17 replies to this topic

[64woody]

I am a newbie to the forum, and have viewed this forum in the past to find answers for the rebuild of my 1964 countryman, but now I need to ask a fueling question.

 

---My Setup ---

- mid 1970's 998 rebuilt with flat top pistons

- 12g295 head ( unskimmed)

- 252/252 camshaft

- stage 1 (torquemaster intake/maniflow exhaust)

- distributor rebuild (by the distributor guy, Minnesota)

- AEM wideband AFR analyzer

 

I rebuilt the HS4 carb (ABD needle) and I am still not impressed with it.  I starves the engine on sudden changes in direction.  Hard cornering to the left is the worst, which sends the AFR into the 20 : 1 area.  What a dog.

 

I have tentatively 3 options

 

OPTION 1 -  keep trying to figure out why the HS4 is operating like it is

 

OPTION 2 -  I have obtained a twin HS2 intake manifold, and a pair of HS2 carbs from a "parts car"  triumph spitfire. --- drawback is manufacturing a location for mounting the throttle return springs, as the spitfire return springs pull from the top.

 

OPTION 3 - I can easily get my hands on a set of early MGB HIF4 carbs and rebuild one to replace the HS4.  --- drawback is manufacturing a throttle lever for a single carb cable pull, and choke pull lever setup.

 

I am looking for suggestions from the community.  Any feed back on the above options or any other suggestions would be greatly appreciated.  Snow has fallen here,  and now is the season for problem solving and upgrades.

 

Thanks in advance

 

Blair

 

[stuart bowes]

pair of HS2 carbs ... drawback is manufacturing a location for mounting the throttle return springs..

 

I believe usually the carbs have a heat shield to protect from the exhaust temperature, that provides the fixing point for the springs

 

will be reading replies interest because my engine build will be coming over the next year or so and I have a similar range of choices (and just generally to learn as much as I can about carbs in general)

 

just out of curiosity what would the compression ratio be with that head being unskimmed

Edited by stuart bowes, 20 November 2023 - 01:28 PM.

[64woody]

Stuart:

 

As for the compression ratio,  I'm not sure.  The compression test just after rebuild showed 195 PSI across the engine.

 

Blair

[nicklouse]

The spitfire manifold will not fit.

 

What is the actual cam?

 

would not bother with any twins.

 

a single HIF38 will do.

[johnR]

I am a newbie to the forum, and have viewed this forum in the past to find answers for the rebuild of my 1964 countryman, but now I need to ask a fuelling question.

 

---My Setup ---

- mid 1970's 998 rebuilt with flat top pistons

- 12g295 head ( unskimmed)

- 252/252 camshaft

- stage 1 (torquemaster intake/maniflow exhaust)

- distributor rebuild (by the distributor guy, Minnesota)

- AEM wideband AFR analyzer

 

I rebuilt the HS4 carb (ABD needle) and I am still not impressed with it.  I have good AFR cruising and idling but it starves the engine on sudden changes in direction.  Hard cornering to the left is the worst, which sends the AFR into the 20+ : 1 area.  What a dog.

 

I have tentatively 3 options

 

OPTION 1 -  keep trying to figure out why the HS4 is operating like it is

 

OPTION 2 -  I have obtained a twin HS2 intake manifold, and a pair of HS2 carbs from a "parts car"  triumph spitfire. --- drawback is manufacturing a location for mounting the throttle return springs, as the spitfire return springs pull from the top.

 

OPTION 3 - I can easily get my hands on a set of early MGB HIF4 carbs and rebuild one to replace the HS4.  --- drawback is manufacturing a throttle lever for a single carb cable pull, and choke pull lever setup.

 

I am looking for suggestions from the community.  Any feed back on the above options or any other suggestions would be greatly appreciated.  Snow has fallen here,  and now is the season for problem solving and upgrades.

 

Thanks in advance

 

Blair

I cut down my twin HS2 throttle and choke rods to fit my 'new' HS4s

[64woody]

The camshaft is a Keith Calvert grind of the 997 cooper.

 

HIF38's are a little harder to find around here.

 

The carbs are off a spitfire. . . no manifold.  I do have a Twin HS2 intake manifold from an earlier mini. 

