Author Topic: Has anyone done a C5 carb conversion  (Read 2035 times)

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Snotball

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on: March 09, 2021, 04:03:02 am
Has anyone done a Mikuni carb conversion such as offered by Hitchcock’s on a Euro IV C5. Are there any tips and tricks and in terms of overall performance is it worth doing. I’m not after any increase in top speed but would like it to hold speed better up hills.  ;)


AzCal Retred

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Reply #1 on: March 09, 2021, 05:52:04 am
Here's some info from two of our luminaries in the "Bullet with UCE" thread. The Hitchcocks carb kit will be very close, and they will have tuning information and parts as well. It'll save a lot of flailing. If I had a UCE it'd get a carb immediately, I see no point to overly complicating a nicely designed long-stroke, 2-valve, pushrod equipped "classic". If it stops running well, dump the water out of the float bowl and blow out the dirt. With a good filter even that's unlikely to happen. Modern electronic ignitions are pretty bulletproof. - ACR -

From ACE:
 Re: Bullet 500 that won't rev past 3750rpm ; Reply #36 on: September 27, 2020, 01:22:53 pm
I am pretty sure there is a way to change the electronics over to the one used on the AVL . The early Hitchcock carb conversion kits had something like that with it.
The injector housing bolt spacing is the same as the carbed Bullets. Get a manifold and bolt it right on. However, I strongly recommend a Mikuni. Amal carbs are very poorly made, and the cost a lot of money compared to Mikuni.
You need to get a petcock conversion for the tank after removing the fuel pump.


From Adrian II:
Re: Bullet 500 that won't rev past 3750rpm ;Reply #37 on: September 27, 2020, 02:40:44 pm
If this was a carb-fitted model from the factory (some home market UCE Bullets were, the 350 carb-fiited UCEs were also exported to some markets) it will already have a petcock, probably the same one fitted to the tank with two M6 hex set screws as used on the Electra-X (but not the AVL Classic!).
For some reason the iron barrel Bullets (or at least the later ones) have 58mm carb stud centers, the spacing on the UCE 500s is 60mm, same as the AVL, I bought a UCE carb rubber cheap which also fits the PWK34 clone I bought ludicrously cheaply to try on an Electra-X, these rubbers take carbs with a 40mm stub, so a VM series Mikuni of the right size will fit, presumably the TM will as well if there's enough under-tank clearance. There's plenty of information elsewhere on the forum about folks' successful settings for various carbs, so something that works on a 500 AVL would be a good starting point.



A brace of 1999 Bullets: 1 Red Deluxe, 1 Green Standard. Also, 1 wee orphan 1956 Fire Arrow project.


viczena

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Reply #2 on: March 09, 2021, 06:04:40 am
You loose control over your ignition. It is fixed with carb, because the EFi uses the Throttle to determine the ignition timing. This leads to 20% less power.
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AzCal Retred

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Reply #3 on: March 09, 2021, 08:23:10 am
   Hitchcocks is pretty clear that the carb conversion doesn't lose you any performance. I'd talk to them, then decide. Viczena keeps bringing this up, but I don't see any data forthcoming to back it up. It has to be working well for most folks or they'd shitcan it. H's would be losing business & be out some refund cash if their products didn't perform as advertised, and I'm not seeing that happening.
   This isn't a 12,000 RPM, 5 valve Honda-saki-aha, it's a one cylinder 500cc long stroke 2 valve pushrod motor. Even the ancient Pre-Unit Bullet can make 35 HP with points, a fixed ignition advance curve and about $3500 worth of needle bearing crankshaft, steel con rod & forged piston to replace the factory "Velveeta Cheese" parts. The C5 already has all that good stuff. Your C5 isn't going to drop 7 HP because you bolted on a Mikuni. Will it be more altitude & temperature sensitive? Sure, a bit. That's what EFI is all about. Will a carb be good enough 98% of the time? 70+ years of Bulleteering says yes. If you wanted a powerful big single, is would have been just too easy to get the KLR650, Honda 600, KTM, Husqvarna, etc. Short stroke OHC motors with 4 valves are the proper tools for that game. But that's not why the UCE's sell, they're all about the "thump", that old skool cadence. Leave the racing to the racers. Simpler is good.
   H's has the $1400 stroker crank for your machine. Displacement generally equates to more low & mid-range "umpf". Maybe a $300 535 forged piston would get you to where you think you want to be. Bullet Whisperer, Ace & Adrian II all have vast expertise in making these machines fly. How much do you want to spend?
   It's cheaper to just downshift and take your time - the machine will tell you the speed it's happy to take the grade at. My old 22 HP Pre-Unit Bullet really sets the pace, I've learned to just enjoy wherever I am at the speed it's willing to go. I could always get a Hayabusa and turn every bit of road into a blur, but where's the fun in that?

