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Author Topic: Flat slides versus round slides  (Read 723 times)

goodatbeingyoung

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Flat slides versus round slides
« on: August 08, 2017, 11:02:01 pm »
All,

I'm working on a 2005 with an ACE air canister and a Goldie silencer. It's been giving me carb troubles for a while now so it's time to replace. I'd absolutely love to put an AMAL on the bull, but with how often I ride it, I'd like some reliability.

Looks like Mikuni is the way to go. But, I don't understand the difference between the performance of the flat slide and round slide models. Can someone explain. The other issue I'm having is the lack of space between the Mikarb I've got now and the bottom of the gas tank. There's not much clearance and it seems to be stressing the throttle cable where it enters the carb. Any fixes for that? Or is that out of the ordinary?

Thanks for all the help so far.
Full-time Musician; Part-time Wannabe Mechanic.
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Ice

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Re: Flat slides versus round slides
« Reply #1 on: August 08, 2017, 11:56:56 pm »
 Flat slide can be a misnomer.  A true flat slide has a slide that is just that, flat.

 D slide carbs are quite often ( incorrectly ) called flat slide despite the slide being neither flat nor round but D shaped. The situation is what it is.

 The shape of the slide has an effect on the behavior air as it flows through the carby and gets fuel mixed int to that mass.

In general:
 Round slide carbs tend to be easiest to tune and the round shape of the slide helps them transition smoothly from idle to mid range to WOT.

 Flat Slides can offer incredible throttle response and are hard to beat in the mid and upper revs. In the lower revs it can be a challenge to get and maintain a good fuel air flow and mix. They can test your patience with tuning.

 Between the two is the other "flat slide" the D slide. It has the lovely low end smoothness of the round slide combined with most of the characteristics of the  Flat Slide at higher revs. IIRC most of them have an oval shaped throat with the upper half being wider than the lower half. This offers good vacuum and a strong airflow at lower revs for good fuel air mixing and better cylinder fill while the upper half offers a large volume of flow in the huger revs which allows for better breathing more revs and more power.

  A perennial favorite of the forum for less than all out modded Bullets in the heyday or the Iron Barrel was the 30mm "flat slide".

I can break it better,,,,at night, in the rain, on the trail,, 20 miles from nowhere.

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"TIMEX", the '06 Iron Barrel Military that takes me everywhere I want to go... and some places I shouldn't.

ace.cafe

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Re: Flat slides versus round slides
« Reply #2 on: August 09, 2017, 01:25:53 am »
Cable clearance can be tight under the tank on all the Mikarb and Mikuni carbs. Careful routing helps.
 
I almost always recommend the Mikuni TM32, but on a stock Bullet a VM32 is probably as good for a bit lower cost if a few dollars is a factor. The TM32 is the Fireball carb because the modified engine likes the performance carb. They both need new jets right off the bat, and jetting combinations and settings has a thread in the Tech section they need a matching manifold from Sudco or Ebay.


I haven't used the D slide JRC that was sold here, but some have reported that they liked it.

tooseevee

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Re: Flat slides versus round slides
« Reply #3 on: August 09, 2017, 08:27:43 am »
All,

I'm working on a 2005 with an ACE air canister and a Goldie silencer. It's been giving me carb troubles for a while now so it's time to replace. I'd absolutely love to put an AMAL on the bull, but with how often I ride it, I'd like some reliability.

Looks like Mikuni is the way to go. But, I don't understand the difference between the performance of the flat slide and round slide models. Can someone explain. The other issue I'm having is the lack of space between the Mikarb I've got now and the bottom of the gas tank. There's not much clearance and it seems to be stressing the throttle cable where it enters the carb. Any fixes for that? Or is that out of the ordinary?

Thanks for all the help so far.

            I'm very happy with the TM32 I installed on my '08 AVL after the ACE headwork in 2014. It was a season long learning experience, but I soon understood the little bastard in detail and can remove and reinstall it in my sleep now. Much tweaking can be done without removing it, but not everything. I can't give you tuning advice for your particular engine because my engine is far from stock (totally reshaped comb chamber, better flow, huge valves, 9.8:1 comp) and I had to learn what my engine wanted from the carb by lots of experimentation. My only "big" problem is with the spring and top cover when removing and replacing it is necessary as in playing with needle types and height  adjustments, but that's to do more with my hands and wrists (they don't do what I need them to do any more) than the actual difficulty level. No problem for people with no pain issues.

