|
|
Post by pmcburney on Nov 14, 2010 18:30:39 GMT -5
Hi all, As promised (threatened?) I'm starting a thread to detail the progress of my CV carb conversion to my RE5. The carb I'll be using/trialling is a Mikuni BST 40SS. It's a semi-flatslide 40mm CV carb. Originally fitted to Suzuki DR650's from the late 90's onwards, it does a fair job, but the slide has a tendency to oscillate badly (because of the big single's large piston pulses) causing fuelling issues which result in poor running at low revs. A slide carb works much better on this engine, which is what I've done and it transforms the bike. I've purchased a DR650 OEM intake manifold (AU$46) which will form part of the 'adapter' I have planned. Here's some pics of the carb, manifold and RE5 intake to give you an idea of where I'm headed:       As y'all can see, I have to create a plate which will convert the two-hole RE5 intake to a single 40mm hole and allow space to bolt down the DR650 intake manifold. Should be a piece of piss... (oz slang for REALLY easy). We'll see. I'll keep you posted as I progress. I'm off today now to see a man in an engineering shop about a piece of aluminium. Cheers Paul |
|
|
|
Post by mike500 on Nov 15, 2010 10:20:23 GMT -5
dont forget about the oil supply pipe fitting regards mike
|
|
|
|
Post by gokart on Nov 15, 2010 10:21:37 GMT -5
Hi Paul,
Thanks for sharing your RE5 carb conversion. I'm just curious to know if there will be a great running difference with the original carb.
Here in France, one owner made something similar. He said it's better ...but he wasn't able to set properly the original carb....
Here is a video of his bike:
He races every year in the French Dark Dog Moto Tour with his RE5. Not ridiculous ...!
Alain
|
|
|
|
Post by steveuk on Nov 15, 2010 12:49:46 GMT -5
on my last re5 i brought it had a modified manifold on it, i will dig it out of one of box's and post a pic
Steve
|
|
|
|
Post by steveuk on Nov 15, 2010 13:01:38 GMT -5
|
|
|
|
Post by pmcburney on Nov 17, 2010 3:23:18 GMT -5
Hi Paul, Thanks for sharing your RE5 carb conversion. I'm just curious to know if there will be a great running difference with the original carb. Here in France, one owner made something similar. He said it's better ...but he wasn't able to set properly the original carb.... Here is a video of his bike: He races every year in the French Dark Dog Moto Tour with his RE5. Not ridiculous ...! Alain Hi Alain, That would be Christian you're talking about! I've spoken with him on a couple of occasions. He's very knowledgeable about RE5's having done a complete proper-unit refurbishment at least once. He's using a Keihin FCR flat-slide carb on a bespoke manifold and adapter. Apparently it runs very well with this setup. He's done other mods to his bike including a rear disc brake and suspension and cosmetic modifications. I quizzed him about an adapter, but the setup he has is fairly sophisticated (CAD machined) so would be quite expensive to make. Hopefully, what I'm trying to achieve will be a lot simpler (and cheaper!). I dropped the RE intake and carb manifold off at a local tooling workshop on Monday - I should hear back from them in a couple of weeks. More pics and info to come. Cheers PMcB |
|
|
|
Post by pmcburney on Jun 6, 2011 16:55:47 GMT -5
Ok, some news...
After finally getting all the bits back from the various folk doing the work, and performing some judicious porting work, gasket making and other various cutting, drilling, tapping and filing on cable brackets and such, it runs!
But, not all that well, yet.
It's jetted way too lean. I'll need a much bigger pilot jet and a much thinner needle at the very least.
Obviously a single-cylinder 650 requires less fuel than a rotary 500...
So, I'll take some pics of the various bits and the carb installed on the bike, shortly, and I'll post some more replies as I go through the jetting and testing process.
Cheers
Paul McB
|
|
|
|
Post by pmcburney on Jun 6, 2011 16:58:06 GMT -5
Hey Steve... You still have that modified manifold? Would you like to sell it? I want to continue experimenting with my bike, even beyond what I'm doing at the moment. I'd be keen to try out any other attempts at adapting other carbs to an RE. Cheers Paul McB |
|
|
|
Post by steveuk on Jun 7, 2011 15:42:01 GMT -5
|
|
gerryggg
2nd Gear
I'm Lost In Thought, Please Send a Search Party.