https://accessories.hitchcocksmotorcycles.com/accessory-shop/Mikuni-Conversion-Kit-EFI-Models/38128
PART No. 90089 ; CARBURETTOR KIT, MIKUNI 32mm (2017 on C5 EFI) ; £375.00
This is a comprehensive Mikuni Carburettor kit to replace the fuel injection system on the Euro-4 C5 EFI models from 2017. This kit comprises of the carburettor and exposed S&B air filter, petrol tap and adaptor plate and all necessary: cables, gaskets, resistor plug and fittings etc.
Extensive dyno testing has shown good increases in both torque and BHP to be amongst the benefits. This kit allows the user to utilise many different exhausts, air filters and other tuning parts on the bike without being restricted by the injection system parameters. 


xxxx
A brace of 1999 Bullets: 1 Red Deluxe, 1 Green Standard. Also, 1 wee orphan 1956 Fire Arrow project.


Snotball

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Reply #4 on: March 09, 2021, 09:47:57 am
Thanks for the replies. My concern as  has been mentioned above is what effect the carb conversion would have on the ignition timing. No-one seems to know exactly the relationship between the ECU and the EFI regarding the ignition timing. I suspect the basic span from around 10 and 32 degrees or so would remain with the fine tuning aspects from the throttle and MAP sensor being disabled? However that is only a guess. Hitchcock’s claim both HP and torque increases so it is likely the ignition timing still operates satisfactorily. Again just a question
« Last Edit: March 09, 2021, 09:50:14 am by Snotball »


viczena

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Reply #5 on: March 09, 2021, 10:42:39 am
Easy. The EFI reads the Throttle position sensor, and decides together with the rpm what timing the bike gets in that situation. There is a timing map.
If you throw out the TPS, the EFi has just one timing. No advance.
So it looses around 20%.
It gains something by the overly fat mixture, but if you enrich the EFI the same way, you get much more.
There are a lot of infos on india pages, which confirm the 20% loss. They normally change to Carb due to rust und clutter in the tank.
« Last Edit: March 09, 2021, 10:52:57 am by viczena »
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Snotball

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Reply #6 on: March 09, 2021, 11:11:57 am
I have contacted Hitchcock’s regarding what happens to the ignition timing once the sensors have been removed. I am sure they would have carried out testing on this while developing the carb replacement kit.


Adrian II

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Reply #7 on: March 09, 2021, 12:23:49 pm
There is an Indian carburetor conversion, the carb used for this (I think it's a 33mm CV carb) DOES have a TPS which is hooked up to the existing ECU. Otherwise as ACE suggests you can bin the ECU and fit the alternator rotor and TCI for a 500 AVL, but I would also think Hitchcock's have dome their homework on this.

A.

Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


TrianglePete

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Reply #8 on: March 09, 2021, 01:41:39 pm
The problem we fight with the 500 and 535 UCE s  are that they are delivered with 350

camshafts , check the part #.   Since we don't ride around with the family at 30 mph on bad roads

we in the USA need proper cams...  Instead of carbs that really are not compatible with modern fuel (vented to atmosphere) maybe put in 500 cams and reprogram the computer.  MAYBE ??