         You can get any shape throttle cable entry tube you might need (straight, 90 or 45 degree) from SUDCO. I've got perfect, smooth action with the straight one by meticulous tweaking, cable routing, etc.. (I'm a meticulous tweaker by nature  :) :) :) ).

          Remove the hot tube (if you have one) from the muffler end of your header pipe if you haven't already; it's very restrictive. You don't want to go through dialing in a TM32 (or any other) with it in there and then do it all over again when you realize you need to remove it to get the most out of what you've already done (carb, exhaust, air intake). 

        Radiator hose is good for your transition tubes from head to carb and from carb to canister.
« Last Edit: August 09, 2017, 08:38:52 am by tooseevee »
2008 AVL Classic. Extensive head work by Ace. Ace canister. TM32 Mikuni/Ace manifold. Small bottle open exhaust/hot tube removed. Pertronix Coil. Little hard-ass bobber seat. All emissions/PAV mandates removed. Battery in right side case. 7" headlight, '30s Lucas repro taillight.

Adrian II

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Re: Flat slides versus round slides
« Reply #4 on: August 09, 2017, 10:29:44 am »
Quote
You can get any shape throttle cable entry tube you might need (straight, 90 or 45 degree) from SUDCO. I've got perfect, smooth action with the straight one by meticulous tweaking, cable routing, etc..

tooseevee is on the money here, part of the problem is that the factory changed the carb mounting over the years, later ones have an alloy stub bolted to the inlet flange on the cylinder head, with the carb fitted via a piece of rubber hose. Compared with the one-piece mounting rubber used on the earlier 500 Indian Bullets, this moves the carburettor backwards, which means that the throttle cable run now risks fouling the underside of the gas tank, which never used to be a problem.

Let's say you're going to use a Mikuni VM30 roundslide carb (I think Niche Cycle on are still selling them as part of the complete Sudco kit for the 500 Bullet cheap on ebay), the Sudco kit has a spacer and one-piece rubber mounting that will keep the carb closer to the engine. Anything mounting the carb further back will probably benefit from the angled throttle cable ferrule. This also needs a shorter outer cable to compensate, if you're careful and don't damage the inner, you can trim back the outer of an existing cable.

A.
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goodatbeingyoung

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Re: Flat slides versus round slides
« Reply #5 on: August 09, 2017, 11:44:42 am »
In general:
Round slide carbs tend to be easiest to tune and the round shape of the slide helps them transition smoothly from idle to mid range to WOT.

Flat Slides can offer incredible throttle response and are hard to beat in the mid and upper revs. In the lower revs it can be a challenge to get and maintain a good fuel air flow and mix. They can test your patience with tuning.

Between the two is the other "flat slide" the D slide. ...

Most of my riding is done in the city and I'm lucky to be in 4th or 5th gear for more than half a mile or so. Sounds like the round slide will better meet my needs for now. Otherwise, do recommend a particular D slide carb to check out?
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goodatbeingyoung

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Re: Flat slides versus round slides
« Reply #6 on: August 09, 2017, 12:05:34 pm »
Cable clearance can be tight under the tank on all the Mikarb and Mikuni carbs. Careful routing helps.

I almost always recommend the Mikuni TM32, but on a stock Bullet a VM32 is probably as good for a bit lower cost if a few dollars is a factor. The TM32 is the Fireball carb because the modified engine likes the performance carb. They both need new jets right off the bat, and jetting combinations and settings has a thread in the Tech section they need a matching manifold from Sudco or Ebay.

Cable clearance is indeed tight. I'll have to look into the angled cables that TooSeeVee mentioned. I'll definitely check out that tech thread too. Do I have to change the intake manifold? Seems like what I've already got might be just fine (which is a radiator hose cut to size) as shown.

If I do need to change it, I'd love to replace it with a metal part instead of rubber, but I can't seem to find one. This is about the best I could find: https://www.ebay.com/sch/m.html?_odkw=&_ssn=niche-cycle&_armrs=1&_osacat=0&_from=R40&_trksid=p2046732.m570.l1313.TR12.TRC2.A0.H0.Xmanifold.TRS0&_nkw=manifold&_sacat=0

I like this setup but don't need the air filter or throttle cable (the bike came with a replacement):
http://www.ebay.com/itm/Royal-Enfield-500-30mm-VM30-Complete-Mikuni-Carburetor-Kit-2000-Later-/171814323098
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goodatbeingyoung

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Re: Flat slides versus round slides
« Reply #7 on: August 09, 2017, 12:14:39 pm »
tooseevee is on the money here, part of the problem is that the factory changed the carb mounting over the years, later ones have an alloy stub bolted to the inlet flange on the cylinder head, with the carb fitted via a piece of rubber hose. Compared with the one-piece mounting rubber used on the earlier 500 Indian Bullets, this moves the carburettor backwards, which means that the throttle cable run now risks fouling the underside of the gas tank, which never used to be a problem.

