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Author: Subject: RED TOP - Advice needed regarding R1 carbs

posted on 14/7/18 at 05:54 PM Reply With Quote
RED TOP - Advice needed regarding R1 carbs


I have put my old Spartan back on the road after being laid up for over 12 years. Really pleased with how its running, but the 1600 Crossflow that is currently fitted lacks punch out of corners; is only returning 30 to 32 mpg: and is not as smooth as modern engines. Consequently over the winter I am looking to fit a larger 16 valver.

Left over from other projects in my workshop I have an old Red Top; a Yukspeed bellhousing to mate it to a Type 9; the Red Top exhaust manifold; some R1 carbs; a Megajolt and various other bits and bobs. Therefore, this could be a relatively cheap engine swap.

The car will be used for lots of touring round Europe, so I am looking for good torque to give me punch out of corners, good 50mph to 70 mph acceleration for overtaking, and reasonable economy of say 35 mpg. Therefore, I was hoping to tap the collective Locost knowledge regarding :

1. Whether the R1 carbs would be suitable for my needs?

2. Whether anyone has any experience of the fuel economy from these carbs on a Red Top?

3. Whether anyone has any experience of what jets, etc the R1 carbs need on a standard Red Top?

4. What sort of performance gains you get from the R1 carbs?

5. Anything to watch out for when fitting the carbs (I already have a Mitsuba electric Fuel Pump and Malpassi fuel pressure regulator fitted, so I can optimise the fuel pressure for the R1 carbs).

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posted on 15/7/18 at 04:01 PM Reply With Quote
Lots of people use R1 carbs & I think they would be well suited to a Redtop.

I have ZX6R Mikunis which work really wel on my 2.0 Zetec. The R1's are a bit bigger - 40mm I think vs 38mm for mine - but should work equally well.

In my car I have 1.6mm mains and get high 30s MPG quite easily on a run.

Don't use anything other than the fuel pump from an R1. Loads of people have had issues using non bike pumps and they don't cost much secondhand plus are very reliable.


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posted on 15/7/18 at 07:02 PM Reply With Quote
Thanks Stu, I have been searching round on the forums and lots of people have said its best to stick with the R1 pump, so it looks like my current fuel pump and regulator will be destined for another project! Quite happy to do this as it will remove the regulator from the engine bay.

I was worried the R1 carbs might be a little too big and although they are a bit larger that yours, you are getting high 30s then that's great. If I end up getting mid 30s I will be well happy as the Red Top will be putting out significantly more torque and power than the crossflow and more economical as well.

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NS Dev

posted on 18/7/18 at 12:27 PM Reply With Quote
I have a redtop on R1 carbs in my autograss special. (I'm actually replacing them with injection and a different spec redtop but that's not relevant)

it was making 220hp on the dyno at last visit, runs well, does everything it's supposed to. Only gripe for me is that the carbs have a tendency to cause issues when left for 8 months without being run, and usually require a fiddle for each new racing season.

Certainly do the job though.

Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion retro car restoration and tuning

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