been bugging me. When I corner really hard, my mini stumbles. What's the cause of that? I have a single SU 1.5 i believe. I think during such right turns the oil light also comes on. hg. Fuel surge, what they were talking about happens with the bike carbs. When you turn right all the oil and fuel goes to the left side of the engine. Due to inertia and circular motion and lots of boring physics stuff. The oil light would come on because im assuming you dont have a centre oil pickup and all the oil is being pulled to the left side of the gearbox therefore starving the engine of oil. This is very bad so id reccommend you dont do this until you get a centre oil pickup. The fuel problem is less severe as the fuel still goes to the left of the float bowl but as it is deeper its a less noticeable change, more a stumble than a full on miss. This is part of the design of the su carb, and all carbs are effected by this in some way because theyre pressurised like fuel injection.

Author:	headgasket [ Tue Mar 09, 2010 1:48 am ]
Post subject:
Ah the float bowl, of course... I wonder if i can install a baffle of some sort in there.... Hey I just realized that this is the same problem the old spitfires had (also SU carbs!) They couldn't go into a quick dive because the fuel would jump up in the float bowls. That's why they did the half-roll to enter a dive. The luftwaffe had fuel injection. http://en.wikipedia.org/wiki/Comparison ... rburettors Apparently a female engineer solved this by fitting a diaphragm with a hole in it. 'Miss Shillings Orifice'. Regarding the oil pickup... does air actually get pumped through the engine, or is it just momentary lack of oil pressure?

Author:	drmini in aust [ Tue Mar 09, 2010 8:30 am ]
Post subject:
blue_deluxe wrote: headgasket wrote: This would be a good place to ask a question that's been bugging me. When I corner really hard, my mini stumbles. What's the cause of that? I have a single SU 1.5 i believe. I think during such right turns the oil light also comes on. hg. Fuel surge, what they were talking about happens with the bike carbs. When you turn right all the oil and fuel goes to the left side of the engine. Due to inertia and circular motion and lots of boring physics stuff. The oil light would come on because im assuming you dont have a centre oil pickup and all the oil is being pulled to the left side of the gearbox therefore starving the engine of oil. This is very bad so id reccommend you dont do this until you get a centre oil pickup. The fuel problem is less severe as the fuel still goes to the left of the float bowl but as it is deeper its a less noticeable change, more a stumble than a full on miss. This is part of the design of the su carb, and all carbs are effected by this in some way because theyre pressurised like fuel injection. Keep the oil level ABOVE the full mark. Add another 500mL. It won't hurt, but will save your bearings.

Author:	mini_mad_matt [ Tue Mar 09, 2010 6:50 pm ]
Post subject:
Yea second what doc said, check your oil level, if its not full top it up, and if you like doing long right hand turns put it a little bit over full.

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Author:	david rosenthal [ Tue Mar 09, 2010 9:53 pm ]
Post subject:
all the late model [post 1985] keihin bike carbs have a dual float with a baffel between them. The emulson tube pick up is in the center and they do not suffer from fuel starvation. The biggest problem is the fuel pump. A standard type SU pump is not really suitable. The bikes have a specically designed pulse pump which keeps the fuel flow up without over filling the fuel bowl.