Replacing Dellorto's with Mikuni or Keihin. Was it worth it?

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1200ts

1200ts

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I have the Dellorto's in the ultrasonic cleaner at the moment for a rebuild on my 3CL. Now I am wondering for those that are now using Japanese carbs, was it worth it? Does it actually run that much better? My 3CL has always run fine on the Dellorto's and on the dyno has 72HP at the rear wheel.

So was it worth the time and expense to make the conversion? If so what is the preferred carb to use and from where did you get the carbs?

I have too many projects to work on (over 30 bikes) and if I decide to do it, I am looking for a complete kit.

I am old so am not looking for 100HP and 150MPH. I have modern bikes that can do this. Just a Laverda triple that runs better, although I have no complaints about the Dellorto's.
 
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You would get both more hp and better economy. However, if your PHF's are not too worn, then they will work great when properly set up. Conversion involves a fair amount of fabrication. Likely elimination of original air box. Possible interference with fuel taps. I understand syncing them not that easy. Some don't have vacuum ports for your gauges. With 30 bikes the return on investment in fuel savings probably not appreciable, unless you ride this bike most of all, and want an engineering project.
 
Depends mostly on how much you intend using the bike. If it's restricted to tootling around the block on a sunny Sunday, the original Dellortos are well up to that. However, if you want to put up serious mileage, a set of Mikunis might be the better option. They won't magically produce bags of extra power, they'll just make the engine more manageable in the long term. Don't think you can expect much from new carbs if the engine isn't in its prime, though.

Running clapped-out PHBs can be a nightmare. To get the best out of the original carbs, they do need to be in the best possible condition, ie, the bodies not too worn, same for the slides and their linkages. All brassware, pump diaphragms and seals should be replaced, float heights exactly set. This can be a costly operation, often quite close to the price of a set of Mikunis. But, be aware there are a few extras required to fit the Miks, this is often overseen and does tip the scales back a bit in favour of the Dellortos. AfaIk, Keihins are quite bit more expensive.

I fitted RS36 to my 3C, mainly because I wanted to, and could. The old, worn modded engine gave almost identical dyno figures with both 36mm PHBs and the Mikunis. The new carbs were easy to set up, can be tuned finer and hold their tune better (probably mostly because they are new). The carbs are fitted to rubber inlet stubs as supplied by the Mikuni distributor and mated to a modded stock airbox sans filter. However, the slide rattle at idle drives me nuts. The original throttle return spring was too heavy for my liking, I removed one of the 2 fitted. I also retained the stock throttle with a single cable for a while, now swapped for a later generic RH switch/throttle block, but still single cable operated. Choke actuation is now by cable, as the original knob was obstructed by the fuel tap.

Would I do it again? Probably not, at least not if the originals can be feasably salvaged. The PHB 36 are now earmarked for fitting to my RGS when its motor calls it quits and I dig into that.

I regularly overhaul Dellortos, the bikes fitted with these run fine and are not at all disappointing. Properly set up, they consume only a little more than with new Mikunis.

piet
 
As Piet said, here is an illustration. After an engine rebuild I went to the local Ducati Club Concourse and as I rode in some random stranger came up to me and commented on how quiet my engine sounded at idle. Some time later the Mikunis went on and there was this rattle it made at idle. I thought it was from the clutch at first, bloody annoying. Nobody had mentioned that all these Mikunis make that sound at idle. They improve fuel use a hell of a lot and work really well, but that rattle is annoying. Its not so quiet at idle now.
 
Went to keihin cv carbs 10 years ago on the 3c when the dellorto bodies where worn beyond repair, needed replacing. If i could have rebuilt the dells, i would still have them. Keihins dont rattle at idle, but where a bitch to get right, good fuel range.
 
After a couple years sodding around with the Dellortos on the SFC1000 (after good advice and suggestions from various sources on this forum) finally bit the bullet and fitted a Red Mikuni kit. Easy to fit - only minor hassle being fitting the return cable. Question for me now is why I didnt do this years ago - difference is huge. Only grumble is that the balancing adjusters under the caps are super sensitive and a bit of a pain. Otherwise as close to "plug and play" as one can get.
 
Brother Marty has the red RGS formerly owned by Paul Casson.
He fitted flat slides from Red and had it tuned locally and it was transformed. Fires first hit of the starter and leaps out of corners like it never did before. First time I rode it after the new carbs I returned with a smile from ear to ear.
On a recent open road run to Clare Valley and back he got 52mpg.
And no aching arms from the throttle springs any more, using the one that came with the kit from Red. I know you can go for lighter springs on the dell’ortos, but blimey the originals were worse than intolerable.
 
helicopterjim said:
Don't let Paul Marx know that you have PHB 36's not in use.

Jim
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I only need one now, rh if I remember rightly. Ebay was my friend.

Otherwise, I endorse Piets comments re carb changing.
First question is: how many miles do you ride the bike annually and how often do you ride?

Paul
 
My experience when swapping from Dells to Mikuni RS36 on my Jota was that it made bugger-all difference to the power of feel of the bike, except for a slightly lighter throttle pull. Dyno runs before and after the conversion showed a pretty much identical power curve once the Mick's were dialled in. The only meaningful difference to me was a big improvement in fuel economy.
 
When I overhauled Sasha's 1981 jota with the mikuni carbs, I thought I had blown up the motor, rattle was so bad. Softer springs in the dellortos on my 120 jota make it much easier for long distance riding.
 
There is a way to reduce the return spring preload on the Miks, I could hardly blip the throatal when first fitted Mark Muir backed this off and it was much better. Maybe reducing that spring pressure makes them rattle more. Just my guess, I would rather have some rattle and less harder pull.
 
Vince said:
There is a way to reduce the return spring preload on the Miks, I could hardly blip the throatal when first fitted Mark Muir backed this off and it was much better. Maybe reducing that spring pressure makes them rattle more. Just my guess, I would rather have some rattle and less harder pull.
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Nope.

The return spring acts on the linkage shaft, the slides simply hang off this and are not spring-loaded at all.

piet
 
I fitted a set of Mikunis to the Flying Kangaroo 1200. For me the difference was magic - the mid-range pulls like a train; I have been gibbering on about how much I appreciate them ever since. I was musing today to TC and Pete about putting a set on the Jota, but that's probably a way off. Maybe FKs carbies were in need of a tune, dunno, but like I say the difference was like night and day. Oh yeah it also idles beautifully and improves fuel economy.
 
When we used to fit Keihin CRs to Kwaka 9s and the like the difference was also immediately noticeable. Better everywhere. Flat slides are even better. My 39mm FCRs are going to be a great addition to the SFQ.
 
I,m considering the same change ... fitting mikunis to my 180 Jota. Reading all the above still hasnt convinced me either way. For me the dellortos are fine at highway speeds but way too rich for city work and idle. Can anyone confirm the mikunis clean up fuelling at low revs. Thanks
 
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