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Author: Subject: DCOE 40s

posted on 14/5/20 at 11:24 AM Reply With Quote
DCOE 40s

I've been pratting about for years trying to get a pair of old and abused 40s to run properly. I'm happy I've got the jetting etc right but I could never get a consistent balance across the rev range. I could have an awful idle or a horribly burbly mid range. I bought a WebCon synchro meter and improved things but never got all 4 chokes with the same amount of suck.

In lock down I decided to take the manifold and the carbs off together and have another go.
Using my shop vacuum as the source of suck (it was a great fit in the manifold inlets), I've manged to get them all there or there about. All 4 are now very similar all through the range from idle to WOT

I knew there were two basic problems. The inter linkage between the carbs was and still is a weak point, and the differences between the carbs and between the individual chokes in each carb was due to a combination of the butterflies not being as well aligned as they could be, and bent throttle spindles.

I re-aligned all 4 butterflies by loosening the 2 securing screws, opening them wide and allowing them to snap shut with a 2 thou feeler gauge in the choke at the top. This gave me the same seating across all 4 and significantly cut the suck of the stronger carb. Then I was able to do some spindle twisting using wrenches on the ends of the spindles. Apart from my noisy vacuum cleaner annoying the neighbours. a lot quieter than having the Pinto sitting at each thousand in the rev range while taking measurements (I never did that at home, always somewhere with no neighbours!)

Can't wait to get out on the road and try it out.
flow bench
flow bench

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Mr Whippy

posted on 14/5/20 at 11:44 AM Reply With Quote
Good work and like the idea of using the vacuum cleaner and probably far more consistent than the engine

But then that may be a issue as will you not have to balance them again once fitted since the flow to each cylinder would be slightly different depending on it's actual flow rate compared to it's neighbours? (I've never balanced carbs being far too lazy and so am not sure if this is an issue)

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posted on 14/5/20 at 01:24 PM Reply With Quote
I spent a few quid on a Morgantune years back when I had bikes and if you have a vacuum take off it's great.

I have Mikunis on my Zetec and find it super easy to balance them with the Morgantune as you do them all at the same time so can see how changing one carb affects the flow on the others.

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posted on 14/5/20 at 02:43 PM Reply With Quote
I've used the vacuum cleaner ploy too. I recently replaced a set of GSXR750 itbs with Hayabusa ones. On the 750 variant the idle adjust screws are accessible from above when in situ. On the 'Busa ones the screws end up underneath and at angle that makes adjustment virtually impossible.
Using a vacuum cleaner and a Synchrometer it was easy to balance them as a set on the bench.
No problems with disassembly, they are re-spaced and locked together by the usual long bolts and all bolted to an additional long angle stiffener.
I rechecked the balance after fitting and they are fine.

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