Snotball

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Reply #9 on: March 09, 2021, 11:55:48 pm
Well I got a reply from Hitchcock’s. Apparantly the crank position sensor and ECU look after the ignition timing   with the injector and TPS replaced with resistors. I then referred to the factory workshop manual for this bike and that is absolutely correct. The only thing that effects ignition timing is the crank position sensor which feeds into the ECU and adjusts ignition timing purely based on the speed of the engine. All other sensors effect the EFI only which is made redundant when the carb is installed and the injector removed. Foe me the problem is solved!
« Last Edit: March 10, 2021, 12:08:27 am by Snotball »


AzCal Retred

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Reply #10 on: March 10, 2021, 12:53:25 am
If the throttle position sensor is replaced by a resistor, it probably relates to maintaining a specific per-determined RPM dependent advance curve. The ECU would know RPM and trigger the spark time BTDC according to the pre-programmed curve. Lots of Bullets and Fury's have made plenty of HP and ran just fine on a fixed advance curve for a very long time. The parameters can be determined empirically or you could just ride it and be happy. H's couldn't get good dyno numbers without having a working advance curve. If it didn't advance and just parked at a fixed number, you'd run in to detonition numbers or retardation overheating pretty fast. Having only a fixed degree ignition advance can't square with H's statement of equal or better power output curves on the dyno. For one, it'd blow apart the starter if it was fixed at 25-35 degrees BTDC. There's more going on here - keep pinging H's, they'll know.

From Adrian II : "There is an Indian carburetor conversion, the carb used for this (I think it's a 33mm CV carb) DOES have a TPS which is hooked up to the existing ECU"
When the ECU knows both RPM and throttle position, a pretty good guess about airflow can happen, so a "Vacuum advance" curve function could be built in to optimize spark advance & fuel economy for low throttle/ high vacuum application. Probably a big deal for the Indian market. My old 6.5/1 compression ratio Iron Barrel has only a set of advance weights for ignition timing. It returns MPG's in the high 60's & 70's for me. Unless you spend a lot of time now ghosting along at 35-45, I doubt you'll see any significant mileage difference.
A brace of 1999 Bullets: 1 Red Deluxe, 1 Green Standard. Also, 1 wee orphan 1956 Fire Arrow project.


Snotball

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Reply #11 on: March 10, 2021, 01:59:57 am
Yes agree totally. The CPS will tell the ECU the engine speed and just like the old cast iron with the mechanical advance it will probably start at around 8 Degrees and end up around 32 degrees on a fixed curve around 3000 RPM. The extra bit of fine tuning for throttle position that the TPS provides will be missing.


viczena

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Reply #12 on: March 10, 2021, 02:45:28 pm
That depends on the ignition map in the ECU. If you fix the TPS value, you are running up and down a column. Depends if and what the values in this column are. In idle TPS position all these values are equal.

Modern ignition modules dont just use RPM, but are able to measure the speed difference between up and downgoing piston in the cylinder and recalculate the second parameter for an ignition map. So there is a different spark timing when running free or under load.
« Last Edit: March 10, 2021, 02:49:52 pm by viczena »
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TrianglePete

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Reply #13 on: March 10, 2021, 03:38:03 pm
I gave up trying to get the stock map from the manufacture .

The ECU needs a signal from the map and tps to choose the timing. very conservative considering the fuel

in India.


AzCal Retred

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Reply #14 on: March 10, 2021, 06:54:05 pm
Viczena - are you saying the spark is parked at 8 degrees advance all the time? At least your starter would survive. As a tinkerer, what were YOUR carbed-UCE spark advance numbers?

We need someone with a carb conversion to put a timing light on their machine and end this. Either H's is completely fabricating dyno numbers and using those to sell a kit to the retail public, or there's more going on. It would be difficult to match or exceed stock HP /torque ratings, as is the claim, under dyno load without having the ignition spark happen at the correct time. 8 degrees BTDC wouldn't cut it. Who has a carbed UCE and a timing light? This isn't rocket science.
A brace of 1999 Bullets: 1 Red Deluxe, 1 Green Standard. Also, 1 wee orphan 1956 Fire Arrow project.