Let's say you're going to use a Mikuni VM30 roundslide carb (I think Niche Cycle on are still selling them as part of the complete Sudco kit for the 500 Bullet cheap on ebay), the Sudco kit has a spacer and one-piece rubber mounting that will keep the carb closer to the engine. Anything mounting the carb further back will probably benefit from the angled throttle cable ferrule. This also needs a shorter outer cable to compensate, if you're careful and don't damage the inner, you can trim back the outer of an existing cable...

This is definitely spot on as it's not a problem on most of the bikes I've seen online. The added distance in my setup (I attached a picture above) moves the carb a little too far from the intake and causes exactly this problem. I'm having a hard time finding only the intake parts included in this ad (as shown below): http://www.ebay.com/itm/Royal-Enfield-500-30mm-VM30-Complete-Mikuni-Carburetor-Kit-2000-Later-/171814323098

I've got a fresh new throttle cable that I'm sure I could trim down if needed.
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Adrian II

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Re: Flat slides versus round slides
« Reply #8 on: August 09, 2017, 03:33:56 pm »
That is the same kit I was referring to. Your picture clearly shows how the carb is pushed too far back with the later manifold.

If you want the individual parts try contacting Sudco, I think they have a fairly large on-line catalogue.

A.
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strat71

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Re: Flat slides versus round slides
« Reply #9 on: August 09, 2017, 07:12:35 pm »
for illustration..
i put a TM32 Mikuni on 2003 bullet.. with Ace manifold and air box... here's the layout...
not sure a VM32 would fit with this manifold.. the flat side has a lower profile than the VM32.
Ben
« Last Edit: August 09, 2017, 07:15:39 pm by strat71 »

Ice

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Re: Flat slides versus round slides
« Reply #10 on: August 09, 2017, 08:34:50 pm »
Here's a pic of the D Slide "flat slide" carb on Bill Harris's AVL powered Harris Scrambler.

I can break it better,,,,at night, in the rain, on the trail,, 20 miles from nowhere.

REA #136

"TIMEX", the '06 Iron Barrel Military that takes me everywhere I want to go... and some places I shouldn't.

finbullet

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Re: Flat slides versus round slides
« Reply #11 on: August 10, 2017, 12:26:42 am »
Most of my riding is done in the city and I'm lucky to be in 4th or 5th gear for more than half a mile or so. Sounds like the round slide will better meet my needs for now. Otherwise, do recommend a particular D slide carb to check out?

This is a really good D slide carb. I have one installed to my iron barrel. And not even expensive. I used a mikuni rubber manifold for older snowmobiles ( more info about the setup, if you type "cheap performance" on the search)which brings the carb near the head, so there is plenty of room for the cable.
http://m.ebay.com/itm/32mm-High-Performance-Carburetor-GY6-Baster-Banshee-Scooter-Like-PWK-Black-Serie-/161810498601
« Last Edit: August 10, 2017, 12:47:38 am by finbullet »

Adrian II

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Re: Flat slides versus round slides
« Reply #12 on: August 10, 2017, 07:17:25 am »
I have wondered about these bargain basement carbs, what if any re-jetting did you have to do to get your C.I. Bullet running sweetly with this one?

A.
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Bill Harris

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Re: Flat slides versus round slides
« Reply #13 on: August 10, 2017, 11:10:24 am »
For the Harris Scrambler, I got the Taiwan PWK 32mm carb from JRC Engineering.  They manufactured and mounted the flange on the carburetor for me, all I need to do was to rejet: 42 pilot, 142 main and moved the needle one notch richer.

jrcengineering.com

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Cheers,
Bill
« Last Edit: August 10, 2017, 11:16:07 am by Bill Harris »

finbullet

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Re: Flat slides versus round slides
« Reply #14 on: August 12, 2017, 02:47:24 pm »
I have wondered about these bargain basement carbs, what if any re-jetting did you have to do to get your C.I. Bullet running sweetly with this one?

A.
I got it jetted with those jets, which came with the carb (usually 3 main jets and 2 pilot jets and 2 needles).  The carb uses the same jets (those hexagonal jets) as a genuine keihin does.
But if you order one of these carbs, make sure the picture shows those hexagonal jets and not the small round ones.