Posts: 225
|
Post by gerryggg on Jun 18, 2011 8:25:51 GMT -5
I would think the FCR carb would work much better than the BST as it has an accelerator pump. That said, having had experience with the FCR carbs on competition 4-stroke motorcycles, they can be quite touchy to tune.
|
|
|
|
Post by pmcburney on Jun 19, 2011 19:02:25 GMT -5
I would think the FCR carb would work much better than the BST as it has an accelerator pump. That said, having had experience with the FCR carbs on competition 4-stroke motorcycles, they can be quite touchy to tune. You're probably right on the money there... The bike is a little difficult to start when cold. A carb with an accel pump would certainly help in that regard. However, my thinking was that as everyone used to fit 3/4" SU's to their RE5's back in the day, a 40mm BST would be pretty-much the same. SU's don't have accel pumps and worked well (as far as I know). I'm going to fiddle with needles and main jets on the weekend. It runs fairly well, but feels very flat in the mid-range, which I'm thinking is a lack of fuel. I'll submit a report shortly. Cheers Paul McB |
|
gerryggg
2nd Gear
I'm Lost In Thought, Please Send a Search Party.
Posts: 225
|
Post by gerryggg on Jun 26, 2011 8:02:48 GMT -5
The bike I just purchased yesterday had a VM flat slide Mikuni fitted. It has no accelerator pump. I asked the previous owner about it, but he indicated he only had it fired once or twice after got it 7 years ago and it tended to foul plugs. Obviously it hasn't been dialed in. I don't know the size yet as the markings are all worn off and i haven't had a chance to measure it yet. It's pretty gummed up (slide is stuck) and was full of water. Once I determine whether the rotor proper is usable I'll investigate further. Since I have the carb, I might as well play with it before I buy something else. Isn't experimentation fun?  |
|
gerryggg
2nd Gear
I'm Lost In Thought, Please Send a Search Party.
Posts: 225
|
Post by gerryggg on Jun 26, 2011 8:11:31 GMT -5
[quote author=gerryggg board=general thread=708 post=4571 time=1308403551 SU's don't have accel pumps and worked well (as far as I know). I'm going to fiddle with needles and main jets on the weekend. It runs fairly well, but feels very flat in the mid-range, which I'm thinking is a lack of fuel. I'll submit a report shortly. Cheers Paul McB Since the CVs work off differentials in vacuum, I'm wondering if that could be part of the problem. I don't know what the intake vacuum is like on the RE, but I know 2-strokes never worked that well with CVs from my experience because they had so much lower intake vacuum than 4 strokes. I had considered trying to get a CV to work on the one I just got, but the intake vacuum issue was one of my concerns. Have you ever checked to see what it was? I know when I use to do carb synch on bikes the 4 strokes were always running at least double the intake vacuum of the 2 strokes. I suspect the primary compression of the 2-stroke helps compensate for that. Since the RE5s only had one carb there was never any reason to check the intake vacuum. If you get I chance to check it I'd be interested in what you get. If I ever get this one running I'll check it.. |
|
gerryggg
2nd Gear
I'm Lost In Thought, Please Send a Search Party.
Posts: 225
|
Post by gerryggg on Jul 6, 2011 7:54:16 GMT -5
I just got a line on an carb in Alabama that has been sitting around in a shed for years. It is supposedly in good condition so I may pick that up before I spend a lot of time trying to adapt something. Once I get it running I can always try something else.
|
|
|
|
Post by pmcburney on Jun 15, 2014 5:00:21 GMT -5
Ok, so this is a fairly old thread to revive, but I do actually have an update.
Having persevered with the diabolical abomination that Suzuki deigned to put on the RE for too long and gotten nowhere, I thought I'd try my Keihin FCR setup one more time.
And, I can report great success!
Working on the assumption that a big opening would require a lot of fuel to counteract the amount of air being drawn in, I initially tried some quite large pilot jets.
Well, that wasn't the case - the RE engine on the primary 'circuit' (i.e. with the PV closed) doesn't need huge amounts of fuel, so I've gone down to a 40 pilot and it seems to be close.
Without two separate carb barrels, the timing of the PV is now quite critical to getting the engine to produce power and rev cleanly too - I now have it opening pretty early.
This makes sense as that port valve is now the only way to 'changeover' from the two small primary ports in the combustion chamber to the large main intake port.
The engine seems to respond better to the main port opening sooner as the air and fuel flow picks up.
Anyway... the result?
My bike now has NO hesitation and pulls strongly from idle to full revs.
I can open the throttle hard anywhere and all it does is accelerate!
It seems to have more pull in the upper rev range and the grinding vibe seems lessened.
I still have some experimenting to do as it's still not absolutely perfect.
I may drop the main jet down in size to see how that affects the midrange and I may go even smaller on the pilot as the mixture screw is still not having much effect - the bike will still idle with it all the way in...
But, I am extremely happy with the results so far.
I've loaded up a vid on Youtube of a startup and rev here -
You'll notice I kill it on particularly vicious full throttle rev at the end of the vid, but I'd expect that having just given it a gut-full of fuel and air from a carb that size.
I'll post up all the specs in this thread when I'm finished or gotten it to as good as it can be for future reference.
|
|
