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 850 Methanol Carb Recipe 
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Joined: Mon Mar 20, 2017 8:47 pm
Posts: 5
I'm in the process of building a 850 for methanol. The center section is older model and has straight boosters. I have a pair of holley methanol metering blocks from a HP950 I wanna use. What is a good recipe. Truck pulling application. Don't plan to use power valves. Will have the notched black floats and big n/s assemblies

mainwell size?
cross channel size?
booster size (id")?
hi speed bleed?
idle bleed?
idle feed?
emulsion?
jets (these blocks use the big threaded jets)?
squirters?
pump cams?
pump diaphrams?
anything else I need to know?

Thanks,
Scooter


Mon Mar 20, 2017 8:53 pm
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Joined: Thu May 08, 2014 7:47 pm
Posts: 234
If the center section was a gas carb, you will need something that will pass the volume. Gas Boosters are not going to work, unless modified to do so.


Tue Mar 21, 2017 12:56 am
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With straight boosters you may be able to ream them, I would try them at .190. If it doesn't work you will need new booster installed, I like an annular depending on the engine size.

Get a set of 5135 metering blocks from BLP, if you want I do have a set of purple ones with BLP engraved in the I can sell you cheaper. In a rush at the moment, I can get the rest later.


Tue Mar 21, 2017 10:15 am
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Joined: Mon Mar 20, 2017 8:47 pm
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Mark,

I really want to use these (already own them) methanol metering blocks that came from an alky HP950. I'll Just modify them as needed.

I'd also like to keep the straight boosters since it already as them. This 850 center section was previously methanol I think. I'll check the current id of the boosters.

Thanks and I look forward to your more detailed response when you are not busy.

Scooter


Tue Mar 21, 2017 10:25 am
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Joined: Mon Oct 21, 2013 12:15 am
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Location: San Diego, CA
Boosters - .196"
Wells - .221"
Exit Channels - .196"
TFR - .060"-.070"
IFR - Open
PVCR - .120" (primary)
Emulsion - .028"
IAB - .068"
HSAB - .028"


Tue Mar 21, 2017 1:15 pm
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Joined: Mon Mar 20, 2017 8:47 pm
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These metering blocks have a "divorced" idle circuit from Holley.

Revved Up, I don't plan to use power valves. What primary and secondary jets?

Scooter


Tue Mar 21, 2017 1:53 pm
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Joined: Mon Oct 21, 2013 12:15 am
Posts: 226
Location: San Diego, CA
I would recommend .155" squared to start.

Shooters, I would start with .055" with hollow screws, and 50cc pumps with brown cams to start (GFLT Diaphragms are a must with alky).

.150" stainless N/S

I would also recommend bowl extensions (that would be my preference).


Tue Mar 21, 2017 2:10 pm
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I would fix the divorced idle, change it to mainwell fed, it's a little work but can be done. Idle feed .050, IAB .050 to .060 as needed. 2 emulsion at .026, three at .021. .026 MAB. Main jet you will have to play with, not sure what the straight banjos will need, maybe a .170 to start.


Tue Mar 21, 2017 3:26 pm
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Joined: Mon Mar 20, 2017 8:47 pm
Posts: 5
What is PVCR? I assumed power valve channel restriction? Not needed since power valves will be plugged correct?

So far I have gathered from the responses...

primary jet - 155-170 range
secondary jet - 155-170 range
mainwell size - 0.221"
booster size - .196"
Cross/exit channel - 0.196"
Idle feed and/or transfer feed - .050 or up to .070? Seems like a large range?
Idle air bleed - .050 - .068?? Seems like a large range?
Hi speed bleed - .026-.028
squirters - .055
diaphrams - 50cc
cams - brown

Why is the straight booster harder to suggest a main jet for?

Just measured the current boosters. They are .204" already. Carb center section was originally a C&S Specialties. Will be measuring the metering blocks soon. But since they are stock holley methanol blocks I figure they should be close?

Scooter


Tue Mar 21, 2017 4:22 pm
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Joined: Mon Oct 21, 2013 12:15 am
Posts: 226
Location: San Diego, CA
In my experience, the 4150 carburetors do not need small air bleeds, they typically fall in the 60's for me. I think the smaller venturi and throttle plate sizing plays into that, and when you reach the 2.0" range of the Dominators, they definitely respond to the smaller air bleeds. However, it doesn't hurt to try either way. Your engine combination will dictate where to go with them. Your goal is to achieve the strongest idle vacuum signal in Park and in gear with minimal RPM drop, without having the idle mixture screws out too far (past 2 turns), or closed down too far (.75 turns and down). Everything seems to work best with 1-2 turns out.

As far as making recommendations on jetting; straight leg boosters have a different signal than down-leg and annular. Down-leg boosters and annulars are the norm for performance carburetors in general, due to their higher signal strength (alky carbs, especially). With a straight-leg booster, it will not atomize as well and will most likely require more jet than what their alternatives would. In the application that you are stating, annular boosters would reign supreme.

With regard to the booster leg sizing, .204" would be a good start and most likely work quite well, depending on how the rest of the metering circuits are mapped out.

The PVCRs would not require any modifications if you do not intend to use a power valve. However, I like to plug the PVCRs when I am not using a power valve. This way, the jets are isolated from one another, and not bleeding fuel to one another. To some, that seems like overkill, but that is my personal preference.


Wed Mar 22, 2017 10:47 am
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