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Bike carbs hate me…


Snapperpaul
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So I have just had the most difficult of journeys with fitting a new set of bike carbs and manifold from DanST to my home build 2.1 Pinto, I will try and keep it short…

I bought a new set because I was convinced my old spaced parallel set did not work properly so invested in a set of DanST carbs with manifold vac takeoffs, Pipercross air filter back plate and long trumpets.

my engine was run up on Penguin motors engine dyno (Graham Bahr, he of Turbosports and Classic Ford mag game) with his distributor and 45DCOE’s to set a bench mark we achieved 166bhp on 36mm chokes and 175 on 38mm chokes (please see his YouTube videos, my engine is the blue one with alloy rocker cover) other dyno runs were done with several different exhaust manifolds before we fitted my bike carbs which made 7bhp on the first run (yes only 7bhp) the slides were not lifting so I took them away and rebuilt them with new seals, O rings and float valves (I had previously cleaned out all the jets) i had trouble with the slide diaphragms and with advice from DanST managed to get the diaphragms to fit and took them back the Penguin motors dyno where we achieved 87bhp, Graham commented that in any other scenario a gain of 80bhp would be considered an excellent result…

I took them away again…

you can see where this is going but Graham put my old set of carbs on and drilled out the biggest jets I had provided and raised the needles produced 173bhp, how annoying that I spent well over £750 unnecessarily.

I dug deeply and whilst Graham thought this was job done I really wanted the new carbs to work.

First thing to note is that the dyno jet needles and block air jet was wrong for this setup, DanST said they wouldn’t fit dyno jet kits but that is what it had so he sent a set of standard profile adjustable needles, I drilled out the air jets and made a special diaphragm stretch tool out of an old aerosol cap and a heat gun and we tried again, all slides rise at the same time and torque and bhp were very close to the old bike carbs.

Last job was to get the ignition timing spot on with my Megajolt, Graham had previously fitted an Emerald ECU when the bike carbs got in the way of the distributor so I only needed to transfer the timing to my Megajolt, the mappable ignition timing smoothed out the torque curve and gained a few Ft/Lbs and BHP, both sets of carbs work albeit with one making a bit more bhp and the other more torque.

I learned so much with this journey and whilst Graham is not convinced about bike carbs he to has increased his knowledge.

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Sounds like a trip - I have never worked with carbs and you have ensured I never will 🙂  - fuel injection is the future. Actually, sadly, even that is going - amps and volts are next...

 

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My dyno man reduced my carbs to a pile of about 200 pieces in about 10 minutes, changed the chokes and drilled out the jets in about another 15 and then did a power run resulting in 180 odd hp. Not satisfied with that he took the distributor off and did something with the advance retard giving over 200 hp with a slightly restricted exhaust. This was on a redtop with twin 45s. All in about 90 minutes, just needs the right person. Didn't really want anyone learning on my time. He left school at 15 and considers himself uneducated. I consider him a genius 

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  • 4 weeks later...

A final run with my new but massively worked on Keihins now with the Robin Hood 4-1 exhaust (more on that later) and the longest alloy spun trumpets DanST produces made a huge difference.

Power now 173bhp, the torque is up and the large dip in torque has gone.

It seems that the bike carbs work better with the RH 4-1 than the Weber’s do, the Megajolt works better than the Burton dizzy on my engine and the longer trumpets make up an earlier loss.

Now a Turbosports forum member had kindly ran the numbers on my full engine spec and gave me the best diameters of the exhaust pipes and all the possible pipe lengths that would work with the pulse harmonics and the RH 4-1 was bloody close so when I had the exhaust made by Paul Gooderham I got him to change the collector to fit a 2 ½” exhaust.

The calculations also gave an ideal inlet tract length of 332mm to head face and with the 90mm trumpets I got about 285mm, this gave me those extra horses and more torque.

I am not sure I can find another 47mm as it will almost push the carbs outside the bonnet.

Watch this space…

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Weber 45’s with 36mm & 38mm chokes

https://youtu.be/0KHCZapyZd4

Small Vs big bore 4-2-1 exhaust

https://youtu.be/nVBN_zEfpzg

Distributor Vs Mapped ignition

https://youtu.be/8PeoLFK3eTE

Pinto 2.1 Bike carb test

https://youtu.be/QiJG_i53nIA

Weber Vs Bike carbs

https://youtu.be/Ta9MGDktTsI

 

It is clear Graham prefers Weber’s over bike carbs but after a lot of work on the bike carbs, with the Megajolt mapped ignition working better with bike carbs than Weber’s and the RH 4-1 manifold liking the bike carbs better than the Weber’s we finally ran the Keihins with 90mm trumpets fitted and got within a few bhp of the Weber’s.

There are 3 articles in Classic Ford magazine March, May & June and other Pinto videos on Penguin Motors YouTube feed.

 

 

 

 

 

 

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On 7/6/2022 at 8:17 PM, richyb66 said:

This thread needs pictures.

I find it impossible to post photos on this site but I’ve added links to the videos

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