HS6's on a BJ8 motor

[Lotuswins]

Hello All,

I was wondering if anyone can help. I have a
BJ8 motor in my Healey, with HS6 carbs. I've installed needles and springs from a BJ7, rich set, to see if they would work, but the cold start seems pretty lean as it backfires alot. I've richened it out, but it still runs lean, and I fear it will be lean when on the road. I haven't gotten the car on the road as yet since I'm in the middle of body work, but I was wondering if anyone out there has installed the smaller carbs on a BJ8 motor which apparently has a cam with a longer duration and perhaps higher lift.

Since my original HD8's were in very poor condition I opted for the HS6's off a volvo until I got the coin for a new or used set of them. Anyways, perhaps they'll give better gas mileage too......

So, would anyone have the HS6's on a BJ8 motor, and could you recommend needles/springs for this combination?

thanks for any help, and Merry Christmas

Jerry Rude
BJ8 Healey
Lotus Europa TCS

 

[David_K]

I would send them off to a respected rebuilder. Shouldn't cost more than $400 for the pair for a rebuild.

 

[tahoe healey]

Did you replace the intake manifold as well. I seem to remember (perhaps not well) that the ports were larger on the BJ8. I don't know if that makes a difference. You might be better off getting the originals rebuilt by someone like Joe C.

 

[big6]

The BJ7 from VIN 29F/2286 came from the factory with HS6 carbs and the new cam and valve springs. The later BJ7 cam and valve springs were used in the BJ8 engines until the end of production in March of 1968.

 

[Randy Forbes]

Set up properly, there's no reason to think the HS6s wouldn't be satisfactory, after all, the displacement is the same.

As long as the fuel is in proportion to the air, you could run the BJ8 on a single Spridget carb, it just won't rev very high :wink:

 

[Keoke]

Set up properly, there's no reason to think the HS6s wouldn't be satisfactory, after all, the displacement is the same.

As long as the fuel is in proportion to the air, you could run the BJ8 on a single Spridget carb, it just won't rev very high :wink:

However, selecting the proper needles can be a chore.--Keoke

 

[Johnny]

I wouldn't use them on a BJ8. You should have the original HD8 carbs rebuilt as mentioned. Wait until "you have the coin". The HS6's are 1 3/4" and your intake should be 2", at least that what memory says.

 

[John Turney]

According to my Haynes SU Manual, with HS6's yoiu should have BC needles and green springs for a 3000 MkII.

 

[Lotuswins]

Hi all,

Thanks for the comments, to respond to a few of the questions:

1) I didn't have to change the manifold, the bolt pattern is the same on the HS6 and the HD8 carbs, and the gaskets fit fine.
2) The cams, from what I can determine from the shop manual and the parts manual show that from 29F-2286 to 6188 (VIN 25314) the cam was P/N 12B594 with a duration of 240 degrees (intake and exhaust). That was the end of the BJ7 run.
The BJ8 starts with 29K-H101 and they had cam P/N AEC865 with a duration of 252 degrees Intake & Exhaust.

I understand that when you increase the efficiency of the engine by additional flow potential (cams, headers, porting, etc.) the carburators generally need to be richened up to compensate? The HS6 carbs should perform okay as the SU manual shows two of them good to a maximum of 3 liters.

Anyways, I was just wondering if anyone had toyed with changing the needles to get the right configuration for the combination of the BJ8 cam and HS6 carbs....

I'll check if the needles are BC....I think they are, along with the green springs.

Thanks again, Jerry

 

[Legal Bill]

Yes, the carbs fit the manifolds, but the manifold ports are bigger so the flow from the little carbs to the big manifold is not smooth and you interrupt the flow. I would have the right carbs rebuilt.

 

[big6]

Referencing the Anderson / Moment Restoration Guide (Gary G Anderson, 2000) page 181 Table 4.3. No drivetrain change to the BJ8 cam is indicated after 10/62…

The BMC BJ7 and BJ8 Mechanical Service Parts List indicates three camshafts – ACE 2029 (29F-H101 to 2285), 12B 594 (29F-H2286 to 6188 29FF-H101 to 164) and AEC 865 (29K-H101 on 29KF-H101 on).

Can I assume the Anderson / Moment Guide table is incorrect?

Any cam lift changes or just the 12 degree duration change Jerry indicated with the later BJ8 camshaft?

 

[Big6Mark]

Lots of misinformation out there.

The BJ8 had a different cam from all the earlier cars, but it had been used as the standard Competition spec cam for the earlier cars as well. And this cam profile was carried over to the MGC.

This cam should work for any carb combination you can find that fits the Healey, twin HS6/HD6, triple HS4, triple HS6, twin HD8 or triple HD8s like I have. Simply a matter of having the right setup in the carbs.

Yes there will be a step from the carb throat into the manifold, but it shouldn't affect mixture. That is a function of vacuum, needles, springs and dampers.

You should be able to properly setup the HS6s to the BJ7 tuning and get by temporarily, but I would expect a BJ8 to have twin HD8s. Get yours professionally rebuilt as soon as you can. They will work better that way.

C Ya,
Mark