 

Blair

[PACINO]

Hif 38 should be nice. Easier to regulate than Hs4 and a more evolved carb. Hif44 and Twin S.u Hs2 is a little bit too much for you configuration.

[stuart bowes]

what I'm trying to work out (and getting mixed answers depending who's writing about it) .. when you have twins, does it suck through both carbs together or is it more like 1 carb for the left two cylinders and 1 for the right 2 cylinders, in which case kind of what's the point you might as well just have 1

 

or is the reality somewhere between the two (because surely there must be some advantage otherwise no-one would have ever done it )

 

sorry if this is a really stupid question, I'm sure some people will be rolling their eyes at how ridiculous it is to ask lol

Edited by stuart bowes, 20 November 2023 - 04:37 PM.

[eric67]

An HIF38 will be very tight on the bulkhead, not impossible to fit, but, I’d be inclined to stick with the HS4

[Spider]

You only need fit enough carburation to match what power the engine is capable of producing. Fitting more will not increase the power and more usually will loose lower RPM Power (or what many refer to as Torque).

Comparing your build to the 998 Cooper engine, I'd guesstimate yours may see 60 - 65 HP. The HS4 is good for at least 80 HP.

Given you'll find little advantage going to a HIF38, which is the same size, just a more modern layout, I'd suggest as eric67 has, stick with the 1-1/2" you have.

The issue you are finding is most likely related to the float level and / or fuel pressure. Check too that the float chamber has the right angle block on it so that the lid sits flat. This could also come from using the wrong manifold.

[64woody]

Does anybody have the dimensions ( length of carb ) from intake manifold face to air horn face on the HIF4 vs HS4 ?

 

Blair

[eric67]

Does anybody have the dimensions ( length of carb ) from intake manifold face to air horn face on the HIF4 vs HS4 ?

 

Blair

It’s not the size of the carb, front to back, that is the problem as I think they are quite similar but the float bowl sits under the HIF and is quite large. I got one to fit on my Elf and I think it is the better carburettor but hardly worth the trouble. The mixture adjustment screw is particularly difficult to access. 
I’d send you a picture to show you but am currently in the process of changing back!

[cal844]

HS4 carb on a mini manifold will do the job just fine, you will have clearance issues with the bulkhead using an HIF carb. (when the HIF carb and SPI injection units were tested, the engine had to be mounted 1/2 inch forward of where it is in your '64 car.)





What you are experiencing is fuel starvation.

What pressure is your fuel pump set to?
Have you baseline set the carb and centered the needle in the jet...

What needle is fitted?
Have you set the CO or AFR as needed?

Edited by cal844, 20 November 2023 - 08:43 PM.

[timmy850]

The fuel bowl lid on an HS4 carb can be installed in 3 possible positions. In one orientation it's more likely to starve of fuel - the fuel sloshes to the side and hold up the float. If you remove the fuel bowl lid, make a note to see if the fuel bowl is swinging on a side to side axis or a front to back. As mentioned above, check the fuel pressure, tank level and fuel bowl level are correct as these can all give similar symptoms 

 

The main difference between the HIF4 and HIF38 is the dashpot and damper assembly. The HIF4 has the earlier HS4 type setup and the HIF38 has the later ball bearing type. Otherwise the HIF4 and HIF38 are pretty much equivalent 

[64woody]

HS4 carb on a mini manifold will do the job just fine, you will have clearance issues with the bulkhead using an HIF carb. (when the HIF carb and SPI injection units were tested, the engine had to be mounted 1/2 inch forward of where it is in your '64 car.)





What you are experiencing is fuel starvation.

What pressure is your fuel pump set to?
Have you baseline set the carb and centered the needle in the jet...

What needle is fitted?
Have you set the CO or AFR as needed?

The fuel pump pressure is 3.5 PSI

I baseline set the jet at 12 flats down and tuned it from there until I reached  14.5 AFR at idle.  I took it for a spin and the engine cruised at 14.0 AFR.  When I quickly accelerate the AFR jumps to 17 then immediately falls to 13.0 and gradually increases with engine speed back to 14.5.  To gain more performance, I lowered  the jet to 14 AFR at idle, and it performed better.  But still the fuel starvation on sudden velocity changes ( i.e. hard braking, hard cornering) is still a conundrum.  If I coast into an intersection, push in the clutch and make a U turn, by the time I come out of the U turn the engine is dead.