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puch maxi tuning,anyone done it.


Albert 888
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How is the carb inlet for air temperature?

A common issue on VW Bugs running modified carb's was that the fuel air mix became too cold and the fuel would condense out, a common cure is to add a velocity stack to effectively increase the size of the chamber for mixing fuel and air and also to draw slightly warmer air from the bottom half of the engine into the air cleaner.

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Inlet will be just above ambient temperature I think. The carb sucks air like a trooper, my exhaust is also larger and heavily modified, 

I did think about a venturie type stack for air flow, I fell the bigger dellortro will work better as it's more suited to my exhaust. 

Im after speed with torque.

Had a few vw's my favourite was my t25 2.1i

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48 minutes ago, Albert 888 said:

Inlet will be just above ambient temperature I think. The carb sucks air like a trooper, my exhaust is also larger and heavily modified, 

I did think about a venturie type stack for air flow, I fell the bigger dellortro will work better as it's more suited to my exhaust. 

Im after speed with torque.

Had a few vw's my favourite was my t25 2.1i

I believe a stack improves the airflow so improves the mix, i think it makes it more turbulent, but maybe it's the other way round.

I suspect that your right, the bigger carb may well better match your higher flow exhaust.

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Many years ago when tuning car engines, in simple terms, we always wanted more cold dense air to allow more fuel in to the cylinders and a better spark at the right time over the correct gap. I remember having 16 different gapped NGK Spark plugs, Drive hard at 120 mph, pull in to a lay-by, lift bonnet, put gloves on. Plugs out, next gap size in, bonnet down and off to do two runs and back in to the lay-by. Found that a certain gap (40 thou) allowed the 2 litre engine and gear box to pull like an absolute train in 3rd. Top speed was very high too, but fuel economy was poor!

The cold dense air was delivered through a K+N Filter. The ECU was remapped electronically. The spark from NGK's wonderful plugs, good fuel and correct tyre pressures.

I could drive long cross country distances at great speed. (before the advent of the Speed Camera's).

An interesting thread, the smooth air / swirling air debate has always gone on, I went along the smooth route and it worked for me.

Albert, I hope you find the magic set up.

Good luck

Edited by TIGHTCHOKE
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New 19mm phbg carb, 60 choke,45 starter,262 atomiser, 95 main jet, w7 needle second clip up. Starts ticks over and revs up great, 38mph max boggy as hell running very rich, going to drop the pilot to 40-42 and go from there. My intake froze it sucked that much cold air in.

DSC_0475.jpg

Edited by Albert 888
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It is evaporative cooling with the fuel/air mix inside your intake that will cause it to freeze, as well as sucking in very cold air just now.  That will cause the fuel to drop out the mix.

Can you fashion a hood to take some of the warmer air flowing around the cooling fins from the cylinder and direct it over the intake, without it looking rubbish of course?

Edited by grrclark
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Good old carburettor icing- nearly had me in a field back in my Instructing days.

Even diligent use of the ‘Carb Heater’ didn’t stop it forming that time- fortunately a low level circuit inside the airfield boundary got us back onto a piece of tarmac.

Carb icing is the reason that cars such as the early 911 and VW bugs had a bellow system that automatically directed warmer air- only down side is that warmer air is less dense, and so less power..... back then, I know which I preferred 

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I didn't know of carb icing on carbs, my mate a work told me about the old kawasakis and the slides used to stick open..

8 hours ago, grrclark said:

It is evaporative cooling with the fuel/air mix inside your intake that will cause it to freeze, as well as sucking in very cold air just now.  That will cause the fuel to drop out the mix.

Can you fashion a hood to take some of the warmer air flowing around the cooling fins from the cylinder and direct it over the intake, without it looking rubbish of course?

I have made another manifold it's shorter so will be a lot closer now.

Just picked this up today,no compression, big end rattling and main drive bearings goosed, now my plan is to have this new red one as a general runabout suspension lights all the mod cons, then use my gold one as a sunny day bike,so I'm going to be buying more performance bits to go on the race bike and use the stuff I already have for the red one.

Screenshot_20180214-181222.png

Edited by Albert 888
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8 hours ago, Jaymo said:

Good old carburettor icing- nearly had me in a field back in my Instructing days.

Even diligent use of the ‘Carb Heater’ didn’t stop it forming that time- fortunately a low level circuit inside the airfield boundary got us back onto a piece of tarmac.

Carb icing is the reason that cars such as the early 911 and VW bugs had a bellow system that automatically directed warmer air- only down side is that warmer air is less dense, and so less power..... back then, I know which I preferred 

That's one of the main reasons why I dropped the performance carb' off of my Bug, it is just far too fickle to try and maintain a reliable mix.

Gone back to the traditional oil filled air cleaner as well where the intake air is a little bit warmer, it does lose power as less air is being sooked into the engine, but it's a worthwhile sacrifice to keep the car drivable all across the rev range.

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13 minutes ago, Albert 888 said:

Only problem is your proberbly towards 100bhp. 

Standard I'm 2hp,very rough estimate I'm 4.5 - 7.5bhp 

I need everything optimum. 

Absolutely, the two are not really comparable at all, other than icing is to be avoided in all cases.

It would be interesting to know how much difference it would make if you were doing this tuning in the summer where the air is warmer and much less moisture laden.  You might well have to make changes to jet sizes and spark gaps as you get into the warmer weather.

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  • 1 month later...

Nearly finished, 74cc airsal piston port cylinder and head,21mm dellortro phbg carb 45pilot 60 choke,w7 needle 2 clips up 98 main jet,hpi cdi mini rotor -timed at 2mm btdc with auto retarding,domino fast action throttle, all cables shortened,wires hidden. Strengthening bar added,holes and stuff not needed deleted and welded,frame and wheels powder coated,gearing changed to 18:40. Just need some good weather and for the salt to disappear then I can tune and jet correctly. Hoping for 60mph.

Other bike is awaiting paint,that will be standardish. 

DSC_0507.JPG

Edited by Albert 888
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20 minutes ago, Dunkield said:

Sweet :good:

I was wondering what had happened to this project, good luck with speed attempt.

Thanks,

Waiting for glass blasting then waiting for paint,out of my hands that part. Also the herendous weather isn't helping much. Will soon have both done.

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