Modifying A Distributor

[Guest andrewbricknell]

Hi

 

I want to fit bike carbs or sidedraughts, but would need to either change for a non vacuum dizzy or go the Megajolt route.

 

I do remember looking at a website which showed you how to modify one but can not remember where it is, can anyone remind me. Also any comments on experience of the the two, I'm sure Megajolt is the best but do i really want to go the expense and complication when a modified Dizzy will do, I see Burton still sell them so they must be OK!

 

Many Thanks

[richyb66]

Dizzy info here

 

http://nw.rhocar.org/tuningdizzy.htm

[Guest SEgan]

I had a go at modifying my dizzy and although it looks easy I found the drive gear a real pig to remove and I damaged my first one with the puller. Apparently some are easier than others! Other members have told me that getting it back on in the right place with the pin lined up is even harder

 

Not one to give up I went for a different approach, I took the vac unit off the side and with a little key-hole surgery through the hole I removed the smaller spring completely (the smaller spring slows the rate of advance increase at higher rpm's) I put the vac unit back on the side and re-fitted. (Uncle Bob )

 

According to my timing light maximum advance now comes in at 3600 according to my timing light, which is about right for my cam. Setting the timing at a max of 36 degrees advance gives an idle of 18 degrees.

 

This method will not adjust the amount of total advance given by the dizzy and is very crude but it will give full advance earlier.

 

Sean

[Guest andrewbricknell]

Now the complicated bit!

 

I got the timing disc out and marked up the crank pulley from true TDC to check the standard timing first, so I wrote 30/35 and 40 degrees on and warmed the engine up to check the standard settings. Bearing in mind I had set TDC with a DTI to find the true TDC which ended up being 5 degrees retarded from the factory mark on the pulley.

I had also spent a good amount of time senting the car up ear and test runs getting to the point where I had best alround performance, well a good deal quicker than last year as in the winter I had gotten hold of another injection head, ported it as instructed by Des Hamill's book with 3 angle valves (standard sizes) 60 thou skimmed off and fitted a Kent 32 fast road cam.

The tick over is a bit lumpy but still sits happily at 850 rpm but the engine revs cleanly up to and past 6k!

Now to the timing, at tick over with the timing light its at 25 degrees BTDC and reaching 36 at about 3000rpm and topping out at over 40 BTDC at 3600rpm, and this is without any mods to the dizzy!

 

Removing the vacuum advance did not seem to make a huge difference, if any performance was slightly down, but difficult to judge really.

 

I am quite happy with the performance gains but don't know whether to do any more with the Dizzy from the above results, anyone have a view?

 

Thanks

[Peter Bell]

When you checked the timing did you have the vacuum connected? you need to disconnect it as all it does is give lots of advance at tick over and low throttle openings to improve fuel consumption and make it a bit smoother to drive. looks like it is working if you are getting 25° at tick over.

[Guest scrabster]

hi,the modification to a dizzy seems complicated to me,if you intend to fit bike carbs my suggestion would be to get a bestek ignition system.i have fireblade carbs and a bestek system and its working fine at the moment.you get a new dizzy & cap,module and sports coil.just connect 12v and away you go.£180 e-bay.hth.

jess.

[Guest andrewbricknell]

Hi Pete

 

I am pretty sure I did have the vacuum disconnected at the time, but you know how forgetful you can get when messing around, I will have another look. Maybe the springs are just a bit weak on my Dizzy, it came off an 84 car so could be up to 25 years old!

 

Andy

[Guest andrewbricknell]

Jess

 

Thanks I will have a look, did you fit it and did it make much of a difference?

 

Andy

 

hi,the modification to a dizzy seems complicated to me,if you intend to fit bike carbs my suggestion would be to get a bestek ignition system.i have fireblade carbs and a bestek system and its working fine at the moment.you get a new dizzy & cap,module and sports coil.just connect 12v and away you go.£180 e-bay.hth.

jess.

[speedtripledan]

I also went the bestek route for my fireblade bike carb conversion, my car was dyno'd before and after the dizzy was swapped the peak power stayed the same which it would as the final advance is still 35degrees both bestek and the dyno guy said that is the max you need to go, the difference is in the the bottom of the rev range 12degree at tick over then a progressive advance all the way to 5000rpm

The torque on my car is now better than when i had the EFI setup it will pull 5th from 25mph and revs smoothly all the way to redline.

Really easy to fit as well.

 

Dan

[Guest scrabster]

hi,i dont really know what the difference is,as its a new build and i only drove the donor car on and off the trailer,i just rebuilt the engine with the bike carbs bestek and piper cam.but it goes like stink.lol

http://community.rhocar.org/style_emoticon...lt/rolleyes.gif

jess.

[Guest andrewbricknell]

Guys

 

Sleepless night in bed last night mulling this over!!

 

I think what I have done is overset the advance at Tickover which then gives me the figure I need later on in the revrange, it is very lumpy at tickover but when i thought about it the motor was running alot sweeter at around 12 degrees but did not give me the performance later through the range, which I have probably over compensated for by over setting the advance.

 

It looks like Bestek is the way to go for the bike carbs, everyone sounds quite impressed with them.

 

Andy

[Peter Bell]

I think there is a link on the NW hoodies site to a man that modifies dizzys too. Perhaps Jim can confirm.

[Guest andrewbricknell]

Peter

 

I have been playing this afternoon, removed the dizzy and carried out the mod as per the North Westies, just left in the weaker spring, after a bit of road testing I was very pleased with the results, had to keep my eye on the rev counter as revving to 6500 very easy now.

 

It is very fiddly but I would recommend the spring removal via the apertures as per Seans comments, it did the job and saves the hassle of removing the gear.

 

Timing is now set at 14 degrees BTDC with the vacuum disconected and she runs up to 38/40 at 3500rpm.

 

Not sure if this will suffice with the bike carbs though!

 

Thanks for everyones help

 

Andy